Adaptable Diffraction Gratings With Wavefront Transformation

NASA Technical Reports Server (NTRS)

Iazikov, Dmitri; Mossberg, Thomas W.; Greiner, Christoph M.

2010-01-01

Diffraction gratings are optical components with regular patterns of grooves, which angularly disperse incoming light by wavelength. Traditional diffraction gratings have static planar, concave, or convex surfaces. However, if they could be made so that they can change the surface curvature at will, then they would be able to focus on particular segments, self-calibrate, or perform fine adjustments. This innovation creates a diffraction grating on a deformable surface. This surface could be bent at will, resulting in a dynamic wavefront transformation. This allows for self-calibration, compensation for aberrations, enhancing image resolution in a particular area, or performing multiple scans using different wavelengths. A dynamic grating gives scientists a new ability to explore wavefronts from a variety of viewpoints.

Treatment of nonconvergence of Fourier modal method arising from irregular field singularities at lossless metal-dielectric right-angle edges.

PubMed

Mei, Yanpeng; Liu, Haitao; Zhong, Ying

2014-04-01

In a recent work [J. Opt. Soc. Am. A28, 738 (2011)], Lifeng Li and Gerard Granet investigate nonconvergence cases of the Fourier modal method (FMM). They demonstrate that the nonconvergence is due to the irregular field singularities at lossless metal-dielectric right-angle edges. Here we make further investigations on the problem and find that the FMM surprisingly converges for deep sub-wavelength gratings (grating period being much smaller than the illumination wavelength). To overcome the nonconvergence for gratings that are not deep sub-wavelength, we approximately replace the lossless metal-dielectric right-angle edges by a medium with a gradually varied refraction index, so as to remove the irregular field singularities. With such treatment, convergence is observed as the region of the approximate medium approaches vanishing.

3D laser printing by ultra-short laser pulses for micro-optical applications: towards telecom wavelengths

NASA Astrophysics Data System (ADS)

Ryu, Meguya; Mizeikis, Vygantas; Morikawa, Junko; Magallanes, Hernando; Brasselet, Etienne; Varapnickas, Simonas; Malinauskas, Mangirdas; Juodkazis, Saulius

2017-08-01

Three dimensional (3D) fast (< 0.5 hour) printing of micro-optical elements down to sub-wavelength resolution over 100 μm footprint areas using femtosecond (fs-)laser oscillator is presented. Using sub-1 nJ pulse energies, optical vortex generators made of polymerised grating segments with an azimuthally changing orientation have been fabricated in SZ2080 resist; width of polymerised rods was 150 nm and period 0.6-1 μm. Detailed phase retardance analysis was carried out manually with Berek compensator (under a white light illumination) and using an equivalent principle by an automated Abrio implementation at 546 nm. Direct experimental measurements of retardance was required since the period of the grating was comparable (or larger) than the wavelength of visible light. By gold sputtering, transmissive optical vortex generators were turned into reflective ones with augmented retardance, Δn × h defined by the form birefringence, Δn, and the height h = 2d where d is the thickness of the polymerised structure. Retardance reached 315 nm as measured with Berek compensator at visible wavelengths. Birefringent phase delays of π (or λ/2 in wavelength) required for high purity vortex generators can be made based on the proposed approach. Optical vortex generators for telecom wavelengths with sub-wavelength patterns of azimuthally oriented gratings are amenable by direct laser polymerisation.

Behaviour of a ZnO thin film as MSG for biosensing material in sub-wavelength regime

NASA Astrophysics Data System (ADS)

Iftimie, N.; Steigmann, R.; Danila, N. A.; Iacomi, F.; Faktorova, D.; Savin, A.

2016-11-01

Zinc oxide nanostructured materials, such as films and nanoparticles, could provide a suitable platform for development of high performance biosensing material due to their unique fundamental material properties. In this study, the enzyme biosensing consisting of a zinc oxide (ZnO) nanoparticles were grown on SiO2/Si substrates by vacuum thermal evaporation method and their sensing characteristics are examined in air and investigated. The film morphology is characterized by X-ray diffraction (XRD) the film crystalline quality and by scanning electron microscopy (SEM). Also, the interest in surface waves appeared due to evanescent waves in the metallic strip grating structure (MSG-Ag/ZnO/SiO2/Si) in sub-wavelength regime. Before testing the sensor with metamaterials (MMs) lens in the sub-wavelength regime, a simulation of the evanescent wave's formation has been performed at the edge of Ag strips, with thicknesses in the range of micrometers.

Refraction effects in soft x-ray multilayer blazed gratings.

PubMed

Voronov, D L; Salmassi, F; Meyer-Ilse, J; Gullikson, E M; Warwick, T; Padmore, H A

2016-05-30

A 2500 lines/mm Multilayer Blazed Grating (MBG) optimized for the soft x-ray wavelength range was fabricated and tested. The grating coated with a W/B₄C multilayer demonstrated a record diffraction efficiency in the 2nd blazed diffraction order in the energy range from 500 to 1200 eV. Detailed investigation of the diffraction properties of the grating demonstrated that the diffraction efficiency of high groove density MBGs is not limited by the normal shadowing effects that limits grazing incidence x-ray grating performance. Refraction effects inherent in asymmetrical Bragg diffraction were experimentally confirmed for MBGs. The refraction affects the blazing properties of the MBGs and results in a shift of the resonance wavelength of the gratings and broadening or narrowing of the grating bandwidth depending on diffraction geometry. The true blaze angle of the MBGs is defined by both the real structure of the multilayer stack and by asymmetrical refraction effects. Refraction effects can be used as a powerful tool in providing highly efficient suppression of high order harmonics.

Optimization of top coupling grating for very long wavelength QWIP based on surface plasmon

NASA Astrophysics Data System (ADS)

Wang, Guodong; Shen, Junling; Liu, Xiaolian; Ni, Lu; Wang, Saili

2017-09-01

The relative coupling efficiency of two-dimensional (2D) grating based on surface plasmon for very long wavelength quantum well infrared detector is analyzed by using the three-dimensional finite-difference time domain (3D-FDTD) method algorithm. The relative coupling efficiency with respect to the grating parameters, such as grating pitch, duty ratio, and grating thickness, is analyzed. The calculated results show that the relative coupling efficiency would reach the largest value for the 14.5 μm incident infrared light when taking the grating pitch as 4.4 μm, the duty ratio as 0.325, and the grating thickness as 0.07 μm, respectively.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akhmedzhanov, I M; Kibalov, D S; Smirnov, V K

We report a detailed numerical simulation of the reflection of visible light from a sub-wavelength grating with a rectangular profile on the silicon surface. Simulation is carried out by the effective refractive index method and rigorous coupled-wave analysis. The dependences of the reflectance on the grating depth, fill factor and angle of incidence for TE and TM polarisations are obtained and analysed. Good agreement between the results obtained by the two methods for grating periods of ∼100 nm is found. The possibility of reducing the polarised light reflectance to about 1% by adjusting the depth and the grating fill factormore » is demonstrated. The characteristics of the Brewster effect manifestation (pseudo-Brewster angle) in the system under study are considered. The possibility of the pseudo-Brewster angle existence and its absence for both polarisations of the incident light is shown as a function of the parameters of a rectangular nanostructure on the surface. (laser applications and other topics in quantum electronics)« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Seunghoon; Horie, Yu; Faraon, Andrei

An on-chip optical filter having Fabri-Perot resonators and a spectrometer may include a first sub-wavelength grating (SWG) reflecting layer and a second SWG reflecting layer facing each other. A plurality of Fabri-Perot resonators are formed by the first SWG reflecting layer and the second SWG reflecting layer facing each other. Each of the Fabri-Perot resonators may transmit light corresponding to a resonance wavelength of the Fabri-Perot resonator. The resonance wavelengths of the Fabri-Perot resonators may be determined according to duty cycles of grating patterns.

Plasmonic micropolarizers for full Stokes vector imaging

NASA Astrophysics Data System (ADS)

Peltzer, J. J.; Bachman, K. A.; Rose, J. W.; Flammer, P. D.; Furtak, T. E.; Collins, R. T.; Hollingsworth, R. E.

2012-06-01

Polarimetric imaging using micropolarizers integrated on focal plane arrays has previously been limited to the linear components of the Stokes vector because of the lack of an effective structure with selectivity to circular polarization. We discuss a plasmonic micropolarizing filter that can be tuned for linear or circular polarization as well as wavelength selectivity from blue to infrared (IR) through simple changes in its horizontal geometry. The filter consists of a patterned metal film with an aperture in a central cavity that is surrounded by gratings that couple to incoming light. The aperture and gratings are covered with a transparent dielectric layer to form a surface plasmon slab waveguide. A metal cap covers the aperture and forms a metal-insulator-metal (MIM) waveguide. Structures with linear apertures and gratings provide sensitivity to linear polarization, while structures with circular apertures and spiral gratings give circular polarization selectivity. Plasmonic TM modes are transmitted down the MIM waveguide while the TE modes are cut off due to the sub-wavelength dielectric thickness, providing the potential for extremely high extinction ratios. Experimental results are presented for micropolarizers fabricated on glass or directly into the Ohmic contact metallization of silicon photodiodes. Extinction ratios for linear polarization larger than 3000 have been measured.

Slot-grating flat lens for telecom wavelengths.

PubMed

Pugh, Jonathan R; Stokes, Jamie L; Lopez-Garcia, Martin; Gan, Choon-How; Nash, Geoff R; Rarity, John G; Cryan, Martin J

2014-07-01

We present a stand-alone beam-focusing flat lens for use in the telecommunications wavelength range. Light incident on the back surface of the lens propagates through a subwavelength aperture and is heavily diffracted on exit and partially couples into a surface plasmon polariton and a surface wave propagating along the surface of the lens. Interference between the diffracted wave and re-emission from a grating patterned on the surface produces a highly collimated beam. We show for the first time a geometry at which a lens of this type can be used at telecommunication wavelengths (λ=1.55 μm) and identify the light coupling and re-emission mechanisms involved. Measured beam profile results at varying incident wavelengths show excellent agreement with Lumerical FDTD simulation results.

Generation of light from free electrons.

PubMed

Salisbury, W W

1966-10-21

Experiments with the interaction of a rectangular cross- section beam of electrons which is brought into contact with a metallic diffraction grat e ng produce light variable in wavelength throughout the visible spectrum. Con tinuous variation of the beam thickness shows that light is produced by electrons hundreds of wavelengths from the grating, if the side of the beam near the grating is in contact with it. The results can be accounted for by periodic accelerations of the electrons passing over the surface of the grating. These accelerations are caused by electrostatic forces which in turn are due to the average spacecharge of sheets of elec trons reflected from the grating surface, so that in their space- charge structure the periodicity of the grating rulings is preserved.

Large area and deep sub-wavelength interference lithography employing odd surface plasmon modes.

PubMed

Liu, Liqin; Luo, Yunfei; Zhao, Zeyu; Zhang, Wei; Gao, Guohan; Zeng, Bo; Wang, Changtao; Luo, Xiangang

2016-07-28

In this paper, large area and deep sub-wavelength interference patterns are realized experimentally by using odd surface plasmon modes in the metal/insulator/metal structure. Theoretical investigation shows that the odd modes possesses much higher transversal wave vector and great inhibition of tangential electric field components, facilitating surface plasmon interference fringes with high resolution and contrast in the measure of electric field intensity. Interference resist patterns with 45 nm (∼λ/8) half-pitch, 50 nm depth, and area size up to 20 mm × 20 mm were obtained by using 20 nm Al/50 nm photo resist/50 nm Al films with greatly reduced surface roughness and 180 nm pitch exciting grating fabricated with conventional laser interference lithography. Much deeper resolution down to 19.5 nm is also feasible by decreasing the thickness of PR. Considering that no requirement of expensive EBL or FIB tools are employed, it provides a cost-effective way for large area and nano-scale fabrication.

Surface plasmon effects in the absorption enhancements of amorphous silicon solar cells with periodical metal nanowall and nanopillar structures.

PubMed

Lin, Hung-Yu; Kuo, Yang; Liao, Cheng-Yuan; Yang, C C; Kiang, Yean-Woei

2012-01-02

The authors numerically investigate the absorption enhancement of an amorphous Si solar cell, in which a periodical one-dimensional nanowall or two-dimensional nanopillar structure of the Ag back-reflector is fabricated such that a dome-shaped grating geometry is formed after Si deposition and indium-tin-oxide coating. In this investigation, the effects of surface plasmon (SP) interaction in such a metal nanostructure are of major concern. Absorption enhancement in most of the solar spectral range of significant amorphous Si absorption (320-800 nm) is observed in a grating solar cell. In the short-wavelength range of high amorphous Si absorption, the weakly wavelength-dependent absorption enhancement is mainly caused by the broadband anti-reflection effect, which is produced through the surface nano-grating structures. In the long-wavelength range of diminishing amorphous Si absorption, the highly wavelength-sensitive absorption enhancement is mainly caused by Fabry-Perot resonance and SP interaction. The SP interaction includes the contributions of surface plasmon polariton and localized surface plasmon.

Multi-Bandwidth Frequency Selective Surfaces for Near Infrared Filtering: Design and Optimization

NASA Technical Reports Server (NTRS)

Cwik, Tom; Fernandez, Salvador; Ksendzov, A.; LaBaw, Clayton C.; Maker, Paul D.; Muller, Richard E.

1999-01-01

Frequency selective surfaces are widely used in the microwave and millimeter wave regions of the spectrum for filtering signals. They are used in telecommunication systems for multi-frequency operation or in instrument detectors for spectroscopy. The frequency selective surface operation depends on a periodic array of elements resonating at prescribed wavelengths producing a filter response. The size of the elements is on the order of half the electrical wavelength, and the array period is typically less than a wavelength for efficient operation. When operating in the optical region, diffraction gratings are used for filtering. In this regime the period of the grating may be several wavelengths producing multiple orders of light in reflection or transmission. In regions between these bands (specifically in the infrared band) frequency selective filters consisting of patterned metal layers fabricated using electron beam lithography are beginning to be developed. The operation is completely analogous to surfaces made in the microwave and millimeter wave region except for the choice of materials used and the fabrication process. In addition, the lithography process allows an arbitrary distribution of patterns corresponding to resonances at various wavelengths to be produced. The design of sub-millimeter filters follows the design methods used in the microwave region. Exacting modal matching, integral equation or finite element methods can be used for design. A major difference though is the introduction of material parameters and thicknesses tha_ may not be important in longer wavelength designs. This paper describes the design of multi-bandwidth filters operating in the I-5 micrometer wavelength range. This work follows on previous design [1,2]. In this paper extensions based on further optimization and an examination of the specific shape of the element in the periodic cell will be reported. Results from the design, manufacture and test of linear wedge filters built using micro-lithographic techniques and used ir spectral imaging applications will be presented.

Multi-Bandwidth Frequency Selective Surfaces for Near Infrared Filtering: Design and Optimization

NASA Technical Reports Server (NTRS)

Cwik, Tom; Fernandez, Salvador; Ksendzov, A.; LaBaw, Clayton C.; Maker, Paul D.; Muller, Richard E.

1998-01-01

Frequency selective surfaces are widely used in the microwave and millimeter wave regions of the spectrum for filtering signals. They are used in telecommunication systems for multi-frequency operation or in instrument detectors for spectroscopy. The frequency selective surface operation depends on a periodic array of elements resonating at prescribed wavelengths producing a filter response. The size of the elements is on the order of half the electrical wavelength, and the array period is typically less than a wavelength for efficient operation. When operating in the optical region, diffraction gratings are used for filtering. In this regime the period of the grating may be several wavelengths producing multiple orders of light in reflection or transmission. In regions between these bands (specifically in the infrared band) frequency selective filters consisting of patterned metal layers fabricated using electron beam lithography are beginning to be developed. The operation is completely analogous to surfaces made in the microwave and millimeter wave region except for the choice of materials used and the fabrication process. In addition, the lithography process allows an arbitrary distribution of patterns corresponding to resonances at various wavelengths to be produced. The design of sub-millimeter filters follows the design methods used in the microwave region. Exacting modal matching, integral equation or finite element methods can be used for design. A major difference though is the introduction of material parameters and thicknesses that may not be important in longer wavelength designs. This paper describes the design of multi- bandwidth filters operating in the 1-5 micrometer wavelength range. This work follows on a previous design. In this paper extensions based on further optimization and an examination of the specific shape of the element in the periodic cell will be reported. Results from the design, manufacture and test of linear wedge filters built using microlithographic techniques and used in spectral imaging applications will be presented.

Continuous wavelength tunable laser source with optimum positioning of pivot axis for grating

DOEpatents

Pushkarsky, Michael; Amone, David F.

2010-06-08

A laser source (10) for generating a continuously wavelength tunable light (12) includes a gain media (16), an optical output coupler (36F), a cavity collimator (38A), a diffraction grating (30), a grating beam (54), and a beam attacher (56). The diffraction grating (30) is spaced apart from the cavity collimator (38A) and the grating (30) cooperates with the optical output coupler (36F) to define an external cavity (32). The grating (30) includes a grating face surface (42A) that is in a grating plane (42B). The beam attacher (56) retains the grating beam (54) and allows the grating beam (54) and the grating (30) to effectively pivot about a pivot axis (33) that is located approximately at an intersection of a pivot plane (50) and the grating plane (42B). As provided herein, the diffraction grating (30) can be pivoted about the unique pivot axis (33) to move the diffraction grating (30) relative to the gain media (16) to continuously tune the lasing frequency of the external cavity (32) and the wavelength of the output light (12) so that the output light (12) is mode hop free.

Simulation framework for electromagnetic effects in plasmonics, filter apertures, wafer scattering, grating mirrors, and nano-crystals

NASA Astrophysics Data System (ADS)

Ceperley, Daniel Peter

This thesis presents a Finite-Difference Time-Domain simulation framework as well as both scientific observations and quantitative design data for emerging optical devices. These emerging applications required the development of simulation capabilities to carefully control numerical experimental conditions, isolate and quantifying specific scattering processes, and overcome memory and run-time limitations on large device structures. The framework consists of a new version 7 of TEMPEST and auxiliary tools implemented as Matlab scripts. In improving the geometry representation and absorbing boundary conditions in TEMPEST from v6 the accuracy has been sustained and key improvements have yielded application specific speed and accuracy improvements. These extensions include pulsed methods, PML for plasmon termination, and plasmon and scattered field sources. The auxiliary tools include application specific methods such as signal flow graphs of plasmon couplers, Bloch mode expansions of sub-wavelength grating waves, and back-propagation methods to characterize edge scattering in diffraction masks. Each application posed different numerical hurdles and physical questions for the simulation framework. The Terrestrial Planet Finder Coronagraph required accurate modeling of diffraction mask structures too large for solely FDTD analysis. This analysis was achieved through a combination of targeted TEMPEST simulations and full system simulator based on thin mask scalar diffraction models by Ball Aerospace for JPL. TEMPEST simulation showed that vertical sidewalls were the strongest scatterers, adding nearly 2lambda of light per mask edge, which could be reduced by 20° undercuts. TEMPEST assessment of coupling in rapid thermal annealing was complicated by extremely sub-wavelength features and fine meshes. Near 100% coupling and low variability was confirmed even in the presence of unidirectional dense metal gates. Accurate analysis of surface plasmon coupling efficiency by small surface features required capabilities to isolate these features and cleanly illuminate them with plasmons and plane-waves. These features were shown to have coupling cross-sections up to and slightly exceeding their physical size. Long run-times for TEMPEST simulations of finite length gratings were overcome with a signal flow graph method. With these methods a plasmon coupler with over a 10lambda 100% capture length was demonstrated. Simulation of 3D nano-particle arrays utilized TEMPEST v7's pulsed methods to minimize the number of multi-day simulations. These simulations led to the discovery that interstitial plasmons were responsible for resonant absorption and transmission but not reflection. Simulation of a sub-wavelength grating mirror using pulsed sources to map resonant spectra showed that neither coupled guided waves nor coupled isolated resonators accurately described the operation. However, a new model based on vertical propagation of lateral Bloch modes with zero phase progression efficiently characterized the device and provided principles for designing similar devices at other wavelengths.

Physics of near-wavelength high contrast gratings.

PubMed

Karagodsky, Vadim; Chang-Hasnain, Connie J

2012-05-07

We present a simple theory explaining the extraordinary features of high-contrast optical gratings in the near-wavelength regime, particularly the very broadband high reflectivity (>99%) and the ultra-high quality factor resonances (Q>10(7)). We present, for the first time, an intuitive explanation for both features using a simple phase selection rule, and reveal the anti-crossing and crossing effects between the grating modes. Our analytical results agree well with simulations and the experimental data obtained from vertical cavity surface emitting lasers incorporating a high contrast grating as top reflector.

Plasmonics analysis of nanostructures for bioapplications

NASA Astrophysics Data System (ADS)

Xie, Qian

Plasmonics, the science and technology of the plasmons, is a rapidly growing field with substantial broader impact in numerous different fields, especially for bio-applications such as bio-sensing, bio-photonics and photothermal therapy. Resonance effects associated with plasmatic behavior i.e. surface Plasmon resonance (SPR) and localize surface Plasmon resonance (LSPR), are of particular interest because of their strong sensitivity to the local environment. In this thesis, plasmonic resonance effects are discussed from the basic theory to applications, especially the application in photothermal therapy, and grating bio-sensing. This thesis focuses on modeling different metallic nanostructures, i.e. nanospheres, nanorods, core-shell nanoparticles, nanotori and hexagonal closed packed nanosphere structures, to determine their LSPR wavelengths for use in various applications. Experiments regarding photothermal therapy using gold nanorods are described and a comparison is presented with results obtained from simulations. Lastly, experiments of grating-based plasmon-enhanced bio-sensing are also discussed. In chapter one, the physics of plasmonics is reviewed, including surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR). In the section on surface plasmon resonance, the physics behind the phenomenon is discussed, and also, the detection methods and applications in bio-sensing are described. In the section on localized surface plasmon resonance (LSPR), the phenomenon is described with respect to sub wavelength metallic nanoparticles. In chapter two, specific plasmonic-based bio-applications are discussed including plasmonic and magneto-plasmonic enhanced photothermal therapy and grating-based SPR bio-sening. In chapter three, which is the most important part in the thesis, optical modeling of different gold nanostructures is presented. The modeling tools used in this thesis are Comsol and custom developed Matlab programs. In Comsol, the geometries of different metallic nanostructures are drawn and simulated using finite element-based computational electromagnetics. The power absorption of the nanostructures is plotted as a function of wavelength to identify the LSPR wavelength, i.e. the wavelength of peak absorption. In Matlab, Mie scattering theory is programmed in terms of semi-analytical mathematical equations, which predict the power absorption for specific plasmonic geometries, i.e. nanospheres, nanorods and core-shell particles. These predictions, which are much faster than the Comsol analysis, are validated using corresponding numerical simulations. In chapter four, experiments involving novel magneto-plasmonic Nano platforms are described, and experimental data is presented to illustrate the use of the modeling in analyzing these particles. Simulations are performed to determine the influence on the laser absorption of magnetic nanospheres in proximity to metallic nanorods. These results are compared with experimental data. In the last chapter, experiments using a grating-based SPR sensor are described, and modeling results are also presented. In summary, this thesis discusses the physics of plasmonics, electromagnetic analysis for predicting the absorption spectra of metallic nanoparticles and bio-applications that utilize these effects.

Plasmon-emitter interaction using integrated ring grating-nanoantenna structures.

PubMed

Rahbany, Nancy; Geng, Wei; Bachelot, Renaud; Couteau, Christophe

2017-05-05

Overcoming the diffraction limit to achieve high optical resolution is one of the main challenges in the fields of plasmonics, nanooptics and nanophotonics. In this work, we introduce novel plasmonic structures consisting of nanoantennas (nanoprisms, single bowtie nanoantennas and double bowtie nanoantennas) integrated in the center of ring diffraction gratings. Propagating surface plasmon polaritons (SPPs) are generated by the ring grating and coupled with localized surface plasmons (LSPs) at the nanoantennas exciting emitters placed in their gap. SPPs are widely used for optical waveguiding but provide low resolution due to their weak spatial confinement. In contrast, LSPs provide excellent sub-wavelength confinement but induce large losses. The phenomenon of SPP-LSP coupling witnessed in our structures allows for achieving more precise focusing at the nanoscale, causing an increase in the fluorescence emission of the emitters. Finite-difference time-domain simulations as well as experimental fabrication and optical characterization results are presented to study plasmon-emitter coupling between an ensemble of dye molecules and our integrated plasmonic structures. A comparison is given to highlight the importance of each structure on the photoluminescence and radiative decay enhancement of the molecules.

Plasmon-emitter interaction using integrated ring grating-nanoantenna structures

NASA Astrophysics Data System (ADS)

Rahbany, Nancy; Geng, Wei; Bachelot, Renaud; Couteau, Christophe

2017-05-01

Overcoming the diffraction limit to achieve high optical resolution is one of the main challenges in the fields of plasmonics, nanooptics and nanophotonics. In this work, we introduce novel plasmonic structures consisting of nanoantennas (nanoprisms, single bowtie nanoantennas and double bowtie nanoantennas) integrated in the center of ring diffraction gratings. Propagating surface plasmon polaritons (SPPs) are generated by the ring grating and coupled with localized surface plasmons (LSPs) at the nanoantennas exciting emitters placed in their gap. SPPs are widely used for optical waveguiding but provide low resolution due to their weak spatial confinement. In contrast, LSPs provide excellent sub-wavelength confinement but induce large losses. The phenomenon of SPP-LSP coupling witnessed in our structures allows for achieving more precise focusing at the nanoscale, causing an increase in the fluorescence emission of the emitters. Finite-difference time-domain simulations as well as experimental fabrication and optical characterization results are presented to study plasmon-emitter coupling between an ensemble of dye molecules and our integrated plasmonic structures. A comparison is given to highlight the importance of each structure on the photoluminescence and radiative decay enhancement of the molecules.

Grating-coupled surface plasmons on InSb: a versatile platform for terahertz plasmonic sensing (Conference Presentation)

NASA Astrophysics Data System (ADS)

Talbayev, Diyar; Zhou, Jiangfeng; Lin, Shuai; Bhattarai, Khagendra

2017-05-01

Detection and identification of molecular materials based on their THz frequency vibrational resonances remains an open technological challenge. The need for such technology is illustrated by its potential uses in explosives detection (e.g., RDX) or identification of large biomolecules based on their THz-frequency vibrational fingerprints. The prevailing approaches to THz sensing often rely on a form of waveguide spectroscopy, either utilizing geometric waveguides, such as metallic parallel plate, or plasmonic waveguides made of structured metallic surfaces with sub-wavelength corrugation. The sensitivity of waveguide-based sensing devices is derived from the long (1 cm or longer) propagation and interaction distance of the THz wave with the analyte. We have demonstrated that thin InSb layers with metallic gratings can support high quality factor "true" surface plasmon (SP) resonances that can be used for THz plasmonic sensing. We find two strong SP absorption resonances in normal-incidence transmission and investigate their dispersion relations, dependence on InSb thickness, and the spatial distribution of the electric field. The sensitivity of this approach relies on the frequency shift of the SP resonance when the dielectric function changes in the immediate vicinity of the sensor, in the region of deeply sub-wavelength thickness. Our computational modeling indicates that the sensor sensitivity can exceed 0.25 THz per refractive index unit. One of the SP resonances also exhibits a splitting when tuned in resonance with a vibrational mode of an analyte, which could lead to new sensing modalities for the detection of THz vibrational features of the analyte.

Simulation of two-dimensional gratings for SERS-active substrate

NASA Astrophysics Data System (ADS)

Zou, Wenlong; Wu, Jianhong

2016-11-01

Raman spectroscopy provides intrinsic vibrational and rotational mode of molecules in materials, which is widely used in chemical, medical and environmental domains. As known, the magnitude of surface enhanced Raman scattering can be amplified several orders. Nowadays, common Raman scattering has been gradually replaced by surface enhanced Raman scattering in low concentration detection domain. Generally speaking, the signal of surface enhanced Raman scattering on periodic nanostructures is more reliable and reproducible than on irregular nanostructures. In this paper, two-dimensional gratings coated by noble metal are used as SERS-active substrate. The surface plasmon resonance can be obtained by tuning the period of two-dimensional grating when the excitation laser interacts on the grating. The local electric field distribution is simulated by finite-difference-time-domain (FDTD). The wavelength of 632.8nm and 785nm are usually assembled on commercial Raman spectrometer. The optimization procedure of two-dimensional grating period is simulated by FDTD for above two wavelengths. The relation between the grating period and surface plasmon resonance is obtained in theory. The parameters such as depth of photoresist and thickness of coated metal are systematic discussed. The simulation results will greatly guide our post manufacture, which can be served for the commercial Raman spectrometer in SERS detection.

Incorporation of nanovoids into metallic gratings for broadband plasmonic organic solar cells.

PubMed

Lee, Sangjun; In, Sungjun; Mason, Daniel R; Park, Namkyoo

2013-02-25

We present investigation and optimization of a newly proposed plasmonic organic solar cell geometry based on the incorporation of nanovoids into conventional rectangular backplane gratings. Hybridization of strongly localized plasmonic modes of the nanovoids with Fabry-Perot cavity modes originating from surface plasmon reflection at the grating elements is shown to significantly boost performance in the long wavelength regime. This constitutes improved broadband operation while maintaining absorption enhancements at short wavelengths derived from conventional rectangular grating. Our calculations predict a figure of merit enhancement of up to 41% compared to when the nanovoid indented grating is absent. This is a significant improvement over the previously considered rectangular grating structures, which is further shown to be maintained over the entire angular range.

X-ray diffraction gratings: Precise control of ultra-low blaze angle via anisotropic wet etching

DOE Office of Scientific and Technical Information (OSTI.GOV)

Voronov, Dmitriy L.; Naulleau, Patrick; Gullikson, Eric M.

2016-07-25

Diffraction gratings are used from micron to nanometer wavelengths as dispersing elements in optical instruments. At shorter wavelengths, crystals can be used as diffracting elements, but due to the 3D nature of the interaction with light are wavelength selective rather than wavelength dispersing. There is an urgent need to extend grating technology into the x-ray domain of wavelengths from 1 to 0.1 nm, but this requires the use of gratings that have a faceted surface in which the facet angles are very small, typically less than 1°. Small facet angles are also required in the extreme ultra-violet and soft x-ray energymore » ranges in free electron laser applications, in order to reduce power density below a critical damage threshold. In this work, we demonstrate a technique based on anisotropic etching of silicon designed to produce very small angle facets with a high degree of perfection.« less

Infrared wire-grid polarizer with sol-gel zirconia grating

NASA Astrophysics Data System (ADS)

Yamada, Itsunari; Ishihara, Yoshiro

2017-05-01

The infrared wire-grid polarizer consisting of an Al grating, Si, and sol-gel derived zirconia grating film was fabricated by soft imprint process and Al shadow coating processes. A silicone mold was used because of its low surface energy, flexibility, and capability of transferring submicrosized patterns. As a result, the Al grating with a pitch of 400 nm and a depth of 100 nm was obtained on the zirconia grating film. The fabricated polarizer exhibited a polarization function with the TM transmittance greater than that of the Si substrate in the specific wavelength range of 3.6-8.5 μm, because the zirconia film acted as an antireflection film. The maximum value was 63% at a wavelength of 5.2 μm. This increment of the TM transmission spectrum results in interference within the zirconia film. Also, the extinction ratio exceeded almost 20 dB in the 3-8.8 μm wavelength range.

Using optical masks to create and image sub-optical wavelength atomic structures in a MOT

NASA Astrophysics Data System (ADS)

Turlapov, Andrey; Tonyushkin, Aleksey; Sleator, Tycho

2002-05-01

We have used an ``optical mask'' for Rubidium atoms in a magneto-optical trap to create and image atomic density gratings with periodicities as small as 1/8th of an optical wavelength ( ˜ 100 nm). The mask consists of a pulse of an optical standing wave (wavelength λ) resonant to an open atomic transition. The interaction pumps all atoms except those near the nodes into another hyperfine ground state, leaving a grating of ``spikes'' in atomic density in the initial ground state. The nodes of the standing wave serve as slits of the mask. By applying two such masks separated by time T, we have created atomic gratings of period λ/(2n) (or smaller) at times (n+1)/n T after the first mask pulse. For T on the order of the Talbot time (or inverse recoil frequency), quantum effects are important for the dynamics of the atomic center of mass. Under appropriate conditions, these quantum effects led to a reduction of the period of the resulting density gratings (Talbot-Lau effect). The resulting density gratings of period λ/2n (for n=1 to 4) were imaged in real time using an additional optical mask.

Nanostructure Diffraction Gratings for Integrated Spectroscopy and Sensing

NASA Technical Reports Server (NTRS)

Guo, Junpeng (Inventor)

2015-01-01

The present disclosure pertains to metal or dielectric nanostructures of the subwavelength scale within the grating lines of optical diffraction gratings. The nanostructures have surface plasmon resonances or non-plasmon optical resonances. A linear photodetector array is used to capture the resonance spectra from one of the diffraction orders. The combined nanostructure super-grating and photodetector array eliminates the use of external optical spectrometers for measuring surface plasmon or optical resonance frequency shift caused by the presence of chemical and biological agents. The nanostructure super-gratings can be used for building integrated surface enhanced Raman scattering (SERS) spectrometers. The nanostructures within the diffraction grating lines enhance Raman scattering signal light while the diffraction grating pattern of the nanostructures diffracts Raman scattering light to different directions of propagation according to their wavelengths. Therefore, the nanostructure super-gratings allows for the use of a photodetector array to capture the surface enhanced Raman scattering spectra.

Nanostructure Diffraction Gratings for Integrated Spectroscopy and Sensing

NASA Technical Reports Server (NTRS)

Guo, Junpeng (Inventor)

2016-01-01

The present disclosure pertains to metal or dielectric nanostructures of the subwavelength scale within the grating lines of optical diffraction gratings. The nanostructures have surface plasmon resonances or non-plasmon optical resonances. A linear photodetector array is used to capture the resonance spectra from one of the diffraction orders. The combined nanostructure super-grating and photodetector array eliminates the use of external optical spectrometers for measuring surface plasmon or optical resonance frequency shift caused by the presence of chemical and biological agents. The nanostructure super-gratings can be used for building integrated surface enhanced Raman scattering (SERS) spectrometers. The nanostructures within the diffraction grating lines enhance Raman scattering signal light while the diffraction grating pattern of the nanostructures diffracts Raman scattering light to different directions of propagation according to their wavelengths. Therefore, the nanostructure super-gratings allows for the use of a photodetector array to capture the surface enhanced Raman scattering spectra.

Condensation phenomenon detection through surface plasmon resonance.

PubMed

Ibrahim, Joyce; Al Masri, Mostafa; Veillas, Colette; Celle, Frédéric; Cioulachtjian, Serge; Verrier, Isabelle; Lefèvre, Frédéric; Parriaux, Olivier; Jourlin, Yves

2017-10-02

The aim of this work is to optically detect the condensation of acetone vapor on an aluminum plate cooled down in a two-phase environment (liquid/vapor). Sub-micron period aluminum based diffraction gratings with appropriate properties, exhibiting a highly sensitive plasmonic response, were successfully used for condensation experiments. A shift in the plasmonic wavelength resonance has been measured when acetone condensation on the aluminum surface takes place due to a change of the surrounding medium close to the surface, demonstrating that the surface modification occurs at the very beginning of the condensation phenomenon. This paper presents important steps in comprehending the incipience of condensate droplet and frost nucleation (since both mechanisms are similar) and thus to control the phenomenon by using an optimized engineered surface.

Air-suspended TiO2-based HCG reflectors for visible spectral range

NASA Astrophysics Data System (ADS)

Hashemi, Ehsan; Bengtsson, Jörgen; Gustavsson, Johan; Carlsson, Stefan; Rossbach, Georg; Haglund, Åsa

2015-02-01

For GaN-based microcavity light emitters, such as vertical-cavity surface-emitting lasers (VCSELs) and resonant cavity light emitting diodes (RCLEDs) in the blue-green wavelength regime, achieving a high reflectivity wide bandwidth feedback mirror is truly challenging. The material properties of the III-nitride alloys are hardly compatible with the conventional distributed Bragg reflectors (DBRs) and the newly proposed high-contrast gratings (HCGs). Alternatively, at least for the top outcoupling mirror, dielectric materials offer more suitable material combinations not only for the DBRs but also for the HCGs. HCGs may offer advantages such as transverse mode and polarization control, a broader reflectivity spectrum than epitaxially grown DBRs, and the possibility to set the resonance wavelength after epitaxial growth by the grating parameters. In this work we have realized an air-suspended TiO2 grating with the help of a SiO2 sacrificial layer. The deposition processes for the dielectric layers were fine-tuned to minimize the residual stress. To achieve an accurate control of the grating duty cycle, a newly developed lift-off process, using hydrogen silesquioxan (HSQ) and sacrificial polymethyl-methacrylate (PMMA) resists, was applied to deposit the hard mask, providing sub-10 nm resolution. The finally obtained TiO2/air HCGs were characterized in a micro-reflectance measurement setup. A peak power reflectivity in excess of 95% was achieved for TM polarization at the center wavelength of 435 nm, with a reflectivity stopband width of about 80 nm (FWHM). The measured HCG reflectance spectra were compared to corresponding simulations obtained from rigorous coupled-wave analysis and very good agreement was found.

Multimode Surface Plasmon Excitations on Organic Thin Film/Metallic Diffraction Grating

NASA Astrophysics Data System (ADS)

Baba, Akira; Kanda, Kenji; Ohno, Tsutomu; Ohdaira, Yasuo; Shinbo, Kazunari; Kato, Keizo; Kaneko, Futao

2010-01-01

In this work, we demonstrate multimode surface plasmon (SP) excitations by white light irradiation on metallic diffraction grating/plastic substrates. Recordable compact discs were used as the diffraction grating substrates on which silver films were deposited by vacuum evaporation. Since the grating pitch (1.6 µm) was larger than that of diffraction gratings commonly used for the excitation of SPs, multimode SP excitations due to several diffraction orders were observed simultaneously in the wavelength region from 400 to 800 nm. The obtained SP excitations were then compared with the calculated SP dispersion on the grating. The multimode SP excitations were further studied on spin-coated poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) thin film/silver grating substrates. An increased photoluminescence intensity due to SP excitations was observed on MEH-PPV/silver grating surfaces.

Thermal infrared observations of Mars (7.5-12.8 microns) during the 1990 opposition

NASA Technical Reports Server (NTRS)

Roush, T. L.; Witteborn, F.; Lucy, P. G.; Graps, A.; Pollack, J. B.

1991-01-01

Thirteen spectra of Mars, in the 7.5 to 12.8 micron wavelength were obtained on 7 Dec. 1990 from the Infrared Telescope Facility (IRTF). For these observations, a grating with an ultimate resolving power of 120 to 250 was used and wavelengths were calibrated for each grating setting by comparison with the absorption spectrum of polystyrene measured prior to each set of observations. By sampling the Nyquist limit at the shortest wavelengths, an effective resolving power of about 120 over the entire wavelength range was achieved. A total of four grating settings were required to cover the entire wavelength region. A typical observing sequence consisted of: (1) positioning the grating in one of the intervals; (2) calibrating the wavelength of positions; and (3) obtaining spectra for a number of spots on Mars. Several observations of the nearby stellar standard star, alpha Tauri, were also acquired throughout the night. Each Mars spectrum represents an average of 4 to 6 measurements of the individual Mars spots. As a result of this observing sequence, the viewing geometry for a given location or spot on Mars does not change, but the actual location of the spot on Mars's surface varies somewhat between the different grating settings. Other aspects of the study are presented.

Tunable resonance-domain diffraction gratings based on electrostrictive polymers.

PubMed

Axelrod, Ramon; Shacham-Diamand, Yosi; Golub, Michael A

2017-03-01

Critical combination of high diffraction efficiency and large diffraction angles can be delivered by resonance-domain diffractive optics with high aspect ratio and wavelength-scale grating periods. To advance from static to electrically tunable resonance-domain diffraction grating, we resorted to its replication onto 2-5 μm thick P(VDF-TrFE-CFE) electrostrictive ter-polymer membranes. Electromechanical and optical computer simulations provided higher than 90% diffraction efficiency, a large continuous deflection range exceeding 20°, and capabilities for adiabatic spatial modulation of the grating period and slant. A prototype of the tunable resonance-domain diffraction grating was fabricated in a soft-stamp thermal nanoimprinting process, characterized, optically tested, and provided experimental feasibility proof for the tunable sub-micron-period gratings on electrostrictive polymers.

Tunable, superconducting, surface-emitting teraherz source

DOEpatents

Welp, Ulrich [Lisle, IL; Koshelev, Alexei E [Bolingbrook, IL; Gray, Kenneth E [Evanston, IL; Kwok, Wai-Kwong [Evanston, IL; Vlasko-Vlasov, Vitalii [Downers Grove, IL

2009-10-27

A compact, solid-state THz source based on the driven Josephson vortex lattice in a highly anisotropic superconductor such as Bi.sub.2Sr.sub.2CaCu.sub.2O.sub.8 that allows cw emission at tunable frequency. A second order metallic Bragg grating is used to achieve impedance matching and to induce surface emission of THz-radiation from a Bi.sub.2Sr.sub.2CaCu.sub.2O.sub.8 sample. Steering of the emitted THz beam is accomplished by tuning the Josephson vortex spacing around the grating period using a superimposed magnetic control field.

Tunable, superconducting, surface-emitting teraherz source

DOEpatents

Welp, Ulrich; Koshelev, Alexei E.; Gray, Kenneth E.; Kwok, Wai-Kwong; Vlasko-Vlasov, Vitalii

2010-05-11

A compact, solid-state THz source based on the driven Josephson vortex lattice in a highly anisotropic superconductor such as Bi.sub.2Sr.sub.2CaCu.sub.2O.sub.8 that allows cw emission at tunable frequency. A second order metallic Bragg grating is used to achieve impedance matching and to induce surface emission of THz-radiation from a Bi.sub.2Sr.sub.2CaCu.sub.2O.sub.8 sample. Steering of the emitted THz beam is accomplished by tuning the Josephson vortex spacing around the grating period using a superimposed magnetic control field.

The Algorithm for MODIS Wavelength On-Orbit Calibration Using the SRCA

NASA Technical Reports Server (NTRS)

Montgomery, Harry; Che, Nianzeng; Parker, Kirsten; Bowser, Jeff

1998-01-01

The Spectro-Radiometric Calibration Assembly (SRCA) provides on-orbit spectral calibration of the MODerate resolution Imaging Spectroradiometer (MODIS) reflected solar bands and this paper describes how it is accomplished. The SRCA has two adjacent exit slits: 1) Main slit and 2) Calibration slit. The output from the main slit is measured by a reference silicon photo-diode (SIPD) and then passes through the MODIS. The output from the calibration slit passes through a piece of didymium transmission glass and then it is measured by a calibration SIPD. The centroids of the sharp spectral peaks of a didymium glass are utilized as wavelength standards. After normalization using the reference SIPD signal to eliminate the effects of the illuminating source spectra, the calibration SIPD establishes the relationship between the peaks of the didymium spectra and the grating angle; this is accomplished through the grating equation. In the grating equation the monochromator parameters, Beta (half angle between the incident and diffractive beams) and Theta(sub off) (offset angle of the grating motor) are determined by matching, in a least square sense, the known centroid wavelengths of the didymium peaks and the calculated centroid grating angles from the calibration SIPD signals for the peaks. A displacement between the calibration SIPD and the reference SIPD complicates the signal processing.

Spectral and angular characteristics of dielectric resonator metasurface at optical frequencies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zou, Longfang; Department of Electrical and Electronic Engineering, The University of Bristol, Bristol, BS8 1TH; López-García, Martin

2014-11-10

The capability of manipulating light at subwavelength scale has fostered the applications of flat metasurfaces in various fields. Compared to metallic structure, metasurfaces made of high permittivity low-loss dielectric resonators hold the promise of high efficiency by avoiding high conductive losses of metals at optical frequencies. This letter investigates the spectral and angular characteristics of a dielectric resonator metasurface composed of periodic sub-arrays of resonators with a linearly varying phase response. The far-field response of the metasurface can be decomposed into the response of a single grating element (sub-array) and the grating arrangement response. The analysis also reveals that couplingmore » between resonators has a non-negligible impact on the angular response. Over a wide wavelength range, the simulated and measured angular characteristics of the metasurface provide a definite illustration of how different grating diffraction orders can be selectively suppressed or enhanced through antenna sub-array design.« less

Optimal coupling to high-Q whispering gallery modes with a sub-wavelength metallic grating coupler

NASA Astrophysics Data System (ADS)

Zhou, Y.; Gu, B.; Yu, X.; Luan, F.

2015-03-01

Gold grating patterned on the end facet of an optical fiber is able to excite whispering gallery mode (WGM) in a silica microsphere. With a direct pathway of the metal reflection, the coupled WGM is able to superimpose and create an asymmetric Fano resonance. Since multiple resonances are present - the WGM, grating reflection, and a weak Fabry-Perot resonance along the diameter of the sphere - it is difficult to evaluate the power efficiency directly from the measured spectrum. Using temporal coupled-mode theory, a general model is constructed for the end-fire coupling from a grating to a WGM resonator.

Immersion Gratings for Infrared High-resolution Spectroscopy

NASA Astrophysics Data System (ADS)

Sarugaku, Yuki; Ikeda, Yuji; Kobayashi, Naoto; Kaji, Sayumi; Sukegawa, Takashi; Sugiyama, Shigeru; Nakagawa, Takao; Arasaki, Takayuki; Kondo, Sohei; Nakanishi, Kenshi; Yasui, Chikako; Kawakita, Hideyo

2016-10-01

High-resolution spectroscopy in the infrared wavelength range is essential for observations of minor isotopologues, such as HDO for water, and prebiotic organic molecules like hydrocarbons/P-bearing molecules because numerous vibrational molecular bands (including non-polar molecules) are located in this wavelength range. High spectral resolution enables us to detect weak lines without spectral line confusion. This technique has been widely used in planetary sciences, e.g., cometary coma (H2O, CO, and organic molecules), the martian atmosphere (CH4, CO2, H2O and HDO), and the upper atmosphere of gas giants (H3+ and organic molecules such as C2H6). Spectrographs with higher resolution (and higher sensitivity) still have a potential to provide a plenty of findings. However, because the size of spectrographs scales with the spectral resolution, it is difficult to realize it.Immersion grating (IG), which is a diffraction grating wherein the diffraction surface is immersed in a material with a high refractive index (n > 2), provides n times higher spectral resolution compared to a reflective grating of the same size. Because IG reduces the size of spectrograph to 1/n compared to the spectrograph with the same spectral resolution using a conventional reflective grating, it is widely acknowledged as a key optical device to realize compact spectrographs with high spectral resolution.Recently, we succeeded in fabricating a CdZnTe immersion grating with the theoretically predicted diffraction efficiency by machining process using an ultrahigh-precision five-axis processing machine developed by Canon Inc. Using the same technique, we completed a practical germanium (Ge) immersion grating with both a reflection coating on the grating surface and the an AR coating on the entrance surface. It is noteworthy that the wide wavelength range from 2 to 20 um can be covered by the two immersion gratings.In this paper, we present the performances and the applications of the immersion gratings, including the development of a long-NIR (2-5um) high-resolution (R=80,000) spectrograph with Ge-immersion grating, VINROUGE, which is a prototype for the TMT MIR instrument.

Infrared Polarizer Fabrication by Imprinting on Sb-Ge-Sn-S Chalcogenide Glass

NASA Astrophysics Data System (ADS)

Yamada, Itsunari; Yamashita, Naoto; Tani, Kunihiko; Einishi, Toshihiko; Saito, Mitsunori; Fukumi, Kouhei; Nishii, Junji

2012-01-01

We fabricated infrared wire-grid polarizers consisting of a 500-nm pitch Al grating on a low toxic chalcogenide glass (Sb-Ge-Sn-S system) using the direct imprinting of subwavelength grating followed by a deposition of Al metal by thermal evaporation. To fabricate the subwavelength grating on a chalcogenide glass more easily, the sharp grating was formed on the mold surface. The fabricated polarizer with Al thickness of 130 nm exhibited a polarization function with a transverse magnetic transmittance greater than 60% in the 5-9 µm wavelength range, and an extinction ratio greater than 20 dB in 3.5-11 µm wavelength range. The extinction ratio of the element with Al wires of 180-nm thickness reached 27 dB at 5.4-µm wavelength. The polarizer can be fabricated at lower costs and simpler fabrication processes compared to conventional infrared polarizers.

Electrically-programmable diffraction grating

DOEpatents

Ricco, Antonio J.; Butler, Michael A.; Sinclair, Michael B.; Senturia, Stephen D.

1998-01-01

An electrically-programmable diffraction grating. The programmable grating includes a substrate having a plurality of electrodes formed thereon and a moveable grating element above each of the electrodes. The grating elements are electrostatically programmable to form a diffraction grating for diffracting an incident beam of light as it is reflected from the upper surfaces of the grating elements. The programmable diffraction grating, formed by a micromachining process, has applications for optical information processing (e.g. optical correlators and computers), for multiplexing and demultiplexing a plurality of light beams of different wavelengths (e.g. for optical fiber communications), and for forming spectrometers (e.g. correlation and scanning spectrometers).

Recording polarization gratings with a standing spiral wave

NASA Astrophysics Data System (ADS)

Vernon, Jonathan P.; Serak, Svetlana V.; Hakobyan, Rafik S.; Aleksanyan, Artur K.; Tondiglia, Vincent P.; White, Timothy J.; Bunning, Timothy J.; Tabiryan, Nelson V.

2013-11-01

A scalable and robust methodology for writing cycloidal modulation patterns of optical axis orientation in photosensitive surface alignment layers is demonstrated. Counterpropagating circularly polarized beams, generated by reflection of the input beam from a cholesteric liquid crystal, direct local surface orientation in a photosensitive surface. Purposely introducing a slight angle between the input beam and the photosensitive surface normal introduces a grating period/orientation that is readily controlled and templated. The resulting cycloidal diffractive waveplates offer utility in technologies requiring diffraction over a broad range of angles/wavelengths. This simple methodology of forming polarization gratings offers advantages over conventional fabrication techniques.

Distributed feedback InGaN/GaN laser diodes

NASA Astrophysics Data System (ADS)

Slight, Thomas J.; Watson, Scott; Yadav, Amit; Grzanka, Szymon; Stanczyk, Szymon; Docherty, Kevin E.; Rafailov, Edik; Perlin, Piotr; Najda, Steve; Leszczyński, Mike; Kelly, Anthony E.

2018-02-01

We have realised InGaN/GaN distributed feedback laser diodes emitting at a single wavelength in the 42X nm wavelength range. Laser diodes based on Gallium Nitride (GaN) are useful devices in a wide range of applications including atomic spectroscopy, data storage and optical communications. To fully exploit some of these application areas there is a need for a GaN laser diode with high spectral purity, e.g. in atomic clocks, where a narrow line width blue laser source can be used to target the atomic cooling transition. Previously, GaN DFB lasers have been realised using buried or surface gratings. Buried gratings require complex overgrowth steps which can introduce epi-defects. Surface gratings designs, can compromise the quality of the p-type contact due to dry etch damage and are prone to increased optical losses in the grating regions. In our approach the grating is etched into the sidewall of the ridge. Advantages include a simpler fabrication route and design freedom over the grating coupling strength.Our intended application for these devices is cooling of the Sr+ ion and for this objective the laser characteristics of SMSR, linewidth, and power are critical. We investigate how these characteristics are affected by adjusting laser design parameters such as grating coupling coefficient and cavity length.

Grating array systems having a plurality of gratings operative in a coherently additive mode and methods for making such grating array systems

DOEpatents

Kessler, Terrance J [Mendon, NY; Bunkenburg, Joachim [Victor, NY; Huang, Hu [Pittsford, NY

2007-02-13

A plurality of gratings (G1, G2) are arranged together with a wavefront sensor, actuators, and feedback system to align the gratings in such a manner, that they operate like a single, large, monolithic grating. Sub-wavelength-scale movements in the mechanical mounting, due to environmental influences, are monitored by an interferometer (28), and compensated by precision actuators (16, 18, 20) that maintain the coherently additive mode. The actuators define the grating plane, and are positioned in response to the wavefronts from the gratings and a reference flat, thus producing the interferogram that contains the alignment information. Movement of the actuators is also in response to a diffraction-limited spot on the CCD (36) to which light diffracted from the gratings is focused. The actuator geometry is implemented to take advantage of the compensating nature of the degrees of freedom between gratings, reducing the number of necessary control variables.

Electrically-programmable diffraction grating

DOEpatents

Ricco, A.J.; Butler, M.A.; Sinclair, M.B.; Senturia, S.D.

1998-05-26

An electrically-programmable diffraction grating is disclosed. The programmable grating includes a substrate having a plurality of electrodes formed thereon and a moveable grating element above each of the electrodes. The grating elements are electrostatically programmable to form a diffraction grating for diffracting an incident beam of light as it is reflected from the upper surfaces of the grating elements. The programmable diffraction grating, formed by a micromachining process, has applications for optical information processing (e.g. optical correlators and computers), for multiplexing and demultiplexing a plurality of light beams of different wavelengths (e.g. for optical fiber communications), and for forming spectrometers (e.g. correlation and scanning spectrometers). 14 figs.

A noncontact force sensor based on a fiber Bragg grating and its application for corrosion measurement.

PubMed

Pacheco, Clara J; Bruno, Antonio C

2013-08-29

A simple noncontact force sensor based on an optical fiber Bragg grating attached to a small magnet has been proposed and built. The sensor measures the force between the magnet and any ferromagnetic material placed within a few millimeters of the sensor. Maintaining the sensor at a constant standoff distance, material loss due to corrosion increases the distance between the magnet and the corroded surface, which decreases the magnetic force. This will decrease the strain in the optical fiber shifting the reflected Bragg wavelength. The measured shift for the optical fiber used was 1.36 nm per Newton. Models were developed to optimize the magnet geometry for a specific sensor standoff distance and for particular corrosion pit depths. The sensor was able to detect corrosion pits on a fuel storage tank bottom with depths in the sub-millimeter range.

A Noncontact Force Sensor Based on a Fiber Bragg Grating and Its Application for Corrosion Measurement

PubMed Central

Pacheco, Clara J.; Bruno, Antonio C.

2013-01-01

A simple noncontact force sensor based on an optical fiber Bragg grating attached to a small magnet has been proposed and built. The sensor measures the force between the magnet and any ferromagnetic material placed within a few millimeters of the sensor. Maintaining the sensor at a constant standoff distance, material loss due to corrosion increases the distance between the magnet and the corroded surface, which decreases the magnetic force. This will decrease the strain in the optical fiber shifting the reflected Bragg wavelength. The measured shift for the optical fiber used was 1.36 nm per Newton. Models were developed to optimize the magnet geometry for a specific sensor standoff distance and for particular corrosion pit depths. The sensor was able to detect corrosion pits on a fuel storage tank bottom with depths in the sub-millimeter range. PMID:23995095

Nano-optomechanical characterization of surface-plasmon-based tunable filter integrated with comb-drive actuator

NASA Astrophysics Data System (ADS)

Honma, H.; Mitsudome, M.; Ishida, M.; Sawada, K.; Takahashi, K.

2017-03-01

We report a tunable plasmonic color filter consisting of a metamaterial periodic grating and microelectromechanical systems (MEMS) actuator. An aluminum subwavelength grating is integrated with electrostatic comb-drive actuators to expand the metal subwavelength period, which allows continuous control of the excitation wavelength of surface plasmons (SPs). We develop a batch fabrication process by employing a liftoff technique using an electron beam resist altered by the electron dose depending on different aspect ratios (length/width) for various components such as the subwavelength grating, nanohinge flexural suspensions, and comb fingers. We successfully demonstrate a continuous shift in the excitation wavelength over the 514-635 nm range by nanopitch expansion. The design margin of the grating period for SP excitation is evaluated by comparing the experimental pitch variation and theoretically calculated values. The resonance frequency of the tunable filter is optically measured to be approximately 10 kHz. The optically and mechanically obtained values agree well with the theory of electrostatic actuation and finite-difference time-domain simulation.

Direct imprinting on chalcogenide glass and fabrication of infrared wire-grid polarizer

NASA Astrophysics Data System (ADS)

Yamada, Itsunari; Yamashita, Naoto; Einishi, Toshihiko; Saito, Mitsunori; Fukumi, Kouhei; Nishii, Junji

2013-05-01

Infrared wire-grid polarizers were fabricated consisting of a 500-nm pitch Al grating on a low toxic chalcogenide glass (Sb-Ge-Sn-S system) using the direct imprinting of subwavelength grating followed by a deposition of Al metal by thermal evaporation. To fabricate the subwavelength grating on a chalcogenide glass more easily, the sharp grating was formed on the mold surface. The fabricated polarizer with Al thickness of 130 nm exhibited a polarization function with a transverse magnetic transmittance greater than 60% in the 5-9-μm wavelength range, and an extinction ratio greater than 20 dB in the 4-11-μm wavelength range. The polarizer can be fabricated at lower costs and simpler fabrication processes compared to conventional infrared polarizers.

Aplanatic and quasi-aplanatic diffraction gratings

DOEpatents

Hettrick, M.C.

1987-09-14

A reflection diffraction grating having a series of transverse minute grooves of progressively varying spacing along a concave surface enables use of such gratings for x-ray or longer wavelength imaging of objects. The variable groove spacing establishes aplanatism or substantially uniform magnetification across the optical aperture. The grating may be sued, for example, in x-ray microscopes or telescopes of the imaging type and in x-ray microprobed. Increased spatial resolution and field of view may be realized in x-ray imaging. 5 figs.

Mode-splitting of a non-polarizing guided mode resonance filter by substrate overetching effect

NASA Astrophysics Data System (ADS)

Saleem, Muhammad Rizwan; Honkanen, Seppo; Turunen, Jari

2014-03-01

We investigate substrate overetch effect on resonance properties of sub-wavelength titanium oxide (TiO2) Guided Mode Resonance Filters (TiO2-GMRFs). The TiO2-GMRF is designed and fabricated to possess a non-polarizing behavior, which is strongly dependent on substrate (fused silica) overetch depth. For non-polarizing gratings at resonance, TE- and TM-modes have the same propagation constants. However, an overetch substrate effect results in splitting of the degenerate modes, which is studied theoretically and experimentally. The TiO2-SiO2 GMRFs are designed by Fourier Modal method (FMM) based on the rigorous calculation of electromagnetic diffraction theory at a designed wavelength of 850 nm. The TiO2-SiO2 gratings are fabricated by Atomic Layer Deposition (ALD), Electron Beam Lithography (EBL), and Reactive Ion Etching (RIE), and they are subsequently characterized structurally by Scanning Electron Microscopy (SEM) and optically by a spectroscopic ellipsometer. Several grating samples are fabricated by gradually increasing the overetch depth into fused silica and measuring the extent of TE- and TM-mode-splitting. A close agreement between the calculated and experimentally measured resonance wavelength spectral shift is found to describe the mode splitting of non-polarizing gratings.

Fiber Grating Coupled Light Source Capable of Tunable, Single Frequency Operation

NASA Technical Reports Server (NTRS)

Krainak, Michael A. (Inventor); Duerksen, Gary L. (Inventor)

2001-01-01

Fiber Bragg grating coupled light sources can achieve tunable single-frequency (single axial and lateral spatial mode) operation by correcting for a quadratic phase variation in the lateral dimension using an aperture stop. The output of a quasi-monochromatic light source such as a Fabry Perot laser diode is astigmatic. As a consequence of the astigmatism, coupling geometries that accommodate the transverse numerical aperture of the laser are defocused in the lateral dimension, even for apsherical optics. The mismatch produces the quadratic phase variation in the feedback along the lateral axis at the facet of the laser that excites lateral modes of higher order than the TM(sub 00). Because the instability entails excitation of higher order lateral submodes, single frequency operation also is accomplished by using fiber Bragg gratings whose bandwidth is narrower than the submode spacing. This technique is particularly pertinent to the use of lensed fiber gratings in lieu of discrete coupling optics. Stable device operation requires overall phase match between the fed-back signal and the laser output. The fiber Bragg grating acts as a phase-preserving mirror when the Bragg condition is met precisely. The phase-match condition is maintained throughout the fiber tuning range by matching the Fabry-Perot axial mode wavelength to the passband center wavelength of the Bragg grating.

Ultrafast laser-induced reproducible nano-gratings on a molybdenum surface

NASA Astrophysics Data System (ADS)

Dar, Mudasir H.; Saad, Nabil A.; Sahoo, Chakradhar; Naraharisetty, Sri Ram G.; Rao Desai, Narayana

2017-02-01

Wavelength-dependent reproducible nano-gratings were produced on a bulk molybdenum surface upon irradiation with femtosecond laser pulses at near normal incidence in ambient air and water environments. The surface morphology of the irradiated surfaces was characterized by field emission scanning electron microscopy. The ripple spacing was observed to decrease by half when the surface was irradiated with the second harmonic of the fundamental 800 nm radiation. Careful choice of the laser parameters such as fluence, scanning speed, polarization and wavelength were observed to be important for the formation of smooth periodic ripples. The mechanism of formation of polarization-dependent periodic ripples is explained based on the interference model. We also demonstrated the use of a laser direct writing technique for the fabrication of periodic subwavelength structures that have potential applications in photonic devices.

Multiplexing 32,000 spectra onto 8 detectors: the HARMONI field splitting, image slicing, and wavelength selecting optics

NASA Astrophysics Data System (ADS)

Tecza, Matthias; Thatte, Niranjan; Clarke, Fraser; Freeman, David; Kosmalski, Johan

2012-09-01

HARMONI, the High Angular Resolution Monolithic Optical & Near-infrared Integral field spectrograph is one of two first-light instruments for the European Extremely Large Telescope. Over a 256x128 pixel field-of-view HARMONI will simultaneously measure approximately 32,000 spectra. Each spectrum is about 4000 spectral pixels long, and covers a selectable part of the 0.47-2.45 μm wavelength range at resolving powers of either R≍4000, 10000, or 20000. All 32,000 spectra are imaged onto eight HAWAII4RG detectors using a multiplexing scheme that divides the input field into four sub-fields, each imaged onto one image slicer that in turn re-arranges a single sub-field into two long exit slits feeding one spectrograph each. In total we require eight spectrographs, each with one HAWAII4RG detector. A system of articulated and exchangeable fold-mirrors and VPH gratings allows one to select different spectral resolving powers and wavelength ranges of interest while keeping a fixed geometry between the spectrograph collimator and camera avoiding the need for an articulated grating and camera. In this paper we describe both the field splitting and image slicing optics as well as the optics that will be used to select both spectral resolving power and wavelength range.

Compact diffraction grating laser wavemeter with sub-picometer accuracy and picowatt sensitivity using a webcam imaging sensor.

PubMed

White, James D; Scholten, Robert E

2012-11-01

We describe a compact laser wavelength measuring instrument based on a small diffraction grating and a consumer-grade webcam. With just 1 pW of optical power, the instrument achieves absolute accuracy of 0.7 pm, sufficient to resolve individual hyperfine transitions of the rubidium absorption spectrum. Unlike interferometric wavemeters, the instrument clearly reveals multimode laser operation, making it particularly suitable for use with external cavity diode lasers and atom cooling and trapping experiments.

Comparative study of sub-micrometer polymeric structures: Dot-arrays, linear and crossed gratings generated by UV laser based two-beam interference, as surfaces for SPR and AFM based bio-sensing

NASA Astrophysics Data System (ADS)

Csete, M.; Sipos, Á.; Kőházi-Kis, A.; Szalai, A.; Szekeres, G.; Mathesz, A.; Csákó, T.; Osvay, K.; Bor, Zs.; Penke, B.; Deli, M. A.; Veszelka, Sz.; Schmatulla, A.; Marti, O.

2007-12-01

Two-dimensional gratings are generated on poly-carbonate films spin-coated onto thin gold-silver bimetallic layers by two-beam interference method. Sub-micrometer periodic polymer dots and stripes are produced illuminating the poly-carbonate surface by p- and s-polarized beams of a frequency quadrupled Nd:YAG laser, and crossed gratings are generated by rotating the substrates between two sequential treatments. It is shown by pulsed force mode atomic force microscopy that the mean value of the adhesion is enhanced on the dot-arrays and on the crossed gratings. The grating-coupling on the two-dimensional structures results in double peaks on the angle dependent resonance curves of the surface plasmons excited by frequency doubled Nd:YAG laser. The comparison of the resonance curves proves that a surface profile ensuring minimal undirected scattering is required to optimize the grating-coupling, in addition to the minimal modulation amplitude, and to the optimal azimuthal orientation. The secondary minima are the narrowest in presence of linear gratings on multi-layers having optimized composition, and on crossed structures consisting of appropriately oriented polymer stripes. The large coupling efficiency and adhesion result in high detection sensitivity on the crossed gratings. Bio-sensing is realized by monitoring the rotated-crossed grating-coupled surface plasmon resonance curves, and detecting the chemical heterogeneity by tapping-mode atomic force microscopy. The interaction of Amyloid-β peptide, a pathogenetic factor in Alzheimer disease, with therapeutical molecules is demonstrated.

Two-way reflector based on two-dimensional sub-wavelength high-index contrast grating on SOI

NASA Astrophysics Data System (ADS)

Kaur, Harpinder; Kumar, Mukesh

2016-05-01

A two-dimensional (2D) high-index contrast grating (HCG) is proposed as a two-way reflector on Silicon-on-insulator (SOI). The proposed reflector provides high reflectivity over two (practically important) sets of angles of incidence- normal (θ = 0 °) and oblique/grazing (θ = 80 ° - 85 ° / 90 °). Analytical model of 2D HCG is presented using improved Fourier modal method. The vertical incidence is useful for application in VCSEL while oblique/grazing incidence can be utilized in high confinement (HCG mirrors based) hollow waveguides and Bragg reflectors. The proposed two-way reflector also exhibits a large reflection bandwidth (around telecom wavelength) which is an advantage for broadband photonic devices.

Design of vibration sensor based on fiber Bragg grating

NASA Astrophysics Data System (ADS)

Zhang, Zhengyi; Liu, Chuntong

2017-12-01

Fiber grating is a kind of new type of fiber optic light source device which has been rapidly changing in the refractive index of the core in recent years. Especially, it can realize the high precision of the external parameters by means of the special structure design and the encapsulation technology [1, 2]. In this paper, a fiber grating vibration sensor which is suitable for vibration monitoring in key areas is designed based on the technical background of vibration monitoring system. The sensor uses a single beam structure and pastes the fiber Bragg grating (FBG) to measure the vibration wavelength on the surface. When the vibration is simply harmonic vibration, the Bragg reflection wavelength will change periodically, and the periodic variation of the wavelength curve can be measured by the fiber grating demodulator, then the correctness of the experimental results is verified. In this paper, through the analysis of the data measured by the demodulator, the MATLAB software is used to verify the data, and the different frequency domains, the modes, and the phase frequency curves are obtained. The measurement range is 0 Hz-100 Hz, and the natural frequency is 90.6 Hz.

Experimental verification of the rainbow trapping effect in adiabatic plasmonic gratings

PubMed Central

Gan, Qiaoqiang; Gao, Yongkang; Wagner, Kyle; Vezenov, Dmitri; Ding, Yujie J.; Bartoli, Filbert J.

2011-01-01

We report the experimental observation of a trapped rainbow in adiabatically graded metallic gratings, designed to validate theoretical predictions for this unique plasmonic structure. One-dimensional graded nanogratings were fabricated and their surface dispersion properties tailored by varying the grating groove depth, whose dimensions were confirmed by atomic force microscopy. Tunable plasmonic bandgaps were observed experimentally, and direct optical measurements on graded grating structures show that light of different wavelengths in the 500–700-nm region is “trapped” at different positions along the grating, consistent with computer simulations, thus verifying the “rainbow” trapping effect. PMID:21402936

Ultra-broadband and wide-angle perfect absorber based on composite metal-semiconductor grating

NASA Astrophysics Data System (ADS)

Li, Xu; Wang, Zongpeng; Hou, Yumin

2018-01-01

In this letter, we present an ultra-broadband and wide-angle perfect absorber based on composite Ge-Ni grating. Near perfect absorption above 90% is achieved in a wide frequency range from 150 nm to 4200 nm, which covers almost the full spectrum of solar radiation. The absorption keeps robust in a wide range of incident angle from 0º to 60º. The upper triangle Ge grating works as an antireflection coating. The lower Ni grating works as a reflector and an effective energy trapper. The guided modes inside Ge grating are excited due to reflection of the lower Ni grating surface. In longer wavelength band, gap surface plasmons (GSPs) in the Ni grating are excited and couple with the guided modes inside the Ge grating. The coupled modes extend the perfect absorption band to the near-infrared region (150 nm-4200 nm). This design has potential application in photovoltaic devices and thermal emitters.

Surface morphology of refractive-index waveguide gratings fabricated in polymer films

NASA Astrophysics Data System (ADS)

Dong, Yi; Song, Yan-fang; Ma, Lei; Gao, Fang-fang

2016-09-01

The characteristic modifications are reported on the surface of polymeric waveguide film in the process of volume- grating fabrication. The light from a mode-locked 76 MHz femtosecond laser with pulse duration of 200 fs and wavelength of 800 nm is focused normal to the surface of the sample. The surface morphology modifications are ascribed to a fact that surface swelling occurs during the process. Periodic micro-structure is inscribed with increasing incident power. The laser-induced swelling threshold on the grating, which is higher than that of two-photon initiated photo-polymerization (TPIP) (8 mW), is verified to be about 20 mW. It is feasible to enhance the surface smoothness of integrated optics devices for further encapsulation. The variation of modulation depth is studied for different values of incident power and scan spacing. Ablation accompanied with surface swelling appears when the power is higher. By optimizing the laser carving parameters, highly efficient grating devices can be fabricated.

Sub-wavelength grating mode transformers in silicon slab waveguides.

PubMed

Bock, Przemek J; Cheben, Pavel; Schmid, Jens H; Delâge, André; Xu, Dan-Xia; Janz, Siegfried; Hall, Trevor J

2009-10-12

We report on several new types of sub-wavelength grating (SWG) gradient index structures for efficient mode coupling in high index contrast slab waveguides. Using a SWG, an adiabatic transition is achieved at the interface between silicon-on-insulator waveguides of different geometries. The SWG transition region minimizes both fundamental mode mismatch loss and coupling to higher order modes. By creating the gradient effective index region in the direction of propagation, we demonstrate that efficient vertical mode transformation can be achieved between slab waveguides of different core thickness. The structures which we propose can be fabricated by a single etch step. Using 3D finite-difference time-domain simulations we study the loss, polarization dependence and the higher order mode excitation for two types (triangular and triangular-transverse) of SWG transition regions between silicon-on-insulator slab waveguides of different core thicknesses. We demonstrate two solutions to reduce the polarization dependent loss of these structures. Finally, we propose an implementation of SWG structures to reduce loss and higher order mode excitation between a slab waveguide and a phase array of an array waveguide grating (AWG). Compared to a conventional AWG, the loss is reduced from -1.4 dB to < -0.2 dB at the slab-array interface.

Excitation of surface waves on one-dimensional solid–fluid phononic crystals and the beam displacement effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moiseyenko, Rayisa P.; Georgia Institute of Technology, UMI Georgia Tech – CNRS, George W. Woodruff School of Mechanical Engineering, Georgia Tech Lorraine, 2 rue Marconi, 57070 Metz-Technopole; Liu, Jingfei

The possibility of surface wave generation by diffraction of pressure waves on deeply corrugated one-dimensional phononic crystal gratings is studied both theoretically and experimentally. Generation of leaky surface waves, indeed, is generally invoked in the explanation of the beam displacement effect that can be observed upon reflection on a shallow grating of an acoustic beam of finite width. True surface waves of the grating, however, have a dispersion that lies below the sound cone in water. They thus cannot satisfy the phase-matching condition for diffraction from plane waves of infinite extent incident from water. Diffraction measurements indicate that deeply corrugatedmore » one-dimensional phononic crystal gratings defined in a silicon wafer are very efficient diffraction gratings. They also confirm that all propagating waves detected in water follow the grating law. Numerical simulations however reveal that in the sub-diffraction regime, acoustic energy of a beam of finite extent can be transferred to elastic waves guided at the surface of the grating. Their leakage to the specular direction along the grating surface explains the apparent beam displacement effect.« less

Fabrication and Testing of Binary-Phase Fourier Gratings for Nonuniform Array Generation

NASA Technical Reports Server (NTRS)

Keys, Andrew S.; Crow, Robert W.; Ashley, Paul R.; Nelson, Tom R., Jr.; Parker, Jack H.; Beecher, Elizabeth A.

2004-01-01

This effort describes the fabrication and testing of binary-phase Fourier gratings designed to generate an incoherent array of output source points with nonuniform user-defined intensities, symmetric about the zeroth order. Like Dammann fanout gratings, these binary-phase Fourier gratings employ only two phase levels to generate a defined output array. Unlike Dammann fanout gratings, these gratings generate an array of nonuniform, user-defined intensities when projected into the far-field regime. The paper describes the process of design, fabrication, and testing for two different version of the binary-phase grating; one designed for a 12 micron wavelength, referred to as the Long-Wavelength Infrared (LWIR) grating, and one designed for a 5 micron wavelength, referred to as the Mid-Wavelength Infrared Grating (MWIR).

Efficiency calibration of the first multilayer-coated holographic ion-etched flight grating for a sounding rocket high-resolution spectrometer.

PubMed

Kowalski, M P; Barbee, T W; Heidemann, K F; Gursky, H; Rife, J C; Hunter, W R; Fritz, G G; Cruddace, R G

1999-11-01

We have fabricated the four flight gratings for a sounding rocket high-resolution spectrometer using a holographic ion-etching technique. The gratings are spherical (4000-mm radius of curvature), large (160 mm x 90 mm), and have a laminar groove profile of high density (3600 grooves/mm). They have been coated with a high-reflectance multilayer of Mo/Si. Using an atomic force microscope, we examined the surface characteristics of the first grating before and after multilayer coating. The average roughness is approximately 3 A rms after coating. Using synchrotron radiation, we completed an efficiency calibration map over the wavelength range 225-245 A. At an angle of incidence of 5 degrees and a wavelength of 234 A, the average efficiency in the first inside order is 10.4 +/- 0.5%, and the derived groove efficiency is 34.8 +/- 1.6%. These values exceed all previously published results for a high-density grating.

TiO2 surface functionalization of COC based planar waveguide Bragg gratings for refractive index sensing

NASA Astrophysics Data System (ADS)

Rosenberger, M.; Girschikofsky, M.; Förthner, M.; Belle, S.; Rommel, M.; Frey, L.; Schmauss, B.; Hellmann, R.

2018-01-01

We demonstrate the applicability of a planar waveguide Bragg grating in cyclo-olefin copolymer (COC) for refractive index sensing. The polymer planar waveguide Bragg grating fabricated using a single writing step technique is coated with a high-index layer of titanium dioxide (TiO2) leading to a distinct birefringence. This in turn results in the splitting of the Bragg reflection into two distinct Bragg wavelengths, which strongly differ regarding their refractive index sensitivities. Where one wavelength is only slightly affected by the ambient refractive index, the second Bragg peak shows a strong sensitivity. Furthermore, we investigate the temperature behaviour of the functionalized sensor and discuss it with respect to applications in refractive index sensing.

Polarization-independent beam focusing by high-contrast grating reflectors

NASA Astrophysics Data System (ADS)

Su, Wei; Zheng, Gaige; Jiang, Liyong; Li, Xiangyin

2014-08-01

A kind of high-contrast grating (HCG) reflector for beam focusing has been proposed. We design a planar grating structure with a parabolic surface and numerical simulations using a finite different time domain (FDTD) method to verify that the structure has the capability of focusing both transverse-magnetic (TM) and transverse-electric (TE) polarized lights. Finally, we expand the design structure into a three-dimensional (3D) case. Numerical results demonstrate that the power intensities at the focal point are all greater than 8.5 dB compared with incident intensity, which means the structure has a better focusing effect. Further analysis of incident wavelength sensitivity (1.55, 1.79 and 2 μm) reveals that the proposed structure has a wide range of working wavelength.

Wavelength-spacing-tunable multichannel filter incorporating a sampled chirped fiber Bragg grating based on a symmetrical chirp-tuning technique without center wavelength shift

NASA Astrophysics Data System (ADS)

Han, Young-Geun; Dong, Xinyong; Lee, Ju Han; Lee, Sang Bae

2006-12-01

We propose and experimentally demonstrate a simple and flexible scheme for a wavelength-spacing-tunable multichannel filter exploiting a sampled chirped fiber Bragg grating based on a symmetrical modification of the chirp ratio. Symmetrical bending along a sampled chirped fiber Bragg grating attached to a flexible cantilever beam induces a variation of the chirp ratio and a reflection chirp bandwidth of the grating without a center wavelength shift. Accordingly, the wavelength spacing of a sampled chirped fiber Bragg grating is continuously controlled by the reflection chirp bandwidth variation of the grating corresponding to the bending direction, which allows for realization of an effective wavelength-spacing-tunable multichannel filter. Based on the proposed technique, we achieve the continuous tunability of the wavelength spacing in a range from 1.51 to 6.11 nm, depending on the bending direction of the cantilever beam.

NIR spectrometer using a Schottky photodetector enhanced by grating-based SPR.

PubMed

Chen, Wenjing; Kan, Tetsuo; Ajiki, Yoshiharu; Matsumoto, Kiyoshi; Shimoyama, Isao

2016-10-31

We present a near-infrared (NIR) spectrum measurement method using a Schottky photodetector enhanced by surface plasmon resonance (SPR). An Au grating was fabricated on an n-type silicon wafer to form a Schottky barrier and act as an SPR coupler. The resulting photodetector provides wavelength-selective photodetection depending on the SPR coupling angle. A matrix was pre-calculated to describe this characteristic. The spectrum was obtained from this matrix and the measured photocurrents at various SPR coupling angles. Light with single and multiple wavelengths was tested. Comparative measurements showed that our method is able to detect spectra with a wavelength resolution comparable to that of a commercial spectrometer.

Wavelength-conserving grating router for intermediate wavelength density

DOEpatents

Deri, Robert J.; Patel, Rajesh R.; Bond, Steven W.; Bennett, Cory V.

2007-03-20

A wavelength router to be used for fiber optical networking router is based on a diffraction grating which utilizes only N wavelengths to interconnect N inputs to N outputs. The basic approach is to augment the grating with additional couplers or wavelength selective elements so than N-1 of the 2N-1 outputs are combined with other N outputs (leaving only N outputs). One embodiment uses directional couplers as combiners. Another embodiment uses wavelength-selective couplers. Another embodiment uses a pair of diffraction gratings to maintain parallel propagation of all optical beams. Also, beam combining can be implemented either by using retroflection back through the grating pair or by using couplers.

D-shaped tilted fiber Bragg grating using magnetic fluid for magnetic field sensor

NASA Astrophysics Data System (ADS)

Ying, Yu; Zhang, Rui; Si, Guang-Yuan; Wang, Xin; Qi, Yuan-Wei

2017-12-01

In our work, a numerical investigation of a magnetic field sensor based on a D-shaped tilted fiber Bragg grating and magnetic fluid is performed. The sensing probe is constructed by placing the magnetic fluid film on the flat surface of the D-shaped tilted fiber Bragg grating. We investigate the resonance wavelengths of the proposed structure with different tilted angles of grating ranging from 0° to 20°, and analyze the magnetic field sensing characteristics. The simulation results show that the optical fiber sensor exhibits optimal transmission characteristics with a tilted angle of 8°. The wavelength sensitivity of the magnetic field sensor is as high as -0.18nm/Oe in the range of 30Oe-270Oe, and it demonstrates a linearity up to R2= -0.9998. Such sensor has potential applications in determining magnetic sensing field.

1×2 demultiplexer for a light waveguide communications system based on a holographic grating

NASA Astrophysics Data System (ADS)

Ren, Xuechang; Zhang, Xiangsu; Wang, Canhui; Liu, Shou

2009-05-01

2-channel multiplexer/demultiplexer (Muxer/Demuxer) is a key component for bidirectional data traffics applied for optical communication. Up to date various types of Muxer/Demuxer have been proposed and demonstrated. A grating coupler diffracts light into substrates or waveguides, along which light beam propagates by total internal reflection. In addition, one can exploit the dispersive and filtering characteristics of gratings, for dropping or separating one or several wavelengths from one another. When a laser beam containing two wavelengths is striking the surface of the grating with an incident angle within certain range, four diffracted beams will be generated. If two diffracted beams, corresponding to different wavelengths, meet the condition of total internal reflection, they will propagate inside the glass substrate (performs as a waveguide). While the third one cannot meet total reflection condition, and the last one should become the evanescent wave. Therefore it can separate two signals and couple signals to different waveguides. These functions are suited for WDM application and directional couplers. For convenience sake, the visible lights at 458nm and 633nm were used as the incident laser beams. To give a simple sample for 1×2 demultiplexing system, a holographic grating was recorded, with the period around 441nm which was chose discretionally within the certain range. The primary experimental results indicate that the two-wavelength signal can be separated and coupled into the respective waveguide as long as the grating is recorded and operated complying with the certain condition. The average insertion loss and crosstalk of the device were presented in this paper.

Development of a wavelength tunable filter using MEMS technology

NASA Astrophysics Data System (ADS)

Liu, Junting

Microelectromechanical systems (MEMS) for optical applications have received intensive attention in recent years because of their potential applications in optical telecommunication. Traditional wavelength division multiplexing (WDM) offers high capacity but requires the fabrication of selective add-drop filters. MEMS technology offers an effective way to fabricate these components at low cost. This thesis presents the development of a device that tunes the Bragg wavelength by coupling into the evanescent field of the grating. A Bragg grating is a periodic perturbation of the refractive index along a fiber or a periodic perturbation of the structure of a planar waveguide. The Bragg wavelength can be tuned by changing the degree to which a dielectric slab couples into the evanescent field. The result is a change in the effective index of the grating, and thus a change in the wavelength that which it reflects. In this thesis Bragg gratings were successfully written into an optical fiber using phase mask technique. Mechanical polishing was used to side-polish the fiber and remove cladding to expose the core. Grating structures were also fabricated in planar waveguide using E-beam writing and dry etching. In order to achieve the smoothest possible morphology of the waveguide, plasma dry etching of transparent substrates was studied in great detail. It is found that the pre-etch cleaning procedure greatly influences the ability to obtain a smooth etched surface. Upper limits of evanescent field tuning were investigated by applying different index liquids such as D. I. water and index matching oils or by positioning different dielectric materials such as glass and silicon close to the grating. Planar waveguides were found to be more sensitive to effective index change. Two kinds of computer simulation were carried out to understand the mode profile and to estimate the value of effective index of planar waveguide under "dry" and "wet" conditions. The first one used an average depth of grating approximation. The second explicitly considered the corrugated structure of the waveguide. Results of both simulations were compared with the experimental results in order to find the proper simulation approach. The fiber or planar waveguide gratings were "device" integrated and their pro and cons were compared. Devices using an optical fiber employed a microactuator driven by electrothermal vibromotor to change the degree of coupling between fiber and "tuning block". Device using planar waveguides used an electrostatic force actuated membrane, flip-chip mounted atop the waveguide. All devices were fabricated using polysilicon surface micromachining processes. I concluded that devices driven by electrostatic force were easier to actuate and their integration with waveguide less challenging.

Grism and immersion grating for space telescope

NASA Astrophysics Data System (ADS)

Ebizuka, Noboru; Oka, Kiko; Yamada, Akiko; Ishikawa, Mami; Kashiwagi, Masako; Kodate, Kashiko; Hirahara, Yasuhiro; Sato, Shuji; Kawabata, Koji S.; Wakaki, Moriaki; Morita, Shin-ya; Simizu, Tomoyuki; Yin, Shaohui; Omori, Hitoshi; Iye, Masanori

2017-11-01

The grism is a versatile dispersion element for an astronomical instrument ranging from ultraviolet to infrared. Major benefit of using a grism in a space application, instead of a reflection grating, is the size reduction of optical system because collimator and following optical elements could locate near by the grism. The surface relief (SR) grism is consisted a transmission grating and a prism, vertex angle of which is adjusted to redirect the diffracted beam straight along the direct vision direction at a specific order and wavelength. The volume phase holographic (VPH) grism consists a thick VPH grating sandwiched between two prisms, as specific order and wavelength is aligned the direct vision direction. The VPH grating inheres ideal diffraction efficiency on a higher dispersion application. On the other hand, the SR grating could achieve high diffraction efficiency on a lower dispersion application. Five grisms among eleven for the Faint Object Camera And Spectrograph (FOCAS) of the 8.2m Subaru Telescope with the resolving power from 250 to 3,000 are SR grisms fabricated by a replication method. Six additional grisms of FOCAS with the resolving power from 3,000 to 7,000 are VPH grisms. We propose "Quasi-Bragg grism" for a high dispersion spectroscopy with wide wavelength range. The germanium immersion grating for instance could reduce 1/64 as the total volume of a spectrograph with a conventional reflection grating since refractive index of germanium is over 4.0 from 1.6 to 20 μm. The prototype immersion gratings for the mid-InfraRed High dispersion Spectrograph (IRHS) are successfully fabricated by a nano-precision machine and grinding cup of cast iron with electrolytic dressing method.

Deep-etched sinusoidal polarizing beam splitter grating.

PubMed

Feng, Jijun; Zhou, Changhe; Cao, Hongchao; Lv, Peng

2010-04-01

A sinusoidal-shaped fused-silica grating as a highly efficient polarizing beam splitter (PBS) is investigated based on the simplified modal method. The grating structure depends mainly on the ratio of groove depth to grating period and the ratio of incident wavelength to grating period. These ratios can be used as a guideline for the grating design at different wavelengths. A sinusoidal-groove PBS grating is designed at a wavelength of 1310 nm under Littrow mounting, and the transmitted TM and TE polarized waves are mainly diffracted into the zeroth order and the -1st order, respectively. The grating profile is optimized by using rigorous coupled-wave analysis. The designed PBS grating is highly efficient (>95.98%) over the O-band wavelength range (1260-1360 nm) for both TE and TM polarizations. The sinusoidal grating can exhibit higher diffraction efficiency, larger extinction ratio, and less reflection loss than the rectangular-groove PBS grating. By applying wet etching technology on the rectangular grating, which was manufactured by holographic recording and inductively coupled plasma etching technology, the sinusoidal grating can be approximately fabricated. Experimental results are in agreement with theoretical values.

Nanogap embedded silver gratings for surface plasmon enhanced fluorescence

NASA Astrophysics Data System (ADS)

Bhatnagar, Kunal

Plasmonic nanostructures have been extensively used in the past few decades for applications in sub-wavelength optics, data storage, optoelectronic circuits, microscopy and bio-photonics. The enhanced electromagnetic field produced at the metal and dielectric interface by the excitation of surface plasmons via incident radiation can be used for signal enhancement in fluorescence and surface enhanced Raman scattering studies. Novel plasmonic structures have shown to provide very efficient and extreme light concentration at the nano-scale in recent years. The enhanced electric field produced within a few hundred nanometers of these surfaces can be used to excite fluorophores in the surrounding environment. Fluorescence based bio-detection and bio-imaging are two of the most important tools in the life sciences and improving the qualities and capabilities of fluorescence based detectors and imaging equipment remains a big challenge for industry manufacturers. We report a novel fabrication technique for producing nano-gap embedded periodic grating substrates on the nanoscale using a store bought HD-DVD and conventional soft lithography procedures. Polymethylsilsesquioxane (PMSSQ) polymer is used as the ink for the micro-contact printing process with PDMS stamps obtained from the inexpensive HD-DVDs as master molds. Fluorescence enhancement factors of up to 118 times were observed with these silver nanostructures in conjugation with Rhodamine-590 fluorescent dye. These substrates are ideal candidates for a robust and inexpensive optical system with applications such as low-level fluorescence based analyte detection, single molecule imaging, and surface enhanced Raman studies. Preliminary results in single molecule experiments have also been obtained by imaging individual 3 nm and 20 nm dye-doped nanoparticles attached to the silver plasmonic gratings using epi-fluorescence microscopy.

Design of a variable-line-spacing grating pattern for spectrometers based on a grating Fresnel device.

PubMed

Li, Xinghui; Zhang, Jinchao; Zhou, Qian; Ni, Kai; Pang, Jinchao; Tian, Rui

2016-04-01

In this Letter, we propose a variable-line-spacing (VLS) grating pattern for a hybrid diffractive device termed a grating Fresnel (G-Fresnel) lens, which is used in spectrometers to improve spectral resolution over a wide spectral range. The VLS grating pattern disperses light of specific wavelengths with a different angle and position such that the aberration caused by the Fresnel surface can be compensated for. In this manner, high resolution can be achieved over a relatively wide spectral range. The VLS grating pattern is designed based on the least wave-change principle and simulated by ZEMAX. Results reveal that the VLS G-Fresnel device allows a subnanometer resolution over a spectral range of 200 nm.

Broadly tunable picosecond ir source

DOEpatents

Campillo, A.J.; Hyer, R.C.; Shapiro, S.L.

1980-04-23

A picosecond traveling-wave parametric device capable of controlled spectral bandwidth and wavelength in the infrared is reported. Intense 1.064 ..mu..m picosecond pulses (1) pass through a 4.5 cm long LiNbO/sub 3/ optical parametric oscillator crystal (2) set at its degeneracy angle. A broad band emerges, and a simple grating (3) and mirror (4) arrangement is used to inject a selected narrow-band into a 2 cm long LiNbO/sub 3/ optical parametric amplifier crystal (5) along a second pump line. Typical input energies at 1.064 ..mu..m along both pump lines are 6 to 8 mJ for the oscillator and 10 mJ for the amplifier. This yields 1 mJ of tunable output in the range 1.98 to 2.38 ..mu..m which when down-converted in a 1 cm long CdSe crystal mixer (6) gives 2 ..mu..J of tunable radiation over the 14.8 to 18.5 ..mu..m region. The bandwidth and wavelength of both the 2 and 16 ..mu..m radiation output are controlled solely by the diffraction grating.

Broadly tunable picosecond IR source

DOEpatents

Campillo, Anthony J.; Hyer, Ronald C.; Shapiro, Stanley J.

1982-01-01

A picosecond traveling-wave parametric device capable of controlled spectral bandwidth and wavelength in the infrared is reported. Intense 1.064 .mu.m picosecond pulses (1) pass through a 4.5 cm long LiNbO.sub.3 optical parametric oscillator crystal (2) set at its degeneracy angle. A broad band emerges, and a simple grating (3) and mirror (4) arrangement is used to inject a selected narrow-band into a 2 cm long LiNbO.sub.3 optical parametric amplifier crystal (5) along a second pump line. Typical input energies at 1.064 .mu.m along both pump lines are 6-8 mJ for the oscillator and 10 mJ for the amplifier. This yields 1 mJ of tunable output in the range 1.98 to 2.38 .mu.m which when down-converted in a 1 cm long CdSe crystal mixer (6) gives 2 .mu.J of tunable radiation over the 14.8 to 18.5 .mu.m region. The bandwidth and wavelength of both the 2 and 16 .mu.m radiation output are controlled solely by the diffraction grating.

Distributed feedback interband cascade lasers with top grating and corrugated sidewalls

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Feng; Stocker, Michael; Pham, John

Distributed feedback (DFB) interband cascade lasers (ICLs) with a 1st order top surface grating were designed and fabricated. Partially corrugated sidewalls were implemented to suppress high order lateral modes. The DFB ICLs have 4 mm long and 4.5 mu m wide ridge waveguides and are mounted epi-up on AlN submounts. We demonstrated a continuous-wave (CW) DFB ICL, from a first wafer which has a large detuning of the gain peak from the DFB wavelength, with a side mode suppression ratio of 30 dB. With proper matching of grating feedback and the gain peak wavelength for the second wafer, a DFBmore » ICL was demonstrated with a maximum CW output power and a maximum wall plug efficiency reaching 42 mW and 2%, respectively, at 25 degrees C. The lasing wavelengths of both lasers are around 3.3 mu m at 25 degrees C. Published by AIP Publishing.« less

Bandwidth-Tunable Fiber Bragg Gratings Based on UV Glue Technique

NASA Astrophysics Data System (ADS)

Fu, Ming-Yue; Liu, Wen-Feng; Chen, Hsin-Tsang; Chuang, Chia-Wei; Bor, Sheau-Shong; Tien, Chuen-Lin

2007-07-01

In this study, we have demonstrated that a uniform fiber Bragg grating (FBG) can be transformed into a chirped fiber grating by a simple UV glue adhesive technique without shifting the reflection band with respect to the center wavelength of the FBG. The technique is based on the induced strain of an FBG due to the UV glue adhesive force on the fiber surface that causes a grating period variation and an effective index change. This technique can provide a fast and simple method of obtaining the required chirp value of a grating for applications in the dispersion compensators, gain flattening in erbium-doped fiber amplifiers (EDFAs) or optical filters.

Two-dimensional grating guided-mode resonance tunable filter.

PubMed

Kuo, Wen-Kai; Hsu, Che-Jung

2017-11-27

A two-dimensional (2D) grating guided-mode resonance (GMR) tunable filter is experimentally demonstrated using a low-cost two-step nanoimprinting technology with a one-dimensional (1D) grating polydimethylsiloxane mold. For the first nanoimprinting, we precisely control the UV LED irradiation dosage and demold the device when the UV glue is partially cured and the 1D grating mold is then rotated by three different angles, 30°, 60°, and 90°, for the second nanoimprinting to obtain 2D grating structures with different crossing angles. A high-refractive-index film ZnO is then coated on the surface of the grating structure to form the GMR filter devices. The simulation and experimental results demonstrate that the passband central wavelength of the filter can be tuned by rotating the device to change azimuth angle of the incident light. We compare these three 2D GMR filters with differential crossing angles and find that the filter device with a crossing angle of 60° exhibits the best performance. The tunable range of its central wavelength is 668-742 nm when the azimuth angle varies from 30° to 90°.

Enzyme-functionalized thin-cladding long-period fiber grating in transition mode at dispersion turning point for sugar-level and glucose detection

NASA Astrophysics Data System (ADS)

Badmos, Abdulyezir A.; Sun, Qizhen; Sun, Zhongyuan; Zhang, Junxi; Yan, Zhijun; Lutsyk, Petro; Rozhin, Alex; Zhang, Lin

2017-02-01

Enzyme-functionalized dual-peak long-period fiber grating (LPFG) inscribed in 80-μm-cladding B/Ge codoped single-mode fiber is presented for sugar-level and specific glucose detection. Before enzyme functionalization, the dual-peak LPFG was employed for refractive index sensing and sugar-level detection and high sensitivities of ˜4298.20 nm/RIU and 4.6696 nm/% were obtained, respectively. Glucose detection probe was attained by surface functionalization of the dual-peak LPFG via covalent binding with aminopropyl triethoxysilane used as a binding site. Optical micrographs confirmed the presence of enzyme. The surface-functionalized dual-peak LPFG was tested with D-(+)-glucose solution of different concentrations. While the peak 2 at the longer wavelength was suitable only to measure lower glucose concentration (0.1 to 1.6 mg/ml) recording a high sensitivity of 12.21±0.19 nm/(mg/ml), the peak 1 at the shorter wavelength was able to measure a wider range of glucose concentrations (0.1 to 3.2 mg/ml) exhibiting a maximum resonance wavelength shift of 7.12±0.12 nm/mg/ml. The enzyme-functionalized dual-peak LPFG has the advantage of direct inscription of highly sensitive grating structures in thin-cladding fibre without etching, and most significantly, its sensitivity improvement of approximately one order of magnitude higher than previously reported LPFG and excessively tilted fibre grating (Ex-TFG) for glucose detection.

Experimental demonstration of a multi-wavelength distributed feedback semiconductor laser array with an equivalent chirped grating profile based on the equivalent chirp technology.

PubMed

Li, Wangzhe; Zhang, Xia; Yao, Jianping

2013-08-26

We report, to the best of our knowledge, the first realization of a multi-wavelength distributed feedback (DFB) semiconductor laser array with an equivalent chirped grating profile based on equivalent chirp technology. All the lasers in the laser array have an identical grating period with an equivalent chirped grating structure, which are realized by nonuniform sampling of the gratings. Different wavelengths are achieved by changing the sampling functions. A multi-wavelength DFB semiconductor laser array is fabricated and the lasing performance is evaluated. The results show that the equivalent chirp technology is an effective solution for monolithic integration of a multi-wavelength laser array with potential for large volume fabrication.

Theoretical modeling and design of photonic structures in zeolite nanocomposites for gas sensing. Part I: surface relief gratings.

PubMed

Cody, D; Naydenova, I

2017-12-01

The suitability of holographic structures fabricated in zeolite nanoparticle-polymer composite materials for gas sensing applications has been investigated. Theoretical modeling of the sensor response (i.e., change in hologram readout due to a change in refractive index modulation or thickness as a result of gas adsorption) of different sensor designs was carried out using Raman-Nath theory and Kogelnik's coupled wave theory. The influence of a range of parameters on the sensor response of holographically recorded surface and volume photonic grating structures has been studied, namely the phase difference between the diffracted and probe beam introduced by the grating, grating geometry, thickness, spatial frequency, reconstruction wavelength, and zeolite nanoparticle refractive index. From this, the optimum fabrication conditions for both surface and volume holographic gas sensor designs have been identified. Here, in part I, results from theoretical modeling of the influence of design on the sensor response of holographically inscribed surface relief structures for gas sensing applications is reported.

Polarization-independent triangular-groove fused-silica gratings with high efficiency at a wavelength of 1550 nm

NASA Astrophysics Data System (ADS)

Cao, Hongchao; Zhou, Changhe; Feng, Jijun; Lv, Peng; Ma, Jianyong

2010-11-01

We describe polarization-independent triangular-groove fused-silica gratings illuminated by incident lights in the C + L bands as (de)multiplexers for dense wavelength division multiplexing (DWDM) application. The physical mechanisms of the grating can be shown clearly by using the simplified modal method with consideration of the corresponding accumulated average phase difference of two excited propagating grating modes, which illustrates that the grating structure depends mainly on the ratio of the average effective indices difference to the incident wavelength. Exact grating profile is optimized by using the rigorous coupled-wave analysis (RCWA). With the optimized grating parameters, the grating exhibits diffraction efficiencies of greater than 90% under TE- and TM-polarized incident lights for 101 nm spectral bandwidths (1500-1601 nm) and it can reach an efficiency of more than 99% for both polarizations at a wavelength of 1550 nm. Without loss of metal absorption, coating of dielectric film layers, the designed triangular-groove fused-silica grating should be of great interest for DWDM application.

Phase-based Bragg intragrating distributed strain sensor

NASA Astrophysics Data System (ADS)

Huang, S.; Ohn, M. M.; Measures, R. M.

1996-03-01

A strain-distribution sensing technique based on the measurement of the phase spectrum of the reflected light from a fiber-optic Bragg grating is described. When a grating is subject to a strain gradient, the grating will experience a chirp and therefore the resonant wavelength will vary along the grating, causing wavelength-dependent penetration depth. Because the group delay for each wavelength component is related to its penetration depth and the resonant wavelength is determined by strain, a measured phase spectrum can then indicate the local strain as a function of location within the grating. This phase-based Bragg grating sensing technique offers a powerful new means for studying some important effects over a few millimeters or centimeters in smart structures.

A size selective porous silicon grating-coupled Bloch surface and sub-surface wave biosensor.

PubMed

Rodriguez, Gilberto A; Ryckman, Judson D; Jiao, Yang; Weiss, Sharon M

2014-03-15

A porous silicon (PSi) grating-coupled Bloch surface and sub-surface wave (BSW/BSSW) biosensor is demonstrated to size selectively detect the presence of both large and small molecules. The BSW is used to sense large immobilized analytes at the surface of the structure while the BSSW that is confined inside but near the top of the structure is used to sensitively detect small molecules. Functionality of the BSW and BSSW modes is theoretically described by dispersion relations, field confinements, and simulated refractive index shifts within the structure. The theoretical results are experimentally verified by detecting two different small chemical molecules and one large 40 base DNA oligonucleotide. The PSi-BSW/BSSW structure is benchmarked against current porous silicon technology and is shown to have a 6-fold higher sensitivity in detecting large molecules and a 33% improvement in detecting small molecules. This is the first report of a grating-coupled BSW biosensor and the first report of a BSSW propagating mode. © 2013 Published by Elsevier B.V.

Diffraction efficiency of plasmonic gratings fabricated by electron beam lithography using a silver halide film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sudheer,, E-mail: sudheer@rrcat.gov.in, E-mail: sudheer.rrcat@gmail.com; Tiwari, P.; Srivastava, Himanshu

2016-07-28

The silver nanoparticle surface relief gratings of ∼10 μm period are fabricated using electron beam lithography on the silver halide film substrate. Morphological characterization of the gratings shows that the period, the shape, and the relief depth in the gratings are mainly dependent on the number of lines per frame, the spot size, and the accelerating voltage of electron beam raster in the SEM. Optical absorption of the silver nanoparticle gratings provides a broad localized surface plasmon resonance peak in the visible region, whereas the intensity of the peaks depends on the number density of silver nanoparticles in the gratings. Themore » maximum efficiency of ∼7.2% for first order diffraction is observed for the grating fabricated at 15 keV. The efficiency is peaking at 560 nm with ∼380 nm bandwidth. The measured profiles of the diffraction efficiency for the gratings are found in close agreement with the Raman-Nath diffraction theory. This technique provides a simple and efficient method for the fabrication of plasmonic nanoparticle grating structures with high diffraction efficiency having broad wavelength tuning.« less

Overview on grating developments at ESA

NASA Astrophysics Data System (ADS)

Guldimann, B.; Deep, A.; Vink, R.; Harnisch, B.; Kraft, S.; Sierk, B.; Bazalgette, G.; Bézy, J.-L.

2017-11-01

In the frame of recent studies and missions, ESA has been performing various pre-developments of optical gratings for instruments operating at wavelengths from the UV up to the SWIR. The instrument requirements of Sentinel-4, Sentinel-5, CarbonSat and FLEX are driving the need for advanced designs and technologies leading to gratings with high efficiency, high spectral resolution, low stray light and low polarization sensitivities. Typical ESA instruments (e.g. Sciamachy, GOME, MERIS, OLCI, NIRSpec) were and are based on ruled gratings or gratings manufactured with one holographic photoresist mask layer which is transferred to an optical substrate (e.g. glass, glass ceramic) with dry etching methods and subsequently either coated with a reflective coating or used as a mold for replication. These manufacturing methods lead to blazed grating profiles with a metallic reflective surface. The vast majority of spectrometers on ground are still based on such gratings. In general, gratings based on grooved metallic surfaces tend for instance to polarize the incoming light significantly and are therefore not always suitable for ESA's needs of today. Gratings made for space therefore evolved to many other designs and concepts which will be reported in this paper.

Unified design of sinusoidal-groove fused-silica grating.

PubMed

Feng, Jijun; Zhou, Changhe; Cao, Hongchao; Lu, Peng

2010-10-20

A general design rule of deep-etched subwavelength sinusoidal-groove fused-silica grating as a highly efficient polarization-independent or polarization-selective device is studied based on the simplified modal method, which shows that the device structure depends little on the incident wavelength, but mainly on the ratio of groove depth to incident wavelength and the ratio of wavelength to grating period. These two ratios could be used as the design guidelines for wavelength-independent structure from deep ultraviolet to far infrared. The optimized grating profile with a different function as a polarizing beam splitter, a polarization-independent two-port beam splitter, or a polarization-independent grating with high efficiency of -1st order is obtained at a wavelength of 1064 nm, and verified by using the rigorous coupled-wave analysis. The performance of the sinusoidal grating is better than a conventional rectangular one, which could be useful for practical applications.

Incorporation of wavelength selective devices into waveguides with applications to a miniature spectrometer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stallard, B. R.; Kaushik, S.; Hadley, G. R.

1996-02-01

This report pertains to a Laboratory Directed Research and Development project which was funded for FY94 and FY95. The goal was to develop building blocks for small, cheap sensors that use optical spectroscopy as a means of detecting chemical analytes. Such sensors can have an impact on a wide variety of technologies, such as: industrial process control, environmental monitors, chemical analysis in medicine, and automotive monitors. We describe work in fabricating and demonstrating a waveguide/grating device that can serve as the wavelength dispersive component in a miniature spectrometer. Also, we describe the invention and modeling of a new way tomore » construct an array of optical interference filters using sub-wavelength lithography to tune the index of refraction of a fixed Fabry-Perot cavity. Next we describe progress in more efficiently calculating the fields in grating devices. Finally we present the invention of a new type of near field optical probe, applicable to scanning microscopy or optical data storage, which is based on a circular grating constructed in a waveguide. This result diverges from the original goal of the project but is quite significant in that it promises to increase the data storage capacity of CD-ROMs by 10 times.« less

Novel thermal annealing methodology for permanent tuning polymer optical fiber Bragg gratings to longer wavelengths.

PubMed

Pospori, A; Marques, C A F; Sagias, G; Lamela-Rivera, H; Webb, D J

2018-01-22

The Bragg wavelength of a polymer optical fiber Bragg grating can be permanently shifted by utilizing the thermal annealing method. In all the reported fiber annealing cases, the authors were able to tune the Bragg wavelength only to shorter wavelengths, since the polymer fiber shrinks in length during the annealing process. This article demonstrates a novel thermal annealing methodology for permanently tuning polymer optical fiber Bragg gratings to any desirable spectral position, including longer wavelengths. Stretching the polymer optical fiber during the annealing process, the period of Bragg grating, which is directly related with the Bragg wavelength, can become permanently longer. The methodology presented in this article can be used to multiplex polymer optical fiber Bragg gratings at any desirable spectral position utilizing only one phase-mask for their photo-inscription, reducing thus their fabrication cost in an industrial setting.

Direct writing of continuous and discontinuous sub-wavelength periodic surface structures on single-crystalline silicon using femtosecond laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuladeep, Rajamudili; Sahoo, Chakradhar; Narayana Rao, Desai, E-mail: dnrsp@uohyd.ernet.in, E-mail: dnr-laserlab@yahoo.com

Laser-induced ripples or uniform arrays of continuous near sub-wavelength or discontinuous deep sub-wavelength structures are formed on single-crystalline silicon (Si) by femtosecond (fs) laser direct writing technique. Laser irradiation was performed on Si wafers at normal incidence in air and by immersing them in dimethyl sulfoxide using linearly polarized Ti:sapphire fs laser pulses of ∼110 fs pulse duration and ∼800 nm wavelength. Morphology studies of laser written surfaces reveal that sub-wavelength features are oriented perpendicular to laser polarization, while their morphology and spatial periodicity depend on the surrounding dielectric medium. The formation mechanism of the sub-wavelength features is explained by interferencemore » of incident laser with surface plasmon polaritons. This work proves the feasibility of fs laser direct writing technique for the fabrication of sub-wavelength features, which could help in fabrication of advanced electro-optic devices.« less

Multilayer manipulated diffraction in flower beetles Torynorrhina flammea: intraspecific structural colouration variation

NASA Astrophysics Data System (ADS)

Song, C. X.; Liu, F.; Hao, Y. H.; Hu, X. H.; Zhang, Y. F.; Liu, X. H.

2014-10-01

We report that the intraspecific structural colouration variation of the beetle Torynorrhina flammea is a result of diffraction shifting manipulated by a multilayer sub-structure contained in a three-dimensional (3D) photonic architecture. With a perpendicularly 2D quasiperiodic diffraction grating inserted into the multilayer, the 3D photonic structure gives rise to anticrossing bandgaps of diffraction from the coupling of grating and multilayer bands. The angular dispersion of diffraction induced by the multilayer band shift behaves normally, in contrast to the ‘ultranegative’ behaviour controlled by the quasiperiodic grating. In addition, the diffraction wavelength is more sensitive to the multilayer periodicity than the diffraction grating constant, which explains the ‘smart’ biological selection of T. flammea in its intraspecific colouration variation from red to green to blue. The elucidated mechanism could be advantageous for the potential exploration of novel dispersive optical elements.

High-throughput accurate-wavelength lens-based visible spectrometer.

PubMed

Bell, Ronald E; Scotti, Filippo

2010-10-01

A scanning visible spectrometer has been prototyped to complement fixed-wavelength transmission grating spectrometers for charge exchange recombination spectroscopy. Fast f/1.8 200 mm commercial lenses are used with a large 2160 mm(-1) grating for high throughput. A stepping-motor controlled sine drive positions the grating, which is mounted on a precision rotary table. A high-resolution optical encoder on the grating stage allows the grating angle to be measured with an absolute accuracy of 0.075 arc  sec, corresponding to a wavelength error ≤0.005 Å. At this precision, changes in grating groove density due to thermal expansion and variations in the refractive index of air are important. An automated calibration procedure determines all the relevant spectrometer parameters to high accuracy. Changes in bulk grating temperature, atmospheric temperature, and pressure are monitored between the time of calibration and the time of measurement to ensure a persistent wavelength calibration.

High-power, surface-emitting quantum cascade laser operating in a symmetric grating mode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boyle, C.; Sigler, C.; Kirch, J. D.

2016-03-21

Grating-coupled surface-emitting (GCSE) lasers generally operate with a double-lobed far-field beam pattern along the cavity-length direction, which is a result of lasing being favored in the antisymmetric grating mode. We experimentally demonstrate a GCSE quantum-cascade laser design allowing high-power, nearly single-lobed surface emission parallel to the longitudinal cavity. A 2nd-order Au-semiconductor distributed-feedback (DFB)/distributed-Bragg-reflector (DBR) grating is used for feedback and out-coupling. The DFB and DBR grating regions are 2.55 mm- and 1.28 mm-long, respectively, for a total grating length of 5.1 mm. The lasers are designed to operate in a symmetric (longitudinal) grating mode by causing resonant coupling of the guided optical modemore » to the antisymmetric surface-plasmon modes of the 2nd-order metal/semiconductor grating. Then, the antisymmetric modes are strongly absorbed by the metal in the grating, causing the symmetric mode to be favored to lase, which, in turn, produces a single-lobed beam over a range of grating duty-cycle values of 36%–41%. Simulations indicate that the symmetric mode is always favored to lase, independent of the random phase of reflections from the device's cleaved ends. Peak pulsed output powers of ∼0.4 W were measured with nearly single-lobe beam-pattern (in the longitudinal direction), single-spatial-mode operation near 4.75 μm wavelength. Far-field measurements confirm a diffraction-limited beam pattern, in agreement with simulations, for a source-to-detector separation of 2 m.« less

System Construction for the Measurement of Bragg Grating Characteristics in Optical Fibers

NASA Technical Reports Server (NTRS)

West, Douglas P.

1995-01-01

Bragg gratings are used to measure strain in optical fibers. To measure strain they are sometimes used as a smart structure. They must be characterized after they are written to determine their spectral response. This paper deals with the test setup to characterize Bragg grating spectral responses.Bragg gratings are a photo-induced phenomena in optical fibers. The gratings can be used to measure strain by measuring the shift in wavelength. They placed the fibers into a smart structure to measure the stress and strain produced on support columns placed in bridges. As the cable is subjected to strain the grating causes a shift to a longer wavelength if the fiber is stretched and a shift to a shorter wavelength shift if the fiber is compacted. Our applications involve using the fibers to measure stress and strain on airborne systems. There are many ways to write Bragg gratings into optical fibers. Our focus is on side writing the grating. Our capabilities are limited in the production rate of the gratings. The Bragg grating is written into a fiber and becomes a permanent fixture. We are writing the grating to be centered at 1300 nm because that is the standard phase mask wavelength.

Rapid bespoke laser ablation of variable period grating structures using a digital micromirror device for multi-colored surface images.

PubMed

Heath, Daniel J; Mills, Ben; Feinaeugle, Matthias; Eason, Robert W

2015-06-01

A digital micromirror device has been used to project variable-period grating patterns at high values of demagnification for direct laser ablation on planar surfaces. Femtosecond laser pulses of ∼1  mJ pulse energy at 800 nm wavelength from a Ti:sapphire laser were used to machine complex patterns with areas of up to ∼1  cm² on thin films of bismuth telluride by dynamically modifying the grating period as the sample was translated beneath the imaged laser pulses. Individual ∼30 by 30 μm gratings were stitched together to form contiguous structures, which had diffractive effects clearly visible to the naked eye. This technique may have applications in marking, coding, and security features.

Transmission Grating and Optics Technology Development for the Arcus Explorer Mission

NASA Astrophysics Data System (ADS)

Heilmann, Ralf; Arcus Team

2018-01-01

Arcus is a high-resolution x-ray spectroscopy MIDEX mission selected for a Phase A concept study. It is designed to explore structure formation through measurements of hot baryon distributions, feedback from black holes, and the formation and evolution of stars, disks, and exoplanet atmospheres. The design provides unprecedented sensitivity in the 1.2-5 nm wavelength band with effective area above 450 sqcm and spectral resolution R > 2500. The Arcus technology is based on 12 m-focal length silicon pore optics (SPO) developed for the European Athena mission, and critical-angle transmission (CAT) x-ray diffraction gratings and x-ray CCDs developed at MIT. The modular design consists of four parallel channels, each channel holding an optics petal, followed by a grating petal. CAT gratings are lightweight, alignment insensitive, high-efficiency x-ray transmission gratings that blaze into high diffraction orders, leading to high spectral resolution. Each optics petal represents an azimuthal sub-aperture of a full Wolter optic. The sub-aperturing effect increases spectral resolving power further. Two CCD readout strips receive photons from each channel, including higher-energy photons in 0th order. Each optics petal holds 34 SPO modules. Each grating petal holds 34 grating windows, and each window holds 4-6 grating facets. A grating facet consists of a silicon grating membrane, bonded to a flexure frame that interfaces with the grating window. We report on a sequence of tests with increasing complexity that systematically increase the Technology Readiness Level (TRL) for the combination of CAT gratings and SPOs towards TLR 6. CAT gratings have been evaluated in x rays for diffraction efficiency (> 30% at 2.5 nm) and for resolving power (R> 10,000). A CAT grating/SPO combination was measured at R ~ 3100 at blaze angles smaller than design values, exceeding Arcus requirements. Efficiency and resolving power were not impacted by vibration and thermal testing of gratings. A pair of large (32 mm x 32 mm) gratings was aligned using laser metrology, and alignment was verified under x rays. We present results on simultaneous illumination of the aligned grating pair, and describe our progress towards further tests.

Thermal diffusivity determination using heterodyne phase insensitive transient grating spectroscopy

NASA Astrophysics Data System (ADS)

Dennett, Cody A.; Short, Michael P.

2018-06-01

The elastic and thermal transport properties of opaque materials may be measured using transient grating spectroscopy (TGS) by inducing and monitoring periodic excitations in both reflectivity and surface displacement. The "phase grating" response encodes both properties of interest, but complicates quantitative analysis by convolving temperature dynamics with surface displacement dynamics. Thus, thermal transport characteristics are typically determined using the "amplitude grating" response to isolate the surface temperature dynamics. However, this signal character requires absolute heterodyne phase calibration and contains no elastic property information. Here, a method is developed by which phase grating TGS measurements may be consistently analyzed to determine thermal diffusivity with no prior knowledge of the expected properties. To demonstrate this ability, the wavelength-dependent 1D effective thermal diffusivity of pure germanium is measured using this type of response and found to be consistent with theoretical predictions made by solving the Boltzmann transport equation. This ability to determine the elastic and thermal properties from a single set of TGS measurements will be particularly advantageous for new in situ implementations of the technique being used to study dynamic materials systems.

Design and fabrication of a polarization-independent two-port beam splitter.

PubMed

Feng, Jijun; Zhou, Changhe; Zheng, Jiangjun; Cao, Hongchao; Lv, Peng

2009-10-10

We design and manufacture a fused-silica polarization-independent two-port beam splitter grating. The physical mechanism of this deeply etched grating can be shown clearly by using the simplified modal method with consideration of corresponding accumulated phase difference of two excited propagating grating modes, which illustrates that the binary-phase fused-silica grating structure depends little on the incident wavelength, but mainly on the ratio of groove depth to grating period and the ratio of incident wavelength to grating period. These analytic results would also be very helpful for wavelength bandwidth analysis. The exact grating profile is optimized by using the rigorous coupled-wave analysis. Holographic recording technology and inductively coupled plasma etching are used to manufacture the fused-silica grating. Experimental results agree well with the theoretical values.

Femtosecond laser-induced subwavelength ripples formed by asymmetrical grating splitting

NASA Astrophysics Data System (ADS)

Feng, Pin; Jiang, Lan; Li, Xin; Zhang, Kaihu; Shi, Xuesong; Li, Bo; Lu, Yongfeng

2016-05-01

The formation process and mechanism of subwavelength ripples were studied upon irradiation of ZnO by a femtosecond laser (800 nm, 50 fs, 1 kHz). An abnormally asymmetrical grating-splitting phenomenon was discovered. At relatively high laser fluences (F = 0.51-0.63 J/cm2), near-wavelength ripples were split asymmetrically to create subwavelength laser-induced periodic surface structures (LIPSS) with dual gaps (˜230 nm and ˜430 nm) on the primary grooves. At relatively low laser fluences (F = 0.4-0.45 J/cm2), near-wavelength ripples were split symmetrically, leading to the formation of uniform subwavelength structures with a period of ˜340 nm. The splitting phenomena are related to the varying laser beam dose induced by the overlapping during line scanning. The two grating-splitting types further imply that the dominated mechanism for LIPSS formation may be changed under different processing conditions.

Fabrication of tunable diffraction grating by imprint lithography with photoresist mold

NASA Astrophysics Data System (ADS)

Yamada, Itsunari; Ikeda, Yusuke; Higuchi, Tetsuya

2018-05-01

We fabricated a deformable transmission silicone [poly(dimethylsiloxane)] grating using a two-beam interference method and imprint lithography and evaluated its optical characteristics during a compression process. The grating pattern with 0.43 μm depth and 1.0 μm pitch was created on a silicone surface by an imprinting process with a photoresist mold to realize a simple, low-cost fabrication process. The first-order diffraction transmittance of this grating reached 10.3% at 632.8 nm wavelength. We also measured the relationship between the grating period and compressive stress to the fabricated elements. The grating period changed from 1.0 μm to 0.84 μm by 16.6% compression of the fabricated element in one direction, perpendicular to the grooves, and the first-order diffraction transmittance was 8.6%.

Health monitoring of carbon cantilever using femtosecond laser inscribed FBG array in gradient-index CYTOP polymer fibre

NASA Astrophysics Data System (ADS)

Theodosiou, Antreas; Kalli, Kyriacos; Komodromos, Michael

2017-04-01

We report on the femtosecond laser inscription of a fibre Bragg grating array in multimode, gradient-index, CYTOP polymer optical fibre and its demonstration as a quasi-distributed sensor for cantilever health monitoring measurements. We exploit the key advantage of polymer optical fibres, having a significantly lower Young's modulus compared with silica fibres, for vibration measurements. We also modify the typical multi-mode Bragg grating spectrum through control of the femtosecond laser inscription process, thereby producing gratings having single peak wavelength spectra. The sensor array is used to recover the time-dependent, wavelength response from each Bragg grating sensor and extract the mode shape of the beam. The mode shapes of the beam were used to observe "damage" introduced to the cantilever by adding masses to its surface; adjusting the level of damage by using different weights and placing them at different point across the beam. We show that health monitoring measurements are feasible with polymer based fibre Bragg gratings. The accurate and rapid detection of damage points on structural beams and the damage level is an important parameter for improved maintenance and servicing of beams under load and for the prevention of long-term damage.

SiN{sub x} layers on nanostructured Si solar cells: Effective for optical absorption and carrier collection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cho, Yunae; Kim, Eunah; Gwon, Minji

2015-10-12

We compared nanopatterned Si solar cells with and without SiN{sub x} layers. The SiN{sub x} layer coating significantly improved the internal quantum efficiency of the nanopatterned cells at long wavelengths as well as short wavelengths, whereas the surface passivation helped carrier collection of flat cells mainly at short wavelengths. The surface nanostructured array enhanced the optical absorption and also concentrated incoming light near the surface in broad wavelength range. Resulting high density of the photo-excited carriers near the surface could lead to significant recombination loss and the SiN{sub x} layer played a crucial role in the improved carrier collection ofmore » the nanostructured solar cells.« less

Bi-wavelength two dimensional chirped grating couplers for low cost WDM PON transceivers

NASA Astrophysics Data System (ADS)

Xu, Lin; Chen, Xia; Li, Chao; Tsang, Hon Ki

2011-04-01

We propose and demonstrate a bi-wavelength two dimensional (2D) waveguide grating coupler on silicon-on-insulator which has efficient coupling of optical light with two-wavelength bands independently between standard optical single mode fibers and nanophotonic waveguides. The details of design are described and the measurement results as well as system performance are experimentally characterized. The bi-wavelength grating coupler can be used as wavelength-division-multiplexing (WDM) splitter/combiner for monolithically silicon integrated transceivers, potentially meeting the low cost requirements for future WDM passive optical network (PON).

Transmittance enhancement of sapphires with antireflective subwavelength grating patterned UV polymer surface structures by soft lithography.

PubMed

Lee, Soo Hyun; Leem, Jung Woo; Yu, Jae Su

2013-12-02

We report the total and diffuse transmission enhancement of sapphires with the ultraviolet curable SU8 polymer surface structures consisting of conical subwavelength gratings (SWGs) at one- and both-side surfaces for different periods. The SWGs patterns on the silicon templates were transferred into the SU8 polymer film surface on sapphires by a simple and cost-effective soft lithography technique. For the fabricated samples, the surface morphologies, wetting behaviors, and optical characteristics were investigated. For theoretical optical analysis, a rigorous coupled-wave analysis method was used. At a period of 350 nm, the sample with SWGs on SU8 film/sapphire exhibited a hydrophobic surface and higher total transmittance compared to the bare sapphire over a wide wavelength of 450-1000 nm. As the period of SWGs was increased, the low total transmittance region of < 85% was shifted towards the longer wavelengths and became broader while the diffuse transmittance was increased (i.e., larger haze ratio). For the samples with SWGs at both-side surfaces, the total and diffuse transmittance spectra were further enhanced compared to the samples with SWGs at one-side surface. The theoretical optical calculation results showed a similar trend to the experimentally measured data.

Curved grating fabrication techniques for concentric-circle grating, surface-emitting semiconductor lasers

NASA Technical Reports Server (NTRS)

Jordan, Rebecca H.; King, Oliver; Wicks, Gary W.; Hall, Dennis G.; Anderson, Erik H.; Rooks, Michael J.

1993-01-01

We describe the fabrication and operational characteristics of a novel, surface-emitting semiconductor laser that makes use of a concentric-circle grating to both define its resonant cavity and to provide surface emission. A properly fabricated circular grating causes the laser to operate in radially inward- and outward-going circular waves in the waveguide, thus, introducing the circular symmetry needed for the laser to emit a beam with a circular cross-section. The basic circular-grating-resonator concept can be implemented in any materials system; an AlGaAs/GaAs graded-index, separate confinement heterostructure (GRINSCH), single-quantum-well (SQW) semiconductor laser, grown by molecular beam epitaxy (MBE), was used for the experiments discussed here. Each concentric-circle grating was fabricated on the surface of the AlGaAs/GaAs semiconductor laser. The circular pattern was first defined by electron-beam (e-beam) lithography in a layer of polymethylmethacrylate (PMMA) and subsequently etched into the semiconductor surface using chemically-assisted (chlorine) ion-beam etching (CAIBE). We consider issues that affect the fabrication and quality of the gratings. These issues include grating design requirements, data representation of the grating pattern, and e-beam scan method. We provide examples of how these techniques can be implemented and their impact on the resulting laser performance. A comparison is made of the results obtained using two fundamentally different electron-beam writing systems. Circular gratings with period lambda = 0.25 microns and overall diameters ranging from 80 microns to 500 microns were fabricated. We also report our successful demonstration of an optically pumped, concentric-circle grating, semiconductor laser that emits a beam with a far-field divergence angle that is less than one degree. The emission spectrum is quite narrow (less than 0.1 nm) and is centered at wavelength lambda = 0.8175 microns.

Waveguide silicon nitride grating coupler

NASA Astrophysics Data System (ADS)

Litvik, Jan; Dolnak, Ivan; Dado, Milan

2016-12-01

Grating couplers are one of the most used elements for coupling of light between optical fibers and photonic integrated components. Silicon-on-insulator platform provides strong confinement of light and allows high integration. In this work, using simulations we have designed a broadband silicon nitride surface grating coupler. The Fourier-eigenmode expansion and finite difference time domain methods are utilized in design optimization of grating coupler structure. The fully, single etch step grating coupler is based on a standard silicon-on-insulator wafer with 0.55 μm waveguide Si3N4 layer. The optimized structure at 1550 nm wavelength yields a peak coupling efficiency -2.6635 dB (54.16%) with a 1-dB bandwidth up to 80 nm. It is promising way for low-cost fabrication using complementary metal-oxide- semiconductor fabrication process.

Fabrication and Characterization of Tilted Fiber Optic Bragg Grating Filters over Various Wavelengths

NASA Technical Reports Server (NTRS)

Grant, Joseph; Jackson, Kurt V.; Wang, Y.; Sharma, A.; Burdine, Robert V. (Technical Monitor)

2002-01-01

Fiber Optic Bragg Grating taps are fabricated and characterized at various wavelengths using a modified Talbot interferometric technique. Gratings are fabricated by tilting the photosensitive fiber to angles up to 45 degrees w.r.t. the writing angle. Diffraction characteristics of the tilted grating is monitored in first and second orders.

Diffraction encoded position measuring apparatus

DOEpatents

Tansey, Richard J.

1991-01-01

When a lightwave passes through a transmission grating, diffracted beams appear at the output or opposite side of the grating that are effectively Doppler shifted in frequency (phase) whereby a detector system can compare the phase of the zero order and higher order beams to obtain an indication of position. Multiple passes through the grating increase resolution for a given wavelength of a laser signal. The resolution can be improved further by using a smaller wavelength laser to generate the grating itself. Since the grating must only have a pitch sufficient to produce diffracted orders, inexpensive, ultraviolet wavelength lasers can be utilized and still obtain high resolution detection.

Diffraction encoded position measuring apparatus

DOEpatents

Tansey, R.J.

1991-09-24

When a lightwave passes through a transmission grating, diffracted beams appear at the output or opposite side of the grating that are effectively Doppler shifted in frequency (phase) whereby a detector system can compare the phase of the zero order and higher order beams to obtain an indication of position. Multiple passes through the grating increase resolution for a given wavelength of a laser signal. The resolution can be improved further by using a smaller wavelength laser to generate the grating itself. Since the grating must only have a pitch sufficient to produce diffracted orders, inexpensive, ultraviolet wavelength lasers can be utilized and still obtain high resolution detection. 3 figures.

Material removal rate fiber optic corrosion sensor

NASA Astrophysics Data System (ADS)

Trego, Angela; Haugse, Eric D.; Udd, Eric

1998-09-01

Fiber Bragg grating sensors generally consist of a single grating written in a low-birefringent optical fiber. The wavelength shift of the peak in the reflected spectrum from these sensors can be used to measure a single component of strain or a change in temperature [Lawrence, 1997]. Fibers are also available with a significant enough birefringence to maintain the polarization state along great lengths and through many turns. This 'polarization maintaining' fiber is commercially available through several companies and in several configurations (including different cladding material and wavelength shift). The grating usually extends approximately 3 mm - 5 m in length. Udd gives a detailed explanation of fiber optics, Bragg gratings and birefringence [Udd, 1991]. As light from an LED is passed through the fiber, only the wavelength consistent with the grating period will be reflected back towards the source. All other wavelengths will pass through. The reflected spectrum will shift as the fiber is strained along its axis at the grating location. Strain or temperature changes at any other location have negligible effect on the wavelength encoded data output. When the Fiber Bragg grating single-axis sensor (termed fiber hereafter) is strained transversely the wavelength will separate into two distinct peaks according to a mathematical relationship defined by Lawrence and Nelson [Lawrence, Nelson et al. 96]. Using these Fiber Bragg grating fibers a corrosion sensor which measures the rate of material was developed. The principle behind this newly developed corrosion sensor is to pre-stress the fiber with a known load. The load is applied by inducing a uniform hoop stress through pressure fitted cylinders around the fiber. This induced stress creates a broadening of the reflected spectrum until the bifurcation of the reflected intensity peaks is distinguishable. As the material from the outer cylinder corrodes away the applied stress will be relieved. Finally, when no load is achieved, the reflected spectrum will have a single peak centered around the nominal Bragg grating wavelength. If a polarizing-maintaining 3-axis grating is used then the sensor would be even more sensitive, having two distinct peaks in each wavelength regime which shift.

High-power, fixed, and tunable wavelength, grating-free cascaded Raman fiber lasers

NASA Astrophysics Data System (ADS)

Balaswamy, V.; Arun, S.; Aparanji, Santosh; Choudhury, Vishal; Supradeepa, V. R.

2018-04-01

Cascaded Raman lasers enable high powers at various wavelength bands inaccessible with conventional rare-earth doped lasers. The input and output wavelengths of conventional implementations are fixed by the constituent fiber gratings necessary for cascaded Raman conversion. We demonstrate here, a simple architecture for high power, fixed and wavelength tunable, grating-free, cascaded Raman conversion between different wavelength bands. The architecture is based on the recently proposed distributed feedback Raman lasers. Here, we implement a module which converts the Ytterbium band to the eye-safe 1.5micron region. We demonstrate pump-limited output powers of over 30W in fixed and continuously wavelength tunable configurations.

Investigation on the applications of fiber grating lasers in industrial sensing and pollution monitoring

NASA Astrophysics Data System (ADS)

Xu, Yuanzhong

The main objective of the project was to develop ``eye-safe'' fiber-grating lasers for pollution measurement and monitoring. Fiber grating lasers have a number of advantages such as narrow linewidth and precise wavelength control over the semiconductor counterparts. Three types of Erbium doped fiber grating lasers emitting in 1.5 μm band were developed and characterized in this work. We first used an entirely original approach to develop tunable dual-wavelength switchable fiber grating laser for differential absorption spectroscopy. The lam can switch between two wavelengths with each wavelength being independently tunable. It's characterized by >6-mW output power, <2% intensity fluctuation, 100s Hz switching speed and 1:100,000 wavelength extinction ratio. The outstanding advantage of this approach is the simplicity in laser configuration as well as in detection system for dual wavelength laser, because it uses only an overlapped gain medium and one detector for both wavelengths. Main drawbacks of the prototype laser are slow switching speed (100s Hz) and multimode operation, which could be overcome by cavity dampening and modification in laser configuration. Short cavity erbium-doped fiber grating lasers using high Erbium concentration were also studied. A 6-cm long fiber-grating laser pumped by a 980-nm laser diode was constructed. The linewidth of the laser is very narrow (~100s kHz) but its output slope efficiency is relatively low (~1%). Furthermore, the ion clustering effect arising from high Er concentration tends to cause self-pulsation and thus instability to the laser. By replacing the Erbium doped fiber with Er/Yb codoped one, the fiber grating laser was made more stable and efficient. The ion clustering effect disappears in the laser output due to the low Erbium concentration in Er/Yb codoped fiber, while the Er/Yb codoped fiber's two orders higher pump absorption at 980 nm results in as large as 10 ~ 30% output slope efficiency in about 2 cm long laser. On the other hand, strong pump absorption in Er/Yb fiber was found to cause significant thermal effects in Er/Yb fiber grating lasers, which can be eliminated by ensuring proper thermal dissipation. Because of fiber laser's long lifetime at the upper laser level, its wavelength cannot be directly modulated at high speed. The widely used wavelength modulation spectroscopy (WMS) method is thus not suitable when using fiber laser sources in gas detection. The wavelength sweep scheme was thus employed as an alternative. Laser wavelength/frequency requirement and noise cancellation in this scheme are discussed. For a demonstration of fiber grating laser's application to pollutant monitoring and industrial sensing, laser spectroscopy of C2H 2 gas was undertaken with the Er/Yb codoped fiber-grating laser. A 10 -4 detection sensitivity was achieved. This is the first time, to our knowledge, that a single frequency fiber-grating laser was used in rapid laser spectroscopy. The investigation has shown that the fiber grating lasers are high performance as well as low cost, rugged and portable laser sources, very suitable for industrial sensing and pollution monitoring. A number of important pollutants, such as CO, CO2, H2S and C2H2 have absorption peaks around 1.55-μm wavelength and thus can be sensed with these lasers. Although the fiber lasers investigated here operate in the 1.5-μm window, the results are also very useful for fiber lasers that use the same operation principle in other wavelength regions.

Silicon immersion gratings and their spectroscopic applications

NASA Astrophysics Data System (ADS)

Ge, Jian; Zhao, Bo; Powell, Scott; Fletcher, Adam; Wan, Xiaoke; Chang, Liang; Jakeman, Hali; Koukis, Dimitrios; Tanner, David B.; Ebbets, Dennis; Weinberg, Jonathan; Lipscy, Sarah; Nyquist, Rich; Bally, John

2012-09-01

Silicon immersion gratings (SIGs) offer several advantages over the commercial echelle gratings for high resolution infrared (IR) spectroscopy: 3.4 times the gain in dispersion or ~10 times the reduction in the instrument volume, a multiplex gain for a large continuous wavelength coverage and low cost. We present results from lab characterization of a large format SIG of astronomical observation quality. This SIG, with a 54.74 degree blaze angle (R1.4), 16.1 l/mm groove density, and 50x86 mm2 grating area, was developed for high resolution IR spectroscopy (R~70,000) in the near IR (1.1-2.5 μm). Its entrance surface was coated with a single layer of silicon nitride antireflection (AR) coating and its grating surface was coated with a thin layer of gold to increase its throughput at 1.1-2.5 μm. The lab measurements have shown that the SIG delivered a spectral resolution of R=114,000 at 1.55 μm with a lab testing spectrograph with a 20 mm diameter pupil. The measured peak grating efficiency is 72% at 1.55 μm, which is consistent with the measurements in the optical wavelengths from the grating surface at the air side. This SIG is being implemented in a new generation cryogenic IR spectrograph, called the Florida IR Silicon immersion grating spectrometer (FIRST), to offer broad-band high resolution IR spectroscopy with R=72,000 at 1.4-1.8 um under a typical seeing condition in a single exposure with a 2kx2k H2RG IR array at the robotically controlled Tennessee State University 2-meter Automatic Spectroscopic Telescope (AST) at Fairborn Observatory in Arizona. FIRST is designed to provide high precision Doppler measurements (~4 m/s) for the identification and characterization of extrasolar planets, especially rocky planets in habitable zones, orbiting low mass M dwarf stars. It will also be used for other high resolution IR spectroscopic observations of such as young stars, brown dwarfs, magnetic fields, star formation and interstellar mediums. An optimally designed SIG of the similar size can be used in the Silicon Immersion Grating Spectrometer (SIGS) to fill the need for high resolution spectroscopy at mid IR to far IR (~25-300 μm) for the NASA SOFIA airborne mission in the future.

Polymer/silica hybrid integration waveguide Bragg grating based on surface plasmon polaritons.

PubMed

Tian, Liang; Wang, Fei; Wu, Yuanda; Sun, Xiaoqiang; Yi, Yunji; Zhang, Daming

2018-05-01

We proposed a device composed of a Bragg grating and a long-range surface plasmon polariton waveguide. The waveguide is formed by embedding a thin Au stripe in negative UV photoresist (SU-8 2005). The corrugated grating structure is created on a silica substrate using contact lithography and inductively coupled plasma etching, which is transferred onto the SU-8 2005 film by a spin coating process, producing a periodic modulation of refractive index along the waveguide. We achieve a transmission peak with an extinction ratio of 17 dB and a 3-dB bandwidth of 0.9 nm at a wavelength of 1575.2 nm. We achieve a reflection peak with a side-mode suppression ratio of 9.7 dB, a 3-dB bandwidth of 0.9 nm at a wavelength of 1575.2 nm when the heating electrode isn't working. The shift of the reflection peak with heating power over the range 0-6 mW is approximately 2.9 nm. This thermal dependence exhibits an average slope of -0.48  nm/mW.

Dopants concentration effects on the wavelength shift of long-period fiber gratings used as liquid level detectors

NASA Astrophysics Data System (ADS)

Mao, Barerem-Melgueba; Zhou, Bin

2011-12-01

Two liquid level sensors based on different long-period fiber gratings are proposed and compared. The long-period gratings have the same characteristics (length, grating period) but are fabricated in different optical fibers (photosensitive B-Ge codoped optical fibers with different dopants concentrations). The principle of this type of sensor is based on the refractive index sensitivity of long-period fiber gratings. By monitoring the resonant wavelength shifts of a given attenuation band, one can measure the immersed lengths of long-period fiber gratings and then the liquid level. The levels of two different solutions are measured. The maximum shift (7.69 nm) of the investigated resonance wavelength was observed in LPG1 (fabricated in Fibercore PS1250/1500). By controlling the fiber dopants concentrations one can improve the readouts of a fiber-optic liquid level sensor based on long-period fiber gratings.

Wavelength-division multiplexed optical integrated circuit with vertical diffraction grating

NASA Technical Reports Server (NTRS)

Lang, Robert J. (Inventor); Forouhar, Siamak (Inventor)

1994-01-01

A semiconductor optical integrated circuit for wave division multiplexing has a semiconductor waveguide layer, a succession of diffraction grating points in the waveguide layer along a predetermined diffraction grating contour, a semiconductor diode array in the waveguide layer having plural optical ports facing the succession of diffraction grating points along a first direction, respective semiconductor diodes in the array corresponding to respective ones of a predetermined succession of wavelengths, an optical fiber having one end thereof terminated at the waveguide layer, the one end of the optical fiber facing the succession of diffraction grating points along a second direction, wherein the diffraction grating points are spatially distributed along the predetermined contour in such a manner that the succession of diffraction grating points diffracts light of respective ones of the succession of wavelengths between the one end of the optical fiber and corresponding ones of the optical ports.

Surface Modified Long Period Fiber Grating Sensor for Rapid Detection of Aspergillus Niger Fungal Spores

NASA Astrophysics Data System (ADS)

Gambhir, Monika; Gupta, Shilpi; John, Priya; Mahakud, Ramakanta; Kumar, Jitendra; Prakash, Om

2018-03-01

We present development of a compact and label-free sensor based on the surface modification of copper vapor laser fabricated long period fiber gratings for detection of airborne Aspergillus niger (A. niger) fungal spores. Surface of sensors were functionalized with monoclonal glucose oxidases IgG1 for target-specific covalent binding. In process of functionalization and binding of 103 cfu/ml of pathogenic A. niger fungal spores, notable shorter wave transition in resonance wavelength from 1562.93 nm to 1555.97 nm, and significant reduction in peak loss from 61.72 dB to 57.48 dB were recorded. The implementation was cost effective and yielded instantaneous results.

Reannealed Fiber Bragg Gratings Demonstrated High Repeatability in Temperature Measurements

NASA Technical Reports Server (NTRS)

Adamovsky, Grigory; Juergens, Jeffrey R.

2004-01-01

Fiber Bragg gratings (FBGs) are formed by periodic variations of the refractive index of an optical fiber. These periodic variations allow an FBG to act as an embedded optical filter, passing the majority of light propagating through a fiber while reflecting back a narrow band of the incident light. The peak reflected wavelength of the FBG is known as the Bragg wavelength. Since the period and width of the refractive index variation in the fiber determines the wavelengths that are transmitted and reflected by the grating, any force acting on the fiber that alters the physical structure of the grating will change the wavelengths that are transmitted and reflected by it. Both thermal and mechanical forces acting on the grating will alter its physical characteristics, allowing the FBG sensor to detect both the temperature variations and the physical stresses and strains placed upon it. This ability to sense multiple physical forces makes the FBG a versatile sensor. To assess the feasibility of using Bragg gratings as temperature sensors for propulsion applications, researchers at the NASA Glenn Research Center evaluated the performance of Bragg gratings at elevated temperatures for up to 300 C. For these purposes, commercially available polyimide-coated high-temperature gratings were used that were annealed by the manufacturer to 300 C. To assure the most thermally stable gratings at the operating temperatures, we reannealed the gratings to 400 C at a very slow rate for 12 to 24 hr until their reflected optical powers were stabilized. The reannealed gratings were then subjected to periodic thermal cycling from room temperature to 300 C, and their peak reflected wavelengths were monitored. The setup shown is used for reannealing and thermal cycling the FBGs. Signals from the photodetectors and the spectrum analyzer were fed into a computer equipped with LabVIEW software. The software synchronously monitored the oven/furnace temperature and the optical spectrum analyzer as well as processed the data. Experimental results presented in the following graph show typical wavelength versus temperature dependence of a reannealed FBG through six thermal cycles (80 hr). The average standard deviation of the temperature-to-wavelength relationship ranged from 1.86 to 2.92 C over the six thermal cycles each grating was subjected to. This is an error of less than 1.0 percent of full scale throughout the entire evaluation temperature range from ambient to 300 C.

High-power, fixed, and tunable wavelength, grating-free cascaded Raman fiber lasers.

PubMed

Balaswamy, V; Arun, S; Aparanji, Santosh; Choudhury, Vishal; Supradeepa, V R

2018-04-01

Cascaded Raman lasers enable high powers at various wavelength bands inaccessible with conventional rare-earth-doped lasers. The input and output wavelengths of conventional implementations are fixed by the constituent fiber gratings necessary for cascaded Raman conversion. We demonstrate here a simple architecture for high-power, fixed, and wavelength tunable, grating-free, cascaded Raman conversion between different wavelength bands. The architecture is based on the recently proposed distributed feedback Raman lasers. Here, we implement a module which converts the ytterbium band to the eye-safe 1.5 μm region. We demonstrate pump-limited output powers of over 30 W in fixed and continuously wavelength tunable configurations.

Wavelength-division and spatial multiplexing using tandem interferometers for Bragg grating sensor networks

NASA Astrophysics Data System (ADS)

Kalli, K.; Brady, G. P.; Webb, D. J.; Jackson, D. A.; Zhang, L.; Bennion, I.

1995-12-01

We present a new method for the interrogation of large arrays of Bragg grating sensors. Eight gratings operating between the wavelengths of 1533 and 1555 nm have been demultiplexed. An unbalanced Mach-Zehnder interferometer illuminated by a single low-coherence source provides a high-phase-resolution output for each sensor, the outputs of which are sequentially selected in wavelength by a tunable Fabry-Perot interferometer. The minimum detectable strain measured was 90 n 3 / \\radical Hz \\end-radical at 7 Hz for a wavelength of 1535 nm.

Soft X-ray holographic grating beam splitter including a double frequency grating for interferometer pre-alignment.

PubMed

Liu, Ying; Tan, Xin; Liu, Zhengkun; Xu, Xiangdong; Hong, Yilin; Fu, Shaojun

2008-09-15

Grating beam splitters have been fabricated for soft X-ray Mach- Zehnder interferometer using holographic interference lithography. The grating beam splitter consists of two gratings, one works at X-ray laser wavelength of 13.9 nm with the spatial frequency of 1000 lines/mm as the operation grating, the other works at visible wavelength of 632.8 nm for pre-aligning the X-ray interferometer with the spatial frequency of 22 lines/mm as the pre-alignment grating. The two gratings lie vertically on the same substrate. The main feature of the beam splitter is the use of low-spatial- frequency beat grating of a holographic double frequency grating as the pre-alignment grating of the X-ray interferometer. The grating line parallelism between the two gratings can be judged by observing the diffraction patterns of the pre-alignment grating directly.

Enhanced absorption of graphene strips with a multilayer subwavelength grating structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Jin-Hua; Huang, Yong-Qing, E-mail: yqhuang@bupt.edu.cn; Duan, Xiao-Feng

2014-12-01

The optical absorption of graphene strips covered on a multilayer subwavelength grating (MSG) surface is theoretically investigated. The absorption of graphene strips with MSG is enhanced in the wavelength range of 1500 nm to 1600 nm by critical coupling, which is associated with the combined effects of a guided resonance of MSG and its photonic band gap effect. The critical coupling of the graphene strips can be controlled by adjusting the incident angle without changing the structural parameters of MSG. The absorption of graphene strips can also be tuned by varying key parameters, such as grating period, strip width, and incident angle.

Plasmon-enhanced refractometry using silver nanowire coatings on tilted fibre Bragg gratings.

PubMed

Bialiayeu, A; Bottomley, A; Prezgot, D; Ianoul, A; Albert, J

2012-11-09

A novel technique for increasing the sensitivity of tilted fibre Bragg grating (TFBG) based refractometers is presented. The TFBG sensor was coated with chemically synthesized silver nanowires ~100 nm in diameter and several micrometres in length. A 3.5-fold increase in sensor sensitivity was obtained relative to the uncoated TFBG sensor. This increase is associated with the excitation of surface plasmons by orthogonally polarized fibre cladding modes at wavelengths near 1.5 μm. Refractometric information is extracted from the sensor via the strong polarization dependence of the grating resonances using a Jones matrix analysis of the transmission spectrum of the fibre.

Wide wavelength range tunable one-dimensional silicon nitride nano-grating guided mode resonance filter based on azimuthal rotation

NASA Astrophysics Data System (ADS)

Yukino, Ryoji; Sahoo, Pankaj K.; Sharma, Jaiyam; Takamura, Tsukasa; Joseph, Joby; Sandhu, Adarsh

2017-01-01

We describe wavelength tuning in a one dimensional (1D) silicon nitride nano-grating guided mode resonance (GMR) structure under conical mounting configuration of the device. When the GMR structure is rotated about the axis perpendicular to the surface of the device (azimuthal rotation) for light incident at oblique angles, the conditions for resonance are different than for conventional GMR structures under classical mounting. These resonance conditions enable tuning of the GMR peak position over a wide range of wavelengths. We experimental demonstrate tuning over a range of 375 nm between 500 nm˜875 nm. We present a theoretical model to explain the resonance conditions observed in our experiments and predict the peak positions with show excellent agreement with experiments. Our method for tuning wavelengths is simpler and more efficient than conventional procedures that employ variations in the design parameters of structures or conical mounting of two-dimensional (2D) GMR structures and enables a single 1D GMR device to function as a high efficiency wavelength filter over a wide range of wavelengths. We expect tunable filters based on this technique to be applicable in a wide range of fields including astronomy and biomedical imaging.

Binary-Phase Fourier Gratings for Nonuniform Array Generation

NASA Technical Reports Server (NTRS)

Keys, Andrew S.; Crow, Robert W.; Ashley, Paul R.

2003-01-01

We describe a design method for a binary-phase Fourier grating that generates an array of spots with nonuniform, user-defined intensities symmetric about the zeroth order. Like the Dammann fanout grating approach, the binary-phase Fourier grating uses only two phase levels in its grating surface profile to generate the final spot array. Unlike the Dammann fanout grating approach, this method allows for the generation of nonuniform, user-defined intensities within the final fanout pattern. Restrictions governing the specification and realization of the array's individual spot intensities are discussed. Design methods used to realize the grating employ both simulated annealing and nonlinear optimization approaches to locate optimal solutions to the grating design problem. The end-use application driving this development operates in the near- to mid-infrared spectrum - allowing for higher resolution in grating specification and fabrication with respect to wavelength than may be available in visible spectrum applications. Fabrication of a grating generating a user-defined nine spot pattern is accomplished in GaAs for the near-infrared. Characterization of the grating is provided through the measurement of individual spot intensities, array uniformity, and overall efficiency. Final measurements are compared to calculated values with a discussion of the results.

Cross-fiber Bragg grating transducer

NASA Technical Reports Server (NTRS)

Albin, Sacharia (Inventor); Zheng, Jianli (Inventor); Lavarias, Arnel (Inventor)

2000-01-01

A transducer has been invented that uses specially-oriented gratings in waveguide a manner that allows the simultaneous measurement of physical phenomena (such as shear force, strain and temperature) in a single sensing element. The invention has a highly sensitive, linear response and also has directional sensitivity with regard to strain. The transducer has a waveguide with a longitudinal axis as well as two Bragg gratings. The transducer has a first Bragg grating associated with the waveguide that has an angular orientation .theta..sub.a relative to a perpendicular to the longitudinal axis such that 0.degree.<.theta..sub.a <.theta..sub.max. The second Bragg grating is associated with the waveguide in such a way that the angular orientation .theta..sub.b of the grating relative to a perpendicular to the longitudinal axis is (360.degree.-.theta..sub.max)<.theta..sub.b <360.degree.. The first Bragg grating can have a periodicity .LAMBDA..sub.a and the second Bragg grating can have a periodicity .LAMBDA..sub.b such that the periodicity .LAMBDA..sub.a of the first Bragg grating does not equal the periodicity .LAMBDA..sub.b of the second Bragg grating. The angle of the gratings can be such that .theta..sub.a =360.degree.-.theta..sub.b. The waveguide can assume a variety of configurations, including an optical fiber, a rectangular waveguide and a planar waveguide. The waveguide can be fabricated of a variety of materials, including silica and polymer material.

Wavelength-encoded optical psychrometer for relative humidity measurement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Montanini, Roberto

2007-02-15

In this article an optical psychrometer, in which temperature measurements are performed by means of two fiber Bragg grating sensors used as dry-bulb and wet-bulb thermometers, is introduced. The adopted design exploits both the high accuracy of psychrometric-based relative humidity measurements with acknowledged advantages of wavelength-encoded fiber optic sensing. Important metrological issues that have been addressed in the experimental work include calibration of the fiber Bragg grating temperature sensors, evaluation of response time, sensitivity, hysteresis, linearity, and accuracy. The calibration results give confidence that, with the current experimental setup, measurement of temperature can be done with an uncertainty of {+-}0.2more » deg. C and a resolution of 0.1 deg. C. A detailed uncertainty analysis is also presented in the article to investigate the effects produced by different sources of error on the combined standard uncertainty u{sub c}(U) of the relative humidity measurement, which has been estimated to be roughly within {+-}2% in the range close to saturation.« less

Elliptical varied line-space (EVLS) gratings

NASA Astrophysics Data System (ADS)

Thomas, Roger J.

2004-10-01

Imaging spectroscopy at wavelengths below 2000 Å offers an especially powerful method for studying many extended high-temperature astronomical objects, like the Sun and its outer layers. But the technology to make such measurements is also especially challenging, because of the poor reflectance of all standard materials at these wavelengths, and because the observation must be made from above the absorbing effects of the Earth's atmosphere. To solve these problems, single-reflection stigmatic spectrographs for XUV wavelengths have bee flown on several space missions based on designs with toroidal uniform line-space (TULS) or spherical varied line-space (SVLS) gratings that operate at near normal-incidence. More recently, three solar EUV/UV instruments have been selected that use toroidal varied line-space (TVLS) gratings; these are SUMI and RAISE, both sounding rocket payloads, and NEXUS, a SMEX satellite-mission. The next logical extension to such designs is the use of elliptical surfaces for varied line-space (EVLS) rulings. In fact, EVLS designs are found to provide superior imaging even at very large spectrograph magnifications and beam-speeds, permitting extremely high-quality performance in remarkably compact instrument packages. In some cases, such designs may be optimized even further by using a hyperbolic surface for the feeding telescope. The optical characteristics of two solar EUV spectrometers based on these concepts are described: EUS and EUI, both being developed as possible instruments for ESA's Solar Orbiter mission by consortia led by RAL and by MSSL, respectively.

Photothermal effects in phase shifted FBG with varied light wavelength and intensity.

PubMed

Ding, Meng; Chen, Dijun; Fang, Zujie; Wang, Di; Zhang, Xi; Wei, Fang; Yang, Fei; Ying, Kang; Cai, Haiwen

2016-10-31

The intensity enhancement effect of a phase-shifted fiber Bragg grating (PSFBG) is investigated theoretically and experimentally in this paper. Due to the effect, both of the FBG reflection bands and the transmission peak show red-shift with the increase of pump light wavelength from the shorter side to the longer side of the Bragg wavelength. The transmission peak shifts in pace with the pump's wavelength, which is much faster than the reflection band. The maximum shift increases with the pump power. In contrast, the red-shift is very small when the pump light deceases from the longer side of the Bragg wavelength. Such asymmetric behavior is checked dynamically by using a frequency modulated laser in a serrated wave, showing push-pull behavior. The effect of the characteristics of thermal dissipation conditions is also measured. The fiber loss coefficient of FBG being tested is estimated from the measured data to be about 0.001 mm^-1, which may be attributed to the H₂-loading and UV exposure in FBG fabrication. The observed phenomena are believed of importance in application where PSFBG is utilized as a narrow linewidth filter.

Edge Triggered Apparatus and Method for Measuring Strain in Bragg Gratings

NASA Technical Reports Server (NTRS)

Froggatt, Mark E. (Inventor)

2003-01-01

An apparatus and method for measuring strain of gratings written into an optical fiber. Optical radiation is transmitted over one or more contiguous predetermined wavelength ranges into a reference optical fiber network and an optical fiber network under test to produce a plurality of reference interference fringes and measurement interference fringes, respectively. The reference and measurement fringes are detected, and the reference fringes trigger the sampling of the measurement fringes. This results in the measurement fringes being sampled at 2(pi) increments of the reference fringes. Each sampled measurement fringe of each wavelength sweep is transformed into a spatial domain waveform. The spatial domain waveforms are summed to form a summation spatial domain waveform that is used to determine location of each grating with respect to a reference reflector. A portion of each spatial domain waveform that corresponds to a particular grating is determined and transformed into a corresponding frequency spectrum representation. The strain on the grating at each wavelength of optical radiation is determined by determining the difference between the current wavelength and an earlier, zero-strain wavelength measurement.

Review of rigorous coupled-wave analysis and of homogeneous effective medium approximations for high spatial-frequency surface-relief gratings

NASA Technical Reports Server (NTRS)

Glytsis, Elias N.; Brundrett, David L.; Gaylord, Thomas K.

1993-01-01

A review of the rigorous coupled-wave analysis as applied to the diffraction of electro-magnetic waves by gratings is presented. The analysis is valid for any polarization, angle of incidence, and conical diffraction. Cascaded and/or multiplexed gratings as well as material anisotropy can be incorporated under the same formalism. Small period rectangular groove gratings can also be modeled using approximately equivalent uniaxial homogeneous layers (effective media). The ordinary and extraordinary refractive indices of these layers depend on the gratings filling factor, the refractive indices of the substrate and superstrate, and the ratio of the freespace wavelength to grating period. Comparisons of the homogeneous effective medium approximations with the rigorous coupled-wave analysis are presented. Antireflection designs (single-layer or multilayer) using the effective medium models are presented and compared. These ultra-short period antireflection gratings can also be used to produce soft x-rays. Comparisons of the rigorous coupled-wave analysis with experimental results on soft x-ray generation by gratings are also included.

Performance Evaluation of Fiber Bragg Gratings at Elevated Temperatures

NASA Technical Reports Server (NTRS)

Juergens, Jeffrey; Adamovsky, Grigory; Floyd, Bertram

2004-01-01

The development of integrated fiber optic sensors for smart propulsion systems demands that the sensors be able to perform in extreme environments. In order to use fiber optic sensors effectively in an extreme environment one must have a thorough understanding of the sensor s limits and how it responds under various environmental conditions. The sensor evaluation currently involves examining the performance of fiber Bragg gratings at elevated temperatures. Fiber Bragg gratings (FBG) are periodic variations of the refractive index of an optical fiber. These periodic variations allow the FBG to act as an embedded optical filter passing the majority of light propagating through a fiber while reflecting back a narrow band of the incident light. The peak reflected wavelength of the FBG is known as the Bragg wavelength. Since the period and width of the refractive index variation in the fiber determines the wavelengths that are transmitted and reflected by the grating, any force acting on the fiber that alters the physical structure of the grating will change what wavelengths are transmitted and what wavelengths are reflected by the grating. Both thermal and mechanical forces acting on the grating will alter its physical characteristics allowing the FBG sensor to detect both temperature variations and physical stresses, strain, placed upon it. This ability to sense multiple physical forces makes the FBG a versatile sensor. This paper reports on test results of the performance of FBGs at elevated temperatures. The gratings looked at thus far have been either embedded in polymer matrix materials or freestanding with the primary focus of this paper being on the freestanding FBGs. Throughout the evaluation process, various parameters of the FBGs performance were monitored and recorded. These parameters include the peak Bragg wavelength, the power of the Bragg wavelength, and total power returned by the FBG. Several test samples were subjected to identical test conditions to allow for statistical analysis of the data. Test procedures, calibrations, and referencing techniques are presented in the paper along with directions for future research.

Wavelength-tunable, passively mode-locked fiber laser based on graphene and chirped fiber Bragg grating.

PubMed

He, Xiaoying; Liu, Zhi-bo; Wang, D N

2012-06-15

We demonstrate a wavelength-tunable, passively mode-locked erbium-doped fiber laser based on graphene and chirped fiber Bragg grating. The saturable absorber used to enable passive mode-locking in the fiber laser is a section of microfiber covered by graphene film, which allows light-graphene interaction via the evanescent field of the microfiber. The wavelength of the laser can be continuously tuned by adjusting the chirped fiber Bragg grating, while maintaining mode-locking stability. Such a system has high potential in tuning the mode-locked laser pulses across a wide wavelength range.

High channel density wavelength division multiplexer with defined diffracting means positioning

DOEpatents

Jannson, Tomasz P.; Jannson, Joanna L.; Yeung, Peter C.

1990-01-01

A wavelength division multiplexer/demultiplexer having optical path lengths between a fiber array and a Fourier transform lens, and between a dispersion grating and the lens equal to the focal length of the lens. The optical path lengths reduce losses due to angular acceptance mismatch in the multiplexer. Close orientation of the fiber array about the optical axis and the use of a holographic dispersion grating reduces other losses in the system. Multi-exposure holographic dispersion gratings enable the multiplexer/demultiplexer for extremely broad-band simultaneous transmission and reflection operation. Individual Bragg plane sets recorded in the grating are dedicated to and operate efficiently on discrete wavelength ranges.

Interrogation of weak Bragg grating sensors based on dual-wavelength differential detection.

PubMed

Cheng, Rui; Xia, Li

2016-11-15

It is shown that for weak Bragg gratings the logarithmic ratio of reflected intensities at any two wavelengths within the spectrum follows a linear relationship with the Bragg wavelength shift, with a slope proportional to their wavelength spacing. This finding is exploited to develop a flexible, efficient, and cheap interrogation solution of weak fiber Bragg grating (FBGs), especially ultra-short FBGs, in distributed sensing based on dual-wavelength differential detection. The concept is experimentally studied in both single and distributed sensing systems with ultra-short FBG sensors. The work may form the basis of new and promising FBG interrogation techniques based on detecting discrete rather than continuous spectra.

Response of CO2 laser written long period fiber gratings packaged by polymer materials

NASA Astrophysics Data System (ADS)

Wu, Zhaodi; Liu, Yunqi; Zou, Jian; Chen, Na; Pang, Fufei; Wang, Tingyun

2011-12-01

We demonstrate the packaging of CO2 laser written long-period fiber gratings (LPFGs) using different polymer materials. We use three different silicone rubber polymers to package the LPFGs by simply coating it outside the grating. After the polymer coating, the resonance wavelength of LPFG was found to shift towards shorter wavelength by about 6 nm, and the temperature sensitivity of the packaged gratings was studied experimentally. Experiments showed that the gratings packaged by different polymers have different temperature characteristics and all of them have good thermal stability.

Investigation on Periodically Surface-Corrugated Long-Period Gratings Inscribed on Photonic Crystal Fibers

NASA Astrophysics Data System (ADS)

Han, Young-Geun

2017-04-01

Transmission characteristics of periodically surface-corrugated long-period gratings (LPGs) inscribed on photonic crystal fibers (PCFs) using a wet-etching technique were experimentally investigated. A conventional wet method was implemented to periodically engrave the silica cladding region of the PCFs resulting in the periodic surface corrugation in the PCF. After applying the external strain to the PCF with the periodic surface micro-ridges, periodic modulation of refractive index based on the photoelastic effect is induced resulting in the formation of the PCF-based LPG. Increasing the applied strain successfully improves the extinction ratio of the resonant peak of the PCF-based LPG without the resonant wavelength shift. We also measured the transmission characteristics of the PCF-based LPG with variations in temperature and ambient index.

Electrically and mechanically induced long period gratings in liquid crystal photonic bandgap fibers

NASA Astrophysics Data System (ADS)

Noordegraaf, Danny; Scolari, Lara; Lægsgaard, Jesper; Rindorf, Lars; Tanggaard Alkeskjold, Thomas

2007-06-01

We demonstrate electrically and mechanically induced long period gratings (LPGs) in a photonic crystal fiber (PCF) filled with a high-index liquid crystal. The presence of the liquid crystal changes the guiding properties of the fiber from an index guiding fiber to a photonic bandgap guiding fiber - a so called liquid crystal photonic bandgap (LCPBG) fiber. Both the strength and resonance wavelength of the gratings are highly tunable. By adjusting the amplitude of the applied electric field, the grating strength can be tuned and by changing the temperature, the resonance wavelength can be tuned as well. Numerical calculations of the higher order modes of the fiber cladding are presented, allowing the resonance wavelengths to be calculated. A high polarization dependent loss of the induced gratings is also observed.

UV-SPR biosensor for biomolecular interaction studies

NASA Astrophysics Data System (ADS)

Geiss, F. A.; Fossati, S.; Khan, I.; Gisbert Quilis, N.; Knoll, W.; Dostalek, J.

2017-05-01

UV surface plasmon resonance (SPR) for direct in situ detection of protein binding events is reported. A crossed relief aluminum grating was employed for diffraction coupling to surface plasmons as an alternative to more commonly used attenuated total reflection method. Wavelength interrogation of SPR was carried out by using transmission measurements in order to probe odorant-binding protein 14 (OBP14) of the honey bee (Apis mellifera). The native oxide layer on the top of an aluminum grating sensor chip allows for covalent coupling of protein molecules by using regular silane-based linkers. The probing of bound OBP14 protein at UV with confined field of surface plasmons holds potential for further studies of interaction with recently developed artificial fluorescent odorants.

Antireflection effect of femtosecond laser-induced periodic surface structures on silicon.

PubMed

Vorobyev, A Y; Guo, Chunlei

2011-09-12

Following direct femtosecond laser pulse irradiation, we produce a unique grating structure over a large area superimposed by finer nanostructures on a silicon wafer. We study, for the first time, the antireflection effect of this femtosecond laser-induced periodic surface structures (FLIPSSs) in the wavelength range of 250 - 2500 nm. Our study shows that the FLIPSSs suppress both the total hemispherical and specular polarized reflectance of silicon surface significantly over the entire studied wavelength range. The total polarized reflectance of the processed surface is reduced by a factor of about 3.5 in the visible and 7 in the UV compared to an untreated sample. The antireflection effect of the FLIPSS surface is broadband and the suppression stays to the longest wavelength (2500 nm) studied here although the antireflection effect in the infrared is weaker than in the visible. Our FLIPSS structures are free of chemical contamination, highly durable, and easily controllable in size.

Performance characteristics of advanced volume phase holographic gratings for operation in the near infrared

NASA Astrophysics Data System (ADS)

Arns, James A.

2016-07-01

Volume phase holographic (VPH) gratings are proven dispersing elements in astronomical spectrographs over the visible spectrum. VPH gratings have also been successfully deployed for use at cryogenic temperatures. Recent advances in production technology now permit the production of gratings for use in the near infrared up to 2450 nm at cryogenic conditions. This paper describes the requirements of VPH gratings for use in the H (wavelengths from 1500 nm to 1800 nm) and K (wavelengths from 1950 nm to 2450 nm) bands, gives the theoretical performances of diffraction efficiency for the production designs and presents the measured performances on the production gratings

Discrete wavelength-locked external cavity laser

NASA Technical Reports Server (NTRS)

Pilgrim, Jeffrey S. (Inventor); Silver, Joel A. (Inventor)

2005-01-01

An external cavity laser (and method of generating laser light) comprising: a laser light source; means for collimating light output by the laser light source; a diffraction grating receiving collimated light; a cavity feedback mirror reflecting light received from the diffraction grating back to the diffraction grating; and means for reliably tuning the external cavity laser to discrete wavelengths.

Reflectance spectra characteristics from an SPR grating fabricated by nano-imprint lithography technique for biochemical nanosensor applications

NASA Astrophysics Data System (ADS)

Setiya Pradana, Jalu; Hidayat, Rahmat

2018-04-01

In this paper, we report our research work on developing a Surface Plasmon Resonance (SPR) element with sub-micron (hundreds of nanometers) periodicity grating structure. This grating structure was fabricated by using a simple nano-imprint lithography technique from an organically siloxane polymers, which was then covered by nanometer thin gold layer. The formed grating structure was a very well defined square-shaped periodic structure. The measured reflectance spectra indicate the SPR wave excitation on this grating structure. For comparison, the simulations of reflectance spectra have been also carried out by using Rigorous Coupled-Wave Analysis (RCWA) method. The experimental results are in very good agreement with the simulation results.

High-efficiency aperiodic two-dimensional high-contrast-grating hologram

NASA Astrophysics Data System (ADS)

Qiao, Pengfei; Zhu, Li; Chang-Hasnain, Connie J.

2016-03-01

High efficiency phase holograms are designed and implemented using aperiodic two-dimensional (2D) high-contrast gratings (HCGs). With our design algorithm and an in-house developed rigorous coupled-wave analysis (RCWA) package for periodic 2D HCGs, the structural parameters are obtained to achieve a full 360-degree phase-tuning range of the reflected or transmitted wave, while maintaining the power efficiency above 90%. For given far-field patterns or 3D objects to reconstruct, we can generate the near-field phase distribution through an iterative process. The aperiodic HCG phase plates we design for holograms are pixelated, and the local geometric parameters for each pixel to achieve desired phase alternation are extracted from our periodic HCG designs. Our aperiodic HCG holograms are simulated using the 3D finite-difference time-domain method. The simulation results confirm that the desired far-field patterns are successfully produced under illumination at the designed wavelength. The HCG holograms are implemented on the quartz wafers, using amorphous silicon as the high-index material. We propose HCG designs at both visible and infrared wavelengths, and our simulation confirms the reconstruction of 3D objects. The high-contrast gratings allow us to realize low-cost, compact, flat, and integrable holograms with sub-micrometer thicknesses.

High-resolution interferometic microscope for traceable dimensional nanometrology in Brazil

NASA Astrophysics Data System (ADS)

Malinovski, I.; França, R. S.; Lima, M. S.; Bessa, M. S.; Silva, C. R.; Couceiro, I. B.

2016-07-01

The double color interferometric microscope is developed for step height standards nanometrology traceable to meter definition via primary wavelength laser standards. The setup is based on two stabilized lasers to provide traceable measurements of highest possible resolution down to the physical limits of the optical instruments in sub-nanometer to micrometer range of the heights. The wavelength reference is He-Ne 633 nm stabilized laser, the secondary source is Blue-Green 488 nm grating laser diode. Accurate fringe portion is measured by modulated phase-shift technique combined with imaging interferometry and Fourier processing. Self calibrating methods are developed to correct systematic interferometric errors.

Development of Interference Lithography Capability Using a Helium Cadmium Ultraviolet Multimode Laser for the Fabrication of Sub-Micron-Structured Optical Materials

DTIC Science & Technology

2011-03-01

into separate parts, transmitted into different directions , and then recombined upon a surface to produce interference. The concern with this type of...photoresist (PR), is a radiation sensitive compound that is classified as positive or negative, depending on how it responds to radiation . Each is designed...emerging waves, and are referred to as diffraction gratings. Upon reflection from these kinds of gratings, light scattered from the periodic surface

Measurement of distributed strain and temperature based on higher order and higher mode Bragg conditions

NASA Technical Reports Server (NTRS)

Sirkis, James S. (Inventor); Sivanesan, Ponniah (Inventor); Venkat, Venki S. (Inventor)

2001-01-01

A Bragg grating sensor for measuring distributed strain and temperature at the same time comprises an optical fiber having a single mode operating wavelength region and below a cutoff wavelength of the fiber having a multimode operating wavelength region. A saturated, higher order Bragg grating having first and second order Bragg conditions is fabricated in the optical fiber. The first order of Bragg resonance wavelength of the Bragg grating is within the single mode operating wavelength region of the optical fiber and the second order of Bragg resonance wavelength is below the cutoff wavelength of the fiber within the multimode operating wavelength region. The reflectivities of the saturated Bragg grating at the first and second order Bragg conditions are less than two orders of magnitude of one another. In use, the first and second order Bragg conditions are simultaneously created in the sensor at the respective wavelengths and a signal from the sensor is demodulated with respect to each of the wavelengths corresponding to the first and second order Bragg conditions. Two Bragg conditions have different responsivities to strain and temperature, thus allowing two equations for axial strain and temperature to be found in terms of the measure shifts in the primary and second order Bragg wavelengths. This system of equations can be solved for strain and temperature.

New HST/COS FUV Modes G140L/800 and G160M/1533

NASA Astrophysics Data System (ADS)

Sankrit, Ravi; De Rosa, Gisella; Fischer, William J.; Fix, Mees B.; Fox, Andrew; Indriolo, Nick; James, Bethan; Magness, Camellia; Oliveira, Cristina M.; Penton, Steven V.; Plesha, Rachel; Rafelski, Marc; Roman-Duval, Julia; Sahnow, David J.; Snyder, Elaine M.; Taylor, Joanna M.; White, James

2018-06-01

We present two new observing modes that are being offered for the far-ultraviolet (FUV) channel on the Cosmic Origins Spectrograph (COS), and an initial overview of the science investigations they enable. The FUV channel on COS currently operates in the 900-2150 A wavelength region. It consists of two medium resolution gratings G130M and G160M, and a low resolution grating G140L. The detector consists of two segments (FUVB, shortward and FUVA, longward wavelengths) with a gap between them. Each grating has a number of central wavelength settings (cenwaves) available. The settings place different portions of the spectrum on the detector segments, and the focus at each cenwave is set to optimize spectral resolution in the middle of its wavelength range.The first new mode is G140L/800, which places 800-1950 A on FUVA. The grating rotation and focus for this mode are set to minimize the height of the spectrum on the detector, and thereby the background, in the region below 1100 A. This results in an increased sensitivity at these wavelengths compared to the 1280 cenwave. The second mode, G160M/1533, extends the short-wavelength coverage of the grating by 44 A to overlap with the longest wavelengths covered by the G130M/1222 setting. This allows a broad wavelength range to be covered using just two medium resolution settings without placing the key gain-sag contributor, Ly-alpha, on the detector.

Multi-resonance peaks fiber Bragg gratings based on largely-chirped structure

NASA Astrophysics Data System (ADS)

Chen, Chao; Zhang, Xuan-Yu; Wei, Wei-Hua; Chen, Yong-Yi; Qin, Li; Ning, Yong-Qiang; Yu, Yong-Sen

2018-04-01

A composite fiber Bragg grating (FBG) with multi-resonance peaks (MRPs) has been realized by using femtosecond (fs) laser point-by-point inscription in single-mode fiber. This device contains a segment of largely-chirped gratings with the ultrahigh chirp coefficients and a segment of uniform high-order gratings. The observed MRPs are distributed in an ultra-broadband wavelength range from 1200 nm to 1700 nm in the form of quasi-period or multi-peak-group. For the 8th-order MRPs-FBG, we studied the axial strain and high-temperature sensing characteristics of different resonance peaks experimentally. Moreover, we have demonstrated a multi-wavelength fiber lasers with three-wavelength stable output by using a 9th-order MRPs-FBG as the wavelength selector. This work is significant for the fabrication and functionalization of FBGs with complicated spectra characteristics.

High channel density wavelength division multiplexer with defined diffracting means positioning

DOEpatents

Jannson, T.P.; Jannson, J.L.; Yeung, P.C.

1990-05-15

A wavelength division multiplexer/demultiplexer is disclosed having optical path lengths between a fiber array and a Fourier transform lens, and between a dispersion grating and the lens equal to the focal length of the lens. The optical path lengths reduce losses due to angular acceptance mismatch in the multiplexer. Close orientation of the fiber array about the optical axis and the use of a holographic dispersion grating reduces other losses in the system. Multi-exposure holographic dispersion gratings enable the multiplexer/demultiplexer for extremely broad-band simultaneous transmission and reflection operation. Individual Bragg plane sets recorded in the grating are dedicated to and operate efficiently on discrete wavelength ranges. 11 figs.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hand, L.N.

Some proposed techniques for using laser beams to accelerate charged particles are reviewed. Two specific ideas for 'grating-type' accelerating structures are discussed. Speculations are presented about how a successful laser accelerator could be used in a 'multi-pass collider', a type of machine which would have characteristics intermediate between those of synchrotrons and linear (single-pass) colliders. No definite conclusions about practical structures for laser accelerators are reached, but it is suggested that a serious effort be made to design a small prototype machine. Achieving a reasonable luminosity demands that the accelerator either be a cw machine or that laser peak powermore » requirements be much higher than those presently available. Use of superconducting gratings requires a wavelength in the sub-millimeter range.« less

The laser accelerator-another unicorn in the garden

NASA Astrophysics Data System (ADS)

Hand, L. N.

1981-07-01

Some proposed techniques for using laser beams to accelerate charged particles was reviewed. Two specific ideas for grating type accelerating structures are discussed. Speculations are presented about how a successful laser accelerator could be used in a multipass collider; a type of machine which would have characteristics intermediate between those of synchrotrons and linear (single pass) colliders. No definite conclusions about practical structures for laser accelerators are reached, but it is suggested that a serious effort be made to design a small prototype machine. Achieving a reasonable luminosity demands that the accelerator either be a cw machine or that laser peak power requirements to be much higher than those presently available. Use of superconducting gratings requires a wavelength in the sub-millimeter range.

Using a micro-molding process to fabricate polymeric wavelength filters

NASA Astrophysics Data System (ADS)

Chuang, Wei-Ching; Lee, An-Chen; Ho, Chi-Ting

2008-08-01

A procedure for fabricating a high aspect ratio periodic structure on a UV polymer at submicron order using holographic interferometry and molding processes is described. First, holographic interferometry using a He-Cd (325 nm) laser was used to create the master of the periodic line structure on an i-line sub-micron positive photoresist film. A 20 nm nickel thin film was then sputtered on the photoresist. The final line pattern on a UV polymer was obtained from casting against the master mold. Finally, a SU8 polymer was spun on the polymer grating to form a planar waveguide or a channel waveguide. The measurement results show that the waveguide length could be reduced for the waveguide having gratings with a high aspect ratio.

Switchable single-longitudinal-mode dual-wavelength erbium-doped fiber laser based on one polarization-maintaining fiber Bragg grating incorporating saturable absorber

NASA Astrophysics Data System (ADS)

Feng, Suchun; Xu, Ou; Lu, Shaohua; Chen, Ming; Jian, Shuisheng

2009-08-01

Switchable single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber laser at room temperature is demonstrated. One fiber Bragg grating (FBG) directly written in a polarization-maintaining and photosensitive erbiumdoped fiber (PMPEDF) as the wavelength-selective component is used in a linear laser cavity. Due to the polarization hole burning (PHB) enhanced by the polarization-maintaining fiber Bragg grating (PMFBG), the laser can be designed to operate in stable dual-wavelength or wavelength-switching modes with a wavelength spacing of 0.202 nm by adjusting a polarization controller (PC). The stable SLM operation is guaranteed by a saturable absorber (SA). The optical signal-tonoise ratio (OSNR) of the laser is over 40 dB. The amplitude variation in nearly one and half an hour is less than 0.5 dB for both wavelengths.

Quantum dots as contrast agents for endoscopy: mathematical modeling and experimental validation of the optimal excitation wavelength

NASA Astrophysics Data System (ADS)

Roy, Mathieu; DaCosta, Ralph S.; Weersink, Robert; Netchev, George; Davidson, Sean R. H.; Chan, Warren; Wilson, Brian C.

2007-02-01

Our group is investigating the use of ZnS-capped CdSe quantum dot (QD) bioconjugates combined with fluorescence endoscopy for improved early cancer detection in the esophagus, colon and lung. A major challenge in using fluorescent contrast agents in vivo is to extract the relevant signal from the tissue autofluorescence (AF). Our studies are aimed at maximizing the QD signal to AF background ratio (SBR) to facilitate detection. This work quantitatively evaluates the effect of the excitation wavelength on the SBR, using both experimental measurements and mathematical modeling. Experimental SBR measurements were done by imaging QD solutions placed onto (surface) or embedded in (sub-surface) ex vivo murine tissue samples (brain, kidney, liver, lung), using a polymethylmethacrylate (PMMA) microchannel phantom. The results suggest that the maximum contrast is reached when the excitation wavelength is set at 400+/-20 μm for the surface configuration. For the sub-surface configuration, the optimal excitation wavelength varies with the tissue type and QD emission wavelengths. Our mathematical model, based on an approximation to the diffusion equation, successfully predicts the optimal excitation wavelength for the surface configuration, but needs further modifications to be accurate in the sub-surface configuration.

Au-coated tilted fiber Bragg grating twist sensor based on surface plasmon resonance

NASA Astrophysics Data System (ADS)

Shen, Changyu; Zhang, Yang; Zhou, Wenjun; Albert, Jacques

2014-02-01

A fiber twist sensor based on the surface plasmon resonance (SPR) effect of an Au-coated tilted fiber Bragg grating (TFBG) is proposed. The SPR response to the twist effect on an Au-coated TFBG (immersing in distilled water) is studied theoretically and experimentally. The results show that the transmission power around the wavelength of SPR changes with the twist angle. For the twist ranging from 0° to 180° in clockwise or anti-clockwise directions, the proposed sensor shows sensitivities of 0.037 dBm/° (S-polarized) and 0.039 dBm/° (P-polarized), which are almost 7.5 times higher than that of the current similar existing twist sensor.

High speed inscription of uniform, large-area laser-induced periodic surface structures in Cr films using a high repetition rate fs laser.

PubMed

Ruiz de la Cruz, A; Lahoz, R; Siegel, J; de la Fuente, G F; Solis, J

2014-04-15

We report on the fabrication of laser-induced periodic surface structures in Cr films upon high repetition rate fs laser irradiation (up to 1 MHz, 500 fs, 1030 nm), employing beam scanning. Highly regular large-area (9  cm2) gratings with a relative diffraction efficiency of 42% can be produced within less than 6 min. The ripple period at moderate and high fluences is 0.9 μm, with a small period of 0.5 μm appearing at lower energies. The role of the irradiation parameters on the characteristics of the laser-induced periodic surface structures (LIPSS) is studied and discussed in the frame of the models presently used. We have identified the polarization vector orientation with respect to the scan direction as a key parameter for the fabrication of high-quality, large-area LIPSS, which, for perpendicular orientation, allows the coherent extension of the sub-wavelength structure over macroscopic distances. The processing strategy is robust in terms of broad parameter windows and applicable to other materials featuring LIPSS.

Damage Detection of CFRP Plates by Full-Spectral Analysis of a Fibre Bragg Grating Sensor Signal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mizutani, Yoshihiro; Solid and Structures Engineering Laboratory, Department of Mechanical Sciences and Engineering, Tokyo Institute of Technology, Japan, 2-12-1-I1-70, Ookayama, Meguro-ku, Tokyo 152-8552; Groves, Roger M.

2010-05-28

This paper describes the measurement of average strain, strain distribution and vibration of cantilever beam made of Carbon Fiber Reinforced Plastics (CFRP), using a single Fibre Bragg Grating (FBG) sensor mounted on the beam surface. Average strain is determined from the displacement of the peak wavelength of reflected light from the FBG sensor. Unstrained reference FBG sensors were used to compensate for temperature drift and the photoelastic coefficient (P{sub e}), which was used to calculate the gauge factor. Measured strains agree with those measured by a resistance foil strain gauge attached to the sample. Stress distributions are measured by monitoringmore » the variation in the full width half maximum (FWHM) values of the reflected spectrum, using a proposed optical analytical model, described in the paper. FWHM values were measured for both the cantilever test beam and a for a reference beam, loaded using a four-point bending rig. The trend of the stress distribution for the test beam matches with our analytical model, however with a relatively large noise present in the experimentally determined data. The vibration of cantilever beam was measured by temporal analysis of the peak reflection wavelength. This technique is very stable as measurements are not affected by variations in the signal amplitude. Finally an application of FBG sensors for damage detection of CFRP plates is demonstrated, by measuring the average strain and natural frequency. With small defects of different sizes applied to the CFRP plate, average strains were seen to increase with damage size and the natural frequency decreased with damage size.« less

GaAs/AlOx high-contrast grating mirrors for mid-infrared VCSELs

NASA Astrophysics Data System (ADS)

Almuneau, G.; Laaroussi, Y.; Chevallier, C.; Genty, F.; Fressengeas, N. s.; Cerutti, L.; Gauthier-Lafaye, Olivier

2015-02-01

Mid-infrared Vertical cavity surface emitting lasers (MIR-VCSEL) are very attractive compact sources for spectroscopic measurements above 2μm, relevant for molecules sensing in various application domains. A long-standing issue for long wavelength VCSEL is the large structure thickness affecting the laser properties, added for the MIR to the tricky technological implementation of the antimonide alloys system. In this paper, we propose a new geometry for MIR-VCSEL including both a lateral confinement by an oxide aperture, and a high-contrast sub-wavelength grating mirror (HCG mirror) formed by the high contrast combination AIOx/GaAs in place of GaSb/A|AsSb top Bragg reflector. In addition to drastically simplifying the vertical stack, HCG mirror allows to control through its design the beam properties. The robust design of the HCG has been ensured by an original method of optimization based on particle swarm optimization algorithm combined with an anti-optimization one, thus allowing large error tolerance for the nano-fabrication. Oxide-based electro-optical confinement has been adapted to mid-infrared lasers, byusing a metamorphic approach with (Al) GaAs layer directly epitaxially grown on the GaSb-based VCSEL bottom structure. This approach combines the advantages of the will-controlled oxidation of AlAs layer and the efficient gain media of Sb-based for mid-infrared emission. We finally present the results obtained on electrically pumped mid-IR-VCSELs structures, for which we included oxide aperturing for lateral confinement and HCG as high reflectivity output mirrors, both based on AlxOy/GaAs heterostructures.

Intracore and extracore examination of fiber gratings with coherent detection

NASA Astrophysics Data System (ADS)

Froggatt, Mark Earl

2001-06-01

This thesis introduces several new methods of measurement to aid in the production and evaluation of Bragg gratings in optical fiber. Five measurements are described: UV fringe visualization for grating production, weak grating measurement for distributed sensing, strong grating measurement for telecommunication applications, second harmonic grating measurement for grating chirp assessment, and grating visualization using radiation diffraction from strong Bragg gratings. The weak grating measurement for distributed strain sensing is a summary of work published prior to beginning the thesis research, and is provided for background purposes. The UV fringe visualization is accomplished by using a phase mask very close to the plane of the fiber to diffract the incoming beams used to write the Bragg grating into nearly parallel alignment, leading to macroscopic fringes indicative of the phase, frequency, amplitude, and contrast of the microscopic fringes incident on the fiber. The weak grating measurement uses Optical Frequency Domain Reflectometry (OFDR) to measure the spatial distribution of the coupling strength of weak gratings. Included in the description of the OFDR technique are recent advances in the precision monitoring of the emission wavelength of tunable lasers. The precise monitoring of wavelength is critical to the functioning of OFDR. The strong grating measurement is based on a modified form of OFDR and an analysis of the problem in the time and frequency domains to produce accurate measurements of both the reflection and transmission Transfer Functions for Bragg gratings. This measurement technique is also applicable to a wide variety of optical fiber devices, and is shown to be scalable to multiple port devices. The second-harmonic measurement for grating chirp analysis is similar to the weak grating measurement, but it was done at a wavelength resonant with the second- harmonic grating in the fiber-780 nm for 1550 nm reflection gratings. The second-harmonic grating results from nonlinearities in the grating growth process and, due to the great sensitivity of OFDR, is detectable for almost all fiber gratings. The grating visualization also uses half-wavelength (780 nm) illumination of the grating through the core. This technique uses the diffraction of light into the radiation modes to make the grating in the fiber externally visible. By operating near the perpendicular radiation condition, and introducing coherent counter- propagating light, the spatial frequency and the amplitude of the grating as functions of distance along the fiber can be measured. To better understand the radiation from Bragg gratings, a technique known as the Volume Current Method (VCM) was used to derive an expression for the radiation from a Bragg grating for all of the LP fiber modes.

Fiber-ring laser-based intracavity photoacoustic spectroscopy for trace gas sensing.

PubMed

Wang, Qiang; Wang, Zhen; Chang, Jun; Ren, Wei

2017-06-01

We demonstrated a novel trace gas sensing method based on fiber-ring laser intracavity photoacoustic spectroscopy. This spectroscopic technique is a merging of photoacoustic spectroscopy (PAS) with a fiber-ring cavity for sensitive and all-fiber gas detection. A transmission-type PAS gas cell (resonant frequency f₀=2.68  kHz) was placed inside the fiber-ring laser to fully utilize the intracavity laser power. The PAS signal was excited by modulating the laser wavelength at f₀/2 using a custom-made fiber Bragg grating-based modulator. We used this spectroscopic technique to detect acetylene (C₂H₂) at 1531.6 nm as a proof of principle. With a low Q-factor (4.9) of the PAS cell, our sensor achieved a good linear response (R²=0.996) to C₂H₂ concentration and a minimum detection limit of 390 ppbv at 2-s response time.

Spectral characterization of differential group delay in uniform fiber Bragg gratings.

PubMed

Bette, S; Caucheteur, C; Wuilpart, M; Mégret, P; Garcia-Olcina, R; Sales, S; Capmany, J

2005-12-12

In this paper, we completely study the wavelength dependency of differential group delay (DGD) in uniform fiber Bragg gratings (FBG) exhibiting birefringence. An analytical expression of DGD is established. We analyze the impact of grating parameters (physical length, index modulation and apodization profile) on the wavelength dependency of DGD. Experimental results complete the paper. A very good agreement between theory and experience is reported.

Linear Fresnel Spectrometer Chip with Gradient Line Grating

NASA Technical Reports Server (NTRS)

Choi, Sang Hyouk (Inventor); Park, Yeonjoon (Inventor)

2015-01-01

A spectrometer that includes a grating that disperses light via Fresnel diffraction according to wavelength onto a sensing area that coincides with an optical axis plane of the grating. The sensing area detects the dispersed light and measures the light intensity associated with each wavelength of the light. Because the spectrometer utilizes Fresnel diffraction, it can be miniaturized and packaged as an integrated circuit.

Robust Monolithic Ultraviolet Interferometer for the Shimmer Instrument on STPSat-1

DTIC Science & Technology

2003-01-01

wavelength- dependent spatial frequency are produced by a modified Michelson interferometer in which the re- turn mirrors are replaced by conventional...alignment of the spacers, prisms, and gratings to the beam splitter was accom- plished with the aid of a Zerodur plate onto which the bottom surface of

Interaction of surface plasmon polaritons and acoustic waves inside an acoustic cavity.

PubMed

Khokhlov, Nikolai; Knyazev, Grigoriy; Glavin, Boris; Shtykov, Yakov; Romanov, Oleg; Belotelov, Vladimir

2017-09-15

In this Letter, we introduce an approach for manipulation of active plasmon polaritons via acoustic waves at sub-terahertz frequency range. The acoustic structures considered are designed as phononic Fabry-Perot microresonators where mirrors are presented with an acoustic superlattice and the structure's surface, and a plasmonic grating is placed on top of the acoustic cavity so formed. It provides phonon localization in the vicinity of the plasmonic grating at frequencies within the phononic stop band enhancing phonon-light interaction. We consider phonon excitation by shining a femtosecond laser pulse on the plasmonic grating. Appropriate theoretical model was used to describe the acoustic process caused by the pump laser pulse in the GaAs/AlAs-based acoustic cavity with a gold grating on top. Strongest modulation is achieved upon excitation of propagating surface plasmon polaritons and hybridization of propagating and localized plasmons. The relative changes in the optical reflectivity of the structure are more than an order of magnitude higher than for the structure without the plasmonic film.

Non-invasive timing of gas gun-launched projectiles using external surface-mounted optical fiber-Bragg grating strain gauges

NASA Astrophysics Data System (ADS)

Goodwin, Peter M.; Marshall, Bruce R.; Stevens, Gerald D.; Dattelbaum, Dana M.

2013-03-01

Non-invasive detection methods for tracking gun-launched projectiles are important not only for assessment of gun performance but are also essential for timing a variety of diagnostics, for example, to investigate plate-impact events for shock compression experiments. Measurement of the time of passage of a projectile moving inside of the gun barrel can be achieved by detection of the transient hoop strain induced in the barrel of a light-gas gun by the passage of the projectile using external, barrel surface-mounted optical fiber-Bragg grating strain gauges. Optical fiber-Bragg gratings have been implemented and their response characterized on single-stage and two-stage light gas guns routinely used for dynamic experimentation at Los Alamos National Laboratory. Two approaches, using either broadband or narrowband illumination, were used to monitor changes in the Bragg wavelength of the fiber-Bragg gratings. The second approach, using narrowband laser illumination, offered the highest sensitivity. The feasibility of using these techniques to generate early, pre-event signals useful for triggering high-latency diagnostics was demonstrated.

Non-invasive timing of gas gun-launched projectiles using external surface-mounted optical fiber-Bragg grating strain gauges.

PubMed

Goodwin, Peter M; Marshall, Bruce R; Stevens, Gerald D; Dattelbaum, Dana M

2013-03-01

Non-invasive detection methods for tracking gun-launched projectiles are important not only for assessment of gun performance but are also essential for timing a variety of diagnostics, for example, to investigate plate-impact events for shock compression experiments. Measurement of the time of passage of a projectile moving inside of the gun barrel can be achieved by detection of the transient hoop strain induced in the barrel of a light-gas gun by the passage of the projectile using external, barrel surface-mounted optical fiber-Bragg grating strain gauges. Optical fiber-Bragg gratings have been implemented and their response characterized on single-stage and two-stage light gas guns routinely used for dynamic experimentation at Los Alamos National Laboratory. Two approaches, using either broadband or narrowband illumination, were used to monitor changes in the Bragg wavelength of the fiber-Bragg gratings. The second approach, using narrowband laser illumination, offered the highest sensitivity. The feasibility of using these techniques to generate early, pre-event signals useful for triggering high-latency diagnostics was demonstrated.

Emission enhancement of light-emitting diode by localized surface plasmon induced by Ag/p-GaN double grating

NASA Astrophysics Data System (ADS)

Xie, Ruijie; Li, Zhiquan; Li, Xin; Gu, Erdan; Niu, Liyong; Sha, Xiaopeng

2018-07-01

In this paper, a new type of light-emitting diodes (LEDs) structure is designed to enhance the light emission efficiency of GaN-based LEDs. The structure mainly includes Ag grating, ITO layer and p-GaN grating. The principle of stimulating the localized surface plasmon to improve the luminous characteristics of the LED by using this structure is discussed. Based on the COMSOL software, the finite element method is used to simulate the LED structure. The normalized radiated powers, the normalized absorbed powers under different wavelength and geometric parameters, and the distribution of the electric field with the particular geometric parameters are obtained. The simulation results show that with a local ITO thickness of 32 nm, an etching depth of 29 nm, a grating period of 510 nm and a duty ratio of 0.5, the emission intensity of the designed GaN-based LED structure has increased by nearly 55 times than the ordinary LED providing a reliable foundation for the development of high-performance GaN-based LEDs.

Unified beam splitter of fused silica grating under the second Bragg incidence.

PubMed

Sun, Zhumei; Zhou, Changhe; Cao, Hongchao; Wu, Jun

2015-11-01

A unified design for a 1×2 beam splitter of dielectric rectangular transmission gratings under the second Bragg incidence is theoretically investigated for TE- and TM-polarized light. The empirical equations of the relative grating parameters (ratio of the absolute one to incidence wavelength) for this design are also obtained with the simplified modal method (SMM). The influences of polarization of incident light and relative grating parameters on the performance of the beam splitter are thoroughly studied based on the SMM and rigorous coupled-wave analysis. Two specific gratings are demonstrated with an even split and high diffraction efficiency (>94% for TE polarization and >97% for the TM counterpart). The unified profiles of the 1×2 beam splitter are independent from the incidence wavelength since the refractive index of fused silica is roughly a constant over a wide range of wavelengths, which should be promising for future applications.

Numerical modelling of surface plasmonic polaritons

NASA Astrophysics Data System (ADS)

Mansoor, Riyadh; AL-Khursan, Amin Habbeb

2018-06-01

Extending optoelectronics into the nano-regime seems problematic due to the relatively long wavelengths of light. The conversion of light into plasmons is a possible way to overcome this problem. Plasmon's wavelengths are much shorter than that of light which enables the propagation of signals in small size components. In this paper, a 3D simulation of surface plasmon polariton (SPP) excitation is performed. The Finite integration technique was used to solve Maxwell's equations in the dielectric-metal interface. The results show how the surface plasmon polariton was generated at the grating assisted dielectric-metal interface. SPP is a good candidate for signal confinement in small size optoelectronics which allow high density optical integrated circuits in all optical networks.

Large MOEMS diffraction grating results providing an EC-QCL wavelength scan of 20%

NASA Astrophysics Data System (ADS)

Grahmann, Jan; Merten, André; Herrmann, Andreas; Ostendorf, Ralf; Bleh, Daniela; Drabe, Christian; Kamenz, Jörg

2015-02-01

Experimental results of a large scanning grating with a diameter of 5mm and 1 kHz scan frequency are discussed. An optical diffraction grating is fabricated on a mirror single crystal silicon plate to scan the first diffraction order in the MIR-wavelength range over a quantum cascade laser facet. Special emphasis is on the development of the grating technology module to integrate it with high accuracy and reproducibility into the IPMS AME75 process flow. The principle EC-QCL setup with the scanning grating is described and first measurement results concerning laser output power and tuning range are presented.

Coherent pulse interrogation system for fiber Bragg grating sensing of strain and pressure in dynamic extremes of materials.

PubMed

Rodriguez, George; Jaime, Marcelo; Balakirev, Fedor; Mielke, Chuck H; Azad, Abul; Marshall, Bruce; La Lone, Brandon M; Henson, Bryan; Smilowitz, Laura

2015-06-01

A 100 MHz fiber Bragg grating (FBG) interrogation system is described and applied to strain and pressure sensing. The approach relies on coherent pulse illumination of the FBG sensor with a broadband short pulse from a femtosecond modelocked erbium fiber laser. After interrogation of the FBG sensor, a long multi-kilometer run of single mode fiber is used for chromatic dispersion to temporally stretch the spectral components of the reflected pulse from the FBG sensor. Dynamic strain or pressure induced spectral shifts in the FBG sensor are detected as a pulsed time domain waveform shift after encoding by the chromatic dispersive line. Signals are recorded using a single 35 GHz photodetector and a 50 G Samples per second, 25 GHz bandwidth, digitizing oscilloscope. Application of this approach to high-speed strain sensing in magnetic materials in pulsed magnetic fields to ~150 T is demonstrated. The FBG wavelength shifts are used to study magnetic field driven magnetostriction effects in LaCoO₃. A sub-microsecond temporal shift in the FBG sensor wavelength attached to the sample under first order phase change appears as a fractional length change (strain: ΔL/L<10^-4) in the material. A second application used FBG sensing of pressure dynamics to nearly 2 GPa in the thermal ignition of the high explosive PBX-9501 is also demonstrated. Both applications demonstrate the use of this FBG interrogation system in dynamical extreme conditions that would otherwise not be possible using traditional FBG interrogation approaches that are deemed too slow to resolve such events.

Near-field analysis of metallic DFB lasers at telecom wavelengths.

PubMed

Greusard, L; Costantini, D; Bousseksou, A; Decobert, J; Lelarge, F; Duan, G-H; De Wilde, Y; Colombelli, R

2013-05-06

We image in near-field the transverse modes of semiconductor distributed feedback (DFB) lasers operating at λ ≈ 1.3 μm and employing metallic gratings. The active region is based on tensile-strained InGaAlAs quantum wells emitting transverse magnetic polarized light and is coupled via an extremely thin cladding to a nano-patterned gold grating integrated on the device surface. Single mode emission is achieved, which tunes with the grating periodicity. The near-field measurements confirm laser operation on the fundamental transverse mode. Furthermore--together with a laser threshold reduction observed in the DFB lasers--it suggests that the patterning of the top metal contact can be a strategy to reduce the high plasmonic losses in this kind of systems.

All-fiber pulse shortening of passively Q-switched microchip laser pulses down to sub-200 fs.

PubMed

Lehneis, R; Steinmetz, A; Limpert, J; Tünnermann, A

2014-10-15

We present an all-fiber concept that generates ultrashort pulses using a passively Q-switched microchip seed laser. A proof-of-principle configuration combines nonlinear pulse compression applying a chirped fiber-Bragg-grating, dispersion-free pulse shortening by means of a fiber-integrated spectral filtering, and a final hollow-core-fiber compression to reach the sub-200-fs pulse-duration region. In a compact all-fiber pulse-shortening unit, initial 100 ps long microchip pulses at 1064 nm wavelength have been shortened to 174 fs and shifted to 1034 nm while preserving a high temporal quality.

Fiber-laser-based, green-pumped, picosecond optical parametric oscillator using fan-out grating PPKTP.

PubMed

Chaitanya Kumar, S; Parsa, S; Ebrahim-Zadeh, M

2016-01-01

We report a stable, Yb-fiber-laser-based, green-pumped, picosecond optical parametric oscillator (OPO) for the near-infrared based on periodically poled potassium titanyl phosphate (PPKTP) nonlinear crystal, using fan-out grating design and operating near room temperature. The OPO is continuously tunable across 726-955 nm in the signal and 1201-1998 nm in the idler, resulting in a total signal plus idler wavelength coverage of 1026 nm by grating tuning at a fixed temperature. The device generates up to 580 mW of average power in the signal at 765 nm and 300 mW in the idler at 1338 nm, with an overall extraction efficiency of up to 52% and a pump depletion >76%. The extracted signal at 765 nm and idler at 1746 nm exhibit excellent passive power stability better than 0.5% and 0.8% rms, respectively, over 1 h with good beam quality in TEM₀₀ mode profile. The output signal pulses have a Gaussian temporal duration of 13.2 ps, with a FWHM spectral bandwidth of 3.4 nm at 79.5 MHz repetition rate. Power scaling limitations of the OPO due to the material properties of PPKTP are studied.

Application of 1D Array FBG Configuration for Impact Localization on Composite Wing under Simulated Noise

DTIC Science & Technology

2016-03-30

Grating Sensor Fundamentals FBG sensors consists of grating with periodic variation in the refractive index which reflects certain wavelengths of...is the grating’s effective refractive index and  is the grating period. Bragg wavelength is sensitive to any changes in strain or temperature...Conference on Composite Materials. 2007: Kyoto, Japan. 2. Cartz, L., Nondestructive Testing: Radiography, Ultrasonics, Liquid Penetrant, Magnetic Particle

Holographic Reflection Filters in Photorefractive LiNbO3 Channel Waveguides

NASA Astrophysics Data System (ADS)

Kip, Detlef; Hukriede, Joerg

Permanent refractive-index gratings in waveguide devices are of considerable interest for optical communication systems that make use of the high spectral selectivity of holographic filters, e.g. dense wavelength division multiplexing (DWDM) or narrow-bandwidth mirrors for integrated waveguide lasers in LiNbO3. Other possible applications include grating couplers and optical sensors. In this contribution we investigate such holographic wavelength filters in Fe- and Cu-doped LiNbO3 channel waveguides. Permanent refractive-index gratings are generated by thermal fixing of holograms in the waveguides. The samples are fabricated by successive in-diffusion of Ti stripes and thin layers of either Fe or Cu. After high-temperature recording with green light, refractive-index changes up to δ, ~10^-4 for infrared light ( 1.55,m) are obtained, resulting in a reflection efficiency well above 99% for a 15 mm-long grating. Several gratings for different wavelengths can be superimposed in the same sample, which may enable the fabrication of more complex filters, laser mirrors or optical sensors. By changing the sample temperature the reflection wavelength can be tuned by thermal expansion of the grating, and wavelength filters can be switched on and off by applying moderate voltages using the electro-optic effect. Furthermore, we report on a new thermal fixing mechanism that does not need any additional development by homogeneous light illumination and therefore does not suffer from the non-vanishing dark conductivity of the material.

A printable color filter based on the micro-cavity incorporating a nano-grating

NASA Astrophysics Data System (ADS)

Ye, Yan; Xu, Fengchuan; Wu, Shangliang; Wan, Wenqiang; Huang, Wenbin; Liu, Yanhua; Pu, Donglin; Wei, Guojun; Zhou, Yun; Wang, Yanyan; Qiao, Wen; Xu, Yishen; Chen, Linsen

2016-10-01

A printable color filter based on the photonic micro-cavity incorporating a nanostructure is proposed, which consists of a nano-metallic grating, a dielectric layer and aluminum (Al) film. According to the resonance induced by different dielectric depths of the micro-cavity, two dielectric heights for the same resonant wavelength are chosen to form the grating heights relative to the Al film. With the contribution of the cavity resonance and the surface plasmon resonance, the proposed structure performs enhanced broadband filtering characteristics with good angular tolerance up to 48° compared to the one of the micro-cavity as well as the one of the metallic grating. Therefore, reflective filters for RGB colors are designed incorporating the proposed structure. Furthermore, for the proposed structure shows great polarization dependence even at normal incidence, it can also be utilized as an anticounterfeiting certificate.

1-D grating based SPR biosensor for the detection of lung cancer biomarkers using Vroman effect

NASA Astrophysics Data System (ADS)

Teotia, Pradeep Kumar; Kaler, R. S.

2018-01-01

Grating based surface plasmon resonance waveguide biosensor have been reported for the detection of lung cancer biomarkers using Vroman effect. The proposed grating based multilayered biosensor is designed with high detection accuracy for Epidermal growth factor receptor (EGFR) and also analysed to show high detection accuracy with acceptable sensitivity for both cancer biomarkers. The introduction of periodic grating with multilayer metals generates a good resonance that make it possible for early detection of cancerous cells. Using finite difference time domain method, it is observed wavelength of biosensor get red-shifted on variations of the refractive index due to the presence of both the cancerous bio-markers. The reported detection accuracy and sensitivity of proposed biosensor is quite acceptable for both lung cancer biomarkers i.e. Carcinoembryonic antigen (CEA) and Epidermal growth factor receptor (EGFR) which further offer us label free early detection of lung cancer using these biomarkers.

Processing of Signals from Fiber Bragg Gratings Using Unbalanced Interferometers

NASA Technical Reports Server (NTRS)

Adamovsky, Grigory; Juergens, Jeff; Floyd, Bertram

2005-01-01

Fiber Bragg gratings (FBG) have become preferred sensory structures in fiber optic sensing system. High sensitivity, embedability, and multiplexing capabilities make FBGs superior to other sensor configurations. The main feature of FBGs is that they respond in the wavelength domain with the wavelength of the returned signal as the indicator of the measured parameter. The wavelength is then converted to optical intensity by a photodetector to detect corresponding changes in intensity. This wavelength-to-intensity conversion is a crucial part in any FBG-based sensing system. Among the various types of wavelength-to-intensity converters, unbalanced interferometers are especially attractive because of their small weight and volume, lack of moving parts, easy integration, and good stability. In this paper we investigate the applicability of unbalanced interferometers to analyze signals reflected from Bragg gratings. Analytical and experimental data are presented.

Co- and contra-directional vertical coupling between ferromagnetic layers with grating for short-wavelength spin wave generation

NASA Astrophysics Data System (ADS)

Graczyk, Piotr; Zelent, Mateusz; Krawczyk, Maciej

2018-05-01

The possibility to generate short spin waves (SWs) is of great interest in the field of magnonics nowadays. We present an effective and technically affordable way of conversion of long SWs, which may be generated by conventional microwave antenna, to the short, sub-micrometer waves. It is achieved by grating-assisted resonant dynamic dipolar interaction between two ferromagnetic layers separated by some distance. We analyze criteria for the optimal conversion giving a semi-analytical approach for the coupling coefficient. We show by the numerical calculations the efficient energy transfer between layers which may be either of co-directional or contra-directional type. Such a system may operate either as a short spin wave generator or a frequency filter, moving forward possible application of magnonics.

A functional probe with bowtie aperture and bull's eye structure for nanolithograph

NASA Astrophysics Data System (ADS)

Wang, Shuo; Li, Xu-Feng; Wang, Qiao; Guo, Ying-Yan; Pan, Shi

2012-10-01

The bowtie aperture surrounded by concentric gratings (the bull's eye structure) integrated on the near-field scanning optical microscopy (NSOM) probe (aluminum coated fiber tip) for nanolithography has been investigated using the finite-difference time domain (FDTD) method. By modifying the parameters of the bowtie aperture and the concentric gratings, a maximal field enhancement factor of 391.69 has been achieved, which is 18 times larger than that obtained from the single bowtie aperture. Additionally, the light spot depends on the gap size of the bowtie aperture and can be confined to sub-wavelength. The superiority of the combination of the bowtie aperture and the bull's eye structure is confirmed, and the mechanism for the electric field enhancement in this derived structure is analyzed.

Sub-5-ps, multimegawatt peak-power pulses from a fiber-amplified and optically compressed passively Q-switched microchip laser.

PubMed

Steinmetz, A; Jansen, F; Stutzki, F; Lehneis, R; Limpert, J; Tünnermann, A

2012-07-01

We report on high-energy picosecond pulse generation from a passively Q-switched and fiber-amplified microchip laser system. Initially, the utilized microchip lasers produce pulses with durations of around 100 ps at 1064 nm central wavelength. These pulses are amplified to energies exceeding 100 μJ, simultaneously chirped and spectrally broadened by self-phase modulation using a double stage amplifier based on single-mode LMA photonic crystal fibers at repetition rates of up to 1 MHz. Subsequently, the pulse duration of chirped pulses is reduced by means of nonlinear pulse compression to durations of 2.7 ps employing a conventional grating compressor and 4.7 ps using a compact compressor based on a chirped volume Bragg grating.

Design and analysis of a worm gear turntable off-axis assembly method in a three-grating monochromator.

PubMed

Chen, Jianjun; Cui, Jicheng; Yao, Xuefeng; Liu, Jianan; Sun, Ci

2018-04-01

To solve the problem where the actual grating aperture decreases with an increasing scanning angle during the scanning of a three-grating monochromator, we propose an off-axis assembly method for the worm gear turntable that makes it possible to suppress this aperture reduction. We simulated and compared the traditional assembly method with the off-axis assembly method in the three-grating monochromator. Results show that the actual grating aperture can be improved by the off-axis assembly method. In fact, for any one of the three gratings, when the monochromator outputs the longest wavelength in the corresponding wavelength band, the actual grating aperture increases by 45.93%. Over the entire monochromator output band, the actual grating aperture increased by an average of 32.56% and can thus improve the monochromator's output energy. Improvement of the actual grating aperture can also reduce the stray light intensity in the monochromator and improve its output signal-to-noise ratio.

The vertical-cavity surface-emitting laser incorporating a high contrast grating mirror as a sensing device

NASA Astrophysics Data System (ADS)

Marciniak, Magdalena; Gebski, Marcin; Piskorski, Łukasz; Dems, Maciej; Wasiak, M.; Panajotov, Krassimir; Lott, James A.; Czyszanowski, Tomasz

2018-02-01

We propose a novel optical sensing system based on one device that both emits and detects light consisting of a verticalcavity surface-emitting laser (VCSEL) incorporating an high contrast grating (HCG) as a top mirror. Since HCGs can be very sensitive to the optical properties of surrounding media, they can be used to detect gases and liquid. The presence of a gas or a liquid around an HCG mirror causes changes of the power reflectance of the mirror, which corresponds to changes of the VCSEL's cavity quality factor and current-voltage characteristic. By observation of the current-voltage characteristic we can collect information about the medium around the HCG. In this paper we investigate how the properties of the HCG mirror depend on the refractive index of the HCG surroundings. We present results of a computer simulation performed with a three-dimensional fully vectorial model. We consider silicon HCGs on silica and designed for a 1300 nm VCSEL emission wavelength. We demonstrate that our approach can be applied to other wavelengths and material systems.

Experimental demonstration of a ferroelectric liquid crystal tunable filter for fast demodulation of FBG sensors

NASA Astrophysics Data System (ADS)

Mathews, Sunish; Semenova, Yuliya; Rajan, Ginu; Farrell, Gerald

2009-05-01

A discretely tunable Surface-Stabilized Ferroelectric Liquid Crystal based Lyot Filter, with tuning speeds in the order of microseconds, is demonstrated experimentally as a channel dropper for the demodulation of multiple Fibre Bragg Grating sensors. The 3-stage Lyot Filter designed and experimentally verified can be used together with the high-speed ratiometric wavelength measurement system employing a fibre bend loss edge filter. Such systems can be used for the demodulation of distributed Fibre Bragg Grating sensors employed in applications such as structural monitoring, industrial sensing and haptic telerobotic surgical systems.

Fabrication of Extremely Short Length Fiber Bragg Gratings for Sensor Applications

NASA Technical Reports Server (NTRS)

Wu, Meng-Chou; Rogowski, Robert S.; Tedjojuwono, Ken K.

2002-01-01

A new technique and a physical model for writing extremely short length Bragg gratings in optical fibers have been developed. The model describes the effects of diffraction on the spatial spectra and therefore, the wavelength spectra of the Bragg gratings. Using an interferometric technique and a variable aperture, short gratings of various lengths and center wavelengths were written in optical fibers. By selecting the related parameters, the Bragg gratings with typical length of several hundred microns and bandwidth of several nanometers can be obtained. These short gratings can be apodized with selected diffraction patterns and hence their broadband spectra have a well-defined bell shape. They are suitable for use as miniaturized distributed strain sensors, which have broad applications to aerospace research and industry as well.

Two-dimensional Ag/SiO2 and Cu/SiO2 nanocomposite surface-relief grating couplers and their vertical input coupling properties

NASA Astrophysics Data System (ADS)

Wang, Jun; Mu, Xiaoyu; Wang, Gang; Liu, Changlong

2017-11-01

By etching two SiO2 optical waveguide slabs separately implanted with 90 keV Ag ions and 60 keV Cu ions at the same dose of 6 × 1016 cm-2, two-dimensional Ag/SiO2 and Cu/SiO2 nanocomposite surface-relief grating couplers with 600-nm periodicity and 100-nm thickness were fabricated, and their structural and vertical input coupling properties were investigated. Experimental results revealed that the two couplers could convert light beams at wavelengths of 620-880 nm into guided waves with different efficiencies, highlighting the special importance of metal nanoparticles (NPs). Further discussions also revealed that owing to the introduction of periodically distributed metal NPs, the periodical phase modification of the transmitted beam was enhanced drastically, and the nanocomposite veins could behave as efficient light scatterers. As a result, the two couplers were much larger in coupling efficiency than the NP-free one with identical morphological parameters. The above findings may be useful to construct thin and short but efficient surface-relief grating couplers on glass optical waveguides.

Wide-band/angle Blazed Surfaces using Multiple Coupled Blazing Resonances

PubMed Central

Memarian, Mohammad; Li, Xiaoqiang; Morimoto, Yasuo; Itoh, Tatsuo

2017-01-01

Blazed gratings can reflect an oblique incident wave back in the path of incidence, unlike mirrors and metal plates that only reflect specular waves. Perfect blazing (and zero specular scattering) is a type of Wood’s anomaly that has been observed when a resonance condition occurs in the unit-cell of the blazed grating. Such elusive anomalies have been studied thus far as individual perfect blazing points. In this work, we present reflective blazed surfaces that, by design, have multiple coupled blazing resonances per cell. This enables an unprecedented way of tailoring the blazing operation, for widening and/or controlling of blazing bandwidth and incident angle range of operation. The surface can thus achieve blazing at multiple wavelengths, each corresponding to different incident wavenumbers. The multiple blazing resonances are combined similar to the case of coupled resonator filters, forming a blazing passband between the incident wave and the first grating order. Blazed gratings with single and multi-pole blazing passbands are fabricated and measured showing increase in the bandwidth of blazing/specular-reflection-rejection, demonstrated here at X-band for convenience. If translated to appropriate frequencies, such technique can impact various applications such as Littrow cavities and lasers, spectroscopy, radar, and frequency scanned antenna reflectors. PMID:28211506

Design and fabrication of label-free biochip using a guided mode resonance filter with nano grating structures by injection molding process.

PubMed

Cho, E; Kim, B; Choi, S; Han, J; Jin, J; Han, J; Lim, J; Heo, Y; Kim, S; Sung, G Y; Kang, S

2011-01-01

This paper introduces technology to fabricate a guided mode resonance filter biochip using injection molding. Of the various nanofabrication processes that exist, injection molding is the most suitable for the mass production of polymer nanostructures. Fabrication of a nanograting pattern for guided mode resonance filters by injection molding requires a durable metal stamp, because of the high injection temperature and pressure. Careful consideration of the optimized process parameters is also required to achieve uniform sub-wavelength gratings with high fidelity. In this study, a metallic nanostructure pattern to be used as the stamp for the injection molding process was fabricated using electron beam lithography, a UV nanoimprinting process, and an electroforming process. A one-dimensional nanograting substrate was replicated by injection molding, during which the process parameters were controlled. To evaluate the geometric quality of the injection molded nanograting patterns, the surface profile of the fabricated nanograting for different processing conditions was analyzed using an atomic force microscope and a scanning electron microscope. Finally, to demonstrate the feasibility of the proposed process for fabricating guided mode resonance filter biochips, a high-refractive-index material was deposited on the polymer nanograting and its guided mode resonance characteristics were analyzed.

In-line optofluidic refractive index sensing in a side-channel photonic crystal fiber.

PubMed

Zhang, Nan; Humbert, Georges; Wu, Zhifang; Li, Kaiwei; Shum, Perry Ping; Zhang, Nancy Meng Ying; Cui, Ying; Auguste, Jean-Louis; Dinh, Xuan Quyen; Wei, Lei

2016-11-28

An in-line optofluidic refractive index (RI) sensing platform is constructed by splicing a side-channel photonic crystal fiber (SC-PCF) with side-polished single mode fibers. A long-period grating (LPG) combined with an intermodal interference between LP₀₁ and LP₁₁ core modes is used for sensing the RI of the liquid in the side channel. The resonant dip shows a nonlinear wavelength shift with increasing RI over the measured range from 1.3330 to 1.3961. The RI response of this sensing platform for a low RI range of 1.3330-1.3780 is approximately linear, and exhibits a sensitivity of 1145 nm/RIU. Besides, the detection limit of our sensing scheme is improved by around one order of magnitude by introducing the intermodal interference.

Bio-sensing based on plasmon-coupling caused by rotated sub-micrometer gratings in metal-dielectric interfacial layers

NASA Astrophysics Data System (ADS)

Csete, M.; Sipos, Á.; Szalai, A.; Mathesz, A.; Deli, M. A.; Veszelka, Sz.; Schmatulla, A.; Kőházi-Kis, A.; Osvay, K.; Marti, O.; Bor, Zs.

2007-09-01

Novel plasmonic sensor chips are prepared by generating sub-micrometer periodic patterns in the interfacial layers of bimetal-polymer films via master-grating based interference method. Poly-carbonate films spin-coated onto vacuum evaporated silver-gold bimetallic layers are irradiated by the two interfering UV beams of a Nd:YAG laser. It is proven by pulsed force mode AFM that periodic adhesion pattern corresponds to the surface relief gratings, consisting of sub-micrometer droplet arrays and continuous polymer stripes, induced by p- and s-polarized beams, respectively. The characteristic periods are the same, but more complex and larger amplitude adhesion modulation is detectable on the droplet arrays. The polar and azimuthal angle dependence of the resonance characteristic of plasmons is studied by combining the prism- and grating-coupling methods in a modified Kretschmann arrangement, illuminating the structured metal-polymer interface by a frequency doubled Nd:YAG laser through a semi-cylinder. It is proven that the grating-coupling results in double-peaked plasmon resonance curves on both of the droplet arrays and line gratings, when the grooves are rotated to an appropriate azimuthal angle, and the modulation amplitude of the structure is sufficiently large. Streptavidin seeding is performed to demonstrate that small amount of protein can be detected monitoring the shift of the secondary resonance minima. The available high concentration sensitivity is explained by the promotion of protein adherence in the structure's valleys due to the enhanced adhesion. The line-shaped polymer gratings resulting in narrow resonance peaks are utilized to demonstrate the effect of therapeutic molecules on Amyloid-Β peptide, a pathogenic factor in Alzheimer disease.

Development and Testing of a Plastic Optical Fiber Grating Biosensor for Detection of Glucose in the Blood

NASA Astrophysics Data System (ADS)

Yunianto, M.; Eka, D.; Permata, A. N.; Ariningrum, D.; Wahyuningsih, S.; Marzuki, A.

2017-02-01

The objective of this study is to detect glucose content in human blood serum using optical fiber grating with LED wavelength corresponding to the absorption of glucose content in blood serum. The testing used a UV-Vis spectrometer and Rays spectrometers, in which in the ray spectrometer it was used optical fiber biosensor using optical fiber grating. The result obtained is the typical peak of glucose absorption in UV-Vis at 581 nm wavelength and rays spectrometer on green LED at 514.2 nm wavelength with linear regression result by 0.97 and 0.94, respectively.

Sub-diffraction Imaging via Surface Plasmon Decompression

DTIC Science & Technology

2014-06-08

of the local wavelength of a surface plasmon polariton supported by two adjoining curved metal surfaces. The views, opinions and/or findings...adiabatic decompression of the local wavelength of a surface plasmon polariton supported by two adjoining curved metal surfaces. Conference Name...diffraction imaging based on a process of adiabatic decompression of the local wavelength of a surface plasmon polariton supported by two adjoining curved

Anisotropic Dispersion and Partial Localization of Acoustic Surface Plasmons on an Atomically Stepped Surface: Au(788)

NASA Astrophysics Data System (ADS)

Smerieri, M.; Vattuone, L.; Savio, L.; Langer, T.; Tegenkamp, C.; Pfnür, H.; Silkin, V. M.; Rocca, M.

2014-10-01

Understanding acoustic surface plasmons (ASPs) in the presence of nanosized gratings is necessary for the development of future devices that couple light with ASPs. We show here by experiment and theory that two ASPs exist on Au(788), a vicinal surface with an ordered array of monoatomic steps. The ASPs propagate across the steps as long as their wavelength exceeds the terrace width, thereafter becoming localized. Our investigation identifies, for the first time, ASPs coupled with intersubband transitions involving multiple surface-state subbands.

Analysis of reflection-peak wavelengths of sampled fiber Bragg gratings with large chirp.

PubMed

Zou, Xihua; Pan, Wei; Luo, Bin

2008-09-10

The reflection-peak wavelengths (RPWs) in the spectra of sampled fiber Bragg gratings with large chirp (SFBGs-LC) are theoretically investigated. Such RPWs are divided into two parts, the RPWs of equivalent uniform SFBGs (U-SFBGs) and the wavelength shift caused by the large chirp in the grating period (CGP). We propose a quasi-equivalent transform to deal with the CGP. That is, the CGP is transferred into quasi-equivalent phase shifts to directly derive the Fourier transform of the refractive index modulation. Then, in the case of both the direct and the inverse Talbot effect, the wavelength shift is obtained from the Fourier transform. Finally, the RPWs of SFBGs-LC can be achieved by combining the wavelength shift and the RPWs of equivalent U-SFBGs. Several simulations are shown to numerically confirm these predicted RPWs of SFBGs-LC.

Writing Bragg Gratings in Multicore Fibers.

PubMed

Lindley, Emma Y; Min, Seong-Sik; Leon-Saval, Sergio G; Cvetojevic, Nick; Lawrence, Jon; Ellis, Simon C; Bland-Hawthorn, Joss

2016-04-20

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong suppression at a single wavelength requires that all cores have matching transmission profiles. These gratings cannot be inscribed using the same method as for single-core fibers because the curved surface of the cladding acts as a lens, focusing the incoming UV laser beam and causing variations in exposure between cores. Therefore we use an additional optical element to ensure that the beam shape does not change while passing through the cross-section of the multicore fiber. This consists of a glass capillary tube which has been polished flat on one side, which is then placed over the section of the fiber to be inscribed. The laser beam enters the fiber through the flat surface of the capillary tube and hence maintains its original dimensions. This paper demonstrates the improvements in core-to-core uniformity for a 7-core fiber using this method. The technique can be generalized to larger multicore fibers.

Writing Bragg Gratings in Multicore Fibers

PubMed Central

Lindley, Emma Y.; Min, Seong-sik; Leon-Saval, Sergio G.; Cvetojevic, Nick; Lawrence, Jon; Ellis, Simon C.; Bland-Hawthorn, Joss

2016-01-01

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong suppression at a single wavelength requires that all cores have matching transmission profiles. These gratings cannot be inscribed using the same method as for single-core fibers because the curved surface of the cladding acts as a lens, focusing the incoming UV laser beam and causing variations in exposure between cores. Therefore we use an additional optical element to ensure that the beam shape does not change while passing through the cross-section of the multicore fiber. This consists of a glass capillary tube which has been polished flat on one side, which is then placed over the section of the fiber to be inscribed. The laser beam enters the fiber through the flat surface of the capillary tube and hence maintains its original dimensions. This paper demonstrates the improvements in core-to-core uniformity for a 7-core fiber using this method. The technique can be generalized to larger multicore fibers. PMID:27167576

Inverse Optimization of Plasmonic and Antireflective Grating in Thin Film PV Cells

NASA Astrophysics Data System (ADS)

Hajimirza, Shima; Howell, John

2012-06-01

This work addresses inverse optimization of three dimensional front and back surface texture grating specifications, for the purpose of shaping the absorptivity spectrum of silicon thin film cells in targeted ways. Periodic plasmonic gratings with dimensions comparable or less than the incident light wavelength are known to enhance light absorption. We consider surface patterning of amorphous silicon (a-Si) thin films using front and/or back metallic nanostrips and ITO coatings, and show that wideband enhancement in unpolarized absorptivity spectrum can be achieved when back reflectors are used. The overall short circuit current enhancement using such structures is significant and can be as high as 97%. For TM-polarized wave it can be even higher as reported in previous work. In this work however, we focus on the optimization for the more realistic unpolarized radiation which is of significantly higher complexity. In addition, optimization is done with respect to two objective functions independently: spectral absorptivity and gain-bandwidth product of the absorptivity spectrum.

Electron acceleration and high harmonic generation by relativistic surface plasmons

NASA Astrophysics Data System (ADS)

Cantono, Giada; Luca Fedeli Team; Andrea Sgattoni Team; Andrea Macchi Team; Tiberio Ceccotti Team

2016-10-01

Intense, short laser pulses with ultra-high contrast allow resonant surface plasmons (SPs) excitation on solid wavelength-scale grating targets, opening the way to the extension of Plasmonics in the relativistic regime and the manipulation of intense electromagnetic fields to develop new short, energetic, laser-synchronized radiation sources. Recent theoretical and experimental studies have explored the role of SP excitation in increasing the laser-target coupling and enhancing ion acceleration, high-order harmonic generation and surface electron acceleration. Here we present our results on SP driven electron acceleration from grating targets at ultra-high laser intensities (I = 5 ×1019 W/cm2, τ = 25 fs). When the resonant condition for SP excitation is fulfilled, electrons are emitted in a narrow cone along the target surface, with a total charge of about 100 pC and energy spectra peaked around 5 MeV. Distinguishing features of the resonant process were investigated by varying the incidence angle, grating type and with the support of 3D PIC simulations, which closely reproduced the experimental data. Open challenges and further measurements on high-order harmonic generation in presence of a relativistic SP will also be discussed.

Gold reflective metallic gratings with high absorption efficiency

NASA Astrophysics Data System (ADS)

Zhang, Zhaojian; Liang, Linmei; Yang, Junbo

2017-10-01

Electromagnetic (EM) wave absorbers are devices in which the incident radiation at the operating wavelengths can be efficiently absorbed and then transformed into ohmic heat or other forms of energy. Especially, EM absorbers based on metallic structures have distinct advantages in comparison with the traditional counterparts. Thus, they have different potential applications at different frequency ranges such as absorbing devices in solar energy harvesting systems. The reflective metallic grating is a kind of metallic EM absorbers and has the fascinating property of efficiently absorbing the incident light due to the excitation of surface plasmon polaritons (SPPs), consequently drawing more and more attention. In this paper, the absorption effect of a reflective metallic grating made of gold is studied by changing grating parameters such as the period, polarization direction of the incident light and so on. We use finite difference time-domain (FDTD) method to design the grating, and simulate the process and detect the absorption spectrum. In our design, the grating has rectangular shaped grooves and has the absorption efficiency 99% for the vertically incident transverse magnetic (TM) light at the wavelength of 818nm with the period of 800 nm, the width of 365 nm and the height of 34 nm. And then we find that the absorption spectrum is blue-shifted about 87 nm with decreasing period from 800 nm to700 nm and red-shifted about 14 nm with increasing the width of the block from 305 nm to 405 nm. The absorption becomes gradually weaker from 98% to almost zero with the polarization angle from 0° to 90°. Finally, we make a theoretical explanation to these phenomena in details. It is believed that the results may provide useful guidance for the design of EM wave absorbers with high absorption efficiency.

Design and experiment of spectrometer based on scanning micro-grating integrating with angle sensor

NASA Astrophysics Data System (ADS)

Biao, Luo; Wen, Zhi-yu

2014-01-01

A compact, low cost, high speed, non-destructive testing NIR (near infrared) spectrometer optical system based on MOEMS grating device is developed. The MOEMS grating works as the prismatic element and wavelength scanning element in our optical system. The MOEMS grating enables the design of compact grating spectrometers capable of acquiring full spectra using a single detector element. This MOEMS grating is driven by electromagnetic force and integrated with angle sensor which used to monitored deflection angle while the grating working. Comparing with the traditional spectral system, there is a new structure with a single detector and worked at high frequency. With the characteristics of MOEMS grating, the structure of the spectrometer system is proposed. After calculating the parameters of the optical path, ZEMAX optical software is used to simulate the system. According the ZEMAX output file of the 3D model, the prototype is designed by SolidWorks rapidly, fabricated. Designed for a wavelength range between 800 nm and 1500 nm, the spectrometer optical system features a spectral resolution of 16 nm with the volume of 97 mm × 81.7 mm × 81 mm. For the purpose of reduce modulated effect of sinusoidal rotation, spectral intensity of the different wavelength should be compensated by software method in the further. The system satisfies the demand of NIR micro-spectrometer with a single detector.

Long-period fiber grating fabricated by 800 nm femtosecond laser pulses

NASA Astrophysics Data System (ADS)

Zhang, Yani; Xi, Yaru; Liu, Sicong; Jiang, Peng; Zhao, Ya; Xu, Qiang

2018-02-01

In this paper, the long period fiber gratings (LPFGs) in standard SMF-28 telecommunication fibers without hydrogen loading were inscribed by using point-to-point direct writing method of femtosecond laser pulses with pulse duration of 100 fs, repetition rate of 1kHz and a central wavelength of 800 nm. The LPFGs with different spectral characteristics were fabricated by adjusting grating period, grating length and duty ratio. The results show that the resonant peak wavelengths shift to the long-wave direction with the increase of the grating length increasing. The variations of duty ratio will lead to the generation of resonance rejection band of LPFGs from singlepeak to multi-peak plus lesser out-of-band loss.

Widely tunable long-period waveguide grating couplers

NASA Astrophysics Data System (ADS)

Bai, Y.; Liu, Q.; Lor, K. P.; Chiang, K. S.

2006-12-01

We demonstrate experimentally two widely tunable optical couplers formed with parallel long-period polymer waveguide gratings. One of the couplers consists of two parallel gratings and shows a peak coupling efficiency of ~34%. The resonance wavelength of the coupler can be tuned thermally with a sensitivity of 4.7 nm/°C. The experimental results agree well with the coupled-mode analysis. The other coupler consists of an array of ten widely separated gratings. A peak coupling efficiency of ~11% is obtained between the two best matched gratings in the array and the resonance wavelength can be tuned thermally with a sensitivity of -3.8 nm/°C. These couplers have the potential to be further developed into practical broadband add/drop multiplexers and signal dividers.

Narrow-stripe broad-area lasers with distributed-feedback surface gratings as brilliant sources for high power spectral beam combining systems

NASA Astrophysics Data System (ADS)

Decker, J.; Crump, P.; Fricke, J.; Wenzel, H.; Maaβdorf, A.; Erbert, G.; Tränkle, G.

2014-03-01

Laser systems based on spectral beam combining (SBC) of broad-area (BA) diode lasers are promising tools for material processing applications. However, the system brightness is limited by the in-plane beam param- eter product, BPP, of the BA lasers, which operate with a BPP of < 3mm-mrad. The EU project BRIDLE (www.bridle.eu) is developing novel diode laser sources for such systems, and several technological advances are sought. For increased system brightness and optimal ber-coupling the diode lasers should operate with reduced BPP and vertical far eld angle (95% power content), μV 95. The resulting diode lasers are fabricated as mini- bars for reduced assembly costs. Gratings are integrated into the mini-bar, with each laser stripe emitting at a different wavelength. In this way, each emitter can be directed into a single bre via low-cost dielectric filters. Distributed-feedback narrow-stripe broad-area (DFB-NBA) lasers are promising candidates for these SBC sys- tems. We review here the design process and performance achieved, showing that DFB-NBA lasers with stripe width, W = 30 μm, successfully cut of higher-order lateral modes, improving BPP. Uniform, surface-etched, 80th-order Bragg gratings are used, with weak gratings essential for high e ciency. To date, such DFB-NBA sources operate with < 50% effciency at output power, Pout < 6 W, with BPP < 1.8 mm-mrad and offV 95 36 . The emission wavelength is about 970 nm and the spectral width is < 0.7 nm (95% power). The BPP is half that of a DFB-BA lasers with W = 90 um. We conclude with a review of options for further performance improvements.

Study of collisional deactivation of O{sub 2}(b{sup 1}{Sigma}{sub g}{sup +}) molecules in a hydrogen-oxygen mixture at high temperatures using laser-induced gratings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kozlov, D. N., E-mail: dnk@kapella.gpi.ru; Kobtsev, V. D.; Stel'makh, O. M.

2013-07-15

Collisional deactivation of O{sub 2}(b{sup 1}{Sigma}{sub g}{sup +}) molecules resonantly excited by a 10 ns pulse of laser radiation with a wavelength of 762 nm in H{sub 2}/O{sub 2} mixtures is experimentally studied. The radiation intensity and hence the molecule excitation efficiency have a spatially periodic modulation that leads to the formation of laser-induced gratings (LIGs) of the refractive index. The study of LIG temporal evolution allows collisional relaxation rates of molecular excited states and gas temperature to be determined. In this work, the b{sup 1}{Sigma}{sub g}{sup +} state of O{sub 2} molecules deactivation rates are measured in a 4.3more » vol % H{sub 2} mixture at the number density of 2 amg in the temperature range 291-850 K. The physical deactivation is shown to dominate in the collisions of H{sub 2} with O{sub 2}(b{sup 1}{Sigma}{sub g}{sup +}) and O{sub 2}(a{sup 1}{Delta}{sub g}) up to temperatures of 780-790 K at time delays up to 10 {mu}s after the excitation pulse. The parameters of the obtained temperature dependence of the (b{sup 1}{Sigma}{sub g}{sup +} state deactivation rate agree well with the data of independent measurements performed earlier at lower temperatures (200-400 K). Tunable diode laser absorption spectroscopy is used to measure the temperature dependence of the number density of the H{sub 2}O molecules which appear as the mixture, as the result of the dark gross reaction with O{sub 2} molecules in the ground state, O{sub 2} + 2H{sub 2} {yields} 2H{sub 2}O. The measurements show that this reaction results in complete transformation of H{sub 2} into H{sub 2}O at temperatures of 790-810 K.« less

[Spectral analysis of fiber bragg grating modulated by double long period grating and its application in smart structure monitoring].

PubMed

Lu, Ji-Yun; Liang, Da-Kai; Zhang, Xiao-Li; Zhu, Zhu

2009-12-01

Spectrum of fiber bragg grating (FBG) sensor modulated by double long period grating (LPFG) is proposed in the paper. Double LPFG consists of two LPFGS whose center wavelengths are the same and reflection spectrum of FBG sensor is located in linear range of double LPFG transmission spectrum. Based on spectral analysis of FBG and double LPFG, reflection spectrum of FBG modulated by double LPFG is obtained and studied by use of band-hider filter characteristics for double LPFG. An FBG sensor is attached on the surface of thin steel beam, which is strained by bending, and the center wavelength of FBG sensor will shift. The spectral peak of FBG sensor modulated by double LPFG is changed correspondingly, and the spectral change will lead to variation in exit light intensity from double LPFG. Experiment demonstrates that the relation of filtering light intensity from double LPFG monitored by optical power meter to center wavelength change of FBG sensor is linear and the minimum strain of material (steel beam) detected by the modulation and demodulation system is 1.05 microepsilon. This solution is used in impact monitoring of optical fibre smart structure, and FBG sensor is applied for impulse response signal monitoring induced by low-velocity impact, when impact pendulum is loaded to carbon fiber-reinforced plastics (CFP). The acquired impact response signal and fast Fourier transform of the signal detected by FBG sensor agree with the measurement results of eddy current displacement meter attached to the FBG sensor. From the results, the present method using FBG sensor is found to be effective for monitoring the impact. The research provides a practical reference in dynamic monitoring of optical fiber smart structure field.

Design of compressors for FEL pulses using deformable gratings

NASA Astrophysics Data System (ADS)

Bonora, Stefano; Fabris, Nicola; Frassetto, Fabio; Giovine, Ennio; Miotti, Paolo; Quintavalla, Martino; Poletto, Luca

2017-06-01

We present the optical layout of soft X-rays compressors using reflective grating specifically designed to give both positive or negative group-delay dispersion (GDD). They are tailored for chirped-pulse-amplification experiments with FEL sources. The optical design originates from an existing compressor with plane gratings already realized and tested at FERMI, that has been demonstrated capable to introduce tunable negative GDD. Here, we discuss two novel designs for compressors using deformable gratings capable to give both negative and positive GDD. Two novel designs are discussed: 1) a design with two deformable gratings and an intermediate focus between the twos, that is demonstrated capable to introduce positive GDD; 2) a design with one deformable grating giving an intermediate focus, followed by a concave mirror and a plane grating, that is capable to give both positive and negative GDD depending on the distance between the second mirror and the second grating. Both the designs are tunable in wavelength and GDD, by acting on the deformable gratings, that are rotated to tune the wavelength and the GDD and deformed to introduce the radius required to keep the spectral focus. The deformable gratings have a laminar profile and are ruled on a thin silicon plane substrate. A piezoelectric actuator is glued on the back of the substrate and is actuated to give a radius of curvature that is varying from infinite (plane) to few meters. The ruling procedure, the piezoelectric actuator and the efficiency measurements in the soft X-rays will be presented. Some test cases are discussed for wavelengths shorter than 12 nm.

Study of silicon strip waveguides with diffraction gratings and photonic crystals tuned to a wavelength of 1.5 µm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barabanenkov, M. Yu., E-mail: barab@iptm.ru; Vyatkin, A. F.; Volkov, V. T.

2015-12-15

Single-mode submicrometer-thick strip waveguides on silicon-on-insulator substrates, fabricated by silicon-planar-technology methods are considered. To solve the problem of 1.5-µm wavelength radiation input-output and its frequency filtering, strip diffraction gratings and two-dimensional photonic crystals are integrated into waveguides. The reflection and transmission spectra of gratings and photonic crystals are calculated. The waveguide-mode-attenuation coefficient for a polycrystalline silicon waveguide is experimentally estimated.

Enhanced second-harmonic generation from resonant GaAs gratings.

PubMed

de Ceglia, D; D'Aguanno, G; Mattiucci, N; Vincenti, M A; Scalora, M

2011-03-01

We theoretically study second harmonic generation in nonlinear, GaAs gratings. We find large enhancement of conversion efficiency when the pump field excites the guided mode resonances of the grating. Under these circumstances the spectrum near the pump wavelength displays sharp resonances characterized by dramatic enhancements of local fields and favorable conditions for second-harmonic generation, even in regimes of strong linear absorption at the harmonic wavelength. In particular, in a GaAs grating pumped at 1064 nm, we predict second-harmonic conversion efficiencies approximately 5 orders of magnitude larger than conversion rates achievable in either bulk or etalon structures of the same material.

Photonic structures in diamond based on femtosecond UV laser induced periodic surface structuring (LIPSS).

PubMed

Granados, Eduardo; Martinez-Calderon, Miguel; Gomez, Mikel; Rodriguez, Ainara; Olaizola, Santiago M

2017-06-26

We study the fabrication of photonic surface structures in single crystal diamond by means of highly controllable direct femtosecond UV laser induced periodic surface structuring. By appropriately selecting the excitation wavelength, intensity, number of impinging pulses and their polarization state, we demonstrate emerging high quality and fidelity diamond grating structures with surface roughness below 1.4 nm. We characterize their optical properties and study their potential for the fabrication of photonic structure anti-reflection coatings for diamond Raman lasers in the near-IR.

Multichannel photonic Hilbert transformers based on complex modulated integrated Bragg gratings.

PubMed

Cheng, Rui; Chrostowski, Lukas

2018-03-01

Multichannel photonic Hilbert transformers (MPHTs) are reported. The devices are based on single compact spiral integrated Bragg gratings on silicon with coupling coefficients precisely modulated by the phase of each grating period. MPHTs with up to nine wavelength channels and a single-channel bandwidth of up to ∼625  GHz are achieved. The potential of the devices for multichannel single-sideband signal generation is suggested. The work offers a new possibility of utilizing wavelength as an extra degree of freedom in designing radio-frequency photonic signal processors. Such multichannel processors are expected to possess improved capacities and a potential to greatly benefit current widespread wavelength division multiplexed systems.

10th order laterally coupled GaN-based DFB laser diodes with V-shaped surface gratings

NASA Astrophysics Data System (ADS)

Kang, J. H.; Wenzel, H.; Hoffmann, V.; Freier, E.; Sulmoni, L.; Unger, R.-S.; Einfeldt, S.; Wernicke, T.; Kneissl, M.

2018-02-01

Single longitudinal mode operation of laterally coupled distributed feedback (DFB) laser diodes (LDs) based on GaN containing 10th-order surface Bragg gratings with V-shaped grooves is demonstrated using i-line stepper lithography and inductively coupled plasma etching. A threshold current of 82 mA, a slope efficiency of 1.7 W/A, a single peak emission at 404.5 nm with a full width at half maximum of 0.04 nm and a side mode suppression ratio of > 23 dB at an output power of about 46 mW were achieved under pulsed operation. The shift of the lasing wavelength of DFB LDs with temperature was around three times smaller than that of conventional ridge waveguide LDs.

Extended and quasi-continuous tuning of quantum cascade lasers using superstructure gratings and integrated heaters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bidaux, Yves, E-mail: yves.bidaux@alpeslasers.ch; Institute for Quantum Electronics, ETH-Zurich, CH-8093 Zurich; Bismuto, Alfredo, E-mail: alfredo.bismuto@alpeslasers.ch

2015-11-30

In this work, we demonstrate broad electrical tuning of quantum cascade lasers at 9.25 μm, 8.5 μm, and 4.4 μm in continuous wave operation using Vernier-effect distributed Bragg reflectors based on superstructure gratings. Integrated micro-heaters allow to switch from one Vernier channel to the other, while predictable and mode-hop free tuning can be obtained in each channel modulating the laser current with a side mode suppression ratio as high as 30 dB. The resulting device behaves effectively as a switchable multicolour tunable source. Tuning up to 6.5% of the central wavelength is observed. To prove the importance of the developed devices for high resolutionmore » molecular spectroscopy, a N{sub 2}O absorption spectrum has been measured.« less

Nano-patterned visible wavelength filter integrated with an image sensor exploiting a 90-nm CMOS process

NASA Astrophysics Data System (ADS)

Yoon, Yeo-Taek; Lee, Sang-Shin; Lee, Byoung-Su

2012-01-01

A highly efficient visible wavelength filter enabling a homogeneous integration with an image sensor was proposed and manufactured by employing a standard 90-nm CMOS process. A one dimensional subwavelength Al grating overlaid with an oxide film was built on top of an image sensor to serve as a low-pass wavelength filter; a microlens was then formed atop the filter to achieve beam focusing. The structural parameters for the filter were: a grating pitch of 300 nm, a grating height of 170 nm, and a 150-nm thick oxide overlay. The overall transmission was observed to reach up to 80% in the visible band with a decent roll-off near ∼700 nm. Finally, the discrepancy between the observed and calculated result was accounted for by appropriately modeling the implemented metallic grating structure, accompanying an undercut sidewall.

A Sagnac Fourier spectrometer

DOE PAGES

Lenzner, Matthias; Diels, Jean -Claude

2017-03-09

A spectrometer based on a Sagnac interferometer, where one of the mirrors is replaced by a transmission grating, is introduced. Since the action of a transmission grating is reversible, both directions experience the same diffraction at a given wavelength. At the output, the crossed wavefronts are imaged onto a camera, where their Fizeau fringe pattern is recorded. Each spectral element produces a unique spatial frequency, hence the Fourier transform of the recorded interferogram contains the spectrum. Since the grating is tuned to place zero spatial frequency at a selected wavelength, the adjoining spectrum is heterodyned with respect to this wavelength.more » This spectrum can then be discriminated at a high spectral resolution from relatively low spatial frequencies. The spectrometer can be designed without moving parts for a relatively narrow spectral range or with a rotatable grating. As a result, the latter version bears the potential to be calibrated without a calibrated light source.« less

A Sagnac Fourier spectrometer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lenzner, Matthias; Diels, Jean -Claude

A spectrometer based on a Sagnac interferometer, where one of the mirrors is replaced by a transmission grating, is introduced. Since the action of a transmission grating is reversible, both directions experience the same diffraction at a given wavelength. At the output, the crossed wavefronts are imaged onto a camera, where their Fizeau fringe pattern is recorded. Each spectral element produces a unique spatial frequency, hence the Fourier transform of the recorded interferogram contains the spectrum. Since the grating is tuned to place zero spatial frequency at a selected wavelength, the adjoining spectrum is heterodyned with respect to this wavelength.more » This spectrum can then be discriminated at a high spectral resolution from relatively low spatial frequencies. The spectrometer can be designed without moving parts for a relatively narrow spectral range or with a rotatable grating. As a result, the latter version bears the potential to be calibrated without a calibrated light source.« less

Structural coloration of metallic surfaces with micro/nano-structures induced by elliptical vibration texturing

NASA Astrophysics Data System (ADS)

Yang, Yang; Pan, Yayue; Guo, Ping

2017-04-01

Creating orderly periodic micro/nano-structures on metallic surfaces, or structural coloration, for control of surface apparent color and optical reflectivity has been an exciting research topic over the years. The direct applications of structural coloration include color marking, display devices, and invisibility cloak. This paper presents an efficient method to colorize metallic surfaces with periodic micro/nano-gratings using elliptical vibration texturing. When the tool vibration is coupled with a constant cutting velocity, controlled periodic ripples can be generated due to the overlapping tool trajectory. These periodic ripples with a wavelength near visible spectrum can act as micro-gratings to introduce iridescent colors. The proposed technique also provides a flexible method for color marking of metallic surfaces with arbitrary patterns and images by precise control of the spacing distance and orientation of induced micro/nano-ripples. Theoretical analysis and experimental results are given to demonstrate structural coloration of metals by a direct mechanical machining technique.

Normal incidence infrared modulator based on single quantum well intersubband transitions

NASA Astrophysics Data System (ADS)

Vandermeiren, W.; Stiens, J.; Shkerdin, G.; De Tandt, C.; Vounckx, R.

2014-01-01

An infrared modulator of which the working principle is based on evanescent wave generation and intersubband transitions in a single AlGaAs/GaAs quantum well is presented here. CO2 laser light at normal incidence is coupled to an evanescent wave by means of a sub-wavelength diffraction grating. Modulation of the zeroth order reflective mode is achieved by applying an electric field across the quantum well. The model for deriving the complex refractive index of the quantum well region is presented and used for numerical diffraction efficiency simulations as a function of the groove height and period. Two specimens with different groove heights were fabricated. Experiments are conducted at a wavelength of 10.6 µm. At this wavelength a relatively strong absolute modulation depth of about 20% could be observed. The experimental results are in good agreement with our model and diffraction efficiency calculations.

Wavelength shifts of cladding-mode resonance in corrugated long-period fiber gratings under torsion.

PubMed

Ivanov, Oleg V; Wang, Lon A

2003-05-01

A finite deformation theory of elasticity and a theory of nonlinear photoelasticity are applied to describe the wavelength shifts of cladding-mode resonance in corrugated long-period fiber gratings under torsion. The deformation of fiber is found by use of the Murnaghan model of a solid elastic body. The quadratic photoelastic effect that is proportional to the second-order displacement gradient is investigated and compared with the classical photoelastic effect. The electromagnetic field in the twisted corrugated structure is presented as a superposition of circularly polarized modes of the etched fiber section. The wavelength shift is found to be proportional to the square of the twist angle. As predicted by our theory, a wavelength shift of the same nature has been found in a conventionally photoinduced long-period fiber grating.

High sensitivity long-period grating-based temperature monitoring using a wide wavelength range to 2.2 μm

NASA Astrophysics Data System (ADS)

Venugopalan, Thillainathan; Yeo, Teck L.; Sun, Tong; Grattan, Kenneth T. V.

2006-12-01

Temperature effects on the various cladding modes of a long-period grating (LPG) fabricated in B-Ge co-doped fibre have been investigated to create a high sensitivity measurement device. The temperature sensitivities of the attenuation bands of the LPG over the wavelength region 1.2-2.2 μm, for a grating with a 330 μm period, were obtained by monitoring the wavelength shift of each attenuation band, with a temperature increment of 20 °C, over the range from 23 °C to 140 °C. The attenuation band appearing over the 1.8-2.0 μm wavelength range has shown a nearly five times higher temperature sensitivity than that of lower order modes, and thus it shows significant promise for fibre optic temperature sensor applications.

MEMS infrared approaches to detector based on nonlinear oscillation and wavelength selective emitter using surface plasmon polariton

NASA Astrophysics Data System (ADS)

Sasaki, Minoru; Kumagai, Shinya

2014-03-01

The suspended MEMS structure is suitable for reducing the energy loss due to the thermal conduction. There is the possibility that IR photon energy can be well-controlled to generate some physical effects. A new method bases on the nonlinear oscillation for the detector. The thin film torsional spring exhibits a large hard spring effect when the deflection occurs in the out-of-plane direction of the film. When IR is absorbed, the resonator bends due to the thermal expansion. The torsional spring becomes harder increasing the resonant frequency. The frequency measurement is suited for the precise sensing. The device response is measured using the laser (wavelength of 650nm). The resonant frequency is 88-94kHz. Q factor is about 1600 in vacuum (1Pa). The sensitivity is -0.144[kHz/(kW/m2)]. As for the emitter, nondispersive IR gas sensor is considered. The molecules have their intrinsic absorptions. CO2 absorbs the wavelength 4.2- 4.3μm. The major incandescent light bulbs have the broad spectrum emitting IR which is not used for gas sensing. The wavelength selectivity at the gas bandwidth will improve the efficiency. A new principle uses the microheater placed facing to the grating. SPP is excited carrying IR energy on the grating surface. IR emission is the reverse process of excitation occurring at the output end. The emission spectra show SPP related peak having the width of 190nm. When the input power increases from 0.3 to 1.9W, the peak at wavelength of 3.5μm becomes clearer.

Diffraction-Based Optical Switch

NASA Technical Reports Server (NTRS)

Sperno, Stevan M. (Inventor); Fuhr, Peter L. (Inventor); Schipper, John F. (Inventor)

2005-01-01

Method and system for controllably redirecting a light beam, having a central wavelength lambda, from a first light-receiving site to a second light-receiving site. A diffraction grating is attached to or part of a piezoelectric substrate, which is connected to one or two controllable voltage difference sources. When a substrate voltage difference is changed and the diffraction grating length in each of one or two directions is thereby changed, at least one of the diffraction angle, the diffraction order and the central wavelength is controllably changed. A diffracted light beam component, having a given wavelength, diffraction angle and diffraction order, that is initially received at a first light receiving site (e.g., a detector or optical fiber) is thereby controllably shifted or altered and can be received at a second light receiving site. A polynomially stepped, chirped grating is used in one embodiment. In another embodiment, an incident light beam, having at least one of first and second wavelengths, lambda1 and lambda2, is received and diffracted at a first diffraction grating to provide a first diffracted beam. The first diffracted beam is received and diffracted at a second diffraction grating to produce a second diffracted beam. The second diffracted beam is received at a light-sensitive transducer, having at least first and second spaced apart light detector elements that are positioned so that, when the incident light beam has wavelength lambda1 or lambda2 (lambda1 not equal to lambda2), the second diffracted beam is received at the first element or at the second element, respectively; change in a selected physical parameter at the second grating can also be sensed or measured. A sequence of spaced apart light detector elements can be positioned along a linear or curvilinear segment with equal or unequal spacing.

Micro spectrometer for parallel light and method of use

NASA Technical Reports Server (NTRS)

Park, Yeonjoon (Inventor); Choi, Sang H. (Inventor); King, Glen C. (Inventor); Elliott, James R. (Inventor)

2011-01-01

A spectrometer system includes an optical assembly for collimating light, a micro-ring grating assembly having a plurality of coaxially-aligned ring gratings, an aperture device defining an aperture circumscribing a target focal point, and a photon detector. An electro-optical layer of the grating assembly may be electrically connected to an energy supply to change the refractive index of the electro-optical layer. Alternately, the gratings may be electrically connected to the energy supply and energized, e.g., with alternating voltages, to change the refractive index. A data recorder may record the predetermined spectral characteristic. A method of detecting a spectral characteristic of a predetermined wavelength of source light includes generating collimated light using an optical assembly, directing the collimated light onto the micro-ring grating assembly, and selectively energizing the micro-ring grating assembly to diffract the predetermined wavelength onto the target focal point, and detecting the spectral characteristic using a photon detector.

Using resistive readout to probe ultrafast dynamics of a plasmonic sensor

NASA Astrophysics Data System (ADS)

Cheney, Alec; Chen, Borui; Cartwright, Alexander; Thomay, Tim

2018-02-01

Surface plasmons in a DC current lead to an increase in scattering processes, resulting in a measurable increase in electrical resistance of a plasmonic nano-grating. This enables a purely electronic readout of plasmonically mediated optical absorption. We show that there is a time-dependence in these resistance changes on the order of 100ps that we attribute to electron-phonon and phonon-phonon scattering processes in the metal of the nano-gratings. Since plasmonic responses are strongly structurally dependent, an appropriately designed plasmoelectronic detector could potentially offer an extremely fast response at communication wavelengths in a fully CMOS compatible system.

Experimental results of antigliadin antibodies detection using long period fiber grating

NASA Astrophysics Data System (ADS)

Corres, J. M.; Matias, I. R.; Goicoechea, J.; Arregui, F. J.; Viegas, D.; Araújo, F. M.; Santos, J. L.

2008-04-01

In this work a new nano-biofilm is proposed for the detection of celiac disease (CD). A long-period fiber grating (LPFG) is used as a transducer and the surface of the fiber is coated with a precursor layer of SiO2-nanospheres using the electrostatic self-assembly technique (ESA). This layer has been designed in order to create a substrate of high porosity where the gliadins could be deposited. Under the presence of specific antibodies antigliadin antibodies (AGA) the refractive index of the overlay changes giving a detectable shift in the resonance wavelength of the LPFG. Concentrations as low as 5 ppm were detected.

Techniques for writing and reading data on an optical disk which include formation of holographic optical gratings in plural locations on the optical disk

NASA Technical Reports Server (NTRS)

Liu, Tsuen-Hsi (Inventor); Psaltis, Demetri (Inventor); Mok, Fai H. (Inventor); Zhou, Gan (Inventor)

2005-01-01

An optical memory for storing and/or reading data on an optical disk. The optical disk incorporates a material in which holographic gratings can be created, and subsequently detected, at plural locations within the disk by an electro-optical head. Creation and detection of holographic gratings with variable diffraction efficiency is possible with the electro-optical head. Multiple holographic gratings can also be created at each one of the plural locations via a beam of light which has a different wavelength or point of focus. These data elements can be read by the electro-optical head using a beam of light sequentially varied in wavelength or point of focus to correspond to the multiple holographic gratings to be recorded.

Research on fiber Bragg grating heart sound sensing and wavelength demodulation method

NASA Astrophysics Data System (ADS)

Zhang, Cheng; Miao, Chang-Yun; Gao, Hua; Gan, Jing-Meng; Li, Hong-Qiang

2010-11-01

Heart sound includes a lot of physiological and pathological information of heart and blood vessel. Heart sound detecting is an important method to gain the heart status, and has important significance to early diagnoses of cardiopathy. In order to improve sensitivity and reduce noise, a heart sound measurement method based on fiber Bragg grating was researched. By the vibration principle of plane round diaphragm, a heart sound sensor structure of fiber Bragg grating was designed and a heart sound sensing mathematical model was established. A formula of heart sound sensitivity was deduced and the theoretical sensitivity of the designed sensor is 957.11pm/KPa. Based on matched grating method, the experiment system was built, by which the excursion of reflected wavelength of the sensing grating was detected and the information of heart sound was obtained. Experiments show that the designed sensor can detect the heart sound and the reflected wavelength variety range is about 70pm. When the sampling frequency is 1 KHz, the extracted heart sound waveform by using the db4 wavelet has the same characteristics with a standard heart sound sensor.

Polarization-sensitive color in butterfly scales: polarization conversion from ridges with reflecting elements.

PubMed

Zhang, Ke; Tang, Yiwen; Meng, Jinsong; Wang, Ge; Zhou, Han; Fan, Tongxiang; Zhang, Di

2014-11-03

Polarization-sensitive color originates from polarization-dependent reflection or transmission, exhibiting abundant light information, including intensity, spectral distribution, and polarization. A wide range of butterflies are physiologically sensitive to polarized light, but the origins of polarized signal have not been fully understood. Here we systematically investigate the colorful scales of six species of butterfly to reveal the physical origins of polarization-sensitive color. Microscopic optical images under crossed polarizers exhibit their polarization-sensitive characteristic, and micro-structural characterizations clarify their structural commonality. In the case of the structural scales that have deep ridges, the polarization-sensitive color related with scale azimuth is remarkable. Periodic ridges lead to the anisotropic effective refractive indices in the parallel and perpendicular grating orientations, which achieves form-birefringence, resulting in the phase difference of two different component polarized lights. Simulated results show that ridge structures with reflecting elements reflect and rotate the incident p-polarized light into s-polarized light. The dimensional parameters and shapes of grating greatly affect the polarization conversion process, and the triangular deep grating extends the outstanding polarization conversion effect from the sub-wavelength period to the period comparable to visible light wavelength. The parameters of ridge structures in butterfly scales have been optimized to fulfill the polarization-dependent reflection for secret communication. The structural and physical origin of polarization conversion provides a more comprehensive perspective on the creation of polarization-sensitive color in butterfly wing scales. These findings show great potential in anti-counterfeiting technology and advanced optical material design.

GaAs/GaAlAs distributed Bragg reflector laser with a focused ion beam, low dose dopant implanted grating

NASA Technical Reports Server (NTRS)

Wu, M. C.; Boenke, M. M.; Wang, S.; Clark, W. M., Jr.; Stevens, E. H.

1988-01-01

The performance of a GaAs/GaAlAs distributed Bragg reflector (DBR) laser using a focused ion beam implanted grating (FIB-DBR) is reported for the first time. Stripes of Si(2+) with a period of 2300 A and a dose about 10 to the 14th/sq cm are directly implanted into the passive large optical cavity layer to provide the distributed feedback. Surface-emitting light from the second-order grating is observed. Threshold current of 110 mA and single DBR mode operation from 20 to 40 C are obtained. The wavelength tuning rate with temperature is 0.8 A/C. The coupling coefficient is estimated to be 15/cm. The results show that FIB technology is practical for distributed feedback and DBR lasers and optoelectronic integrated circuits.

Sub-wavelength efficient polarization filter (SWEP filter)

DOEpatents

Simpson, Marcus L.; Simpson, John T.

2003-12-09

A polarization sensitive filter includes a first sub-wavelength resonant grating structure (SWS) for receiving incident light, and a second SWS. The SWS are disposed relative to one another such that incident light which is transmitted by the first SWS passes through the second SWS. The filter has a polarization sensitive resonance, the polarization sensitive resonance substantially reflecting a first polarization component of incident light while substantially transmitting a second polarization component of the incident light, the polarization components being orthogonal to one another. A method for forming polarization filters includes the steps of forming first and second SWS, the first and second SWS disposed relative to one another such that a portion of incident light applied to the first SWS passes through the second SWS. A method for separating polarizations of light, includes the steps of providing a filter formed from a first and second SWS, shining incident light having orthogonal polarization components on the first SWS, and substantially reflecting one of the orthogonal polarization components while substantially transmitting the other orthogonal polarization component. A high Q narrowband filter includes a first and second SWS, the first and second SWS are spaced apart a distance being at least one half an optical wavelength.

Design of a compact and high sensitive refractive index sensor base on metal-insulator-metal plasmonic Bragg grating.

PubMed

Binfeng, Yun; Guohua, Hu; Ruohu, Zhang; Yiping, Cui

2014-11-17

A nanometric and high sensitive refractive index sensor based on the metal-insulator-metal plasmonic Bragg grating is proposed. The wavelength encoded sensing characteristics of the refractive index sensor were investigated by analyzing its transmission spectrum. The numerical results show that a good linear relationship between the Bragg wavelength and the refractive index of the sensing material can be obtained, which is in accordance with the analytical results very well. A high refractive index sensitivity of 1,488 nm/RIU around Bragg resonance wavelength of 1,550 nm was obtained. Besides, the simulation results show that the sensitivity is depended on the Bragg resonance wavelength and the longer the Bragg resonance wavelength, the higher sensitivity can be obtained. Furthermore, the figure of merit of the refractive index sensor can be greatly increased by introducing a nano-cavity in the proposed plasmonic Bragg grating structure. This work pave the way for high sensitive nanometric refractive index sensor design and application.

Low reflection and field localization over surface plasmon device with subwavelength patterned aluminum film

NASA Astrophysics Data System (ADS)

Yuan, Ying; Peng, Sha; Long, Huabao; Liu, Runhan; Wei, Dong; Zhang, Xinyu; Wang, Haiwei; Xie, Changsheng

2018-02-01

In this paper, we propose a new device composed of patterned sub-wavelength arrays to investigate surface plasmons (SPs) over sub-wavelength metal nano-structures. The device consists of silicon substrate and sub-wavelength patterns fabricated on a layer of aluminum film with nanometer thickness. Each sub-wavelength pattern formed in aluminum film is composed of a basic nano-square and twelve triangles for shaping single nano-pattern, which are uniformly distributed on the four sides of each square. Reflectance spectra and electric field distribution in infrared region are simulated. Numerical simulation results demonstrate that the device can efficiently lower its reflectance in infrared spectrum, and the response frequency can be controlled by only changing the device parameters such as square side length and then triangle vertex angle. Besides, the simulated electric field distribution of the device shows obviously field localization effect at the edges of aluminum film nano-structure. The electric filed around the tips of aluminum triangles is localized into sub-wavelength scale, so as to be beyond the common diffraction limitation. Our work will help to reveal the interesting properties of SPs device, and also bring new prospect of photonic device.

Software Development to Assist in the Processing and Analysis of Data Obtained Using Fiber Bragg Grating Interrogation Systems

NASA Technical Reports Server (NTRS)

Hicks, Rebecca

2009-01-01

A fiber Bragg grating is a portion of a core of a fiber optic strand that has been treated to affect the way light travels through the strand. Light within a certain narrow range of wavelengths will be reflected along the fiber by the grating, while light outside that range will pass through the grating mostly undisturbed. Since the range of wavelengths that can penetrate the grating depends on the grating itself as well as temperature and mechanical strain, fiber Bragg gratings can be used as temperature and strain sensors. This capability, along with the light-weight nature of the fiber optic strands in which the gratings reside, make fiber optic sensors an ideal candidate for flight testing and monitoring in which temperature and wing strain are factors. The purpose of this project is to research the availability of software capable of processing massive amounts of data in both real-time and post-flight settings, and to produce software segments that can be integrated to assist in the task as well.

Fiber-Optic Gratings for Lidar Measurements of Water Vapor

NASA Technical Reports Server (NTRS)

Vann, Leila B.; DeYoung, Russell J.

2006-01-01

Narrow-band filters in the form of phase-shifted Fabry-Perot Bragg gratings incorporated into optical fibers are being developed for differential-absorption lidar (DIAL) instruments used to measure concentrations of atmospheric water vapor. The basic idea is to measure the relative amounts of pulsed laser light scattered from the atmosphere at two nearly equal wavelengths, one of which coincides with an absorption spectral peak of water molecules and the other corresponding to no water vapor absorption. As part of the DIAL measurement process, the scattered light is made to pass through a filter on the way to a photodetector. Omitting other details of DIAL for the sake of brevity, what is required of the filter is to provide a stop band that: Surrounds the water-vapor spectral absorption peaks at a wavelength of 946 nm, Has a spectral width of at least a couple of nanometers, Contains a pass band preferably no wider than necessary to accommodate the 946.0003-nm-wavelength water vapor absorption peak [which has 8.47 pm full width at half maximum (FWHM)], and Contains another pass band at the slightly shorter wavelength of 945.9 nm, where there is scattering of light from aerosol particles but no absorption by water molecules. Whereas filters used heretofore in DIAL have had bandwidths of =300 pm, recent progress in the art of fiber-optic Bragg-grating filters has made it feasible to reduce bandwidths to less than or equal to 20 pm and thereby to reduce background noise. Another benefit of substituting fiber-optic Bragg-grating filters for those now in use would be significant reductions in the weights of DIAL instruments. Yet another advantage of fiber-optic Bragg-grating filters is that their transmission spectra can be shifted to longer wavelengths by heating or stretching: hence, it is envisioned that future DIAL instruments would contain devices for fine adjustment of transmission wavelengths through stretching or heating of fiber-optic Bragg-grating filters nominally designed and fabricated to have transmission wavelengths that, in the absence of stretching, would be slightly too short.

Extreme ultraviolet performance of a multilayer coated high density toroidal grating

NASA Technical Reports Server (NTRS)

Thomas, Roger J.; Keski-Kuha, Ritva A. M.; Neupert, Werner M.; Condor, Charles E.; Gum, Jeffrey S.

1991-01-01

The performance of a multilayer coated diffraction grating has been evaluated at EUV wavelengths both in terms of absolute efficiency and spectral resolution. The application of ten-layer Ir/Si multilayer coating to a 3600-lines/mm blazed toroidal replica grating produced a factor of 9 enhancement in peak efficiency near the design wavelength of about 30 nm in first order, without degrading its excellent quasistigmatic spectral resolution. The measured EUV efficiency peaked at 3.3 percent and was improved over the full spectral range between 25 and 35 nm compared with the premultilayer replica which had a standard gold coating. In addition, the grating's spectral resolution of greater than 5000 was maintained.

Identification of modal strains using sub-microstrain FBG data and a novel wavelength-shift detection algorithm

NASA Astrophysics Data System (ADS)

Anastasopoulos, Dimitrios; Moretti, Patrizia; Geernaert, Thomas; De Pauw, Ben; Nawrot, Urszula; De Roeck, Guido; Berghmans, Francis; Reynders, Edwin

2017-03-01

The presence of damage in a civil structure alters its stiffness and consequently its modal characteristics. The identification of these changes can provide engineers with useful information about the condition of a structure and constitutes the basic principle of the vibration-based structural health monitoring. While eigenfrequencies and mode shapes are the most commonly monitored modal characteristics, their sensitivity to structural damage may be low relative to their sensitivity to environmental influences. Modal strains or curvatures could offer an attractive alternative but current measurement techniques encounter difficulties in capturing the very small strain (sub-microstrain) levels occurring during ambient, or operational excitation, with sufficient accuracy. This paper investigates the ability to obtain sub-microstrain accuracy with standard fiber-optic Bragg gratings using a novel optical signal processing algorithm that identifies the wavelength shift with high accuracy and precision. The novel technique is validated in an extensive experimental modal analysis test on a steel I-beam which is instrumented with FBG sensors at its top and bottom flange. The raw wavelength FBG data are processed into strain values using both a novel correlation-based processing technique and a conventional peak tracking technique. Subsequently, the strain time series are used for identifying the beam's modal characteristics. Finally, the accuracy of both algorithms in identification of modal characteristics is extensively investigated.

Substrate Oxide Layer Thickness Optimization for a Dual-Width Plasmonic Grating for Surface-Enhanced Raman Spectroscopy (SERS) Biosensor Applications

PubMed Central

Bauman, Stephen J.; Brawley, Zachary T.; Darweesh, Ahmad A.; Herzog, Joseph B.

2017-01-01

This work investigates a new design for a plasmonic SERS biosensor via computational electromagnetic models. It utilizes a dual-width plasmonic grating design, which has two different metallic widths per grating period. These types of plasmonic gratings have shown larger optical enhancement than standard single-width gratings. The new structures have additional increased enhancement when the spacing between the metal decreases to sub-10 nm dimensions. This work integrates an oxide layer to improve the enhancement even further by carefully studying the effects of the substrate oxide thickness on the enhancement and reports ideal substrate parameters. The combined effects of varying the substrate and the grating geometry are studied to fully optimize the device’s enhancement for SERS biosensing and other plasmonic applications. The work reports the ideal widths and substrate thickness for both a standard and a dual-width plasmonic grating SERS biosensor. The ideal geometry, comprising a dual-width grating structure atop an optimal SiO2 layer thickness, improves the enhancement by 800%, as compared to non-optimized structures with a single-width grating and a non-optimal oxide thickness. PMID:28665308

Detection of glycoprotein using fiber optic surface plasmon resonance sensors with boronic acid

NASA Astrophysics Data System (ADS)

Wang, Fang; Zhang, Yang; Liu, Zigeng; Qian, Siyu; Gu, Yiying; Jing, Zhenguo; Sun, Changsen; Peng, Wei

2017-04-01

In this paper, we present a tilted fiber Bragg gratings (TFBG) based surface Plasmon resonance (SPR) label-free sensors with boronic acid derivative (ABA-PBA) as receptor molecule to detect glycoprotein with high sensitivity and selectivity. Tilted fiber Bragg gratings (TFBG) as a near infrared wavelengths detecting element can be able to excite a number of cladding modes whose properties can be detected accurately by measuring the variation of transmitted spectra. A 10° TFBG coated by 50nm gold film was manufactured to stimulate surface plasmon resonance on the surface of the sensor. The sensor was loaded with boronic acid derivative as the recognition molecule which has been widely used in various areas for the recognition matrix of diol-containing biomolecules. The proposed TFBG-SPR sensors exhibit good selectivity and repeatability with the protein concentration sensitivity up to 2.867dB/ (mg/ml) and the limit of detection was 2*10-5g/ml.

Low-cost CWDM transmitter package

NASA Astrophysics Data System (ADS)

Bhandarkar, Navin; Castillega, Jaime

2005-03-01

A low-cost coarse-wavelength-division multiplexer (CWDM) transmitter that combines four channels (wavelengths) in the infrared spectrum (~1310 nm) in a small form-factor un-cooled package is demonstrated. The package utilizes precision molded optics to multiplex beams from four grating-outcoupled surface-emitting (GSE) lasers into a single beam suitable for coupling into multimode fiber. This paper summarizes the optical and opto-mechanical design, fabrication and assembly of prototypes, and optical, thermal and electrical measurement results of the prototypes. This unique design enables multiplexing of wavelengths without the use of filters, waveguides, couplers and fiber splicing. Commercial fabrication and alignment technology is used to manufacture the package, resulting in a more robust, reliable and low-cost transmitter. The transmitter package is enabled by the unique characteristics of the long-wavelength GSE laser.

Method to reduce CO.sub.2 to CO using plasmon-enhanced photocatalysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huber, George W.; Upadhye, Aniruddha A.; Kim, Hyung Ju

Described is a method of reducing CO.sub.2 to CO using visible radiation and plasmonic photocatalysts. The method includes contacting CO.sub.2 with a catalyst, in the presence of H.sub.2, wherein the catalyst has plasmonic photocatalytic reductive activity when exposed to radiation having a wavelength between 380 nm and 780 nm. The catalyst, CO.sub.2, and H.sub.2 are exposed to non-coherent radiation having a wavelength between 380 nm and 780 nm such that the catalyst undergoes surface plasmon resonance. The surface plasmon resonance increases the rate of CO.sub.2 reduction to CO as compared to the rate of CO.sub.2 reduction to CO without surfacemore » plasmon resonance in the catalyst.« less

Continuous-wave dual-wavelength operation of a distributed feedback laser diode with an external cavity using a volume Bragg grating

NASA Astrophysics Data System (ADS)

Zheng, Yujin; Sekine, Takashi; Kurita, Takashi; Kato, Yoshinori; Kawashima, Toshiyuki

2018-03-01

We demonstrate continuous-wave dual-wavelength operation of a broad-area distributed feedback (DFB) laser diode with a single external-cavity configuration. This high-power DFB laser has a narrow bandwidth (<0.29 nm) and was used as a single-wavelength source. A volume Bragg grating was used as an output coupler for the external-cavity DFB laser to output another stable wavelength beam with a narrow bandwidth of 0.27 nm. A frequency difference for dual-wavelength operation of 0.88 THz was achieved and an output power of up to 415 mW was obtained. The external-cavity DFB laser showed a stable dual-wavelength operation over the practical current and temperature ranges.

Analytical modeling of conformal mantle cloaks for cylindrical objects using sub-wavelength printed and slotted arrays

NASA Astrophysics Data System (ADS)

Padooru, Yashwanth R.; Yakovlev, Alexander B.; Chen, Pai-Yen; Alù, Andrea

2012-08-01

Following the idea of "cloaking by a surface" [A. Alù, Phys. Rev. B 80, 245115 (2009); P. Y. Chen and A. Alù, Phys. Rev. B 84, 205110 (2011)], we present a rigorous analytical model applicable to mantle cloaking of cylindrical objects using 1D and 2D sub-wavelength conformal frequency selective surface (FSS) elements. The model is based on Lorenz-Mie scattering theory which utilizes the two-sided impedance boundary conditions at the interface of the sub-wavelength elements. The FSS arrays considered in this work are composed of 1D horizontal and vertical metallic strips and 2D printed (patches, Jerusalem crosses, and cross dipoles) and slotted structures (meshes, slot-Jerusalem crosses, and slot-cross dipoles). It is shown that the analytical grid-impedance expressions derived for the planar arrays of sub-wavelength elements may be successfully used to model and tailor the surface reactance of cylindrical conformal mantle cloaks. By properly tailoring the surface reactance of the cloak, the total scattering from the cylinder can be significantly reduced, thus rendering the object invisible over the range of frequencies of interest (i.e., at microwaves and far-infrared). The results obtained using our analytical model for mantle cloaks are validated against full-wave numerical simulations.

Thermal tuning On narrow linewidth fiber laser

NASA Astrophysics Data System (ADS)

Han, Peiqi; Liu, Tianshan; Gao, Xincun; Ren, Shiwei

2010-10-01

At present, people have been dedicated to high-speed and large-capacity optical fiber communication system. Studies have been shown that optical wavelength division multiplexing (WDM) technology is an effective means of communication to increase the channel capacity. Tunable lasers have very important applications in high-speed, largecapacity optical communications, and distributed sensing, it can provide narrow linewidth and tunable laser for highspeed optical communication. As the erbium-doped fiber amplifier has a large gain bandwidth, the erbium-doped fiber laser can be achieved lasing wavelength tunable by adding a tunable filter components, so tunable filter device is the key components in tunable fiber laser.At present, fiber laser wavelength is tuned by PZT, if thermal wavelength tuning is combined with PZT, a broader range of wavelength tuning is appearance . Erbium-doped fiber laser is used in the experiments,the main research is the physical characteristics of fiber grating temperature-dependent relationship and the fiber grating laser wavelength effects. It is found that the fiber laser wavelength changes continuously with temperature, tracking several temperature points observed the self-heterodyne spectrum and found that the changes in spectra of the 3dB bandwidth of less than 1kHz, and therefore the fiber laser with election-mode fiber Bragg grating shows excellent spectral properties and wavelength stability.

Diffraction Revisited: Position of Diffraction Spots upon Rotation of a Transmission Grating

ERIC Educational Resources Information Center

Vollmer, Michael

2005-01-01

Diffraction gratings are often used in the laboratory to determine the wavelength of laser light. What happens to the spots on the screen if the grating is rotated in this set-up? The answer is nontrivial and instructive.

A pulse-front-tilt–compensated streaked optical spectrometer with high throughput and picosecond time resolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katz, J., E-mail: jkat@lle.rochester.edu; Boni, R.; Rivlis, R.

A high-throughput, broadband optical spectrometer coupled to the Rochester optical streak system equipped with a Photonis P820 streak tube was designed to record time-resolved spectra with 1-ps time resolution. Spectral resolution of 0.8 nm is achieved over a wavelength coverage range of 480 to 580 nm, using a 300-groove/mm diffraction grating in conjunction with a pair of 225-mm-focal-length doublets operating at an f/2.9 aperture. Overall pulse-front tilt across the beam diameter generated by the diffraction grating is reduced by preferentially delaying discrete segments of the collimated input beam using a 34-element reflective echelon optic. The introduced delay temporally aligns themore » beam segments and the net pulse-front tilt is limited to the accumulation across an individual sub-element. The resulting spectrometer design balances resolving power and pulse-front tilt while maintaining high throughput.« less

A tunable single-monochromator Raman system based on the supercontinuum laser and tunable filters for resonant Raman profile measurements.

PubMed

Liu, X-L; Liu, H-N; Tan, P-H

2017-08-01

Resonant Raman spectroscopy requires that the wavelength of the laser used is close to that of an electronic transition. A tunable laser source and a triple spectrometer are usually necessary for resonant Raman profile measurements. However, such a system is complex with low signal throughput, which limits its wide application by scientific community. Here, a tunable micro-Raman spectroscopy system based on the supercontinuum laser, transmission grating, tunable filters, and single-stage spectrometer is introduced to measure the resonant Raman profile. The supercontinuum laser in combination with transmission grating makes a tunable excitation source with a bandwidth of sub-nanometer. Such a system exhibits continuous excitation tunability and high signal throughput. Its good performance and flexible tunability are verified by resonant Raman profile measurement of twisted bilayer graphene, which demonstrates its potential application prospect for resonant Raman spectroscopy.

Wavelength stabilized DBR high power diode laser using EBL optical confining grating technology

NASA Astrophysics Data System (ADS)

Paoletti, R.; Codato, S.; Coriasso, C.; Gotta, P.; Meneghini, G.; Morello, G.; De Melchiorre, P.; Riva, E.; Rosso, M.; Stano, A.; Gattiglio, M.

2018-02-01

This paper reports a DBR High Power Diode Laser (DBR-HPDL) realization, emitting up to 10W in the 920 nm range. High spectral purity (90% power in about 0.5 nm), and wavelength stability versus injected current (about 5 times more than standard FP laser) candidates DBR-HPDL as a suitable device for wavelength stabilized pump source, and high brightness applications exploiting Wavelength Division Multiplexing. Key design aspect is a multiple-orders Electron Beam Lithography (EBL) optical confining grating, stabilizing on same wafer multiple wavelengths by a manufacturable and reliable technology. Present paper shows preliminary demonstration of wafer with 3 pitches, generating DBRHPDLs 2.5 nm spaced.

Wavelength interrogation of fiber Bragg grating sensors using tapered hollow Bragg waveguides.

PubMed

Potts, C; Allen, T W; Azar, A; Melnyk, A; Dennison, C R; DeCorby, R G

2014-10-15

We describe an integrated system for wavelength interrogation, which uses tapered hollow Bragg waveguides coupled to an image sensor. Spectral shifts are extracted from the wavelength dependence of the light radiated at mode cutoff. Wavelength shifts as small as ~10  pm were resolved by employing a simple peak detection algorithm. Si/SiO₂-based cladding mirrors enable a potential operational range of several hundred nanometers in the 1550 nm wavelength region for a taper length of ~1  mm. Interrogation of a strain-tuned grating was accomplished using a broadband amplified spontaneous emission (ASE) source, and potential for single-chip interrogation of multiplexed sensor arrays is demonstrated.

Characterization of FBG sensor interrogation based on a FDML wavelength swept laser

PubMed Central

Jung, Eun Joo; Kim, Chang-Seok; Jeong, Myung Yung; Kim, Moon Ki; Jeon, Min Yong; Jung, Woonggyu; Chen, Zhongping

2012-01-01

In this study, we develop an ultra-fast fiber Bragg grating sensor system that is based on the Fourier domain mode-locked (FDML) swept laser. A FDML wavelength swept laser has many advantages compared to the conventional wavelength swept laser source, such as high-speed interrogation, narrow spectral sensitivity, and high phase stability. The newly developed FDML wavelength swept laser shows a superior performance of a high scan rate of 31.3 kHz and a broad scan range of over 70 nm simultaneously. The performance of the grating sensor interrogating system using a FDML wavelength swept laser is characterized in both static and dynamic strain responses. PMID:18852764

Diffraction Gratings for High-Intensity Laser Applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Britten, J

The scattering of light into wavelength-dependent discrete directions (orders) by a device exhibiting a periodic modulation of a physical attribute on a spatial scale similar to the wavelength of light has been the subject of study for over 200 years. Such a device is called a diffraction grating. Practical applications of diffraction gratings, mainly for spectroscopy, have been around for over 100 years. The importance of diffraction gratings in spectroscopy for the measurement of myriad properties of matter can hardly be overestimated. Since the advent of coherent light sources (lasers) in the 1960's, applications of diffraction gratings in spectroscopy havemore » further exploded. Lasers have opened a vast application space for gratings, and apace, gratings have enabled entirely new classes of laser systems. Excellent reviews of the history, fundamental properties, applications and manufacturing techniques of diffraction gratings up to the time of their publication can be found in the books by Hutley (1) and more recently Loewen and Popov (2). The limited scope of this chapter can hardly do justice to such a comprehensive subject, so the focus here will be narrowly limited to characteristics required for gratings suitable for high-power laser applications, and methods to fabricate them. A particular area of emphasis will be on maximally-efficient large-aperture gratings for short-pulse laser generation.« less

760 nm high-performance VCSEL growth and characterization

NASA Astrophysics Data System (ADS)

Rinaldi, Fernando; Ostermann, Johannes M.; Kroner, Andrea; Riedl, Michael C.; Michalzik, Rainer

2006-04-01

High-performance vertical-cavity surface-emitting lasers (VCSELs) with an emission wavelength of approximately 764 nm are demonstrated. This wavelength is very attractive for oxygen sensing. Low threshold currents, high optical output power, single-mode operation, and stable polarization are obtained. Using the surface relief technique and in particular the grating relief technique, we have increased the single-mode output power to more than 2.5mW averaged over a large device quantity. The laser structure was grown by molecular beam epitaxy (MBE) on GaAs (100)-oriented substrates. The devices are entirely based on the AlGaAs mixed compound semiconductor material system. The growth process, the investigations of the epitaxial material together with the device fabrication and characterization are discussed in detail.

Strain dependence of perfluorinated polymer optical fiber Bragg grating measured at different wavelengths

NASA Astrophysics Data System (ADS)

Ishikawa, Ryo; Lee, Heeyoung; Lacraz, Amédée; Theodosiou, Antreas; Kalli, Kyriacos; Mizuno, Yosuke; Nakamura, Kentaro

2018-03-01

We measure the strain dependence of multiple Bragg wavelengths (corresponding to different diffraction orders) of a fiber Bragg grating (FBG) inscribed in a perfluorinated graded-index polymer optical fiber (PFGI-POF) in the wavelength range up to 1550 nm. On the basis of this result, we show that the fractional sensitivity, which has been conventionally used as a wavelength-independent index for fair comparison of the FBG performance measured at different wavelengths, is dependent on wavelength in this range. The reason for this behavior seems to originate from the non-negligible wavelength dependence of refractive index and its strain-dependence coefficient. Using the wavelength dependence of the refractive index already reported for bulk, we deduce the wavelength dependence of the strain coefficient of the refractive index. This information will be a useful archive in implementing PFGI-POF-based strain sensors based on not only FBGs but also Brillouin scattering in the future.

Monolithic single mode interband cascade lasers with wide wavelength tunability

NASA Astrophysics Data System (ADS)

von Edlinger, M.; Weih, R.; Scheuermann, J.; Nähle, L.; Fischer, M.; Koeth, J.; Kamp, M.; Höfling, S.

2016-11-01

Monolithic two-section interband cascade lasers offering a wide wavelength tunability in the wavelength range around 3.7 μm are presented. Stable single mode emission in several wavelength channels was realized using the concept of binary superimposed gratings and two-segment Vernier-tuning. The wavelength selective elements in the two segments were based on specially designed lateral metal grating structures defined by electron beam lithography. A dual-step dry etch process provided electrical separation between the segments. Individual current control of the segments allowed wavelength channel selection as well as continuous wavelength tuning within channels. A discontinuous tuning range extending over 158 nm in up to six discrete wavelength channels was achieved. Mode hop free wavelength tuning up to 14 nm was observed within one channel. The devices can be operated in continuous wave mode up to 30 °C with the output powers of 3.5 mW around room temperature.

High-sensitivity cryogenic temperature sensors using pressurized fiber Bragg gratings

NASA Technical Reports Server (NTRS)

Wu, Meng-Chou; DeHaven, Stanton L.

2006-01-01

Cryogenic temperature sensing was studied using a pressurized fiber Bragg grating (PFBG). The PFBG was obtained by simply applying a small diametric load to a regular fiber Bragg grating (FBG), which was coated with polyimide of a thickness of 11 micrometers. The Bragg wavelength of the PFBG was measured at temperatures from 295 to 4.2 K. A pressure-induced transition occurred at 200 K during the cooling cycle. As a result the temperature sensitivity of the PFBG was found to be nonlinear but reach 24 pm/K below 200 K, more than three times the regular FBG. For the temperature change from 80 K to 10 K, the PFBG has a total Bragg wavelength shift of about 470 pm, 10 times more than the regular FBG. From room temperature to liquid helium temperature the PFBG gives a total wavelength shift of 3.78 nm, compared to the FBG of 1.51 nm. The effect of the coating thickness on the temperature sensitivity of the gratings is also discussed.

High-sensitivity Cryogenic Temperature Sensors using Pressurized Fiber Bragg Gratings

NASA Technical Reports Server (NTRS)

Wu, Meng-Chou; DeHaven, Stanton L.

2006-01-01

Cryogenic temperature sensing was studied using a pressurized fiber Bragg grating (PFBG). The PFBG was obtained by simply applying a small diametric load to a regular fiber Bragg grating (FBG), which was coated with polyimide of a thickness of 11 micrometers. The Bragg wavelength of the PFBG was measured at temperatures from 295 to 4.2 K. A pressure-induced transition occurred at 200 K during the cooling cycle. As a result the temperature sensitivity of the PFBG was found to be nonlinear but reach 24 pm/K below 200 K, more than three times the regular FBG. For the temperature change from 80 K to 10 K, the PFBG has a total Bragg wavelength shift of about 470 pm, 10 times more than the regular FBG. From room temperature to liquid helium temperature the PFBG gives a total wavelength shift of 3.78 nm, compared to the FBG of 1.51 nm. The effect of the coating thickness on the temperature sensitivity of the gratings is also discussed.

Monolithically Integrated Fiber Optic Coupler

DTIC Science & Technology

2013-01-14

tilted Bragg gratings 24 are thermoelectric coolers (TECs) 30 that can modify the pitch of the tilted Bragg gratings 24, thereby changing their...reflective properties at specific wavelengths to provide tunability. Heating or cooling by thermoelectric coolers 30 causes expansion or contraction of...of a different wavelength of light. While thermoelectric coolers are preferred, devices 30 can be any reversible cooling/heating device that is

Ultra-broad range organic solid-state laser from a dye-doped holographic grating quasi-waveguide configuration

NASA Astrophysics Data System (ADS)

Liu, Minghuan; Liu, Yonggang; Peng, Zenghui; Mu, Quanquan; Cao, Zhaoliang; Lu, Xinghai; Ma, Ji; Xuan, Li

2017-08-01

This paper reports the ultra-broad 149.1 nm lasing emission from 573.2 to 722.3 nm using a simple [4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran] (DCM)-doped holographic polymer-dispersed liquid crystal (HPDLC) grating quasi-waveguide configuration by varying the grating period. The lasing emission beams show s-polarization property. The quasi-waveguide structure, which contained the cover glass, the DCM-doped HPDLC grating, the semiconducting polymer film poly[-methoxy-5-(2‧-ethyl-hexyloxy)-1,4-phenylene-vinylene] (MEH-PPV), and the substrate were confirmed to decrease lasing threshold and broaden lasing wavelength. The operational lifetime of the device is 240 000 pulses, which corresponds to an overall laser duration of more than 6 h at a repetition rate of 10 Hz. In addition, the dual-wavelength lasing range from the 8th and 9th order is over 40 nm. The electrical tunability of the dual-wavelength lasing emission is over 1 nm. The experimental results facilitated the decreased lasing threshold and broadened lasing wavelength range of organic solid-state lasers.

Surface leakage current in 12.5  μm long-wavelength HgCdTe infrared photodiode arrays.

PubMed

Qiu, Weicheng; Hu, Weida; Lin, Chun; Chen, Xiaoshuang; Lu, Wei

2016-02-15

Long-wavelength (especially >12  μm) focal plane array (FPA) infrared detection is the cutting edge technique for third-generation infrared remote sensing. However, dark currents, which are very sensitive to the growth of small Cd composition HgCdTe, strongly limits the performance of long wavelength HgCdTe photodiode arrays in FPAs. In this Letter, 12.5 μm long-wavelength Hg_1-xCd_xTe (x≈0.219) infrared photodiode arrays are reported. The variable-area and variable-temperature electrical characteristics of the long-wavelength infrared photodiodes are measured. The characteristics of the extracted zero-bias resistance-area product (l/R₀A) varying with the perimeter-to-area (P/A) ratio clearly show that surface leakage current mechanisms severely limit the overall device performance. A sophisticated model has been developed for investigating the leakage current mechanism in the photodiodes. Modeling of temperature-dependent I-V characteristic indicates that the trap-assisted tunneling effect dominates the dark current at 50 K resulting in nonuniformities in the arrays. The extracted trap density, approximately 10¹³-10¹⁴  cm^-3, with an ionized energy of 30 meV is determined by simulation. The work described in this Letter provides the basic mechanisms for a better understanding of the leakage current mechanism for long-wavelength (>12  μm) HgCdTe infrared photodiode arrays.

Physical principles of monolithic high-contrast gratings

NASA Astrophysics Data System (ADS)

Dems, Maciej

2017-02-01

In this work I present visually the results of a numerical analysis of the transition between classical High-Contrast Gratings (HCGs) and Monolithic High-Contrast Gratings (MHCGs) and I identify the source of the differences between the scatterless reflection peaks and those that either show strong scattering or do not occur in MHCGs. I show that the key property of MHCGs is the independence of the peak reflectivity wavelength on the substrate refractive index, which results from the modal interference inside the grating and the special form of its impedance/admittance matrix. This form of matrix can be obtained for any wavelength and in almost any material system by tuning the geometrical parameters of the grating—its pitch, fill-factor, and height.

An analysis of scattered light in low dispersion IUE spectra

NASA Technical Reports Server (NTRS)

Basri, G.; Clarke, J. T.; Haisch, B. M.

1985-01-01

A detailed numerical simulation of light scattering from the low-resolution grating in the short wavelength spectrograph of the IUE Observatory was developed, in order to quantitatively analyze the effects of scattering on both continuum and line emission spectra. It is found that: (1) the redistribution of light by grating scattering did not appreciably alter either the shape or the absolute flux level of continuum spectra for A-F stars; (2) late-type stellar continua showed a tendency to flatten when observed in scattered light toward the shorter wavelengths; and (3) the effect of grating scattering on emission lines is to decrease measured line intensities by an increasing percentage toward the shorter wavelengths. The spectra obtained from scattering experiments for solar-type and late type stars are reproduced in graphic form.

2-Dimensional beamsteering using dispersive deflectors and wavelength tuning.

PubMed

Chan, Trevor; Myslivets, Evgeny; Ford, Joseph E

2008-09-15

We introduce a 2D beamscanner which is controlled by wavelength tuning. Two passive dispersive devices are aligned orthogonally to deflect the optical beam in two dimensions. We provide a proof of principle demonstration by combining an arrayed waveguide grating with a free space optical grating and using various input sources to characterize the beamscanner. This achieved a discrete 10.3 degrees by 11 degrees output field of view with attainable angles existing on an 8 by 6 grid of directions. The entire range was reached by scanning over a 40 nm wavelength range. We also analyze an improved system combining a virtually imaged phased array with a diffraction grating. This device is much more compact and produces a continuous output scan in one direction while being discrete in the other.

Mathematical Simulation for Integrated Linear Fresnel Spectrometer Chip

NASA Technical Reports Server (NTRS)

Park, Yeonjoon; Yoon, Hargoon; Lee, Uhn; King, Glen C.; Choi, Sang H.

2012-01-01

A miniaturized solid-state optical spectrometer chip was designed with a linear gradient-gap Fresnel grating which was mounted perpendicularly to a sensor array surface and simulated for its performance and functionality. Unlike common spectrometers which are based on Fraunhoffer diffraction with a regular periodic line grating, the new linear gradient grating Fresnel spectrometer chip can be miniaturized to a much smaller form-factor into the Fresnel regime exceeding the limit of conventional spectrometers. This mathematical calculation shows that building a tiny motionless multi-pixel microspectrometer chip which is smaller than 1 cubic millimter of optical path volume is possible. The new Fresnel spectrometer chip is proportional to the energy scale (hc/lambda), while the conventional spectrometers are proportional to the wavelength scale (lambda). We report the theoretical optical working principle and new data collection algorithm of the new Fresnel spectrometer to build a compact integrated optical chip.

Fiber Bragg Grating Based System for Temperature Measurements

NASA Astrophysics Data System (ADS)

Tahir, Bashir Ahmed; Ali, Jalil; Abdul Rahman, Rosly

In this study, a fiber Bragg grating sensor for temperature measurement is proposed and experimentally demonstrated. In particular, we point out that the method is well-suited for monitoring temperature because they are able to withstand a high temperature environment, where standard thermocouple methods fail. The interrogation technologies of the sensor systems are all simple, low cost and effective as well. In the sensor system, fiber grating was dipped into a water beaker that was placed on a hotplate to control the temperature of water. The temperature was raised in equal increments. The sensing principle is based on tracking of Bragg wavelength shifts caused by the temperature change. So the temperature is measured based on the wavelength-shifts of the FBG induced by the heating water. The fiber grating is high temperature stable excimer-laser-induced grating and has a linear function of wavelength-temperature in the range of 0-285°C. A dynamic range of 0-285°C and a sensitivity of 0.0131 nm/°C almost equal to that of general FBG have been obtained by this sensor system. Furthermore, the correlation of theoretical analysis and experimental results show the capability and feasibility of the purposed technique.

Fiber Bragg Grating Filter High Temperature Sensors

NASA Technical Reports Server (NTRS)

Lyons, Donald R.; Brass, Eric D.; Pencil, Eric (Technical Monitor)

2001-01-01

We present a scaled-down method for determining high temperatures using fiber-based Bragg gratings. Bragg gratings are distributed along the length of the optical fiber, and have high reflectivities whenever the optical wavelength is twice the grating spacing. These spatially distinct Bragg regions (located in the core of a fiber) are sensitive to local temperature changes. Since these fibers are silica-based they are easily affected by localized changes in temperature, which results in changes to both the grating spacing and the wavelength reflectivity. We exploit the shift in wavelength reflectivity to measure the change in the local temperature. Note that the Bragg region (sensing area) is some distance away from where the temperature is being measured. This is done so that we can measure temperatures that are much higher than the damage threshold of the fiber. We do this by affixing the fiber with the Bragg sensor to a material with a well-known coefficient of thermal expansion, and model the heat gradient from the region of interest to the actual sensor. The research described in this paper will culminate in a working device as well as be the second portion of a publication pending submission to Optics Letters.

Post-inscription tuning of multicore fiber Bragg gratings

NASA Astrophysics Data System (ADS)

Lindley, Emma Y.; Min, Seong-sik; Leon-Saval, Sergio G.; Bland-Hawthorn, Joss

2016-07-01

Fiber Bragg gratings are used in astronomy for their ability to suppress narrow atmospheric emission lines of temporally varying brightness before the light is dispersed. These gratings can only operate in a single-mode fiber as the suppressed wavelength depends on mode velocity in the core. Recent experiments with fibers containing multiple single-moded cores have demonstrated the potential for inscribing identical gratings across all cores in a single pass. We have already improved the uniformity of gratings in 7-core fibers via modifications to the writing process; further progress can be achieved by tuning the gratings of the outer and inner cores relative to one another. Our eventual goal is to make the entire fiber suppress one wavelength to a depth of 30 dB or greater. By coating the fiber in a heat-conductive material with a high expansion coefficient, we can examine the effects of temperature and strain on the spectral response of each core. In this paper we present methods and results from experiments concerning the post-write tuning of gratings in multicore fibers.

The SALT HRS Spectrograph

NASA Astrophysics Data System (ADS)

Tyas, Luke Martin Graham

2012-05-01

SALT HRS (Southern African Large Telescope High Resolution Échelle Spectrograph) is a high-resolution, high-efficiency spectrograph for the 11m SALT telescope in Sutherland, South Africa. The initial optical design work was performed at the University of Canterbury, New Zealand. Revisions to the concept, the mechanical design, manufacture, assembly and testing have been handled by the Centre for Advanced Instrumentation, at Durham University in the United Kingdom. SALT HRS is a fibre-fed échelle grating spectrograph with four operational modes: low-, medium- and high-resolution and high-stability modes, having spectral resolutions of R≈16000, 37000, 67000 and 67000 respectively over a wavelength range of 370-890nm. The instrument is of a dual channel, 'white pupil' design, in which the primary mirror acts to collimate light onto a single R4 échelle grating, and also to focus dispersed light to an intermediate focus. A dichroic beam-splitter separates the dispersed light into two separate spectral channels. Spherical pupil mirrors transfer the separated beams via a fold mirror to two wavelength-specific volume-phase holographic gratings (VPHGs) used as cross-dispersers. Cross-dispersed spectra are then imaged by two fully dioptric camera systems onto optimized CCD detectors. This thesis presents the results of the laboratory testing and specification of several critical sub-systems of SALT HRS, as well as the development of key software tools for the design verification and operation at the telescope. In Chapter 1 we first review the technical development of high-resolution spectroscopy and its specific implementation in SALT HRS. In Chapter 2 we develop a comprehensive throughput model of the entire system based on a combination of as-built performance and specific throughput measurements in the laboratory. This is used to make some specific predictions for the on-sky performance of SALT HRS and the magnitude limits for science targets. We also present a graphical exposure time calculator based on these measurements which can be used by an astronomer to plan their observations with SALT HRS. Chapter 3 contains a detailed treatise on the optical fibre system of SALT HRS. Considerations for the use of optical fibres in astronomy are provided, as are details of an optional double scrambler, and the various instrument fibre modes. Extensive measurements of focal ratio degradation (FRD) are also presented, with testing of input beam speed; wavelength; fibre bending; variable pupil mirror illumination; and vacuum tank pressure dependency. The systems for fibre management are reviewed, as is the fibre bundle assembly process. Testing of two further sub-systems is described in Chapter 4. Firstly the long-term stability of the mirror mounting mechanisms is determined. The advantages of cross-dispersion of échelle spectra using volume-phase holographic gratings are then discussed, and the results of diffraction efficiency measurements are given for both red and blue channel gratings. Modern CCD technologies are examined in Chapter 5, and the blue detector is experimentally characterized using photon transfer and quantum efficiency curves. It is also used for an investigation into cosmic ray events in CCDs. Results from shielding the detector using lead are described, as is an attempt to distinguish the source of the events based on their morphology. Finally, Chapter 6 deals with the handling of data produced by SALT HRS. Methods of wavelength calibration of the spectra are discussed, including the use of Thorium-Argon lamps and an iodine absorption cell. The implementation of a Python based quick-look data reduction pipeline is reviewed, with a description of the processes performed. A summary of the thesis is given in Chapter 7.

Variable magnification variable dispersion glancing incidence imaging x-ray spectroscopic telescope

NASA Technical Reports Server (NTRS)

Hoover, Richard B. (Inventor)

1991-01-01

A variable magnification variable dispersion glancing incidence x-ray spectroscopic telescope capable of multiple high spatial revolution imaging at precise spectral lines of solar and stellar x-ray and extreme ultraviolet radiation sources includes a pirmary optical system which focuses the incoming radiation to a primary focus. Two or more rotatable carries each providing a different magnification are positioned behind the primary focus at an inclination to the optical axis, each carrier carrying a series of ellipsoidal diffraction grating mirrors each having a concave surface on which the gratings are ruled and coated with a mutlilayer coating to reflect by diffraction a different desired wavelength. The diffraction grating mirrors of both carriers are segments of ellipsoids having a common first focus coincident with the primary focus. A contoured detector such as an x-ray sensitive photogrpahic film is positioned at the second respective focus of each diffraction grating so that each grating may reflect the image at the first focus to the detector at the second focus. The carriers are selectively rotated to position a selected mirror for receiving radiation from the primary optical system, and at least the first carrier may be withdrawn from the path of the radiation to permit a selected grating on the second carrier to receive radiation.

Variable magnification variable dispersion glancing incidence imaging x ray spectroscopic telescope

NASA Technical Reports Server (NTRS)

Hoover, Richard (Inventor)

1990-01-01

A variable magnification variable dispersion glancing incidence x ray spectroscopic telescope capable of multiple high spatial revolution imaging at precise spectral lines of solar and stellar x ray and extreme ultraviolet radiation sources includes a primary optical system which focuses the incoming radiation to a primary focus. Two or more rotatable carriers each providing a different magnification are positioned behind the primary focus at an inclination to the optical axis, each carrier carrying a series of ellipsoidal diffraction grating mirrors each having a concave surface on which the gratings are ruled and coated with a multilayer coating to reflect by diffraction a different desired wavelength. The diffraction grating mirrors of both carriers are segments of ellipsoids having a common first focus coincident with the primary focus. A contoured detector such as an x ray sensitive photographic film is positioned at the second respective focus of each diffraction grating so that each grating may reflect the image at the first focus to the detector at the second focus. The carriers are selectively rotated to position a selected mirror for receiving radiation from the primary optical system, and at least the first carrier may be withdrawn from the path of the radiation to permit a selected grating on the second carrier to receive radiation.

Flattop wideband wavelength converters based on cascaded sum and difference-frequency generation using step-chirped gratings

NASA Astrophysics Data System (ADS)

Tehranchi, Amirhossein; Kashyap, Raman

2011-03-01

We investigate the role of step-chirped gratings (SCG) for flattening of conversion efficiency response and enhancing the pump bandwidth in cascaded sum and difference frequency generation (SFG + DFG) with a large pump wavelength difference. To obtain a flat response with maximum efficiency, using SCG instead of uniform grating with the same length, the appropriate critical period shifts are presented for the reasonable number of sections and chirp steps feasible for fabrication. Furthermore, it is shown that adding the section numbers for SCG structure increases the pump bandwidth.

High-speed two-dimensional laser scanner based on Bragg gratings stored in photothermorefractive glass.

PubMed

Yaqoob, Zahid; Arain, Muzammil A; Riza, Nabeel A

2003-09-10

A high-speed free-space wavelength-multiplexed optical scanner with high-speed wavelength selection coupled with narrowband volume Bragg gratings stored in photothermorefractive (PTR) glass is reported. The proposed scanner with no moving parts has a modular design with a wide angular scan range, accurate beam pointing, low scanner insertion loss, and two-dimensional beam scan capabilities. We present a complete analysis and design procedure for storing multiple tilted Bragg-grating structures in a single PTR glass volume (for normal incidence) in an optimal fashion. Because the scanner design is modular, many PTR glass volumes (each having multiple tilted Bragg-grating structures) can be stacked together, providing an efficient throughput with operations in both the visible and the infrared (IR) regions. A proof-of-concept experimental study is conducted with four Bragg gratings in independent PTR glass plates, and both visible and IR region scanner operations are demonstrated.

Chirped Grating Tunable Lasers for the Infrared Molecular Fingerprint Spectral Region

DTIC Science & Technology

2013-09-01

lasers with chirped gratings and compare both normal DFB (pump stripe perpendicular to grating) and -DFB (pump stripe perpendicular to facets...structure. Because the period of grating increases gradually laterally, wavelength tuning is implemented by shifting pump stripe to different positions on...tilted with respect to facets and adjusting the pump stripe normal to the grating. Continuous tuning of 30 nm around 3.1 µm with 320 mW single facet

Reflection characterization of nano-sized dielectric structure in Morpho butterfly wings

NASA Astrophysics Data System (ADS)

Zhu, Dong

2017-10-01

Morpho butterflies living in Central and South America are well-known for their structural-colored blue wings. The blue coloring originates from the interaction of light with nano-sized dielectric structures that are equipped on the external surface of scales covering over their wings. The high-accuracy nonstandard finite-difference time domain (NS-FDTD) method is used to investigate the reflection characterization from the nanostructures. In the NS-FDTD calculation, a computational model is built to mimic the actual tree-like multilayered structures wherever possible using the hyperbolic tangent functions. It is generally known that both multilayer interference and diffraction grating phenomena can occur when light enters the nano-sized multilayered structure. To answer the question that which phenomenon is mainly responsible for the blue coloring, the NS-FDTD calculation is performed under various incidence angles at wavelengths from 360 to 500 nm. The calculated results at one incident wavelength under different incidence angles are visualized in a two-dimensional mapping image, where horizontal and vertical axes are incidence and reflection angles, respectively. The images demonstrate a remarkable transition from a ring-like pattern at shorter wavelengths to a retro-reflection pattern at longer wavelengths. To clarify the origin of the pattern transition, the model is separated into several simpler parts and compared their mapping images with the theoretical diffraction calculations. It can be concluded that the blue coloring at longer wavelengths is mainly caused by the cooperation of multilayer interference and retro-reflection while the effect of diffraction grating is predominant at shorter wavelengths.

Full-mesh T- and O-band wavelength router based on arrayed waveguide gratings.

PubMed

Idris, Nazirul A; Yoshizawa, Katsumi; Tomomatsu, Yasunori; Sudo, Makoto; Hajikano, Tadashi; Kubo, Ryogo; Zervas, Georgios; Tsuda, Hiroyuki

2016-01-11

We propose an ultra-broadband full-mesh wavelength router supporting the T- and O-bands using 3 stages of cascaded arrayed waveguide gratings (AWGs). The router architecture is based on a combination of waveband and channel routing by coarse and fine AWGs, respectively. We fabricated several T-band-specific silica-based AWGs and quantum dot semiconductor optical ampliers as part of the router, and demonstrated 10 Gbps data transmission for several wavelengths throughout a range of 7.4 THz. The power penalties were below 1 dB. Wavelength routing was also demonstrated, where tuning time within a 9.4-nm-wide waveband was below 400 ms.

Optical Fiber Thermometer Based on Fiber Bragg Gratings

NASA Astrophysics Data System (ADS)

Rosli, Ekbal Bin; Mohd. Noor, Uzer

2018-03-01

Fiber Bragg grating has generated much interest in use as sensors to measure strain, temperature, and other physical parameters. It also the most common component used to develop this sensor with the advantages of simple, intrinsic sensing elements, electrically passive operation, EMI immunity, high sensitivity, compact size and potentially low cost [6]. This paper reports the design of an optical fiber thermometer based on fiber Bragg gratings. The system was developed for detecting temperature and strain by monitoring the shift of Bragg wavelength. The shifting of Bragg wavelength is used to indicate the temperature and strain due to the change in the surrounding temperature and strain. When the temperature and strain reach the exact wavelength level of the system, the temperature and strain value will display on the Arduino liquid crystal display (LCD). The optical fiber will provide the broadband light source and after passing the FBG the Bragg wavelength into the optical spectrum analyzer (OSA). The system is based on FBG as a physical quantity sensor. The temperatures measured is taken from the water bath and that of the strain is provided by amount of slotted mass used. The outcome of this project is to characterize the Bragg wavelength shifting from the fiber Bragg grating output. As the conclusion, this project provides an efficient optical fiber thermometer in measuring temperature and strain in order to replace the use of conventional electrical instruments.

Uniform spacing interrogation of a Fourier domain mode-locked fiber Bragg grating sensor system using a polarization-maintaining fiber Sagnac interferometer

PubMed Central

Lee, Hwi Don; Jung, Eun Joo; Jeong, Myung Yung; Chen, Zhongping; Kim, Chang-Seok

2014-01-01

A novel linearized interrogation method is presented for a Fourier domain mode-locked (FDML) fiber Bragg grating (FBG) sensor system. In a high speed regime over several tens of kHz modulations, a sinusoidal wave is available to scan the center wavelength of an FDML wavelength-swept laser, instead of a conventional triangular wave. However, sinusoidal wave modulation suffers from an exaggerated non-uniform wavelength-spacing response in demodulating the time-encoded parameter to the absolute wavelength. In this work, the calibration signal from a polarization-maintaining fiber Sagnac interferometer shares the FDML wavelength-swept laser for FBG sensors to convert the time-encoded FBG signal to the wavelength-encoded uniform-spacing signal. PMID:24489440

An analysis of the surface-normal coupling efficiency of a metal grating coupler embedded in a Scotch tape optical waveguide

NASA Astrophysics Data System (ADS)

Barrios, Carlos Angulo; Canalejas-Tejero, Víctor

2017-01-01

The coupling efficiency at normal incidence of recently demonstrated aluminum grating couplers integrated in flexible Scotch tape waveguides has been analyzed theoretically and experimentally. Finite difference time domain (FDTD) and rigorously coupled wave analysis (RCWA) methods have been used to optimize the dimensions (duty cycle and metal thickness) of Scotch tape-embedded 1D Al gratings for maximum coupling at 635 nm wavelength. Good dimension and tape refractive index tolerances are predicted. FDTD simulations reveal the incident beam width and impinging position (alignment) values that avoid rediffraction and thus maximize the coupling efficiency. A 1D Al diffraction grating integrated into a Scotch tape optical waveguide has been fabricated and characterized. The fabrication process, based on pattern transfer, has been optimized to allow complete Al grating transfer onto the Scotch tape waveguide. A maximum coupling efficiency of 20% for TM-polarized normal incidence has been measured, which is in good agreement with the theoretical predictions. The measured coupling efficiency is further increased up to 28% for TM polarization under oblique incidence. Temperature dependence measurements have been also achieved and related to the simulations results and fabrication procedure.

Wavelength independent interferometer

NASA Technical Reports Server (NTRS)

Hochberg, Eric B. (Inventor); Page, Norman A. (Inventor)

1991-01-01

A polychromatic interferometer utilizing a plurality of parabolic reflective surfaces to properly preserve the fidelity of light wavefronts irrespective of their wavelengths as they pass through the instrument is disclosed. A preferred embodiment of the invention utilizes an optical train which comprises three off-axis parabolas arranged in conjunction with a beam-splitter and a reference mirror to form a Twyman-Green interferometer. An illumination subsystem is provided and comprises a pair of lasers at different preselected wavelengths in the visible spectrum. The output light of the two lasers is coaxially combined by means of a plurality of reflectors and a grating beam combiner to form a single light source at the focal point of the first parabolic reflection surface which acts as a beam collimator for the rest of the optical train. By using visible light having two distinct wavelengths, the present invention provides a long equivalent wavelength interferogram which operates at visible light wherein the effective wavelength is equal to the product of the wavelengths of the two laser sources divided by their difference in wavelength. As a result, the invention provides the advantages of what amounts to long wavelength interferometry but without incurring the disadvantage of the negligible reflection coefficient of the human eye to long wavelength frequencies which would otherwise defeat any attempt to form an interferogram at that low frequency using only one light source.

Wavelength selection by dielectric-loaded plasmonic components

NASA Astrophysics Data System (ADS)

Holmgaard, Tobias; Chen, Zhuo; Bozhevolnyi, Sergey I.; Markey, Laurent; Dereux, Alain; Krasavin, Alexey V.; Zayats, Anatoly V.

2009-02-01

Fabrication, characterization, and modeling of waveguide-ring resonators and in-line Bragg gratings for wavelength selection in the telecommunication range are reported utilizing dielectric-loaded surface plasmon-polariton waveguides. The devices were fabricated by depositing subwavelength-sized polymer ridges on a smooth gold film using industrially compatible large-scale UV photolithography. We demonstrate efficient and compact wavelength-selective filters, including waveguide-ring resonators with an insertion loss of ˜2 dB and a footprint of only 150 μm2 featuring narrow bandwidth (˜20 nm) and high contrast (˜13 dB) features in the transmission spectrum. The performance of the components is found in good agreement with the results obtained by full vectorial three-dimensional finite element simulations.

Experimental investigation of colorless ONU employing superstructured fiber Bragg gratings in WDM/OCDMA-PON

NASA Astrophysics Data System (ADS)

Wang, Dawei; Cheng, Liang; Chen, Biao

2009-11-01

Colorless optical network unit (ONU) is a very important concept for the wavelength division multiplexing (WDM) based passive optical networks (PON). We present a novel scheme to construct non-wavelength-selective ONUs in WDM/OCDMA-PON by making use of the broad spectrum band of superstructure fiber Bragg gratings (SSFBGs). The experiment results reveal that the spectrum-sliced encoded signals from different wavelength channels can be successfully decoded with the same SSFBGs, and thus the proposed colorless ONU scheme is proved to be feasible.

Long period grating refractive-index sensor: optimal design for single wavelength interrogation.

PubMed

Kapoor, Amita; Sharma, Enakshi K

2009-11-01

We report the design criteria for the use of long period gratings (LPGs) as refractive-index sensors with output power at a single interrogating wavelength as the measurement parameter. The design gives maximum sensitivity in a given refractive-index range when the interrogating wavelength is fixed. Use of the design criteria is illustrated by the design of refractive-index sensors for specific application to refractive-index variation of a sugar solution with a concentration and detection of mole fraction of xylene in heptane (paraffin).

Design and Performance of Micro-Spec, an Ultra Compact High-Sensitivity Far-Infrared Spectrometer for SPICA

NASA Technical Reports Server (NTRS)

Cataldo, Giuseppe; Moseley, S. H.; Hsieh, W.-T.; Huang, W,-C,; Stevenson, T. R.; Wollak, E. J.

2012-01-01

Micro-Spec (u-Spec) is a high-performance spectrometer working in the 250-700-micrometer wavelength range, whose modules use low-loss superconducting microstrip transmission lines on a single 4-inch-diameter silicon wafer. Creating the required phase delays in transmission lines rather than free space allows such an instrument to have, in principle, the performance of a meter-scale grating spectrometer. Such a dramatic size reduction enables classes of instruments for space that would be impossible with conventional technologies. This technology can dramatically enhance the long-wavelength capability of the space infrared telescope for cosmology and astrophysics SPICA. u-Spec is analogous to a grating spectrometer. The phase retardation generated by the reflection from the grating grooves is instead produced by propagation through a transmission line. The power received by a broadband antenna is progressively divided by binary microstrip power dividers, and the required phase delays are generated by different lengths of microstrip transmission lines. by arranging these outputs along a circular focal surface, the analog of a Rowland spectrometer can he created. The procedure to optimize the Micro-Spec design is based on the stigmatization and minimization of the light path function in a two-dimensional hounded region, which results in an optimized geometry arrangement with three stigmatic points. In addition, in order to optimize the overall efficiency of the instrument, the emitters are directed to the center of the focal surface. The electric field amplitude and phase as well as the power transmitted and absorbed throughout the region are analyzed. Measurements are planned in late summer to validate the designs.

Diffraction-based optical correlator

NASA Technical Reports Server (NTRS)

Spremo, Stevan M. (Inventor); Fuhr, Peter L. (Inventor); Schipper, John F. (Inventor)

2005-01-01

Method and system for wavelength-based processing of a light beam. A light beam, produced at a chemical or physical reaction site and having at least first and second wavelengths, ?1 and ?2, is received and diffracted at a first diffraction grating to provide first and second diffracted beams, which are received and analyzed in terms of wavelength and/or time at two spaced apart light detectors. In a second embodiment, light from first and second sources is diffracted and compared in terms of wavelength and/or time to determine if the two beams arise from the same source. In a third embodiment, a light beam is split and diffracted and passed through first and second environments to study differential effects. In a fourth embodiment, diffracted light beam components, having first and second wavelengths, are received sequentially at a reaction site to determine whether a specified reaction is promoted, based on order of receipt of the beams. In a fifth embodiment, a cylindrically shaped diffraction grating (uniform or chirped) is rotated and translated to provide a sequence of diffracted beams with different wavelengths. In a sixth embodiment, incident light, representing one or more symbols, is successively diffracted from first and second diffraction gratings and is received at different light detectors, depending upon the wavelengths present in the incident light.

Analysis of a multi-wavelength multi-camera phase-shifting profilometric system for real-time operation

NASA Astrophysics Data System (ADS)

Stoykova, Elena; Gotchev, Atanas; Sainov, Ventseslav

2011-01-01

Real-time accomplishment of a phase-shifting profilometry through simultaneous projection and recording of fringe patterns requires a reliable phase retrieval procedure. In the present work we consider a four-wavelength multi-camera system with four sinusoidal phase gratings for pattern projection that implements a four-step algorithm. Successful operation of the system depends on overcoming two challenges which stem out from the inherent limitations of the phase-shifting algorithm, namely the demand for a sinusoidal fringe profile and the necessity to ensure equal background and contrast of fringes in the recorded fringe patterns. As a first task, we analyze the systematic errors due to the combined influence of the higher harmonics and multi-wavelength illumination in the Fresnel diffraction zone considering the case when the modulation parameters of the four gratings are different. As a second task we simulate the system performance to evaluate the degrading effect of the speckle noise and the spatially varying fringe modulation at non-uniform illumination on the overall accuracy of the profilometric measurement. We consider the case of non-correlated speckle realizations in the recorded fringe patterns due to four-wavelength illumination. Finally, we apply a phase retrieval procedure which includes normalization, background removal and denoising of the recorded fringe patterns to both simulated and measured data obtained for a dome surface.

Efficient flattop ultra-wideband wavelength converters based on double-pass cascaded sum and difference frequency generation using engineered chirped gratings.

PubMed

Tehranchi, Amirhossein; Morandotti, Roberto; Kashyap, Raman

2011-11-07

High-efficiency ultra-broadband wavelength converters based on double-pass quasi-phase-matched cascaded sum and difference frequency generation including engineered chirped gratings in lossy lithium niobate waveguides are numerically investigated and compared to the single-pass counterparts, assuming a large twin-pump wavelength difference of 75 nm. Instead of uniform gratings, few-section chirped gratings with the same length, but with a small constant period change among sections with uniform gratings, are proposed to flatten the response and increase the mean efficiency by finding the common critical period shift and minimum number of sections for both single-pass and double-pass schemes whilst for the latter the efficiency is remarkably higher in a low-loss waveguide. It is also verified that for the same waveguide length and power, the efficiency enhancement expected due to the use of the double-pass scheme instead of the single-pass one, is finally lost if the waveguide loss increases above a certain value. For the double-pass scheme, the criteria for the design of the low-loss waveguide length, and the assignment of power in the pumps to achieve the desired efficiency, bandwidth and ripple are presented for the optimum 3-section chirped-gratings-based devices. Efficient conversions with flattop bandwidths > 84 nm for lengths < 3 cm can be obtained.

High-efficiency volume holograms recording on acrylamide and N,N'methylene-bis-acrylamide photopolymer with pulsed laser

NASA Astrophysics Data System (ADS)

Gallego, Sergi; Ortuno, Manuel; Garcia, Celia; Neipp, Cristian; Belendez, Augusto; Pascual, Inmaculada V.

2004-09-01

In order to achieve higher diffraction efficiencies of the volume gratings stored in acrylamide based photopolymer, we introduce in the photopolymer a crosslinker (N,N'methylene-bis-acrylamide). The presence of this component increase the rate polymerization and the modulation of refraction index. The recording was performed using a holographic copying process. The original was a grating of 1000 lines/mm processed using silver halide sensitized gelatine, with diffraction efficiency around 50 % for a reconstruction wavelength of 532 nm. The main beam was split in two secondary beams by the original grating, with an intensity ratio 1:1. The results obtained using the new composition of material are compared with the composition without crosslinker. In the other hand the no linearity of the material's response is also studied comparing the energetic sensitivity, diffraction efficiencies and index modulation of gratings recorded with pulsed and continuous laser. This study is realized fitting the angular scan of each grating using Kogelnik's theory. The gratings are recorded with wavelength of 532 nm when pulsed exposure is used and with wavelength of 514 nm when continues exposure is used. Using pulsed laser at 532 nm the photopolymer without crosslinker presents the diffraction efficiencies lightly smaller than 60%. In the other hand when the crosslinker has been introduced in photopolymer composition, the diffraction efficiencies achieves are higher than 85 %.

Metrology of variable-line-spacing x-ray gratings using the APS Long Trace Profiler

NASA Astrophysics Data System (ADS)

Sheung, Janet; Qian, Jun; Sullivan, Joseph; Thomasset, Muriel; Manton, Jonathan; Bean, Sunil; Takacs, Peter; Dvorak, Joseph; Assoufid, Lahsen

2017-09-01

As resolving power targets have increased with each generation of beamlines commissioned in synchrotron radiation facilities worldwide, diffraction gratings are quickly becoming crucial optical components for meeting performance targets. However, the metrology of variable-line-spacing (VLS) gratings for high resolution beamlines is not widespread; in particular, no metrology facility at any US DOE facility is currently equipped to fully characterize such gratings. To begin to address this issue, the Optics Group at the Advanced Photon Source at Argonne, in collaboration with SOLEIL and with support from Brookhaven National Laboratory (BNL), has developed an alternative beam path addition to the Long Trace Profiler (LTP) at Argonne's Advanced Photon Source. This significantly expands the functionality of the LTP not only to measure mirrors surface slope profile at normal incidence, but also to characterize the groove density of VLS diffraction gratings in the Littrow incidence up to 79°, which covers virtually all diffraction gratings used at synchrotrons in the first order. The LTP light source is a 20mW HeNe laser, which yields enough signal for diffraction measurements to be performed on low angle blazed gratings optimized for soft X-ray wavelengths. We will present the design of the beam path, technical requirements for the optomechanics, and our data analysis procedure. Finally, we discuss challenges still to be overcome and potential limitations with use of the LTP to perform metrology on diffraction gratings.

Pressure Effects on the Temperature Sensitivity of Fiber Bragg Gratings

NASA Technical Reports Server (NTRS)

Wu, Meng-Chou

2012-01-01

A 3-dimensional physical model was developed to relate the wavelength shifts resulting from temperature changes of fiber Bragg gratings (FBGs) to the thermal expansion coefficients, Young s moduli of optical fibers, and thicknesses of coating polymers. Using this model the Bragg wavelength shifts were calculated and compared with the measured wavelength shifts of FBGs with various coating thickness for a finite temperature range. There was a discrepancy between the calculated and measured wavelength shifts. This was attributed to the refractive index change of the fiber core by the thermally induced radial pressure. To further investigate the pressure effects, a small diametric load was applied to a FBG and Bragg wavelength shifts were measured over a temperature range of 4.2 to 300K.

Development and operation of a high-throughput accurate-wavelength lens-based spectrometer a)

DOE PAGES

Bell, Ronald E.

2014-07-11

A high-throughput spectrometer for the 400-820 nm wavelength range has been developed for charge exchange recombination spectroscopy or general spectroscopy. A large 2160 mm -1 grating is matched with fast f /1.8 200 mm lenses, which provide stigmatic imaging. A precision optical encoder measures the grating angle with an accuracy ≤ 0.075 arc seconds. A high quantum efficiency low-etaloning CCD detector allows operation at longer wavelengths. A patch panel allows input fibers to interface with interchangeable fiber holders that attach to a kinematic mount behind the entrance slit. The computer-controlled hardware allows automated control of wavelength, timing, f-number, automated datamore » collection, and wavelength calibration.« less

Fabrication of 200 nanometer period centimeter area hard x-ray absorption gratings by multilayer deposition

PubMed Central

Lynch, S K; Liu, C; Morgan, N Y; Xiao, X; Gomella, A A; Mazilu, D; Bennett, E E; Assoufid, L; de Carlo, F; Wen, H

2012-01-01

We describe the design and fabrication trials of x-ray absorption gratings of 200 nm period and up to 100:1 depth-to-period ratios for full-field hard x-ray imaging applications. Hard x-ray phase-contrast imaging relies on gratings of ultra-small periods and sufficient depth to achieve high sensitivity. Current grating designs utilize lithographic processes to produce periodic vertical structures, where grating periods below 2.0 μm are difficult due to the extreme aspect ratios of the structures. In our design, multiple bilayers of x-ray transparent and opaque materials are deposited on a staircase substrate, and mostly on the floor surfaces of the steps only. When illuminated by an x-ray beam horizontally, the multilayer stack on each step functions as a micro-grating whose grating period is the thickness of a bilayer. The array of micro-gratings over the length of the staircase works as a single grating over a large area when continuity conditions are met. Since the layers can be nanometers thick and many microns wide, this design allows sub-micron grating periods and sufficient grating depth to modulate hard x-rays. We present the details of the fabrication process and diffraction profiles and contact radiography images showing successful intensity modulation of a 25 keV x-ray beam. PMID:23066175

Evaluation of gratings for the Extreme Ultraviolet Explorer

NASA Technical Reports Server (NTRS)

Mrowka, Stan; Martin, Chris; Bowyer, Stuart; Malina, Roger F.

1986-01-01

Extensive grating calibration facilities have been developed at the Space Sciences Laboratory at Berkley, which are now being used for the evaluation of the gratings for the spectrometer on the Extreme Ultraviolet Explorer. Measurements of efficiency scattering and imaging quality can be made at wavelengths from 44A to 2500A.

Optically Tuned Fiber Gratings

DTIC Science & Technology

1998-03-01

why we use a bulk polarization beam splitter . The fibre grating length was 50 cm with centre wavelength at 1550 nm. Fig.8 shows results of the...characteristics of glasses with enhanced non -linearity. In accordance with the specification, a fiber grating should be tuned within the range of 1...intensity pulse and has successfully demonstrated optically-tuned fiber grating. 19980617 115 14. SUBJECT TERMS Fibre Optics, Non -linear Optical

Fibre gratings for high temperature sensor applications

NASA Astrophysics Data System (ADS)

Canning, J.; Sommer, K.; Englund, M.

2001-07-01

Phosphosilicate fibre gratings can be stabilized at temperatures in excess of 500 °C for sensor applications by optimizing thermal and UV presensitization recipes. Furthermore, the use of 193 nm presensitization prevents the formation of OH absorption bands, extending the use of fibre gratings across the entire wavelength spectrum. Gratings for operation at 700 °C retaining up to 70% reflectivity after 30 min are demonstrated.

Low threshold optical bistability in one-dimensional gratings based on graphene plasmonics.

PubMed

Guo, Jun; Jiang, Leyong; Jia, Yue; Dai, Xiaoyu; Xiang, Yuanjiang; Fan, Dianyuan

2017-03-20

Optical bistability of graphene surface plasmon is investigated numerically, using grating coupling method at normal light incidence. The linear surface plasmon resonance is strongly dependent on Femi-level of graphene, hence it can be tuned in a large wavelength range. Due to the field enhancement of graphene surface plasmon resonance and large third-order nonlinear response of graphene, a low-threshold optical hysteresis has been observed. The threshold value with 20MW/cm² and response time with 1.7ps have been verified. Especially, it is found that this optical bistability phenomenon is angular insensitivity for near 15° incident angle. The threshold of optical bistability can be further lowered to 0.5MW/cm² by using graphene nanoribbons, and the response time is also shorten to 800fs. We believe that our results will find potential applications in bistable devices and all-optical switching from mid-IR to THz range.

Wavelength interrogation of fiber Bragg grating sensors based on crossed optical Gaussian filters.

PubMed

Cheng, Rui; Xia, Li; Zhou, Jiaao; Liu, Deming

2015-04-15

Conventional intensity-modulated measurements require to be operated in linear range of filter or interferometric response to ensure a linear detection. Here, we present a wavelength interrogation system for fiber Bragg grating sensors where the linear transition is achieved with crossed Gaussian transmissions. This unique filtering characteristic makes the responses of the two branch detections follow Gaussian functions with the same parameters except for a delay. The substraction of these two delayed Gaussian responses (in dB) ultimately leads to a linear behavior, which is exploited for the sensor wavelength determination. Beside its flexibility and inherently power insensitivity, the proposal also shows a potential of a much wider operational range. Interrogation of a strain-tuned grating was accomplished, with a wide sensitivity tuning range from 2.56 to 8.7 dB/nm achieved.

Multi-Stress Monitoring System with Fiber-Optic Mandrels and Fiber Bragg Grating Sensors in a Sagnac Loop

PubMed Central

Kim, Hyunjin; Sampath, Umesh; Song, Minho

2015-01-01

Fiber Bragg grating sensors are placed in a fiber-optic Sagnac loop to combine the grating temperature sensors and the fiber-optic mandrel acoustic emission sensors in single optical circuit. A wavelength-scanning fiber-optic laser is used as a common light source for both sensors. A fiber-optic attenuator is placed at a specific position in the Sagnac loop in order to separate buried Bragg wavelengths from the Sagnac interferometer output. The Bragg wavelength shifts are measured with scanning band-pass filter demodulation and the mandrel output is analyzed by applying a fast Fourier transform to the interference signal. This hybrid-scheme could greatly reduce the size and the complexity of optical circuitry and signal processing unit, making it suitable for low cost multi-stress monitoring of large scale power systems. PMID:26230700

Diffraction-based BioCD biosensor for point-of-care diagnostics

NASA Astrophysics Data System (ADS)

Choi, H.; Chang, C.; Savran, C.; Nolte, D.

2018-02-01

The BioCD platform technology uses spinning-disk interferometry to detect molecular binding to target molecular probes in biological samples. Interferometric configurations have included differential phase contrast and in-line quadrature detection. For the detection of extremely low analyte concentrations, nano- or microparticles can enhance the signal through background-free diffraction detection. Diffraction signal measurements on BioCD biosensors are achieved by forming gratings on a disc surface. The grating pattern was printed with biotinylated bovine serum albumin (BSA) and streptavidin coated beads were deployed. The diameter of the beads was 1 micron and strong protein bonding occurs between BSA and streptavidin-coated beads at the printed location. The wavelength for the protein binding detection was 635 nm. The periodic pattern on the disc amplified scattered light into the first-order diffraction position. The diffracted signal contains Mie scattering and a randomly-distributed-bead noise contributions. Variation of the grating pattern periodicity modulates the diffraction efficiency. To test multiple spatial frequencies within a single scan, we designed a fan-shaped grating to perform frequency filter multiplexing on a diffraction-based BioCD.

Stratified Volume Diffractive Optical Elements as Low-Mass Coherent Lidar Scanners

NASA Technical Reports Server (NTRS)

Chambers, Diana M.; Nordin, Gregory P.; Kavaya, Michael J.

1999-01-01

Transmissive scanning elements for coherent laser radar systems are typically optical wedges, or prisms, which deflect the lidar beam at a specified angle and are then rotated about the instrument optical axis to produce a scan pattern. The wedge is placed in the lidar optical system subsequent to a beam-expanding telescope, implying that it has the largest diameter of any element in the system. The combination of the wedge diameter and asymmetric profile result in the element having very large mass and, consequently, relatively large power consumption required for scanning. These two parameters, mass and power consumption, are among the instrument requirements which need to be minimized when designing a lidar for a space-borne platform. Reducing the scanner contributions in these areas will have a significant effect on the overall instrument specifications, Replacing the optical wedge with a diffraction grating on the surface of a thin substrate is a straight forward approach with potential to reduce the mass of the scanning element significantly. For example, the optical wedge that will be used for the SPAce Readiness Coherent Lidar Experiment (SPARCLE) is approximately 25 cm in diameter and is made from silicon with a wedge angle designed for 30 degree deflection of a beam operating at approx. 2 micrometer wavelength. The mass of this element could be reduced by a factor of four by instead using a fused silica substrate, 1 cm thick, with a grating fabricated on one of the surfaces. For a grating to deflect a beam with a 2 micrometer wavelength by 30 degrees, a period of approximately 4 micrometers is required. This is small enough that fabrication of appropriate high efficiency blazed or multi-phase level diffractive optical gratings is prohibitively difficult. Moreover, bulk or stratified volume holographic approaches appear impractical due to materials limitations at 2 micrometers and the need to maintain adequate wavefront quality. In order to avoid the difficulties encountered in these approaches, we have developed a new type of high-efficiency grating which we call a Stratified Volume Diffractive Optical Element (SVDOE). The features of the gratings in this approach can be easily fabricated using standard photolithography and etching techniques and the materials used in the grating can be chosen specifically for a given application, In this paper we will briefly discuss the SVDOE technique and will present an example design of a lidar scanner using this approach. We will also discuss performance predictions for the example design.

Femtosecond laser-controlled self-assembly of amorphous-crystalline nanogratings in silicon

NASA Astrophysics Data System (ADS)

Puerto, Daniel; Garcia-Lechuga, Mario; Hernandez-Rueda, Javier; Garcia-Leis, Adianez; Sanchez-Cortes, Santiago; Solis, Javier; Siegel, Jan

2016-07-01

Self-assembly (SA) of molecular units to form regular, periodic extended structures is a powerful bottom-up technique for nanopatterning, inspired by nature. SA can be triggered in all classes of solid materials, for instance, by femtosecond laser pulses leading to the formation of laser-induced periodic surface structures (LIPSS) with a period slightly shorter than the laser wavelength. This approach, though, typically involves considerable material ablation, which leads to an unwanted increase of the surface roughness. We present a new strategy to fabricate high-precision nanograting structures in silicon, consisting of alternating amorphous and crystalline lines, with almost no material removal. The strategy can be applied to static irradiation experiments and can be extended into one and two dimensions by scanning the laser beam over the sample surface. We demonstrate that lines and areas with parallel nanofringe patterns can be written by an adequate choice of spot size, repetition rate and scan velocity, keeping a constant effective pulse number (N eff) per area for a given laser wavelength. A deviation from this pulse number leads either to inhomogeneous or ablative structures. Furthermore, we demonstrate that this approach can be used with different laser systems having widely different wavelengths (1030 nm, 800 nm, 400 nm), pulse durations (370 fs, 100 fs) and repetition rates (500 kHz, 100 Hz, single pulse) and that the grating period can also be tuned by changing the angle of laser beam incidence. The grating structures can be erased by irradiation with a single nanosecond laser pulse, triggering recrystallization of the amorphous stripes. Given the large differences in electrical conductivity between the two phases, our structures could find new applications in nanoelectronics.

Femtosecond laser-controlled self-assembly of amorphous-crystalline nanogratings in silicon.

PubMed

Puerto, Daniel; Garcia-Lechuga, Mario; Hernandez-Rueda, Javier; Garcia-Leis, Adianez; Sanchez-Cortes, Santiago; Solis, Javier; Siegel, Jan

2016-07-01

Self-assembly (SA) of molecular units to form regular, periodic extended structures is a powerful bottom-up technique for nanopatterning, inspired by nature. SA can be triggered in all classes of solid materials, for instance, by femtosecond laser pulses leading to the formation of laser-induced periodic surface structures (LIPSS) with a period slightly shorter than the laser wavelength. This approach, though, typically involves considerable material ablation, which leads to an unwanted increase of the surface roughness. We present a new strategy to fabricate high-precision nanograting structures in silicon, consisting of alternating amorphous and crystalline lines, with almost no material removal. The strategy can be applied to static irradiation experiments and can be extended into one and two dimensions by scanning the laser beam over the sample surface. We demonstrate that lines and areas with parallel nanofringe patterns can be written by an adequate choice of spot size, repetition rate and scan velocity, keeping a constant effective pulse number (N eff) per area for a given laser wavelength. A deviation from this pulse number leads either to inhomogeneous or ablative structures. Furthermore, we demonstrate that this approach can be used with different laser systems having widely different wavelengths (1030 nm, 800 nm, 400 nm), pulse durations (370 fs, 100 fs) and repetition rates (500 kHz, 100 Hz, single pulse) and that the grating period can also be tuned by changing the angle of laser beam incidence. The grating structures can be erased by irradiation with a single nanosecond laser pulse, triggering recrystallization of the amorphous stripes. Given the large differences in electrical conductivity between the two phases, our structures could find new applications in nanoelectronics.

Smart architecture for stable multipoint fiber Bragg grating sensor system

NASA Astrophysics Data System (ADS)

Yeh, Chien-Hung; Tsai, Ning; Zhuang, Yuan-Hong; Huang, Tzu-Jung; Chow, Chi-Wai; Chen, Jing-Heng; Liu, Wen-Fung

2017-12-01

In this work, we propose and investigate an intelligent fiber Bragg grating (FBG)-based sensor system in which the proposed stabilized and wavelength-tunable single-longitudinal-mode erbium-doped fiber laser can improve the sensing accuracy of wavelength-division-multiplexing multiple FBG sensors in a longer fiber transmission distance. Moreover, we also demonstrate the proposed sensor architecture to enhance the FBG capacity for sensing strain and temperature, simultaneously.

Wavelength stabilized multi-kW diode laser systems

NASA Astrophysics Data System (ADS)

Köhler, Bernd; Unger, Andreas; Kindervater, Tobias; Drovs, Simon; Wolf, Paul; Hubrich, Ralf; Beczkowiak, Anna; Auch, Stefan; Müntz, Holger; Biesenbach, Jens

2015-03-01

We report on wavelength stabilized high-power diode laser systems with enhanced spectral brightness by means of Volume Holographic Gratings. High-power diode laser modules typically have a relatively broad spectral width of about 3 to 6 nm. In addition the center wavelength shifts by changing the temperature and the driving current, which is obstructive for pumping applications with small absorption bandwidths. Wavelength stabilization of high-power diode laser systems is an important method to increase the efficiency of diode pumped solid-state lasers. It also enables power scaling by dense wavelength multiplexing. To ensure a wide locking range and efficient wavelength stabilization the parameters of the Volume Holographic Grating and the parameters of the diode laser bar have to be adapted carefully. Important parameters are the reflectivity of the Volume Holographic Grating, the reflectivity of the diode laser bar as well as its angular and spectral emission characteristics. In this paper we present detailed data on wavelength stabilized diode laser systems with and without fiber coupling in the spectral range from 634 nm up to 1533 nm. The maximum output power of 2.7 kW was measured for a fiber coupled system (1000 μm, NA 0.22), which was stabilized at a wavelength of 969 nm with a spectral width of only 0.6 nm (90% value). Another example is a narrow line-width diode laser stack, which was stabilized at a wavelength of 1533 nm with a spectral bandwidth below 1 nm and an output power of 835 W.

High-power linearly-polarized operation of a cladding-pumped Yb fibre laser using a volume Bragg grating for wavelength selection.

PubMed

Jelger, P; Wang, P; Sahu, J K; Laurell, F; Clarkson, W A

2008-06-23

In this work a volume Bragg grating is used as a wavelength selective element in a high-power cladding-pumped Yb-doped silica fiber laser. The laser produced 138 W of linearly-polarized single-spatial-mode output at 1066 nm with a relatively narrow linewidth of 0.2 nm for approximately 202 W of launched pump power at 976 nm. The beam propagation factor (M(2)) for the output beam was determined to be 1.07. Thermal limitations of volume Bragg gratings are discussed in the context of power scaling for fiber lasers.

Optical-fiber-to-waveguide coupling using carbon-dioxide-laser-induced long-period fiber gratings.

PubMed

Bachim, Brent L; Ogunsola, Oluwafemi O; Gaylord, Thomas K

2005-08-15

Optical fibers are expected to play a role in chip-level and board-level optical interconnects because of limitations on the bandwidth and level of integration of electrical interconnects. Therefore, methods are needed to couple optical fibers directly to waveguides on chips and on boards. We demonstrate optical-fiber-to-waveguide coupling using carbon-dioxide laser-induced long-period fiber gratings (LPFGs). Such gratings can be written in standard fiber and offer wavelength multiplexing-demultiplexing performance. The coupler fabrication process and the characterization apparatus are presented. The operation and the wavelength response of a LPFG-based optical-fiber-to-waveguide directional coupler are demonstrated.

Broadband spatial optical filtering with a volume Bragg grating and a blazed grating pair

NASA Astrophysics Data System (ADS)

Chen, Guanjin; Sun, Xiaojie; Yuan, Xiao; Zhang, Guiju

2017-10-01

A broadband spatial optical filtering system is presented in this paper, which is composed of a Volume Bragg Grating (VBG) and a blazed grating pair. The diffraction efficiency and filtering properties are calculated and simulated by using Fourier diffraction analysis and Coupled Wave Theory. A blazed grating pair and VBG structures are designed and optimized in our simulation. The diffraction efficiency of filtering system shows more than 77.2% during the wavelength period from 953nm to 1153nm, especially 84.1% at the center wavelength. The beam quality is described with near-field modulation (M) and contrast ratio (C). The M of filtering beam are 1.44, 1.49 and 1.55, respectively and the C of filtering beam are 10.1%, 10.2% and 10.5% , respectively and the beam intensity distribution is great improved. The cut-off frequencies of three filtering systems are 1.57mm-1 , 2.06 mm-1 and 2.38 mm-1 , respectively from power spectral density (PSD) curve. It's clear that the cut-off frequency of filtering system is closely related to the angular selectivity of VBG, and the value of cut-off frequency is decided by VBG's Half Width at First Zero (HWFZ) and center wavelength.

Ultra Narrowband Optical Filters for Water Vapor Differential Absorption Lidar (DIAL) Atmospheric Measurements

NASA Technical Reports Server (NTRS)

Stenholm, Ingrid; DeYoung, Russell J.

2001-01-01

Differential absorption lidar (DIAL) systems are being deployed to make vertical profile measurements of atmospheric water vapor from ground and airborne platforms. One goal of this work is to improve the technology of such DIAL systems that they could be deployed on space-based platforms. Since background radiation reduces system performance, it is important to reduce it. One way to reduce it is to narrow the bandwidth of the optical receiver system. However, since the DIAL technique uses two or more wavelengths, in this case separated by 0.1 nm, a fixed-wavelength narrowband filter that would encompass both wavelengths would be broader than required for each line, approximately 0.02 nm. The approach employed in this project is to use a pair of tunable narrowband reflective fiber Bragg gratings. The Bragg gratings are germanium-doped silica core fiber that is exposed to ultraviolet radiation to produce index-of-refraction changes along the length of the fiber. The gratings can be tuned by stretching. The backscattered laser radiation is transmitted through an optical circulator to the gratings, reflected back to the optical circulator by one of the gratings, and then sent to a photodiode. The filter reflectivities were >90 percent, and the overall system efficiency was 30 percent.

Laterally coupled distributed feedback lasers emitting at 2 μm with quantum dash active region and high-duty-cycle etched semiconductor gratings

NASA Astrophysics Data System (ADS)

Papatryfonos, Konstantinos; Saladukha, Dzianis; Merghem, Kamel; Joshi, Siddharth; Lelarge, Francois; Bouchoule, Sophie; Kazazis, Dimitrios; Guilet, Stephane; Le Gratiet, Luc; Ochalski, Tomasz J.; Huyet, Guillaume; Martinez, Anthony; Ramdane, Abderrahim

2017-02-01

Single-mode diode lasers on an InP(001) substrate have been developed using InAs/In0.53Ga0.47As quantum dash (Qdash) active regions and etched lateral Bragg gratings. The lasers have been designed to operate at wavelengths near 2 μm and exhibit a threshold current of 65 mA for a 600 μm long cavity, and a room temperature continuous wave output power per facet >5 mW. Using our novel growth approach based on the low ternary In0.53Ga0.47As barriers, we also demonstrate ridge-waveguide lasers emitting up to 2.1 μm and underline the possibilities for further pushing the emission wavelength out towards longer wavelengths with this material system. By introducing experimentally the concept of high-duty-cycle lateral Bragg gratings, a side mode suppression ratio of >37 dB has been achieved, owing to an appreciably increased grating coupling coefficient of κ ˜ 40 cm-1. These laterally coupled distributed feedback (LC-DFB) lasers combine the advantage of high and well-controlled coupling coefficients achieved in conventional DFB lasers, with the regrowth-free fabrication process of lateral gratings, and exhibit substantially lower optical losses compared to the conventional metal-based LC-DFB lasers.

Fabrication of high aspect ratio TiO{sub 2} and Al{sub 2}O{sub 3} nanogratings by atomic layer deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shkondin, Evgeniy, E-mail: eves@fotonik.dtu.dk; Takayama, Osamu; Lavrinenko, Andrei V.

The authors report on the fabrication of TiO{sub 2} and Al{sub 2}O{sub 3} nanostructured gratings with an aspect ratio of up to 50. The gratings were made by a combination of atomic layer deposition (ALD) and dry etch techniques. The workflow included fabrication of a Si template using deep reactive ion etching followed by ALD of TiO{sub 2} or Al{sub 2}O{sub 3}. Then, the template was etched away using SF{sub 6} in an inductively coupled plasma tool, which resulted in the formation of isolated ALD coatings, thereby achieving high aspect ratio grating structures. SF{sub 6} plasma removes silicon selectively withoutmore » any observable influence on TiO{sub 2} or Al{sub 2}O{sub 3}, thus revealing high selectivity throughout the fabrication. Scanning electron microscopy was used to analyze every fabrication step. Due to nonreleased stress in the ALD coatings, the top parts of the gratings were observed to bend inward as the Si template was removed, thus resulting in a gradual change in the pitch value of the structures. The pitch on top of the gratings is 400 nm, and it gradually reduces to 200 nm at the bottom. The form of the bending can be reshaped by Ar{sup +} ion beam etching. The chemical purity of the ALD grown materials was analyzed by x-ray photoelectron spectroscopy. The approach presented opens the possibility to fabricate high quality optical metamaterials and functional nanostructures.« less

Enhanced light absorption of solar cells and photodetectors by diffraction

DOEpatents

Zaidi, Saleem H.; Gee, James M.

2005-02-22

Enhanced light absorption of solar cells and photodetectors by diffraction is described. Triangular, rectangular, and blazed subwavelength periodic structures are shown to improve performance of solar cells. Surface reflection can be tailored for either broadband, or narrow-band spectral absorption. Enhanced absorption is achieved by efficient optical coupling into obliquely propagating transmitted diffraction orders. Subwavelength one-dimensional structures are designed for polarization-dependent, wavelength-selective absorption in solar cells and photodetectors, while two-dimensional structures are designed for polarization-independent, wavelength-selective absorption therein. Suitable one and two-dimensional subwavelength periodic structures can also be designed for broadband spectral absorption in solar cells and photodetectors. If reactive ion etching (RIE) processes are used to form the grating, RIE-induced surface damage in subwavelength structures can be repaired by forming junctions using ion implantation methods. RIE-induced surface damage can also be removed by post RIE wet-chemical etching treatments.

EUV efficiency of a 6000-grooves per mm diffraction grating

NASA Technical Reports Server (NTRS)

Hurwitz, Mark; Bowyer, Stuart; Edelstein, Jerry; Harada, Tatsuo; Kita, Toshiaki

1990-01-01

In order to explore whether grooves ruled mechanically at a density of 6000 per mm can perform well at EUV wavelengths, a sample grating is measured with this density in an EUV calibration facility. Measurements are presented of the planar uniform line-space diffraction grating's efficiency and large-angle scattering.

Switchable single-longitudinal-mode dual-wavelength erbium-doped fiber ring laser based on one polarization-maintaining fiber Bragg grating incorporating saturable absorber and feedback fiber loop

NASA Astrophysics Data System (ADS)

Feng, Suchun; Xu, Ou; Lu, Shaohua; Ning, Tigang; Jian, Shuisheng

2009-06-01

Switchable single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber ring laser based on one polarization-maintaining fiber Bragg grating (PMFBG) is demonstrated. Due to the enhancement of the polarization hole burning (PHB) by the PMFBG, the laser can be designed to operate in stable dual-wavelength or wavelength-switching modes with a wavelength spacing of 0.336 nm at room temperature by adjusting a polarization controller (PC). The stable SLM operation is guaranteed by a compound-ring cavity and a saturable absorber (SA). The optical signal-to-noise ratio (OSNR) is over 45 dB. The amplitude variation in nearly one and half an hour is less than 0.2 dB.

Fibre Bragg grating encapted with no-core fibre sensors for SRI and temperature monitoring

NASA Astrophysics Data System (ADS)

Daud, S.; Amiri, I. S.; Noorden, A. F. A.; Ali, J.; Yupapin, P.

2018-06-01

In this work, a Fibre Bragg grating (FBG) encapted with no-core fibre (NCF) as surrounding refractive index (SRI) and temperature sensors are practically demonstrated. A FBG with 1550 nm wavelength was attached with 5 cm length of no-core fibre (NCF) is used as SRI and temperature sensing probe. The change of temperature and SRI induced the wavelength shift in FBG. The wavelength shift in FBG reacts directly proportional to the temperature with a sensitivity of while the sensitivity of NCF was measured as 13.13 pm °C-1.

Formation of laser-induced periodic surface structures on niobium by femtosecond laser irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pan, A.; Dias, A.; Gomez-Aranzadi, M.

2014-05-07

The surface morphology of a Niobium sample, irradiated in air by a femtosecond laser with a wavelength of 800 nm and pulse duration of 100 fs, was examined. The period of the micro/nanostructures, parallel and perpendicularly oriented to the linearly polarized fs-laser beam, was studied by means of 2D Fast Fourier Transform analysis. The observed Laser-Induced Periodic Surface Structures (LIPSS) were classified as Low Spatial Frequency LIPSS (periods about 600 nm) and High Spatial Frequency LIPSS, showing a periodicity around 300 nm, both of them perpendicularly oriented to the polarization of the incident laser wave. Moreover, parallel high spatial frequency LIPSS were observedmore » with periods around 100 nm located at the peripheral areas of the laser fingerprint and overwritten on the perpendicular periodic gratings. The results indicate that this method of micro/nanostructuring allows controlling the Niobium grating period by the number of pulses applied, so the scan speed and not the fluence is the key parameter of control. A discussion on the mechanism of the surface topology evolution was also introduced.« less

Error analysis of mechanical system and wavelength calibration of monochromator

NASA Astrophysics Data System (ADS)

Zhang, Fudong; Chen, Chen; Liu, Jie; Wang, Zhihong

2018-02-01

This study focuses on improving the accuracy of a grating monochromator on the basis of the grating diffraction equation in combination with an analysis of the mechanical transmission relationship between the grating, the sine bar, and the screw of the scanning mechanism. First, the relationship between the mechanical error in the monochromator with the sine drive and the wavelength error is analyzed. Second, a mathematical model of the wavelength error and mechanical error is developed, and an accurate wavelength calibration method based on the sine bar's length adjustment and error compensation is proposed. Based on the mathematical model and calibration method, experiments using a standard light source with known spectral lines and a pre-adjusted sine bar length are conducted. The model parameter equations are solved, and subsequent parameter optimization simulations are performed to determine the optimal length ratio. Lastly, the length of the sine bar is adjusted. The experimental results indicate that the wavelength accuracy is ±0.3 nm, which is better than the original accuracy of ±2.6 nm. The results confirm the validity of the error analysis of the mechanical system of the monochromator as well as the validity of the calibration method.

Geometrically tunable Fabry-Perot filters based on reflection phase shift of high contrast gratings

NASA Astrophysics Data System (ADS)

Fang, Liang; Shi, Zhendong; Cheng, Xin; Peng, Xiang; Zhang, Hui

2016-03-01

We propose tunable Fabry-Perot filters constituted by double high contrast gratings (HCGs) arrays with different periods acting as reflectors separated by a fixed short cavity, based on high reflectivity and the variety reflection phase shift of HCG array which realize dynamic regulation of the filtering condition. Single optimized HCG obtains the reflectivity of higher than 99% in a grating period ranging from 0.68μm to 0.8μm across a bandwidth of 30nm near the 1.55μm wavelength. The filters can achieve the full width at half maximum (FWHM) of spectral line of less than 0.15nm, and the linear relationship of peak wavelengths and grating periods is established. The simulation results indicate a potential new approach to design a tunable narrowband transmission filter.

Mitigation of stimulated Raman scattering in high power fiber lasers using transmission gratings

NASA Astrophysics Data System (ADS)

Heck, Maximilian; Bock, Victor; Krämer, Ria G.; Richter, Daniel; Goebel, Thorsten A.; Matzdorf, Christian; Liem, Andreas; Schreiber, Thomas; Tünnermann, Andreas; Nolte, Stefan

2018-02-01

The average output power of fiber lasers have been scaled deep into the kW regime within the recent years. However a further scaling is limited due to nonlinear effects like stimulated Raman scattering (SRS). Using the special characteristics of femtosecond laser pulse written transmission fiber gratings, it is possible to realize a notch filter that mitigates efficiently this negative effect by coupling the Raman wavelength from the core into the cladding of the fiber. To the best of our knowledge, we realized for the first time highly efficient gratings in large mode area (LMA) fibers with cladding diameters up to 400 μm. The resonances show strong attenuation at design wavelength and simultaneously low out of band losses. A high power fiber amplifier with an implemented passive fiber grating is shown and its performance is carefully investigated.

Detection, Evaluation, and Optimization of Optical Signals Generated by Fiber Optic Bragg Gratings Under Dynamic Excitations

NASA Technical Reports Server (NTRS)

Adamovsky, Grigory; Lekki, John; Lock, James A.

2002-01-01

The dynamic response of a fiber optic Bragg grating to mechanical vibrations is examined both theoretically and experimentally. The theoretical expressions describing the consequences of changes in the grating's reflection spectrum are derived for partially coherent beams in an interferometer. The analysis is given in terms of the dominant wavelength, optical bandwidth, and optical path difference of the interfering signals. Changes in the reflection spectrum caused by a periodic stretching and compression of the grating were experimentally measured using an unbalanced Michelson interferometer, a Michelson interferometer with a non-zero optical path difference. The interferometer's sensitivity to changes in dominant wavelength of the interfering beams was measured as a function of interferometer unbalance and was compared to theoretical predictions. The theoretical analysis enables the user to determine the optimum performance for an unbalanced interferometer.

Flat-field VLS spectrometers for laboratory applications

NASA Astrophysics Data System (ADS)

Ragozin, Evgeny N.; Belokopytov, Aleksei A.; Kolesnikov, Aleksei O.; Muslimov, Eduard R.; Shatokhin, Aleksei N.; Vishnyakov, Eugene A.

2017-05-01

Our intention is to develop high-resolution stigmatic spectral imaging in the XUV (2 - 40 nm). We have designed, aligned and tested a broadband stigmatic spectrometer for a range of 12-30 nm, which makes combined use of a normalincidence multilayer mirror (MM) (in particular, a broadband aperiodic MM) and a grazing-incidence plane varied linespace (VLS) reflection grating. The concave MM produces a slightly astigmatic image of the radiation source (for instance, the entrance slit), and the VLS grating produces a set of its dispersed stigmatic spectral images. The multilayer structure determines the spectral width of the operating range, which may amount to more than an octave in wavelength (e.g. 12.5-30 nm for an aperiodic Mo/Si MM), while the VLS grating controls the spectral focal curve. The stigmatism condition is satisfied simultaneously for two wavelengths, 14 and 27 nm. In this case, the condition of non-rigorous stigmatism is fulfilled for the entire wavelength range. A LiF laser plasma spectrum was recorded in one 0.5 J laser shot. A spatial resolution of 26 μm and a spectral resolution of 900 were demonstrated in the 12.5 - 25 nm range. We also report the design of a set of flat-field spectrometers of Harada type with VLS gratings. VLS gratings were made by ebeam and interference lithography. A technique (analytical + numerical) was developed for calculating optical schemes for writing plane and concave VLS gratings with predefined line density variation.

Sensitivity Enhancement in Low Cutoff Wavelength Long-Period Fiber Gratings by Cladding Diameter Reduction.

PubMed

Del Villar, Ignacio; Partridge, Matthew; Rodriguez, Wenceslao Eduardo; Fuentes, Omar; Socorro, Abian Bentor; Diaz, Silvia; Corres, Jesus Maria; James, Stephen Wayne; Tatam, Ralph Peter

2017-09-13

The diameter of long-period fiber gratings (LPFGs) fabricated in optical fibers with a low cutoff wavelength was be reduced by hydrofluoric acid etching, enhancing the sensitivity to refractive index by more than a factor of 3, to 2611 nm/refractive index unit in the range from 1.333 to 1.4278. The grating period selected for the LPFGs allowed access to the dispersion turning point at wavelengths close to the visible range of the optical spectrum, where optical equipment is less expensive. As an example of an application, a pH sensor based on the deposition of a polymeric coating was analyzed in two situations: with an LPFG without diameter reduction and with an LPFG with diameter reduction. Again, a sensitivity increase of a factor of near 3 was obtained, demonstrating the ability of this method to enhance the sensitivity of thin-film-coated LPFG chemical sensors.

High accuracy wavelength calibration for a scanning visible spectrometer.

PubMed

Scotti, Filippo; Bell, Ronald E

2010-10-01

Spectroscopic applications for plasma velocity measurements often require wavelength accuracies ≤0.2 Å. An automated calibration, which is stable over time and environmental conditions without the need to recalibrate after each grating movement, was developed for a scanning spectrometer to achieve high wavelength accuracy over the visible spectrum. This method fits all relevant spectrometer parameters using multiple calibration spectra. With a stepping-motor controlled sine drive, an accuracy of ∼0.25 Å has been demonstrated. With the addition of a high resolution (0.075 arc  sec) optical encoder on the grating stage, greater precision (∼0.005 Å) is possible, allowing absolute velocity measurements within ∼0.3 km/s. This level of precision requires monitoring of atmospheric temperature and pressure and of grating bulk temperature to correct for changes in the refractive index of air and the groove density, respectively.

A Near-Infrared Spectrometer Based on Novel Grating Light Modulators

PubMed Central

Wei, Wei; Huang, Shanglian; Wang, Ning; Jin, Zhu; Zhang, Jie; Chen, Weimin

2009-01-01

A near-infrared spectrometer based on novel MOEMS grating light modulators is proposed. The spectrum detection method that combines a grating light modulator array with a single near-infrared detector has been applied. Firstly, optics theory has been used to analyze the essential principles of the proposed spectroscopic sensor. Secondly, the grating light modulators have been designed and fabricated by micro-machining technology. Finally, the principles of this spectroscopic sensor have been validated and its key parameters have been tested by experiments. The result shows that the spectral resolution is better than 10 nm, the wavelength deviation is less than 1 nm, the deviation of the intensity of peak wavelength is no more than 0.5%, the driving voltage of grating light modulators array device is below 25 V and the response frequency of it is about 5 kHz. With low cost, satisfactory precision, portability and other advantages, the spectrometer should find potential applications in food safety and quality monitoring, pharmaceutical identification and agriculture product quality classification. PMID:22574065

A near-infrared spectrometer based on novel grating light modulators.

PubMed

Wei, Wei; Huang, Shanglian; Wang, Ning; Jin, Zhu; Zhang, Jie; Chen, Weimin

2009-01-01

A near-infrared spectrometer based on novel MOEMS grating light modulators is proposed. The spectrum detection method that combines a grating light modulator array with a single near-infrared detector has been applied. Firstly, optics theory has been used to analyze the essential principles of the proposed spectroscopic sensor. Secondly, the grating light modulators have been designed and fabricated by micro-machining technology. Finally, the principles of this spectroscopic sensor have been validated and its key parameters have been tested by experiments. The result shows that the spectral resolution is better than 10 nm, the wavelength deviation is less than 1 nm, the deviation of the intensity of peak wavelength is no more than 0.5%, the driving voltage of grating light modulators array device is below 25 V and the response frequency of it is about 5 kHz. With low cost, satisfactory precision, portability and other advantages, the spectrometer should find potential applications in food safety and quality monitoring, pharmaceutical identification and agriculture product quality classification.

Direct and Inverse Techniques of Guided-Mode Resonance Filters Designs

NASA Technical Reports Server (NTRS)

Tibuleac, Sorin; Magnusson, Robert; Maldonado, Theresa A.; Zuffada, Cinzia

1997-01-01

Guided-mode resonances arise in single or multilayer waveguides where one or more homogeneous layers are replaced by diffraction gratings (Fig. 1.) The diffractive element enables an electromagnetic wave incident on a waveguide grating to be coupled to the waveguide modes supportable by the structure in the absence of the modulation (i.e. the difference between the high and low dielectric constants of the grating) at specific values of the wavelength and incident angle. The periodic modulation of the guide makes the structure leaky, preventing sustained propagation of modes in the waveguide and coupling the waves out into the substrate and cover. As the wavelength is varied around resonance a rapid variation in the intensities of the external propagating waves occurs. By selecting a grating period small enough to eliminate the higher-order propagating waves, an increase in the zero-order intensities up to 100% can result. The pronounced frequency selectivity of guided-mode resonances in dielectric waveguide gratings can be applied to design high-efficiency reflection and transmission filters [1-3].

Controlling the size and optical properties of ZnO nanoparticles by capping with SiO{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Babu, K. Sowri, E-mail: sowribabuk@gmail.com; Reddy, A. Ramachandra; Reddy, K. Venugopal

Graphical abstract: - Highlights: • Small and uniform sized ZnO nanoparticles were obtained with SiO{sub 2} coating. • ZnO and ZnO–SiO{sub 2} nanocomposite exhibited excitation wavelength dependent PL. • Maximum UV emission intensity was obtained with 353 nm excitation wavelength. • Excitation processes in SiO{sub 2} were also contributed to the UV intensity. • It was found that oxygen vacancies and interstitials enhanced with SiO{sub 2} coating. - Abstract: The size and shape of the ZnO nanoparticles synthesized through sol–gel method were controlled by capping with SiO{sub 2}. X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM) and Highmore » Resolution Transmission Electron Microscope (HR-TEM) results demonstrated that the particle growth of the ZnO nanoparticles has been restricted to 5 nm with SiO{sub 2} capping. As a result, the absorption spectra of ZnO nanoparticles capped with SiO{sub 2} got blue shifted (toward lower wavelength side) due to strong quantum confinement effects. BET (Brunauer–Emmet–Teller) surface area pore size analyzer results showed that surface area of samples increased monotonously with increase of SiO{sub 2} concentration. It was observed that the absorption spectra of ZnO capped with SiO{sub 2} broadened with increase of SiO{sub 2} concentration. Absorption and photoluminescence excitation results (PLE) confirmed that this broadening is due to the absorption of non-bridging oxygen hole centers (NBOHC) of SiO{sub 2}. These results also indicated that ZnO nanoparticles capped with SiO{sub 2} are insensitive to Raman scattering. Maximum UV emission intensity was achieved with 353 nm excitation wavelength compared to 320 nm in ZnO as well as in SiO{sub 2} capped ZnO nanoparticles. Furthermore, there is an enhancement in the intensities of emission peaks related to oxygen vacancies and interstitials with SiO{sub 2} capping. The enhancement in the UV intensity is attributed to the surface passivation of ZnO nanoparticles and excitation processes in SiO{sub 2}.« less

Design of distributed FBG vibration measuring system based on Fabry-Perot tunable filter

NASA Astrophysics Data System (ADS)

Zhang, Cheng; Miao, Changyun; Li, Hongqiang; Gao, Hua; Gan, Jingmeng

2011-11-01

A distributed optical fiber grating wavelength interrogator based on fiber Fabry Perot tunable filter(FFP-TF) was proposed, which could measure dynamic strain or vibration of multi-sensing fiber gratings in one optical fiber by time division way. The wavelength demodulated mathematical model was built, the formulas of system output voltage and sensitivity were deduced and the method of finding static operating point was determined. The wavelength drifting characteristic of FFP-TF was discussed when the center wavelength of FFP-TF was set on the static operating point. A wavelength locking method was proposed by introducing a high-frequency driving voltage signal. A demodulated system was established based on Labview and its demodulated wavelength dynamic range is 290pm in theory. In experiment, by digital filtering applied to the system output data, 100Hz and 250Hz vibration signals were measured. The experiment results proved the feasibility of the demodulated method.

Fiber-bragg grating-loop ringdown method and apparatus

DOEpatents

Wang, Chuji [Starkville, MS

2008-01-29

A device comprising a fiber grating loop ringdown (FGLRD) system of analysis is disclosed. A fiber Bragg grating (FBG) or Long-Period grating (LPG) written in a section of single mode fused silica fiber is incorporated into a fiber loop. By utilizing the wing areas of the gratings' bandwidth as a wavelength dependent attenuator of the light transmission, a fiber grating loop ringdown concept is formed. One aspect of the present invention is temperature sensing, which has been demonstrated using the disclosed device. Temperature measurements in the areas of accuracy, stability, high temperature, and dynamic range are also described.

Three-port beam splitter of a binary fused-silica grating.

PubMed

Feng, Jijun; Zhou, Changhe; Wang, Bo; Zheng, Jiangjun; Jia, Wei; Cao, Hongchao; Lv, Peng

2008-12-10

A deep-etched polarization-independent binary fused-silica phase grating as a three-port beam splitter is designed and manufactured. The grating profile is optimized by use of the rigorous coupled-wave analysis around the 785 nm wavelength. The physical explanation of the grating is illustrated by the modal method. Simple analytical expressions of the diffraction efficiencies and modal guidelines for the three-port beam splitter grating design are given. Holographic recording technology and inductively coupled plasma etching are used to manufacture the fused-silica grating. Experimental results are in good agreement with the theoretical values.

Improved Phase-Mask Fabrication of Fiber Bragg Gratings

NASA Technical Reports Server (NTRS)

Grant, Joseph; Wang, Ying; Sharma, Anup

2004-01-01

An improved method of fabrication of Bragg gratings in optical fibers combines the best features of two prior methods: one that involves the use of a phase mask and one that involves interference between the two coherent laser beams. The improved method affords flexibility for tailoring Bragg wavelengths and bandwidths over wide ranges. A Bragg grating in an optical fiber is a periodic longitudinal variation in the index of refraction of the fiber core. The spatial period (Bragg wavelength) is chosen to obtain enhanced reflection of light of a given wavelength that would otherwise propagate relatively unimpeded along the core. Optionally, the spatial period of the index modulation can be made to vary gradually along the grating (such a grating is said to be chirped ) in order to obtain enhanced reflection across a wavelength band, the width of which is determined by the difference between the maximum and minimum Bragg wavelengths. In the present method as in both prior methods, a Bragg grating is formed by exposing an optical fiber to an ultraviolet-light interference field. The Bragg grating coincides with the pattern of exposure of the fiber core to ultraviolet light; in other words, the Bragg grating coincides with the interference fringes. Hence, the problem of tailoring the Bragg wavelength and bandwidth is largely one of tailoring the interference pattern and the placement of the fiber in the interference pattern. In the prior two-beam interferometric method, a single laser beam is split into two beams, which are subsequently recombined to produce an interference pattern at the location of an optical fiber. In the prior phase-mask method, a phase mask is used to diffract a laser beam mainly into two first orders, the interference between which creates the pattern to which an optical fiber is exposed. The prior two-beam interferometric method offers the advantage that the period of the interference pattern can be adjusted to produce gratings over a wide range of Bragg wavelengths, but offers the disadvantage that success depends on precise alignment and high mechanical stability. The prior phase-mask method affords the advantages of compactness of equipment and relative insensitivity to both misalignment and vibration, but does not afford adjustability of the Bragg wavelength. The present method affords both the flexibility of the prior two-beam interferometric method and the compactness and stability of the prior phase-mask method. In this method (see figure), a laser beam propagating along the x axis is normally incident on a phase mask that lies in the (y,z) plane. The phase of light propagating through the mask is modulated with a spatial periodicity, p, along the y axis chosen to diffract the laser light primarily to first order at the angle . (The zero-order laser light propagating along the x axis can be used for alignment and thereafter suppressed during exposure of the fiber.) The diffracted light passes through a concave cylindrical lens, which converts the flat diffracted wave fronts to cylindrical ones, as though the light emanated from a line source. Then two parallel flat mirrors recombine the diffracted beams to form an interference field equivalent to that of two coherent line sources at positions A and B (virtual sources). The interference pattern is a known function of the parameters of the apparatus and of position (x,y) in the interference field. Hence, the tilt, wavelength, and chirp of the Bragg grating can be chosen through suitable adjustments of the apparatus and/or of the position and orientation of the optical fiber. In particular, the Bragg wavelength can be adjusted by moving the fiber along the x axis, and the bandwidth can be modified over a wide range by changing the fiber tilt angle or by moving the phase mask and/or the fiber. Alignment is easy because the zero-order beam defines the x axis. The interference is relatively stable and insensitive to the mechanical vibration because of the gh symmetry and compactness of the apparatus, the fixed positions of the mirrors and lens, and the consequent fixed positions of the two virtual line sources, which are independent of the translations of the phase mask and the laser relative to the lens.

Aliased tidal errors in TOPEX/POSEIDON sea surface height data

NASA Technical Reports Server (NTRS)

Schlax, Michael G.; Chelton, Dudley B.

1994-01-01

Alias periods and wavelengths for the M(sub 2, S(sub 2), N(sub 2), K(sub 1), O(sub 1), and P(sub 1) tidal constituents are calculated for TOPEX/POSEIDON. Alias wavelenghts calculated in previous studies are shown to be in error, and a correct method is presented. With the exception of the K(sub 1) constituent, all of these tidal aliases for TOPEX/POSEIDON have periods shorter than 90 days and are likely to be confounded with long-period sea surface height signals associated with real ocean processes. In particular, the correspondence between the periods and wavelengths of the M(sub 2) alias and annual baroclinic Rossby waves that plagued Geosat sea surface height data is avoided. The potential for aliasing residual tidal errors in smoothed estimates of sea surface height is calculated for the six tidal constituents. The potential for aliasing the lunar tidal constituents M(sub 2), N(sub 2) and O(sub 1) fluctuates with latitude and is different for estimates made at the crossovers of ascending and descending ground tracks than for estimates at points midway between crossovers. The potential for aliasing the solar tidal constituents S(sub 2), K(sub 1) and P(sub 1) varies smoothly with latitude. S(sub 2) is strongly aliased for latitudes within 50 degress of the equator, while K(sub 1) and P(sub 1) are only weakly aliased in that range. A weighted least squares method for estimating and removing residual tidal errors from TOPEX/POSEIDON sea surface height data is presented. A clear understanding of the nature of aliased tidal error in TOPEX/POSEIDON data aids the unambiguous identification of real propagating sea surface height signals. Unequivocal evidence of annual period, westward propagating waves in the North Atlantic is presented.

Plasmonic Optical Fiber-Grating Immunosensing: A Review

PubMed Central

Loyez, Médéric; Caucheteur, Christophe

2017-01-01

Plasmonic immunosensors are usually made of a noble metal (in the form of a film or nanoparticles) on which bioreceptors are grafted to sense analytes based on the antibody/antigen or other affinity mechanism. Optical fiber configurations are a miniaturized counterpart to the bulky Kretschmann prism and allow easy light injection and remote operation. To excite a surface plasmon (SP), the core-guided light is locally outcoupled. Unclad optical fibers were the first configurations reported to this end. Among the different architectures able to bring light in contact with the surrounding medium, a great quantity of research is today being conducted on metal-coated fiber gratings photo-imprinted in the fiber core, as they provide modal features that enable SP generation at any wavelength, especially in the telecommunication window. They are perfectly suited for use with cost-effective high-resolution interrogators, allowing both a high sensitivity and a low limit of detection to be reached in immunosensing. This paper will review recent progress made in this field with different kinds of gratings: uniform, tilted and eccentric short-period gratings as well as long-period fiber gratings. Practical cases will be reported, showing that such sensors can be used in very small volumes of analytes and even possibly applied to in vivo diagnosis. PMID:29186871

Plasmonic Optical Fiber-Grating Immunosensing: A Review.

PubMed

Guo, Tuan; González-Vila, Álvaro; Loyez, Médéric; Caucheteur, Christophe

2017-11-26

Plasmonic immunosensors are usually made of a noble metal (in the form of a film or nanoparticles) on which bioreceptors are grafted to sense analytes based on the antibody/antigen or other affinity mechanism. Optical fiber configurations are a miniaturized counterpart to the bulky Kretschmann prism and allow easy light injection and remote operation. To excite a surface plasmon (SP), the core-guided light is locally outcoupled. Unclad optical fibers were the first configurations reported to this end. Among the different architectures able to bring light in contact with the surrounding medium, a great quantity of research is today being conducted on metal-coated fiber gratings photo-imprinted in the fiber core, as they provide modal features that enable SP generation at any wavelength, especially in the telecommunication window. They are perfectly suited for use with cost-effective high-resolution interrogators, allowing both a high sensitivity and a low limit of detection to be reached in immunosensing. This paper will review recent progress made in this field with different kinds of gratings: uniform, tilted and eccentric short-period gratings as well as long-period fiber gratings. Practical cases will be reported, showing that such sensors can be used in very small volumes of analytes and even possibly applied to in vivo diagnosis.

Microsecond switchable thermal antenna

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ben-Abdallah, Philippe, E-mail: pba@institutoptique.fr; Benisty, Henri; Besbes, Mondher

2014-07-21

We propose a thermal antenna that can be actively switched on and off at the microsecond scale by means of a phase transition of a metal-insulator material, the vanadium dioxide (VO{sub 2}). This thermal source is made of a periodically patterned tunable VO{sub 2} nanolayer, which support a surface phonon-polariton in the infrared range in their crystalline phase. Using electrodes properly registered with respect to the pattern, the VO{sub 2} phase transition can be locally triggered by ohmic heating so that the surface phonon-polariton can be diffracted by the induced grating, producing a highly directional thermal emission. Conversely, when heatingmore » less, the VO{sub 2} layers cool down below the transition temperature, the surface phonon-polariton cannot be diffracted anymore so that thermal emission is inhibited. This switchable antenna could find broad applications in the domain of active thermal coatings or in those of infrared spectroscopy and sensing.« less

Passive microwave studies of frozen lakes

NASA Technical Reports Server (NTRS)

Hall, D. K.; Foster, J. L.; Rango, A.; Chang, A. T. C.

1978-01-01

Lakes of various sizes, depths and ice thicknesses in Alaska, Utah and Colorado were overflown with passive microwave sensors providing observations at several wavelengths. A layer model is used to calculate the microwave brightness temperature, T sub B (a function of the emissivity and physical temperatures of the object), of snowcovered ice underlain with water. Calculated T sub B's are comparable to measured T sub B's. At short wavelengths, e.g., 0.8 cm, T sub B data provide information on the near surface properties of ice covered lakes where the long wavelength, 21.0 cm, observations sense the entire thickness of ice including underlying water. Additionally, T sub B is found to increase with ice thickness. 1.55 cm observations on Chandalar Lake in Alaska show a T sub B increase of 38 K with an approximate 124 cm increase in ice thickness.

Plasmon-enhanced tilted fiber Bragg gratings with oriented silver nanowire coatings

NASA Astrophysics Data System (ADS)

Renoirt, J.-M.; Debliquy, M.; Albert, J.; Ianoul, A.; Caucheteur, C.

2014-05-01

(TFBG) covered by silver nanowires aligned perpendicularly to the fiber axis. TBFGs are a convenient way to measure surrounding refractive index, as they provide intrinsic temperature-insensitivity and preserve the optical fiber structural integrity. With bare TFBGs, sensitivity is about 60 nm/RIU (refractive index unit) while when coated with a gold thin film, surface plasmon resonance can be excited leading to a sensitivity about 600 nm/RIU. In our case, we show that localized plasmon resonances can be excited on silver nanowires. These nanowires (100 nm diameter and about 2.5 µm length) were synthetized by polyol process (ethylene glycol reducing silver nitrate in the presence of poly (vinyl pyrrolidone and sodium chloride). The nanowires were aligned and deposited perpendicularly to the fiber axis on the gratings using the Langmuir-Blodgett technique in order to maximise the coupling between azimuthally polarized light modes and the localized plasmons. Excitation of surface plasmons at wavelengths around 1.5 µm occurred, leading to a dip in the polarization dependent losses of the grating. This dip is highly dependent of the surrounding refractive index, leading to a sensitivity of 650 nm/RIU, which is a 10-fold increase compared to bare gratings. We obtain results equal or slightly higher than those obtained using a gold layer on TFBGs. In spite of the comparable bulk refractometric sensitivity, the use of these oriented nanowire layers provide significantly higher contact surface area for biochemical analysis using bioreceptors, and benefit from stronger polarization selectivity between azimuthal and radially polarized modes.

[Integration design and diffraction characteristics analysis of prism-grating-prism].

PubMed

He, Tian-Bo; Bayanheshig; Li, Wen-Hao; Kong, Peng; Tang, Yu-Guo

2014-01-01

Prism-grating-prism (PGP) module is the important dispersing component in the hyper spectral imager. In order to effectively predict the distribution of diffraction efficiency of the whole PGP component and its diffraction characteristics before fabrication, a method of the PGP integration design is proposed. From the point of view of the volume phase holographic grating (VPHG) design, combined with the restrictive correlation between the various parameters of prisms and grating, we compiled the analysis software for calculating the whole PGP's diffraction efficiency. Furthermore, the effects of the structure parameters of prisms and grating on the PGP's diffraction characteristics were researched in detail. In particular we discussed the Bragg wavelength shift behaviour of the grating and a broadband PGP spectral component with high diffraction efficiency was designed for the imaging spectrometers. The result of simulation indicated that the spectral bandwidth of the PGP becomes narrower with the dispersion coefficient of prism 1 material decreasing; Bragg wavelength shift characteristics broaden the bandwidth of VPHG both spectrally and angularly, higher angular selectivity is desirable for selection requirements of the prism 1 material, and it can be easily tuned to achieve spectral bandwidth suitable for imaging PGP spectrograph; the vertex angle of prism 1, the film thickness and relative permittivity modulation of the grating have a significant impact on the distribution of PGP's diffraction efficiency, so precision control is necessary when fabrication. The diffraction efficiency of the whole PGP component designed by this method is no less than 50% in the wavelength range from 400 to 1000 nm, the specific design parameters have been given in this paper that have a certain reference value for PGP fabrication.

VizieR Online Data Catalog: Radial velocity curves of LMC ellipsoidal variables (Nie+, 2014)

NASA Astrophysics Data System (ADS)

Nie, J. D.; Wood, P. R.

2014-11-01

We initially selected 86 sequence E candidates from those given in Soszynski et al. 2004 (cat. J/AcA/54/347). The radial velocity observations were taken using the Wide Field Spectrograph (WiFeS) mounted on the Australian National University 2.3m telescope at Siding Spring Observatory. WiFes has six gratings. For our observations, the gratings B7000 (wavelength coverage of 4184-5580Å) and I7000 (wavelength coverage of 6832-9120Å) were chosen for the blue and red CCD, respectively. These two gratings give a two-pixel resolution R=7000. We carried out 18 weeks of radial velocity monitoring, from 2010 September to 2012 March. (2 data files).

Surface normal coupling to multiple-slot and cover-slotted silicon nanocrystalline waveguides and ring resonators

NASA Astrophysics Data System (ADS)

Covey, John; Chen, Ray T.

2014-03-01

Grating couplers are ideal for coupling into the tightly confined propagation modes of semiconductor waveguides. In addition, nonlinear optics has benefited from the sub-diffraction limit confinement of horizontal slot waveguides. By combining these two advancements, slot-based nonlinear optics with mode areas less than 0.02 μm2 can become as routine as twisting fiber connectors together. Surface normal fiber alignment to a chip is also highly desirable from time, cost, and manufacturing considerations. To meet these considerable design challenges, a custom genetic algorithm is created which, starting from purely random designs, creates a unique four stage grating coupler for two novel horizontal slot waveguide platforms. For horizontal multiple-slot waveguides filled with silicon nanocrystal, a theoretical fiber-towaveguide coupling efficiency of 68% is obtained. For thin silicon waveguides clad with optically active silicon nanocrystal, known as cover-slot waveguides, a theoretical fiber-to-waveguide coupling efficiency of 47% is obtained, and 1 dB and 3 dB theoretical bandwidths of 70 nm and 150 nm are obtained, respectively. Both waveguide platforms are fabricated from scratch, and their respective on-chip grating couplers are experimentally measured from a standard single mode fiber array that is mounted surface normally. The horizontal multiple-slot grating coupler achieved an experimental 60% coupling efficiency, and the horizontal cover-slot grating coupler achieved an experimental 38.7% coupling efficiency, with an extrapolated 1 dB bandwidth of 66 nm. This report demonstrates the promise of genetic algorithm-based design by reducing to practice the first large bandwidth vertical grating coupler to a novel silicon nanocrystal horizontal cover-slot waveguide.

Distributed feedback laser biosensor incorporating a titanium dioxide nanorod surface

NASA Astrophysics Data System (ADS)

Ge, Chun; Lu, Meng; Zhang, Wei; Cunningham, Brian T.

2010-04-01

A dielectric nanorod structure is used to enhance the label-free detection sensitivity of a vertically-emitting distributed feedback laser biosensor (DFBLB). The device is comprised of a replica molded plastic grating that is subsequently coated with a dye-doped polymer layer and a TiO2 nanorod layer produced by the glancing angle deposition technique. The DFBLB emission wavelength is modulated by the adsorption of biomolecules, whose greater dielectric permittivity with respect to the surrounding liquid media will increase the laser wavelength in proportion to the density of surface-adsorbed biomaterial. The nanorod layer provides greater surface area than a solid dielectric thin film, resulting in the ability to incorporate a greater number of molecules. The detection of a monolayer of protein polymer poly (Lys, Phe) is used to demonstrate that a 90 nm TiO2 nanorod structure improves the detection sensitivity by a factor of 6.6 compared to an identical sensor with a nonporous TiO2 surface.

Resonance surface plasmon spectroscopy by tunable enhanced light transmission through nanostructured gratings and thin films

NASA Astrophysics Data System (ADS)

Yeh, Wei-Hsun

Surface plasmon resonance (SPR) is a powerful tool in probing interfacial events in that any changes of effective refractive index in the interface directly impact the behavior of surface plasmons, an electromagnetic wave, travelling along the interface. Surface plasmons (SPs) are generated only if the momemtum of incident light matches that of SPs in the interface. This thesis focuses on tuning the behavior of SPs by changing the topology of diffraction gratings, monitoring the thickness of thin films by diffraction gratings, and use of dispersion images to analyze complex optical responses of SPs through diffraction gratings. Chapter 1 covers the background/principle of SPR, comprehensive literature review, sensor applications, control of SPR spectral responses, and sensitivity of SPR. In Chapter 2, we illustrate a chirped grating with varying surface topology along its spatial position. We demonstrated that the features of nanostructure such as pitch and amplitude significantly impact the behavior of enhanced transmission. In addition, we also illustrate the sensing application of chirped grating and the results indicate that the chirped grating is a sensitive and information rich SPR platform. In chapter 3, we used a commercial DVD diffraction grating as a SPR coupler. A camera-mounted microscope with Bertrend lens attachment is used to observe the enhanced transmission. We demonstrate that this system can monitor the SPR responses and track the thickness of a silicon monoxide film without using a spectrophotometer. Surface plasmons are a result of collective oscillation of free electrons in the metal/dielectric interface. Thus, the interaction of SPs with delocalized electrons from molecular resonance is complex. In chapter 4, we perform both experimental and simulation works to address this complex interaction. Detailed examination and analysis show nontypical SPR responses. For p-polarized light, a branch of dispersion curve and quenching of SPs in the Q band of zinc phthalocyanine are observed. For both p- and s-polarized light, additional waveguided modes are observed and the wavelength from different guided modes are dispersed. Diffraction gratings can provide complicated optical information about SPs. Both front side (air/metal) and back side (metal/substrate) provide SPR signals simultaneously. In chapter 5, we use dispersion images to analyze the complicated optical responses of SPR from an asymmetrical diffraction grating consisting of three layers (air/gold/polycarbonate). We illustrate that clear identification of SPR responses from several diffraction orders at front side and back side can be achieved by the use of dispersion images. Theoretical prediction and experimental results show consistency. We also show that only the behavior of SPs from the front side is impacted by the deposition of Langmuir-Blodgett dielectric films. In chapter 6, we construct a diffraction grating that has a fixed pitch and several amplitudes on its surface by using interference lithography. The purpose of this work is to examine how the amplitude impacts the behavior of transmission peaks. Different amplitudes are successfully fabricated by varying development time in the lithography process. We observed that largest (optimized) enhanced transmission peak shows as the amplitude approach a critical value. Transmission is not maximized below or beyond a critical amplitude. We also found that transmission enhancements are strongly affected by the diffraction efficiencies. A maximum enhancement is observed as diffraction efficiency is largest where amplitude reaches the critical value. The experimental results are then compared to the simulation. (Abstract shortened by UMI.)

High frequency resonant waveguide grating imager for assessing drug-induced cardiotoxicity

NASA Astrophysics Data System (ADS)

Ferrie, Ann M.; Wu, Qi; Deichmann, Oberon D.; Fang, Ye

2014-05-01

We report a high-frequency resonant waveguide grating imager for assessing compound-induced cardiotoxicity. The imager sweeps the wavelength range from 823 nm to 838 nm every 3 s to identify and monitor compound-induced shifts in resonance wavelength and then switch to the intensity-imaging mode to detect the beating rhythm and proarrhythmic effects of compounds on induced pluripotent stem cell-derived cardiomyocytes. This opens possibility to study cardiovascular biology and compound-induced cardiotoxicity.

Fiber comb filters based on UV-writing Bragg gratings in graded-index multimode fibers

NASA Astrophysics Data System (ADS)

Liu, Yu; Lit, John; Gu, Xijia; Wei, Li

2005-10-01

We report a new kind of comb filters based on fiber Bragg gratings in graded-index multimode fibers. It produces two groups of spectra with a total of 36 reflection peaks that correspond to 18 principal modes and cross coupled modes. The mode indices and wavelength spacings have been investigated theoretically and experimentally. This kind of comb filters may be used to construct multi-wavelength light sources for sensing, optical communications, and instrumentations

High resolution PFPE-based molding High resolution PFPE-based molding High resolution PFPE-based molding techniques for nanofabrication of high pattern density sub-20 nm features: A fundamental materials approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williams, Stuart S; Samulski, Edward; Lopez, Renee

2010-01-01

ABSTRACT. Described herein is the development and investigation of PFPE-based elastomers for high resolution replica molding applications. The modulus of the elastomeric materials was increased through synthetic and additive approaches while maintaining relatively low surface energies (<25 mN/m). Using practically relevant large area master templates, we show that the resolution of the molds is strongly dependant upon the elastomeric mold modulus. A composite mold approach was used to form flexible molds out of stiff, high modulus materials that allow for replication of sub-20 nm post structures. Sub-100 nm line grating master templates, formed using e-beam lithography, were used to determinemore » the experimental stability of the molding materials. It was observed that as the feature spacing decreased, high modulus composite molds were able to effectively replicate the nano-grating structures without cracking or tear-out defects that typically occur with high modulus elastomers.« less

Sub-wavelength modulation of χ (2) optical nonlinearity in organic thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Yixin; Yuan, Yakun; Wang, Baomin

Modulating the second-order nonlinear optical susceptibility (χ (2)) of materials at the nanoscale represents an ongoing technological challenge for a variety of integrated frequency conversion and nonlinear nanophotonic applications. Here we exploit the large hyperpolarizability of intermolecular charge transfer states, naturally aligned at an organic semiconductor donor–acceptor (DA) interface, as a means to control the magnitude and sign of χ (2) at the nanoscale. Focusing initially on a single pentacene-C 60 DA interface, we confirm that the charge transfer transition is strongly aligned orthogonal to the heterojunction and find that it is responsible for a large interfacial nonlinearity probed viamore » second harmonic generation that is sufficient to achieve d 33 > 10pm V –1, when incorporated in a non-centrosymmetric DA multilayer stack. Lastly, using grating-shadowed oblique-angle deposition to laterally structure the DA interface distribution in such multilayers subsequently enables the demonstration of a χ (2) grating with 280 nm periodicity, which is the shortest reported to date.« less

Sub-wavelength modulation of χ(2) optical nonlinearity in organic thin films

NASA Astrophysics Data System (ADS)

Yan, Yixin; Yuan, Yakun; Wang, Baomin; Gopalan, Venkatraman; Giebink, Noel C.

2017-01-01

Modulating the second-order nonlinear optical susceptibility (χ(2)) of materials at the nanoscale represents an ongoing technological challenge for a variety of integrated frequency conversion and nonlinear nanophotonic applications. Here we exploit the large hyperpolarizability of intermolecular charge transfer states, naturally aligned at an organic semiconductor donor-acceptor (DA) interface, as a means to control the magnitude and sign of χ(2) at the nanoscale. Focusing initially on a single pentacene-C60 DA interface, we confirm that the charge transfer transition is strongly aligned orthogonal to the heterojunction and find that it is responsible for a large interfacial nonlinearity probed via second harmonic generation that is sufficient to achieve d33>10 pm V-1, when incorporated in a non-centrosymmetric DA multilayer stack. Using grating-shadowed oblique-angle deposition to laterally structure the DA interface distribution in such multilayers subsequently enables the demonstration of a χ(2) grating with 280 nm periodicity, which is the shortest reported to date.

Sub-wavelength modulation of χ (2) optical nonlinearity in organic thin films

DOE PAGES

Yan, Yixin; Yuan, Yakun; Wang, Baomin; ...

2017-01-27

Modulating the second-order nonlinear optical susceptibility (χ (2)) of materials at the nanoscale represents an ongoing technological challenge for a variety of integrated frequency conversion and nonlinear nanophotonic applications. Here we exploit the large hyperpolarizability of intermolecular charge transfer states, naturally aligned at an organic semiconductor donor–acceptor (DA) interface, as a means to control the magnitude and sign of χ (2) at the nanoscale. Focusing initially on a single pentacene-C 60 DA interface, we confirm that the charge transfer transition is strongly aligned orthogonal to the heterojunction and find that it is responsible for a large interfacial nonlinearity probed viamore » second harmonic generation that is sufficient to achieve d 33 > 10pm V –1, when incorporated in a non-centrosymmetric DA multilayer stack. Lastly, using grating-shadowed oblique-angle deposition to laterally structure the DA interface distribution in such multilayers subsequently enables the demonstration of a χ (2) grating with 280 nm periodicity, which is the shortest reported to date.« less

Silicon graphene Bragg gratings.

PubMed

Capmany, José; Domenech, David; Muñoz, Pascual

2014-03-10

We propose the use of interleaved graphene sections on top of a silicon waveguide to implement tunable Bragg gratings. The filter central wavelength and bandwidth can be controlled changing the chemical potential of the graphene sections. Apodization techniques are also presented.

Fabrication of Fiber-Optic Tilted Bragg Grating Filter in 40 nm Range with A Single Phase Mask

NASA Technical Reports Server (NTRS)

Grant, Joseph; Wang, Y.; Sharma, A.; Burdine, Robert V. (Technical Monitor)

2002-01-01

Fiber-optic Bragg grating filters are fabricated with a range of Bragg wavelength between 1296 and 1336 nm, using a single phase mask. 30 mW of continuous-wave light at 244 nm is used from a frequency-doubled argon-ion laser having an intracavity etalon. Gratings are fabricated by tilting the photosensitive fiber with respect to the phase mask up to an angle of 15 degrees. The variation of Bragg wavelength with the fiber-tilt is explained with a simple formula. High spatial coherence of 244 nm light makes it possible to displace the fiber as much as 6 mm in front of the phase mask and tilt the fiber by as much as 15 degrees. This results in nearly constant band-width and near 100% reflectively for all gratings throughout the 40 nm range.

Effects of thermal loading and hydrostatic pressure on reflecting wavelengths of double-coated fiber Bragg grating with different coating-layer thickness

NASA Astrophysics Data System (ADS)

Seraji, Faramarz E.; Toutian, Golnoush

2017-10-01

Fiber Bragg grating (FBG) of different configurations used as sensing devices are vulnerable to environmental factors, such as static pressures and thermal loading, which cause their characteristic Bragg reflecting wavelengths to up/down-shift. In this paper, by considering double-coated FBG with different primary and secondary coating materials, the effects of thermal loading and hydrostatic pressure on FBG with different coating-layer thicknesses are analyzed to find design criteria for controlling the Bragg wavelength shift. The obtained results of the analysis may be employed as criteria to design pressure and temperature sensors when using double-coated FBGs.

High resolution resonance ionization imaging detector and method

DOEpatents

Winefordner, James D.; Matveev, Oleg I.; Smith, Benjamin W.

1999-01-01

A resonance ionization imaging device (RIID) and method for imaging objects using the RIID are provided, the RIID system including a RIID cell containing an ionizable vapor including monoisotopic atoms or molecules, the cell being positioned to intercept scattered radiation of a resonance wavelength .lambda..sub.1 from the object which is to be detected or imaged, a laser source disposed to illuminate the RIID cell with laser radiation having a wavelength .lambda..sub.2 or wavelengths .lambda..sub.2, .lambda..sub.3 selected to ionize atoms in the cell that are in an excited state by virtue of having absorbed the scattered resonance laser radiation, and a luminescent screen at the back surface of the RIID cell which presents an image of the number and position of charged particles present in the RIID cell as a result of the ionization of the excited state atoms. The method of the invention further includes the step of initially illuminating the object to be detected or imaged with a laser having a wavelength selected such that the object will scatter laser radiation having the resonance wavelength .lambda..sub.1.

On the use of a chirped Bragg grating as a cavity mirror of a picosecond Nd : YAG laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zubko, A E; Shashkov, E V; Smirnov, A V

2016-02-28

The first experimental evidence is presented that the use of a chirped volume Bragg grating (CVBG) as a cavity mirror of a Q-switched picosecond Nd : YAG laser with self-mode-locking leads to significant changes in the temporal parameters of the laser output. Measurements have been performed at two positions of the CVBG: with the grating placed so that shorter wavelengths reflected from its front part lead longer wavelengths or with the grating rotated through 180°, so that longer wavelengths are reflected first. In the former case, the duration of individual pulses in a train increased from ∼35 to ∼300 ps,more » whereas the pulse train shape and duration remained the same as in the case of a conventional laser with a mirror cavity. In the latter case, the full width at half maximum of pulse trains increased from ∼70 ns (Nd : YAG laser with a mirror cavity) to ∼1 ms, and the duration of individual pulses increased from 35 ps to ∼1.2 ns, respectively, which is more typical of free-running laser operation. (laser crystals and braggg ratings)« less

Optical power-based interrogation of plasmonic tilted fiber Bragg grating biosensors

NASA Astrophysics Data System (ADS)

González-Vila, Á.; Lopez-Aldaba, A.; Kinet, D.; Mégret, P.; Lopez-Amo, M.; Caucheteur, C.

2017-04-01

Two interrogation techniques for plasmonic tilted fiber Bragg grating sensors are reported and experimentally tested. Typical interrogation methods are usually based on tracking the wavelength shift of the most sensitive cladding mode, but for biosensing applications, spectrometer-based methods can be replaced by more efficient solutions. The proposed techniques thus rely on the measurement of the induced changes in optical power. The first one consists of a properly polarized tunable laser source set to emit at the wavelength of the sensor most sensitive mode and an optical power meter to measure the transmitted response. For the second method, a uniform fiber Bragg grating is photo-inscribed beyond the sensor in such a way that its central wavelength matches the sensor most sensitive mode, acting as an optical filter. Using a LED source, light reflected backwards by this grating is partially attenuated when passing through the sensor due to plasmon wave excitation and the power changes are quantified once again with an optical power meter. A performance analysis of the techniques is carried out and they both result competitive interrogation solutions. The work thus focuses on the development of cost-effective alternatives for monitoring this kind of biosensors in practical situations.

Characteristics of a dynamic holographic sensor for shape control of a large reflector

NASA Technical Reports Server (NTRS)

Welch, Sharon S.; Cox, David E.

1991-01-01

Design of a distributed holographic interferometric sensor for measuring the surface displacement of a large segmented reflector is proposed. The reflector's surface is illuminated by laser light of two wavelengths and volume holographic gratings are formed in photorefractive crystals of the wavefront returned from the surface. The sensor is based on holographic contouring with a multiple frequency source. It is shown that the most stringent requirement of temporal stability affects both the temporal resolution and the dynamic range. Principal factor which limit the sensor performance include the response time of photorefractive crystal, laser power required to write a hologram, and the size of photorefractive crystal.

A surface impedance-based three-channel acoustic metasurface retroreflector

NASA Astrophysics Data System (ADS)

Shen, Chen; Díaz-Rubio, Ana; Li, Junfei; Cummer, Steven A.

2018-04-01

We propose the design and measurement of an acoustic metasurface retroreflector that works at three discrete incident angles. An impedance model is developed such that for acoustic waves impinging at -60°, the reflected wave is defined by the surface impedance of the metasurface, which is realized by a periodic grating. At 0° and 60°, the retroreflection condition can be fulfilled by the diffraction of the surface. The thickness of the metasurface is about half of the operating wavelength and the retroreflector functions without parasitic diffraction associated with conventional gradient-index metasurfaces. Such highly efficient and compact retroreflectors open up possibilities in metamaterial-based acoustic sensing and communications.

Excitation of multiple surface-plasmon-polariton waves using a compound surface-relief grating

NASA Astrophysics Data System (ADS)

Faryad, Muhammad; Lakhtakia, Akhlesh

2012-01-01

The excitation of multiple surface-plasmon-polariton waves, all of the same frequency but different polarization states, phase speeds, spatial profiles and degrees of localization, by a compound surface-relief grating formed by a metal and a rugate filter, both of finite thickness, was studied using the rigorous coupled-wave approach. Each period of the compound surface-relief grating was chosen to have an integral number of periods of two different simple surface-relief gratings. The excitation of different SPP waves was inferred from the absorptance peaks that were independent of the thickness of the rugate filter. The excitation of each SPP wave could be attributed to either a simple surface-relief grating present in the compound surface-relief grating or to the compound surface-relief grating itself. However, the excitation of SPP waves was found to be less efficient with the compound surface-relief grating than with a simple surface-relief grating.

4.3 μm quantum cascade detector in pixel configuration.

PubMed

Harrer, A; Schwarz, B; Schuler, S; Reininger, P; Wirthmüller, A; Detz, H; MacFarland, D; Zederbauer, T; Andrews, A M; Rothermund, M; Oppermann, H; Schrenk, W; Strasser, G

2016-07-25

We present the design simulation and characterization of a quantum cascade detector operating at 4.3μm wavelength. Array integration and packaging processes were investigated. The device operates in the 4.3μm CO₂ absorption region and consists of 64 pixels. The detector is designed fully compatible to standard processing and material growth methods for scalability to large pixel counts. The detector design is optimized for a high device resistance at elevated temperatures. A QCD simulation model was enhanced for resistance and responsivity optimization. The substrate illuminated pixels utilize a two dimensional Au diffraction grating to couple the light to the active region. A single pixel responsivity of 16mA/W at room temperature with a specific detectivity D^* of 5⋅10⁷ cmHz/W was measured.

Tunable Infrared Semiconductor Lasers

DTIC Science & Technology

2013-12-20

stripe to different positions of an addressable chirped, location-dependent period grating to select the different lasing wavelengths. Interferometric...grating or vernier effects. Our tuning mechanism is to shift the pump stripe to different positions of an addressable chirped, location-dependent period... stripe is applied and the lateral direction is the perpendicular direction across the pump stripe and parallel to the grating lines.  The chirped

Optical second-harmonic diffraction study of anisotropic surface diffusion: CO on Ni(110)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiao, X.; Zhu, X.D.; Daum, W.

We describe in detail a technique using optical second-harmonic (SH) diffraction from a one-dimensional laser-induced monolayer grating to probe surface diffusion of adsorbates and its anisotropy on a solid surface. The case of CO on Ni(110) is used as a demonstration. The two orthogonal and independent diffusion tensor components along (1{bar 1}0) and (001) are measured, exhibiting a strong anisotropy in both the activation energy {ital E}{sub diff} and the preexponential factor {ital D}{sub 0} in the diffusion coefficients. A compensation effect between {ital E}{sub diff} and {ital D}{sub 0} is observed. In comparison with CO/Ni(111) and CO/Ni(100), our resultmore » suggests that the Ni(110) surface seen by CO is much smoother than Ni(111) and Ni(100). Both advantages and limitations of the present technique are mentioned and possible complications in the data analysis are discussed.« less

Multilayer diffraction grating

DOEpatents

Barbee, T.W. Jr.

1990-04-10

This invention is for a reflection diffraction grating that functions at X-ray to VUV wavelengths and at normal angles of incidence. The novel grating is comprised of a laminar grating of period D with flat-topped grating bars. A multiplicity of layered synthetic microstructures, of period d and comprised of alternating flat layers of two different materials, are disposed on the tops of the grating bars of the laminar grating. In another embodiment of the grating, a second multiplicity of layered synthetic microstructures are also disposed on the flat faces, of the base of the grating, between the bars. D is in the approximate range from 3,000 to 50,000 Angstroms, but d is in the approximate range from 10 to 400 Angstroms. The laminar grating and the layered microstructures cooperatively interact to provide many novel and beneficial instrumentational advantages. 2 figs.

Multilayer diffraction grating

DOEpatents

Barbee, Jr., Troy W.

1990-01-01

This invention is for a reflection diffraction grating that functions at X-ray to VUV wavelengths and at normal angles of incidence. The novel grating is comprised of a laminar grating of period D with flat-topped grating bars. A multiplicity of layered synthetic microstructures, of period d and comprised of alternating flat layers of two different materials, are disposed on the tops of the grating bars of the laminar grating. In another embodiment of the grating, a second multiplicity of layered synthetic microstructures are also disposed on the flat faces, of the base of the grating, between the bars. D is in the approximate range from 3,000 to 50,000 Angstroms, but d is in the approximate range from 10 to 400 Angstroms. The laminar grating and the layered microstructures cooperatively interact to provide many novel and beneficial instrumentational advantages.

Rotated grating coupled surface plasmon resonance on wavelength-scaled shallow rectangular gratings

NASA Astrophysics Data System (ADS)

Szalai, A.; Szekeres, G.; Balázs, J.; Somogyi, A.; Csete, Maria

2013-09-01

Theoretical investigation of rotated grating coupling phenomenon was performed on a multilayer comprising 416-nmperiodic shallow rectangular polymer grating on bimetal film made of gold and silver layers. During the multilayer illumination by 532 nm wavelength p-polarized light the polar and azimuthal angles were varied. In presence of 0-35 nm, 0-50 nm and 15-50 nm thick polymer-layers at the valleys and hills splitting was observed on the dual-angle dependent reflectance in two regions: (i) close to 0° azimuthal angle corresponding to incidence plane parallel to the periodic pattern (P-orientation); and (ii) around ~33.5°/29°/30° azimuthal angle (C-orientation), in agreement with our previous experimental studies. The near-field study revealed that in P-orientation the E-field is enhanced at the glass side with p/2 periodicity at the first minimum appearing at 49°/50°/52° polar angles, and comprises maxima below both the valleys and hills; while E-field enhancement is observable both at the glass and polymer side with p-periodicity at the second minimum developing at 55°/63/64° tilting, comprising maxima intermittently below the valleys or above the hills. In Corientation coupled plasmonic modes are observable, involving modes propagating along the valleys at the secondary maxima appearing at ~35°/32°/32° azimuthal and ~49°/51°/56° polar angles, while modes confined along the polymer hills are observable at the primary minima, which are coupled most strongly at the ~31.5°/25°/28° azimuthal and ~55°/63°/66° polar angles. The secondary peak observable in C-orientation is proposed for biosensing applications, since the supported modes are confined along the valleys, where biomolecules prefer to attach.

Optically imprinted reconfigurable photonic elements in a VO{sub 2} nanocomposite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jostmeier, Thorben; Betz, Markus; Zimmer, Johannes

We investigate the optical and thermal hysteresis of single-domain vanadium dioxide nanocrystals fabricated by ion beam synthesis in a fused silica matrix. The nanocrystals exhibit a giant hysteresis, which permits to optically generate a long-time stable supercooled metallic phase persistent down to practically room temperature. Spatial patterns of supercooled and insulating nanocrystals feature a large dielectric contrast, in particular, for telecom wavelengths. We utilize this contrast to optically imprint reconfigurable photonic elements comprising diffraction gratings as well as on- and off-axis zone plates. The structures allow for highly repetitive (>10{sup 4}) cycling through the phase transition without structural damage.

Optical temperature sensing on flexible polymer foils

NASA Astrophysics Data System (ADS)

Sherman, Stanislav; Xiao, Yanfen; Hofmann, Meike; Schmidt, Thomas; Gleissner, Uwe; Zappe, Hans

2016-04-01

In contrast to established semiconductor waveguide-based or glass fiber-based integrated optical sensors, polymerbased optical systems offer tunable material properties, such as refractive index or viscosity, and thus provide additional degrees of freedom for sensor design and fabrication. Of particular interest in sensing applications are fully-integrated optical waveguide-based temperature sensors. These typically rely on Bragg gratings which induce a periodic refractive index variation in the waveguide so that a resonant wavelength of the structure is reflected.1,2 With broad-band excitation, a dip in the spectral output of the waveguide is thus generated at a precisely-defined wavelength. This resonant wavelength depends on the refractive index of the waveguide and the grating period, yet both of these quantities are temperature dependent by means of the thermo-optic effect (change in refractive index with temperature) and thermal expansion (change of the grating period with temperature). We show the design and fabrication of polymer waveguide-integrated temperature sensors based on Bragggratings, fabricated by replication technology on flexible PMMA foil substrates. The 175 μm thick foil serves as lower cladding for a polymeric waveguide fabricated from a custom-made UV-crosslinkable co-monomer composition. The fabrication of the grating structure includes a second replication step into a separate PMMA-foil. The dimensions of the Bragg-gratings are determined by simulations to set the bias point into the near infrared wavelength range, which allows Si-based detectors to be used. We present design considerations and performance data for the developed structures. The resulting sensor's signal is linear to temperature changes and shows a sensitivity of -306 nm/K, allowing high resolution temperature measurements.

Toroidal Variable-Line-Space Gratings: The Good, the Bad and The Ugly

NASA Technical Reports Server (NTRS)

West, Edward A.; Kobayashi, Ken; Cirtain, Jonathan; Gary, Allen; Davis, John; Reader, Joseph

2009-01-01

Toroidal variable-line-space (VLS) gratings are an important factor in the design of an efficient VUV solar telescope that will measure the CIV (155nm) and MgII (280nm) emissions lines in the Sun's transition region. In 1983 Kita and Harada described spherical VLS gratings but the technology to commercially fabricate these devices is a recent development, especially for toroidal surfaces. This paper will describe why this technology is important in the development of the Solar Ultraviolet Magnetograph Investigation (SUMI) sounding rocket program (the good), the delays due to the conversion between the TVLS grating design and the optical fabrication (the bad), and finally the optical testing, alignment and tolerancing of the gratings (the ugly). The Solar Ultraviolet Magnetograph Investigation, SUMI, has been reported in several papers since this program began in 2000. The emphasis of this paper is to describe SUMI's Toroidal Variable-Line-Space (TVLS) gratings. These gratings help SUMI meet its scientific goals which require both high spectral resolution and high optical efficiency for magnetic field measurements in the vacuum ultraviolet wavelength band of the solar spectrum (the good). Unfortunately, the technology readiness level of these gratings has made their implementation difficult, especially for a sounding rocket payload (the bad). Therefore, this paper emphasizes the problems and solutions that were developed to use these gratings in SUMI (the ugly). Section 2 contains a short review of the scientific goals of SUMI and why this mission is important in the understanding of the 3D structure of the magnetic field on the Sun. The flight hardware that makes up the SUMI payload is described in Section 3 with emphasis on those components that affect the TVLS gratings. Section 4 emphasizes the alignment, testing and optical modeling that were developed to optimize the performance of these gratings.

A Fiber Bragg Grating Sensor Interrogation System Based on a Linearly Wavelength-Swept Thermo-Optic Laser Chip

PubMed Central

Lee, Hyung-Seok; Lee, Hwi Don; Kim, Hyo Jin; Cho, Jae Du; Jeong, Myung Yung; Kim, Chang-Seok

2014-01-01

A linearized wavelength-swept thermo-optic laser chip was applied to demonstrate a fiber Bragg grating (FBG) sensor interrogation system. A broad tuning range of 11.8 nm was periodically obtained from the laser chip for a sweep rate of 16 Hz. To measure the linear time response of the reflection signal from the FBG sensor, a programmed driving signal was directly applied to the wavelength-swept laser chip. The linear wavelength response of the applied strain was clearly extracted with an R-squared value of 0.99994. To test the feasibility of the system for dynamic measurements, the dynamic strain was successfully interrogated with a repetition rate of 0.2 Hz by using this FBG sensor interrogation system. PMID:25177803

Moiré phase-shifted fiber Bragg gratings in polymer optical fibers

NASA Astrophysics Data System (ADS)

Min, Rui; Marques, Carlos; Bang, Ole; Ortega, Beatriz

2018-03-01

We demonstrate a simple way to fabricate phase-shifted fiber Bragg grating in polymer optical fibers as a narrowband transmission filter for a variety of applications at telecom wavelengths. The filters have been fabricated by overlapping two uniform fiber Bragg gratings with slightly different periods to create a Moiré grating with only two pulses (one pulse is 15 ns) of UV power. Experimental characterization of the filter is provided under different conditions where the strain and temperature sensitivities were measured.

Numerical Modeling of Sub-Wavelength Anti-Reflective Structures for Solar Module Applications

PubMed Central

Han, Katherine; Chang, Chih-Hung

2014-01-01

This paper reviews the current progress in mathematical modeling of anti-reflective subwavelength structures. Methods covered include effective medium theory (EMT), finite-difference time-domain (FDTD), transfer matrix method (TMM), the Fourier modal method (FMM)/rigorous coupled-wave analysis (RCWA) and the finite element method (FEM). Time-based solutions to Maxwell’s equations, such as FDTD, have the benefits of calculating reflectance for multiple wavelengths of light per simulation, but are computationally intensive. Space-discretized methods such as FDTD and FEM output field strength results over the whole geometry and are capable of modeling arbitrary shapes. Frequency-based solutions such as RCWA/FMM and FEM model one wavelength per simulation and are thus able to handle dispersion for regular geometries. Analytical approaches such as TMM are appropriate for very simple thin films. Initial disadvantages such as neglect of dispersion (FDTD), inaccuracy in TM polarization (RCWA), inability to model aperiodic gratings (RCWA), and inaccuracy with metallic materials (FDTD) have been overcome by most modern software. All rigorous numerical methods have accurately predicted the broadband reflection of ideal, graded-index anti-reflective subwavelength structures; ideal structures are tapered nanostructures with periods smaller than the wavelengths of light of interest and lengths that are at least a large portion of the wavelengths considered. PMID:28348287

Multi-function all optical packet switch by periodic wavelength arrangement in an arrayed waveguide grating and wideband optical filters.

PubMed

Feng, Kai-Ming; Wu, Chung-Yu; Wen, Yu-Hsiang

2012-01-16

By utilizing the cyclic filtering function of an NxN arrayed waveguide grating (AWG), we propose and experimentally demonstrate a novel multi-function all optical packet switching (OPS) architecture by applying a periodical wavelength arrangement between the AWG in the optical routing/buffering unit and a set of wideband optical filters in the switched output ports to achieve the desired routing and buffering functions. The proposed OPS employs only one tunable wavelength converter at the input port to convert the input wavelength to a designated wavelength which reduces the number of active optical components and thus the complexity of the traffic control is simplified in the OPS. With the proposed OPS architecture, multiple optical packet switching functions, including arbitrary packet switching and buffering, first-in-first-out (FIFO) packet multiplexing, packet demultiplexing and packet add/drop multiplexing, have been successfully demonstrated.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Austin, Dane R.; Witting, Tobias; Walmsley, Ian A.

We describe the elimination of the astigmatism of a Czerny-Turner imaging spectrometer, built using spherical optics and a plane grating, over a broad spectral region. Starting with the principle of divergent illumination of the grating, which removes astigmatism at one chosen wavelength, we obtain design equations for the distance from the grating to the focusing mirror and the detector angle that remove the astigmatism to first order in wavelength. Experimentally, we demonstrate near diffraction-limited performance from 740 to 860 nm and over a 5 mm transverse spatial extent, while ray-tracing calculations show that barring finite-aperture and detector size limitations, thismore » range extends from 640 to 900 nm and over 10 mm transversely. Our technique requires no additional optics and uses standard off-the-shelf components.« less

On-chip broadband spectral filtering using planar double high-contrast grating reflectors

NASA Astrophysics Data System (ADS)

Horie, Yu; Arbabi, Amir; Faraon, Andrei

2015-02-01

We propose a broadband free-space on-chip spectrometer based on an array of integrated narrowband filters consisting of Fabry-Perot resonators formed by two high-contrast grating (HCG) based reflectors separated by a low-index thin layer with a fixed cavity thickness. Using numerical simulations, broadband tunability of resonance wavelengths was achieved only by changing the in-plane grating parameters such as period or duty cycle of HCGs while the substrate geometry was kept fixed. Experimentally, the HCG reflectors were fabricated on silicon on insulator (SOI) substrates and high reflectivity was measured, fabrication process for the proposed double HCG-based narrowband filter array was developed. The filtering function that can be spanned over a wide range of wavelengths was measured.

Thin film solar cell design based on photonic crystal and diffractive grating structures.

PubMed

Mutitu, James G; Shi, Shouyuan; Chen, Caihua; Creazzo, Timothy; Barnett, Allen; Honsberg, Christiana; Prather, Dennis W

2008-09-15

In this paper we present novel light trapping designs applied to multiple junction thin film solar cells. The new designs incorporate one dimensional photonic crystals as band pass filters that reflect short light wavelengths (400 - 867 nm) and transmit longer wavelengths(867 -1800 nm) at the interface between two adjacent cells. In addition, nano structured diffractive gratings that cut into the photonic crystal layers are incorporated to redirect incoming waves and hence increase the optical path length of light within the solar cells. Two designs based on the nano structured gratings that have been realized using the scattering matrix and particle swarm optimization methods are presented. We also show preliminary fabrication results of the proposed devices.

One-step sol-gel imprint lithography for guided-mode resonance structures.

PubMed

Huang, Yin; Liu, Longju; Johnson, Michael; C Hillier, Andrew; Lu, Meng

2016-03-04

Guided-mode resonance (GMR) structures consisting of sub-wavelength periodic gratings are capable of producing narrow-linewidth optical resonances. This paper describes a sol-gel-based imprint lithography method for the fabrication of submicron 1D and 2D GMR structures. This method utilizes a patterned polydimethylsiloxane (PDMS) mold to fabricate the grating coupler and waveguide for a GMR device using a sol-gel thin film in a single step. An organic-inorganic hybrid sol-gel film was selected as the imprint material because of its relatively high refractive index. The optical responses of several sol-gel GMR devices were characterized, and the experimental results were in good agreement with the results of electromagnetic simulations. The influence of processing parameters was investigated in order to determine how finely the spectral response and resonant wavelength of the GMR devices could be tuned. As an example potential application, refractometric sensing experiments were performed using a 1D sol-gel device. The results demonstrated a refractive index sensitivity of 50 nm/refractive index unit. This one-step fabrication process offers a simple, rapid, and low-cost means of fabricating GMR structures. We anticipate that this method can be valuable in the development of various GMR-based devices as it can readily enable the fabrication of complex shapes and allow the doping of optically active materials into sol-gel thin film.

Nanophotonic lab-on-a-chip platforms including novel bimodal interferometers, microfluidics and grating couplers.

PubMed

Duval, Daphné; González-Guerrero, Ana Belén; Dante, Stefania; Osmond, Johann; Monge, Rosa; Fernández, Luis J; Zinoviev, Kirill E; Domínguez, Carlos; Lechuga, Laura M

2012-05-08

One of the main limitations for achieving truly lab-on-a-chip (LOC) devices for point-of-care diagnosis is the incorporation of the "on-chip" detection. Indeed, most of the state-of-the-art LOC devices usually require complex read-out instrumentation, losing the main advantages of portability and simplicity. In this context, we present our last advances towards the achievement of a portable and label-free LOC platform with highly sensitive "on-chip" detection by using nanophotonic biosensors. Bimodal waveguide interferometers fabricated by standard silicon processes have been integrated with sub-micronic grating couplers for efficient light in-coupling, showing a phase resolution of 6.6 × 10(-4)× 2π rad and a limit of detection of 3.3 × 10(-7) refractive index unit (RIU) in bulk. A 3D network of SU-8 polymer microfluidics monolithically assembled at the wafer-level was included, ensuring perfect sealing and compact packaging. To overcome some of the drawbacks inherent to interferometric read-outs, a novel all-optical wavelength modulation system has been implemented, providing a linear response and a direct read-out of the phase variation. Sensitivity, specificity and reproducibility of the wavelength modulated BiMW sensor has been demonstrated through the label-free immunodetection of the human hormone hTSH at picomolar level using a reliable biofunctionalization process.

Fast integral methods for integrated optical systems simulations: a review

NASA Astrophysics Data System (ADS)

Kleemann, Bernd H.

2015-09-01

Boundary integral equation methods (BIM) or simply integral methods (IM) in the context of optical design and simulation are rigorous electromagnetic methods solving Helmholtz or Maxwell equations on the boundary (surface or interface of the structures between two materials) for scattering or/and diffraction purposes. This work is mainly restricted to integral methods for diffracting structures such as gratings, kinoforms, diffractive optical elements (DOEs), micro Fresnel lenses, computer generated holograms (CGHs), holographic or digital phase holograms, periodic lithographic structures, and the like. In most cases all of the mentioned structures have dimensions of thousands of wavelengths in diameter. Therefore, the basic methods necessary for the numerical treatment are locally applied electromagnetic grating diffraction algorithms. Interestingly, integral methods belong to the first electromagnetic methods investigated for grating diffraction. The development started in the mid 1960ies for gratings with infinite conductivity and it was mainly due to the good convergence of the integral methods especially for TM polarization. The first integral equation methods (IEM) for finite conductivity were the methods by D. Maystre at Fresnel Institute in Marseille: in 1972/74 for dielectric, and metallic gratings, and later for multiprofile, and other types of gratings and for photonic crystals. Other methods such as differential and modal methods suffered from unstable behaviour and slow convergence compared to BIMs for metallic gratings in TM polarization from the beginning to the mid 1990ies. The first BIM for gratings using a parametrization of the profile was developed at Karl-Weierstrass Institute in Berlin under a contract with Carl Zeiss Jena works in 1984-1986 by A. Pomp, J. Creutziger, and the author. Due to the parametrization, this method was able to deal with any kind of surface grating from the beginning: whether profiles with edges, overhanging non-functional profiles, very deep ones, very large ones compared to wavelength, or simple smooth profiles. This integral method with either trigonometric or spline collocation, iterative solver with O(N2) complexity, named IESMP, was significantly improved by an efficient mesh refinement, matrix preconditioning, Ewald summation method, and an exponentially convergent quadrature in 2006 by G. Schmidt and A. Rathsfeld from Weierstrass-Institute (WIAS) Berlin. The so-called modified integral method (MIM) is a modification of the IEM of D. Maystre and has been introduced by L. Goray in 1995. It has been improved for weak convergence problems in 2001 and it was the only commercial available integral method for a long time, known as PCGRATE. All referenced integral methods so far are for in-plane diffraction only, no conical diffraction was possible. The first integral method for gratings in conical mounting was developed and proven under very weak conditions by G. Schmidt (WIAS) in 2010. It works for separated interfaces and for inclusions as well as for interpenetrating interfaces and for a large number of thin and thick layers in the same stable way. This very fast method has then been implemented for parallel processing under Unix and Windows operating systems. This work gives an overview over the most important BIMs for grating diffraction. It starts by presenting the historical evolution of the methods, highlights their advantages and differences, and gives insight into new approaches and their achievements. It addresses future open challenges at the end.

Cylinder and metal grating polarization beam splitter

NASA Astrophysics Data System (ADS)

Yang, Junbo; Xu, Suzhi

2017-08-01

We propose a novel and compact metal grating polarization beam splitter (PBS) based on its different reflected and transmitted orders. The metal grating exhibits a broadband high reflectivity and polarization dependence. The rigorous coupled wave analysis is used to calculate the reflectivity and the transmitting spectra and optimize the structure parameters to realize the broadband PBS. The finite-element method is used to calculate the field distribution. The characteristics of the broadband high reflectivity, transmitting and the polarization dependence are investigated including wavelength, period, refractive index and the radius of circle grating. When grating period d = 400 nm, incident wavelength λ = 441 nm, incident angle θ = 60° and radius of circle d/5, then the zeroth reflection order R0 = 0.35 and the transmission zeroth order T0 = 0.08 for TE polarization, however, T0 = 0.34 and R0 = 0.01 for TM mode. The simple fabrication method involves only single etch step and good compatibility with complementary metal oxide semiconductor technology. PBS designed here is particularly suited for optical communication and optical information processing.

Wavelength-Agile External-Cavity Diode Laser for DWDM

NASA Technical Reports Server (NTRS)

Pilgrim, Jeffrey S.; Bomse, David S.

2006-01-01

A prototype external-cavity diode laser (ECDL) has been developed for communication systems utilizing dense wavelength- division multiplexing (DWDM). This ECDL is an updated version of the ECDL reported in Wavelength-Agile External- Cavity Diode Laser (LEW-17090), NASA Tech Briefs, Vol. 25, No. 11 (November 2001), page 14a. To recapitulate: The wavelength-agile ECDL combines the stability of an external-cavity laser with the wavelength agility of a diode laser. Wavelength is modulated by modulating the injection current of the diode-laser gain element. The external cavity is a Littman-Metcalf resonator, in which the zeroth-order output from a diffraction grating is used as the laser output and the first-order-diffracted light is retro-reflected by a cavity feedback mirror, which establishes one end of the resonator. The other end of the resonator is the output surface of a Fabry-Perot resonator that constitutes the diode-laser gain element. Wavelength is selected by choosing the angle of the diffracted return beam, as determined by position of the feedback mirror. The present wavelength-agile ECDL is distinguished by design details that enable coverage of all 60 channels, separated by 100-GHz frequency intervals, that are specified in DWDM standards.

Multi-directional emission and detection of spin waves propagating in yttrium iron garnet with wavelengths down to about 100 nm

NASA Astrophysics Data System (ADS)

Maendl, Stefan; Grundler, Dirk

2018-05-01

We performed broadband spin-wave spectroscopy on 200 nm thick yttrium iron garnet containing arrays of partially embedded magnetic nanodisks. Using integrated coplanar waveguides (CPWs), we studied the excitation and transmission of spin waves depending on the presence of nanomagnet arrays of different lateral extensions. By means of the grating coupler effect, we excited spin waves propagating in multiple lateral directions with wavelengths down to 111 nm. They exhibited group velocities of up to 1 km/s. Detection of such short-wavelength spin waves was possible only in symmetrically designed emitter/detector configurations, not with a bare CPW. We report spin waves propagating between grating couplers under oblique angles exhibiting a wave vector component parallel to the CPW. The effective propagation distance amounted to about 80 μm. Such transmission signals were not addressed before and substantiate the versatility of the grating coupler effect for implementing nanomagnonic circuits.

Laser bandwidth interlock capable of single pulse detection and rejection

DOEpatents

Armstrong, James P; Telford, Steven James; Lanning, Rodney Kay; Bayramian, Andrew James

2012-10-09

A pulse of laser light is switched out of a pulse train and spatially dispersed into its constituent wavelengths. The pulse is collimated to a suitable size and then diffracted by high groove density multilayer dielectric gratings. This imparts a different angle to each individual wavelength so that, when brought to the far field with a lens, the colors have spread out in a linear arrangement. The distance between wavelengths (resolution) can be tailored for the specific laser and application by altering the number of times the beam strikes the diffraction gratings, the groove density of the gratings and the focal length of the lens. End portions of the linear arrangement are each directed to a respective detector, which converts the signal to a 1 if the level meets a set-point, and a 0 if the level does not. If both detectors produces a 1, then the pulse train is allowed to propagate into an optical system.

Recent developments in the fabrication of infrared fiber Bragg gratings

NASA Astrophysics Data System (ADS)

Busse, Lynda; Florea, Catalin; Shaw, Brandon; Sanghera, Jas; Nguyen, Vinh; Chin, Geoff; Aggarwal, Ishwar

2012-02-01

We report on the study of adding metal dopants in chalcogenide glasses to enhance the photosensitivity of the fiber core versus cladding compositions, with goal to enable high reflectivity gratings in infrared-transmitting fibers. Results for the optical and thermal properties of these glasses will be presented, as well as for gratings formation in the glasses using various writing wavelengths for the different doped compositions.

Dual-function beam splitter of a subwavelength fused-silica grating.

PubMed

Feng, Jijun; Zhou, Changhe; Zheng, Jiangjun; Cao, Hongchao; Lv, Peng

2009-05-10

We present the design and fabrication of a novel dual-function subwavelength fused-silica grating that can be used as a polarization-selective beam splitter. For TM polarization, the grating can be used as a two-port beam splitter at a wavelength of 1550 nm with a total diffraction efficiency of 98%. For TE polarization, the grating can function as a high-efficiency grating, and the diffraction efficiency of the -1st order is 95% under Littrow mounting. This dual-function grating design is based on a simplified modal method. By using the rigorous coupled-wave analysis, the optimum grating parameters can be determined. Holographic recording technology and inductively coupled plasma etching are used to manufacture the fused-silica grating. Experimental results are in agreement with the theoretical values.

Observation of sagittal X-ray diffraction by surface acoustic waves in Bragg geometry.

PubMed

Vadilonga, Simone; Zizak, Ivo; Roshchupkin, Dmitry; Evgenii, Emelin; Petsiuk, Andrei; Leitenberger, Wolfram; Erko, Alexei

2017-04-01

X-ray Bragg diffraction in sagittal geometry on a Y-cut langasite crystal (La 3 Ga 5 SiO 14 ) modulated by Λ = 3 µm Rayleigh surface acoustic waves was studied at the BESSY II synchrotron radiation facility. Owing to the crystal lattice modulation by the surface acoustic wave diffraction, satellites appear. Their intensity and angular separation depend on the amplitude and wavelength of the ultrasonic superlattice. Experimental results are compared with the corresponding theoretical model that exploits the kinematical diffraction theory. This experiment shows that the propagation of the surface acoustic waves creates a dynamical diffraction grating on the crystal surface, and this can be used for space-time modulation of an X-ray beam.

Observation of sagittal X-ray diffraction by surface acoustic waves in Bragg geometry1

PubMed Central

Vadilonga, Simone; Zizak, Ivo; Roshchupkin, Dmitry; Evgenii, Emelin; Petsiuk, Andrei; Leitenberger, Wolfram; Erko, Alexei

2017-01-01

X-ray Bragg diffraction in sagittal geometry on a Y-cut langasite crystal (La3Ga5SiO14) modulated by Λ = 3 µm Rayleigh surface acoustic waves was studied at the BESSY II synchrotron radiation facility. Owing to the crystal lattice modulation by the surface acoustic wave diffraction, satellites appear. Their intensity and angular separation depend on the amplitude and wavelength of the ultrasonic superlattice. Experimental results are compared with the corresponding theoretical model that exploits the kinematical diffraction theory. This experiment shows that the propagation of the surface acoustic waves creates a dynamical diffraction grating on the crystal surface, and this can be used for space–time modulation of an X-ray beam. PMID:28381976

Broadband absorption enhancement in amorphous Si solar cells using metal gratings and surface texturing

NASA Astrophysics Data System (ADS)

Magdi, Sara; Swillam, Mohamed A.

2017-02-01

The efficiencies of thin film amorphous silicon (a-Si) solar cells are restricted by the small thickness required for efficient carrier collection. This thickness limitations result in poor light absorption. In this work, broadband absorption enhancement is theoretically achieved in a-Si solar cells by using nanostructured back electrode along with surface texturing. The back electrode is formed of Au nanogratings and the surface texturing consists of Si nanocones. The results were then compared to random texturing surfaces. Three dimensional finite difference time domain (FDTD) simulations are used to design and optimize the structure. The Au nanogratings achieved absorption enhancement in the long wavelengths due to sunlight coupling to surface plasmon polaritons (SPP) modes. High absorption enhancement was achieved at short wavelengths due to the decreased reflection and enhanced scattering inside the a-Si absorbing layer. Optimizations have been performed to obtain the optimal geometrical parameters for both the nanogratings and the periodic texturing. In addition, an enhancement factor (i.e. absorbed power in nanostructured device/absorbed power in reference device) was calculated to evaluate the enhancement obtained due to the incorporation of each nanostructure.

D-shaped fiber grating refractive index sensor induced by an ultrashort pulse laser.

PubMed

Liao, Changrui; Wang, Qiao; Xu, Lei; Liu, Shen; He, Jun; Zhao, Jing; Li, Zhengyong; Wang, Yiping

2016-03-01

The fabrication of fiber Bragg gratings was here demonstrated using ultrashort pulse laser point-by-point inscription. This is a very convenient means of creating fiber Bragg gratings with different grating periods and works by changing the translation speed of the fiber. The laser energy was first optimized in order to improve the spectral properties of the fiber gratings. Then, fiber Bragg gratings were formed into D-shaped fibers for use as refractive index sensors. A nonlinear relationship was observed between the Bragg wavelength and liquid refractive index, and a sensitivity of ∼30  nm/RIU was observed at 1.450. This shows that D-shaped fiber Bragg gratings might be used to develop promising biochemical sensors.

Wavelength adjustability of frequency conversion light of Yb-doped fiber laser based on FBGs

NASA Astrophysics Data System (ADS)

Dobashi, Kazuma; Tomihari, Yasuhiro; Imai, Koichi; Hirohashi, Junji; Makio, Satoshi

2018-02-01

We focused on wavelength conversion of simple and compact CW Yb-Doped fiber laser based on FBGs with wavelength adjustable function. By controlling temperatures of FBGs in fiber laser, it was possible to tune oscillated wavelength from 1064.101 nm to 1064.414 nm with more than 20 W in CW operation mode. Based on this fundamental light, frequency converted light (SHG and THG) were generated by utilizing two PP:Mg-SLT devises. We obtained more than 3 W of SHG light with tuning range of 150 pm and more than 35 mW of THG with tuning range of 100 pm. By selecting FBG grating and QPM grating properly, we can realize adjustable wavelength laser with the same scheme from 1040 nm to 1090 nm and their SHG/THG. With this combination of FBG based fiber laser and QPM devices, it is possible to tune the wavelength just by temperature tuning without any changes of beam shape and beam pointing.

Impact damage monitoring in CFRP using fiber Bragg grating ultrasound sensors

NASA Astrophysics Data System (ADS)

Tsuda, Hiroshi; Lee, Jung-Ryul; Eguchi, Shunji

2006-03-01

Impact damage in CFRP was monitored by ultrasonic inspection method using small-diameter fiber Bragg grating (FBG) sensors. The FBG ultrasound detection system consisted of broadband light source, FBG sensor and tunable optical filter. Broadband light was launched into the FBG sensor. Light reflected from the FBG sensor was transmitted through the tunable optical filter whose transmissive wavelength range is comparable to the reflected wavelength range of the FBG sensor. The operating wavelength of tunable filter was set to optimize the sensitivity of ultrasound detection. Ultrasound vibration was converted into change in intensity of light transmitted through the filter. A cross-ply carbon fiber-reinforced plastic (CFRP) plate was used as a test specimen for impact damage monitoring. A 6.3 X 9mm2 impact damage was introduced by ball dropping. Both FBG ultrasound sensor and piezoelectric ultrasound transmitter were attached on the CFRP surface. The change in responses to ultrasound excited by either spike signal or toneburst signal before and after impact damage was investigated. In response to ultrasound excited by spike signal, the response after impact damage showed a scattered behavior where the period of response signal got longer. In response to ultrasound excited by toneburst signal, damage signal features scattered and distorted waveform. Experimental results proved that the FBG inspection system could monitor a 6.3 X 9mm2 impact damage in CFRP.

Evaluation of the effects of varying moisture contents on microwave thermal emissions from agriculture fields

NASA Technical Reports Server (NTRS)

Burke, H. H. K.

1980-01-01

Three tasks related to soil moisture sensing at microwave wavelengths were undertaken: (1) analysis of data at L, X and K sub 21 band wavelengths over bare and vegetated fields from the 1975 NASA sponsored flight experiment over Phoenix, Arizona; (2) modeling of vegetation canopy at microwave wavelengths taking into consideration both absorption and volume scattering effects; and (3) investigation of overall atmospheric effects at microwave wavelengths that can affect soil moisture retrieval. Data for both bare and vegetated fields are found to agree well with theoretical estimates. It is observed that the retrieval of surface and near surface soil moisture information is feasible through multi-spectral and multi-temporal analysis. It is also established that at long wavelengths, which are optimal for surface sensing, atmospheric effects are generally minimal. At shorter wavelengths, which are optimal for atmosheric retrieval, the background surface properties are also established.

Economic fabrication of a novel hybrid planar Grating/Fresnel lens for miniature spectrometers.

PubMed

Zhou, Qian; Li, Xinghui; Geng, Menglin; Hu, Haifei; Ni, Kai; Zhong, Lunchao; Yan, Peng; Wang, Xiaohao

2018-03-05

We propose a new technique to fabricate a highly specialized optical element, a hybrid planar Grating/Fresnel lens (G-Fresnel), which is particularly useful to improve or enable more-affordable miniature/portable spectrometers. Both the Fresnel and the grating surface are fabricated simultaneously by sandwiching soft PDMS between a hard grating and a pre-replicated negative Fresnel surface. Several adhesion reduction techniques are also investigated that help improve both fabrication and cost efficiency (by reducing the solidification time) as well as the lifetime of the mold. Alignment errors are systematically analyzed, and their effects on the G-Fresnel lens evaluated. A compact fabrication platform was built, which is smaller than a volume of 160☓140☓106 mm 3 to fit into a conventional vacuum drying oven, for the fabrication of a G-Fresnel lens with a diameter of 25.4 mm, an equivalent focal length of 25 mm, and a blazed grating pattern with 600 lines/mm spacing. The solidification time was reduced to 2 hours thanks to the improved adhesion reduction technique that permits a PDMS drying-temperature as high as 65 °C. The fabricated G-Fresnel lens was evaluated with regard to both geometrical fabrication precision and optical performance. The measured results, using a step gauge and atomic force microscopy, confirm that this replication technique produces high-quality replicates of the master surface-profile. Furthermore, a prototype spectrometer that uses a G-Fresnel lens was built and evaluated. The spectrometer fits within a volume of about 100 mm☓50 mm☓30 mm, and it operates across a wide wavelength spectrum (450 nm to 650 nm). Both the calculation based on the optical software ZEMAX and the experimental measurements are consistent and confirm that the spectrometer with the G-Fresnel lens can provide a spectral resolution of better than 1.2nm.

Switchable dual-wavelength erbium-doped fiber laser based on the photonic crystal fiber loop mirror and chirped fiber Bragg grating

NASA Astrophysics Data System (ADS)

Chen, Wei-Guo; Lou, Shu-Qin; Wang, Li-Wen; Li, Hong-Lei; Guo, Tieying; Jian, Shui-Sheng

2010-03-01

The switchable dual-wavelength erbium-doped fiber laser (EDFL) with a two-mode photonic crystal fiber (PCF) loop mirror and a chirped fiber Bragg grating (CFBG) at room temperature is proposed and experimentally demonstrated. The two-mode PCF loop mirror is formed by inserting a piece of two-mode PCF into a Sagnac loop mirror, with the air-holes of the PCF intentionally collapsing at the splices. By adjusting the state of the polarization controller (PC) appropriately, the laser can be switched between the stable single- and dual-wavelength operations by means of the polarization hole burning (PHB) and spectral hole burning (SHB) effects.

An FPGA-based demodulation system for fiber Bragg grating sensing

NASA Astrophysics Data System (ADS)

Li, Yongqian; He, Haitao; Yao, Guozhen

2010-11-01

This paper introduces the principle of fiber Bragg grating (FBG) sensor, designs and realizes a compact wavelength demodulation system for FBG sensing using a Fabry-Perot (F-P) filter. FPGA is adopted as a main controller to control a D/A converter to produce a sawtooth wave for driving the F-P filter, and to design the data acquisition circuit for collecting the output signals of photoelectric detector. The collected data is processed after transmitting to PC through the data transmission circuit, and then the demodulation of FBG wavelength is completed finally. This compact FBG wavelength demodulation system is expected to have wide applications in on-line monitoring of electric power equipment and large structures.

A novel fiber Bragg grating wavelength demodulation system based on F-P etalon

NASA Astrophysics Data System (ADS)

Yang, Gang; Guo, Jinghong; Xu, Guoliang; Lv, Lidong; Tu, Guojie; Xia, Lan

2014-10-01

This paper designs and implies a high precision FBG demodulation system which based on F-P etalon. In order to reduce the influence of the temperature drift effect, the peristaltic effect, and the nonlinear effect of F-P filter in traditional tunable filter method, F-P etalon is added as dynamical calibration and wavelength reference. Meanwhile segmentation demodulation which uses ASE spectral characteristics is applied to achieve high accuracy of the center wavelength of FBG. The experiment shows that the stability, resolution are 0.65pm, 0.23pm, respectively. Key words: fiber optics; fiber Bragg grating sensor system; tunable Fabry-Perot filter; F-P etalon; spectrum segmentation demodulation

Silicon/III-V laser with super-compact diffraction grating for WDM applications in electronic-photonic integrated circuits.

PubMed

Wang, Yadong; Wei, Yongqiang; Huang, Yingyan; Tu, Yongming; Ng, Doris; Lee, Cheewei; Zheng, Yunan; Liu, Boyang; Ho, Seng-Tiong

2011-01-31

We have demonstrated a heterogeneously integrated III-V-on-Silicon laser based on an ultra-large-angle super-compact grating (SCG). The SCG enables single-wavelength operation due to its high-spectral-resolution aberration-free design, enabling wavelength division multiplexing (WDM) applications in Electronic-Photonic Integrated Circuits (EPICs). The SCG based Si/III-V laser is realized by fabricating the SCG on silicon-on-insulator (SOI) substrate. Optical gain is provided by electrically pumped heterogeneous integrated III-V material on silicon. Single-wavelength lasing at 1550 nm with an output power of over 2 mW and a lasing threshold of around 150 mA were achieved.

Tunable high-power blue external cavity semiconductor laser

NASA Astrophysics Data System (ADS)

Ding, Ding; Lv, Xueqin; Chen, Xinyi; Wang, Fei; Zhang, Jiangyong; Che, Kaijun

2017-09-01

A commercially available high-power GaN-based blue laser diode has been operated in a simple Littrow-type external cavity (EC). Two kinds of EC configurations with the grating lines perpendicular (A configuration) and parallel (B configuration) to the p-n junction are evaluated. Good performance has been demonstrated for the EC laser with B configuration due to the better mode selection effect induced by the narrow feedback wavelength range from the grating. Under an injection current of 1100 mA, the spectral linewidth is narrowed significantly down to ∼0.1 nm from ∼1 nm (the free-running width), with a good wavelength-locking behavior and a higher than 35 dB-amplified spontaneous emission suppression ratio. Moreover, a tuning bandwidth of 3.6 nm from 443.9 nm to 447.5 nm is realized with output power of 1.24 W and EC coupling efficiency of 80% at the central wavelength. The grating-coupled blue EC laser with narrow spectral linewidth, flexible wavelength tunability, and high output power shows potential applications in atom cooling and trapping, high-resolution spectroscopy, second harmonic generation, and high-capacity holographic data storage.

Thick-SOI Echelle grating for any-to-any wavelength routing interconnection in multi-socket computing environments

NASA Astrophysics Data System (ADS)

Dabos, G.; Pitris, S.; Mitsolidou, C.; Alexoudi, T.; Fitsios, D.; Cherchi, M.; Harjanne, M.; Aalto, T.; Kanellos, G. T.; Pleros, N.

2017-02-01

As data centers constantly expand, electronic switches are facing the challenge of enhanced scalability and the request for increased pin-count and bandwidth. Photonic technology and wavelength division multiplexing have always been a strong alternative for efficient routing and their potential was already proven in the telecoms. CWDM transceivers have emerged in the board-to-board level interconnection, revealing the potential for wavelength-routing to be applied in the datacom and an AWGR-based approach has recently been proposed towards building an optical multi-socket interconnection to offer any-to-any connectivity with high aggregated throughput and reduced power consumption. Echelle gratings have long been recognized as the multiplexing block exhibiting smallest footprint and robustness in a wide number of applications compared to other alternatives such as the Arrayed Waveguide Grating. Such filtering devices can also perform in a similar way to cyclical AWGR and serve as mid-board routing platforms in multi-socket environments. In this communication, we present such a 3x3 Echelle grating integrated on thick SOI platform with aluminum-coated facets that is shown to perform successful wavelength-routing functionality at 10 Gb/s. The device exhibits a footprint of 60x270 μm2, while the static characterization showed a 3 dB on-chip loss for the best channel. The 3 dB-bandwidth of the channels was 4.5 nm and the free spectral range was 90 nm. The echelle was evaluated in a 2x2 wavelength routing topology, exhibiting a power penalty of below 0.4 dB at 10-9 BER for the C-band. Further experimental evaluations of the platform involve commercially available CWDM datacenter transceivers, towards emulating an optically-interconnected multi-socket environment traffic scenario.

Development of new maskless manufacturing method for anti-reflection structure and application to large-area lens with curved surface

NASA Astrophysics Data System (ADS)

Yamamoto, Kazuya; Takaoka, Toshimitsu; Fukui, Hidetoshi; Haruta, Yasuyuki; Yamashita, Tomoya; Kitagawa, Seiichiro

2016-03-01

In general, thin-film coating process is widely applied on optical lens surface as anti-reflection function. In normal production process, at first lens is manufactured by molding, then anti-reflection is added by thin-film coating. In recent years, instead of thin-film coating, sub-wavelength structures adding on surface of molding die are widely studied and development to keep anti-reflection performance. As merits, applying sub-wavelength structure, coating process becomes unnecessary and it is possible to reduce man-hour costs. In addition to cost merit, these are some technical advantages on this study. Adhesion of coating depends on material of plastic, and it is impossible to apply anti-reflection function on arbitrary surface. Sub-wavelength structure can solve both problems. Manufacturing method of anti-reflection structure can be divided into two types mainly. One method is with the resist patterning, and the other is mask-less method that does not require patterning. What we have developed is new mask-less method which is no need for resist patterning and possible to impart an anti-reflection structure to large area and curved lens surface, and can be expected to apply to various market segments. We report developed technique and characteristics of production lens.

Dense periodical patterns in photonic devices: Technology for fabrication and device performance

NASA Astrophysics Data System (ADS)

Chandramohan, Sabarish

For the fabrication, focused ion beam parameters are investigated to successfully fabricate dense periodical patterns, such as gratings, on hard transition metal nitride such as zirconium nitride. Transition metal nitrides such as titanium nitride and zirconium nitride have recently been studied as alternative materials for plasmonic devices because of its plasmonic resonance in the visible and near-infrared ranges, material strength, CMOS compatibility and optical properties resembling gold. Coupling of light on the surface of these materials using sub-micrometer gratings gives additional capabilities for wider applications. Here we report the fabrication of gratings on the surface of zirconium nitride using gallium ion 30keV dual beam focused ion beam. Scanning electron microscope imaging and atomic force microscope profiling is used to characterize the fabricated gratings. Appropriate values for FIB parameters such as ion beam current, magnification, dwell time and milling rate are found for successful milling of dense patterns on zirconium nitride. For the device performance, a real-time image-processing algorithm is developed to enhance the sensitivity of an optical miniature spectrometer. The novel approach in this design is the use of real-time image-processing algorithm to average the image intensity along the arc shaped images registered by the monochromatic inputs on the CMOS image sensor. This approach helps to collect light from the entire arc and thus enhances the sensitivity of the device. The algorithm is developed using SiTiO2 planar waveguide. The accuracy of the mapping from x-pixel number scale of the CMOS image sensor to the wavelength spectra of the miniature spectrometer is demonstrated by measuring the spectrum of a known LED source using a conventional desktop spectrometer and comparing it with the spectrum measured by the miniature spectrometer. The sensitivity of miniature spectrometer is demonstrated using two methods. In the first method, the input laser power is attenuated to 0.1 nW and the spectra is measured using the miniature spectrometer. Even at low input power of 0.1nW, the spectrum of monochromatic inputs is observed well above the noise level. Second method is by quantitative analysis, which measures the absorption of CdSeS/ZnS quantum dots drop casted between the gratings of Ta2O5 planar single-mode waveguide. The expected guided mode attenuation introduced by monolayer of quantum dots is found to be approximately 11 times above the highest noise level from the absorption measurements. Thus, the miniature spectrometer is capable of detecting the signal from the noise level even with the absorption introduced by monolayer of quantum dots.

Development of a flat-field spectrometer with a wideband Ni/C multilayer grating in the 1–3.5 keV range

DOE Office of Scientific and Technical Information (OSTI.GOV)

Imazono, Takashi

2016-07-27

To develop a flat-field spectrometer with coverage of the 1–3.5 keV range, a wideband Ni/C multilayer grating was invented. The multilayer consists of two kinds of layer structures. One is a conventional periodic multilayer of thickness D{sub 1} = 5.6 nm, Ni thickness ratio to the multilayer period γ{sub 1} = 0.5 and the number of layers N{sub 1} = 79. Both the first and last layers are Ni. The other is a C/Ni bilayer of D{sub 2} = 8.4 nm, γ{sub 2} = 0.53 and N{sub 2} = 2. The first layer is C and then Ni. The aperiodicmore » multilayer from the topmost C/Ni bilayer was coated on a laminar-type grating having an effective grating constant of 1/2400 mm, groove depth of 2.8 nm, and duty ratio (land width/groove period) of 0.5. In a preliminary experiment, the diffraction efficiency was in excess of 0.8% in the energy range of 2.1-3.3 keV and the maximum of 5.4% at 3.1 keV at a constant angle of incidence of 88.54°, which is considerably higher than that of an Au-coated grating before deposition of the multilayer.« less

Plasmonic fiber-optic vector magnetometer

NASA Astrophysics Data System (ADS)

Zhang, Zhaochuan; Guo, Tuan; Zhang, Xuejun; Xu, Jian; Xie, Wenping; Nie, Ming; Wu, Qiang; Guan, Bai-Ou; Albert, Jacques

2016-03-01

A compact fiber-optic vector magnetometer based on directional scattering between polarized plasmon waves and ferro-magnetic nanoparticles is demonstrated. The sensor configuration reported in this work uses a short section of tilted fiber Bragg grating (TFBG) coated with a nanometer scale gold film and packaged with a magnetic fluid (Fe3O4) inside a capillary. The transmission spectrum of the sensor provides a fine comb of narrowband resonances that overlap with a broader absorption of the surface plasmon resonance (SPR). The wavelength of the SPR attenuation in transmission shows high sensitivity to slight perturbations by magnetic fields, due to the strong directional scattering between the SPR attenuated cladding modes and the magnetic fluid near the fiber surface. Both the orientation (2 nm/deg) and the intensity (1.8 nm/mT) of magnetic fields can be determined unambiguously from the TFBG spectrum. Temperature cross sensitivity can be referenced out by monitoring the wavelength of the core mode resonance simultaneously.

Grapefruit photonic crystal fiber sensor for gas sensing application

NASA Astrophysics Data System (ADS)

Tao, Chuanyi; Wei, Heming; Zhu, Yinian; Krishnaswamy, Sridhar

2016-05-01

Use of long period gratings (LPGs) formed in grapefruit photonic crystal fiber (PCF) with thin-film overlay coated on the inner surface of air holes for gas sensing is demonstrated. The finite-element method was used to numerically simulate the grapefruit PCF-LPG modal coupling characteristics and resonance spectral response with respect to the refractive index of thin-film inside the holey region. A gas analyte-induced index variation of the thin-film immobilized on the inner surface of the holey region of the fiber can be observed by a shift of the resonance wavelength. As an example, we demonstrate a 2,4-dinitrotoluene (DNT) sensor using grapefruit PCF-LPGs. The sensor exhibits a wavelength blue-shift of ˜820 pm as a result of exposure to DNT vapor with a vapor pressure of 411 ppbv at 25°C, and a sensitivity of 2 pm ppbv-1 can be achieved.

The influence of grating shape formation fluctuation on DFB laser diode threshold condition

NASA Astrophysics Data System (ADS)

Bao, Shiwei; Song, Qinghai; Xie, Chunmei

2018-03-01

Not only the grating material refractive index itself but also the Bragg grating physical shape formation affects the coupling strength greatly. The Bragg grating shape includes three factors, namely grating depth, duty ratio and grating angle. During the lithography and wet etching process, there always will be some fluctuation between the target and real grating shape formation after fabrication process. This grating shape fluctuation will affect the DFB coupling coefficient κ , and then consequently threshold current and corresponding wavelength. This paper studied the grating shape formation fluctuation influence to improve the DFB fabrication yield. A truncated normal random distribution fluctuation is considered in this paper. The simulation results conclude that it is better to choose relative thicker grating depth with lower refractive index to obtain a better fabrication tolerance, while not quite necessary to spend too much effort on improving lithography and wet etching process to get a precisely grating duty ratio and grating angle.

The influence of grating shape formation fluctuation on DFB laser diode threshold condition

NASA Astrophysics Data System (ADS)

Bao, Shiwei; Song, Qinghai; Xie, Chunmei

2018-06-01

Not only the grating material refractive index itself but also the Bragg grating physical shape formation affects the coupling strength greatly. The Bragg grating shape includes three factors, namely grating depth, duty ratio and grating angle. During the lithography and wet etching process, there always will be some fluctuation between the target and real grating shape formation after fabrication process. This grating shape fluctuation will affect the DFB coupling coefficient κ, and then consequently threshold current and corresponding wavelength. This paper studied the grating shape formation fluctuation influence to improve the DFB fabrication yield. A truncated normal random distribution fluctuation is considered in this paper. The simulation results conclude that it is better to choose relative thicker grating depth with lower refractive index to obtain a better fabrication tolerance, while not quite necessary to spend too much effort on improving lithography and wet etching process to get a precisely grating duty ratio and grating angle.

Rare-earth-ion-doped ultra-narrow-linewidth lasers on a silicon chip and applications to intra-laser-cavity optical sensing

NASA Astrophysics Data System (ADS)

Bernhardi, E. H.; de Ridder, R. M.; Wörhoff, K.; Pollnau, M.

2013-03-01

We report on diode-pumped distributed-feedback (DFB) and distributed-Bragg-reflector (DBR) channel waveguide lasers in Er-doped and Yb-doped Al2O3 on standard thermally oxidized silicon substrates. Uniform surface-relief Bragg gratings were patterned by laser-interference lithography and etched into the SiO2 top cladding. The maximum grating reflectivity exceeded 99%. Monolithic DFB and DBR cavities with Q-factors of up to 1.35×106 were realized. The Erdoped DFB laser delivered 3 mW of output power with a slope efficiency of 41% versus absorbed pump power. Singlelongitudinal- mode operation at a wavelength of 1545.2 nm was achieved with an emission line width of 1.70 0.58 kHz, corresponding to a laser Q-factor of 1.14×1011. Yb-doped DFB and DBR lasers were demonstrated at wavelengths near 1020 nm with output powers of 55 mW and a slope efficiency of 67% versus launched pump power. An Yb-doped dualwavelength laser was achieved based on the optical resonances induced by two local phase shifts in the DFB structure. A stable microwave signal at ~15 GHz with a -3-dB width of 9 kHz and a long-term frequency stability of +/- 2.5 MHz was created via the heterodyne photo-detection of the two laser wavelengths. By measuring changes in the microwave beat signal as the intra-cavity evanescent laser field interacts with micro-particles on the waveguide surface, we achieved real-time detection and accurate size measurement of single micro-particles with diameters ranging between 1 μm and 20 μm, which represents the typical size of many fungal and bacterial pathogens. A limit of detection of ~500 nm was deduced.

Analysis of grating doublets for achromatic beam-splitting

PubMed Central

Pacheco, Shaun; Milster, Tom; Liang, Rongguang

2015-01-01

Achromatic beam-splitting grating doublets are designed for both continuous phase and binary phase gratings. By analyzing the sensitivity to lateral shifts between the two grating layers, it is shown that continuous-profile grating doublets are extremely difficult to fabricate. Achromatic grating doublets that have profiles with a constant first spatial derivative are significantly more resistant to lateral shifts between grating layers, where one design case showed a 17 times improvement in performance. Therefore, binary phase, multi-level phase, and blazed grating doublets perform significantly better than continuous phase grating doublets in the presence of a lateral shift between two grating layers. By studying the sensitivity to fabrication errors in the height of both grating layers, one grating layer height can be adjusted to maintain excellent performance over a large wavelength range if the other grating layer is fabricated incorrectly. It is shown in one design case that the performance of an achromatic Dammann grating doublet can be improved by a factor of 215 if the heights of the grating layers are chosen to minimize the performance change in the presence of fabrication errors. PMID:26368261

Tunable sub-wavelength acoustic energy harvesting with a metamaterial plate

NASA Astrophysics Data System (ADS)

Oudich, Mourad; Li, Yong

2017-08-01

We report theoretically on sub-wavelength acoustic energy harvesting (AEH) using a thin acoustic metamaterial (AM) made of spring-mass resonators attached to the surface of a homogeneous elastic thin plate. Considering an incident acoustic wave hitting the AM plate, tunable and highly efficient AEH is achieved by introducing a sub-wavelength defect inside the AM structure to confine the elastic energy into a spot which is then electromechanically converted into electrical power using a ceramic PZT patch. Several types of sub-wavelength cavities capable of confining acoustic energy at the sonic regime are extensively investigated for the optimization of AEH. Three analytical approaches—band structure, sound transmission loss and electrical-to-mechanical energy conversion—are proposed to fully describe the system interaction with the acoustic wave and quantify the AEH performance. The computed results show that an average power of 18 μW can be harvested using a specific cavity design of only 3 × 3 cm2 size from an incident acoustic wave with a sound pressure level of 100 dB at 520 Hz. Such a system can open up a way through the design of effective tunable sub-wavelength acoustic energy harvesters based on AM applied to scavenge energy from sound.

A distributed fluid level sensor suitable for monitoring fuel load on board a moving fuel tank

NASA Astrophysics Data System (ADS)

Arkwright, John W.; Parkinson, Luke A.; Papageorgiou, Anthony W.

2018-02-01

A temperature insensitive fiber Bragg grating sensing array has been developed for monitoring fluid levels in a moving tank. The sensors are formed from two optical fibers twisted together to form a double helix with pairs of fiber Bragg gratings located above one another at the points where the fibers are vertically disposed. The sensing mechanism is based on a downwards deflection of the section of the double helix containing the FBGs which causes the tension in the upper FBG to decrease and the tension in the lower FBG to increase with concomitant changes in Bragg wavelength in each FBG. Changes in ambient temperature cause a common mode increase in Bragg wavelength, thus monitoring the differential change in wavelength provides a temperature independent measure of the applied pressure. Ambient temperature can be monitored simultaneously by taking the average wavelength of the upper and lower FBGs. The sensors are able to detect variations in pressure with resolutions better than 1 mmH2O and when placed on the bottom of a tank can be used to monitor fluid level based on the recorded pressure. Using an array of these sensors located along the bottom of a moving tank it was possible to monitor the fluid level at multiple points and hence dynamically track the total fluid volume in the tank. The outer surface of the sensing array is formed from a thin continuous Teflon sleeve, making it suitable for monitoring the level of volatile fluids such as aviation fuel and gasoline.

Color separation gratings

NASA Technical Reports Server (NTRS)

Farn, Michael W.; Knowlden, Robert E.

1993-01-01

In this paper, we describe the theory, fabrication and test of a binary optics 'echelon'. The echelon is a grating structure which separates electromagnetic radiation of different wavelengths, but it does so according to diffraction order rather than by dispersion within one diffraction order, as is the case with conventional gratings. A prototype echelon, designed for the visible spectrum, is fabricated using the binary optics process. Tests of the prototype show good agreement with theoretical predictions.

On-Chip Photonic Circuits for Atom-Light Interaction in Quantum Information and Integrated Optical Spectrometer for Astrophotonics

NASA Astrophysics Data System (ADS)

Meng, Yang

Photonic circuits are becoming very promising in many different applications, such as optical amplification, optical switching and wavelength division multiplexing optical networks, lab-on-chip in bioengineering, atom-light interaction in quantum information processing, wavelength selecting and filtering in astronomy, etc. Thanks to major developments in the nanofabrication technology, smaller but more powerful photonic circuits can be made to realize more complex applications. Here we propose two on-chip photonic circuits: one is for atom-light interaction in quantum information, and the other is for an optical spectrometer in astronomy. Part I. The atom-light interaction can be used for a number of quantum based application, such as quantum information processing and atomic sensing. These significant applications make atom-light interaction a strong candidate for next-generation quantum computers and ultraprecise magnetic or navigation sensors. People have proposed various types of atom-photon interaction, and enhancing the interaction by using a small mode area has also been demonstrated in several platforms such as a hollow-core fiber, a hollow-core waveguide, a tapered fiber, and a nanowaveguide. In our work, we propose a nanowaveguide platform for collective atom-light interaction through the evanescent optical field coupling. We have demonstrated a centimeter-long silicon nitride nanowaveguide that has a sub-micrometer mode area and high fiber-to-waveguide coupling efficiencies for near-infrared wavelengths, working as evanescent field atom trapping/probing of an ensemble of 87Rb atoms. Inverse tapers are made at both ends of the waveguide that adiabatically transfer the weakly guided fiber-coupled mode to a strongly guided mode with an evanescent field for a better fiber-waveguide coupling efficiency. The coupling efficiency improves from around 2% to around 80% for both wavelengths. Trapping atoms by nanowaveguide modes is challenging because the small mode area generates high heat flux at the waveguide in an ultra-high vacuum. This platform has good thermal conductance and could transfer high enough optical powers to trap atoms in an ultra-high vacuum compared to a standalone photonic crystal waveguide with no substrate or an evanescent field coupled with a nanofiber. We have experimentally measured the optical absorption of thermal 87Rb atoms through the guided waveguide mode. We have also demonstrated an atom-chip mirror MOT with the same dimension of the platform that can be transferred to the proximity of the surface by magnetic field controls. Part II. In astronomical applications, wavelength analysis is very important especially for the wavelength selecting and filtering. Here we focus on the wavelength range from 1microm to 1.7microm. There are many valuable applications that make this near infrared wavelength range so important. For example, the Lyman-alpha line of hydrogen is one of the very important emission lines of hydrogen for understanding the origin and creation of the universe. Since the universe has expanded for more than 10 billion years after the big bang, the Lyman-alpha line of hydrogen has redshifted from 121.5nm to the 1microm-to-1.7microm wavelength range according to Hubble's Law. In addition, analysis of this wavelength range can also help us understand many other cosmic phenomena such as quasars, Gamma-ray bursts, etc. Therefore, a good spectrometer is needed to achieve this. Here we present an echelle grating which is based on an on-chip spectrometer that covers the near infrared wavelength range from 1.45um to 1.7um. To begin with, we use optical waveguides as the input and output channels. We have successfully achieved a reliable fabrication process to make the on-chip echelle-grating spectrometer. We have also achieved high fiber-waveguide coupling efficiency (94% per facet at 1550nm) and low propagation loss (-0.975dB/cm at 1550nm) for the input and output waveguides. In addition, we have characterized the bending loss of the waveguide. Finally, we have successfully measured the output spectrum of the echelle grating we designed and found it to be in good agreement with our simulation.

Simulation of path delay multiplexing-based Fourier transform spectrometer for fiber Bragg grating interrogation.

PubMed

Chelliah, Pandian; Sahoo, Trilochan; Singh, Sheela; Sujatha, Annie

2015-10-20

A Fourier transform spectrometer (FTS) used for interrogating a fiber Bragg grating (FBG) consists of a scanning-type interferometer. The FTS has a broad wavelength range of operation and good multiplexing capability. However, it has poor wavelength resolution and interrogation speed. We propose a modification to the FTS using path delay multiplexing to improve the same. Using this method, spatial resolution and interrogation time can be improved by n times by using n path delays. In this paper, simulation results for n=2, 5 are shown.

Multiple infrared bands absorber based on multilayer gratings

NASA Astrophysics Data System (ADS)

Liu, Xiaoyi; Gao, Jinsong; Yang, Haigui; Wang, Xiaoyi; Guo, Chengli

2018-03-01

The present study offers an Ag/Si multilayer-grating microstructure based on an Si substrate. The microstructure exhibits designable narrowband absorption in multiple infrared wavebands, especially in mid- and long-wave infrared atmospheric windows. We investigate its resonance mode mechanism, and calculate the resonance wavelengths by the Fabry-Perot and metal-insulator-metal theories for comparison with the simulation results. Furthermore, we summarize the controlling rules of the absorption peak wavelength of the microstructure to provide a new method for generating a Si-based device with multiple working bands in infrared.

Spectral evolution with incremental nanocoating of long period fiber gratings

NASA Astrophysics Data System (ADS)

Del Villar, Ignacio; Corres, Jesus M.; Achaerandio, Miguel; Arregui, Francisco J.; Matias, Ignacio R.

2006-12-01

The incremental deposition of a thin overlay on the cladding of a long-period fiber grating (LPFG) induces important resonance wavelength shifts in the transmission spectrum. The phenomenon is proved theoretically with a vectorial method based on hybrid modes and coupled mode theory, and experimentally with electrostatic self-assembly monolayer process. The phenomenon is repeated periodically for specific overlay thickness values with the particularity that the shape of the resonance wavelength shift depends on the thickness of the overlay. The main applications are the design of wide optical filters and multiparameter sensing devices.

Simultaneous measurement of refractive index and temperature based on intensity demodulation using matching grating method.

PubMed

Qi, Liang; Zhao, Chun-Liu; Kang, Juan; Jin, Yongxing; Wang, Jianfeng; Ye, Manping; Jin, Shangzhong

2013-07-01

A solution refractive index (SRI) and temperature simultaneous measurement sensor with intensity-demodulation system based on matching grating method were demonstrated. Long period grating written in a photonic crystal fiber (LPG-PCF), provides temperature stable and wavelength dependent optical intensity transmission. The reflective peaks of two fiber Bragg gratings (FBGs), one of which is etched then sensitive to both SRI and temperature, another (FBG2) is only sensitive to temperature, were located in the same linear range of the LPG-PCF's transmission spectrum. An identical FBG with FBG2 was chosen as a matching FBG. When environments (SRI and temperature) change, the wavelength shifts of the FBGs are translated effectively to the reflection intensity changes. By monitoring output lights of unmatching and matching paths, the SRI and temperature were deduced by a signal processing unit. Experimental results show that the simultaneous refractive index and temperature measurement system work well. The proposed sensor system is compact and suitable for in situ applications at lower cost.

High resolution EUV monochromator/spectrometer

DOEpatents

Koike, Masako

1996-01-01

This invention is related to a monochromator which employs a spherical mirror, a traveling plane mirror with simultaneous rotation, and a varied spacing plane grating. The divergent beam from the entrance slit is converged by the spherical mirror located at the various positions in the monochromator depending of the inventive system. To provide the meaningful diffraction efficiencies and to reduce unwanted higher order lights, the deviation angle subtending the incidence and diffraction beams for the plane grating is varied with the position of the traveling plane mirror with simultaneous rotation located in the front or back of the plane grating with wavelength scanning. The outgoing beam from the monochromator goes through the fixed exit slit and has same beam direction regardless of the scanning wavelength. The combination of properly designed motions of the plane mirror and novel varied-spacing parameters of the inventive plane grating corrects the aberrations and focuses the monochromatic spectral image on the exit slit, enabling measurements at high spectral resolution.

High resolution EUV monochromator/spectrometer

DOEpatents

Koike, Masako

1996-06-18

This invention is related to a monochromator which employs a spherical mirror, a traveling plane mirror with simultaneous rotation, and a varied spacing plane grating. The divergent beam from the entrance slit is converged by the spherical mirror located at the various positions in the monochromator depending of the inventive system. To provide the meaningful diffraction efficiencies and to reduce unwanted higher order lights, the deviation angle subtending the incidence and diffraction beams for the plane grating is varied with the position of the traveling plane mirror with simultaneous rotation located in the front or back of the plane grating with wavelength scanning. The outgoing beam from the monochromator goes through the fixed exit slit and has same beam direction regardless of the scanning wavelength. The combination of properly designed motions of the plane mirror and novel varied-spacing parameters of the inventive plane grating corrects the aberrations and focuses the monochromatic spectral image on the exit slit, enabling measurements at high spectral resolution. 10 figs.

HST-STIS Spectra of Saturn's Rings and Implications for Their Reddening Agent

NASA Technical Reports Server (NTRS)

Cuzzi, Jeff

2016-01-01

We obtained HST-STIS spectra of Saturn's main rings in May 2011, using the G230L (and G430L) gratings, with final averaged radial resolution of 160 (and 330) km/pixel. The dataset filled a previous 200-330nm "spectral gap" between Cassini and ground-based spectra. The data provide radial profiles as a function of wavelength, but our most basic product at this point is a set of very low-noise spectra, radially averaged over broad regions of the rings (A, B, C, and Cassini Division). The raw spectra required special processing to remove artifacts due to extended-source grating scatter. We have modeled the spectra using a new particle surface model, which corrects for on-surface shadowing due to the likely very rough ring particle surfaces, and avoids overestimation of intra-mixed "neutral absorber". We correct for non-classical layer effects and finite ring optical depth, and relate our observed reflectivities to the spherical albedos of individual smooth particles. We model these smooth particle albedos using standard Hapke theory for regolith grain mixtures that are either homogeneous and "intramixed" (nonicy absorbers dispersed in water ice regolith grains) or heterogeneous "intimate" mixtures. As candidates for the nonicy contaminants we have considered amorphous carbon, aromatic-rich and aliphatic-rich organic tholins, silicates, hematite and iron metal. For the A and B rings, we find that iron metal (including a new theoretical estimate of the refractive indices of nanometer-sized grains of iron) is not spectrally steep enough in the 200-300nm range, and that aliphatic-rich tholins are either too steep at short wavelengths or too flat at long wavelengths. However, less than 1% by mass of aromatic-rich tholins provides a very good fit across the entire spectral range with no gratuitous "neutral absorber" needed, and a minimum of additional free parameters. The best fits require forward-scattering regolith grains. For the C Ring and Cassini Division, additional absorbers are needed (updated results will be given).

Diffraction-analysis-based characterization of very fine gratings

NASA Astrophysics Data System (ADS)

Bischoff, Joerg; Truckenbrodt, Horst; Bauer, Joachim J.

1997-09-01

Fine gratings with spatial periods below one micron, either ruled mechanically or patterned holographically, play a key role as encoders in high precision translational or rotational coordinate or measuring machines. Besides, the fast in-line characterization of submicron patterns is a stringent demand in recent microelectronic technology. Thus, a rapid, destruction free and highly accurate measuring technique is required to ensure the quality during manufacturing and for final testing. We propose an optical method which was already successfully introduced in semiconductor industry. Here, the inverse scatter problem inherent in this diffraction based approach is overcome by sophisticated data analysis such as multivariate regression or neural networks. Shortly sketched, the procedure is as follows: certain diffraction efficiencies are measured with an optical angle resolved scatterometer and assigned to a number of profile parameters via data analysis (prediction). Before, the specific measuring model has to be calibrated. If the wavelength-to-period rate is well below unity, it is quite easy to gather enough diffraction orders. However, for gratings with spatial periods being smaller than the probing wavelength, merely the specular reflex will propagate for perpendicular incidence (zero order grating). Consequently, it is virtually impossible to perform a regression analysis. A proper mean to tackle this bottleneck is to record the zero-order reflex as a function of the incident angle. In this paper, the measurement of submicron gratings is discussed with the examples of 0.8, 1.0 and 1.4 micron period resist gratings on silicon, etched silicon oxide on silicon (same periods) and a 512 nm pitch chromium grating on quartz. Using a He-Ne laser with 633 nm wavelength and measuring the direct reflex in both linear polarizations, it is shown that even submicron patterning processes can be monitored and the resulting profiles with linewidths below a half micron can be characterized reliably with 2(theta) - scatterometry.

Research on a new type of fiber Bragg grating based corrosion sensor

NASA Astrophysics Data System (ADS)

Li, Peng; Song, Shide; Wang, Xiaona; Zhou, Weijie; Zhang, Zuocai

2015-08-01

Investigations of the corrosion of rebars in concrete structures are widely studied because of the serious damage to concrete caused by rebar corrosion. The rebar corrosion products in reinforced concrete take up 2~6 times the volume of the rebar. Based on this principle, a new type of fiber Bragg grating (FBG) corrosion sensor is proposed in this paper, which consists of two sensors, an FBG corrosion measurement sensor to measure the expansion strain caused by rebar corrosion, and a temperature compensation sensor to eliminate the cross-sensitivity of FBG corrosion sensor. The corrosion rate is derived by the wavelength shift of FBG corrosion sensor, so rebar corrosion can be monitored and assessed by the FBG wavelength shift. A customized rebar with epoxy fixing groove is designed to install a corrosion sensor on its surface and an embedded temperature compensation sensor. The corrosion sensor is embedded in cement mortar and subsequently casted in concrete. The performance of the corrosion sensor is studied in an accelerated electrochemical corrosion test. Experimental results show that the new type of corrosion sensor has advantage of relatively large measurement range of corrosion rate. The corrosion sensor is suitable to monitor slightly and moderately corroded rebars.

Fiber Bragg grating inscription in optical multicore fibers

NASA Astrophysics Data System (ADS)

Becker, Martin; Elsmann, Tino; Lorenz, Adrian; Spittel, Ron; Kobelke, Jens; Schuster, Kay; Rothhardt, Manfred; Latka, Ines; Dochow, Sebastian; Bartelt, Hartmut

2015-09-01

Fiber Bragg gratings as key components in telecommunication, fiber lasers, and sensing systems usually rely on the Bragg condition for single mode fibers. In special applications, such as in biophotonics and astrophysics, high light coupling efficiency is of great importance and therefore, multimode fibers are often preferred. The wavelength filtering effect of Bragg gratings in multimode fibers, however is spectrally blurred over a wide modal spectrum of the fiber. With a well-designed all solid multicore microstructured fiber a good light guiding efficiency in combination with narrow spectral filtering effect by Bragg gratings becomes possible.

Nanoimprint-defined, large-area meta-surfaces for unidirectional optical transmission with superior extinction in the visible-to-infrared range.

PubMed

Yao, Yuhan; Liu, He; Wang, Yifei; Li, Yuanrui; Song, Boxiang; Wang, Richard P; Povinelli, Michelle L; Wu, Wei

2016-07-11

Optical devices with asymmetric transmission have important applications in optical systems, but optical isolators with the modal asymmetry can only be built using magneto-optical or nonlinear materials, as dictated by the Lorentz reciprocity theorem. However, optical devices with the power asymmetry can be achieved by linear materials such as metals and dielectrics. In this paper, we report a large-area, nanoimprint-defined meta-surface (stacked subwavelength gratings) with high-contrast asymmetric transmittance in the visible-to-infrared wavelength range for TM-polarized light. The physical origin of asymmetric transmission through the meta-surface is studied by analyzing the scattering matrix.

Generation of individually modulated femtosecond pulse string by multilayer volume holographic gratings.

PubMed

Yan, Xiaona; Gao, Lirun; Yang, Xihua; Dai, Ye; Chen, Yuanyuan; Ma, Guohong

2014-10-20

A scheme to generate individually modulated femtosecond pulse string by multilayer volume holographic grating (MVHG) is proposed. Based on Kogelnik's coupled-wave theory and matrix optics, temporal and spectral expressions of diffracted field are given when a femtosecond pulse is diffracted by a MVHG. It is shown that the number of diffracted sub-pulses in the pulse string equals to the number of grating layers of the MVHG, peak intensity and duration of each diffracted sub-pulse depend on thickness of the corresponding grating layer, whereas pulse interval between adjacent sub-pulses is related to thickness of the corresponding buffer layer. Thus by modulating parameters of the MVHG, individually modulated femtosecond pulse string can be acquired. Based on Bragg selectivity of the volume grating and phase shift provided by the buffer layers, we give an explanation on these phenomena. The result is useful to design MVHG-based devices employed in optical communications, pulse shaping and processing.

VCSEL transmission at 10 Gb/s for 20 km single mode fiber WDM-PON without dispersion compensation or injection locking

NASA Astrophysics Data System (ADS)

Gibbon, T. B.; Prince, K.; Pham, T. T.; Tatarczak, A.; Neumeyr, C.; Rönneberg, E.; Ortsiefer, M.; Monroy, I. Tafur

2011-01-01

Vertical Cavity Surface Emitting Lasers (VCSELs) are extremely cost effective, energy efficient optical sources ideal for passive optical access networks. However, wavelength chirp and chromatic dispersion severely limit VCSEL performance at bit rates of 10 Gb/s and above. We experimentally show how off-center wavelength filtering of the VCSEL spectrum at an array waveguide grating can be used to mitigate the effect of chirp and the dispersion penalty. Transmission at 10 Gb/s VCSEL over 23.6 km of single mode fiber is experimentally demonstrated, with a dispersion penalty of only 2.9 dB. Simulated results are also presented which show that off-center wavelength filtering can extend the 10 Gb/s network reach from 11.7 km to 25.8 km for a 4 dB dispersion penalty. This allows for cheap and simple dispersion mitigation in next generation VCSEL-based optical access networks.

Effect of surface fields on the dynamic resistance of planar HgCdTe mid-wavelength infrared photodiodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Kai; Wang, Xi; Zhang, Peng

2015-05-28

This work investigates the effect of surface fields on the dynamic resistance of a planar HgCdTe mid-wavelength infrared photodiode from both theoretical and experimental aspects, considering a gated n-on-p diode with the surface potential of its p-region modulated. Theoretical models of the surface leakage current are developed, where the surface tunnelling current in the case of accumulation is expressed by modifying the formulation of bulk tunnelling currents, and the surface channel current for strong inversion is simulated with a transmission line method. Experimental data from the fabricated devices show a flat-band voltage of V{sub FB}=−5.7 V by capacitance-voltage measurement, and thenmore » the physical parameters for bulk properties are determined from the resistance-voltage characteristics of the diode working at a flat-band gate voltage. With proper values of the modeling parameters such as surface trap density and channel electron mobility, the theoretical R{sub 0}A product and corresponding dark current calculated from the proposed model as functions of the gate voltage V{sub g} demonstrate good consistency with the measured values. The R{sub 0}A product remarkably degenerates when V{sub g} is far below or above V{sub FB} because of the surface tunnelling current or channel current, respectively; and it attains the maximum value of 5.7×10{sup 7} Ω · cm{sup 2} around the transition between surface depletion and weak inversion when V{sub g}≈−4 V, which might result from reduced generation-recombination current.« less

Studies of snowpack properties by passive microwave radiometry

NASA Technical Reports Server (NTRS)

Chang, A. T. C.; Hall, D. K.; Foster, J. L.; Rango, A.; Schmugge, T. J.

1979-01-01

Research involving the microwave characteristics of snow was undertaken in order to expand the information content currently available from remote sensing, namely the measurement of snowcovered area. Microwave radiation emitted from beneath the snow surface can be sensed and thus permits information on internal snowpack properties to be inferred. The intensity of radiation received is a function of the average temperature and emissivity of the snow layers and is commonly referred to as the brightness temperature (T sub B). The T sub B varies with snow grain and crystal sizes, liquid water content, and snowpack temperature. The T sub B of the 0.8 cm wavelength channel was found to decrease more so with increasing snow depth than the 1.4 cm channel. More scattering of the shorter wavelength radiation occurs thus resulting in a lower T sub B for shorter wavelengths in a dry snowpack. The longer 21.0 cm wavelength was used to assess the condition of the underlying ground.

Uniquely identifiable tamper-evident device using coupling between subwavelength gratings

NASA Astrophysics Data System (ADS)

Fievre, Ange Marie Patricia

Reliability and sensitive information protection are critical aspects of integrated circuits. A novel technique using near-field evanescent wave coupling from two subwavelength gratings (SWGs), with the input laser source delivered through an optical fiber is presented for tamper evidence of electronic components. The first grating of the pair of coupled subwavelength gratings (CSWGs) was milled directly on the output facet of the silica fiber using focused ion beam (FIB) etching. The second grating was patterned using e-beam lithography and etched into a glass substrate using reactive ion etching (RIE). The slightest intrusion attempt would separate the CSWGs and eliminate near-field coupling between the gratings. Tampering, therefore, would become evident. Computer simulations guided the design for optimal operation of the security solution. The physical dimensions of the SWGs, i.e. period and thickness, were optimized, for a 650 nm illuminating wavelength. The optimal dimensions resulted in a 560 nm grating period for the first grating etched in the silica optical fiber and 420 nm for the second grating etched in borosilicate glass. The incident light beam had a half-width at half-maximum (HWHM) of at least 7 microm to allow discernible higher transmission orders, and a HWHM of 28 microm for minimum noise. The minimum number of individual grating lines present on the optical fiber facet was identified as 15 lines. Grating rotation due to the cylindrical geometry of the fiber resulted in a rotation of the far-field pattern, corresponding to the rotation angle of moire fringes. With the goal of later adding authentication to tamper evidence, the concept of CSWGs signature was also modeled by introducing random and planned variations in the glass grating. The fiber was placed on a stage supported by a nanomanipulator, which permitted three-dimensional displacement while maintaining the fiber tip normal to the surface of the glass substrate. A 650 nm diode laser was fixed to a translation mount that transmitted the light source through the optical fiber, and the output intensity was measured using a silicon photodiode. The evanescent wave coupling output results for the CSWGs were measured and compared to the simulation results.

Magnetic field sensing based on tilted fiber Bragg grating coated with nanoparticle magnetic fluid

NASA Astrophysics Data System (ADS)

Yang, Dexing; Du, Lei; Xu, Zengqi; Jiang, Yajun; Xu, Jian; Wang, Meirong; Bai, Yang; Wang, Haiyan

2014-02-01

A magnetic field sensor based on a tilted fiber Bragg grating (TFBG) coated with magnetic fluid is proposed and demonstrated experimentally. The sensing element is made by injecting the magnetic fluid into a capillary tube which contains a TFBG. The resonant wavelengths of the cladding modes of TFBG shift by varying the magnetic field which is perpendicular to the axis of TFBG. The results indicate that the resonant wavelength shifts of the cladding modes show a nonlinear dependence on the magnetic field. As the magnetic field increases to 32 mT, the largest resonant wavelength shift reaches to 106 pm. Moreover, this sensor shows good repeatability when it is used for magnetic field sensing.

A 16-Channel Distributed-Feedback Laser Array with a Monolithic Integrated Arrayed Waveguide Grating Multiplexer for a Wavelength Division Multiplex-Passive Optical Network System Network

NASA Astrophysics Data System (ADS)

Zhao, Jian-Yi; Chen, Xin; Zhou, Ning; Huang, Xiao-Dong; Cao, Ming-De; Liu, Wen

2014-07-01

A 16-channel distributed-feedback (DFB) laser array with a monolithic integrated arrayed waveguide grating multiplexer for a wavelength division multiplex-passive optical network system is fabricated by using the butt-joint metal organic chemical vapor deposition technology and nanoimpirnt technology. The results show that the threshold current is about 20-30 mA at 25°C. The DFB laser side output power is about 16 mW with a 150 mA injection current. The lasing wavelength is from 1550 nm to 1575 nm covering a more than 25 nm range with 200 GHz channel space. A more than 55 dB sidemode suppression ratio is obtained.

Novel plasmonic polarimeter for biomedical imaging applications

NASA Astrophysics Data System (ADS)

Cheney, Alec; Chen, Borui; Cartwright, Alexander; Thomay, Tim

2018-02-01

Using polarized light in medical imaging is a valuable tool for diagnostic purposes since light traveling through scattering tissues such as skin, blood, or cartilage may be subject to changes in polarization. We present a new detection scheme and sensor that allows for directly measuring the polarization of light electronically using a plasmonic sensor. The sensor we fabricated consists of a plasmonic nano-grating that is embedded in a Wheatstone circuit. Using resistive losses induced by optically excited plasmons has shown promise as a CMOScompatible plasmonic light detector. Since the plasmonic response is sensitive to polarization with respect to the grating orientation, measuring the resistance change under incident light supplies a direct electronic measure of the polarization of light without polarization optics. Increased electron scattering introduced by plasmons in an applied current results in a measurable decrease in electrical conductance of a grating, allowing a purely electronic readout of a plasmonic excitation. Accordingly, because of its plasmonic nature, such a detector is dependent on both the wavelength and polarization of incident light with a response time limited by the surface plasmon lifetime.

Human heart failure biomarker immunosensor based on excessively tilted fiber gratings.

PubMed

Luo, Binbin; Wu, Shengxi; Zhang, Zhonghao; Zou, Wengen; Shi, Shenghui; Zhao, Mingfu; Zhong, Nianbing; Liu, Yong; Zou, Xue; Wang, Lingling; Chai, Weina; Hu, Chuanmin; Zhang, Lin

2017-01-01

A label-free immunosensor platform based on excessively tilted fiber gratings (Ex-TFGs) was developed for highly specific and fast detection of human N-terminal pro-B-type natriuretic peptide (NT-proBNP), which is considered a powerful biomarker for prognosis and risk stratification of heart failure (HF). High-purity anti-NT-proBNP monoclonal antibodies (MAbs) prepared in our laboratory were immobilized on fiber surface through the staphylococcal protein A (SPA) method for subsequent specific binding of the targeted NT-proBNP. Utilizing fiber optic grating demodulation system (FOGDS), immunoassays were carried out in vitro by monitoring the resonance wavelength shift of Ex-TFG biosensor with immobilized anti-NT-proBNP MAbs. Lowest detectable concentration of ~0.5ng/mL for NT-proBNP was obtained, and average sensitivity for NT-proBNP at a concentration range of 0~1.0 ng/mL was approximately 45.967 pm/(ng/mL). Several human serum samples were assessed by the proposed Ex-TFG biomarker sensor, with high specificity for NT-proBNP, indicating potential application in early diagnosing patients with acute HF symptoms.

High-efficiency, broad-band and wide-angle optical absorption in ultra-thin organic photovoltaic devices.

PubMed

Wang, Wenyan; Hao, Yuying; Cui, Yanxia; Tian, Ximin; Zhang, Ye; Wang, Hua; Shi, Fang; Wei, Bin; Huang, Wei

2014-03-10

Metal nanogratings as one of the promising architectures for effective light trapping in organic photovoltaics (OPVs) have been actively studied over the past decade. Here we designed a novel metal nanowall grating with ultra-small period and ultra-high aspect-ratio as the back electrode of the OPV device. Such grating results in the strong hot spot effect in-between the neighboring nanowalls and the localized surface plasmon effect at the corners of nanowalls. These combined effects make the integrated absorption efficiency of light over the wavelength range from 400 to 650 nm in the active layer for the proposed structure, with respect to the equivalent planar structure, increases by 102% at TM polarization and by 36.5% at the TM/TE hybrid polarization, respectively. Moreover, it is noted that the hot spot effect in the proposed structure is more effective for ultra-thin active layers, which is very favorable for the exciton dissociation and charge collection. Therefore such a nanowall grating is expected to improve the overall performance of OPV devices.

Immunosensing with Near-Infrared Plasmonic Optical Fiber Gratings.

PubMed

Caucheteur, Christophe; Ribaut, Clotilde; Malachovska, Viera; Wattiez, Ruddy

2017-01-01

Surface Plasmon resonance (SPR) optical fiber biosensors constitute a miniaturized counterpart to the bulky prism configuration and offer remote operation in very small volumes of analyte. They are a cost-effective and relatively straightforward technique to yield in situ (or even possibly in vivo) molecular detection. They are usually obtained from a gold-coated fiber segment for which the core-guided light is brought into contact with the surrounding medium, either by etching (or side-polishing) or by using grating coupling. Recently, SPR generation was achieved in gold-coated tilted fiber Bragg gratings (TFBGs). These sensors probe the surrounding medium with near-infrared narrowband resonances, which enhances both the penetration depth of the evanescent field in the external medium and the wavelength resolution of the interrogation. They constitute the unique configuration able to probe all the fiber cladding modes individually, with high Q-factors. We use these unique spectral features in our work to sense proteins and extra-cellular membrane receptors that are both overexpressed in cancerous tissues. Impressive limit of detection (LOD) and sensitivity are reported, which paves the way for the further use of such immunosensors for cancer diagnosis.

Investigation and optimal design of Photonic Crystal Fiber Bragg Grating using the Bat Algorithm and Binary Morse-Thue fractal Sequence, for eye-safe Tunable Fiber and Solid-State Lasers

NASA Astrophysics Data System (ADS)

Al-Muraeb, Ahmed Mohammed Maim

This dissertation presents new approaches to design photonic crystal fiber Bragg grating, which is a main component in wavelength-tunable fiber and solid-state laser (SSL) systems operating in eye-safe wavelength region (1.4 - 2 mum). Although they have their own name, fiber lasers can be categorized as SSL as they are being used in making Ion-doped SSL. Today however, fiber lasers compete with and threaten to replace most of high-power, bulk SSLs and even some gas lasers. Hence, an eye-safe dual-wavelength Tunable Fiber Ring Laser (TFRL) system is considered in this work. This work addresses: 1. Eye-safe region laser areas of applications, TFRL system description, and wavelength tuning mechanisms with focus on (1.8 - 2 mum) range. 2. Optimal design method for Fiber Bragg Grating (FBG) using the Bat Algorithm, with the novel Adaptive Position Update (APU-BA) (our work [1]). The latter enhances the search performance and accuracy of BA for FBG design. Also, APU-BA shows better search performance and higher accuracy against previously reported methods and algorithms. 3. Investigation and design of novel High-Birefringence Photonic Crystal Fiber (JIBPCF) structures based on the Binary Morse-Thue fractal Sequence (BMTS) [2]. The latter offers desirably higher birefringence and lower confinement loss with dispersion-free single-mode operation in the eye-safe region of interest (1.8 - 2 microm). 4. Combining the above results, for final design of the photonic crystal fiber Bragg grating device (serving as wavelength-selective reflector in TFRL). Fiber Bragg grating design and analysis were carried out using MATLAG RTM. Resulting in refractive index modulation over the designed FBG length for a given target FBG reflectance spectrum. Hexagonal standard Silica Glass solid-core 5-ring HB-PCF with circular air holes, is designed based on BMTS. COMSOL MultiphysicsRTM - Wave Optics Module is used in modeling and analysis for the design. Four BMTS formations were proposed, and compared in terms of PCF design parameters (mainly: birefringence). Fabrication in agreement with commercially available PCFs, are concerned in structure geometrical design.

Mode Tracker for Mode-Hop-Free Operation of a Laser

NASA Technical Reports Server (NTRS)

Wysocki, Gerard; Tittel, Frank K.; Curl, Robert F.

2010-01-01

A mode-tracking system that includes a mode-controlling subsystem has been incorporated into an external-cavity (EC) quantum cascade laser that operates in a mid-infrared wavelength range. The mode-tracking system makes it possible to perform mode-hop-free wavelength scans, as needed for high-resolution spectroscopy and detection of trace gases. The laser includes a gain chip, a beam-collimating lens, and a diffraction grating. The grating is mounted on a platform, the position of which can be varied to effect independent control of the EC length and the grating angle. The position actuators include a piezoelectric stage for translation control and a motorized stage for coarse rotation control equipped with a piezoelectric actuator for fine rotation control. Together, these actuators enable control of the EC length over a range of about 90 m with a resolution of 0.9 nm, and control of the grating angle over a coarse-tuning range of +/-6.3deg and a fine-tuning range of +/-520 microrad with a resolution of 10 nrad. A mirror mounted on the platform with the grating assures always the same direction of the output laser beam.

Novel fiber optic sensor for grip testing

NASA Astrophysics Data System (ADS)

Zhao, Li Ping; Fang, Zhong Ping; Paul, Jinu; Ngoi, Bryan K. A.; Ng, Jun Hong

2004-12-01

Grip strength is an easy measure of skeletal muscle function as well as a powerful predictor of disability, morbidity and mortality. In order to measure the grip strength, a novel fiber optic approach is proposed and demonstrated. Strain dependent wavelength response of fiber Bragg gratings (FBGs) has been utilized to obtain the strength of individual fingers. Five FBGs are written at different center wavelengths on a single photosensitive fiber. Each FBG is used to get the response from each individual finger. The fiber containing the gratings is attached to a suitable grip holder, which can effectively transfer the grip force to the FBGs. An additional reference FBG is also provided to make the device temperature insensitive. Experimental results show that the wavelength shifts of the order of 0.2-0.5 nm can be achieved for individual fingers. The device is calibrated in terms of load to convert the wavelength shift to the strength of the grip. The time dependent wavelength fluctuations was also studied and presented in this paper.

Design and fabrication of an elliptical micro-lens array with grating for laser safety

NASA Astrophysics Data System (ADS)

Li, L. H.; Wu, B. Q.; Chan, C. Y.; Lee, W. B.; Dong, L. H.

2015-10-01

With the enormous expansion of laser usage in medicine, industry and research, all facilities must formulate and adhere to specific safety methods that appropriately address user protection. The protective ellipticalal microstructure with grating is a novel technology which can provide the principal means of ensuring against ocular injury, and must be worn at all times during laser operation. On the basis of Fresnel's law and the diffractive law, Solidworks and Lighttools software are applied to design the elliptical micro-lens array and correspondent grating. The height of the microstructure is 100um and its period is 3mm. The period of grating is 5um. It is shown that the amount of emergent light of a specific wavelength (1064nm) can reflect more than 40° from the incident light through simulation, while the incident light is perpendicular to the microstructure. The fabrication adopts the ultra-precision single point diamond method and injection molding method. However, it is found in the test that the surface roughness has a serious effect on the angle between the emergent and incident light. As a result, the element can reflect the vertical incidence beam into a tilted emergent beam with a certain angular degree , as well as protecting users from laser damage injures.

Fiber-optic sensor for handgrip-strength monitoring: conception and design

NASA Astrophysics Data System (ADS)

Paul, Jinu; Zhao, Liping; Ngoi, Bryan K. A.

2005-06-01

Handgrip strength is an easy measure of skeletal muscle function as well as a powerful predictor of disability, morbidity, and mortality. In order to measure grip strength, a novel fiber-optic approach is proposed and demonstrated. The strain-dependent wavelength response of fiber Bragg gratings has been utilized to obtain the strength of individual fingers. Finite-element analysis is carried out to optimize the pressure transmission from the finger to the fiber Bragg grating. The effect of stiffness of the pressurizing media, its thickness, and the effect of contact fraction are evaluated. It is found that significant enhancement in the pressure sensitivity and wavelength-tuning range is achievable by optimizing these parameters. Also the stress-induced birefringence could be reduced to an insignificant near-zero value. The device is calibrated in terms of load to convert the wavelength shift to the strength of the grip. The time-dependent wavelength fluctuation is also studied and presented.

Free-space wavelength-multiplexed optical scanner demonstration.

PubMed

Yaqoob, Zahid; Riza, Nabeel A

2002-09-10

Experimental demonstration of a no-moving-parts free-space wavelength-multiplexed optical scanner (W-MOS) is presented. With fast tunable lasers or optical filters and planar wavelength dispersive elements such as diffraction gratings, this microsecond-speed scanner enables large several-centimeter apertures for subdegree angular scans. The proposed W-MOS design incorporates a unique optical amplifier and variable optical attenuator combination that enables the calibration and modulation of the scanner response, leading to any desired scanned laser beam power shaping. The experimental setup uses a tunable laser centered at 1560 nm and a 600-grooves/mm blazed reflection grating to accomplish an angular scan of 12.92 degrees as the source is tuned over an 80-nm bandwidth. The values for calculated maximum optical beam divergance, required wavelength resolution, beam-pointing accuracy, and measured scanner insertion loss are 1.076 mrad, 0.172 nm, 0.06 mrad, and 4.88 dB, respectively.

Silicon structuring by etching with liquid chlorine and fluorine precursors using femtosecond laser pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Radu, C.; Simion, S.; Zamfirescu, M.

2011-08-01

The aim of this study is to investigate the micrometer and submicrometer scale structuring of silicon by liquid chlorine and fluorine precursors with 200 fs laser pulses working at both fundamental (775 nm) and frequency doubled (387 nm) wavelengths. The silicon surface was irradiated at normal incidence by immersing the Si (111) substrates in a glass container filled with liquid chlorine (CCl{sub 4}) and fluorine (C{sub 2}Cl{sub 3}F{sub 3}) precursors. We report that silicon surfaces develop an array of spikes with single step irradiation processes at 775 nm and equally at 387 nm. When irradiating the Si surface with 400more » pulses at 330 mJ/cm{sup 2} laser fluence and a 775 nm wavelength, the average height of the formed Si spikes in the case of fluorine precursors is 4.2 {mu}m, with a full width at half maximum of 890 nm. At the same irradiation wavelength chlorine precursors develop Si spikes 4 {mu}m in height and with a full width at half maximum of 2.3 {mu}m with irradiation of 700 pulses at 560 mJ/cm{sup 2} laser fluence. Well ordered areas of submicrometer spikes with an average height of about 500 nm and a width of 300 nm have been created by irradiation at 387 nm by chlorine precursors, whereas the fluorine precursors fabricate spikes with an average height of 700 nm and a width of about 200 nm. Atomic force microscopy and scanning electron microscopy of the surface show that the formation of the micrometer and sub-micrometer spikes involves a combination of capillary waves on the molten silicon surface and laser-induced etching of silicon, at both 775 nm and 387 nm wavelength irradiation. The energy-dispersive x-ray measurements indicate the presence of chlorine and fluorine precursors on the structured surface. The fluorine precursors create a more ordered area of Si spikes at both micrometer and sub-micrometer scales. The potential use of patterned Si substrates with gradient topography as model scaffolds for the systematic exploration of the role of 3D micro/nano morphology on cell adhesion and growth is envisaged.« less

Experimental observation of acoustic sub-harmonic diffraction by a grating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jingfei, E-mail: benjamin.jf.liu@gatech.edu; Declercq, Nico F., E-mail: declercqdepatin@gatech.edu

2014-06-28

A diffraction grating is a spatial filter causing sound waves or optical waves to reflect in directions determined by the frequency of the waves and the period of the grating. The classical grating equation is the governing principle that has successfully described the diffraction phenomena caused by gratings. However, in this work, we show experimental observation of the so-called sub-harmonic diffraction in acoustics that cannot be explained by the classical grating equation. Experiments indicate two physical phenomena causing the effect: internal scattering effects within the corrugation causing a phase shift and nonlinear acoustic effects generating new frequencies. This discovery expandsmore » our current understanding of the diffraction phenomenon, and it also makes it possible to better design spatial diffraction spectra, such as a rainbow effect in optics with a more complicated color spectrum than a traditional rainbow. The discovery reveals also a possibly new technique to study nonlinear acoustics by exploitation of the natural spatial filtering effect inherent to an acoustic diffraction grating.« less

Research on the demodulation techniques of long-period fiber gratings strain sensing with low cost

NASA Astrophysics Data System (ADS)

Wang, Qingwei; Liu, Yueming; Tian, Weijian; Feng, Guilan

2012-10-01

The working principle of LPFG(Long-Period Fiber Grating) is based on coupling effect between propagating core-mode and co-propagating cladding-modes. The effective refractive index of cladding-modes could be obviously influenced by the environmental changes resulting in LPFG more sensitive than FBG (Fiber Bragg Grating) in sensing areas, such as temperature, strain, concentration, bending and etc. LPFG should have more potential in the field of sensors compared with FBG. One of the challenges in using LPFG for environmental sensing is how to interrogate the signal from the LPFG transmission spectrum, due to the large spectral range of the resonant dip. Nowadays the application of LPFG is normally limited in signal interrogation of FBG as optical edge filter. The signal interrogation of LPFG itself needs further research. Presently research on signal interrogation of fiber grating focuses on wavelength interrogation. The aim of wavelength interrogation is to get the wavelength shift caused by environmental change. To solve these problems, a kind of strain sensing interrogation technique for LPFG with low-cost based on tunable FBGs has been developed. Comparing with the method using Fabry-Perot cavity, tunable FBGs can lower the cost with the guarantee of sensing precision. The cost is further lowered without using expensive optical instruments such as optical switch. The problem of temperature cross-sensitivity was solved by using reference gratings. An experiment was performed to demonstrate the interrogation system. And in the experiment, the sensing signal of LPFG applied 0-1300μɛ was successfully interrogated. The results of the interrogation system and OSA are similar.

Real-Time Label-Free Surface Plasmon Resonance Biosensing with Gold Nanohole Arrays Fabricated by Nanoimprint Lithography

PubMed Central

Martinez-Perdiguero, Josu; Retolaza, Aritz; Otaduy, Deitze; Juarros, Aritz; Merino, Santos

2013-01-01

In this work we present a surface plasmon resonance sensor based on enhanced optical transmission through sub-wavelength nanohole arrays. This technique is extremely sensitive to changes in the refractive index of the surrounding medium which result in a modulation of the transmitted light. The periodic gold nanohole array sensors were fabricated by high-throughput thermal nanoimprint lithography. Square periodic arrays with sub-wavelength hole diameters were obtained and characterized. Using solutions with known refractive index, the array sensitivities were obtained. Finally, protein absorption was monitored in real-time demonstrating the label-free biosensing capabilities of the fabricated devices. PMID:24135989

Volume phase holographic grating used for beams combination of RGB primary colors

NASA Astrophysics Data System (ADS)

Liu, Hui; Zhang, Xizhao; Tang, Minxue

2013-12-01

Volume phase holographic grating (VPHG) has the characteristics of high diffraction efficiency, high signal to noise ratio, high wavelength and angular selectivity, low scattering , low absorption and low cost. It has been widely used in high resolution spectrometer, wavelength division multiplexing and pulse compression technique. In this paper, a novel kind of RGB primary colors beams combiner which is consisted of a transmission VPHG and a reflection VPHG as core components is proposed. The design idea of the element is described in detail. Based on the principle of VPHG, the rigorous coupled wave analysis (RCWA) and Kogelnik's coupled wave theory, diffraction properties of the transmission and reflection VPHG are studied theoretically. As an example, three primary colors at wavelengths of 632.8nm, 532nm and 476.5nm are taken into account. Dichromated gelatin (DCG) is used as the holographic recording material. The grating parameters are determined by the Bragg conditions. The TE and TM wave diffraction efficiency, the wavelength selectivity and the angular selectivity of the transmission and reflection VPHG are calculated and optimized by setting the amplitude of the index modulation (Δn) and the thickness of the gelatin layer (d) by applying Kogelnik's coupled wave theory and G-solver software, respectively. The theoretical calculating results give guidance for further manufacture of the element.

Sub-200 femtosecond dispersion-managed soliton ytterbium-doped fiber laser based on carbon nanotubes saturable absorber.

PubMed

Hou, Lei; Guo, Hongyu; Wang, Yonggang; Sun, Jiang; Lin, Qimeng; Bai, Yang; Bai, Jintao

2018-04-02

Ultrafast fiber laser light sources attract enormous interest due to the booming applications they are enabling, including long-distance communication, optical metrology, detecting technology of infra-biophotons, and novel material processing. In this paper, we demonstrate 175 fs dispersion-managed soliton (DMS) mode-locked ytterbium-doped fiber (YDF) laser based on single-walled carbon nanotubes (SWCNTs) saturable absorber (SA). The output DMSs have been achieved with repetition rate of 21.2 MHz, center wavelength of 1025.5 nm, and a spectral width of 32.7 nm. The operation directly pulse duration of 300 fs for generated pulse is the reported shortest pulse width for broadband SA based YDF lasers. By using an external grating-based compressor, the pulse duration could be compressed down to 175 fs. To the best of our knowledge, it is the shortest pulse duration obtained directly from YDF laser based on broadband SAs. In this paper, SWCNTs-SA has been utilized as the key optical component (mode locker) and the grating pair providing negative dispersion acts as the dispersion controller.

Effective grating theory for resonance domain surface-relief diffraction gratings.

PubMed

Golub, Michael A; Friesem, Asher A

2005-06-01

An effective grating model, which generalizes effective-medium theory to the case of resonance domain surface-relief gratings, is presented. In addition to the zero order, it takes into account the first diffraction order, which obeys the Bragg condition. Modeling the surface-relief grating as an effective grating with two diffraction orders provides closed-form analytical relationships between efficiency and grating parameters. The aspect ratio, the grating period, and the required incidence angle that would lead to high diffraction efficiencies are predicted for TE and TM polarization and verified by rigorous numerical calculations.

High efficiency spectrographs for the EUV and soft X-rays

NASA Technical Reports Server (NTRS)

Cash, W.

1983-01-01

The use of grazing incidence optics and reflection grating designs is shown to be a method that improves the performance of spectrographs at wavelengths shorter than 1200 A. Emphasis is laid on spectroscopic designs for X ray and EUV astronomy, with sample designs for an objective reflection grating spectrograph (ORGS) and an echelle spectrograph for wavelengths longer than 100 A. Conical diffraction allows operations at grazing incidence in the echelle spectrograph. In ORGS, the extreme distance of X ray objects aids in collimating the source radiation, which encounters conical diffraction within the instrument, proceeds parallel to the optical axis, and arrives at the detector. A series of gratings is used to achieve the effect. A grazing echelle is employed for EUV observations, and offers a resolution of 20,000 over a 300 A bandpass.

Spoof four-wave mixing for all-optical wavelength conversion.

PubMed

Gong, Yongkang; Huang, Jungang; Li, Kang; Copner, Nigel; Martinez, J J; Wang, Leirang; Duan, Tao; Zhang, Wenfu; Loh, W H

2012-10-08

We present for the first time an all-optical wavelength conversion (AOWC) scheme supporting modulation format independency without requiring phase matching. The new scheme is named "spoof" four wave mixing (SFWM) and in contrast to the well-known FWM theory, where the induced dynamic refractive index grating modulates photons to create a wave at a new frequency, the SFWM is different in that the dynamic refractive index grating is generated in a nonlinear Bragg Grating (BG) to excite additional reflective peaks at either side of the original BG bandgap in reflection spectrum. This fundamental difference enable the SFWM to avoid the intrinsic shortcoming of stringent phase matching required in the conventional FWM, and allows AOWC with modulation format transparency and ultrabroad conversion range, which may have great potential applications for next generation of all-optical networks.

Polarization-independent broadband dielectric bilayer gratings for spectral beam combining system

NASA Astrophysics Data System (ADS)

Li, Linxin; Liu, Quan; Chen, Junming; Wang, Leilei; Jin, Yunxia; Yang, Yifeng; Shao, Jianda

2017-02-01

We report on a polarization-independent all-dielectric trapezoidal bilayer grating with broadband and high diffraction efficiency. The bilayer trapezoidal grating ridge on a reflector consists of an HfO2 layer and a SiO2 layer. The theoretical -1st order efficiencies of the grating are more than 95% with wavelength range from 1010 nm to 1080 nm for both TE and TM polarizations. The fabrication tolerances depending on the HfO2 and SiO2 layer grating ridge depths are enough to obtain the designed grating using current craft. The fabricated grating with exceeding 94% efficiency from 1000 nm to 1085 nm measured by a non-polarization laser has been fabricated and applied in a spectral beam combining external cavity to combine eight beams into one beam output with 10.77 kW.

Characterization of diffraction gratings scattering in uv and ir for space applications

NASA Astrophysics Data System (ADS)

Achour, Sakina; Kuperman-Le Bihan, Quentin; Etcheto, Pierre

2017-09-01

The use of Bidirectional Scatter Distribution Function (BSDF) in space industry and especially when designing telescopes is a key feature. Indeed when speaking about space industry, one can immediately think about stray light issues. Those important phenomena are directly linked to light scattering. Standard BSDF measurement goniophotometers often have a resolution of about 0.1° and are mainly working in or close to the visible spectrum. This resolution is far too loose to characterize ultra-polished surfaces. Besides, wavelength range of BSDF measurements for space projects needs to be done far from visible range. How can we measure BSDF of ultra-polished surfaces and diffraction gratings in the UV and IR range with high resolution? We worked on developing a new goniophometer bench in order to be able to characterize scattering of ultra-polished surfaces and diffraction gratings used in everyday space applications. This ten meters long bench was developed using a collimated beam approach as opposed to goniophotometer using focused beam. Sources used for IR characterization were CO2 (10.6?m) and Helium Neon (3.39?m) lasers. Regarding UV sources, a collimated and spatially filtered UV LED was used. The detection was ensure by a photomultiplier coupled with synchronous detection as well as a MCT InSb detector. The so-built BSDF measurement instrument allowed us to measure BSDF of ultra-polished surfaces as well as diffraction gratings with an angular resolution of 0.02° and a dynamic of 1013 in the visible range. In IR as well as in UV we manage to get 109 with same angular resolution of 0.02°. The 1m arm and translation stages allows us to measure samples up to 200mm. Thanks to such a device allowing ultra-polished materials as well as diffraction gratings scattering characterization, it is possible to implement those BSDF measurements into simulation software and predict stray light issues. This is a big help for space industry engineers to apprehend stray light due to surface finishes and to delete those effects before the whole project is done. We are now thinking of possible improvement on our optical bench to try to get dynamic in IR and UV similar to what we have in visible range (e.g. 1013).

Single-mode fiber laser based on core-cladding mode conversion.

PubMed

Suzuki, Shigeru; Schülzgen, Axel; Peyghambarian, N

2008-02-15

A single-mode fiber laser based on an intracavity core-cladding mode conversion is demonstrated. The fiber laser consists of an Er-doped active fiber and two fiber Bragg gratings. One Bragg grating is a core-cladding mode converter, and the other Bragg grating is a narrowband high reflector that selects the lasing wavelength. Coupling a single core mode and a single cladding mode by the grating mode converter, the laser operates as a hybrid single-mode laser. This approach for designing a laser cavity provides a much larger mode area than conventional large-mode-area step-index fibers.

Wideband plasmonic beam steering in metal gratings.

PubMed

de Ceglia, Domenico; Vincenti, Maria Antonietta; Scalora, Michael

2012-01-15

We demonstrate controllable light deflection in thick metal gratings with periodic subwavelength slits filled with an active material. Under specific illumination conditions, the grating becomes nearly transparent and acts as a uniform optical phased-array antenna where the phase of the radiating elements is controlled by modifying the index of refraction of the material that fills each slit. The beam-steering operational regime occurs in a wide wavelength band, and it is relatively insensitive to the input angle.

Design And Performance Of Micro-Spec, An Ultra Compact High-sensitivity Far-infrared Spectrometer For SPICA

NASA Astrophysics Data System (ADS)

Cataldo, Giuseppe; Moseley, S. H.; Hsieh, W.; Huang, W.; Stevenson, T. R.; Wollack, E. J.

2012-05-01

Micro-Spec (µ-Spec) is a high-performance spectrometer working in the 250-700-µm wavelength range, whose modules use low-loss superconducting microstrip transmission lines on a single 4-inch-diameter silicon wafer. Creating the required phase delays in transmission lines rather than free space allows such an instrument to have, in principle, the performance of a meter-scale grating spectrometer. Such a dramatic size reduction enables classes of instruments for space that would be impossible with conventional technologies. This technology can dramatically enhance the long-wavelength capability of the space infrared telescope for cosmology and astrophysics SPICA. µ-Spec is analogous to a grating spectrometer. The phase retardation generated by the reflection from the grating grooves is instead produced by propagation through a transmission line. The power received by a broadband antenna is progressively divided by binary microstrip power dividers, and the required phase delays are generated by different lengths of microstrip transmission lines. By arranging these outputs along a circular focal surface, the analog of a Rowland spectrometer can be created. The procedure to optimize the Micro-Spec design is based on the stigmatization and minimization of the light path function in a two-dimensional bounded region, which results in an optimized geometry arrangement with three stigmatic points. In addition, in order to optimize the overall efficiency of the instrument, the emitters are directed to the center of the focal surface. The electric field amplitude and phase as well as the power transmitted and absorbed throughout the region are analyzed. Measurements are planned in late summer to validate the designs. This material is based upon work supported by NASA through the ROSES/APRA program. This research was supported by an appointment (Cataldo) at the Goddard Space Flight Center administered by Universities Space Research Association through a contract with NASA.

Development of the multiwavelength monolithic integrated fiber optics terminal

NASA Technical Reports Server (NTRS)

Chubb, C. R.; Bryan, D. A.; Powers, J. K.; Rice, R. R.; Nettle, V. H.; Dalke, E. A.; Reed, W. R.

1982-01-01

This paper describes the development of the Multiwavelength Monolithic Integrated Fiber Optic Terminal (MMIFOT) for the NASA Johnson Space Center. The program objective is to utilize guided wave optical technology to develop wavelength-multiplexing and -demultiplexing units, using a single mode optical fiber for transmission between terminals. Intensity modulated injection laser diodes, chirped diffraction gratings and thin film lenses are used to achieve the wavelength-multiplexing and -demultiplexing. The video and audio data transmission test of an integrated optical unit with a Luneburg collimation lens, waveguide diffraction grating and step index condensing lens is described.

Low-cost vibration sensor based on dual fiber Bragg gratings and light intensity measurement.

PubMed

Gao, Xueqing; Wang, Yongjiao; Yuan, Bo; Yuan, Yinquan; Dai, Yawen; Xu, Gang

2013-09-20

A vibration monitoring system based on light intensity measurement has been constructed, and the designed accelerometer is based on steel cantilever frame and dual fiber Bragg gratings (FBGs). By using numerical simulations for the dual FBGs, the dependence relationship of the area of main lobes on the difference of initial central wavelengths is obtained and the most optimal choice for the initial value and the vibration amplitude of the difference of central wavelengths of two FBGs is suggested. The vibration monitoring experiments are finished, and the measured data are identical to the simulated results.

Ultra-long-period grating as a novel tool for multi-wavelength ultrafast photonics

NASA Astrophysics Data System (ADS)

Guo, Bo; Yang, Wen-Lei

2017-10-01

Here, we demonstrate the six-wavelength mode-locking and hybrid mode-locking operation in an erbium-doped fiber laser (EDFL) with an ultra-long-period grating (ULPG) by properly adjusting the pump power and the cavity parameters. The ULPG is fabricated by using the fused biconical method with a GPX-3000 glass processing system. Study found that, the ULPG exhibits dual-function, that is, mode-locker and multiwavelength filter. Our finding implies that apart from its fantastic sensing application, the ULPG may also possess attractive nonlinear optical property for ultrafast photonics.

Grism manufacturing by low temperature mineral bonding

NASA Astrophysics Data System (ADS)

Kalkowski, G.; Grabowski, K.; Harnisch, G.; Flügel-Paul, T.; Zeitner, U.; Risse, S.

2017-09-01

By uniting a grating with a prism to a GRISM compound, the optical characteristics of diffractive and refractive elements can be favorably combined to achieve outstanding spectral resolution features. Ruling the grating structure into the prism surface is common for wavelengths around 1 μm and beyond, while adhesive bonding of two separate parts is generally used for shorter wavelengths and finer structures. We report on a manufacturing approach for joining the corresponding glass elements by the technology of hydrophilic direct bonding. This allows to manufacture the individual parts separately and subsequently combine them quasimonolithically by generating stiff and durable bonds of vanishing thickness, high strength and excellent transmission. With this approach for GRISM bonding, standard direct-write- or mask-lithography equipment may be used for the fabrication of the grating structure and the drawbacks of adhesive bonding (thermal mismatch, creep, aging) are avoided. The technology of hydrophilic bonding originates from "classical" optical contacting [1], but has been much improved and perfected during the last decades in the context of 3-dimensinal stacking Si-wafers for microelectronic applications [2]. It provides joins through covalent bonds of the Si-O-Si type at the nanometer scale, i.e. the elementary bond type in many minerals and glasses. The mineral nature of the bond is perfectly adapted to most optical materials and the extremely thin bonding layers generated with this technology are well suited for transmission optics. Creeping under mechanical load, as commonly observed with adhesive bonding, is not an issue. With respect to diffusion bonding, which operates at rather high temperatures close to the glass transition or crystal melting point, hydrophilic bonding is a low temperature process that needs only moderate heating. This facilitates provision of handling and alignment means for the individual parts during the set-up stages and greatly eases joining optical materials of different thermal expansion. The technology has been successfully used in the past for bonding various glasses as well as crystalline optical materials [3, 4]. Here we will focus on bonding prisms elements and binary gratings of fused silica with and without coatings at the bonding interface. Further, preliminary results on bonding prism-grating-prism (PGP) combinations will be presented.

16-channel arrayed waveguide grating (AWG) demultiplexer design on SOI wafer for application in CWDM-PON

NASA Astrophysics Data System (ADS)

Juhari, Nurjuliana; Menon, P. Susthitha; Ehsan, Abang Annuar; Shaari, Sahbudin

2015-01-01

Arrayed Waveguide Grating (AWG) functioning as a demultiplexer is designed on SOI platform with rib waveguide structure to be utilized in coarse wavelength division multiplexing-passive optical network (CWDM-PON) systems. Two design approaches; conventional and tapered configuration of AWG was developed with channel spacing of 20 nm that covers the standard transmission spectrum of CWDM ranging from 1311 nm to 1611 nm. The performance of insertion loss for tapered configuration offered the lowest insertion loss of 0.77 dB but the adjacent crosstalk gave non-significant relation for both designs. With average channel spacing of 20.4 nm, the nominal central wavelength of this design is close to the standard CWDM wavelength grid over 484 nm free spectrum range (FSR).

Effect of etching parameters on antireflection properties of Si subwavelength grating structures for solar cell applications

NASA Astrophysics Data System (ADS)

Leem, J. W.; Song, Y. M.; Lee, Y. T.; Yu, J. S.

2010-09-01

Silicon (Si) subwavelength grating (SWG) structures were fabricated on Si substrates by holographic lithography and subsequent inductively coupled plasma (ICP) etching process using SiCl4 with or without Ar addition for solar cell applications. To ensure a good nanosized pattern transfer into the underlying Si layer, the etch selectivity of Si over the photoresist mask is optimized by varying the etching parameters, thus improving antireflection characteristics. For antireflection analysis of Si SWG surfaces, the optical reflectivity is measured experimentally and it is also calculated theoretically by a rigorous coupled-wave analysis. The reflectance depends on the height, period, and shape of two-dimensional periodic Si subwavelength structures, correlated with ICP etching parameters. The optimized Si SWG structure exhibits a dramatic decrease in optical reflection of the Si surface over a wide angle of incident light ( θ i ), i.e. less than 5% at wavelengths of 300-1100 nm, leading to good wide-angle antireflection characteristics (i.e. solar-weighted reflection of 1.7-4.9% at θ i <50°) of Si solar cells.

ISO observations of Titan with SWS/grating

NASA Technical Reports Server (NTRS)

Coustenis, A.; Encrenaz, T.; Salama, A.; Lellouch, E.; Gautier, D.; Kessler, M. F.; deGraauw, T.; Samuelson, R. E.; Bjoraker, G.; Orton, G.

1997-01-01

The observations of Titan performed by the Infrared Space Observatory (ISO) short wavelength spectrometer (SWS), in the 2 micrometer to 45 micrometer region using the grating mode, are reported on. Special attention is given to data from Titan concerning 7 micrometer to 45 micrometer spectral resolution. Future work for improving Titan's spectra investigation is suggested.

Design and fabrication of a metamaterial gradient index diffraction grating at infrared wavelengths.

PubMed

Tsai, Yu-Ju; Larouche, Stéphane; Tyler, Talmage; Lipworth, Guy; Jokerst, Nan M; Smith, David R

2011-11-21

We demonstrate the design, fabrication and characterization of an artificially structured, gradient index metamaterial with a linear index variation of Δn ~ 3.0. The linear gradient profile is repeated periodically to form the equivalent of a blazed grating, with the gradient occurring across a spatial distance of 61 μm. The grating, which operates at a wavelength of 10.6 μm, is composed of non-resonant, progressively modified "I-beam" metamaterial elements and approximates a linear phase shift gradient using 61 distinguishable phase levels. The grating structure consists of four layers of lithographically patterned metallic I-beam elements separated by dielectric layers of SiO(2). The index gradient is confirmed by comparing the measured magnitudes of the -1, 0 and +1 diffracted orders to those obtained from full wave simulations incorporating all material properties of the metals and dielectrics of the structures. The large index gradient has the potential to enable compact infrared diffractive and gradient index optics, as well as more exotic transformation optical media. © 2011 Optical Society of America

Multiple wavelengths filtering of light through inner resonances.

PubMed

Felbacq, Didier; Larciprete, Maria Cristina; Sibilia, Concita; Bertolotti, Mario; Scalora, Michael

2005-12-01

We show that by using the internal resonances of a grating, it is possible to design a filter working for multiple wavelengths. We study the characteristics of the device with respect to the constituting parameters and we propose a realization process.

Infrared Space Observatory Observations of Far-Infrared Rotational Emission Lines of Water Vapor Toward the Supergiant Star VY Canis Majoris

NASA Technical Reports Server (NTRS)

Neufeld, David A.; Feuchtgruber, Helmut; Harwit, Martin; Melnick, Gary J.

1999-01-01

We report the detection of numerous far-infrared emission lines of water vapor toward the supergiant star VY Canis Majoris. A 29.5-45 micron grating scan of VY CMa, obtained using the Short-Wavelength Spectrometer (SWS) of the Infrared Space Observatory at a spectral resolving power lambda/delat.lambda of approximately 2000, reveals at least 41 spectral features due to water vapor that together radiate a total luminosity of approximately 25 solar luminosity . In addition to pure rotational transitions within the ground vibrational state, these features include rotational transitions within the (010) excited vibrational state. The spectrum also shows the (sup 2)product(sub 1/2) (J = 5/2) left arrow (sup 2)product(sub 3/2) (J = 3/2) OH feature near 34.6 micron in absorption. Additional SWS observations of VY CMa were carried out in the instrument's Fabry-Perot mode for three water transitions: the 7(sub 25)-6(sub 16) line at 29.8367 micron, the 4(sub 41)-3(sub 12) line at 31.7721 micron, and the 4(sub 32)-3(sub 03) line at 40.6909 micron. The higher spectral resolving power lambda/delta.lambda of approximately 30,000 thereby obtained permits the line profiles to be resolved spectrally for the first time and reveals the "P Cygni" profiles that are characteristic of emission from an outflowing envelope.

Large strain detection of SRM composite shell based on fiber Bragg grating sensor

NASA Astrophysics Data System (ADS)

Zhang, Lei; Chang, Xinlong; Zhang, Youhong; Yang, Fan

2017-12-01

There may be more than 2% strain of carbon fiber composite material on solid rocket motor (SRM) in some extreme cases. A surface-bonded silica fiber Bragg grating (FBG) strain sensor coated by polymer is designed to detect the large strain of composite material. The strain transfer relation of the FBG large strain sensor is deduced, and the strain transfer mechanism is verified by finite element simulation. To calibrate the sensors, the tensile test is done by using the carbon fiber composite plate specimen attached to the designed strain sensor. The results show that the designed sensor can detect the strain more than 3%, the strain sensitivity is 0.0762 pm/μɛ, the resolution is 13.13μɛ, and the fitting degree of the wavelength-strain curve fitting function is 0.9988. The accuracy and linearity of the sensor can meet the engineering requirements.

pH-sensing properties of cascaded long- and short-period fiber grating with poly acrylic acid/poly allylamine hydrochloride thin-film overlays

NASA Astrophysics Data System (ADS)

Yang, Ying

2014-11-01

Based on coupled-mode theory and transfer matrix method, the mode coupling mechanism and the reflection spectral properties of coated cascaded long- and short-period gratings (CLBG) are discussed. The effects of the thin-film parameters (film refractive index and film thickness) on the reflection spectra of the coated CLBG are simulated. By using electrostatic self-assembly method, poly acrylic acid (PAA) and poly allylamine hydrochloride (PAH) multilayer molecular pH-sensitive thin-films are assembled on the surface of the partial corroded CLBG. When the CLBG coated with PAA/PAH films are used to sense pH values, the resonant wavelengths of the CLBG have almost no shift, whereas the resonance peak reflectivities change with pH values. In addition, the sensitivities of the resonance peak reflectivities responding to pH values are improved by an order of magnitude.

MEMS tunable grating micro-spectrometer

NASA Astrophysics Data System (ADS)

Tormen, Maurizio; Lockhart, R.; Niedermann, P.; Overstolz, T.; Hoogerwerf, A.; Mayor, J.-M.; Pierer, J.; Bosshard, C.; Ischer, R.; Voirin, G.; Stanley, R. P.

2017-11-01

The interest in MEMS based Micro-Spectrometers is increasing due to their potential in terms of flexibility as well as cost, low mass, small volume and power savings. This interest, especially in the Near-Infrared and Mid- Infrared, ranges from planetary exploration missions to astronomy, e.g. the search for extra solar planets, as well as to many other terrestrial fields of application such as, industrial quality and surface control, chemical analysis of soil and water, detection of chemical pollutants, exhausted gas analysis, food quality control, process control in pharmaceuticals, to name a few. A compact MEMS-based Spectrometer for Near- Infrared and Mid-InfraRed operation have been conceived, designed and demonstrated. The design based on tunable MEMS blazed grating, developed in the past at CSEM [1], achieves state of the art results in terms of spectral resolution, operational wavelength range, light throughput, overall dimensions, and power consumption.

Controlling material birefringence in sapphire via self-assembled, sub-wavelength defects

NASA Astrophysics Data System (ADS)

Singh, Astha; Sharma, Geeta; Ranjan, Neeraj; Mittholiya, Kshitij; Bhatnagar, Anuj; Singh, B. P.; Mathur, Deepak; Vasa, Parinda

2018-02-01

Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. Generally, this is an intrinsic optical property of a material and cannot be altered. Here, we report a novel technique—direct laser writing—that enables us to control the natural, material birefringence of sapphire over a broad range of wavelengths. The broadband form birefringence originating from self-assembled, periodic array of sub-wavelength (˜ 50-200 nm) defects created by laser writing, can enhance, suppress or maintain the material birefringence of sapphire without affecting its transparency range in visible or its surface quality.

High Pressure Sensing and Dynamics Using High Speed Fiber Bragg Grating Interrogation Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodriguez, G.; Sandberg, R. L.; Lalone, B. M.

2014-06-01

Fiber Bragg gratings (FBGs) are developing into useful sensing tools for measuring high pressure dynamics in extreme environments under shock loading conditions. Approaches using traditional diode array coupled FBG interrogation systems are often limited to readout speeds in the sub-MHz range. For shock wave physics, required detection speeds approaching 100 MHz are desired. We explore the use of two types of FBG sensing systems that are aimed at applying this technology as embedded high pressure probes for transient shock events. Both approaches measure time resolved spectral shifts in the return light from short (few mm long) uniform FBGs at 1550more » nm. In the first approach, we use a fiber coupled spectrometer to demultiplex spectral channels into an array (up to 12) of single element InGaAs photoreceivers. By monitoring the detectors during a shock impact event with high speed recording, we are able to track the pressure induced spectral shifting in FBG down to a time resolution of 20 ns. In the second approach, developed at the Special Technologies Lab, a coherent mode-locked fiber laser is used to illuminate the FBG sensor. After the sensor, wavelength-to-time mapping is accomplished with a chromatic dispersive element, and entire spectra are sampled using a single detector at the modelocked laser repetition rate of 50 MHz. By sampling with a 12 GHz InGaAs detector, direct wavelength mapping in time is recorded, and the pressure induced FBG spectral shift is sampled at 50 MHz. Here, the sensing systems are used to monitor the spectral shifts of FBGs that are immersed into liquid water and shock compressed using explosives. In this configuration, the gratings survive to pressures approaching 50 kbar. We describe both approaches and present the measured spectral shifts from the shock experiments.« less

Polarizing beam splitter of deep-etched triangular-groove fused-silica gratings.

PubMed

Zheng, Jiangjun; Zhou, Changhe; Feng, Jijun; Wang, Bo

2008-07-15

We investigated the use of a deep-etched fused-silica grating with triangular-shaped grooves as a highly efficient polarizing beam splitter (PBS). A triangular-groove PBS grating is designed at a wavelength of 1550 nm to be used in optical communication. When it is illuminated in Littrow mounting, the transmitted TE- and TM-polarized waves are mainly diffracted in the minus-first and zeroth orders, respectively. The design condition is based on the average differences of the grating mode indices, which is verified by using rigorous coupled-wave analysis. The designed PBS grating is highly efficient over the C+L band range for both TE and TM polarizations (>97.68%). It is shown that such a triangular-groove PBS grating can exhibit a higher diffraction efficiency, a larger extinction ratio, and less reflection loss than the binary-phase fused-silica PBS grating.

In situ high temperature microwave microscope for nondestructive detection of surface and sub-surface defects.

PubMed

Wang, Peiyu; Li, Zhencheng; Pei, Yongmao

2018-04-16

An in situ high temperature microwave microscope was built for detecting surface and sub-subsurface structures and defects. This system was heated with a self-designed quartz lamp radiation module, which is capable of heating to 800°C. A line scanning of a metal grating showed a super resolution of 0.5 mm (λ/600) at 1 GHz. In situ scanning detections of surface hole defects on an aluminium plate and a glass fiber reinforced plastic (GFRP) plate were conducted at different high temperatures. A post processing algorithm was proposed to remove the background noises induced by high temperatures and the 3.0 mm-spaced hole defects were clearly resolved. Besides, hexagonal honeycomb lattices were in situ detected and clearly resolved under a 1.0 mm-thick face panel at 20°C and 50°C, respectively. The core wall positions and bonding width were accurately detected and evaluated. In summary, this in situ microwave microscope is feasible and effective in sub-surface detection and super resolution imaging at different high temperatures.

Two-color temporal focusing multiphoton excitation imaging with tunable-wavelength excitation

NASA Astrophysics Data System (ADS)

Lien, Chi-Hsiang; Abrigo, Gerald; Chen, Pei-Hsuan; Chien, Fan-Ching

2017-02-01

Wavelength tunable temporal focusing multiphoton excitation microscopy (TFMPEM) is conducted to visualize optical sectioning images of multiple fluorophore-labeled specimens through the optimal two-photon excitation (TPE) of each type of fluorophore. The tunable range of excitation wavelength was determined by the groove density of the grating, the diffraction angle, the focal length of lenses, and the shifting distance of the first lens in the beam expander. Based on a consideration of the trade-off between the tunable-wavelength range and axial resolution of temporal focusing multiphoton excitation imaging, the presented system demonstrated a tunable-wavelength range from 770 to 920 nm using a diffraction grating with groove density of 830 lines/mm. TPE fluorescence imaging examination of a fluorescent thin film indicated that the width of the axial confined excitation was 3.0±0.7 μm and the shifting distance of the temporal focal plane was less than 0.95 μm within the presented wavelength tunable range. Fast different wavelength excitation and three-dimensionally rendered imaging of Hela cell mitochondria and cytoskeletons and mouse muscle fibers were demonstrated. Significantly, the proposed system can improve the quality of two-color TFMPEM images through different excitation wavelengths to obtain higher-quality fluorescent signals in multiple-fluorophore measurements.

The effect of aberrated recording beams on reflecting Bragg gratings

NASA Astrophysics Data System (ADS)

SeGall, Marc; Ott, Daniel; Divliansky, Ivan; Glebov, Leonid B.

2013-03-01

The effect of aberrations present in the recording beams of a holographic setup is discussed regarding the period and spectral response of a reflecting volume Bragg grating. Imperfect recording beams result in spatially varying resonant wavelengths and the side lobes of the spectrum are washed out. Asymmetrical spectra, spectral broadening, and a reduction in peak diffraction efficiency may also be present, though these effects are less significant for gratings with wider spectral widths. Reflecting Bragg gratings (RBGs) are used as elements in a variety of applications including spectral beam combining1,2, mode locking3,4, longitudinal and transverse mode selection in lasers5,6, and sensing7,8. For applications requiring narrow spectral selectivity9, or large apertures10, these gratings must have a uniform period throughout the length of the recording medium, which may be on the order of millimeters. However, when using typical recording techniques such as two-beam interference for large aperture gratings and phase-mask recording of fiber gratings, aberrations from the optical elements in the system result in an imperfect grating structure11-13. In this paper we consider the effects of aberrations on large aperture gratings recorded in thick media using the two-beam interference technique. Previous works in analyzing the effects of aberrations have considered the effects of aberrations in a single recording plane where the beams perfectly overlap. Such an approach is valid for thin media (on the order of tens of microns), but for thick recording media (on the order of several millimeters) there will be a significant shift in the positions of the beams relative to each other as they traverse the recording medium. Therefore, the fringe pattern produced will not be constant throughout the grating if one or both beams have a non-uniform wavefront. Such non-uniform gratings may have a wider spectral width, a shifted resonant wavelength, or other problems. It is imperative therefore to know what the effects of aberrations will have on the properties of the RBGs. Thus, in this paper we consider the imperfect fringe pattern caused by the recording beams and its effect on the diffraction efficiency and spectral profile of the recorded reflecting volume Bragg gratings.

Continuous-Wave Single-Frequency Operation of Fabry-Perot Laser Diodes by Self-Injection Phase Locking Using Feedback from a Fiber Bragg Grating

NASA Technical Reports Server (NTRS)

Duerksen, Gary L.; Krainak, Michael A.

1998-01-01

Single-frequency operation of uncoated Fabry-Perot laser diodes is demonstrated by phase- locking the laser oscillations through self-injection seeding with feedback from a fiber Bragg grating. By precisely tuning the laser temperature so that an axial-mode coincides with the short-wavelength band edge of the grating, the phase of the feedback is made conjugate to that of the axial mode, locking the phase of the laser oscillations to that mode.

Error Measurements in an Acousto-Optic Tunable Filter Fiber Bragg Grating Sensor System

DTIC Science & Technology

1994-05-01

for an ideal AOTF, at 833 and 838 nm using a TeO2 crystal ............................ 33 Figure 3.12. Frequency characteristics of Equation (3.43...multiple channels in an AOTF requires the presence of multiple RF frequencies to establish the complex grating. Since the crystal used in the AOTF ( TeO2 ) is...in germano- silicate glass . This index modulation, Bragg grating, acts as an optical band rejection filter for those wavelengths that meet the Bragg

Fine-filter method for Raman lidar based on wavelength division multiplexing and fiber Bragg grating.

PubMed

Wang, Jun; Zheng, Jiao; Lu, Hong; Yan, Qing; Wang, Li; Liu, Jingjing; Hua, Dengxin

2017-11-01

Atmospheric temperature is one of the important parameters for the description of the atmospheric state. Most of the detection approaches to atmospheric temperature monitoring are based on rotational Raman scattering for better understanding atmospheric dynamics, thermodynamics, atmospheric transmission, and radiation. In this paper, we present a fine-filter method based on wavelength division multiplexing, incorporating a fiber Bragg grating in the visible spectrum for the rotational Raman scattering spectrum. To achieve high-precision remote sensing, the strong background noise is filtered out by using the secondary cascaded light paths. Detection intensity and the signal-to-noise ratio are improved by increasing the utilization rate of return signal form atmosphere. Passive temperature compensation is employed to reduce the temperature sensitivity of fiber Bragg grating. In addition, the proposed method provides a feasible solution for the filter system with the merits of miniaturization, high anti-interference, and high stability in the space-based platform.

On-sky tests of a polarization grating for visible astronomy

NASA Astrophysics Data System (ADS)

Millar-Blanchaer, Maxwell A.; Moon, Dae-Sik; Graham, James R.; Williams, Michael

2016-08-01

Polarization gratings (PGs) are a type of diffraction grating that take advantage of birefringent liquid crystal polymers to simultaneously act as a polarizing beam splitter and as a spectral dispersive element. Furthermore, PGs are capable of providing high diffraction efficiency (>90%) over a very broad wavelength range. These properties make PGs ideal for spectropolarimetry and/or high throughput, broad wavelength observations for a range of astronomical objects. Here we report on the design and on-sky testing of a prototype spectropolarimeter instrument that employs a PG optimized for operation from 500 nm to 900 nm. The prototype was mounted on a 16-inch telescope at the University of Toronto, where we carried out observations of the polarized twilight sky, a polarized standard star and two spectroscopic standard stars. Using these observations we demonstrate the PG's ability to measure linear polarization fraction and position angle, as well as recover spectra from astronomical objects.

Low cost and high performance GPON, GEPON and RFoG optical network pentaplexer module design using diffractive grating approach

NASA Astrophysics Data System (ADS)

Chen, I.-Ju; Chi, Chang-Chia; Tarn, Chen-Wen

2016-01-01

A new architecture of a pentaplexer transceiver module which can be used in GPON/GEPON and RFoG triple play optical networks with supporting of the multiple optical wavelengths of 1310 nm, 1490 nm, 1550 nm, 1610 nm, and 1650 nm, is proposed. By using diffractive grating elements combing with market readily available GRIN (Gradient-Index) lens, grating, mirrors, beamsplitter, LDs (Laser Diodes), and PDs (Photodetectors), the proposed design have the advantages of low cost, high efficiency/performance, easy design and manufacturing, over the contemporary triplex transceivers which are made of multilayer filters or waveguides that increase the complexity of manufacturing and reduce the performance efficiency. With the proposed design, a pentaplexer system can accommodate GPON/GEPON, RFoG, and monitoring integration services, total five optical wavelength channels into a hybrid-integrated TO-CAN package platform with sufficient efficiency.

Distributed feedback fiber laser based on a fiber Bragg grating inscribed using the femtosecond point-by-point technique

NASA Astrophysics Data System (ADS)

Skvortsov, M. I.; Wolf, A. A.; Dostovalov, A. V.; Vlasov, A. A.; Akulov, V. A.; Babin, S. A.

2018-03-01

A distributed feedback (DFB) fiber laser based on a 32-mm long pi-phase-shifted fiber Bragg grating inscribed using the femtosecond point-by-point technique in a single-mode erbium-doped optical fiber (CorActive EDF-L 1500) is demonstrated. The lasing power of the DFB laser reaches 0.7 mW at a wavelength of 1550 nm when pumped with a laser diode at a wavelength of 976 nm and power of 525 mW. The width of the lasing spectrum is 17 kHz. It is shown that the pi-phase-shifted fiber Bragg grating fs-inscribed in a non-PM fiber provides the selection of the single polarization mode of the DFB laser. DFB laser formation in a highly doped non-photosensitive optical fiber (CoreActive SCF-ER60-8/125-12) is also demonstrated.

Studies of snowpack properties by passive microwave radiometry

NASA Technical Reports Server (NTRS)

Chang, A. T. C.; Hall, D. K.; Foster, J. L.; Rango, A.; Schmugge, T. J.

1978-01-01

Research involving the microwave characteristics of snow was undertaken in order to expand the information content currently available from remote sensing, namely the measurement of snowcovered area. Microwave radiation emitted from beneath the snow surface can be sensed and thus permits information on internal snowpack properties to be inferred. The intensity of radiation received is a function of the average temperature and emissivity of the snow layers and is commonly referred to as the brightness temperature (T sub b). The T sub b varies with snow grain and crystal sizes, liquid water content and snowpack temperature. The T sub b of the 0.8 cm wavelength channel was found to decrease moreso with increasing snow depth than the 1.4 cm channel. More scattering of the shorter wavelength radiation occurs thus resulting in a lower T sub b for shorter wavelengths in a dry snowpack. The longer 21.0 cm wavelength was used to assess the condition of the underlying ground. Ultimately it may be possible to estimate snow volume over large areas using calibrated brightness temperatures and consequently improve snowmelt runoff predictions.

[The Research on Optic Fiber FBG Corrosion Sensor Based on the Analysis of the Spectral Characteristics].

PubMed

Zhang, Jun; Zeng, Jie; Wang, Bo; Wang, Wen-juan; Liang, Da-kai; Liu, Xiao-ying

2016-03-01

Aiming at meeting the need of aluminum corrosion monitoring in aerospace field, a pre-load type fiber grating corrosion sensor based on an aluminum thin tube structure is proposed. The corrosion sensor of aluminum alloy structure in-service monitoring mechanism is studied, a theoretical model about the relation of FBG reflection spectral characteristics and aluminum thickness variation is also obtained. Optical fiber grating corrosion monitoring test system based on the capillary structure of aluminum alloy is constructed by acid-base environment. The problem of cross sensitivity of temperature and strain is solved by configuring an optical fiber grating which is not affected by strain and only sensitive to temperature inside the aluminum alloy tube. The results shows that he aluminum tube packaging design not only can sense the effects of corrosion on the mechanical properties, but also can interference shielding effect of corrosion on the tube optical fiber sensing device. With the deepening of the metal tube corrosion and aluminum alloy tube thickness gradually thinning, fiber grating reflective spectrum gradually shift to the short wavelength and the wall thickness and the grating center wavelength offset has a good monotonic relation. These characteristics can provide useful help to further research corrosion online monitoring based on optic fiber sensor.