Fabrication of SiC membrane HCG blue reflector using nanoimprint lithography

NASA Astrophysics Data System (ADS)

Lai, Ying-Yu; Matsutani, Akihiro; Lu, Tien-Chang; Wang, Shing-Chung; Koyama, Fumio

2015-02-01

We designed and fabricated a suspended SiC-based membrane high contrast grating (HCG) reflectors. The rigorous coupled-wave analysis (RCWA) was employed to verify the structural parameters including grating periods, grating height, filling factors and air-gap height. From the optimized simulation results, the designed SiC-based membrane HCG has a wide reflection stopband (reflectivity (R) <90%) of 135 nm for the TE polarization, which centered at 480 nm. The suspended SiC-based membrane HCG reflectors were fabricated by nanoimprint lithography and two-step etching technique. The corresponding reflectivity was measured by using a micro-reflectivity spectrometer. The experimental results show a high reflectivity (R<90%), which is in good agreement with simulation results. This achievement should have an impact on numerous III-N based photonic devices operating in the blue wavelength or even ultraviolet region.

Widely tunable mid-infrared quantum cascade lasers using sampled grating reflectors.

PubMed

Mansuripur, Tobias S; Menzel, Stefan; Blanchard, Romain; Diehl, Laurent; Pflügl, Christian; Huang, Yong; Ryou, Jae-Hyun; Dupuis, Russell D; Loncar, Marko; Capasso, Federico

2012-10-08

We demonstrate a three-section, electrically pulsed quantum cascade laser which consists of a Fabry-Pérot section placed between two sampled grating distributed Bragg reflectors. The device is current-tuned between ten single modes spanning a range of 0.46 μm (63 cm(-1)), from 8.32 to 8.78 μm. The peak optical output power exceeds 280 mW for nine of the modes.

Grating tuned unstable resonator laser cavity

DOEpatents

Johnson, Larry C.

1982-01-01

An unstable resonator to be used in high power, narrow line CO.sub.2 pump lasers comprises an array of four reflectors in a ring configuration wherein spherical and planar wavefronts are separated from each other along separate optical paths and only the planar wavefronts are impinged on a plane grating for line tuning. The reflector array comprises a concave mirror for reflecting incident spherical waves as plane waves along an output axis to form an output beam. A plane grating on the output axis is oriented to reflect a portion of the output beam off axis onto a planar relay mirror spaced apart from the output axis in proximity to the concave mirror. The relay mirror reflects plane waves from the grating to impinge on a convex expanding mirror spaced apart from the output axis in proximity to the grating. The expanding mirror reflects the incident planar waves as spherical waves to illuminate the concave mirror. Tuning is provided by rotating the plane grating about an axis normal to the output axis.

Enhanced light absorption of silicon solar cells with dielectric nanostructured back reflector

NASA Astrophysics Data System (ADS)

Ren, Rui; Zhong, Zheng

2018-06-01

This paper investigates the light absorption property of nanostructured dielectric reflectors in silicon thin film solar cells using numerical simulation. Flat thin film solar cell with ZnO nanostructured back reflector can produce comparable photocurrent to the control model with Ag nanostructured back reflector. Furthermore, when it is integrated with nano-pillar surface decoration, a photocurrent density of 29.5 mA/cm2 can be achieved, demonstrating a photocurrent enhancement of 5% as compared to the model with Ag nanostructured back reflector.

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.

Concentric circular focusing reflector realized using high index contrast gratings

NASA Astrophysics Data System (ADS)

Fang, Wenjing; Huang, Yongqing; Fei, Jiarui; Duan, Xiaofeng; Liu, Kai; Ren, Xiaomin

2017-11-01

A non-periodic concentric circular high index contrast grating (CC-HCG) focusing reflector on 500 nm silicon-on-insulator (SOI) platform is fabricated and experimentally demonstrated. The proposed mirror is realized with phase modulation of wave front in a high reflectivity region. The circular structure based HCG focusing reflector has a spot of high concentration at the 10.87 mm with normal incidence for radially polarization, along with the center wavelength set at 1550 nm. The FWHM spot size of the focusing beam decreases to 260 μm, and the intensity increases to 1.26 compared with the incident beam. The focusing efficiency of about 80% is observed at 1550 nm in the experimental measurement.

Guided-mode resonance nanophotonics in materially sparse architectures

NASA Astrophysics Data System (ADS)

Magnusson, Robert; Niraula, Manoj; Yoon, Jae W.; Ko, Yeong H.; Lee, Kyu J.

2016-03-01

The guided-mode resonance (GMR) concept refers to lateral quasi-guided waveguide modes induced in periodic layers. Whereas these effects have been known for a long time, new attributes and innovations continue to appear. Here, we review some recent progress in this field with emphasis on sparse, or minimal, device embodiments. We discuss properties of wideband resonant reflectors designed with gratings in which the grating ridges are matched to an identical material to eliminate local reflections and phase changes. This critical interface therefore possesses zero refractive-index contrast; hence we call them "zero-contrast gratings." Applying this architecture, we present single-layer, wideband reflectors that are robust under experimentally realistic parametric variations. We introduce a new class of reflectors and polarizers fashioned with dielectric nanowire grids that are mostly empty space. Computed results predict high reflection and attendant polarization extinction for these sparse lattices. Experimental verification with Si nanowire grids yields ~200-nm-wide band of high reflection for one polarization state and free transmission of the orthogonal state. Finally, we present bandpass filters using all-dielectric resonant gratings. We design, fabricate, and test nanostructured single layer filters exhibiting high efficiency and sub-nanometer-wide passbands surrounded by 100-nm-wide stopbands.

Non-periodic high-index contrast gratings reflector with large-angle beam forming ability

NASA Astrophysics Data System (ADS)

Fang, Wenjing; Huang, Yongqing; Duan, Xiaofeng; Fei, Jiarui; Ren, Xiaomin; Mao, Min

2016-05-01

A non-periodic high-index contrast gratings (HCGs) reflector on SOI wafer with large-angle beam forming ability has been proposed and fabricated. The proposed reflector was designed using rigorous coupled-wave analysis (RCWA) and finite-element-method (FEM). A deflection angle of 17.35° and high reflectivity of 92.31% are achieved under transverse magnetic (TM) polarized light in numerical simulation. Experimental results show that the reflected power peaked at 17.2° under a 1550 nm incident light, which is in good accordance with the simulation results. Moreover, the reflected power spectrum was also measured. Under different incident wavelengths around 1550 nm, reflected powers all peaked at 17.2°. The results show that the proposed non-periodic HCGs reflector has a good reflection and beam forming ability in a wavelength range as wide as 40 nm around 1550 nm.

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

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.

Electrophoretic deposited TiO 2 pigment-based back reflectors for thin film solar cells

DOE PAGES

Bills, Braden; Morris, Nathan; Dubey, Mukul; ...

2015-01-16

Highly reflective coatings with strong light scattering effect have many applications in optical components and optoelectronic devices. This paper reports titanium dioxide (TiO 2) pigment-based reflectors that have 2.5 times higher broadband diffuse reflection than commercially produced aluminum or silver based reflectors and result in efficiency enhancements of a single-junction amorphous Si solar cell. Electrophoretic deposition is used to produce pigment-based back reflectors with high pigment density, controllable film thickness and site-specific deposition. Electrical conductivity of the pigment-based back reflectors is improved by creating electrical vias throughout the pigment-based back reflector by making holes using an electrical discharge / dielectricmore » breakdown approach followed by a second electrophoretic deposition of conductive nanoparticles into the holes. While previous studies have demonstrated the use of pigment-based back reflectors, for example white paint, on glass superstrate configured thin film Si solar cells, this work presents a scheme for producing pigment-based reflectors on complex shape and flexible substrates. Finally, mechanical durability and scalability are demonstrated on a continuous electrophoretic deposition roll-to-roll system which has flexible metal substrate capability of 4 inch wide and 300 feet long.« less

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.

Inline microring reflector for photonic applications

NASA Astrophysics Data System (ADS)

Kang, Young Mo

The microring is a compact resonator that is used as a versatile building block in photonic circuits ranging from filters, modulators, logic gates, sensors, switches, multiplexers, and laser cavities. The Bragg grating is a periodic structure that allows the selection of a narrow bandwidth of spectrum for stable lasing operation. In this dissertation, we study analysis and simulations of a compact microring based reflector assembled by forming a Bragg grating into a loop. With the appropriate design, the microring resonance can precisely align with the reflection peak of the grating while all other peaks are suppressed by reflection nulls of the grating. The field buildup at the resonance effectively amplifies small reflection of the grating, thereby producing significant overall reflection from the ring, and it is possible to achieve a stable narrow linewidth compact laser by forming a single mode laser cavity. The device operation principle is studied from two distinct perspectives; the first looks at coupling of two contra-directional traveling waves within the ring whereas the second aspect investigates relative excitation of the two competing microring resonant modes. In the former method, we relate the steady state amplitudes of the two traveling waves to the reflection spectrum of the grating and solve for the reflection and transmission response for each wavelength of interest. In the latter approach, we expand the field in terms of the resonant modes of the ring cavity and derive transfer functions for reflection and transmission from the nearby mode frequencies. The angular periodicity of the reflective microring geometry allows us to effectively simulate the resonant modes from a computational domain of a single period grating when the continuity boundary condition is applied. We successfully predict the reflection and transmission response of a Si3N 4/SiO2 microring reflector using this method---otherwise too large to carry out full-wave simulation---and show that the prediction agrees very well with the measurement result.

Silicon nitride back-end optics for biosensor applications

NASA Astrophysics Data System (ADS)

Romero-García, Sebastian; Merget, Florian; Zhong, Frank C.; Finkelstein, Hod; Witzens, Jeremy

2013-05-01

Silicon nitride (SiN) is a promising candidate material for becoming a standard high-performance solution for integrated biophotonics applications in the visible spectrum. As a key feature, its compatibility with the complementary-oxidemetal- semiconductor (CMOS) technology permits cost reduction at large manufacturing volumes that is particularly advantageous for manufacturing consumables. In this work, we show that the back-end deposition of a thin SiN film enables the large light-cladding interaction desirable for biosensing applications while the refractive index contrast of the technology (Δn ≍ 0.5) also enables a considerable level of integration with reduced waveguide bend radii. Design and experimental validation also show that several advantages are derived from the moderate SiN/SiO2 refractive index contrast, such as lower scattering losses in interconnection waveguides and relaxed tolerances to fabrication imperfections as compared to higher refractive index contrast material systems. As a drawback, a moderate refractive index contrast also makes the implementation of compact grating couplers more challenging, due to the fact that only a relatively weak scattering strength can be achieved. Thereby, the beam diffracted by the grating tends to be rather large and consequently exhibit stringent angular alignment tolerances. Here, we experimentally demonstrate how a proper design of the bottom and top cladding oxide thicknesses allows reduction of the full-width at half maximum (FWHM) and alleviates this problem. Additionally, the inclusion of a CMOS-compatible AlCu/TiN bottom reflector further decreases the FWHM and increases the coupling efficiency. Finally, we show that focusing grating designs greatly reduce the device footprint without penalizing the device metrics.

Solar cell comprising a plasmonic back reflector and method therefor

DOEpatents

Ding, I-Kang; Zhu, Jia; Cui, Yi; McGehee, Michael David

2014-11-25

A method for forming a solar cell having a plasmonic back reflector is disclosed. The method includes the formation of a nanoimprinted surface on which a metal electrode is conformally disposed. The surface structure of the nanoimprinted surface gives rise to a two-dimensional pattern of nanometer-scale features in the metal electrode enabling these features to collectively form the plasmonic back reflector.

Application of a broadly tunable SG-DBR QCL for multi-species trace gas spectroscopy.

PubMed

Diba, Abdou S; Xie, Feng; Gross, Barry; Hughes, Lawrence C; Zah, Chung-en; Moshary, Fred

2015-10-19

Feasibility of using a mid-Infrared tunable sampled-grating distributed Bragg reflectors quantum cascade laser for high resolution multicomponent trace gas spectroscopy is demonstrated. By controlling the driving currents to the front and back sections of the laser, we were able to tune a pulsed 4.55 µm laser over a frequency range a of 30 cm(-1) with high resolution, accuracy and repeatability. The laser was applied to absorption spectroscopy of ambient and reduced pressure (150 Torr) air in a 205 meters multi-pass Herriott cell, and by using standard LSQ fitting to a spectral database of these trace gases (HITRAN), the concentrations of nitrous oxide, carbon monoxide, and water vapor were retrieved.

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.

High-temperature-resistant distributed Bragg reflector fiber laser written in Er/Yb co-doped fiber.

PubMed

Guan, Bai-Ou; Zhang, Yang; Wang, Hong-Jun; Chen, Da; Tam, Hwa-Yaw

2008-03-03

We present a high-temperature-resistant distributed Bragg reflector fiber laser photowritten in Er/Yb codoped phosphosilicate fiber that is capable of long-term operation at 500 degrees C. Highly saturated Bragg gratings are directly inscribed into the Er/Yb fiber without hydrogen loading by using a 193 nm excimer laser and phase mask method. After annealing at elevated temperature, the remained gratings are strong enough for laser oscillation. The laser operates in robust single mode with output power more than 1 dBm and signal-to-noise ratio better than 70 dB over the entire temperature range from room temperature to 500 degrees C.

Optimization of imprintable nanostructured a-Si solar cells: FDTD study.

PubMed

Fisker, Christian; Pedersen, Thomas Garm

2013-03-11

We present a finite-difference time-domain (FDTD) study of an amorphous silicon (a-Si) thin film solar cell, with nano scale patterns on the substrate surface. The patterns, based on the geometry of anisotropically etched silicon gratings, are optimized with respect to the period and anti-reflection (AR) coating thickness for maximal absorption in the range of the solar spectrum. The structure is shown to increase the cell efficiency by 10.2% compared to a similar flat solar cell with an optimized AR coating thickness. An increased back reflection can be obtained with a 50 nm zinc oxide layer on the back reflector, which gives an additional efficiency increase, leading to a total of 14.9%. In addition, the patterned cells are shown to be up to 3.8% more efficient than an optimized textured reference cell based on the Asahi U-type glass surface. The effects of variations of the optimized solar cell structure due to the manufacturing process are investigated, and shown to be negligible for variations below ±10%.

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.

Optical Phased Array Using Guided Resonance with Backside Reflectors

NASA Technical Reports Server (NTRS)

Horie, Yu (Inventor); Arbabi, Amir (Inventor); Faraon, Andrei (Inventor)

2016-01-01

Methods and systems for controlling the phase of electromagnetic waves are disclosed. A device can consist of a guided resonance grating layer, a spacer, and a reflector. A plurality of devices, arranged in a grid pattern, can control the phase of reflected electromagnetic phase, through refractive index control. Carrier injection, temperature control, and optical beams can be applied to control the refractive index.

Optical phased array using guided resonance with backside reflectors

DOEpatents

Horie, Yu; Arbabi, Amir; Faraon, Andrei

2016-11-01

Methods and systems for controlling the phase of electromagnetic waves are disclosed. A device can consist of a guided resonance grating layer, a spacer, and a reflector. A plurality of devices, arranged in a grid pattern, can control the phase of reflected electromagnetic phase, through refractive index control. Carrier injection, temperature control, and optical beams can be applied to control the refractive index.

Optical phased array using guided resonance with backside reflectors

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

Horie, Yu; Arbabi, Amir; Faraon, Andrei

2018-03-13

Methods and systems for controlling the phase of electromagnetic waves are disclosed. A device can consist of a guided resonance grating layer, a spacer, and a reflector. A plurality of devices, arranged in a grid pattern, can control the phase of reflected electromagnetic phase, through refractive index control. Carrier injection, temperature control, and optical beams can be applied to control the refractive index.

Optical Phased Array Using Guided Resonance with Backside Reflectors

NASA Technical Reports Server (NTRS)

Horie, Yu (Inventor); Arbabi, Amir (Inventor); Faraon, Andrei (Inventor)

2018-01-01

Methods and systems for controlling the phase of electromagnetic waves are disclosed. A device can consist of a guided resonance grating layer, a spacer, and a reflector. A plurality of devices, arranged in a grid pattern, can control the phase of reflected electromagnetic phase, through refractive index control. Carrier injection, temperature control, and optical beams can be applied to control the refractive index.

Terahertz bandwidth photonic Hilbert transformers based on synthesized planar Bragg grating fabrication.

PubMed

Sima, Chaotan; Gates, J C; Holmes, C; Mennea, P L; Zervas, M N; Smith, P G R

2013-09-01

Terahertz bandwidth photonic Hilbert transformers are proposed and experimentally demonstrated. The integrated device is fabricated via a direct UV grating writing technique in a silica-on-silicon platform. The photonic Hilbert transformer operates at bandwidths of up to 2 THz (~16 nm) in the telecom band, a 10-fold greater bandwidth than any previously reported experimental approaches. Achieving this performance requires detailed knowledge of the system transfer function of the direct UV grating writing technique; this allows improved linearity and yields terahertz bandwidth Bragg gratings with improved spectral quality. By incorporating a flat-top reflector and Hilbert grating with a waveguide coupler, an ultrawideband all-optical single-sideband filter is demonstrated.

Flat Engineered Multichannel Reflectors

NASA Astrophysics Data System (ADS)

Asadchy, V. S.; Díaz-Rubio, A.; Tcvetkova, S. N.; Kwon, D.-H.; Elsakka, A.; Albooyeh, M.; Tretyakov, S. A.

2017-07-01

Recent advances in engineered gradient metasurfaces have enabled unprecedented opportunities for light manipulation using optically thin sheets, such as anomalous refraction, reflection, or focusing of an incident beam. Here, we introduce a concept of multichannel functional metasurfaces, which are able to control incoming and outgoing waves in a number of propagation directions simultaneously. In particular, we reveal a possibility to engineer multichannel reflectors. Under the assumption of reciprocity and energy conservation, we find that there exist three basic functionalities of such reflectors: specular, anomalous, and retroreflections. Multichannel response of a general flat reflector can be described by a combination of these functionalities. To demonstrate the potential of the introduced concept, we design and experimentally test three different multichannel reflectors: three- and five-channel retroreflectors and a three-channel power splitter. Furthermore, by extending the concept to reflectors supporting higher-order Floquet harmonics, we forecast the emergence of other multichannel flat devices, such as isolating mirrors, complex splitters, and multi-functional gratings.

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.

Fabrication and characterization of W/B4C lamellar multilayer grating and NbC/Si multilayer phase-shift reflector

NASA Astrophysics Data System (ADS)

Pradhan, P. C.; Bhartiya, S.; Singh, A.; Majhi, A.; Gome, A.; Dhawan, R.; Nayak, M.; Sahoo, P. K.; Rai, S. K.; Reddy, V. R.

2017-08-01

We present fabrication and structural analysis of two different multilayer grating structures. W/B4C based lamellar multilayer grating (LMG) was studied for high resolution monochomator application near soft x-ray region ( 1.5 keV). Whereas NbC/Si based multilayer phase-shift reflector (MPR) was studied for high reflection at normal incidence near Si L-edge ( 99 eV) and simultaneously to suppress the unwanted vacuum ultraviolet / infrared radiation. The grating patterns of different periods down to D = 10 micron were fabricated on Si substrates by using photolithography, and multilayers (MLs) of different periodicity (d = 10 to 2 nm) and number of layer pairs (15 to 100) were coated using sputtering techniques by optimizing the process parameters. The LMG and MPR samples are characterized by x-ray reflectivity (XRR) and atomic force microscopy (AFM) measurements. XRR results show successive higher order Bragg peaks that reveal a well-defined vertical periodic structure in LMG, MPR and ML structures. The lateral periodicity of the grating and depth of the rectangular groves were analyzed using AFM. The AFM results show good quality of lateral periodic structures in terms of groove profile. The effect of the process parameters on the microstructure (both on vertical and lateral patterns) of ML, LMG and MPR were analyzed.

Ultra-low loss fully-etched grating couplers for perfectly vertical coupling compatible with DUV lithography tools

NASA Astrophysics Data System (ADS)

Dabos, G.; Pleros, N.; Tsiokos, D.

2016-03-01

Hybrid integration of VCSELs onto silicon-on-insulator (SOI) substrates has emerged as an attractive approach for bridging the gap between cost-effective and energy-efficient directly modulated laser sources and silicon-based PICs by leveraging flip-chip (FC) bonding techniques and silicon grating couplers (GCs). In this context, silicon GCs, should comply with the process requirements imposed by the complimentary-metal-oxide-semiconductor manufacturing tools addressing in parallel the challenges originating from the perfectly vertical incidence. Firstly, fully etched GCs compatible with deep-ultraviolet lithography tools offering high coupling efficiencies are imperatively needed to maintain low fabrication cost. Secondly, GC's tolerance to VCSEL bonding misalignment errors is a prerequisite for practical deployment. Finally, a major challenge originating from the perfectly vertical coupling scheme is the minimization of the direct back-reflection to the VCSEL's outgoing facet which may destabilize its operation. Motivated from the above challenges, we used numerical simulation tools to design an ultra-low loss, bidirectional VCSEL-to-SOI optical coupling scheme for either TE or TM polarization, based on low-cost fully etched GCs with a Si-layer of 340 nm without employing bottom reflectors or optimizing the buried-oxide layer. Comprehensive 2D Finite-Difference-Time- Domain simulations have been performed. The reported GC layout remains fully compatible with the back-end-of-line (BEOL) stack associated with the 3D integration technology exploiting all the inter-metal-dielectric (IMD) layers of the CMOS fab. Simulation results predicted for the first time in fully etched structures a coupling efficiency of as low as -0.87 dB at 1548 nm and -1.47 dB at 1560 nm with a minimum direct back-reflection of -27.4 dB and -14.2 dB for TE and TM polarization, respectively.

Transversely coupled Fabry-Perot resonators with Bragg grating reflectors.

PubMed

Saber, Md Ghulam; Wang, Yun; El-Fiky, Eslam; Patel, David; Shahriar, Kh Arif; Alam, Md Samiul; Jacques, Maxime; Xing, Zhenping; Xu, Luhua; Abadía, Nicolás; Plant, David V

2018-01-01

We design and demonstrate Fabry-Perot resonators with transverse coupling using Bragg gratings as reflectors on the silicon-on-insulator (SOI) platform. The effects of tailoring the cavity length and the coupling coefficient of the directional coupler on the spectral characteristics of the device are studied. The fabricated resonators achieved an extinction ratio (ER) of 37.28 dB and a Q-factor of 3356 with an effective cavity length of 110 μm, and an ER of 8.69 dB and a Q-factor of 23642 with a 943 μm effective cavity length. The resonator structure presented here has the highest reported ER on SOI and provides additional degrees of freedom compared to an all-pass ring resonator to tune the spectral characteristics.

Diameter measurement of optical nanofiber based on high-order Bragg reflections using a ruled grating.

PubMed

Zhu, Ming; Wang, Yao-Ting; Sun, Yi-Zhi; Zhang, Lijian; Ding, Wei

2018-02-01

A convenient method using a commercially available ruled grating for precise and overall diameter measurement of optical nanofibers (ONFs) is presented. We form a composite Bragg reflector with a micronscale period by dissolving aluminum coating, slicing the grating along ruling lines, and mounting it on an ONF. The resonant wavelengths of high-order Bragg reflections possess fiber diameter dependence, enabling nondestructive measurement of the ONF diameter profile. This method provides an easy and economic diagnostic tool for wide varieties of ONF-based applications.

High resolution on-chip optical filter array based on double subwavelength grating reflectors

DOE PAGES

Horie, Yu; Arbabi, Amir; Han, Seunghoon; ...

2015-11-05

An optical filter array consisting of vertical narrow-band Fabry-Pèrot (FP) resonators formed by two highly reflective high contrast subwavelength grating mirrors is reported. The filters are designed to cover a wide range of operation wavelengths ( Δλ/λ=5%) just by changing the in-plane grating parameters while the device thickness is maintained constant. In conclusion, operation in the telecom band with transmission efficiencies greater than 40% and quality factors greater than 1,000 are measured experimentally for filters fabricated on the same substrate.

High resolution on-chip optical filter array based on double subwavelength grating reflectors

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

Horie, Yu; Arbabi, Amir; Han, Seunghoon

An optical filter array consisting of vertical narrow-band Fabry-Pèrot (FP) resonators formed by two highly reflective high contrast subwavelength grating mirrors is reported. The filters are designed to cover a wide range of operation wavelengths ( Δλ/λ=5%) just by changing the in-plane grating parameters while the device thickness is maintained constant. In conclusion, operation in the telecom band with transmission efficiencies greater than 40% and quality factors greater than 1,000 are measured experimentally for filters fabricated on the same substrate.

Novel back-reflector architecture with nanoparticle based buried light-scattering microstructures for improved solar cell performance

NASA Astrophysics Data System (ADS)

Desta, Derese; Ram, Sanjay K.; Rizzoli, Rita; Bellettato, Michele; Summonte, Caterina; Jeppesen, Bjarke R.; Jensen, Pia B.; Tsao, Yao-Chung; Wiggers, Hartmut; Pereira, Rui N.; Balling, Peter; Larsen, Arne Nylandsted

2016-06-01

A new back-reflector architecture for light-management in thin-film solar cells is proposed that includes a morphologically smooth top surface with light-scattering microstructures buried within. The microstructures are pyramid shaped, fabricated on a planar reflector using TiO2 nanoparticles and subsequently covered with a layer of Si nanoparticles to obtain a flattened top surface, thus enabling growth of good quality thin-film solar cells. The optical properties of this back-reflector show high broadband haze parameter and wide angular distribution of diffuse light-scattering. The n-i-p amorphous silicon thin-film solar cells grown on such a back-reflector show enhanced light absorption resulting in improved external quantum efficiency. The benefit of the light trapping in those solar cells is evidenced by the gains in short-circuit current density and efficiency up to 15.6% and 19.3% respectively, compared to the reference flat solar cells. This improvement in the current generation in the solar cells grown on the flat-topped (buried pyramid) back-reflector is observed even when the irradiation takes place at large oblique angles of incidence. Finite-difference-time-domain simulation results of optical absorption and ideal short-circuit current density values agree well with the experimental findings. The proposed approach uses a low cost and simple fabrication technique and allows effective light manipulation by utilizing the optical properties of micro-scale structures and nanoscale constituent particles.

Tunable ring laser with internal injection seeding and an optically-driven photonic crystal reflector.

PubMed

Zheng, Jie; Ge, Chun; Wagner, Clark J; Lu, Meng; Cunningham, Brian T; Hewitt, J Darby; Eden, J Gary

2012-06-18

Continuous tuning over a 1.6 THz region in the near-infrared (842.5-848.6 nm) has been achieved with a hybrid ring/external cavity laser having a single, optically-driven grating reflector and gain provided by an injection-seeded semiconductor amplifier. Driven at 532 nm and incorporating a photonic crystal with an azobenzene overlayer, the reflector has a peak reflectivity of ~80% and tunes at the rate of 0.024 nm per mW of incident green power. In a departure from conventional ring or external cavity lasers, the frequency selectivity for this system is provided by the passband of the tunable photonic crystal reflector and line narrowing in a high gain amplifier. Sub - 0.1 nm linewidths and amplifier extraction efficiencies above 97% are observed with the reflector tuned to 842.5 nm.

Piezocomposite Actuator Arrays for Correcting and Controlling Wavefront Error in Reflectors

NASA Technical Reports Server (NTRS)

Bradford, Samuel Case; Peterson, Lee D.; Ohara, Catherine M.; Shi, Fang; Agnes, Greg S.; Hoffman, Samuel M.; Wilkie, William Keats

2012-01-01

Three reflectors have been developed and tested to assess the performance of a distributed network of piezocomposite actuators for correcting thermal deformations and total wave-front error. The primary testbed article is an active composite reflector, composed of a spherically curved panel with a graphite face sheet and aluminum honeycomb core composite, and then augmented with a network of 90 distributed piezoelectric composite actuators. The piezoelectric actuator system may be used for correcting as-built residual shape errors, and for controlling low-order, thermally-induced quasi-static distortions of the panel. In this study, thermally-induced surface deformations of 1 to 5 microns were deliberately introduced onto the reflector, then measured using a speckle holography interferometer system. The reflector surface figure was subsequently corrected to a tolerance of 50 nm using the actuators embedded in the reflector's back face sheet. Two additional test articles were constructed: a borosilicate at window at 150 mm diameter with 18 actuators bonded to the back surface; and a direct metal laser sintered reflector with spherical curvature, 230 mm diameter, and 12 actuators bonded to the back surface. In the case of the glass reflector, absolute measurements were performed with an interferometer and the absolute surface was corrected. These test articles were evaluated to determine their absolute surface control capabilities, as well as to assess a multiphysics modeling effort developed under this program for the prediction of active reflector response. This paper will describe the design, construction, and testing of active reflector systems under thermal loads, and subsequent correction of surface shape via distributed peizeoelctric actuation.

Mercapto-based coupling agent for improved thermophotovoltaic device back surface reflector adhesion and reflectance

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

Wernsman, Bernard; Fiedor, Joseph N.; Irr, Lawrence G.

2016-10-04

A back surface reflector (BSR) is described. The BSR includes a reflecting layer, a substrate and an adhesion layer between the reflecting layer and the substrate. The adhesion layer includes 3-mercaptopropyl (trimethoxy) silane (a.k.a. Merc).

Monolithic subwavelength high refractive-index-contrast grating VCSELs

NASA Astrophysics Data System (ADS)

Gebski, Marcin; Dems, Maciej; Lott, James A.; Czyszanowski, Tomasz

2016-03-01

In this paper we present optical design and simulation results of vertical-cavity surface-emitting lasers (VCSELs) that incorporate monolithic subwavelength high refractive-index-contrast grating (MHCG) mirrors - a new variety of HCG mirror that is composed of high index material surrounded only on one side by low index material. We show the impact of an MHCG mirror on the performance of 980 nm VCSELs designed for high bit rate and energy-efficient optical data communications. In our design, all or part of the all-semiconductor top coupling distributed Bragg reflector mirror is replaced by an undoped gallium-arsenide MHCG. We show how the optical field intensity distribution of the VCSEL's fundamental mode is controlled by the combination of the number of residual distributed Bragg reflector (DBR) mirror periods and the physical design of the topmost gallium-arsenide MHCG. Additionally, we numerically investigate the confinement factors of our VCSELs and show that this parameter for the MHCG DBR VCSELs may only be properly determined in two or three dimensions due to the periodic nature of the grating mirror.

IER 203 CED-2 Report: LLNL Final Design for BERP Ball With a Composite Reflector of Thin Polyethylene Backed by Nickel

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

Percher, C. M.; Heinrichs, D. P.; Kim, S. K.

2016-07-18

This report documents the results of final design (CED-2) for IER 203, BERP Ball Composite Reflection, and focuses on critical configurations with a 4.5 kg α-phase plutonium sphere reflected by a combination of thin high-density polyethylene (HDPE) backed by a thick nickel reflector. The Lawrence Livermore National Laboratory’s (LLNL’s) Nuclear Criticality Safety Division, in support of fissile material operations, calculated surprisingly reactive configurations when a fissile core was surrounded by a thin, moderating reflector backed by a thick metal reflector. These composite reflector configurations were much more reactive than either of the single reflector materials separately. The calculated findings havemore » resulted in a stricter-than-anticipated criticality control set, impacting programmatic work. IER 203 was requested in response to these seemingly anomalous calculations to see if the composite reflection effect could be shown experimentally. This report focuses on the Beryllium Reflected Plutonium (BERP) ball as a fissile material core reflected by polyethylene and nickel. A total of four critical configurations were designed as part of CED-2. Fabrication costs are estimated to be $98,500, largely due to the cost of the large nickel reflectors. The IER 203 experiments could reasonably be expected to begin in early FY2017.« less

Measurements of CO, CO2, OH, and H2O in room-temperature and combustion gases by use of a broadly current-tuned multisection InGaAsP diode laser.

PubMed

Upschulte, B L; Sonnenfroh, D M; Allen, M G

1999-03-20

A new laser technology that achieves nearly 100-nm quasi-continuous tuning with only injection-current control in a four-section grating-coupler sampled-reflector laser was used to detect CO and CO(2) simultaneously in room-temperature gas mixtures. The same grating-coupler sampled-reflector laser was used to perform in situ measurements of CO, H(2)O, and OH in the exhaust gases of a CH(4)-air flame. This laser is being evaluated for inclusion in a multispecies combustion-emissions exhaust-analysis sensor, and its operational characteristics as they have an impact on gas sensing are described. Preliminary results suggest that this single laser can be used to replace multilaser sensor configurations for some combustion-emissions monitoring applications.

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.

DBR laser with nondynamic plasma grating formed by focused ion beam implanted dopants

NASA Technical Reports Server (NTRS)

Boenke, Myra M.; Wu, M. C.; Wang, Shyh; Clark, William M., Jr.; Stevens, Eugene H.

1989-01-01

A static plasma grating has been demonstrated experimentally (Wu et al., 1988) in a large-optical-cavity focused-ion-beam-distributed-Bragg-reflector (FIB-DBR) GaAlAs/GaAs laser diode. The grating is formed by implanting stripes of dopants with a focused ion beam. The dopants ionize to form periodic fluctuations in the carrier concentration which, through the Kramers-Kronig relations, form an index grating. A model of the grating strength for optimizaton of the laser design is developed and presented. The computed results show that the coupling coefficient k can be increased by more than an order of magnitude over the 15/cm experimentally. Therefore, FIB-DBR or FIB-distributed-feedback (DFB) lasers with performance comparable to that of conventional DBR (or DFB) lasers can be expected.

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.

Terrace retro-reflector array for poloidal polarimeter on ITER.

PubMed

Imazawa, R; Kawano, Y; Ono, T; Kusama, Y

2011-02-01

A new concept of a terrace retro-reflector array (TERRA) as part of the poloidal polarimeter for ITER is proposed in this paper. TERRA reflects a laser light even from a high incident angle in the direction of the incident-light path, while a conventional retro-reflector array cannot. Besides, TERRA can be installed in a smaller space than a corner-cube retro-reflector. In an optical sense, TERRA is equivalent to a Littrow grating, the blaze angle of which varies, depending on the incident angle. The reflected light generates a bright and dark fringe, and the bright fringe is required to travel along the incident-light path to achieve the objects of laser-aided diagnostics. In order to investigate the propagation properties of laser light reflected by TERRA, we have developed a new diffraction formula. Conditions for the propagation of the bright fringe in the direction of the incident light have been obtained using the Littrow grating model and have been confirmed in a simulation applying the new diffraction formula. Finally, we have designed laser transmission optics using TERRA for the ITER poloidal polarimeter and have calculated the light propagation of the system. The optical design obtains a high transmission efficiency, with 88.6% of the incident power returned. These results demonstrate the feasibility of applying TERRA to the ITER poloidal polarimeter.

Approaching conversion limit with all-dielectric solar cell reflectors.

PubMed

Fu, Sze Ming; Lai, Yi-Chun; Tseng, Chi Wei; Yan, Sheng Lun; Zhong, Yan Kai; Shen, Chang-Hong; Shieh, Jia-Min; Li, Yu-Ren; Cheng, Huang-Chung; Chi, Gou-chung; Yu, Peichen; Lin, Albert

2015-02-09

Metallic back reflectors has been used for thin-film and wafer-based solar cells for very long time. Nonetheless, the metallic mirrors might not be the best choices for photovoltaics. In this work, we show that solar cells with all-dielectric reflectors can surpass the best-configured metal-backed devices. Theoretical and experimental results all show that superior large-angle light scattering capability can be achieved by the diffuse medium reflectors, and the solar cell J-V enhancement is higher for solar cells using all-dielectric reflectors. Specifically, the measured diffused scattering efficiency (D.S.E.) of a diffuse medium reflector is >0.8 for the light trapping spectral range (600nm-1000nm), and the measured reflectance of a diffuse medium can be as high as silver if the geometry of embedded titanium oxide(TiO(2)) nanoparticles is optimized. Moreover, the diffuse medium reflectors have the additional advantage of room-temperature processing, low cost, and very high throughput. We believe that using all-dielectric solar cell reflectors is a way to approach the thermodynamic conversion limit by completely excluding metallic dissipation.

Back reflectors based on buried Al{sub 2}O{sub 3} for enhancement of photon recycling in monolithic, on-substrate III-V solar cells

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

García, I.; Instituto de Energía Solar, Universidad Politécnica de Madrid, Avda Complutense s/n, 28040 Madrid; Kearns-McCoy, C. F.

Photon management has been shown to be a fruitful way to boost the open circuit voltage and efficiency of high quality solar cells. Metal or low-index dielectric-based back reflectors can be used to confine the reemitted photons and enhance photon recycling. Gaining access to the back of the solar cell for placing these reflectors implies having to remove the substrate, with the associated added complexity to the solar cell manufacturing. In this work, we analyze the effectiveness of a single-layer reflector placed at the back of on-substrate solar cells, and assess the photon recycling improvement as a function of themore » refractive index of this layer. Al{sub 2}O{sub 3}-based reflectors, created by lateral oxidation of an AlAs layer, are identified as a feasible choice for on-substrate solar cells, which can produce a V{sub oc} increase of around 65% of the maximum increase attainable with an ideal reflector. The experimental results obtained using prototype GaAs cell structures show a greater than two-fold increase in the external radiative efficiency and a V{sub oc} increase of ∼2% (∼18 mV), consistent with theoretical calculations. For GaAs cells with higher internal luminescence, this V{sub oc} boost is calculated to be up to 4% relative (36 mV), which directly translates into at least 4% higher relative efficiency.« less

Brownian thermal noise in functional optical surfaces

NASA Astrophysics Data System (ADS)

Kroker, S.; Dickmann, J.; Rojas Hurtado, C. B.; Heinert, D.; Nawrodt, R.; Levin, Y.; Vyatchanin, S. P.

2017-07-01

We present a formalism to compute Brownian thermal noise in functional optical surfaces such as grating reflectors, photonic crystal slabs, or complex metamaterials. Such computations are based on a specific readout variable, typically a surface integral of a dielectric interface displacement weighed by a form factor. This paper shows how to relate this form factor to Maxwell's stress tensor computed on all interfaces of the moving surface. As an example, we examine Brownian thermal noise in monolithic T-shaped grating reflectors. The previous computations by Heinert et al. [Phys. Rev. D 88, 042001 (2013), 10.1103/PhysRevD.88.042001] utilizing a simplified readout form factor produced estimates of thermal noise that are tens of percent higher than those of the exact analysis in the present paper. The relation between the form factor and Maxwell's stress tensor implies a close correlation between the optical properties of functional optical surfaces and thermal noise.

Photonic integrated circuits based on sampled-grating distributed-Bragg-reflector lasers

NASA Astrophysics Data System (ADS)

Barton, Jonathon S.; Skogen, Erik J.; Masanovic, Milan L.; Raring, James; Sysak, Matt N.; Johansson, Leif; DenBaars, Steven P.; Coldren, Larry A.

2003-07-01

The Sampled-Grating Distributed-Bragg-Reflector laser(SGDBR) provides wide tunability (>40nm), and high output power (>10mW). Driven by the demand for network reconfigurability and ease of implementation, the SGDBR has moved from the research lab to be commercially viable in the marketplace. The SGDBR is most often implemented using an offset-quantum well epitaxial structure in which the quantum wells are etched off in the passive sections. Alternatively, quantum well intermixing has been used recently to achieve the same goal - resulting in improved optical gain and the potential for multiple bandgaps along the device structure. These epitaxial "platforms" provide the basis for more exotic opto-electronic device functionality exhibiting low chirp for digital applications and enhanced linearity for analog applications. This talk will cover state-of-the-art opto-electronic devices based on the SGDBR platform including: integrated Mach-Zehnder modulators, and integrated electro-absorption modulators.

Photogrammetrically Measured Distortions of Composite Structure Microwave Reflectors at -90K

NASA Technical Reports Server (NTRS)

Mule, Peter; Hill, Michael D.; Sampler, Henry P.

2000-01-01

The Microwave Anisotropy Probe (MAP) Observatory, scheduled for a late 2000 launch, is designed to measure temperature fluctuations (anisotropy) and produce a high sensitivity and high spatial resolution (better than 0.3 deg. at 90 GHz.) map of the Cosmic Microwave Background (CMB) radiation over the entire sky between 22 and 90 GHz. MAP utilizes back-to-back composite Gregorian telescopes supported on a composite truss structure to focus the microwave signals into 10 differential microwave receivers. Proper position and shape of the telescope reflectors at the operating temperature of -90 K is a critical element to ensure mission success. We describe the methods and analysis used to validate the in-flight position and shape predictions for the reflectors based on photogrammetric metrology data taken under vacuum with the reflectors at -90 K. Contour maps showing reflector distortion were generated. The resulting reflector distortion data are shown to be crucial to the analytical assessment of the MAP instrument's microwave system in-flight performance.

Photogrammetrically Measured Distortions of Composite Structure Microwave Reflectors at Approximately 90 K

NASA Technical Reports Server (NTRS)

Mule, Peter; Hill, Michael D.; Sampler, Henry P.

2000-01-01

The Microwave Anisotropy Probe (MAP) Observatory, scheduled for a fall 2000 launch, is designed to measure temperature fluctuations (anisotropy) and produce a high sensitivity and high spatial resolution (better than 0.3 deg.) map of the cosmic microwave background (CMB) radiation over the entire sky between 22 and 90 GHz. MAP utilizes back-to-back composite Gregorian telescopes supported on a composite truss structure to focus the microwave signals into 10 differential microwave receivers. Proper position and shape of the telescope reflectors at the operating temperature of approximately 90 K is a critical element to ensuring mission success. We describe the methods and analysis used to validate the in-flight position and shape predictions for the reflectors based on photogrammetric (PG) metrology data taken under vacuum with the reflectors at approximately 90 K. Contour maps showing reflector distortion analytical extrapolations were generated. The resulting reflector distortion data are shown to be crucial to the analytical assessment of the MAP instrument's microwave system in-flight performance.

Novel diffraction gratings for next generation spectrographs with high spectral dispersion

NASA Astrophysics Data System (ADS)

Ebizuka, N.; Okamoto, T.; Hosobata, T.; Yamagata, Y.; Sasaki, M.; Uomoto, M.; Shimatsu, T.; Sato, S.; Hashimoto, N.; Tanaka, I.; Hattori, T.; Ozaki, S.; Aoki, W.

2016-07-01

As a transmission grating, a surface-relief (SR) grating with sawtooth shaped ridges and volume phase holographic (VPH) grating are widely used for instruments of astronomical observations. However the SR grating is difficult to achieve high diffraction efficiency at high angular dispersion, and the VPH grating has low diffraction efficiency in high diffraction orders. We propose novel gratings that solve these problems. We introduce the hybrid grism which combines a high refractive index prism with a replicated transmission grating, which has sawtooth shaped ridges of an acute apex angle. The birefringence VPH (B-VPH) grating which contains an anisotropic medium, such as a liquid crystal, achieves diffraction efficiency up to 100% at the first diffraction order for natural polarization and for circular polarization. The quasi-Bragg (QB) grating which consists of long rectangular mirrors aligned in parallel precisely, like a window blind, achieves diffraction efficiency of 60% or more in higher than the 4th diffraction order. The volume binary (VB) grating with narrow grooves also achieves diffraction efficiency of 60% or more in higher than the 6th diffraction order. The reflector facet transmission (RFT) grating which is a SR grating with sawtooth shaped ridges of an acute apex angle achieves diffraction efficiency up to 80% in higher than the 4th diffraction order.

Heterogeneously-integrated VCSEL using high-contrast grating on silicon

NASA Astrophysics Data System (ADS)

Ferrara, James; Zhu, Li; Yang, Weijian; Qiao, Pengfei; Chang-Hasnain, Connie J.

2015-02-01

We present a unique heterogeneous integration approach for VCSELs on silicon using eutectic bonding. An electrically pumped III-V - silicon heterogeneous VCSEL is demonstrated using a high-contrast grating (HCG) reflector on silicon. CW output power >1.5 mW, thermal resistance of 1.46 K/mW, and 5 Gb/s direct modulation is demonstrated. We also explore the possibility of an all-HCG VCSEL structure that would benefit from stronger thermal performance, larger tuning efficiency, and higher direct modulation speeds.

Investigation of the Low Power Stage of an 1178 nm Raman System

DTIC Science & Technology

2013-12-23

LEANNE HENRY, DR-III, DAF KENTON T. WOOD, DR-IV, DAF Work Unit Manager Chief, Laser Division This report is published in the...and 1069 nm pumped Raman laser system where the second Stokes is amplified in a 1121 nm resonator defined by high reflector fiber Bragg gratings (FBGs...the gratings was found to impact the performance of the laser and needs to be dealt with in order to obtain high 1178 nm output power levels. In order

Unidirectional transmission realized by two nonparallel gratings made of isotropic media.

PubMed

Ye, Wei-Min; Yuan, Xiao-Dong; Zeng, Chun

2011-08-01

We realize a unidirectional transmission by cascading two nonparallel gratings (NPGs) made of isotropic, lossless, and linear media. For a pair of orthogonal linear polarizations, one of the gratings is designed as a polarizer, which is a reflector for one polarization and a transmitter for the other; another grating is designed as a polarization converter, which converts most of one polarized incident wave into another polarized transmitted wave. It is demonstrated by numerical calculation that more than 85% of the incident light energy can be transmitted with less than 1% transmission in the opposite direction for linearly polarized light at normal incidence, and the relative bandwidth of the unidirectional transmission is nearly 9%. The maximum transmission contrast ratio between the two directions is 62 dB. Unlike one-way diffraction grating, the transmitted light of the NPGs is collinear with the incident light, but their polarizations are orthogonal. © 2011 Optical Society of America

Tamm plasmon sub-wavelength structuration for loss reduction and resonance tuning

NASA Astrophysics Data System (ADS)

Gubaydullin, A. R.; Symonds, C.; Benoit, J.-M.; Ferrier, L.; Benyattou, T.; Jamois, C.; Lemaître, A.; Senellart, P.; Kaliteevski, M. A.; Bellessa, J.

2017-12-01

We have demonstrated experimentally and theoretically that losses in Tamm plasmon structures can be reduced by using a subwavelength structuration of the metal layer. The structures consist of a GaAs/Al0.95Ga0.05As Bragg reflector covered with a sub-wavelength silver grating. An active quantum dot layer is inserted to perform photoluminescence experiments. Experimental results show that the quality factor of the Tamm plasmon mode with grating increases substantially, with respect to the same structure without a grating. Moreover, a fine-tuning of the Tamm spectral position is obtained by changing the grating parameters. Finite element method simulations are in good agreement with the experimental values. Our results will promote the realization of lasing with the TP based devices at room temperature.

Towards perfect light coupling and absorption in nanomembranes with omni-directional anti-reflection and photonic crystal structures

NASA Astrophysics Data System (ADS)

Chadha, Arvinder Singh

Silicon photonics is realized as a promising platform to meet the requirements of higher bandwidth and low cost high density monolithic integration. More recent demonstrations of a variety of stretchable, foldable and transfer printed ultra-thin silicon integrated circuits have instigated the use of flexible silicon nanomembrane for practical applications. Equally impressive innovations are demonstrated in the area of flat screen displays, smart cards, eyeglasses, and wearable displays. However, the overall efficiency of a variety of optical device is limited by poor light management resulting from difficulty of light coupling, small absorption volume in thin-film nanomembrane, and glare at oblique incidence to name a few. The aim of this thesis is to present the work of micro- and nano-scale structures for out-of-plane light coupling and absorption for integrated silicon photonics and high performance solar cells and photodetectors, with maximum absorption in the functional layer and minimal front-surface reflection and minimal rear-surface transmission. Perfect absorption in a variety of semiconductor nanomembranes (NM) and atomic layers of two dimensional (2D) materials over different wavelength spectrum is realized due to the local field intensity enhancement at critical coupling to the guided resonances of a photonic crystal (PC). A judicious choice of grating parameters tailors the power diffracted in the zeorth order and higher order modes making the device work as a broadband reflector, an in-plane coupler or a combination of both reflector and an in-plane coupler. At surface normal incidence, the polarization dependence of the grating based reflector is eliminated by the use of 2D photonic crystals. The incorporation of such a reflector after the functional nanomembrane layer reduces the back-surface transmission. Effect of incident angle, polarization and incident plane misalignment dependence on the reflection of a silicon NM based reflector are investigated in detail. The front-surface Fresnel reflection is reduced with the incorporation of an omni-directional anti-reflection coating (Omni-ARC) based on nanostructures or by deposition of graded refractive index (GRIN) films. A design methodology based on the comparison of the rate of change of the refractive index profile of nanostructures of different shapes and thickness as an equivalent GRIN film suggests the minimum feature size needed to give near perfect ARC. Numerical models were built to account for the non - uniform GRIN film deposition on both rigid and flexible, flat and curved surfaces resulting from the variation in the resonant infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) process technology. With the miniaturization of the devices, the effect of finite beam size and finite active area of the photonic components on the optical properties like transmission, reflection and scattering loss was studied as well. All the numerical studies presented in the thesis are validated by experimental results.

A geological history of reflecting optics.

PubMed

Parker, Andrew Richard

2005-03-22

Optical reflectors in animals are diverse and ancient. The first image-forming eye appeared around 543 million years ago. This introduced vision as a selection pressure in the evolution of animals, and consequently the evolution of adapted optical devices. The earliest known optical reflectors--diffraction gratings--are 515 Myr old. The subsequent fossil record preserves multilayer reflectors, including liquid crystals and mirrors, 'white' and 'blue' scattering structures, antireflective surfaces and the very latest addition to optical physics--photonic crystals. The aim of this article is to reveal the diversity of reflecting optics in nature, introducing the first appearance of some reflector types as they appear in the fossil record as it stands (which includes many new records) and backdating others in geological time through evolutionary analyses. This article also reveals the commercial potential for these optical devices, in terms of lessons from their nano-level designs and the possible emulation of their engineering processes--molecular self-assembly.

Spectral and angular-selective thermal emission from gallium-doped zinc oxide thin film structures

NASA Astrophysics Data System (ADS)

Sakr, Enas; Bermel, Peter

2017-02-01

Simultaneously controlling both the spectral and angular emission of thermal photons can qualitatively change the nature of thermal radiation, and offers a great potential to improve a broad range of applications, including infrared light sources and thermophotovoltaic (TPV) conversion of waste heat to electricity. For TPV in particular, frequency-selective emission is necessary for spectral matching with a photovoltaic converter, while directional emission is needed to maximize the fraction of emission reaching the receiver at large separation distances. This can allow the photovoltaics to be moved outside vacuum encapsulation. In this work, we demonstrate both directionally and spectrally-selective thermal emission for p-polarization, using a combination of an epsilon-near-zero (ENZ) thin film backed by a metal reflector, a high contrast grating, and an omnidirectional mirror. Gallium-doped zinc oxide is selected as an ENZ material, with cross-over frequency in the near-infrared. The proposed structure relies on coupling guided modes (instead of plasmonic modes) to the ENZ thin film using the high contrast grating. The angular width is thus controlled by the choice of grating period. Other off-directional modes are then filtered out using the omnidirectional mirror, thus enhancing frequency selectivity. Our emitter design maintains both a high view factor and high frequency selectivity, leading to a factor of 8.85 enhancement over a typical blackbody emitter, through a combination of a 22.26% increase in view factor and a 6.88x enhancement in frequency selectivity. This calculation assumes a PV converter five widths away from the same width emitter in 2D at 1573 K.

A low-threshold high-index-contrast grating (HCG)-based organic VCSEL

NASA Astrophysics Data System (ADS)

Shayesteh, Mohammad Reza; Darvish, Ghafar; Ahmadi, Vahid

2015-12-01

We propose a low-threshold high-index-contrast grating (HCG)-based organic vertical-cavity surface-emitting laser (OVCSEL). The device has the feasibility to apply both electrical and optical excitation. The microcavity of the laser is a hybrid photonic crystal (HPC) in which the top distributed Bragg reflector (DBR) is replaced by a sub-wavelength high-contrast-grating layer, and provides a high-quality factor. The simulated quality factor of the microcavity is shown to be as high as 282,000. We also investigate the threshold behavior and the dynamics of the OVCSEL optically pumped with sub-picosecond pulses. Results from numerical simulation show that lasing threshold is 75 nJ/cm2.

Improvement on RCS reduction using flat lossy focusing reflectors.

PubMed

Chin, Cheng-Yuan; Jou, Christina F

2013-12-30

In this paper, we propose a planar non-periodic subwavelength resistive grating (SWRG). The phase front of the scattered fields can be completely manipulated through non-periodic design of the grating while high absorptivity is preserved. The SWRG has an interesting property similar to a resistive concave reflecting lens. Scattered wave is focused in the near-field region, and spread out in the far-field. This feature of non-periodic resistive grating can improve the original radar cross section (RCS) reduction up to 22.86 dB in the boresight direction comparing to the periodic counterpart. Non-periodic design of SWRG could have a substantial impact on stealth technology, aerospace engineering, and microwave anechoic chamber.

Discharge lamp with reflective jacket

DOEpatents

MacLennan, Donald A.; Turner, Brian P.; Kipling, Kent

2001-01-01

A discharge lamp includes an envelope, a fill which emits light when excited disposed in the envelope, a source of excitation power coupled to the fill to excite the fill and cause the fill to emit light, and a reflector disposed around the envelope and defining an opening, the reflector being configured to reflect some of the light emitted by the fill back into the fill while allowing some light to exit through the opening. The reflector may be made from a material having a similar thermal index of expansion as compared to the envelope and which is closely spaced to the envelope. The envelope material may be quartz and the reflector material may be either silica or alumina. The reflector may be formed as a jacket having a rigid structure which does not adhere to the envelope. The lamp may further include an optical clement spaced from the envelope and configured to reflect an unwanted component of light which exited the envelope back into the envelope through the opening in the reflector. Light which can be beneficially recaptured includes selected wavelength regions, a selected polarization, and selected angular components.

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.

Wideband QAMC reflector's antenna for low profile applications

NASA Astrophysics Data System (ADS)

Grelier, M.; Jousset, M.; Mallégol, S.; Lepage, A. C.; Begaud, X.; LeMener, J. M.

2011-06-01

A wideband reflector's antenna based on quasi-artificial magnetic conductor is proposed. To validate the design, an Archimedean spiral has been backed to this new reflector. In comparison to classical solution using absorbent material, the prototype presents a very low thickness of λ/15 at the lowest operating frequency and an improved gain over a 2.4:1 bandwidth. The whole methodology to design this reflector can be applied to other wideband antennas.

Studies of Beam Expansion and Distributed Bragg Reflector Lasers for Fiber Optics and Optical Signal Processing.

DTIC Science & Technology

1981-03-03

described theory and experiments on the DBR laser and on the use of the Distributed Bragg Deflector ( DBD ) to act as a grating bean expander. The DBD is a...and telescope. 9 .\\pplications requiring more power can use the DBD as a power combiner for several laser stripes, as shown in Fig. 3. In design...Bragg deflector ( DBD ). This device consists of a corrugated waveguide, whose grating is slanted at an angle 6 with respect to the incident beam. The

Novel gratings for next-generation instruments of astronomical observations

NASA Astrophysics Data System (ADS)

Ebizuka, N.; Okamoto, T.; Takeda, M.; Hosobata, T.; Yamagata, Y.; Sasaki, M.; Uomoto, M.; Shimatsu, T.; Sato, S.; Hashimoto, N.; Tanaka, I.; Hattori, T.; Ozaki, S.; Aoki, W.

2017-05-01

We will introduce current status of development of a birefringence volume phase holographic (B-VPH) grating, volume binary (VB) grating and reflector facet transmission (RFT) grating developing as the novel dispersive optical element for astronomical instruments for the 8.2m Subaru Telescope, for next generation 30 m class huge ground-based telescopes and for next generation large space-bone telescopes. We will also introduce a hybrid grism developed for MOIRCS (Multi-Object InfraRed Camera and Spectrograph) of the Subaru Telescope and a quasi-Bragg (QB) immersion grating. Test fabrication of B-VPH gratings with a liquid crystal (LC) of UV curable and normal LCs or a resin of visible light curable are performed. We successfully fabricated VB gratings of silicon as a mold with ridges of a high aspect ratio by means of the cycle etching process, oxidation and removal of silicon oxide. The RFT grating which is a surface-relief (SR) transmission grating with sawtooth shaped ridges of an acute vertex angle. The hybrid grism, as a prototype of the RFT grating, combines a high-index prism and SR transmission grating with sawtooth shape ridges of an acute vertex angle. The mold of the SR grating for the hybrid grism on to a work of Ni-P alloy of non-electrolysic plating successfully fabricated by using our ultra-precision machine and a single-crystal diamond bite. The QB immersion grating was fabricated by a combination of an inclined QB grating, Littrow prism and surface reflection mirror.

Effect of back reflectors on photon absorption in thin-film amorphous silicon solar cells

NASA Astrophysics Data System (ADS)

Hossain, Mohammad I.; Qarony, Wayesh; Hossain, M. Khalid; Debnath, M. K.; Uddin, M. Jalal; Tsang, Yuen Hong

2017-10-01

In thin-film solar cells, the photocurrent conversion productivity can be distinctly boosted-up utilizing a proper back reflector. Herein, the impact of different smooth and textured back reflectors was explored and effectuated to study the optical phenomena with interface engineering strategies and characteristics of transparent contacts. A unique type of wet-chemically textured glass-substrate 3D etching mask used in superstrate (p-i-n) amorphous silicon-based solar cell along with legitimated back reflector permits joining the standard light-trapping methodologies, which are utilized to upgrade the energy conversion efficiency (ECE). To investigate the optical and electrical properties of solar cell structure, the optical simulations in three-dimensional measurements (3D) were performed utilizing finite-difference time-domain (FDTD) technique. This design methodology allows to determine the power losses, quantum efficiencies, and short-circuit current densities of various layers in such solar cell. The short-circuit current densities for different reflectors were varied from 11.50 to 13.27 and 13.81 to 16.36 mA/cm2 for the smooth and pyramidal textured solar cells, individually. Contrasted with the comparable flat reference cell, the short-circuit current density of textured solar cell was increased by around 24%, and most extreme outer quantum efficiencies rose from 79 to 86.5%. The photon absorption was fundamentally improved in the spectral region from 600 to 800 nm with no decrease of photocurrent shorter than 600-nm wavelength. Therefore, these optimized designs will help to build the effective plans next-generation amorphous silicon-based solar cells.

Weakly modulated silicon-dioxide-cladding gratings for silicon waveguide Fabry-Pérot cavities.

PubMed

Grote, Richard R; Driscoll, Jeffrey B; Biris, Claudiu G; Panoiu, Nicolae C; Osgood, Richard M

2011-12-19

We show by theory and experiment that silicon-dioxide-cladding gratings for Fabry-Pérot cavities on silicon-on-insulator channel ("wire") waveguides provide a low-refractive-index perturbation, which is required for several important integrated photonics components. The underlying refractive index perturbation of these gratings is significantly weaker than that of analogous silicon gratings, leading to finer control of the coupling coefficient κ. Our Fabry-Pérot cavities are designed using the transfer-matrix method (TMM) in conjunction with the finite element method (FEM) for calculating the effective index of each waveguide section. Device parameters such as coupling coefficient, κ, Bragg mirror stop band, Bragg mirror reflectivity, and quality factor Q are examined via TMM modeling. Devices are fabricated with representative values of distributed Bragg reflector lengths, cavity lengths, and propagation losses. The measured transmission spectra show excellent agreement with the FEM/TMM calculations.

Data appendix: F-number=1.0 EMR with a flexible back electrode

NASA Technical Reports Server (NTRS)

Mihora, D. J.

1984-01-01

A 12.5 micron Tedlar low f-number electrostatic membrane reflector was tested. The antenna reflector was designed to achieve a spherical reflector surface with a focal length to diameter ratio f(sub n) of one and a potential accuracy of 1.0 over its 4.88 m diameter. The configuration required the cutting and joining of twelve pie-shaped panels to form the reflector surface. Electrostatic forces are used to tension this preformed membrane reflector. The test data is spare-only three sets of measurements were taken due to lack of funds.

Corrugated grating on organic multilayer Bragg reflector

NASA Astrophysics Data System (ADS)

Jaquet, Sylvain; Scharf, Toralf; Herzig, Hans Peter

2007-08-01

Polymeric multilayer Bragg structures are combined with diffractive gratings to produce artificial visual color effects. A particular effect is expected due to the angular reflection dependence of the multilayer Bragg structure and the dispersion caused by the grating. The combined effects can also be used to design particular filter functions and various resonant structures. The multilayer Bragg structure is fabricated by spin-coating of two different low-cost polymer materials in solution on a cleaned glass substrate. These polymers have a refractive index difference of about 0.15 and permit multilayer coatings without interlayer problems. Master gratings of different periods are realized by laser beam interference and replicated gratings are superimposed on the multilayer structure by soft embossing in a UV curing glue. The fabrication process requires only polymer materials. The obtained devices are stable and robust. Angular dependent reflection spectrums for the visible are measured. These results show that it is possible to obtain unexpected reflection effects. A rich variety of color spectra can be generated, which is not possible with a single grating. This can be explained by the coupling of transmission of grating orders and the Bragg reflection band. A simple model permits to explain some of the spectral vs angular dependence of reflected light.

Aberration-free, all-reflective laser pulse stretcher

DOEpatents

Perry, Michael D.; Banks, Paul S.; Stuart, Brent C.; Fochs, Scott N.

1999-09-28

An all-reflective pulse stretcher for laser systems employing chirped-pulse amplification enables on-axis use of the focusing mirror which results in ease of use, significantly decreased sensitivity to alignment and near aberration-free performance. By using a new type of diffraction grating which contains a mirror incorporated into the grating, the stretcher contains only three elements: 1) the grating, 2) a spherical or parabolic focusing mirror, and 3) a flat mirror. Addition of a fourth component, a retro-reflector, enables multiple passes of the same stretcher resulting in stretching ratios beyond the current state of the art in a simple and compact design. The pulse stretcher has been used to stretch pulses from 20 fsec to over 600 psec (a stretching ratio in excess of 30,000).

New symmetric reflector ultrasonic transducers (SRUT).

PubMed

Toda, Minoru

2009-10-01

This paper proposes a new structure composed of reflector plates mounted in front and in back of the transducer at an angle of 45 degrees, so that acoustic waves from front and back of the transducer are combined to form a single main beam. This principle is applicable to both transmitters and receivers. Because the propagation path lengths of the 2 beams are identical, they constructively add at all frequencies. Theoretical investigations revealed that far field directivity becomes sharper and acoustic pressure output is doubled. Experiments using an air ultrasonic transducer constructed of 50-kHz polyvinylidene fluoride corrugated film has shown doubled acoustic pressure in the far field, and the predicted sharper directivity has been observed. The reflector structure has been also applied to a 2.6-MHz lead zirconate titanate transducer in water with matching layers at both surfaces which has shown almost doubled bandwidth compared with an air backing structure, and doubled output power in continuous drive. Also pulse echo experiments have shown the effectiveness of this scheme.

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.

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.

High-sensitivity bend angle measurements using optical fiber gratings.

PubMed

Rauf, Abdul; Zhao, Jianlin; Jiang, Biqiang

2013-07-20

We present a high-sensitivity and more flexible bend measurement method, which is based on the coupling of core mode to the cladding modes at the bending region in concatenation with optical fiber grating serving as band reflector. The characteristics of a bend sensing arm composed of bending region and optical fiber grating is examined for different configurations including single fiber Bragg grating (FBG), chirped FBG (CFBG), and double FBGs. The bend loss curves for coated, stripped, and etched sections of fiber in the bending region with FBG, CFBG, and double FBG are obtained experimentally. The effect of separation between bending region and optical fiber grating on loss is measured. The loss responses for single FBG and CFBG configurations are compared to discover the effectiveness for practical applications. It is demonstrated that the sensitivity of the double FBG scheme is twice that of the single FBG and CFBG configurations, and hence acts as sensitivity multiplier. The bend loss response for different fiber diameters obtained through etching in 40% hydrofluoric acid, is measured in double FBG scheme that resulted in a significant increase in the sensitivity, and reduction of dead-zone.

Transparent conducting oxide contacts and textured metal back reflectors for thin film silicon solar cells

NASA Astrophysics Data System (ADS)

Franken, R. H.-J.

2006-09-01

With the growing population and the increasing environmental problems of the 'common' fossil and nuclear energy production, the need for clean and sustainable energy sources is evident. Solar energy conversion, such as in photovoltaic (PV) systems, can play a major role in the urgently needed energy transition in electricity production. At the present time PV module production is dominated by the crystalline wafer technology. Thin film silicon technology is an alternative solar energy technology that operates at lower efficiencies, however, it has several significant advantages, such as the possibility of deposition on cheap (flexible) substrates and the much smaller silicon material consumption. Because of the small thickness of the solar cells, light trapping schemes are needed in order to obtain enough light absorption and current generation. This thesis describes the research on thin film silicon solar cells with the focus on the optimization of the transparent conducting oxide (TCO) layers and textured metal Ag substrate layers for the use as enhanced light scattering back reflectors in n-i-p type of solar cells. First we analyzed ZnO:Al (TCO) layers deposited in an radio frequent (rf) magnetron deposition system equipped with a 7 inch target. We have focused on the improvement of the electrical properties without sacrificing the optical properties by increasing the mobility and decreasing the grain boundary density. Furthermore, we described some of the effects on light trapping of ZnO:Al enhanced back reflectors. The described effects are able to explain the observed experimental data. Furthermore, we present a relation between the surface morphology of the Ag back contact and the current enhancement in microcrystalline (muc-Si:H) solar cells. We show the importance of the lateral feature sizes of the Ag surface on the light scattering and introduce a method to characterize the quality of the back reflector by combining the vertical and lateral feature sizes at this surface. Additionally, we show that we can control the lateral feature sizes and obtain an optimized roughness for light scattering. With this new knowledge we were able to indicate the influence of the surface plasmon absorption of the textured Ag layers on the current enhancement and recognize this effect as one of the limiting factors to the current increase in thin film solar cells. Finally we present the dark and light current voltage (J-V) parameters of muc-Si:H solar cells as a function of the rms roughness of the substrate. We show that increased roughness can result in an increased defect density of the absorbing silicon layer (i layer), which limits the current collection in the solar cell. The presented research gives better understanding of the effect of TCOs and textured interfaces on light trapping and current enhancement in thin film silicon solar cells. The thesis explains some fundamental insights in light scattering and reveals some material and morphology features that are dominantly limiting the current generation in muc-Si:H solar cells deposited on light scattering back reflectors. Furthermore, it presents a method to obtain optimized back scattering contacts at deposition temperatures below 300 oC, which opens the possibility for the use of heat resistant plastic substrates. We improved the muc-Si:H solar cell efficiency with flat back reflectors from 4.5 % and 14.6 mA/cm2 to 8.5 % and 23.4 mA/cm2 with the use of optimized back reflectors.

Satellite-Tracking Millimeter-Wave Reflector Antenna System For Mobile Satellite-Tracking

NASA Technical Reports Server (NTRS)

Densmore, Arthur C. (Inventor); Jamnejad, Vahraz (Inventor); Woo, Kenneth E. (Inventor)

2001-01-01

A miniature dual-band two-way mobile satellite-tracking antenna system mounted on a movable vehicle includes a miniature parabolic reflector dish having an elliptical aperture with major and minor elliptical axes aligned horizontally and vertically, respectively, to maximize azimuthal directionality and minimize elevational directionality to an extent corresponding to expected pitch excursions of the movable ground vehicle. A feed-horn has a back end and an open front end facing the reflector dish and has vertical side walls opening out from the back end to the front end at a lesser horn angle and horizontal top and bottom walls opening out from the back end to the front end at a greater horn angle. An RF circuit couples two different signal bands between the feed-horn and the user. An antenna attitude controller maintains an antenna azimuth direction relative to the satellite by rotating it in azimuth in response to sensed yaw motions of the movable ground vehicle so as to compensate for the yaw motions to within a pointing error angle. The controller sinusoidally dithers the antenna through a small azimuth dither angle greater than the pointing error angle while sensing a signal from the satellite received at the reflector dish, and deduces the pointing angle error from dither-induced fluctuations in the received signal.

A satellite-tracking millimeter-wave reflector antenna system for mobile satellite-tracking

NASA Technical Reports Server (NTRS)

Densmore, Arthur C. (Inventor); Jamnejad, Vahraz (Inventor); Woo, Kenneth E. (Inventor)

1995-01-01

A miniature dual-band two-way mobile satellite tracking antenna system mounted on a movable ground vehicle includes a miniature parabolic reflector dish having an elliptical aperture with major and minor elliptical axes aligned horizontally and vertically, respectively, to maximize azimuthal directionality and minimize elevational directionality to an extent corresponding to expected pitch excursions of the movable ground vehicle. A feed-horn has a back end and an open front end facing the reflector dish and has vertical side walls opening out from the back end to the front end at a lesser horn angle and horizontal top and bottom walls opening out from the back end to the front end at a greater horn angle. An RF circuit couples two different signal bands between the feed-horn and the user. An antenna attitude controller maintains an antenna azimuth direction relative to the satellite by rotating it in azimuth in response to sensed yaw motions of the movable ground vehicle so as to compensate for the yaw motions to within a pointing error angle. The controller sinusoidally dithers the antenna through a small azimuth dither angle greater than the pointing error angle while sensing a signal from the satellite received at the reflector dish, and deduces the pointing angle error from dither-induced fluctuations in the received signal.

The Corner Reflector.

ERIC Educational Resources Information Center

Harris, Whitney S., Jr.

1983-01-01

The nature of the corner reflector array left on the moon by the July 1969 Apollo astronauts is described. The array was used to reflect earth-originating laser beams back to earth, and yielded a more accurate determination (to within six inches) of distance from the earth to the moon. (MP)

Multi-parameter optimization of monolithic high-index contrast grating reflectors

NASA Astrophysics Data System (ADS)

Marciniak, Magdalena; Gebski, Marcin; Dems, Maciej; Wasiak, Michał; Czyszanowski, Tomasz

2016-03-01

Conventional High-index Contrast Gratings (HCG) consist of periodically distributed high refractive index stripes surrounded by low index media. Practically, such low/high index stack can be fabricated in several ways however low refractive index layers are electrical insulators of poor thermal conductivities. Monolithic High-index Contrast Gratings (MHCGs) overcome those limitations since they can be implemented in any material with a real refractive index larger than 1.75 without the need of the combination of low and high refractive index materials. The freedom of use of various materials allows to provide more efficient current injection and better heat flow through the mirror, in contrary to the conventional HCGs. MHCGs can simplify the construction of VCSELs, reducing their epitaxial design to monolithic wafer with carrier confinement and active region inside and etched stripes on both surfaces in post processing. We present numerical analysis of MHCGs using a three-dimensional, fully vectorial optical model. We investigate possible designs of MHCGs using multidimensional optimization of grating parameters for different refractive indices.

Comparison of distributed Bragg reflector ridge waveguide diode lasers and monolithic master oscillator power amplifiers

NASA Astrophysics Data System (ADS)

Werner, Nils; Wegemund, Jan; Gerke, Sebastian; Feise, David; Bugge, Frank; Paschke, Katrin; Tränkle, Günther

2018-02-01

Diode lasers with ridge waveguide structures and wavelength stabilization by a distributed Bragg-reflector (DBR) are key components for many different applications. These lasers provide diffraction limited laser emission in a single spectral mode, while an arbitrary emission wavelength can be chosen as long as the semiconductor allows for amplification. Furthermore, the DBR grating can be fabricated during the lateral structuring of the device which makes them well suited for mass production. A variety of different concepts can be used for the actual realization of the laser. While standard DBR ridge waveguide lasers (DBR-RWL) with a DBR as reflection grating provide up to 1W optical output power, the DBR can be also used as transmission grating for improved efficiency. Furthermore, more complex structures like monolithic master oscillator power amplifiers (MOPA), which show less spectral mode hops than DBR-RWLs, have been fabricated. The wide range of possible applications have different requirements on the emission characteristic of the used lasers. While the lasers can fulfill the requirements on the emission spectrum and the optical output power, the effects due to optical feedback from optical elements of the setup may limit their practical use in the respective application. Thus, it is of high importance to analyze the emission behavior of the different laser designs at various operation conditions with and without optical feedback. Here, the detailed investigation of the emission characteristics of lasers at an exemplary emission wavelength of 1120 nm is be presented.

An Acoustic Charge Transport Imager for High Definition Television Applications: Low-Voltage SAW Amplifiers on Multilayer GaAs/ZnO Substrates

NASA Technical Reports Server (NTRS)

Hunt, W. D.; Brennan, K. F.; Summers, C. J.; Cameron, Thomas P.

1996-01-01

This thesis addresses the acoustoelectric issues concerning the amplification of surface acoustic waves (SAWs) and the reflection of SAWs from slanted reflector gratings on GaAs, with application to a novel acoustic charge transport (ACT) device architecture. First a simple model of the SAWAMP was developed, which was subsequently used to define the epitaxially grown material structure necessary to provide simultaneously high resistance and high electron mobility. In addition, a segmented SAWAMP structure was explored with line widths on the order of an acoustic wavelength. This resulted in the demonstration of SAWAMPS with an order of magnitude less voltage and power requirements than previously reported devices. A two-dimensional model was developed to explain the performance of devices with charge confinement layers less then 0.5 mm, which was experimentally verified. This model was extended to predict a greatly increased gain from the addition of a ZnO overlay. These overlays were experimentally attempted, but no working devices were reported due to process incompatibilities. In addition to the SAWAMP research, the reflection of SAWs from slanted gratings on GaAs was also studied and experimentally determined reflection coefficients for both 45 deg grooves and Al stripes on GaAs have been reported for the first time. The SAWAMp and reflector gratings were combined to investigate the integrated ring oscillator for application to the proposed ACT device and design parameters for this device have been provided.

Novel large deployable antenna backing structure concepts for foldable reflectors

NASA Astrophysics Data System (ADS)

Fraux, V.; Lawton, M.; Reveles, J. R.; You, Z.

2013-12-01

This paper describes a number of large deployable antenna (LDA) reflector structure concepts developed at EnerSys-ABSL. Furthermore, EnerSys-ABSL has confirmed the desire to build a breadboard demonstrator of a backing deployable structure for a foldable reflector in the diameter range of 4-9 m. As part of this project EnerSys-ABSL has explored five novel deployable structure concepts. This paper presents the top level definition of these concepts together with the requirements considered in the design and selection of the preferred candidate. These new concepts are described and then compared through a trade-off analysis to identify the most suitable concept that EnerSys-ABSL would like to consider for the breadboard demonstrator. Finally, the kinematics of the chosen concept is described in more detail and future steps in the development process are highlighted.

Recirculating Etalon Spectrometer

NASA Technical Reports Server (NTRS)

Stephen, Mark A. (Inventor); Fahey, Molly E. (Inventor); Krainak, Michael A. (Inventor)

2017-01-01

Systems, methods, and devices may provide an optical scheme that achieves simultaneous wavelength channels and maintains the resolution and luminosity of an etalon. Various embodiments may provide a method to optically recirculate the light reflected from the etalon back through the same etalon at new angles. Various embodiments create an etalon spectrometer based on angular dispersion without moving parts and without losing the light that is not initially transmitted. Various embodiments may provide a spectrally-resolved receiver and/or transmitter. Various embodiments may provide a system including a retro-reflector, a detector or transmitter array, and an etalon disposed between the retro-reflector and the detector or transmitter array, wherein the retro-reflector is configured to redirect light reflected by the etalon back to the etalon at a different angle of incidence than an original angle of incidence on the etalon of the light reflected by the etalon.

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

Low threshold distributed Bragg reflector surface emitting laser diode with semiconductor air-bridge-supported top mirror

NASA Astrophysics Data System (ADS)

Hsin, W.; Du, G.; Gamelin, J. K.; Malloy, K. J.; Wang, S.

1990-03-01

A surface emitting laser diode (SELD) with two distributed Bragg reflectors (DBR) and semiconductor multilayer air-bridge-supported top mirror is fabricated. A low threshold current of 1.5 mA is achieved under room temperature CW operation. The spectrum shows a strong peak at 891 nm with a FWHM of 10 A. With light emission from the top Bragg reflector instead of from the back side of the substrate, laser arrays are easily formed with this novel structure.

Dual-Frequency Operation in a Short-Cavity Ytterbium-Doped Fiber Laser

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

Guan, W.; Maricante, J.R.

2007-02-15

A dual-frequency 2-cm silica fiber laser with a wavelength spacing of 0.3 nm has been demonstrated using a polarization-maintaining (PM) fiber-Bragg-grating (FBG) reflector. The birefringence of the PM FBG was used to generate the two single-mode (SM) lasing frequencies of orthogonal polarizations. The SM operation in each wavelength has been verified.

Effects of pitch and shape for diffraction grating in LED fog lamp

NASA Astrophysics Data System (ADS)

Chen, Hsi-Chao; Lin, Jun-Yu; Wu, Jih-Huah; Ma, Shih-Hsin; Yang, Chi-Hao

2011-10-01

The characteristics of light-emitting diodes (LEDs) that make them energy-efficient and long-lasting light source for general illumination have attracted a great attention from the lighting industry and commercial market. As everyone know LEDs have the advantages of environmental protection, long lifetime, fast response time (μs), low voltage and good mechanical properties. Their high luminance and the wide region of the dominant wavelengths within the entire visible spectrum mean that people have high anticipations for the applications of LEDs. The output lighting from reflector in the traditional fog lamp was required to fit the standard of the ECE R19 F3 regulation. Therefore, this study investigated the effects of pitch and angle for a diffraction grating in LED fog lamp. The light pattern of fog lamp must be satisfied ECE regulations, so a design of diffraction grating to shift down the lighting was required. There are three LEDs (Cree XLamp XPE LEDs) as the light source in the fog lamp for the illumination efficiency. Then, an optimal simulation of diffraction grating was done for the pitch and angle of the diffraction grating at the test distance of 25 meters. The best pitch and angle was 2mm and 60 degree for the grating shape of wedge type.

Guided-mode resonant filters and reflectors: Principles, design, and fabrication

NASA Astrophysics Data System (ADS)

Niraula, Manoj

In this dissertation, we overview the operational principles of these resonant periodic structures, discuss the methods of their design and fabrication, and propose and demonstrate novel functionalities for spatial and spectral filtering, and unpolarized wideband reflection. Fashioned with materially sparse gratings, these optical devices are easy to fabricate and integration friendly compared to their traditional multi-layer counterparts making their research and development critical for practical applications. We study, theoretically, modal properties and parametric dependence of resonant periodic bandpass filters operating in the mid- and near-infrared spectral domains. We investigate three different device architectures consisting of single, double, and triple layers based on all-transparent dielectric and semiconductor thin films. We present three modal coupling configurations forming complex mixtures of two or three distinct leaky modes coupling at different evanescent diffraction orders. Our modal analysis demonstrates key attributes of subwavelength periodic thin-film structures in multiple-modal blending to achieve desired transmission spectra. We provide the first experimental demonstration of high-efficiency and narrow-linewidth resonant bandpass filter applying a single patterned silicon layer on a quartz substrate. Its performance corresponds to bandpass filters requiring 15 traditional Si/SiO2 thin-film layers. The feasibility of sparse narrowband, high-efficiency bandpass filters with extremely wide, flat, and low sidebands is thereby demonstrated. The proposed technology is integration-friendly and opens doors for further development in various disciplines and spectral regions where thin-film solutions are traditionally applied. We demonstrate concurrent spatial and spectral filtering as a new outstanding attribute of resonant periodic devices. This functionality is enabled by a unique, near-complete, reflection state that is discrete in both angular and spectral domains and realized with carefully crafted nanogratings operating in the non-subwavelength regime. We study the pathway and inter-modal interference effects inducing this intriguing reflection state. In a proof-of-concept experiment, we obtain angular and spectral bandwidths of 4 mrad and 1 nm, respectively. This filter concept can be used for focus-free spectral and spatial filtering in compact holographic and interferometric optical instruments. We report unpolarized broadband reflectors enabled by a serial arrangement of a pair of polarized subwavelength gratings. Optimized with inverse numerical methods, our elemental gratings consist of a partially etched crystalline-silicon film on a quartz substrate. The resulting reflectors exhibit extremely wide spectral reflection bands in one polarization. By arranging two such reflectors sequentially with orthogonal periodicities, there results an unpolarized spectral band possessing bandwidth exceeding those of the individual polarized bands. In the experiments reported herein, we achieve zero-order reflectance exceeding 97% under unpolarized light incidence over a 500-nm-wide wavelength band in the near-infrared domain. Moreover, the resonant unpolarized broadband accommodates an ultra-high-reflection band spanning 85 nm and exceeding 99.9% in efficiency. The elemental polarization-sensitive reflectors based on one-dimensional resonant gratings have simple design, robust performance, and are straightforward to fabricate. Hence, this technology is a promising alternative to traditional multilayer thin-film reflectors especially at longer wavelengths of light where multilayer deposition may be infeasible or impractical. We demonstrate an interesting attribute of resonant bandpass filters which is high angular stability for fully conical light incidence. Fashioning an experimental bandpass filter with a subwavelength silicon grating on a quartz substrate, we show that fully conical incidence provides an angular full-width at half-maximum linewidth of 9.5° compared to a linewidth of 0.1° for classical incidence. Slow angular variation of the central wavelength with full conical incidence arises via a corresponding slow angular variation of the resonant second diffraction orders driving the pertinent leaky modes. Moreover, full conical incidence maintains a profile with a single passband as opposed to the formation of two passbands characteristic of resonant subwavelength gratings under classical incidence. Our experimental results demonstrate excellent stability in angle, spectral profile, linewidth, and efficiency. Finally, we propose a novel method of design and fabrication of photonic lattices that incorporates the best of both worlds: a polarized resonant grating can be designed and converted to its unpolarized lattice equivalent using the same design parameters to obtain a similar performance. We show this in context of a single-layer polarized bandpass filter operating at 1550 nm with 100% transmission efficiency. An unpolarized square-hole lattice with identical parameters operates as a bandpass filter at 1560 nm with 70% transmission efficiency. Moreover, conventional laser interference lithography technique for mask patterning is limited to circular-hole photoresist lattice. We propose a method to lay down a metal hard-mask by lifting-off patterned photoresist in two steps for a square-hole lattice. Our comprehensive study provides new principles for easy design and fabrication of square-hole photonic lattices for unpolarized guided-mode resonance applications. (Abstract shortened by ProQuest.).

Chirped fiber Bragg grating written in highly birefringent fiber in simultaneous strain and temperature monitoring.

PubMed

Bieda, Marcin S; Sobotka, Piotr; Woliński, Tomasz R

2017-02-20

A new sensor configuration is proposed for simultaneous strain and temperature monitoring in a composite material that is based on a chirped fiber Bragg grating (CFBG) written in a highly birefringent (HB) polarization-maintaining fiber. The sensor is designed in the reflective configuration in which the CFBG acts both as a reflector and a sensing element. Since CFBG and HB fiber induce changes in the state of polarization (SOP), interference between polarization modes in the reflected spectrum is observed and analyzed. We used a simple readout setup to enable fast, linear operation of strain sensing as well simultaneous strain and temperature measurements in the composite.

DBR, Sub-wavelength grating, and Photonic crystal slab Fabry-Perot cavity design using phase analysis by FDTD.

PubMed

Kim, Jae Hwan Eric; Chrostowski, Lukas; Bisaillon, Eric; Plant, David V

2007-08-06

We demonstrate a Finite-Difference Time-Domain (FDTD) phase methodology to estimate resonant wavelengths in Fabry-Perot (FP) cavity structures. We validate the phase method in a conventional Vertical-Cavity Surface-Emitting Laser (VCSEL) structure using a transfer-matrix method, and compare results with a FDTD reflectance method. We extend this approach to a Sub-Wavelength Grating (SWG) and a Photonic Crystal (Phc) slab, either of which may replace one of the Distributed Bragg Reflectors (DBRs) in the VCSEL, and predict resonant conditions with varying lithographic parameters. Finally, we compare the resonant tunabilities of three different VCSEL structures, taking quality factors into account.

The Position and Attitude of Sub-reflector Modeling for TM65 m Radio Telescope

NASA Astrophysics Data System (ADS)

Sun, Z. X.; Chen, L.; Wang, J. Q.

2016-01-01

In the course of astronomical observations, with changes in angle of pitch, the large radio telescope will have different degrees of deformation in the sub-reflector support, back frame, main reflector etc, which will lead to the dramatic decline of antenna efficiency in both high and low elevation. A sub-reflector system of the Tian Ma 65 m radio telescope has been installed in order to compensate for the gravitational deformations of the sub-reflector support and the main reflector. The position and attitude of the sub-reflector are variable in order to improve the pointing performance and the efficiency at different elevations. In this paper, it is studied that the changes of position and attitude of the sub-reflector have influence on the efficiency of antenna in the X band and Ku band. A model has been constructed to determine the position and attitude of the sub-reflector with elevation, as well as the point compensation model, by observing the radio source. In addition, antenna efficiency was tested with sub-reflector position adjusted and fixed. The results show that the model of sub-reflector can effectively improve the efficiency of the 65 m radio telescope. In X band, the aperture efficiency of the radio telescope reaches more than 60% over the entire elevation range.

Active Q switching of a fiber laser with a microsphere resonator

NASA Astrophysics Data System (ADS)

Kieu, Khanh; Mansuripur, Masud

2006-12-01

We propose and demonstrate an active Q-switched fiber laser using a high-Q microsphere resonator as the Q-switching element. The laser cavity consists of an Er-doped fiber as the gain medium, a glass microsphere reflector (coupled through a fiber taper) at one end of the cavity, and a fiber Bragg grating reflector at the other end. The reflectivity of the microsphere is modulated by changing the gap between the microsphere and the fiber taper. Active Q switching is realized by oscillating the microsphere in and out of contact with the taper. Using this novel technique, we have obtained giant pulses (maximum peak power ˜102W, duration ˜160ns) at a low pump-power threshold (˜3mW).

Real-time sensing of optical alignment

NASA Technical Reports Server (NTRS)

Stier, Mark T.; Wissinger, Alan B.

1988-01-01

The Large Deployable Reflector and other future segmented optical systems may require autonomous, real-time alignment of their optical surfaces. Researchers have developed gratings located directly on a mirror surface to provide interferometric sensing of the location and figure of the mirror. The grating diffracts a small portion of the incident beam to a diffractive focus where the designed diagnostics can be performed. Mirrors with diffraction gratings were fabricated in two separate ways. The formation of a holographic grating over the entire surface of a mirror, thereby forming a Zone Plate Mirror (ZPM) is described. Researchers have also used computer-generated hologram (CGH) patches for alignment and figure sensing of mirrors. When appropriately illuminated, a grid of patches spread over a mirror segment will yield a grid of point images at a wavefront sensor, with the relative location of the points providing information on the figure and location of the mirror. A particular advantage of using the CGH approach is that the holographic patches can be computed, fabricated, and replicated on a mirror segment in a mass production 1-g clean room environment.

Compact Reflective Imaging Spectrometer Design Utilizing An Immersed Grating And Anamorphic Mirror

DOEpatents

Lerner, Scott A.

2006-01-10

A compact imaging spectrometer comprising an entrance slit, an anamorphic mirror, a grating, and a detector array. The entrance slit directs light to the anamorphic mirror. The anamorphic mirror receives the light and directs the light to the grating. The grating receives the light from the anamorphic mirror and defracts the light back onto the anamorphic mirror. The anamorphic mirror focuses the light onto a detector array.

Analysis of the reflective multibandgap solar cell concept

NASA Technical Reports Server (NTRS)

Stern, T. G.

1983-01-01

A new and unique approach to improving photovoltaic conversion efficiency, the reflective multiband gap solar cell concept, was examined. This concept uses back surface reflectors and light trapping with several physically separated cells of different bandgaps to make more effective use of energy from different portions of the solar spectrum. Preliminary tests performed under General Dynamics Independent Research and Development (IRAD) funding have demonstrated the capability for achieving in excess of 20% conversion efficiency with aluminum gallium arsenide and silicon. This study analyzed the ultimate potential for high conversion efficiency with 2, 3, 4, and 5 different bandgap materials, determined the appropriate bandgaps needed to achieve this optimized efficiency, and identified potential problems or constraints. The analysis indicated that an improvement in efficiency of better than 40% could be attained in this multibandgap approach, compared to a single bandgap converter under the same assumptions. Increased absorption loss on the back surface reflector was found to incur a minimal penalty on efficiency for two and three bandgap systems. Current models for bulk absorption losses in 3-5 materials were found to be inadequate for explaining laboratory observed transmission losses. Recommendations included the continued development of high bandgap back surface reflector cells and basic research on semiconductor absorption mechanisms.

Artificially controlled backscattering in single mode fibers based on femtosecond laser fabricated reflectors

NASA Astrophysics Data System (ADS)

Wang, Xiaoliang; Chen, Daru; Li, Haitao; Wu, Qiong

2018-04-01

A novel method to artificially control the backscattering of the single-mode fiber (SMF) is proposed and investigated for the first time. This method can help to fabricate a high backscattering fiber (HBSF), such as by fabricating reflectors in every one meter interval of an SMF based on the exposure of the femtosecond laser beam. The artificially controlled backscattering (ACBS) can be much higher than the natural Rayleigh backscattering (RB) of the SMF. The RB power and ACBS power in the unit length fiber are derived according to the theory of the RBS. The total relative power and the relative back power reflected in the unit length of the HBSF have been simulated and presented. The simulated results show that the HBSF has the characteristics of both low optical attenuation and high backscattering. The relative back power reflected in the unit length of the HBSF is 25dB larger than the RB power of the SMF when the refractive index modulation quantity of the reflectors is 0.009. Some preliminary experiments also indicate that the method fabricating reflectors to increase the backscattering power of the SMF is practical and promising.

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.

High-Precision Shape Control of In-Space Deployable Large Membrane/Thin-Shell Reflectors

NASA Technical Reports Server (NTRS)

Watkins, Ronald; Goebel, Dan; Hofer, Richard

2010-01-01

This innovation has been developed to improve the resolutions of future spacebased active and passive microwave antennas for earth-science remote sensing missions by maintaining surface figure precisions of large membrane/thin-shell reflectors during orbiting. The intention is for these sensing instruments to be deployable at orbit altitudes one or two orders of magnitude higher than Low Earth Orbit (LEO), but still being able to acquire measurements at spatial resolution and sensitivity similar to those of LEO. Because active and passive microwave remote sensors are able to penetrate through clouds to acquire vertical profile measurements of geophysical parameters, it is desirable to elevate them to the higher orbits to obtain orbital geometries that offer large spatial coverage and more frequent observations. This capability is essential for monitoring and for detailed understanding of the life cycles of natural hazards, such as hurricanes, tropical storms, flash floods, and tsunamis. Major components of this high-precision antenna-surface-control system include a membrane/thin shell reflector, a metrology sensor, a controller, actuators, and corresponding power amplifier and signal conditioning electronics (see figure). Actuators are attached to the back of the reflector to produce contraction/ expansion forces to adjust the shape of the thin-material reflector. The wavefront-sensing metrology system continuously measures the surface figure of the reflector, converts the surface figure to digital data and feeds the data to the controller. The controller determines the control parameters and generates commands to the actuator system. The flexible, piezoelectric polymer actuators are thus activated, providing the control forces needed to correct any distortions that exist in the reflector surface. Piezoelectric polymer actuators are very thin and flexible. They can be implemented on the back of the membrane/thin-shell reflector without introducing significant amounts of mass or stiffness to the reflector. They can be rolled up or folded to accommodate the packaging needed for launch. An analytical model of the system, which includes the membrane reflector, actuator, and controller has been developed to investigate the functionality of this control system on a 35-meter-diameter membrane reflector. The performance of this system under external disturbances such as in space thermal loads and W-error due to inflation has been investigated. A subscale breadboard has been developed, and the functionality of this control concept has been demonstrated by this breadboard.

Computer prediction of large reflector antenna radiation properties

NASA Technical Reports Server (NTRS)

Botula, A.

1980-01-01

A FORTRAN program for calculating reflector antenna radiation patterns was rewritten and extended to include reflectors composed of a number of panels. These individual panels must be analytic surfaces. The theoretical foundation for the program is as follows: Geometrical optics techniques are used to trace rays from a feed antenna to the reflector surface and back to a mathematical plane just in front of the reflector. The resulting tangential electric field distribution, assumed to be the only source of forward radiation, is integrated numerically to calculate the radiation pattern for a desired set of angles. When the reflector is composed of more than one panel, each panel is treated as a separated antenna, the ray-tracing procedure and integration being repeated for each panel. The results of the individual aperture plane integrations are stored and summed to yield the relative electric field strength over the angles of interest. An example and several test cases are included to demonstrate the use of the program and verify the new method of computation.

Long-range, full-duplex, modulated-reflector cell phone for voice/data transmission

DOEpatents

Neagley, Daniel L.; Briles, Scott D.; Coates, Don M.; Freund, Samuel M.

2002-01-01

A long-range communications apparatus utilizing modulated-reflector technology is described. The apparatus includes an energy-transmitting base station and remote units that do not emit radiation in order to communicate with the base station since modulated-reflector technology is used whereby information is attached to an RF carrier wave originating from the base station which is reflected by the remote unit back to the base station. Since the remote unit does not emit radiation, only a low-power power source is required for its operation. Information from the base station is transmitted to the remote unit using a transmitter and receiver, respectively. The range of such a communications system is determined by the properties of a modulated-reflector half-duplex link.

Correcting Thermal Deformations in an Active Composite Reflector

NASA Technical Reports Server (NTRS)

Bradford, Samuel C.; Agnes, Gregory S.; Wilkie, William K.

2011-01-01

Large, high-precision composite reflectors for future space missions are costly to manufacture, and heavy. An active composite reflector capable of adjusting shape in situ to maintain required tolerances can be lighter and cheaper to manufacture. An active composite reflector testbed was developed that uses an array of piezoelectric composite actuators embedded in the back face sheet of a 0.8-m reflector panel. Each individually addressable actuator can be commanded from 500 to +1,500 V, and the flatness of the panel can be controlled to tolerances of 100 nm. Measuring the surface flatness at this resolution required the use of a speckle holography interferometer system in the Precision Environmental Test Enclosure (PETE) at JPL. The existing testbed combines the PETE for test environment stability, the speckle holography system for measuring out-of-plane deformations, the active panel including an array of individually addressable actuators, a FLIR thermal camera to measure thermal profiles across the reflector, and a heat source. Use of an array of flat piezoelectric actuators to correct thermal deformations is a promising new application for these actuators, as is the use of this actuator technology for surface flatness and wavefront control. An isogrid of these actuators is moving one step closer to a fully active face sheet, with the significant advantage of ease in manufacturing. No extensive rib structure or other actuation backing structure is required, as these actuators can be applied directly to an easy-to-manufacture flat surface. Any mission with a surface flatness requirement for a panel or reflector structure could adopt this actuator array concept to create lighter structures and enable improved performance on orbit. The thermal environment on orbit tends to include variations in temperature during shadowing or changes in angle. Because of this, a purely passive system is not an effective way to maintain flatness at the scale of microns over several meters. This technology is specifically referring to correcting thermal deformations of a large, flat structure to a specified tolerance. However, the underlying concept (an array of actuators on the back face of a panel for correcting the flatness of the front face) could be extended to many applications, including energy harvesting, changing the wavefront of an optical system, and correcting the flatness of an array of segmented deployable panels.

From the generalized reflection law to the realization of perfect anomalous reflectors

PubMed Central

Díaz-Rubio, Ana; Asadchy, Viktar S.; Elsakka, Amr; Tretyakov, Sergei A.

2017-01-01

The use of the generalized Snell’s law opens wide possibilities for the manipulation of transmitted and reflected wavefronts. However, known structures designed to shape reflection wavefronts suffer from significant parasitic reflections in undesired directions. We explore the limitations of the existing solutions for the design of passive planar reflectors and demonstrate that strongly nonlocal response is required for perfect performance. A new paradigm for the design of perfect reflectors based on energy surface channeling is introduced. We realize and experimentally verify a perfect design of an anomalously reflective surface using an array of rectangular metal patches backed by a metallic plate. This conceptually new mechanism for wavefront manipulation allows the design of thin perfect reflectors, offering a versatile design method applicable to other scenarios, such as focusing reflectors, surface wave manipulations, or metasurface holograms, extendable to other frequencies. PMID:28819642

The effects of stainless steel radial reflector on core reactivity for small modular reactor

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

Kang, Jung Kil, E-mail: jkkang@email.kings.ac.kr; Hah, Chang Joo, E-mail: changhah@kings.ac.kr; Cho, Sung Ju, E-mail: sungju@knfc.co.kr

Commercial PWR core is surrounded by a radial reflector, which consists of a baffle and water. Radial reflector is designed to reflect neutron back into the core region to improve the neutron efficiency of the reactor and to protect the reactor vessels from the embrittling effects caused by irradiation during power operation. Reflector also helps to flatten the neutron flux and power distributions in the reactor core. The conceptual nuclear design for boron-free small modular reactor (SMR) under development in Korea requires to have the cycle length of 4∼5 years, rated power of 180 MWth and enrichment less than 5more » w/o. The aim of this paper is to analyze the effects of stainless steel radial reflector on the performance of the SMR using UO{sub 2} fuels. Three types of reflectors such as water, water/stainless steel 304 mixture and stainless steel 304 are selected to investigate the effect on core reactivity. Additionally, the thickness of stainless steel and double layer reflector type are also investigated. CASMO-4/SIMULATE-3 code system is used for this analysis. The results of analysis show that single layer stainless steel reflector is the most efficient reflector.« less

Compact imaging spectrometer utilizing immersed gratings

DOEpatents

Lerner, Scott A.

2005-12-20

A compact imaging spectrometer comprising an entrance slit for directing light, lens means for receiving the light, refracting the light, and focusing the light; an immersed diffraction grating that receives the light from the lens means and defracts the light, the immersed diffraction grating directing the detracted light back to the lens means; and a detector that receives the light from the lens means.

Imaging Spectrometer Designs Utilizing Immersed Gratings With Accessible Entrance Slit

DOEpatents

Chrisp, Michael P.; Lerner, Scott A.

2006-03-21

A compact imaging spectrometer comprises an entrance slit, a catadioptric lens with a mirrored surface, a grating, and a detector array. The entrance slit directs light to the mirrored surface of the catadioptric lens; the mirrored surface reflects the light back through the lens to the grating. The grating receives the light from the catadioptric lens and diffracts the light to the lens away from the mirrored surface. The lens transmits the light and focuses it onto the detector array.

Optical spectroscopy of V404 Cyg during its latest outburst

NASA Astrophysics Data System (ADS)

Somogyi, Peter

2016-01-01

Low resolution spectra were obtained during the current outburst (announced in ATel #8453) of the microquasar V404 Cyg. Ten 600 sec exposures were obtained on 2015 Dec. 31 (JD 2457388.202 - 0.27) with a 250 mm Newtonian reflector using an LHires III spectrograph with 150 line/mm grating (R ~ 500) spanning 4500-7500A with the combined S/N ~ 10 (continuum at 6000A; calibration used the standard HD192640).

Design for high-power, single-lobe, grating-surface-emitting quantum cascade lasers enabled by plasmon-enhanced absorption of antisymmetric modes

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

Sigler, C.; Kirch, J. D.; Mawst, L. J.

2014-03-31

Resonant coupling of the transverse-magnetic polarized (guided) optical mode of a quantum-cascade laser (QCL) to the antisymmetric surface-plasmon modes of 2nd-order distributed-feedback (DFB) metal/semiconductor gratings results in strong antisymmetric-mode absorption. In turn, lasing in the symmetric mode, that is, surface emission in a single-lobe far-field beam pattern, is strongly favored over controllable ranges in grating duty cycle and tooth height. By using core-region characteristics of a published 4.6 μm-emitting QCL, grating-coupled surface-emitting (SE) QCLs are analyzed and optimized for highly efficient single-lobe operation. For infinite-length devices, it is found that when the antisymmetric mode is resonantly absorbed, the symmetric mode hasmore » negligible absorption loss (∼0.1 cm{sup −1}) while still being efficiently outcoupled, through the substrate, by the DFB grating. For finite-length devices, 2nd-order distributed Bragg reflector (DBR) gratings are used on both sides of the DFB grating to prevent uncontrolled reflections from cleaved facets. Equations for the threshold-current density and the differential quantum efficiency of SE DFB/DBR QCLs are derived. For 7 mm-long, 8.0 μm-wide, 4.6 μm-emitting devices, with an Ag/InP grating of ∼39% duty cycle, and ∼0.22 μm tooth height, threshold currents as low as 0.45 A are projected. Based on experimentally obtained internal efficiency values from high-performance QCLs, slope efficiencies as high as 3.4 W/A are projected; thus, offering a solution for watt-range, single-lobe CW operation from SE, mid-infrared QCLs.« less

Hybrid catadioptric system for advanced optical cavity velocimetry

DOEpatents

Frayer, Daniel K.

2018-02-06

A probe including reflector is disclosed to measure the velocity distribution of a moving surface along many lines of sight. Laser light, directed to the surface by the probe and then reflected back from the surface, is Doppler shifted by the moving surface, collected into probe, and then directed to detection equipment through optic fibers. The received light is mixed with reference laser light and using photonic Doppler velocimetry, a continuous time record of the surface movement is obtained. An array of single-mode optical fibers provides an optic signal to one or more lens groups and a reflector, such as a parabolic reflector having a mirrored interior surface.

Proposed suitable electron reflector layer materials for thin-film CuIn1-xGaxSe2 solar cells

NASA Astrophysics Data System (ADS)

Sharbati, Samaneh; Gharibshahian, Iman; Orouji, Ali A.

2018-01-01

This paper investigates the electrical properties of electron reflector layer to survey materials as an electron reflector (ER) for chalcopyrite CuInGaSe solar cells. The purpose is optimizing the conduction-band and valence-band offsets at ER layer/CIGS junction that can effectively reduce the electron recombination near the back contact. In this work, an initial device model based on an experimental solar cell is established, then the properties of a solar cell with electron reflector layer are physically analyzed. The electron reflector layer numerically applied to baseline model of thin-film CIGS cell fabricated by ZSW (efficiency = 20.3%). The improvement of efficiency is achievable by electron reflector layer materials with Eg > 1.3 eV and -0.3 < Δχ < 0.7, depends on bandgap. Our simulations examine various electron reflector layer materials and conclude the most suitable electron reflector layer for this real CIGS solar cells. ZnSnP2, CdSiAs2, GaAs, CdTe, Cu2ZnSnS4, InP, CuO, Pb10Ag3Sb11S28, CuIn5S8, SnS, PbCuSbS3, Cu3AsS4 as well as CuIn1-xGaxSe (x > 0.5) are efficient electron reflector layer materials, so the potential improvement in efficiency obtained relative gain of 5%.

Characteristics of several NIR tuneable diode lasers for spectroscopic based gas sensing: a comparison.

PubMed

Weldon, Vincent; McInerney, David; Phelan, Richard; Lynch, Michael; Donegan, John

2006-04-01

Tuneable laser diodes were characterized and compared for use as tuneable sources in gas absorption spectroscopy. Specifically, the characteristics of monolithic widely tuneable single frequency lasers, such as sampled grating distributed Bragg reflector laser and modulated grating Y-branch laser diodes, recently developed for optical communications, with operating wavelengths in the 1,520 nm

Miniaturized imaging spectrometer based on Fabry-Perot MOEMS filters and HgCdTe infrared focal plane arrays

NASA Astrophysics Data System (ADS)

Velicu, S.; Buurma, C.; Bergeson, J. D.; Kim, Tae Sung; Kubby, J.; Gupta, N.

2014-05-01

Imaging spectrometry can be utilized in the midwave infrared (MWIR) and long wave infrared (LWIR) bands to detect, identify and map complex chemical agents based on their rotational and vibrational emission spectra. Hyperspectral datasets are typically obtained using grating or Fourier transform spectrometers to separate the incoming light into spectral bands. At present, these spectrometers are large, cumbersome, slow and expensive, and their resolution is limited by bulky mechanical components such as mirrors and gratings. As such, low-cost, miniaturized imaging spectrometers are of great interest. Microfabrication of micro-electro-mechanicalsystems (MEMS)-based components opens the door for producing low-cost, reliable optical systems. We present here our work on developing a miniaturized IR imaging spectrometer by coupling a mercury cadmium telluride (HgCdTe)-based infrared focal plane array (FPA) with a MEMS-based Fabry-Perot filter (FPF). The two membranes are fabricated from silicon-oninsulator (SOI) wafers using bulk micromachining technology. The fixed membrane is a standard silicon membrane, fabricated using back etching processes. The movable membrane is implemented as an X-beam structure to improve mechanical stability. The geometries of the distributed Bragg reflector (DBR)-based tunable FPFs are modeled to achieve the desired spectral resolution and wavelength range. Additionally, acceptable fabrication tolerances are determined by modeling the spectral performance of the FPFs as a function of DBR surface roughness and membrane curvature. These fabrication non-idealities are then mitigated by developing an optimized DBR process flow yielding high-performance FPF cavities. Zinc Sulfide (ZnS) and Germanium (Ge) are chosen as the low and the high index materials, respectively, and are deposited using an electron beam process. Simulations are presented showing the impact of these changes and non-idealities in both a device and systems level.

Experimental Modal Analysis and Dynaic Strain Fiber Bragg Gratings for Structural Health Monitoring of Composite Aerospace Structures

NASA Astrophysics Data System (ADS)

Panopoulou, A.; Fransen, S.; Gomez Molinero, V.; Kostopoulos, V.

2012-07-01

The objective of this work is to develop a new structural health monitoring system for composite aerospace structures based on dynamic response strain measurements and experimental modal analysis techniques. Fibre Bragg Grating (FBG) optical sensors were used for monitoring the dynamic response of the composite structure. The structural dynamic behaviour has been numerically simulated and experimentally verified by means of vibration testing. The hypothesis of all vibration tests was that actual damage in composites reduces their stiffness and produces the same result as mass increase produces. Thus, damage was simulated by slightly varying locally the mass of the structure at different zones. Experimental modal analysis based on the strain responses was conducted and the extracted strain mode shapes were the input for the damage detection expert system. A feed-forward back propagation neural network was the core of the damage detection system. The features-input to the neural network consisted of the strain mode shapes, extracted from the experimental modal analysis. Dedicated training and validation activities were carried out based on the experimental results. The system showed high reliability, confirmed by the ability of the neural network to recognize the size and the position of damage on the structure. The experiments were performed on a real structure i.e. a lightweight antenna sub- reflector, manufactured and tested at EADS CASA ESPACIO. An integrated FBG sensor network, based on the advantage of multiplexing, was mounted on the structure with optimum topology. Numerical simulation of both structures was used as a support tool at all the steps of the work. Potential applications for the proposed system are during ground qualification extensive tests of space structures and during the mission as modal analysis tool on board, being able via the FBG responses to identify a potential failure.

A figure control sensor for the Large Deployable Reflector (LDR)

NASA Technical Reports Server (NTRS)

Bartman, R.; Dubovitsky, S.

1988-01-01

A sensing and control system is required to maintain high optical figure quality in a segmented reflector. Upon detecting a deviation of the segmented surface from its ideal form, the system drives segment mounted actuators to realign the individual segments and thereby return the surface to its intended figure. When the reflector is in use, a set of figure sensors will determine positions of a number of points on the back surface of each of the reflector's segments, each sensor being assigned to a single point. By measuring the positional deviations of these points from previously established nominal values, the figure sensors provide the control system with the information required to maintain the reflector's optical figure. The optical lever, multiple wavelength interferometer, and electronic capacitive sensor, the most promising technologies for the development of the figure sensor, are illustrated. It is concluded that to select a particular implementation of the figure sensors, performance requirement will be refined and relevant technologies investigated further.

DBR and DFB Lasers in Neodymium- and Ytterbium-Doped Photothermorefractive Glasses

NASA Technical Reports Server (NTRS)

Ryasnyanskiy, Aleksandr; Vorobiev, N.; Smirnov, V.; Lumeau, J.; Glebov, A.; Mokhun, O..; Spiegelberg, Ch.; Krainak, Michael A.; Glebov, A.; Glebov, L.

2014-01-01

The first demonstration, to the best of our knowledge, of distributed Bragg reflector (DBR) and monolithic distributed feedback (DFB) lasers in photothermorefractive glass doped with rare-earth ions is reported. The lasers were produced by incorporation of the volume Bragg gratings into the laser gain elements. A monolithic single-frequency solid-state laser with a line width of 250 kHz and output power of 150 mW at 1066 nm is demonstrated.

Chirped circular dielectric gratings for near-unity collection efficiency from quantum emitters in bulk diamond

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

Zheng, Jiabao; Liapis, Andreas C.; Chen, Edward H.

Effcient collection of fluorescence from nitrogen vacancy (NV) centers in diamond underlies the spin-dependent optical read-out that is necessary for quantum information processing and enhanced sensing applications. The optical collection effciency from NVs within diamond substrates is limited primarily due to the high refractive index of diamond and the non-directional dipole emission. Here we introduce a light collection strategy based on chirped, circular dielectric gratings that can be fabricated on a bulk diamond substrate to redirect an emitter’s far-field radiation pattern. Using a genetic optimization algorithm, these grating designs achieve 98.9% collection effciency for the NV zero-phonon emission line, collectedmore » from the back surface of the diamond with an objective of aperture 0.9. Across the broadband emission spectrum of the NV (600-800 nm), the chirped grating achieves 82.2% collection e ciency into a numerical aperture of 1.42, corresponding to an oil immersion objective again on the back side of the diamond. Our proposed bulk-dielectric grating structures are applicable to other optically active solid state quantum emitters in high index host materials.« less

Chirped circular dielectric gratings for near-unity collection efficiency from quantum emitters in bulk diamond

DOE PAGES

Zheng, Jiabao; Liapis, Andreas C.; Chen, Edward H.; ...

2017-12-13

Effcient collection of fluorescence from nitrogen vacancy (NV) centers in diamond underlies the spin-dependent optical read-out that is necessary for quantum information processing and enhanced sensing applications. The optical collection effciency from NVs within diamond substrates is limited primarily due to the high refractive index of diamond and the non-directional dipole emission. Here we introduce a light collection strategy based on chirped, circular dielectric gratings that can be fabricated on a bulk diamond substrate to redirect an emitter’s far-field radiation pattern. Using a genetic optimization algorithm, these grating designs achieve 98.9% collection effciency for the NV zero-phonon emission line, collectedmore » from the back surface of the diamond with an objective of aperture 0.9. Across the broadband emission spectrum of the NV (600-800 nm), the chirped grating achieves 82.2% collection e ciency into a numerical aperture of 1.42, corresponding to an oil immersion objective again on the back side of the diamond. Our proposed bulk-dielectric grating structures are applicable to other optically active solid state quantum emitters in high index host materials.« less

Systematic analysis of diffuse rear reflectors for enhanced light trapping in silicon solar cells

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

Pfeffer, Florian; Eisenlohr, Johannes; Basch, Angelika

Simple diffuse rear reflectors can enhance the light path length of weakly absorbed near infrared light in silicon solar cells and set a benchmark for more complex and expensive light trapping structures like dielectric gratings or plasmonic particles. We analyzed such simple diffuse rear reflectors systematically by optical and electrical measurements. We applied white paint, TiO 2 nanoparticles, white backsheets and a silver mirror to bifacial silicon solar cells and measured the enhancement of the external quantum efficiency for three different solar cell geometries: planar front and rear side, textured front and planar rear side, and textured front and rearmore » side. We showed that an air-gap between the solar cell and the reflector decreases the absorption enhancement significantly, thus white paint and TiO 2 nanoparticles directly applied to the rear cell surface lead to the highest short circuit current density enhancements. Here, the short circuit current density gains for a 200 um thick planar solar cell reached up to 1.8 mA/cm 2, compared to a non-reflecting black rear side and up to 0.8 mA/cm 2 compared to a high-quality silver mirror rear side. For solar cells with textured front side the short circuit current density gains are in the range between 0.5 and 1.0 mA/cm 2 compared to a non-reflecting black rear side and do not significantly depend on the angular characteristic of the rear side reflector but mainly on its absolute reflectance.« less

Systematic analysis of diffuse rear reflectors for enhanced light trapping in silicon solar cells

DOE PAGES

Pfeffer, Florian; Eisenlohr, Johannes; Basch, Angelika; ...

2016-04-08

Simple diffuse rear reflectors can enhance the light path length of weakly absorbed near infrared light in silicon solar cells and set a benchmark for more complex and expensive light trapping structures like dielectric gratings or plasmonic particles. We analyzed such simple diffuse rear reflectors systematically by optical and electrical measurements. We applied white paint, TiO 2 nanoparticles, white backsheets and a silver mirror to bifacial silicon solar cells and measured the enhancement of the external quantum efficiency for three different solar cell geometries: planar front and rear side, textured front and planar rear side, and textured front and rearmore » side. We showed that an air-gap between the solar cell and the reflector decreases the absorption enhancement significantly, thus white paint and TiO 2 nanoparticles directly applied to the rear cell surface lead to the highest short circuit current density enhancements. Here, the short circuit current density gains for a 200 um thick planar solar cell reached up to 1.8 mA/cm 2, compared to a non-reflecting black rear side and up to 0.8 mA/cm 2 compared to a high-quality silver mirror rear side. For solar cells with textured front side the short circuit current density gains are in the range between 0.5 and 1.0 mA/cm 2 compared to a non-reflecting black rear side and do not significantly depend on the angular characteristic of the rear side reflector but mainly on its absolute reflectance.« less

Multiperiod-grating surface-emitting lasers

NASA Technical Reports Server (NTRS)

Lang, Robert J. (Inventor)

1992-01-01

Surface-emitting distributed feedback (DFB) lasers are disclosed with hybrid gratings. A first-order grating is provided at one or both ends of the active region of the laser for retroreflection of light back into the active region, and a second-order or nonresonant grating is provided at the opposite end for coupling light out perpendicular to the surfaces of the laser or in some other selected direction. The gratings may be curved to focus light retroreflected into the active region and to focus light coupled out to a point. When so focused to a point, the DFB laser may be part of a monolithic read head for a laser recorded disk, or an optical coupler into an optical fiber.

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.

All optical mode controllable Er-doped random fiber laser with distributed Bragg gratings.

PubMed

Zhang, W L; Ma, R; Tang, C H; Rao, Y J; Zeng, X P; Yang, Z J; Wang, Z N; Gong, Y; Wang, Y S

2015-07-01

An all-optical method to control the lasing modes of Er-doped random fiber lasers (RFLs) is proposed and demonstrated. In the RFL, an Er-doped fiber (EDF) recoded with randomly separated fiber Bragg gratings (FBG) is used as the gain medium and randomly distributed reflectors, as well as the controllable element. By combining random feedback of the FBG array and Fresnel feedback of a cleaved fiber end, multi-mode coherent random lasing is obtained with a threshold of 14 mW and power efficiency of 14.4%. Moreover, a laterally-injected control light is used to induce local gain perturbation, providing additional gain for certain random resonance modes. As a result, active mode selection of the RFL is realized by changing locations of the laser cavity that is exposed to the control light.

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

Theoretical investigation and optimization of fiber grating based slow light

NASA Astrophysics Data System (ADS)

Wang, Qi; Wang, Peng; Du, Chao; Li, Jin; Hu, Haifeng; Zhao, Yong

2017-07-01

On the edge of bandgap in a fiber grating, narrow peaks of high transimittivity exist at frequencies where light interferes constructively in the forward direction. In the vicinity of these transmittivity peaks, light reflects back and forth numerous times across the periodic structure and experiences a large group delay. In order to generate the extremely slow light in fiber grating for applications, in this research, the common sense of formation mechanism of slow light in fiber grating was introduced. The means of producing and operating fiber grating was studied to support structural slow light with a group index that can be in principle as high as several thousand. The simulations proceeded by transfer matrix method in the paper were presented to elucidate how the fiber grating parameters effect group refractive index. The main parameters that need to be optimized include grating length, refractive index contrast, grating period, loss coefficient, chirp and apodization functions, those can influence fiber grating characteristics.

Integration of GaAs-based VCSEL array on SiN platform with HCG reflectors for WDM applications

NASA Astrophysics Data System (ADS)

Kumari, Sulakshna; Gustavsson, Johan S.; Wang, Ruijun; Haglund, Emanuel P.; Westbergh, Petter; Sanchez, Dorian; Haglund, Erik; Haglund, Åsa; Bengtsson, Jörgen; Le Thomas, Nicolas; Roelkens, Gunther; Larsson, Anders; Baets, Roel

2015-02-01

We present a GaAs-based VCSEL structure, BCB bonded to a Si3N4 waveguide circuit, where one DBR is substituted by a free-standing Si3N4 high-contrast-grating (HCG) reflector realized in the Si3N4 waveguide layer. This design enables solutions for on-chip spectroscopic sensing, and the dense integration of 850-nm WDM data communication transmitters where individual channel wavelengths are set by varying the HCG parameters. RCWA shows that a 300nm-thick Si3N4 HCG with 800nm period and 40% duty cycle reflects strongly (<99%) over a 75nm wavelength range around 850nm. A design with a standing-optical-field minimum at the III-V/airgap interface maximizes the HCG's influence on the VCSEL wavelength, allowing for a 15-nm-wide wavelength setting range with low threshold gain (<1000 cm-1).

New Martian climate constraints from radar reflectivity within the north polar layered deposits

NASA Astrophysics Data System (ADS)

Lalich, D. E.; Holt, J. W.

2017-01-01

The north polar layered deposits (NPLD) of Mars represent a global climate record reaching back millions of years, potentially recorded in visible layers and radar reflectors. However, little is known of the specific link between those layers, reflectors, and the global climate. To test the hypothesis that reflectors are caused by thick and indurated layers known as "marker beds," the reflectivity of three reflectors was measured, mapped, and compared to a reflectivity model. The measured reflectivities match the model and show a strong sensitivity to layer thickness, implying that radar reflectivity may be used as a proxy for short-term accumulation patterns and that regional climate plays a strong role in layer thickness variations. Comparisons to an orbitally forced NPLD accumulation model show a strong correlation with predicted marker bed formation, but dust content is higher than expected, implying a stronger role for dust in Mars polar climate than previously thought.

FIR and sub-mm direct detection spectrometers for spaceborne astronomy

NASA Astrophysics Data System (ADS)

Wijnbergen, Jan J.; de Graauw, Thijs

1990-12-01

Candidate spaceborne sub-mm instrumentation proposed for space projects with large passively cooled telescopes are reviewed. Grating instruments and Fourier transform spectroscopy (FTS) spectrometers are discussed. Particular attention is given to imaging Fabry-Perot spectrometers. The special needs of the Large Deployable Reflector (LDR) and for the Far InfraRed Space Telescope (FIRST) missions in this area are outlined. Possible Fabry-Perot spectrometer setups are diagrammed and outlined. The use of spherical and multiplex Fabry-Perot spectrometers is discussed.

Multistage Passive Cooler for Spaceborne Instruments

NASA Technical Reports Server (NTRS)

Rodriquez, Jose I.

2007-01-01

A document describes a three-stage passive radiative cooler for a cryogenic spectrometer to be launched into a low orbit around the Moon. This cooler is relatively lightweight and compact, and its basic design is scalable and otherwise adaptable to other applications in which there are requirements for cooling instrumentation in orbit about planets. The cooler includes multiple lightweight flat radiator blades alternating with cylindrical parabolic infrared reflectors. The radiator blades are oriented at an angle chosen to prevent infrared loading from the Moon limb at the intended orbital altitude and attitude. The reflectors are shaped and oriented to position their foci outside the radiator surfaces. There are six radiator-blade/reflector pairs - two pairs for each stage of cooling. The radiator blades and reflectors are coated on their front and back surfaces with materials having various infrared emissivities, infrared reflectivities, and solar reflectivities so as to maximize infrared radiation to cold outer space and minimize inadvertent solar heating. The radiator blades and reflectors are held in place by a lightweight support structure, the components of which are designed to satisfy a complex combination of thermal and mechanical requirements.

Double-loop frequency selective surfaces for multi frequency division multiplexing in a dual reflector antenna

NASA Technical Reports Server (NTRS)

Wu, Te-Kao (Inventor)

1994-01-01

A multireflector antenna utilizes a frequency-selective surface (FSS) in a subreflector to allow signals in two different RF bands to be selectively reflected back into a main reflector and to allow signals in other RF bands to be transmitted through it to the main reflector for primary focus transmission. A first approach requires only one FSS at the subreflector which may be an array of double-square-loop conductive elements. A second approach uses two FSS's at the subreflector which may be an array of either double-square-loop (DSL) or double-ring (DR). In the case of DR elements, they may be advantageously arranged in a triangular array instead of the rectangular array for the DSL elements.

Evaluation of cable tension sensors of FAST reflector from the perspective of EMI

NASA Astrophysics Data System (ADS)

Zhu, Ming; Wang, Qiming; Egan, Dennis; Wu, Mingchang; Sun, Xiao

2016-06-01

The active reflector of FAST (five-hundred-meter aperture spherical radio telescope) is supported by a ring beam and a cable-net structure, in which nodes are actively controlled to form series of real-time paraboloids. To ensure the security and stability of the supporting structure, tension must be monitored for some typical cables. Considering the stringent requirements in accuracy and long-term stability, magnetic flux sensor, vibrating wire strain gauge and fiber bragg grating strain gauge are screened for the cable tension monitoring of the supporting cable-net. Specifically, receivers of radio telescopes have strict restriction on electro magnetic interference (EMI) or radio frequency interference (RFI). These three types of sensors are evaluated from the view of EMI/RFI. Firstly, these fundamentals are theoretically analyzed. Secondly, typical sensor signals are collected in the time and analyzed in the frequency domain, which shows the characteristic in the frequency domain. Finally, typical sensors are tested in an anechoic chamber to get the EMI levels. Theoretical analysis shows that Fiber Bragg Grating strain gauge itself will not lead to EMI/RFI. According to GJB151A, frequency domain analysis and test results show that for the vibrating wire strain gauge and magnetic flux sensor themselves, testable EMI/RFI levels are typically below the background noise of the anechoic chamber. FAST finally choses these three sensors as the monitoring sensors of its cable tension. The proposed study is also a reference to the monitoring equipment selection of other radio telescopes and large structures.

Narrow-line, cw orange light generation in a diode-pumped Nd:YVO4 laser using volume Bragg gratings.

PubMed

Chen, Y L; Chen, W W; Du, C E; Chang, W K; Wang, J L; Chung, T Y; Chen, Y H

2009-12-07

We report on the demonstration of a narrow-line, cw orange 593-nm laser achieved via intracavity sum-frequency generation (SFG) of a diode-pumped dual-wavelength (1064 and 1342 nm) Nd:YVO(4) laser using two volume Bragg grating (VBG) reflectors. At diode pump power of up to 3.6 W, the 593-nm intracavity SFG laser radiates at the single longitudinal mode of spectral linewidth as narrow as approximately 15 MHz. More than 23-mW single-longitudinal-mode or 40-mW, <8.5-GHz (10-pm) linewidth (at 4.2-W diode pump power) 593-nm orange lights can be obtained from this compact laser system. Spectral tuning of the orange light was performed via the temperature tuning of the two VBGs in this system, achieving an effective tuning rate of ~5 pm/degrees C.

Total absorption peak by use of a rigid frame porous layer backed by a rigid multi-irregularities grating.

PubMed

Groby, J-P; Lauriks, W; Vigran, T E

2010-05-01

The acoustic properties of a low resistivity porous layer backed by a rigid plate containing periodic rectangular irregularities, creating a multicomponent diffraction gratings, are investigated. Numerical and experimental results show that the structure possesses a total absorption peak at the frequency of the modified mode of the layer, when designed as proposed in the article. These results are explained by an analysis of the acoustic response of the whole structure and especially by the modal analysis of the configuration. When more than one irregularity per spatial period is considered, additional higher frequency peaks are observed.

Plasmonic silicon solar cells: impact of material quality and geometry.

PubMed

Pahud, Celine; Isabella, Olindo; Naqavi, Ali; Haug, Franz-Josef; Zeman, Miro; Herzig, Hans Peter; Ballif, Christophe

2013-09-09

We study n-i-p amorphous silicon solar cells with light-scattering nanoparticles in the back reflector. In one configuration, the particles are fully embedded in the zinc oxide buffer layer; In a second configuration, the particles are placed between the buffer layer and the flat back electrode. We use stencil lithography to produce the same periodic arrangement of the particles and we use the same solar cell structure on top, thus establishing a fair comparison between a novel plasmonic concept and its more traditional counterpart. Both approaches show strong resonances around 700 nm in the external quantum efficiency the position and intensity of which vary strongly with the nanoparticle shape. Moreover, disagreement between simulations and our experimental results suggests that the dielectric data of bulk silver do not correctly represent the reality. A better fit is obtained by introducing a porous interfacial layer between the silver and zinc oxide. Without the interfacial layer, e.g. by improved processing of the nanoparticles, our simulations show that the nanoparticles concept could outperform traditional back reflectors.

Effect of Rayleigh-scattering distributed feedback on multiwavelength Raman fiber laser generation.

PubMed

El-Taher, A E; Harper, P; Babin, S A; Churkin, D V; Podivilov, E V; Ania-Castanon, J D; Turitsyn, S K

2011-01-15

We experimentally demonstrate a Raman fiber laser based on multiple point-action fiber Bragg grating reflectors and distributed feedback via Rayleigh scattering in an ~22-km-long optical fiber. Twenty-two lasing lines with spacing of ~100 GHz (close to International Telecommunication Union grid) in the C band are generated at the watt level. In contrast to the normal cavity with competition between laser lines, the random distributed feedback cavity exhibits highly stable multiwavelength generation with a power-equalized uniform distribution, which is almost independent on power.

Narrow-band double-pass superluminescent diodes emitting at 1060 nm

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

Lobintsov, A A; Perevozchikov, M V; Shramenko, M V

2009-09-30

Experimental data are presented which show that double-pass superluminescent diodes (SLDs) with fibre Bragg grating (FBG) based spectrally selective external reflectors offer emission linewidths in the range 0.1-1.0 nm, i.e., one to two orders of magnitude narrower in comparison with conventional SLDs and considerably broader in comparison with single-frequency semiconductor lasers. Their optical power at the single-mode fibre output reaches 5.0-8.0 mW, and can be raised to 50 mW using a semiconductor optical amplifier. (lasers)

Stable multi-wavelength fiber lasers for temperature measurements using an optical loop mirror.

PubMed

Diaz, Silvia; Socorro, Abian Bentor; Martínez Manuel, Rodolfo; Fernandez, Ruben; Monasterio, Ioseba

2016-10-10

In this work, two novel stable multi-wavelength fiber laser configurations are proposed and demonstrated by using a spool of a single-mode fiber as an optical loop mirror and one or two fiber ring cavities, respectively. The lasers are comprised of fiber Bragg grating reflectors as the oscillation wavelength selecting filters. The influence of the length of the spool of fiber on the laser stability both in terms of wavelength and laser output power was investigated. An application for temperature measurement is also shown.

Temperature sensing through long period fiber gratings mechanically induced on tapered optical fibers.

PubMed

Pulido-Navarro, María Guadalupe; Escamilla-Ambrosio, Ponciano Jorge; Marrujo-García, Sigifredo; Álvarez-Chávez, José Alfredo; Martínez-Piñón, Fernando

2017-07-01

In this work the feasibility of employing two well-known techniques already used on designing optical fiber sensors is explored. The first technique employed involves monomode tapered fibers, which were fabricated using a taper machine designed, built, and implemented in our laboratory. This implementation greatly reduced the costs and fabrication time allowing us to produce the desired taper length and transmission conditions. The second technique used fiber Bragg gratings, which we decided to have mechanically induced and for that reason we devised and produced our own mechanical gratings with the help of a computer numerical control tool. This grating had to be fabricated with aluminum to withstand temperatures of up to 600°C. When light traveling through an optical fiber reaches a taper it couples into the cladding layer and comes back into the core when the taper ends. In the same manner, when the light encounters gratings in the fiber, it couples to the cladding modes, and when the gratings end, the light couples back into the core. For our experimentation, the tapering machine was programmed to fabricate single-mode tapers with 3 cm length, and the mechanically induced gratings characteristics were 5 cm length, and had a period of 500 μm and depth of the period of 300 μm. For the conducting tests, the tapered fiber is positioned in between two aluminum slabs, one grooved and the other plane. These two blocks accomplish the mechanically induced long period grating (LPG); the gratings on the grooved plaque are imprinted on the taper forming the period gratings. An optical spectrum analyzer is used to observe the changes on the transmission spectrum as the temperature varies from 20°C to 600°C. The resultant attenuation peak wavelength in the transmission spectrum shifts up to 8 nm, which is a higher shift compared to what has been reported using nontapered fibers. As the temperature increases there is no longer a shift, but there is significant power loss. Such a characteristic can be used as well for sensing applications.

Crustal structure and tectonics of the Hidaka Collision Zone, Hokkaido (Japan), revealed by vibroseis seismic reflection and gravity surveys

NASA Astrophysics Data System (ADS)

Arita, Kazunori; Ikawa, Takashi; Ito, Tanio; Yamamoto, Akihiko; Saito, Matsuhiko; Nishida, Yasunori; Satoh, Hideyuki; Kimura, Gaku; Watanabe, Teruo; Ikawa, Takeshi; Kuroda, Toru

1998-05-01

This study is the first integrated geological and geophysical investigation of the Hidaka Collision Zone in southern Central Hokkaido, Japan, which shows complex collision tectonics with a westward vergence. The Hidaka Collision Zone consists of the Idon'nappu Belt (IB), the Poroshiri Ophiolite Belt (POB) and the Hidaka Metamorphic Belt (HMB) with the Hidaka Belt from west to east. The POB (metamorphosed ophiolites) is overthrust by the HMB (steeply eastward-dipping palaeo-arc crust) along the Hidaka Main Thrust (HMT), and in turn, thrusts over the Idon'nappu Belt (melanges) along the Hidaka Western Thrust (HWT). Seismic reflection and gravity surveys along a 20-km-long traverse across the southern Hidaka Mountains revealed hitherto unknown crustal structures of the collision zone such as listric thrusts, back thrusts, frontal thrust-and-fold structures, and duplex structures. The main findings are as follows. (1) The HMT, which dips steeply at the surface, is a listric fault dipping gently at a depth of ˜7 km beneath the eastern end of the HMB, and cutting across the lithological boundaries and schistosity of the Hidaka metamorphic rocks. (2) A second reflector is detected 1 km below the HMT reflector. The intervening part between these two reflectors is inferred to be the POB, which is only little exposed at the surface. This inference is supported by the high positive Bouguer anomalies along the Hidaka Mountains. (3) The shallow portion of the IB at the front of the collision zone has a number of NNE-dipping reflectors, indicative of imbricated fold-and-thrust structures. (4) Subhorizontal reflectors at a depth of 14 km are recognized intermittently at both sides of the seismic profile. These reflectors may correspond to the velocity boundary (5.9-6.6 km/s) previously obtained from seismic refraction profiling in the northern Hidaka Mountains. (5) These crustal structures as well as the back thrust found in the eastern end of the traverse represent characteristics of collisional tectonics resulting from the two collisional events since the Early Tertiary.

Multisite silicon neural probes with integrated silicon nitride waveguides and gratings for optogenetic applications.

PubMed

Shim, Euijae; Chen, Yu; Masmanidis, Sotiris; Li, Mo

2016-03-04

Optimal optogenetic perturbation of brain circuit activity often requires light delivery in a precise spatial pattern that cannot be achieved with conventional optical fibers. We demonstrate an implantable silicon-based probe with a compact light delivery system, consisting of silicon nitride waveguides and grating couplers for out-of-plane light emission with high spatial resolution. 473 nm light is coupled into and guided in cm-long waveguide and emitted at the output grating coupler. Using the direct cut-back and out-scattering measurement techniques, the propagation optical loss of the waveguide is measured to be below 3 dB/cm. The grating couplers provide collimated light emission with sufficient irradiance for neural stimulation. Finally, a probe with multisite light delivery with three output grating emitters from a single laser input is demonstrated.

Optical simulations of organic light-emitting diodes through a combination of rigorous electromagnetic solvers and Monte Carlo ray-tracing methods

NASA Astrophysics Data System (ADS)

Bahl, Mayank; Zhou, Gui-Rong; Heller, Evan; Cassarly, William; Jiang, Mingming; Scarmozzino, Rob; Gregory, G. Groot

2014-09-01

Over the last two decades there has been extensive research done to improve the design of Organic Light Emitting Diodes (OLEDs) so as to enhance light extraction efficiency, improve beam shaping, and allow color tuning through techniques such as the use of patterned substrates, photonic crystal (PCs) gratings, back reflectors, surface texture, and phosphor down-conversion. Computational simulation has been an important tool for examining these increasingly complex designs. It has provided insights for improving OLED performance as a result of its ability to explore limitations, predict solutions, and demonstrate theoretical results. Depending upon the focus of the design and scale of the problem, simulations are carried out using rigorous electromagnetic (EM) wave optics based techniques, such as finite-difference time-domain (FDTD) and rigorous coupled wave analysis (RCWA), or through ray optics based technique such as Monte Carlo ray-tracing. The former are typically used for modeling nanostructures on the OLED die, and the latter for modeling encapsulating structures, die placement, back-reflection, and phosphor down-conversion. This paper presents the use of a mixed-level simulation approach which unifies the use of EM wave-level and ray-level tools. This approach uses rigorous EM wave based tools to characterize the nanostructured die and generate both a Bidirectional Scattering Distribution function (BSDF) and a far-field angular intensity distribution. These characteristics are then incorporated into the ray-tracing simulator to obtain the overall performance. Such mixed-level approach allows for comprehensive modeling of the optical characteristic of OLEDs and can potentially lead to more accurate performance than that from individual modeling tools alone.

High-reflectivity high-contrast grating focusing reflector on silicon-on-insulator wafer

NASA Astrophysics Data System (ADS)

Fang, Wenjing; Huang, Yongqing; Duan, Xiaofeng; Liu, Kai; Fei, Jiarui; Ren, Xiaomin

2016-11-01

A high-contrast grating (HCG) focusing reflector providing phase front control of reflected light and high reflectivity is proposed and fabricated. Basic design rules to engineer this category of structures are given in detail. A 1550 nm TM polarized incident light of 11.86 mm in focal length and 0.8320 in reflectivity is obtained in experiment. The wavelength dependence of the fabricated HCGs from 1530 nm to 1580 nm is also tested. The test results show that the focal length is in the range of 11.81-12 mm, which is close to the designed focal length of 15 mm. The reflectivity is almost above 0.56 within a bandwidth of 50 nm. At a distance of 11.86 mm, the light is focused to a round spot with the highest concentration, which is much smaller than the size of the incident beam. The FWHM of the reflected light beam decreases to 120 nm, and the intensity increases to 1.18. Project supported by the National Natural Science Foundation of China (Grant Nos. 61274044, 61574019 and 61020106007), the National Basic Research Program of China (Grant No. 2010CB327600), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20130005130001), the Natural Science Foundation of Beijing, China (Grant No. 4132069), the Key International Science and Technology Cooperation Project of China (Grant No. 2011RR000100), the 111 Project of China (Grant No. B07005), and the Program for Changjiang Scholars and Innovative Research Team in Universities of China (Grant No. IRT0609).

NEUTRONIC REACTOR

DOEpatents

Hurwitz, H. Jr.; Brooks, H.; Mannal, C.; Payne, J.H.; Luebke, E.A.

1959-03-24

A reactor of the heterogeneous, liquid cooled type is described. This reactor is comprised of a central region of a plurality of vertically disposed elongated tubes surrounded by a region of moderator material. The central region is comprised of a central core surrounded by a reflector region which is surrounded by a fast neutron absorber region, which in turn is surrounded by a slow neutron absorber region. Liquid sodium is used as the primary coolant and circulates through the core which contains the fuel elements. Control of the reactor is accomplished by varying the ability of the reflector region to reflect neutrons back into the core of the reactor. For this purpose the reflector is comprised of moderator and control elements having varying effects on reactivity, the control elements being arranged and actuated by groups to give regulation, shim, and safety control.

Coupling and Switching in Optically Resonant Periodic Electrode Structures

NASA Astrophysics Data System (ADS)

Bieber, Amy Erica

This thesis describes coupling and switching of optical radiation using metal-semiconductor-metal (MSM) structures, specifically in a metal-on-silicon waveguide configuration. The structures which are the subject of this research have the special advantage of being VLSI -compatible; this is very important for the ultimate acceptance of any integrated optoelectronics technology by the mainstream semiconductor community. To date, research efforts in VLSI electronics, MSM detectors, metal devices, and optical switching have existed as separate entities with decidedly different goals. This work attempts to unite these specialties; an interdigitated array of metal fingers on a silicon waveguide allows for (1) fabrication processes which are well-understood and compatible with current or next-generation semiconductor manufacturing standards, (2) electrical bias capability which can potentially provide modulation, tuning, and enhanced speed, and (3) potentially efficient waveguide coupling which takes advantage of TM coupling. The latter two items are made possible by the use of metallic gratings, which sets this work apart from previous optical switching results. This MSM structure represents an important step in uniting four vital technologies which, taken together, can lead to switching performance and operational flexibility which could substantially advance the capabilities of current optoelectronic devices. Three different designs were successfully used to examine modulation and optical switching based upon nonlinear interactions in the silicon waveguide. First, a traditional Bragg reflector design with input and output couplers on either side was used to observe switching of nanosecond-regime Nd:YAG pulses. This structure was thermally tuned to obtain a variety of switching dynamics. Next, a phase-shift was incorporated into the Bragg reflector, and again thermally-tunable switching dynamics were observed, but with the added advantage of a reduction in the energy requirements for optical switching. Finally, the roles of the coupler and Bragg reflector were combined in a normal -incidence structure which exhibited nonlinear reflectivity modulation. This has not only been the first experimental demonstration of optical switching in a metal-semiconductor waveguide structure, but, to our knowledge, one of the first such demonstrations using a nonlinear phase-shifted or normal incidence grating of any kind.

Combined raman and IR fiber-based sensor for gas detection

DOEpatents

Carter, Jerry C; Chan, James W; Trebes, James E; Angel, Stanley M; Mizaikoff, Boris

2014-06-24

A double-pass fiber-optic based spectroscopic gas sensor delivers Raman excitation light and infrared light to a hollow structure, such as a hollow fiber waveguide, that contains a gas sample of interest. A retro-reflector is placed at the end of this hollow structure to send the light back through the waveguide where the light is detected at the same end as the light source. This double pass retro reflector design increases the interaction path length of the light and the gas sample, and also reduces the form factor of the hollow structure.

Photonic generation of ultra-wideband signals by direct current modulation on SOA section of an SOA-integrated SGDBR laser.

PubMed

Lv, Hui; Yu, Yonglin; Shu, Tan; Huang, Dexiu; Jiang, Shan; Barry, Liam P

2010-03-29

Photonic ultra-wideband (UWB) pulses are generated by direct current modulation of a semiconductor optical amplifier (SOA) section of an SOA-integrated sampled grating distributed Bragg reflector (SGDBR) laser. Modulation responses of the SOA section of the laser are first simulated with a microwave equivalent circuit model. Simulated results show a resonance behavior indicating the possibility to generate UWB signals with complex shapes in the time domain. The UWB pulse generation is then experimentally demonstrated for different selected wavelength channels with an SOA-integrated SGDBR laser.

Multiplexing curvature sensors using fibre segment interferometry for lateral vibration measurements

NASA Astrophysics Data System (ADS)

Kissinger, Thomas; Chehura, Edmon; James, Stephen W.; Tatam, Ralph P.

2017-04-01

Dynamic fibre-optic curvature sensing is demonstrated by interrogating chains of fibre segments, separated by broadband Bragg grating reflectors, using range-resolved interferometry (RRI). Four fibre strings, containing four fibre segments each of gauge length 20 cm, are attached to the opposing sides of a support structure and the resulting differential strain measurements allow inference of lateral displacements of a cantilever test object. Dynamic tip displacement resolutions in the micrometre range at an interferometric bandwidth of 21 kHz demonstrate the suitability of this approach for highly sensitive and cost-effective fibre-optic directional vibration measurements of smart structures.

Remote coding scheme based on waveguide Bragg grating in PLC splitter chip for PON monitoring.

PubMed

Zhang, Xuan; Lu, Fengjun; Chen, Si; Zhao, Xingqun; Zhu, Min; Sun, Xiaohan

2016-03-07

A distributing arranged waveguide Bragg gratings (WBGs) in PLC splitter chip based remote coding scheme is proposed and analyzed for passive optical network (PON) monitoring, by which the management system can identify each drop fiber link through the same reflector in the terminal of each optical network unit, even though there exist several equidistant users. The corresponding coding and capacity models are respectively established and investigated so that we can obtain a minimum number of the WBGs needed under the condition of the distributed structure. Signal-to-noise ratio (SNR) model related to the number of equidistant users is also developed to extend the analyses for the overall performance of the system. Simulation results show the proposed scheme is feasible and allow the monitoring of a 64 users PON with SNR range of 7.5~10.6dB. The scheme can solve some of difficulties of construction site at the lower user cost for PON system.

Bend measurement using an etched fiber incorporating a fiber Bragg grating.

PubMed

Rauf, Abdul; Zhao, Jianlin; Jiang, Biqiang; Jiang, Yajun; Jiang, Wei

2013-01-15

A fiber Bragg grating (FBG) based bend measurement method using an etched fiber is proposed that utilizes the coupling of the core mode to the cladding and radiation modes at the bending region. An etching region of 99 µm diameter that serves as bend sensing head is achieved at 10 mm upstream the FBG through processing in 40% hydrofluoric acid, while the FBG acts as a narrowband reflector to enhance the sensitivity. The power variation curves are obtained for a wide range of bend angles, but the performance is limited due to the presence of the loss peaks. The sensing response is improved by immersing the etching region in a refractive index matching gel. The results are analyzed by using curve fitting formulas and are in good agreement. A large dynamic range of -27° to +27° and sensitivity of 0.43 dBm/deg is achieved, which can be enhanced by reducing the etched diameter.

AlGaAs phased array laser for optical communications

NASA Technical Reports Server (NTRS)

Carlson, N. W.

1989-01-01

Phased locked arrays of multiple AlGaAs diode laser emitters were investigated both in edge emitting and surface emitting configurations. CSP edge emitter structures, coupled by either evanescent waves or Y-guides, could not achieve the required powers (greater than or similar to 500 mW) while maintaining a diffraction limited, single lobed output beam. Indeed, although the diffraction limit was achieved in this type of device, it was at low powers and in the double lobed radiation pattern characteristic of out-of-phase coupling. Grating surface emitting (GSE) arrays were, therefore, investigated with more promising results. The incorporation of second order gratings in distribute Bragg reflector (DBR) structures allows surface emission, and can be configured to allow injection locking and lateral coupling to populate 2-D arrays that should be able to reach power levels commensurate with the needs of high performance, free space optical communications levels. Also, a new amplitude modulation scheme was developed for GSE array operation.

3  ×  3 optical switch by exploiting vortex beam emitters based on silicon microrings with superimposed gratings.

PubMed

Scaffardi, Mirco; Malik, Muhammad N; Lazzeri, Emma; Klitis, Charalambos; Meriggi, Laura; Zhang, Ning; Sorel, Marc; Bogoni, Antonella

2017-10-01

A silicon-on-insulator microring with three superimposed gratings is proposed and characterized as a device enabling 3×3 optical switching based on orbital angular momentum and wavelength as switching domains. Measurements show penalties with respect to the back-to-back of <1  dB at a bit error rate of 10 -9 for OOK traffic up to 20 Gbaud. Different switch configuration cases are implemented, with measured power penalty variations of less than 0.5 dB at bit error rates of 10 -9 . An analysis is also carried out to highlight the dependence of the number of switch ports on the design parameters of the multigrating microring.

Apparent bandgap shift in the internal quantum efficiency for solar cells with back reflectors

NASA Astrophysics Data System (ADS)

Steiner, M. A.; Perl, E. E.; Geisz, J. F.; Friedman, D. J.; Jain, N.; Levi, D.; Horner, G.

2017-04-01

We demonstrate that in solar cells with highly reflective back mirrors, the measured internal quantum efficiency exhibits a shift in bandgap relative to the measured external quantum efficiency. The shift arises from the fact that the measured reflectance at the front surface includes a superposition of waves reflecting from the front and back surfaces. We quantify the magnitude of the apparent shift and discuss the errors that can result in determination of quantities such as the photocurrent. Because of this apparent shift, it is important the bandgap be determined from the external quantum efficiency.

Apparent bandgap shift in the internal quantum efficiency for solar cells with back reflectors

DOE PAGES

Steiner, Myles A.; Perl, E. E.; Geisz, J. F.; ...

2017-04-28

Here, we demonstrate that in solar cells with highly reflective back mirrors, the measured internal quantum efficiency exhibits a shift in bandgap relative to the measured external quantum efficiency. The shift arises from the fact that the measured reflectance at the front surface includes a superposition of waves reflecting from the front and back surfaces. We quantify the magnitude of the apparent shift and discuss the errors that can result in determination of quantities such as the photocurrent. Because of this apparent shift, it is important that the bandgap be determined from the external quantum efficiency.

A magneto-sensitive skin for robots in space

NASA Technical Reports Server (NTRS)

Chauhan, D. S.; Dehoff, P. H.

1991-01-01

The development of a robot arm proximity sensing skin that can sense intruding objects is described. The purpose of the sensor would be to prevent the robot from colliding with objects in space including human beings. Eventually a tri-mode system in envisioned including proximity, tactile, and thermal. To date the primary emphasis was on the proximity sensor which evolved from one based on magneto-inductive principles to the current design which is based on a capacitive-reflector system. The capacitive sensing element, backed by a reflector driven at the same voltage and in phase with the sensor, is used to reflect field lines away from the grounded robot toward the intruding object. This results in an increased sensing range of up to 12 in. with the reflector on compared with only 1 in. with it off. It is believed that this design advances the state-of-the-art in capacitive sensor performance.

Integrated high-order surface diffraction gratings for diode lasers

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

Zolotarev, V V; Leshko, A Yu; Pikhtin, N A

2015-12-31

High-order surface diffraction gratings acting as a distributed Bragg reflector (DBR) in mesa stripe semiconductor lasers (λ = 1030 nm) have been studied theoretically and experimentally. Higher order interfering radiation modes (IRMs), which propagate off the plane of the waveguide, have been shown to have a crucial effect on the reflection and transmission spectra of the DBR. The decrease in the reflectivity of the DBR in response to the increase in the diffraction efficiency of these modes may reach 80% and more. According to theoretical analysis results, the intensity of the higher order IRMs is determined by the geometry ofmore » the DBR groove profile. Experimental data demonstrate that the noncavity modes are responsible for parasitic light leakage losses in the laser cavity. It has been shown that, in the case of nonoptimal geometry of the grating groove profile, the overall external differential quantum efficiency of the parasitic laser emission may exceed 45%, which is more than half of the laser output power. The optimal geometry of the DBR groove profile is trapezoidal, with the smallest possible lower base. Experimental evidence has been presented that this geometry considerably reduces the power of the higher order IRMs and minimises the parasitic light leakage loss. (lasers)« less

Realization of back-side heterogeneous hybrid III-V/Si DBR lasers for silicon photonics

NASA Astrophysics Data System (ADS)

Durel, Jocelyn; Ferrotti, Thomas; Chantre, Alain; Cremer, Sébastien; Harduin, Julie; Bernabé, Stéphane; Kopp, Christophe; Boeuf, Frédéric; Ben Bakir, Badhise; Broquin, Jean-Emmanuel

2016-02-01

In this paper, the simulation, design and fabrication of a back-side coupling (BSC) concept for silicon photonics, which targets heterogeneous hybrid III-V/Si laser integration is presented. Though various demonstrations of a complete SOI integration of passive and active photonic devices have been made, they all feature multi-level planar metal interconnects, and a lack of integrated light sources. This is mainly due to the conflict between the need of planar surfaces for III-V/Si bonding and multiple levels of metallization. The proposed BSC solution to this topographical problem consists in fabricating lasers on the back-side of the Si waveguides using a new process sequence. The devices are based on a hybrid structure composed of an InGaAsP MQW active area and a Si-based DBR cavity. The emitted light wavelength is accordable within a range of 20 nm around 1.31μm thanks to thermal heaters and the laser output is fiber coupled through a Grating Coupler (GC). From a manufacturing point of view, the BSC approach provides not only the advantages of allowing the use of a thin-BOX SOI instead of a thick one; but it also shifts the laser processing steps and their materials unfriendly to CMOS process to the far back-end areas of fabrication lines. Moreover, aside from solving technological integration issues, the BSC concept offers several new design opportunities for active and passive devices (heat sink, Bragg gratings, grating couplers enhanced with integrated metallic mirrors, tapers…). These building boxes are explored here theoretically and experimentally.

Direct detector for terahertz radiation

DOEpatents

Wanke, Michael C [Albuquerque, NM; Lee, Mark [Albuquerque, NM; Shaner, Eric A [Albuquerque, NM; Allen, S James [Santa Barbara, CA

2008-09-02

A direct detector for terahertz radiation comprises a grating-gated field-effect transistor with one or more quantum wells that provide a two-dimensional electron gas in the channel region. The grating gate can be a split-grating gate having at least one finger that can be individually biased. Biasing an individual finger of the split-grating gate to near pinch-off greatly increases the detector's resonant response magnitude over prior QW FET detectors while maintaining frequency selectivity. The split-grating-gated QW FET shows a tunable resonant plasmon response to FIR radiation that makes possible an electrically sweepable spectrometer-on-a-chip with no moving mechanical optical parts. Further, the narrow spectral response and signal-to-noise are adequate for use of the split-grating-gated QW FET in a passive, multispectral terahertz imaging system. The detector can be operated in a photoconductive or a photovoltaic mode. Other embodiments include uniform front and back gates to independently vary the carrier densities in the channel region, a thinned substrate to increase bolometric responsivity, and a resistive shunt to connect the fingers of the grating gate in parallel and provide a uniform gate-channel voltage along the length of the channel to increase the responsivity and improve the spectral resolution.

Energy-reduction concept for incandescent lamps

NASA Technical Reports Server (NTRS)

Vorhaben, K. H.

1981-01-01

Reusable infrared reflector maintains filament temperature and reduces power requirements. Fixed installed over light bulb directs energy formerly lost back to lamp filament. This energy aids electric current in heating filament, allowing lower-wattage bulb to produce same amount of light as higher-wattage bulb in ordinary fixture.

Electroluminescence analysis for spatial characterization of parasitic optical losses in silicon heterojunction solar cells

NASA Astrophysics Data System (ADS)

Ahmed, Nuha; Zhang, Lei; Sriramagiri, Gowri; Das, Ujjwal; Hegedus, Steven

2018-04-01

Electroluminescence (EL) coupled with reflection measurements are used to spatially quantify optical losses in silicon heterojunction solar cells due to plasmonic absorption in the metal back contacts. The effect of indium tin oxide back reflector in decreasing this plasmonic absorption is found to increase the reflection from the back nickel (Ni)-aluminum (Al) and Al metals by ˜12% and ˜41%, respectively, in both bifacial and front junction silicon solar cells. Losses due to back reflection are calculated by comparison between the EL emission signals in high and low back reflection samples and are shown to be in agreement with standard reflection measurements. We conclude that the optical properties of the back contact can significantly influence the EL intensity which complicates the interpretation of EL as being primarily due to recombination especially when comparing two different devices with spatially varying back surface structures.

Widely tunable Fabry-Perot filter based MWIR and LWIR microspectrometers

NASA Astrophysics Data System (ADS)

Ebermann, Martin; Neumann, Norbert; Hiller, Karla; Gittler, Elvira; Meinig, Marco; Kurth, Steffen

2012-06-01

As is generally known, miniature infrared spectrometers have great potential, e. g. for process and environmental analytics or in medical applications. Many efforts are being made to shrink conventional spectrometers, such as FTIR or grating based devices. A more rigorous approach for miniaturization is the use of MEMS technologies. Based on an established design for the MWIR new MEMS Fabry-Perot filters and sensors with expanded spectral ranges in the LWIR have been developed. The range 5.5 - 8 μm is particularly suited for the analysis of liquids. A dual-band sensor, which can be simultaneously tuned from 4 - 5 μm and 8 - 11 μm for the measurement of anesthetics and carbon dioxide has also been developed. A new material system is used to reduce internal stress in the reflector layer stack. Good results in terms of finesse (<= 60) and transmittance (<= 80 %) could be demonstrated. The hybrid integration of the filter in a pyroelectric detector results in very compact, robust and cost effective microspectrometers. FP filters with two moveable reflectors instead of only one reduce significantly the acceleration sensitivity and actuation voltage.

Novel hybrid laser modes in composite VCSEL-DFB microcavities (Conference Presentation)

NASA Astrophysics Data System (ADS)

Mischok, Andreas; Wagner, Tim; Sudzius, Markas; Brückner, Robert; Fröb, Hartmut; Lyssenko, Vadim G.; Leo, Karl

2017-02-01

Two of the most successful microcresonator concepts are the vertical cavity surface emitting laser (VCSEL), where light is confined between distributed Bragg reflectors (DBRs), and the distributed feedback (DFB) laser, where a periodic grating provides positive optical feedback to selected modes in an active waveguide (WG) layer. Our work concerns the combination of both into a composite device, facilitating coherent interaction between both regimes and giving rise to novel laser modes in the system. In a first realization, a full VCSEL stack with an organic active layer is evaporated on top of a diffraction grating with a large period (approximately 1 micron), leading to diffraction of waveguided modes into the surface emission of the device. Here, the coherent interaction between VCSEL and WG modes, as observed in an anticrossing of the dispersion lines, facilitates novel hybrid lasing modes with macroscopic in-plane coherence [1]. In further studies, we decrease the grating period of such devices to realise DFB conditions in a second-order Bragg grating which strongly couples photons via first-order light diffraction to the VCSEL. This efficient coupling can be compared to more classical cascade-coupled cavities and is successfully described by a coupled oscillator model [2]. When both resonators are non-degenerate, they are able to function as independent structures without substantial diffraction losses. The realization of such novel devices provides a promising platform for photonic circuits based on organic microlasers. [1] A. Mischok et al., Adv. Opt. Mater., early online, DOI: 10.1002/adom.201600282, (2016) [2] T. Wagner et al., Appl. Phys. Lett., accepted, in production, (2016)

Foil Panel Mirrors for Nonimaging Applications

NASA Technical Reports Server (NTRS)

Kuyper, D. J.; Castillo, A. A.

1984-01-01

Large durable, lightweight mirrors made by bonding thick aluminum foil to honeycomb panels or other rigid, flat backings. Mirrors suitable for use as infrared shields, telescope doors, solar-furnance doors, advertising displays, or other reflectors that require low thermal emissivity and high specularity but do not require precise surface figure necessary for imaging.

Photovoltaic generator with a spherical imaging lens for use with a paraboloidal solar reflector

DOEpatents

Angel, Roger P

2013-01-08

The invention is a generator for photovoltaic conversion of concentrated sunlight into electricity. A generator according to the invention incorporates a plurality of photovoltaic cells and is intended for operation near the focus of a large paraboloidal reflector pointed at the sun. Within the generator, the entering concentrated light is relayed by secondary optics to the cells arranged in a compact, concave array. The light is delivered to the cells at high concentration, consistent with high photovoltaic conversion efficiency and low cell cost per unit power output. Light enters the generator, preferably first through a sealing window, and passes through a field lens, preferably in the form of a full sphere or ball lens centered on the paraboloid focus. This lens forms a concentric, concave and wide-angle image of the primary reflector, where the intensity of the concentrated light is stabilized against changes in the position of concentrated light entering the generator. Receiving the stabilized light are flat photovoltaic cells made in different shapes and sizes and configured in a concave array corresponding to the concave image of a given primary reflector. Photovoltaic cells in a generator are also sized and interconnected so as to provide a single electrical output that remains high and stable, despite aberrations in the light delivered to the generator caused by, for example, mispointing or bending of the primary reflector. In some embodiments, the cells are set back from the image formed by the ball lens, and part of the light is reflected onto each cell small secondary reflectors in the form of mirrors set around its perimeter.

Micromachined force-balance feedback accelerometer with optical displacement detection

DOEpatents

Nielson, Gregory N.; Langlois, Eric; Baker, Michael; Okandan, Murat; Anderson, Robert

2014-07-22

An accelerometer includes a proof mass and a frame that are formed in a handle layer of a silicon-on-an-insulator (SOI). The proof mass is separated from the frame by a back-side trench that defines a boundary of the proof mass. The accelerometer also includes a reflector coupled to a top surface of the proof mass. An optical detector is located above the reflector at the device side. The accelerometer further includes at least one suspension spring. The suspension spring has a handle anchor that extends downwards from the device side to the handle layer to mechanically support upward and downward movement of the proof mass relative to a top surface of the proof mass.

Multi-bounce laser-based sails

NASA Astrophysics Data System (ADS)

Metzger, Robert A.; Landis, Geoffrey

2001-02-01

A laser-based lightsail craft is proposed in which the laser beam is operated in a multi-bounce mode, such that after first striking the lightsail, the beam is reflected back to a source reflector where it is again directed to the lightsail. Recent developments in nearly ideal reflectors permit more than 1000 bounces, which reduce the laser power requirements by a factor of 1000 as compared to conventional laser-based lightsail proposals. Using the multi-bounce lightsail approach coupled with lasers operating in the power range of 100 MW to 1 GW, the details of a mission to Mars requiring only a sub-100 day transit, and an orbital transfer vehicle designed to transport cargo between Phobos and Deimos are examined. .

REACTOR CONTROL

DOEpatents

Ruano, W.J.

1957-12-10

This patent relates to nuclear reactors of the type which utilize elongited rod type fuel elements immersed in a liquid moderator and shows a design whereby control of the chain reaction is obtained by varying the amount of moderator or reflector material. A central tank for containing liquid moderator and fuel elements immersed therein is disposed within a surrounding outer tank providing an annular space between the two tanks. This annular space is filled with liquid moderator which functions as a reflector to reflect neutrons back into the central reactor tank to increase the reproduction ratio. Means are provided for circulating and cooling the moderator material in both tanks and additional means are provided for controlling separately the volume of moderator in each tank, which latter means may be operated automatically by a neutron density monitoring device. The patent also shows an arrangement for controlling the chain reaction by injecting and varying an amount of poisoning material in the moderator used in the reflector portion of the reactor.

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.

[Design method of convex master gratings for replicating flat-field concave gratings].

PubMed

Zhou, Qian; Li, Li-Feng

2009-08-01

Flat-field concave diffraction grating is the key device of a portable grating spectrometer with the advantage of integrating dispersion, focusing and flat-field in a single device. It directly determines the quality of a spectrometer. The most important two performances determining the quality of the spectrometer are spectral image quality and diffraction efficiency. The diffraction efficiency of a grating depends mainly on its groove shape. But it has long been a problem to get a uniform predetermined groove shape across the whole concave grating area, because the incident angle of the ion beam is restricted by the curvature of the concave substrate, and this severely limits the diffraction efficiency and restricts the application of concave gratings. The authors present a two-step method for designing convex gratings, which are made holographically with two exposure point sources placed behind a plano-convex transparent glass substrate, to solve this problem. The convex gratings are intended to be used as the master gratings for making aberration-corrected flat-field concave gratings. To achieve high spectral image quality for the replicated concave gratings, the refraction effect at the planar back surface and the extra optical path lengths through the substrate thickness experienced by the two divergent recording beams are considered during optimization. This two-step method combines the optical-path-length function method and the ZEMAX software to complete the optimization with a high success rate and high efficiency. In the first step, the optical-path-length function method is used without considering the refraction effect to get an approximate optimization result. In the second step, the approximate result of the first step is used as the initial value for ZEMAX to complete the optimization including the refraction effect. An example of design problem was considered. The simulation results of ZEMAX proved that the spectral image quality of a replicated concave grating is comparable with that of a directly recorded concave grating.

Demonstration of transparent solar array module design

NASA Technical Reports Server (NTRS)

Pack, G. J.

1984-01-01

This report discusses the design, development, fabrication and testing of IR transparent solar array modules. Three modules, consisting of a baseline design using back surface reflector cells, and two modules using gridded back contact, IR transparent cells, were subjected to vacuum thermal balance testing to verify analytical predictions of lower operating emperature and increased efficiency. As a result of this test program, LMSC has verified that a significant degree of IR transparency can be designed into a flexible solar array. Test data correlates with both steady state and transient thermal analysis.

30 CFR 77.1608 - Dumping facilities.

Code of Federal Regulations, 2011 CFR

2011-07-01

... weight of a loaded dump truck, trucks shall be dumped a safe distance back from the edge of the bank. (c... material. (d) Grizzlies, grates, and other sizing devices at dump and transfer points shall be anchored...

Photovoltaic module with light reflecting backskin

DOEpatents

Gonsiorawski, Ronald C [Danvers, MA

2007-07-03

A photovoltaic module comprises electrically interconnected and mutually spaced photovoltaic cells that are encapsulated by a light-transmitting encapsulant between a light-transparent front cover and a back cover, with the back cover sheet being an ionomer/nylon alloy embossed with V-shaped grooves running in at least two directions and coated with a light reflecting medium so as to provide light-reflecting facets that are aligned with the spaces between adjacent cells and oriented so as to reflect light falling in those spaces back toward said transparent front cover for further internal reflection onto the solar cells, whereby substantially all of the reflected light will be internally reflected from said cover sheet back to the photovoltaic cells, thereby increasing the current output of the module. The internal reflector improves power output by as much as 67%.

Control system for a small fission reactor

DOEpatents

Burelbach, James P.; Kann, William J.; Saiveau, James G.

1986-01-01

A system for controlling the reactivity of a small fission reactor includes an elongated, flexible hollow tube in the general form of a helical coiled spring axially positioned around and outside of the reactor vessel in an annular space between the reactor vessel and a surrounding cylindrical-shaped neutron reflector. A neutron absorbing material is provided within the hollow tube with the rate of the reaction controlled by the extension and compression of the hollow tube, e.g., extension of the tube increases reactivity while its compression reduces reactivity, in varying the amount of neutron absorbing material disposed between the reactor vessel and the neutron reflector. Conventional mechanical displacement means may be employed to control the coil density of the hollow tube as desired. In another embodiment, a plurality of flexible hollow tubes each containing a neutron absorber are positioned adjacent to one another in spaced relation around the periphery of the reactor vessel and inside the outer neutron reflector with reactivity controlled by the extension and compression of all or some of the coiled hollow tubes. Yet another embodiment of the invention envisions the neutron reflector in the form of an expandable coil spring positioned in an annular space between the reactor vessel and an outer neutron absorbing structure for controlling the neutron flux reflected back into the reactor vessel.

The potential of diffraction grating for spatial applications

NASA Astrophysics Data System (ADS)

Jourlin, Y.; Parriaux, O.; Pigeon, F.; Tischenko, A. V.

2017-11-01

Diffraction gratings are know, and have been fabricated for more than one century. They are now making a come back for two reasons: first, because they are now better understood which leads to the efficient exploitation of what was then called their "anomalies"; secondly, because they are now fabricable by means of the modern manufacturing potential of planar technologies. Novel grating can now perform better than conventional gratings, and address new application fields which were not expected to be theirs. This is the case of spatial applications where they can offer multiple optical functions, low size, low weight and mechanical robustness. The proposed contribution will briefly discuss the use of gratings for spatial applications. One of the most important applications is in the measurement of displacement. Usual translation and rotation sensors are bulky devices, which impose a system breakdown leading to cumbersome and heavy assemblies. We are proposing a miniaturized version of the traditional moving grating technique using submicron gratings and a specific OptoASIC which enables the measurement function to be non-obtrusively inserted into light and compact electro-mechanical systems. Nanometer resolution is possible with no compromise on the length of the measurement range. Another family of spatial application is in the field of spectrometers where new grating types allow a more flexible processing of the optical spectrum. Another family of applications addresses the question of inter-satellite communications: the introduction of gratings in laser cavities or in the laser mirrors enables the stabilization of the emitted polarization, the stabilization of the frequency as well as wide range frequency sweeping without mobile parts.

Fast wavelength tuning techniques for external cavity lasers

DOEpatents

Wysocki, Gerard [Princeton, NJ; Tittel, Frank K [Houston, TX

2011-01-11

An apparatus comprising a laser source configured to emit a light beam along a first path, an optical beam steering component configured to steer the light beam from the first path to a second path at an angle to the first path, and a diffraction grating configured to reflect back at least a portion of the light beam along the second path, wherein the angle determines an external cavity length. Included is an apparatus comprising a laser source configured to emit a light beam along a first path, a beam steering component configured to redirect the light beam to a second path at an angle to the first path, wherein the optical beam steering component is configured to change the angle at a rate of at least about one Kilohertz, and a diffraction grating configured to reflect back at least a portion of the light beam along the second path.

Vertical-cavity in-plane heterostructures: Physics and applications

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

Taghizadeh, Alireza; Mørk, Jesper; Chung, Il-Sug, E-mail: ilch@fotonik.dtu.dk

2015-11-02

We show that in-plane (lateral) heterostructures realized in vertical cavities with high contrast grating reflectors can be used to significantly modify the anisotropic dispersion curvature, also interpreted as the photon effective mass. This design freedom enables exotic configurations of heterostructures and many interesting applications. The effects of the anisotropic photon effective mass on the mode confinement, mode spacing, and transverse modes are investigated. As a possible application, the method of boosting the speed of diode lasers by engineering the photon-photon resonance is discussed. Based on this platform, we propose a system of two laterally coupled cavities, which shows the breakingmore » of parity-time symmetry in vertical cavity structures.« less

Highly integrated optical heterodyne phase-locked loop with phase/frequency detection.

PubMed

Lu, Mingzhi; Park, Hyunchul; Bloch, Eli; Sivananthan, Abirami; Bhardwaj, Ashish; Griffith, Zach; Johansson, Leif A; Rodwell, Mark J; Coldren, Larry A

2012-04-23

A highly-integrated optical phase-locked loop with a phase/frequency detector and a single-sideband mixer (SSBM) has been proposed and demonstrated for the first time. A photonic integrated circuit (PIC) has been designed, fabricated and tested, together with an electronic IC (EIC). The PIC integrates a widely-tunable sampled-grating distributed-Bragg-reflector laser, an optical 90 degree hybrid and four high-speed photodetectors on the InGaAsP/InP platform. The EIC adds a single-sideband mixer, and a digital phase/frequency detector, to provide single-sideband heterodyne locking from -9 GHz to 7.5 GHz. The loop bandwith is 400 MHz. © 2012 Optical Society of America

Flipping interferometry and its application for quantitative phase microscopy in a micro-channel.

PubMed

Roitshtain, Darina; Turko, Nir A; Javidi, Bahram; Shaked, Natan T

2016-05-15

We present a portable, off-axis interferometric module for quantitative phase microscopy of live cells, positioned at the exit port of a coherently illuminated inverted microscope. The module creates on the digital camera an interference pattern between the image of the sample and its flipped version. The proposed simplified module is based on a retro-reflector modification in an external Michelson interferometer. The module does not contain any lenses, pinholes, or gratings and its alignment is straightforward. Still, it allows full control of the off-axis angle and does not suffer from ghost images. As experimentally demonstrated, the module is useful for quantitative phase microscopy of live cells rapidly flowing in a micro-channel.

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.

Inverse design of near unity efficiency perfectly vertical grating couplers.

PubMed

Michaels, Andrew; Yablonovitch, Eli

2018-02-19

Efficient coupling between integrated optical waveguides and optical fibers is essential to the success of silicon photonics. While many solutions exist, perfectly vertical grating couplers that scatter light out of a waveguide in the direction normal to the waveguide's top surface are an ideal candidate due to their potential to reduce packaging complexity. Designing such couplers with high efficiencies, however, has proven difficult. In this paper, we use inverse electromagnetic design techniques to optimize a high efficiency two-layer perfectly vertical silicon grating coupler. Our base design achieves a chip-to-fiber coupling efficiency of 99.2% (-0.035 dB) at 1550 nm. Using this base design as a starting point, we run subsequent constrained optimizations to realize vertical couplers with coupling efficiencies over 96% and back reflections of less than -40 dB which can be fabricated using 65 nm-resolution lithography. These results demonstrate a new path forward for designing fabrication-tolerant ultra high efficiency grating couplers.

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.

Low reflectance high power RF load

DOEpatents

Ives, R. Lawrence; Mizuhara, Yosuke M.

2016-02-02

A load for traveling microwave energy has an absorptive volume defined by cylindrical body enclosed by a first end cap and a second end cap. The first end cap has an aperture for the passage of an input waveguide with a rotating part that is coupled to a reflective mirror. The inner surfaces of the absorptive volume consist of a resistive material or are coated with a coating which absorbs a fraction of incident RF energy, and the remainder of the RF energy reflects. The angle of the reflector and end caps is selected such that reflected RF energy dissipates an increasing percentage of the remaining RF energy at each reflection, and the reflected RF energy which returns to the rotating mirror is directed to the back surface of the rotating reflector, and is not coupled to the input waveguide. Additionally, the reflector may have a surface which generates a more uniform power distribution function axially and laterally, to increase the power handling capability of the RF load. The input waveguide may be corrugated for HE11 mode input energy.

Low reflectance radio frequency load

DOEpatents

Ives, R. Lawrence; Mizuhara, Yosuke M

2014-04-01

A load for traveling microwave energy has an absorptive volume defined by cylindrical body enclosed by a first end cap and a second end cap. The first end cap has an aperture for the passage of an input waveguide with a rotating part that is coupled to a reflective mirror. The inner surfaces of the absorptive volume consist of a resistive material or are coated with a coating which absorbs a fraction of incident RF energy, and the remainder of the RF energy reflects. The angle of the reflector and end caps is selected such that reflected RF energy dissipates an increasing percentage of the remaining RF energy at each reflection, and the reflected RF energy which returns to the rotating mirror is directed to the back surface of the rotating reflector, and is not coupled to the input waveguide. Additionally, the reflector may have a surface which generates a more uniform power distribution function axially and laterally, to increase the power handling capability of the RF load. The input waveguide may be corrugated for HE11 mode input energy.

Full-Field Strain Behavior of Friction Stir-Welded Titanium Alloy

DTIC Science & Technology

2008-01-01

and slag formed on the upper weld surface by the FSW process and the remnant laser weld bead on the underside of the FSW surface were removed from...using 3M brand ‘Super 77’ spray adhesive and then hand sanding against a mechanically flat ceramic backing surface using silicon 32 carbide...weld surface using Loctite brand “5-minute Epoxy” and allowing to cure. Following the required cure period, the aluminum grating glass backing was

Improvement of infrared single-photon detectors absorptance by integrated plasmonic structures

PubMed Central

Csete, Mária; Sipos, Áron; Szalai, Anikó; Najafi, Faraz; Szabó, Gábor; Berggren, Karl K.

2013-01-01

Plasmonic structures open novel avenues in photodetector development. Optimized illumination configurations are reported to improve p-polarized light absorptance in superconducting-nanowire single-photon detectors (SNSPDs) comprising short- and long-periodic niobium-nitride (NbN) stripe-patterns. In OC-SNSPDs consisting of ~quarter-wavelength dielectric layer closed by a gold reflector the highest absorptance is attainable at perpendicular incidence onto NbN patterns in P-orientation due to E-field concentration at the bottom of nano-cavities. In NCAI-SNSPDs integrated with nano-cavity-arrays consisting of vertical and horizontal gold segments off-axis illumination in S-orientation results in polar-angle-independent perfect absorptance via collective resonances in short-periodic design, while in long-periodic NCAI-SNSPDs grating-coupled surface waves promote EM-field transportation to the NbN stripes and result in local absorptance maxima. In NCDAI-SNSPDs integrated with nano-cavity-deflector-array consisting of longer vertical gold segments large absorptance maxima appear in 3p-periodic designs due to E-field enhancement via grating-coupled surface waves synchronized with the NbN stripes in S-orientation, which enable to compensate fill-factor-related retrogression. PMID:23934331

Concepts for thin-film GaAs concentrator cells. [for solar photovoltaic space power systems

NASA Technical Reports Server (NTRS)

Spitzer, M. B.; Gale, R. P.; Mcclelland, R.; King, B.; Dingle, J.

1989-01-01

The development of advanced GaAs concentrator solar cells, and in particular, the use of CLEFT (cleavage of lateral epitaxial films for transfer) processes for formation of thin-film structures is reported. The use of CLEFT has made possible processing of the back, and cells with back surface grids are discussed. Data on patterned junction development are presented; such junctions are expected to be useful in back surface applications requiring point contacts, grating structures, and interdigitated back contacts. CLEFT concentrator solar cells with grids on the front and back surfaces are reported here; these cells are 4 microns thick and are bonded to glass covers for support. Air mass zero efficiency of 18.8 percent has been obtained for a CLEFT concentrator operating at 18.5 suns.

VizieR Online Data Catalog: Abundance ratio for 5 local stellar associations (Reddy+, 2015)

NASA Astrophysics Data System (ADS)

Reddy, A. B. S.; Lambert, D. L.

2018-01-01

In this paper, we have performed a homogeneous and a comprehensive abundance analysis using high-resolution spectroscopy. High-resolution and high signal-to-noise (S/N) spectra of the program stars were obtained during the nights of 2015 February 10-11 with the Robert G. Tull coude cross-dispersed echelle spectrograph (Tull et al. 1995PASP..107..251T) of the 2.7 m Harlan J. Smith reflector at the McDonald Observatory. We employed a Tektronix 2048x2048 24 μm pixel, backside illuminated and anti-reflection coated CCD as a detector and an R2 echelle grating with 52.67 grooves/mm with exposures centred at 5060 Å. (7 data files).

Alignment Measurements of the Microwave Anisotropy Probe (MAP) Instrument in a Thermal/Vacuum Chamber Using Photogrammetry

NASA Technical Reports Server (NTRS)

Hill, Michael D.; Herrera, Acey A.; Crane, J. Allen; Packard, Edward A.; Aviado, Carlos; Sampler, Henry P.; Obenschain, Arthur (Technical Monitor)

2000-01-01

The Microwave Anisotropy Probe (MAP) Observatory, scheduled for a late 2000 launch, is designed to measure temperature fluctuations (anisotropy) and produce a high sensitivity and high spatial resolution (< 0.3 deg at 90 GHz.) map of the cosmic microwave background (CMB) radiation over the entire sky between 22 and 90 GHz. MAP utilizes back-to-back Gregorian telescopes to focus the microwave signals into 10 differential microwave receivers, via 20 feed horns. Proper alignment of the telescope reflectors and the feed horns at the operating temperature of 90 K is a critical element to ensure mission success. We describe the hardware and methods used to validate the displacement/deformation predictions of the reflectors and the microwave feed horns during thermal/vacuum testing of the reflectors and the microwave instrument. The smallest deformations to be resolved by the measurement system were on the order of +/- 0.030 inches (0.762 mm). Performance of these alignment measurements inside a thermal/vacuum chamber with conventional alignment equipment posed several limitations. A photogrammetry (PG) system was chosen to perform the measurements since it is a non-contact measurement system, the measurements can be made relatively quickly and accurately, and the photogrammetric camera can be operated remotely. The hardware and methods developed to perform the MAP alignment measurements using PG proved to be highly successful. The PG measurements met the desired requirements, enabling the desired deformations to be measured and even resolved to an order of magnitude smaller than the imposed requirements. Viable data were provided to the MAP Project for a full analysis of the on-orbit performance of the Instrument's microwave system.

Nanolaminate Mirrors With "Piston" Figure-Control Actuators

NASA Technical Reports Server (NTRS)

Lowman, Andrew; Redding, David; Hickey, Gregory; Knight, Jennifer; Moynihan, Philip; Lih, Shyh0Shiuh; Barbee, Troy

2003-01-01

Efforts are under way to develop a special class of thin-shell curved mirrors for high-resolution imaging in visible and infrared light in a variety of terrestrial or extraterrestrial applications. These mirrors can have diameters of the order of a meter and include metallic film reflectors on nanolaminate substrates supported by multiple distributed piezoceramic gpiston h-type actuators for micron-level figure control. Whereas conventional glass mirrors of equivalent size and precision have areal mass densities between 50 and 150 kg/sq m, the nanolaminate mirrors, including not only the reflector/ shell portions but also the actuators and the backing structures needed to react the actuation forces, would have areal mass densities that may approach .5 kg/m2. Moreover, whereas fabrication of a conventional glass mirror of equivalent precision takes several years, the reflector/shell portion of a nanolaminate mirror can be fabricated in less than a week, and its actuation system can be fabricated in 1 to 2 months. The engineering of these mirrors involves a fusion of the technological heritage of multisegmented adaptive optics and deformable mirrors with more recent advances in metallic nanolaminates and in mathematical modeling of the deflections of thin, curved shells in response to displacements by multiple, distributed actuators. Because a nanolaminate shell is of the order of 10 times as strong as an otherwise identical shell made of a single, high-strength, non-nanolaminate metal suitable for mirror use, a nanolaminate mirror can be made very thin (typically between 100 and 150 m from the back of the nanolaminate substrate to the front reflecting surface). The thinness and strength of the nanolaminate are what make it possible to use distributed gpiston h-type actuators for surface figure control with minimal local concentrated distortion (called print-through in the art) at the actuation points.

Alignment Measurements of the Microwave Anisotropy Probe (MAP) Instrument in a Thermal/Vacuum Chamber

NASA Technical Reports Server (NTRS)

Hill, Michael D.; Herrera, Acey A.; Crane, J. Allen; Packard, Edward A.; Aviado, Carlos; Sampler, Henry P.

2000-01-01

The Microwave Anisotropy Probe (MAP) Observatory, scheduled for a fall 2000 launch, is designed to measure temperature fluctuations (anisotropy) and produce a high sensitivity and high spatial resolution (approximately 0.2 degree) map of the cosmic microwave background (CMB) radiation over the entire sky between 22 and 90 GHz. MAP utilizes back-to-back Gregorian telescopes to focus the microwave signals into 10 differential microwave receivers, via 20 feed horns. Proper alignment of the telescope reflectors and the feed horns at the operating temperature of 90 K is a critical element to ensure mission success. We describe the hardware and methods used to validate the displacement/deformation predictions of the reflectors and the microwave feed horns during thermal/vacuum testing of the reflectors and the microwave instrument. The smallest deformation predictions to be measured were on the order of +/- 0.030 inches (+/- 0.762 mm). Performance of these alignment measurements inside a thermal/vacuum chamber with conventional alignment equipment posed several limitations. The most troublesome limitation was the inability to send personnel into the chamber to perform the measurements during the test due to vacuum and the temperature extremes. The photogrammetry (PG) system was chosen to perform the measurements since it is a non- contact measurement system, the measurements can be made relatively quickly and accurately, and the photogrammetric camera can be operated remotely. The hardware and methods developed to perform the MAP alignment measurements using PG proved to be highly successful. The measurements met the desired requirements, for the metal structures enabling the desired distortions to be measured resolving deformations an order of magnitude smaller than the imposed requirements. Viable data were provided to the MAP Project for a full analysis of the on-orbit performance of the Instrument's microwave system.

Polymer based resonant waveguide grating photonic filter with on-chip thermal tuning

NASA Astrophysics Data System (ADS)

Chaudhuri, Ritesh Ray; Enemuo, Amarachukwu N.; Song, Youngsik; Seo, Sang-Woo

2018-07-01

In this paper, we present the development of a multilayer polymer resonant waveguide grating (RWG)-based optical filter with an integrated microheater for on-chip thermal spectral tuning. RWG optical filter is fabricated using polymer-based materials. Therefore, its integration can be applied to different material platforms. Typical RWG structure is sensitive to back optical reflection from the structures below. To reduce the effect of back reflection from the metal heater and improve the quality of the integrated RWG filter output, an intermediate absorption layer was implemented utilizing an epoxy based carbon coating. This approach effectively suppresses the background noise in the RWG characteristics. The central wavelength of the reported filter was designed around 1550 nm. Experimentally, wavelength tuning of 21.96 nm was achieved for operating temperature range of 81 °C with approximately 150mW power consumption. Based on the layer-by-layer fabrication approach, the presented thermally tunable RWG filter on a chip has potential for use in low cost hybrid communication systems and spectral sensing applications.

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.

High-frequency techniques for RCS prediction of plate geometries and a physical optics/equivalent currents model for the RCS of trihedral corner reflectors, parts 1 and 2

NASA Technical Reports Server (NTRS)

Balanis, Constantine A.; Polka, Lesley A.; Polycarpou, Anastasis C.

1994-01-01

Formulations for scattering from the coated plate and the coated dihedral corner reflector are included. A coated plate model based upon the Uniform Theory of Diffraction (UTD) for impedance wedges was presented in the last report. In order to resolve inaccuracies and discontinuities in the predicted patterns using the UTD-based model, an improved model that uses more accurate diffraction coefficients is presented. A Physical Optics (PO) model for the coated dihedral corner reflector is presented as an intermediary step in developing a high-frequency model for this structure. The PO model is based upon the reflection coefficients for a metal-backed lossy material. Preliminary PO results for the dihedral corner reflector suggest that, in addition to being much faster computationally, this model may be more accurate than existing moment method (MM) models. An improved Physical Optics (PO)/Equivalent Currents model for modeling the Radar Cross Section (RCS) of both square and triangular, perfectly conducting, trihedral corner reflectors is presented. The new model uses the PO approximation at each reflection for the first- and second-order reflection terms. For the third-order reflection terms, a Geometrical Optics (GO) approximation is used for the first reflection; and PO approximations are used for the remaining reflections. The previously reported model used GO for all reflections except the terminating reflection. Using PO for most of the reflections results in a computationally slower model because many integrations must be performed numerically, but the advantage is that the predicted RCS using the new model is much more accurate. Comparisons between the two PO models, Finite-Difference Time-Domain (FDTD) and experimental data are presented for validation of the new model.

Influence of fluvial processes on the quaternary geologic framework of the continental shelf, North Carolina, USA

USGS Publications Warehouse

Boss, S.K.; Hoffman, C.W.; Cooper, B.

2002-01-01

Digital, single-channel, high-resolution seismic reflection profiles were acquired from the insular continental shelf of North Carolina, USA along a data grid extending from Oregon Inlet northward 48 km to Duck, North Carolina and from the nearshore zone seaward approximately 28 km (total surveyed area= 1334 km2). These data were processed and interpreted to delineate principal reflecting horizons and develop a three-dimensional seismic stratigraphic framework for the continental shelf that was compared to stratigraphic data from the shoreward back-barrier (estuarine) and barrier island system. Six principal reflecting horizons (designated R0 through R5) were present within the upper 60 m of the shelf stratigraphic succession. Three-dimensional mapping of reflector R1 demonstrated its origin from fluvial incision of the continental shelf during an episode (or episodes) of lowered sea-level. Fluvial processes during development of reflector R1 were responsible for extensive reworking and re-deposition of sediment throughout most of the northern half of the study area. Five seismic stratigraphic units (designated S1 through S5) were tentatively correlated with depositional sequences previously identified from the North Carolina back-barrier (estuarine) and barrier island system. These five stratigraphic units span the Quaternary Period (S1 = early Holocene; S2 = 51-78 ka; S3 = 330-530 ka; S4 = 1.1-1.8 Ma; S5 = earliest Pleistocene). Unit S1 is composed of fine-grained fluvial/estuarine sediment that back-filled incised streams during early Holocene sea-level rise. The four other stratigraphic units (S2-S5) display tabular depositional geometries, low total relief, and thicken toward the east-southeast as their basal reflectors dip gently between 0.41 m km-1 (0.02??) and 0.54 m km-1 (0.03??). Knowledge of the three-dimensional subsurface stratigraphic architecture of the continental shelf enhances understanding of the development of shelf depositional successions and provides a framework for development of better Quaternary sea-level data, especially offshore North Carolina where such data are sparse. ?? 2002 Elsevier Science B.V. All rights reserved.

A Study of Contacts and Back-Surface Reflectors for 0.6eV Ga0.32In0.68As/InAs0.32P0.68 Thermophotovoltaic Monolithically Interconnected Modules

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

Wu, X.; Duda, A.; Carapella, J. J.

1998-12-23

Thermophotovoltaic (TPV) systems have recently rekindled a high level of interest for a number of applications. In order to meet the requirement of low-temperature ({approx}1000 C) TPV systems, 0.6-eV Ga0.32In0.68As/InAs0.32P0.68 TPV monolithically interconnected modules (MIMs) have been developed at the National Renewable energy Laboratory (NREL)[1]. The successful fabrication of Ga0.32In0.68As/InAs0.32P0.68 MIMs depends on developing and optimizing of several key processes. Some results regarding the chemical vapor deposition (CVD)-SiO2 insulating layer, selective chemical etch via sidewall profiles, double-layer antireflection coatings, and metallization via interconnects have previously been given elsewhere [2]. In this paper, we report on the study of contacts andmore » back-surface reflectors. In the first part of this paper, Ti/Pd/Ag and Cr/Pd/Ag contact to n-InAs0.32P0.68and p-Ga0.32In0.68As are investigated. The transfer length method (TLM) was used for measuring of specific contact resistance Rc. The dependence of Rc on different doping levels and different pre-treatment of the two semiconductors will be reported. Also, the adhesion and the thermal stability of Ti/Pd/Ag and Cr/Pd/Ag contacts to n-InAs0.32P0.68and p-Ga0.32In0.68As will be presented. In the second part of this paper, we discuss an optimum back-surface reflector (BSR) that has been developed for 0.6-eV Ga0.32In0.68As/InAs0.32P0.68 TPV MIM devices. The optimum BSR consists of three layers: {approx}1300{angstrom} MgF2 (or {approx}1300{angstrom} CVD SiO2) dielectric layer, {approx}25{angstrom} Ti adhesion layer, and {approx}1500{angstrom} Au reflection layer. This optimum BSR has high reflectance, good adhesion, and excellent thermal stability.« less

On-line ultrasonic gas entrainment monitor

DOEpatents

Day, Clifford K.; Pedersen, Herbert N.

1978-01-01

Apparatus employing ultrasonic energy for detecting and measuring the quantity of gas bubbles present in liquids being transported through pipes. An ultrasonic transducer is positioned along the longitudinal axis of a fluid duct, oriented to transmit acoustic energy radially of the duct around the circumference of the enclosure walls. The back-reflected energy is received centrally of the duct and interpreted as a measure of gas entrainment. One specific embodiment employs a conical reflector to direct the transmitted acoustic energy radially of the duct and redirect the reflected energy back to the transducer for reception. A modified embodiment employs a cylindrical ultrasonic transducer for this purpose.

Light trapping in thin film solar cells using photonic engineering device concepts

NASA Astrophysics Data System (ADS)

Mutitu, James Gichuhi

In this era of uncertainty concerning future energy solutions, strong reservations have arisen over the continued use and pursuit of fossil fuels and other conventional sources of energy. Moreover, there is currently a strong and global push for the implementation of stringent measures, in order to reduce the amount of green house gases emitted by every nation. As a consequence, there has emerged a sudden and frantic rush for new renewable energy solutions. In this world of renewable energy technologies is where we find photovoltaic (PV) technology today. However, as is, there are still many issues that need to be addressed before solar energy technologies become economically viable and available to all people, in every part of the world. This renewed interest in the development of solar electricity, has led to the advancement of new avenues that address the issues of cost and efficiency associated with PV. To this end, one of the prominent approaches being explored is thin film solar cell (TFSC) technology, which offers prospects of lower material costs and enables larger units of manufacture than conventional wafer based technology. However, TFSC technologies suffer from one major problem; they have lower efficiencies than conventional wafer based solar cell technologies. This lesser efficiency is based on a number of reasons, one of which is that with less material, there is less volume for the absorption of incident photons. This shortcoming leads to the need for optical light trapping; which is concerned with admitting the maximum amount of light into the solar cell and keeping the light within the structure for as long as possible. In this thesis, I present the fundamental scientific ideas, practice and methodology behind the application of photonic engineering device concepts to increase the light trapping capacity of thin film solar cells. In the introductory chapters, I develop the basic ideas behind light trapping in a sequential manner, where the effects of the inclusion of various structures on the front and back surfaces of solar cells are examined. This framework is then adapted as a basis for the development of more advanced topics, such as the inclusion of micro and nano scale surface textures, diffraction gratings and photonic bandgap structures. Analyses of the effects of these light trapping structures is undertaken using performance metrics, such as the short circuit current characteristics and a band-edge enhancement factor, which all serve to quantitatively demonstrate the effects of the optical enhancements. I begin this thesis with an investigation of one dimensional photonic crystals, which are used as selective light filters between vertically stacked tandem multi-junction solar cells. These ideas are then further developed for single junction stand alone thin film solar cells, where the optical enhancement is shown to be very significant. A further investigation on the application of engineered photonic crystal materials as angular selective light filters is then presented; these filters are shown to overcome the physical limitations of light trapping that are imposed by the optical properties of materials; specifically limitations associated with total internal reflection. In the next part of this thesis, I present a fundamental redesign approach to multiple period distributed Bragg reflectors (DBR's) and their applications to solar cell light trapping. As it turns out, multiple period DBR's, which are required for high back surface reflectance - which is especially necessary in thin film solar cells - present formidable challenges in terms of cost and complexity when considered for high volume manufacturing. To this end, I show that when a single period DBR is combined with a phase matching and metallic layer, the combined structure can achieve high back surface reflectance that is comparable to that of a DBR structure with many more layers. This new structure reduces the back reflector complexity and is hence, amenable to large scale fabrication processes. In the latter sections of this thesis, I present a host of fabrication techniques that are used to realize micro and nano scale light trapping features. These techniques range from standard silicon wet etching processes, to customized and elaborate deep ultra-violet lithography, which is combined with inductively coupled plasma etching and used in order to realize sub-micron diffraction gratings. These textures are then applied to substrates on which thin film amorphous silicon solar cell structures are deposited, subsequent analyses on the effectiveness of these texturing processes is performed. Finally, this thesis concludes with the presentation of a blueprint for future explorations and applications of the developed light trapping techniques, to other thin film solar cell materials and technologies.

Image analysis algorithms for the advanced radiographic capability (ARC) grating tilt sensor at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Roberts, Randy S.; Bliss, Erlan S.; Rushford, Michael C.; Halpin, John M.; Awwal, Abdul A. S.; Leach, Richard R.

2014-09-01

The Advance Radiographic Capability (ARC) at the National Ignition Facility (NIF) is a laser system designed to produce a sequence of short pulses used to backlight imploding fuel capsules. Laser pulses from a short-pulse oscillator are dispersed in wavelength into long, low-power pulses, injected in the NIF main laser for amplification, and then compressed into high-power pulses before being directed into the NIF target chamber. In the target chamber, the laser pulses hit targets which produce x-rays used to backlight imploding fuel capsules. Compression of the ARC laser pulses is accomplished with a set of precision-surveyed optical gratings mounted inside of vacuum vessels. The tilt of each grating is monitored by a measurement system consisting of a laser diode, camera and crosshair, all mounted in a pedestal outside of the vacuum vessel, and a mirror mounted on the back of a grating inside the vacuum vessel. The crosshair is mounted in front of the camera, and a diffraction pattern is formed when illuminated with the laser diode beam reflected from the mirror. This diffraction pattern contains information related to relative movements between the grating and the pedestal. Image analysis algorithms have been developed to determine the relative movements between the gratings and pedestal. In the paper we elaborate on features in the diffraction pattern, and describe the image analysis algorithms used to monitor grating tilt changes. Experimental results are provided which indicate the high degree of sensitivity provided by the tilt sensor and image analysis algorithms.

THUNDER Piezoelectric Actuators as a Method of Stretch-Tuning an Optical Fiber Grating

NASA Technical Reports Server (NTRS)

Allison, Sidney G.; Fox, Robert L.; Froggatt, Mark E.; Childers, Brooks A.

2000-01-01

A method of stretching optical fiber holds interest for measuring strain in smart structures where the physical displacement may be used to tune optical fiber lasers. A small, light weight, low power tunable fiber laser is ideal for demodulating strain in optical fiber Bragg gratings attached to smart structures such as the re-usable launch vehicle that is being developed by NASA. A method is presented for stretching optical fibers using the THUNDER piezoelectric actuators invented at NASA Langley Research Center. THUNDER actuators use a piezoelectric layer bonded to a metal backing to enable the actuators to produce displacements larger than the unbonded piezoelectric material. The shift in reflected optical wavelength resulting from stretching the fiber Bragg grating is presented. Means of adapting THUNDER actuators for stretching optical fibers is discussed, including ferrules, ferrule clamp blocks, and plastic hinges made with stereo lithography.

Polarization-independent absorption enhancement in a graphene square array with a cascaded grating structure.

PubMed

Wu, Jun

2018-03-01

The polarization-independent enhanced absorption effect of graphene in the near-infrared range is investigated. This is achieved by placing a graphene square array on top of a dielectric square array backed by a two-dimensional multilayer grating. Total optical absorption in graphene can be attributed to critical coupling, which is achieved through the combined effect of guided-mode resonance with the dielectric square array and the photonic band gap with the two-dimensional multilayer grating. To reveal the physical origin of such a phenomenon, the electromagnetic field distributions for both polarizations are illustrated. The designed graphene absorber exhibits near-unity polarization-independent absorption at resonance with an ultra-narrow spectrum. Moreover, the polarization-independent absorption can be tuned simply by changing the geometric parameters. The results may have promising potential for the design of graphene-based optoelectronic devices.

Back to Bosstown.

ERIC Educational Resources Information Center

Burns, Gary

"Bosstown Sound" was a slogan used to promote several Boston (Massachusetts) rock bands in 1968. In theory, the Bosstown Sound was a logical development to follow the San Francisco "sound," which included the Grateful Dead, Jefferson Airplane, Moby Grape, and other Bay Area bands that had been commercially successful in 1967.…

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.

Comparison of different numerical treatments for x-ray phase tomography of soft tissue from differential phase projections

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

Pelliccia, Daniele; Vaz, Raquel; Svalbe, Imants

X-ray imaging of soft tissue is made difficult by their low absorbance. The use of x-ray phase imaging and tomography can significantly enhance the detection of these tissues and several approaches have been proposed to this end. Methods such as analyzer-based imaging or grating interferometry produce differential phase projections that can be used to reconstruct the 3D distribution of the sample refractive index. We report on the quantitative comparison of three different methods to obtain x-ray phase tomography with filtered back-projection from differential phase projections in the presence of noise. The three procedures represent different numerical approaches to solve themore » same mathematical problem, namely phase retrieval and filtered back-projection. It is found that obtaining individual phase projections and subsequently applying a conventional filtered back-projection algorithm produces the best results for noisy experimental data, when compared with other procedures based on the Hilbert transform. The algorithms are tested on simulated phantom data with added noise and the predictions are confirmed by experimental data acquired using a grating interferometer. The experiment is performed on unstained adult zebrafish, an important model organism for biomedical studies. The method optimization described here allows resolution of weak soft tissue features, such as muscle fibers.« less

Large Deployable Reflector Technologies for Future European Telecom and Earth Observation Missions

NASA Astrophysics Data System (ADS)

Ihle, A.; Breunig, E.; Dadashvili, L.; Migliorelli, M.; Scialino, L.; van't Klosters, K.; Santiago-Prowald, J.

2012-07-01

This paper presents requirements, analysis and design results for European large deployable reflectors (LDR) for space applications. For telecommunications, the foreseeable use of large reflectors is associated to the continuous demand for improved performance of mobile services. On the other hand, several earth observation (EO) missions can be identified carrying either active or passive remote sensing instruments (or both), in which a large effective aperture is needed e.g. BIOMASS. From the European point of view there is a total dependence of USA industry as such LDRs are not available from European suppliers. The RESTEO study is part of a number of ESA led activities to facilitate European LDR development. This paper is focused on the structural-mechanical aspects of this study. We identify the general requirements for LDRs with special emphasis on launcher accommodation for EO mission. In the next step, optimal concepts for the LDR structure and the RF-Surface are reviewed. Regarding the RF surface, both, a knitted metal mesh and a shell membrane based on carbon fibre reinforced silicon (CFRS) are considered. In terms of the backing structure, the peripheral ring concept is identified as most promising and a large number of options for the deployment kinematics are discussed. Of those, pantographic kinematics and a conical peripheral ring are selected. A preliminary design for these two most promising LDR concepts is performed which includes static, modal and kinematic simulation and also techniques to generate the reflector nets.

Primary Objective Grating Astronomical Telescope

NASA Technical Reports Server (NTRS)

Ditto, Thomas D.

2007-01-01

It has been 370 years since a seventeenth century French mathematician, Mersenne, presciently sketched out an astronomical telescope based on dual parabolic reflectors. Since that time the concept of the primary objective has been virtually unchanged. Now a new class of astronomical telescope with a primary objective grating (POG) has been studied as an alternative. The POG competes with mirrors, in part, because diffraction gratings provide the very chromatic dispersion that mirrors defeat. The resulting telescope deals effectively with long-standing restrictions on multiple object spectroscopy (MOS). Other potential benefits include unprecedented apertures and collection areas. The new design also favors space deployment as a gossamer membrane. The inventor, Tom Ditto, first discovered that higher-order diffraction images contain hidden depth cues, for which he was granted a seminal range finding patent in 1987. Subsequently, he invented and patented 3D localizers, profilometers and microscopes using POGs. The POG telescope was placed in the public domain to expedite research. The function of a telescopes primary objective is to collect flux and to deliver images. Both functions dictate that size matters, and bigger is better. For that reason, there has been a steady push over the past century to ramp up the size of the primary mirror. However, for every doubling of mirror diameter, the elapsed time between initial effort and first light has also doubled. Meanwhile, costs escalated beyond the mirror alone, because larger instruments required larger enclosures and better pointing mechanisms. One key catalog of observation, spectrographic data, is far more difficult to amass than two-dimensional imagery. While the number of observable objects has increased with mirror size, the capacity to take spectra has not increased proportionately. In the best of circumstances, spectrograms are available for one per cent of the all objects surveyed. Spectroscopy was a historical afterthought introduced in the nineteenth century shortly after the invention of the diffraction grating and over a century after Newtons 1670 telescope. Spectroscopy is generally accomplished using a diffraction grating as the disperser in the secondary. The light being delivered to the spectrograph is first captured by a primary mirror which provides no chromatic magnification by itself. Sizeable spectrographs could not be deployed while diffraction gratings were rare commodities scribed using mechanical ruling engines that produced one grating line at a time. Today diffraction gratings are commonplace. Their recent availability is a product of both the invention of holography and the mass replication of surface microstructures. Holography permits all lines in a grating to be made simultaneously in a single photographic exposure. Holograms can then be reproduced by embossing processes. The improvement in replication is analogous to how Gutenberg changed the availability of books. The masters may be expensive, but the copies are not. Computer science is another technology that emerged in the second half of the twentieth century without which our proposed spectrographic instrument could not function due to the complexity of image processing required in data reduction. The employment of very large diffraction gratings as primary objectives for astronomical telescopes requires a novel

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.)

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.

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.

Double high refractive-index contrast grating VCSEL

NASA Astrophysics Data System (ADS)

Gebski, Marcin; Dems, Maciej; Wasiak, Michał; Sarzała, Robert P.; Lott, J. A.; Czyszanowski, Tomasz

2015-03-01

Distributed Bragg reflectors (DBRs) are typically used as the highly reflecting mirrors of vertical-cavity surface-emitting lasers (VCSELs). In order to provide optical field confinement, oxide apertures are often incorporated in the process of the selective wet oxidation of high aluminum-content DBR layers. This technology has some potential drawbacks such as difficulty in controlling the uniformity of the oxide aperture diameters across a large-diameter (≥ 6 inch) production wafers, high DBR series resistance especially for small diameters below about 5 μm despite elaborate grading and doping schemes, free carrier absorption at longer emission wavelengths in the p-doped DBRs, reduced reliability for oxide apertures placed close to the quantum wells, and low thermal conductivity for transporting heat away from the active region. A prospective alternative mirror is a high refractive index contrast grating (HCG) monolithically integrated with the VCSEL cavity. Two HCG mirrors potentially offer a very compact and simplified VCSEL design although the problems of resistance, heat dissipation, and reliability are not completely solved. We present an analysis of a double HCG 980 nm GaAs-based ultra-thin VCSEL. We analyze the optical confinement of such a structure with a total optical thickness is ~1.0λ including the optical cavity and the two opposing and parallel HCG mirrors.

Suspended light-emitting diode featuring a bottom dielectric distributed Bragg reflector

NASA Astrophysics Data System (ADS)

Cai, Wei; Wang, Wei; Zhu, Bingcheng; Gao, Xumin; Zhu, Guixia; Yuan, Jialei; Wang, Yongjin

2018-01-01

Here, we propose, fabricate and characterize the light manipulation of a suspended-membrane InGaN/GaN multiple-quantum-well light-emitting diode (MQW-LED) with a dielectric distributed Bragg reflector (DBR) positioned at the bottom, implemented on a GaN-on-silicon platform. Silicon removal is conducted to obtain the suspended MQW-LED architecture, and back wafer thinning of the epitaxial film is performed to improve the device performance. A 6-pair SiO2/Ta2O5 DBR is deposited on the backside to manipulate the emitted light. The experimental results demonstrate that the bottom dielectric DBR exhibits high reflectivity and distinctly changes the light emission, which are consistent with the performed simulation results. This work represents a significant step towards the realization of inexpensive, electrically driven and simply fabricated GaN VCSELs for potential use in number of applications.

Apparatus and method for tuned unsteady flow purging of high pulse rate spark gaps

DOEpatents

Thayer, III, William J.

1990-01-01

A spark gap switch apparatus is disclosed which is capable of operating at a high pulse rate which comprises an insulated housing; a pair of spaced apart electrodes each having one end thereof within a first bore formed in the housing and defining a spark gap therebetween; a pressure wave reflector in the first bore in the housing and spaced from the spark gap and capable of admitting purge flow; and a second enlarged bore contiguous with the first bore and spaced from the opposite side of the spark gap; whereby pressure waves generated during discharge of a spark across the spark gap will reflect off the wave reflector and back from the enlarged bore to the spark gap to clear from the spark gap hot gases residues generated during the discharge and simultaneously restore the gas density and pressure in the spark gap to its initial value.

Interior tomography from differential phase contrast data via Hilbert transform based on spline functions

NASA Astrophysics Data System (ADS)

Yang, Qingsong; Cong, Wenxiang; Wang, Ge

2016-10-01

X-ray phase contrast imaging is an important mode due to its sensitivity to subtle features of soft biological tissues. Grating-based differential phase contrast (DPC) imaging is one of the most promising phase imaging techniques because it works with a normal x-ray tube of a large focal spot at a high flux rate. However, a main obstacle before this paradigm shift is the fabrication of large-area gratings of a small period and a high aspect ratio. Imaging large objects with a size-limited grating results in data truncation which is a new type of the interior problem. While the interior problem was solved for conventional x-ray CT through analytic extension, compressed sensing and iterative reconstruction, the difficulty for interior reconstruction from DPC data lies in that the implementation of the system matrix requires the differential operation on the detector array, which is often inaccurate and unstable in the case of noisy data. Here, we propose an iterative method based on spline functions. The differential data are first back-projected to the image space. Then, a system matrix is calculated whose components are the Hilbert transforms of the spline bases. The system matrix takes the whole image as an input and outputs the back-projected interior data. Prior information normally assumed for compressed sensing is enforced to iteratively solve this inverse problem. Our results demonstrate that the proposed algorithm can successfully reconstruct an interior region of interest (ROI) from the differential phase data through the ROI.

Development of high-efficiency solar cells on silicon web

NASA Technical Reports Server (NTRS)

Rohatgi, A.; Meier, D. L.; Campbell, R. B.; Seidensticker, R. G.; Rai-Choudhury, P.

1985-01-01

High-efficiency dendritic cells were discussed. The influence of twin planes and heat treatment on the location and effect of trace impurities was of particular interest. Proper heat treatment often increases efficiency by causing impurities to pile up at twin planes. Oxide passivation had a beneficial effect on efficiency. A very efficient antireflective (AR) coating of zinc selenide and magnesium fluoride was designed and fabricated. An aluminum back-surface reflector was also effective.

Patterning of graphene on silicon-on-insulator waveguides through laser ablation and plasma etching

NASA Astrophysics Data System (ADS)

Van Erps, Jürgen; Ciuk, Tymoteusz; Pasternak, Iwona; Krajewska, Aleksandra; Strupinski, Wlodek; Van Put, Steven; Van Steenberge, Geert; Baert, Kitty; Terryn, Herman; Thienpont, Hugo; Vermeulen, Nathalie

2016-05-01

We present the use of femtosecond laser ablation for the removal of monolayer graphene from silicon-on-insulator (SOI) waveguides, and the use of oxygen plasma etching through a metal mask to peel off graphene from the grating couplers attached to the waveguides. Through Raman spectroscopy and atomic force microscopy, we show that the removal of graphene is successful with minimal damage to the underlying SOI waveguides. Finally, we employ both removal techniques to measure the contribution of graphene to the loss of grating-coupled graphene-covered SOI waveguides using the cut-back method. This loss contribution is measured to be 0.132 dB/μm.

Infrared wire-grid polarizer with sol-gel antireflection films on both sides

NASA Astrophysics Data System (ADS)

Yamada, Itsunari; Ishihara, Yoshiro

2017-12-01

We fabricated an infrared wire-grid polarizer with the high transverse magnetic (TM) polarization transmittance and high extinction ratio by soft imprint lithography, sol-gel method, and Al shadow coating processes. A zilconia film was coated on Si substrate by using sol-gel method and spin coating method. Then, sol-gel zirconia grating was formed on the back side using imprinting using a silicone mold. The polarizer was produced by depositing Al obliquely on the grating. The TM transmittance of the fabricated element was greater than 80% at a wavelength of 4.8 μm. The sol-gel zilconia films acted as antireflection films. The extinction ratio exceeded 26 dB at its wavelength.

Long-period fiber gratings as ultrafast optical differentiators.

PubMed

Kulishov, Mykola; Azaña, José

2005-10-15

It is demonstrated that a single, uniform long-period fiber grating (LPFG) working in the linear regime inherently behaves as an ultrafast optical temporal differentiator. Specifically, we show that the output temporal waveform in the core mode of a LPFG providing full energy coupling into the cladding mode is proportional to the first derivative of the optical temporal signal (e.g., optical pulse) launched at the input of the LPFG. Moreover, a LPFG providing full energy recoupling back from the cladding mode into the core mode inherently implements second-order temporal differentiation. Our numerical results have confirmed the feasibility of this simple, all-fiber approach to processing optical signals with temporal features in the picosecond and subpicosecond ranges.

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.

Very small IF resonator filters using reflection of shear horizontal wave at free edges of substrate.

PubMed

Kadota, Michio; Ago, Junya; Horiuchi, Hideya; Ikeura, Mamoru

2002-09-01

A shear horizontal (SH) wave has the characteristic of complete reflection at the free edges of a substrate with a large dielectric constant. A conventional surface acoustic wave (SAW) resonator filter requires reflectors consisting of numerous grating fingers on both sides of interdigital transducers (IDTs). On the contrary, it is considered that small-sized and low loss resonator filters without reflectors consisting of grating fingers can be realized by exploiting this characteristic of the SH wave or the Bleustein-Gulyaev-Shimizu (BGS) wave. There are two types of resonator filters: transversely coupled and longitudinally coupled. No transversely coupled filters (neither conventional nor edge-reflection) using the SH wave on a single-crystal substrate have been realized until now, because two transverse modes (symmetrical and asymmetrical modes) are not easily coupled. However, the authors have realized small low loss transversely coupled resonator filters in the range of 25 to 52 MHz using edge reflections of the BGS wave on piezoelectric ceramic (PZT: Pb(Zr,Ti)O3) substrates for the first time by developing methods by which the two transverse modes could be coupled. On the other hand, longitudinally coupled resonator filters using edge reflection of the SH or BGS wave always have large spurious responses because of the even modes in the out-of-band range, because the frequencies of even modes do not coincide with the nulls of the frequency spectra of the IDTs. Consequently, longitudinally coupled resonator filters using the edge reflection of the SH wave have not been realized. By developing a method of reducing the spurious responses without increasing of the insertion loss, the authors have realized small low loss longitudinally coupled resonator filters in the range of 40 to 190 MHz using edge reflection of BGS or SH waves on PZT or 36 degrees-rotated-Y X-propagation LiTaO3 substrates for the first time. Despite being intermediate frequency (IF) filters, their package (3 x 3 x 1.03 mm3) sizes are as small as those of radio frequency (RF) SAW filters.

Thin silicon solar cell performance characteristics

NASA Technical Reports Server (NTRS)

Gay, C. F.

1978-01-01

Refined techniques for surface texturizing, back surface field and back surface reflector formation were evaluated for use with shallow junction, single-crystal silicon solar cells. Each process was characterized individually and collectively as a function of device thickness and bulk resistivity. Among the variables measured and reported are open circuit voltage, short circuit current and spectral response. Substantial improvements were obtained by the utilization of a low cost aluminum paste process to simultaneously remove the unwanted n(+) diffused region, form the back surface field and produce an ohmic contact metallization. The highly effective BSF which results from applying this process has allowed fabrication of cells 0.05 mm thick with initial outputs as high as 79.5 mW/4 sq cm (28 C, AM0) and superior electron radiation tolerance. Cells of 0.02 mm to 0.04 mm thickness have been fabricated with power to mass ratios well in excess of 2 watts per gram.

Rapid subsidence along the Kerama Gap on the Ryukyu Arc, northwestern Pacific

NASA Astrophysics Data System (ADS)

Arai, K.; Inoue, T.; Sato, T.

2017-12-01

The Ryukyu Arc, which extend for over 1200 km along the east coast of Asia from Kyushu to Taiwan, and the associated Ryukyu Trench, are products of the subduction of the Philippine Sea Plate beneath the Eurasian Plate. The Okinawa Trough, a back-arc basin located landward of the Ryukyu Arc, formed in the Late Miocene (Gungor et al., 2012) or the Late Pliocene-Early Pleistocene (Sibuet et al., 1998); its formation is a key geologic event associated with complex tectonic movements and changes in the topographic configuration of the Ryukyu Arc. Geological Survey of Japan (GSJ), AIST has started the marine geological mapping project around the Ryukyu Arc since the 2008 FY. Multi channel (16 ch) high-resolution seismic profiles were acquired during these cruises by the GI-gun (355cu. inch) or the Cluster-gun (30+30 cu. inch) systems. Our survey area around the Okinawa Island is characterized by the shelf, upper forearc slope and slope to the back-arc basin. Seismic reflections of shelf and the upper forearc slope show a distinct reflector which may represent erosional unconformable surface. The distinct reflector had mainly tilted southeastward and was overlain by the stratified sediments. No obvious deformation such as the fold and faults parallel to the Ryukyu Trench axis was found under the upper forearc slope. In contrast, some active faults which were perpendicular to the Ryukyu Trench axis (NW-SE direction) were observed. The most conspicuous normal faults system under the Kerama Gap located on southwest off the Okinawa Island is formed. We will present the seismic profiles around the Kerama Gap. Seismic profiles show a distinct, irregularly undulated reflector as an acoustic basement around the Kerama Gap. The acoustic basement is overlain by the clear stratified sediments. Many normal faults developed NW-SE direction cut the stratified sediments and are deformed the subsurface along the Kerama Gap. Subsidence of the Kerama Gap resulted from large vertical downthrows of NW-SE trending normal faults.

Solar energy emplacement developer

NASA Technical Reports Server (NTRS)

Mortensen, Michael; Sauls, Bob

1991-01-01

A preliminary design was developed for a Lunar Power System (LPS) composed of photovoltaic arrays and microwave reflectors fabricated from lunar materials. The LPS will collect solar energy on the surface of the Moon, transform it into microwave energy, and beam it back to Earth where it will be converted into usable energy. The Solar Energy Emplacement Developer (SEED) proposed will use a similar sort of solar energy collection and dispersement to power the systems that will construct the LPS.

FIBER AND INTEGRATED OPTICS: Multiplexed optical-fiber sensors with autodyne detection

NASA Astrophysics Data System (ADS)

Potapov, V. T.; Mamedov, A. M.; Shatalin, S. V.; Yushkaĭtis, R. V.

1993-09-01

A method is proposed for multiplexing optical-fiber interference sensors. The method involves autodyne reception of frequency-modulated radiation reflected back to the laser. The response of a He-Ne laser with a linearly varying generation frequency to radiation reflected back from a single-mode fiber is studied. The spectrum of beats caused in the laser radiation by the reflection is shown to be governed by the distribution of reflectors along the fiber. The phases of the spectral components contain information about the phase shift of the reflected optical signal. A hydrophone array with a sensitivity of 30 μrad/Hz1/2 is described. A distributed temperature sensor with a spatial resolution of 1 m is also described.

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.

Absorption of a rigid frame porous layer with periodic circular inclusions backed by a periodic grating.

PubMed

Groby, J-P; Duclos, A; Dazel, O; Boeckx, L; Lauriks, W

2011-05-01

The acoustic properties of a periodic rigid frame porous layer with multiple irregularities in the rigid backing and embedded rigid circular inclusions are investigated theoretically and numerically. The theoretical representation of the sound field in the structure is obtained using a combination of multipole method that accounts for the periodic inclusions and multi-modal method that accounts for the multiple irregularities of the rigid backing. The theoretical model is validated against a finite element method. The predictions show that the acoustic response of this structure exhibits quasi-total, high absorption peaks at low frequencies which are below the frequency of the quarter-wavelength resonance typical for a flat homogeneous porous layer backed by a rigid plate. This result is explained by excitation of additional modes in the porous layer and by a complex interaction between various acoustic modes. These modes relate to the resonances associated with the presence of a profiled rigid backing and rigid inclusions in the porous layer.

Solar module having reflector between cells

DOEpatents

Kardauskas, Michael J.

1999-01-01

A photovoltaic module comprising an array of electrically interconnected photovoltaic cells disposed in a planar and mutually spaced relationship between a light-transparent front cover member in sheet form and a back sheet structure is provided with a novel light-reflecting means disposed between adjacent cells for reflecting light falling in the areas between cells back toward said transparent cover member for further internal reflection onto the solar cells. The light-reflecting comprises a flexible plastic film that has been embossed so as to have a plurality of small V-shaped grooves in its front surface, and a thin light-reflecting coating on said front surface, the portions of said coating along the sides of said grooves forming light-reflecting facets, said grooves being formed so that said facets will reflect light impinging thereon back into said transparent cover sheet with an angle of incidence greater than the critical angle, whereby substantially all of the reflected light will be internally reflected from said cover sheet back to said solar modules, thereby increasing the current output of the module.

Single reflector interference spectrometer and drive system therefor

NASA Technical Reports Server (NTRS)

Schindler, R. A. (Inventor)

1974-01-01

In a Fourier interference spectrometer of the doublepass retroreflector type, a single mirror is employed in the path of both split beams of an incoming ray to cause them to double back through separate retroreflectors. Changes in optical path length are achieved by linear displacement of both retroreflectors using a motor driven lead screw on one for large, low frequency changes, a moving-coil actuator on the other for smaller, mid-frequency changes and a piezoelectric actuator on one of these two for small, high frequency changes.

New, Efficient Optically Pumped Solid State Lasers.

DTIC Science & Technology

1989-02-21

Lasers", during the contract period from 15 August 1984 thru 11 November 1988 (AFOSR-88-0378) has led to some notable advances. This effort h,.s focused...lower laser states of both Er and 1Ho. This work has led to the inves t igation of the Nd,Er ion-ion interactions in other crystals such as Nd,Er:YALO...backed pyrex reflector. While the laser may work in a gold-plated cavity, the many visible, blue and near uv pump bands suggest better efficiency is

Ladder-structured photonic variable delay device

NASA Technical Reports Server (NTRS)

Yao, X. Steve (Inventor)

1998-01-01

An ladder-structured variable delay device for providing variable true time delay to multiple optical beams simultaneously. The device comprises multiple basic units stacked on top of each other resembling a ladder. Each basic unit comprises a polarization sensitive corner reflector formed by two polarization beamsplitters and a polarization rotator array placed parallel to the hypotenuse of the corner reflector. Controlling an array element of the polarization rotator array causes an optical beam passing through the array element to either go up to a basic unit above it or reflect back towards output. The beams going higher on the ladder experience longer optical path delay. Finally, the ladder-structured variable device can be cascaded with another multi-channel delay device to form a new device which combines the advantages of the two individual devices. This programmable optic device has the properties of high packing density, low loss, easy fabrication, and virtually infinite bandwidth. In addition, the delay is reversible so that the same delay device can be used for both antenna transmitting and receiving.

Unassisted photoelectrochemical water splitting exceeding 7% solar-to-hydrogen conversion efficiency using photon recycling

PubMed Central

Shi, Xinjian; Jeong, Hokyeong; Oh, Seung Jae; Ma, Ming; Zhang, Kan; Kwon, Jeong; Choi, In Taek; Choi, Il Yong; Kim, Hwan Kyu; Kim, Jong Kyu; Park, Jong Hyeok

2016-01-01

Various tandem cell configurations have been reported for highly efficient and spontaneous hydrogen production from photoelectrochemical solar water splitting. However, there is a contradiction between two main requirements of a front photoelectrode in a tandem cell configuration, namely, high transparency and high photocurrent density. Here we demonstrate a simple yet highly effective method to overcome this contradiction by incorporating a hybrid conductive distributed Bragg reflector on the back side of the transparent conducting substrate for the front photoelectrochemical electrode, which functions as both an optical filter and a conductive counter-electrode of the rear dye-sensitized solar cell. The hybrid conductive distributed Bragg reflectors were designed to be transparent to the long-wavelength part of the incident solar spectrum (λ>500 nm) for the rear solar cell, while reflecting the short-wavelength photons (λ<500 nm) which can then be absorbed by the front photoelectrochemical electrode for enhanced photocurrent generation. PMID:27324578

Post-image acquisition processing approaches for coherent backscatter validation

NASA Astrophysics Data System (ADS)

Smith, Christopher A.; Belichki, Sara B.; Coffaro, Joseph T.; Panich, Michael G.; Andrews, Larry C.; Phillips, Ronald L.

2014-10-01

Utilizing a retro-reflector from a target point, the reflected irradiance of a laser beam traveling back toward the transmitting point contains a peak point of intensity known as the enhanced backscatter (EBS) phenomenon. EBS is dependent on the strength regime of turbulence currently occurring within the atmosphere as the beam propagates across and back. In order to capture and analyze this phenomenon so that it may be compared to theory, an imaging system is integrated into the optical set up. With proper imaging established, we are able to implement various post-image acquisition techniques to help determine detection and positioning of EBS which can then be validated with theory by inspection of certain dependent meteorological parameters such as the refractive index structure parameter, Cn2 and wind speed.

Acoustic waves in tilted fiber Bragg gratings for sensing applications

NASA Astrophysics Data System (ADS)

Marques, Carlos A. F.; Alberto, Nélia J.; Domingues, Fátima; Leitão, Cátia; Antunes, Paulo; Pinto, João. L.; André, Paulo

2017-05-01

Tilted fiber Bragg gratings (TFBGs) are one of the most attractive kind of optical fiber sensor technology due to their intrinsic properties. On the other hand, the acousto-optic effect is an important, fast and accurate mechanism that can be used to change and control several properties of fiber gratings in silica and polymer optical fiber. Several all-optical devices for optical communications and sensing have been successfully designed and constructed using this effect. In this work, we present the recent results regarding the production of optical sensors, through the acousto-optic effect in TFBGs. The cladding and core modes amplitude of a TFBG can be controlled by means of the power levels from acoustic wave source. Also, the cladding modes of a TFBG can be coupled back to the core mode by launching acoustic waves. Induced bands are created on the left side of the original Bragg wavelength due to phase matching to be satisfied. The refractive index (RI) is analyzed in detail when acoustic waves are turned on using saccharose solutions with different RI from 1.33 to 1.43.

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.

Perfect-absorption graphene metamaterials for surface-enhanced molecular fingerprint spectroscopy.

PubMed

Guo, Xiangdong; Hu, Hai; Liao, Baoxin; Zhu, Xing; Yang, Xiaoxia; Dai, Qing

2018-05-04

Graphene plasmon with extremely strong light confinement and tunable resonance frequency represents a promising surface-enhanced infrared absorption (SEIRA) sensing platform. However, plasmonic absorption is relatively weak (approximately 1%-9%) in monolayer graphene nanostructures, which would limit its sensitivity. Here, we theoretically propose a hybrid plasmon-metamaterial structure that can realize perfect absorption in graphene with a low carrier mobility of 1000 cm 2 V -1 s -1 . This structure combines a gold reflector and a gold grating to the graphene plasmon structures, which introduce interference effect and the lightning-rod effect, respectively, and largely enhance the coupling of light to graphene. The vibration signal of trace molecules can be enhanced up to 2000-fold at the hotspot of the perfect-absorption structure, enabling the SEIRA sensing to reach the molecular level. This hybrid metal-graphene structure provides a novel path to generate high sensitivity in nanoscale molecular recognition for numerous applications.

Ka-Band Phased Array System Characterization

NASA Technical Reports Server (NTRS)

Acosta, R.; Johnson, S.; Sands, O.; Lambert, K.

2001-01-01

Phased Array Antennas (PAAs) using patch-radiating elements are projected to transmit data at rates several orders of magnitude higher than currently offered with reflector-based systems. However, there are a number of potential sources of degradation in the Bit Error Rate (BER) performance of the communications link that are unique to PAA-based links. Short spacing of radiating elements can induce mutual coupling between radiating elements, long spacing can induce grating lobes, modulo 2 pi phase errors can add to Inter Symbol Interference (ISI), phase shifters and power divider network introduce losses into the system. This paper describes efforts underway to test and evaluate the effects of the performance degrading features of phased-array antennas when used in a high data rate modulation link. The tests and evaluations described here uncover the interaction between the electrical characteristics of a PAA and the BER performance of a communication link.

Quantum dash based single section mode locked lasers for photonic integrated circuits.

PubMed

Joshi, Siddharth; Calò, Cosimo; Chimot, Nicolas; Radziunas, Mindaugas; Arkhipov, Rostislav; Barbet, Sophie; Accard, Alain; Ramdane, Abderrahim; Lelarge, Francois

2014-05-05

We present the first demonstration of an InAs/InP Quantum Dash based single-section frequency comb generator designed for use in photonic integrated circuits (PICs). The laser cavity is closed using a specifically designed Bragg reflector without compromising the mode-locking performance of the self pulsating laser. This enables the integration of single-section mode-locked laser in photonic integrated circuits as on-chip frequency comb generators. We also investigate the relations between cavity modes in such a device and demonstrate how the dispersion of the complex mode frequencies induced by the Bragg grating implies a violation of the equi-distance between the adjacent mode frequencies and, therefore, forbids the locking of the modes in a classical Bragg Device. Finally we integrate such a Bragg Mirror based laser with Semiconductor Optical Amplifier (SOA) to demonstrate the monolithic integration of QDash based low phase noise sources in PICs.

Simple analytical model for low-frequency frequency-modulation noise of monolithic tunable lasers.

PubMed

Huynh, Tam N; Ó Dúill, Seán P; Nguyen, Lim; Rusch, Leslie A; Barry, Liam P

2014-02-10

We employ simple analytical models to construct the entire frequency-modulation (FM)-noise spectrum of tunable semiconductor lasers. Many contributions to the laser FM noise can be clearly identified from the FM-noise spectrum, such as standard Weiner FM noise incorporating laser relaxation oscillation, excess FM noise due to thermal fluctuations, and carrier-induced refractive index fluctuations from stochastic carrier generation in the passive tuning sections. The contribution of the latter effect is identified by noting a correlation between part of the FM-noise spectrum with the FM-modulation response of the passive sections. We pay particular attention to the case of widely tunable lasers with three independent tuning sections, mainly the sampled-grating distributed Bragg reflector laser, and compare with that of a distributed feedback laser. The theoretical model is confirmed with experimental measurements, with the calculations of the important phase-error variance demonstrating excellent agreement.

Gold bugs and beyond: a review of iridescence and structural colour mechanisms in beetles (Coleoptera)

PubMed Central

Seago, Ainsley E.; Brady, Parrish; Vigneron, Jean-Pol; Schultz, Tom D.

2008-01-01

Members of the order Coleoptera are sometimes referred to as ‘living jewels’, in allusion to the strikingly diverse array of iridescence mechanisms and optical effects that have arisen in beetles. A number of novel and sophisticated reflectance mechanisms have been discovered in recent years, including three-dimensional photonic crystals and quasi-ordered coherent scattering arrays. However, the literature on beetle structural coloration is often redundant and lacks synthesis, with little interchange between the entomological and optical research communities. Here, an overview is provided for all iridescence mechanisms observed in Coleoptera. Types of iridescence are illustrated and classified into three mechanistic groups: multilayer reflectors, three-dimensional photonic crystals and diffraction gratings. Taxonomic and phylogenetic distributions are provided, along with discussion of the putative functions and evolutionary pathways by which iridescence has repeatedly arisen in beetles. PMID:18957361

Portable fiber-coupled diode-laser-based sensor for multiple trace gas detection

NASA Technical Reports Server (NTRS)

Lancaster, D. G.; Richter, D.; Tittel, F. K.

1999-01-01

Tunable narrowband mid-infrared radiation from 3.25 to 4.4 micrometers is generated by a compact fiber-coupled, difference-frequency-based spectroscopic source. A 20-mW external cavity diode laser (with a tuning range from 814 to 870 nm) and a 50-mW distributed-Bragg-reflector diode-laser-seeded ytterbium-doped fiber amplifier operating at 1083 nm are difference-frequency mixed in a multi-grating, temperature-controlled periodically poled LiNbO3 crystal. A conversion efficiency of 0.44 mW/(W2cm) (corresponding to a power of approximately equal to 3 microW at 3.3 micrometers) represents the highest conversion efficiency reported for a portable device. Performance characteristics of such a sensor and its application to spectroscopic detection of CO2, N2O, H2CO, HCl, NO2, and CH4 will be reported in this work.

Perfect-absorption graphene metamaterials for surface-enhanced molecular fingerprint spectroscopy

NASA Astrophysics Data System (ADS)

Guo, Xiangdong; Hu, Hai; Liao, Baoxin; Zhu, Xing; Yang, Xiaoxia; Dai, Qing

2018-05-01

Graphene plasmon with extremely strong light confinement and tunable resonance frequency represents a promising surface-enhanced infrared absorption (SEIRA) sensing platform. However, plasmonic absorption is relatively weak (approximately 1%-9%) in monolayer graphene nanostructures, which would limit its sensitivity. Here, we theoretically propose a hybrid plasmon-metamaterial structure that can realize perfect absorption in graphene with a low carrier mobility of 1000 cm2 V-1 s-1. This structure combines a gold reflector and a gold grating to the graphene plasmon structures, which introduce interference effect and the lightning-rod effect, respectively, and largely enhance the coupling of light to graphene. The vibration signal of trace molecules can be enhanced up to 2000-fold at the hotspot of the perfect-absorption structure, enabling the SEIRA sensing to reach the molecular level. This hybrid metal-graphene structure provides a novel path to generate high sensitivity in nanoscale molecular recognition for numerous applications.

Feasibility study of solid surface subreflector production techniques

NASA Technical Reports Server (NTRS)

1982-01-01

The principal effort was to study technical feasibility and cost aspects of the production technique of spin forming a subreflector reflective surface to a desired surface of revolution, back the surface with fiberglass to stabilize it sufficiently so that it may be machined to the target surface tolerance of .008 inches Root Mean Square (RMS) with a goal of .003 inches RMS. To verify this production technique, analyses was performed to define the production procedure. A price estimate for a 150 inch diameter subreflector for a 34 meter cassegrain antenna. During this feasibility study, numerous production processes were evaluated theoretically as production approaches for single surface, non-welded subreflectors. The first successful was the principal process of spin forming the reflective surface, backing with fiberglass and machining to a final contour. The second successful process was spin forming or bump forming a thicker reflective surface, with an integral (welded in) structure as a backing and machining the mounting pads and reflector to a final configuration.

Back scattering involving embedded silicon nitride (SiN) nanoparticles for c-Si solar cells

NASA Astrophysics Data System (ADS)

Ghosh, Hemanta; Mitra, Suchismita; Siddiqui, M. S.; Saxena, A. K.; Chaudhuri, Partha; Saha, Hiranmay; Banerjee, Chandan

2018-04-01

A novel material, structure and method of synthesis for dielectric light trapping have been presented in this paper. First, the light scattering behaviour of silicon nitride nanoparticles have been theoretically studied in order to find the optimized size for dielectric back scattering by FDTD simulations from Lumerical Inc. The optical results have been used in electrical analysis and thereby, estimate the effect of nanoparticles on efficiency of the solar cells depending on substrate thickness. Experimentally, silicon nitride (SiN) nanoparticles have been formed using hydrogen plasma treatment on SiN layer deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD). The size and area coverage of the nanoparticles were controlled by varying the working pressure, power density and treatment duration. The nanoparticles were integrated with partial rear contact c-Si solar cells as dielectric back reflector structures for the light trapping in thin silicon solar cells. Experimental results revealed the increases of current density by 2.7% in presence of SiN nanoparticles.

Imaging Grating Spectrometer (I-GRASP) for Solar Soft X-Ray Spectral Measurements in Critically Under-Observed 0.5 - 7 nm Spectral Range

NASA Astrophysics Data System (ADS)

Didkovsky, L. V.; Wieman, S. R.; Chao, W.; Woods, T. N.; Jones, A. R.; Thiemann, E.; Mason, J. P.

2016-12-01

We discuss science and technology advantages of the Imaging Grating Spectrometer (I-GRASP) based on a novel transmission diffracting grating (TDG) made possible by technology for fabricating Fresnel zone plates (ZPs) developed at the Lawrence Berkeley National Laboratory (LBNL). Older version TDGs with 200 nm period available in the 1990s became a proven technology for providing 21 years of regular measurements of solar EUV irradiance. I-GRASP incorporates an advanced TDG with a grating period of 50 nm providing four times better diffraction dispersion than the 200 nm period gratings used in the SOHO/CELIAS/SEM, the SDO/EVE/ESP flight spectrophotometers, and the EVE/SAM sounding rocket channel. Such new technology for the TDG combined with a back-illuminated 2000 x 1504 CMOS image sensor with 7 micron pixels, will provide spatially-and-spectrally resolved images and spectra from individual Active Regions (ARs) and solar flares with high (0.15 nm) spectral resolution. Such measurements are not available in the spectral band from about 2 to 6 nm from existing or planned spectrographs and will be significantly important to study ARs and solar flare temperatures and dynamics, to improve existing spectral models, e.g. CHIANTI, and to better understand processes in the Earth's atmosphere processes. To test this novel technology, we have proposed to the NASA LCAS program an I-GRASP version for a sounding rocket flight to increase the TDG TRL to a level appropriate for future CubeSat projects.

High resolution middle infrared spectrometer, a part of atmospheric chemistry suite (ACS) for EXOMARS 2016 trace gas orbiter

NASA Astrophysics Data System (ADS)

Trokhimovskiy, Alexander; Korablev, Oleg; Ivanov, Yurii; Syniavskyi, Ivan; Montmessin, Franck; Fedorova, Anna

2017-11-01

The Atmospheric Chemistry Suite (ACS) package is a part of Russian contribution to ExoMars ESARoscosmos mission for studies of the Martian atmosphere and climate. ACS consists of three separate infrared spectrometers, sharing common mechanical, electrical, and thermal interfaces. The mid-infrared (MIR) channel is a cross-dispersion high resolution echelle instrument dedicated to solar occultation measurements and sensitive studies of trace gases. The MIR channel is a spectrometer working in 2.3-4.2 μm spectral range, covering simultaneously up to almost 300 nm per exposure, targeting the resolving power of 50,000. A crossdispersion concept on echelle and ordinary diffraction grating allows acquisition of the wide wavelength domain at once. That provides a strategic advantage for maximizing the number of gaseous species detected simultaneously and good special resolution of measurements during fast occultation sessions. Moving the second grating allows to switch from one group of the diffraction orders to another prior to a series of measurements, or desired positions during one measurement sequence. The concept of the cross-dispersion echelle instrument, which is widely accepted in astronomy, has been already employed in planetary missions with VIRTIS-H instrument presently in flight on Rosetta and Venus Express missions. Targeting very high spectral resolution the MIR channel operates in solar occultation only. A telescope with relative aperture of 1∶3 forms the image of the solar disk on the slit. The FOV is determined by the slit and it consists 0.1×2.9 mrad. The spectral resolution of the spectrometer is fully slit-limited, and the resolving power of λ/Δλ >= 50000 at 3.3 μm is supported. Two secondary cross-dispersion diffraction gratings (plain, 180 and 361 grooves per mm) are mounted back-to-back on a stepper motor to change observed echelle orders. We have chosen two secondary gratings philosophy to switch between them depending on the long or short wavelength range we are on. Changing the position of the secondary grating in angular steps of 1.8°, from 10 to 30 echelle orders are available for simultaneous record depending on the wavelength. 100 steps are evidently used to switch between gratings prior measurements. The full spectral range is covered on diffraction orders from 142 to 248. For each observation detector area is covered by 10 to 30 stripes, each corresponding to single echelle diffraction order. Given the complexity of the diffraction orders pattern, full detector frames will be transmitted to the ground, with lossless compression. However, the onboard averaging will be possible. Single data frame will be accumulated for 0.5 seconds, stacking of a number of shorter exposures.

Low-loss adiabatically-tapered high-contrast gratings for slow-wave modulators on SOI

NASA Astrophysics Data System (ADS)

Sciancalepore, Corrado; Hassan, Karim; Ferrotti, Thomas; Harduin, Julie; Duprez, Hélène; Menezo, Sylvie; Ben Bakir, Badhise

2015-02-01

In this communication, we report about the design, fabrication, and testing of Silicon-based photonic integrated circuits (Si-PICs) including low-loss flat-band slow-light high-contrast-gratings (HCGs) waveguides at 1.31 μm. The light slowdown is achieved in 300-nm-thick silicon-on-insulator (SOI) rib waveguides by patterning adiabatically-tapered highcontrast gratings, capable of providing slow-light propagation with extremely low optical losses, back-scattering, and Fabry-Pérot noise. In detail, the one-dimensional (1-D) grating architecture is capable to provide band-edge group indices ng ~ 25, characterized by overall propagation losses equivalent to those of the index-like propagation regime (~ 1-2 dB/cm). Such photonic band-edge slow-light regime at low propagation losses is made possible by the adiabatic apodization of such 1-D HCGs, thus resulting in a win-win approach where light slow-down regime is reached without additional optical losses penalty. As well as that, a tailored apodization optimized via genetic algorithms allows the flattening of slow-light regime over the wavelength window of interest, therefore suiting well needs for group index stability for modulation purposes and non-linear effects generation. In conclusion, such architectures provide key features suitable for power-efficient high-speed modulators in silicon as well as an extremely low-loss building block for non-linear optics (NLO) which is now available in the Si photonics toolbox.

Short-range/Long-range Integrated Target (SLIT) for Video Guidance Sensor Rendezvous and Docking

NASA Technical Reports Server (NTRS)

Roe, Fred D. (Inventor); Bryan, Thomas C. (Inventor)

2009-01-01

A laser target reflector assembly for mounting upon spacecraft having a long-range reflector array formed from a plurality of unfiltered light reflectors embedded in an array pattern upon a hemispherical reflector disposed upon a mounting plate. The reflector assembly also includes a short-range reflector array positioned upon the mounting body proximate to the long-range reflector array. The short-range reflector array includes three filtered light reflectors positioned upon extensions from the mounting body. The three filtered light reflectors retro-reflect substantially all incident light rays that are transmissive by their monochromatic filters and received by the three filtered light reflectors. In one embodiment the short-range reflector array is embedded within the hemispherical reflector,

KSC-00pp0821

NASA Image and Video Library

2000-06-30

In the early morning hours on Launch Pad 36A, Cape Canaveral Air Force Station, the tower rolls back from NASA’s Tracking and Data Relay Satellite (TDRS-H) before liftoff atop an Atlas IIA/Centaur rocket. One of three satellites (labeled H, I and J) being built by the Hughes Space and Communications Company, the latest TDRS uses an innovative springback antenna design. A pair of 15-foot-diameter, flexible mesh antenna reflectors fold up for launch, then spring back into their original cupped circular shape on orbit. The new satellites will augment the TDRS system’s existing Sand Ku-band frequencies by adding Ka-band capability. TDRS will serve as the sole means of continuous, high-data-rate communication with the Space Shuttle, with the International Space Station upon its completion, and with dozens of unmanned scientific satellites in low earth orbit

KSC00pp0821

NASA Image and Video Library

2000-06-30

In the early morning hours on Launch Pad 36A, Cape Canaveral Air Force Station, the tower rolls back from NASA’s Tracking and Data Relay Satellite (TDRS-H) before liftoff atop an Atlas IIA/Centaur rocket. One of three satellites (labeled H, I and J) being built by the Hughes Space and Communications Company, the latest TDRS uses an innovative springback antenna design. A pair of 15-foot-diameter, flexible mesh antenna reflectors fold up for launch, then spring back into their original cupped circular shape on orbit. The new satellites will augment the TDRS system’s existing Sand Ku-band frequencies by adding Ka-band capability. TDRS will serve as the sole means of continuous, high-data-rate communication with the Space Shuttle, with the International Space Station upon its completion, and with dozens of unmanned scientific satellites in low earth orbit

Investigation of Analog Photonic Link Technology for Timing and Metrological Applications

DTIC Science & Technology

2015-05-18

same model bias tee in each case. Fig. 1.8: Measured residual single-sideband (SSB) phase noise for two amplifiers with various RF pads at...deflection at the AO output. The deflected signal is reflected onto a tilted diffraction grating and passed backed through the device to the output...Other TTD modulation mechanisms have been considered including fiber stretches (mechanical and piezoelectric ), electro-optic modulators (i.e

Steady-state, cavityless, multimode superradiance in a cold vapor

NASA Astrophysics Data System (ADS)

Greenberg, Joel A.; Gauthier, Daniel J.

2012-07-01

We demonstrate steady-state, mirrorless superradiance in a cold vapor pumped by weak optical fields. Beyond a critical pump intensity of 1 mW/cm2, the vapor spontaneously transforms into a spatially self-organized state: a density grating forms. Scattering of the pump beams off this grating generates a pair of new, intense optical fields that act back on the vapor to enhance the atomic organization. We map out experimentally the superradiant phase transition boundary and show that it is well described by our theoretical model. The resulting superradiant emission is nearly coherent, persists for several seconds, displays strong temporal correlations between the various modes, and has a coherence time of several hundred μs. This system therefore has applications in fundamental studies of many-body physics with long-range interactions as well as all-optical and quantum information processing.

Free-standing GaN grating couplers and rib waveguide for planar photonics at telecommunication wavelength

NASA Astrophysics Data System (ADS)

Liu, Qifa; Wang, Wei

2018-01-01

Gallium Nitride (GaN) free-standing planar photonic device at telecommunication wavelength based on GaN-on-silicon platform was presented. The free-standing structure was realized by particular double-side fabrication process, which combining GaN front patterning, Si substrate back releasing and GaN slab etching. The actual device parameters were identified via the physical characterizations employing scanning electron microscope (SEM), atomic force microscope (AFM) and reflectance spectra testing. High coupling efficiency and good light confinement properties of the gratings and rib waveguide at telecommunication wavelength range were verified by finite element method (FEM) simulation. This work illustrates the potential of new GaN photonic structure which will enable new functions for planar photonics in communication and sensing applications, and is favorable for the realization of integrated optical circuit.

Dynamic Photorefractive Memory and its Application for Opto-Electronic Neural Networks.

NASA Astrophysics Data System (ADS)

Sasaki, Hironori

This dissertation describes the analysis of the photorefractive crystal dynamics and its application for opto-electronic neural network systems. The realization of the dynamic photorefractive memory is investigated in terms of the following aspects: fast memory update, uniform grating multiplexing schedules and the prevention of the partial erasure of existing gratings. The fast memory update is realized by the selective erasure process that superimposes a new grating on the original one with an appropriate phase shift. The dynamics of the selective erasure process is analyzed using the first-order photorefractive material equations and experimentally confirmed. The effects of beam coupling and fringe bending on the selective erasure dynamics are also analyzed by numerically solving a combination of coupled wave equations and the photorefractive material equation. Incremental recording technique is proposed as a uniform grating multiplexing schedule and compared with the conventional scheduled recording technique in terms of phase distribution in the presence of an external dc electric field, as well as the image gray scale dependence. The theoretical analysis and experimental results proved the superiority of the incremental recording technique over the scheduled recording. Novel recirculating information memory architecture is proposed and experimentally demonstrated to prevent partial degradation of the existing gratings by accessing the memory. Gratings are circulated through a memory feed back loop based on the incremental recording dynamics and demonstrate robust read/write/erase capabilities. The dynamic photorefractive memory is applied to opto-electronic neural network systems. Module architecture based on the page-oriented dynamic photorefractive memory is proposed. This module architecture can implement two complementary interconnection organizations, fan-in and fan-out. The module system scalability and the learning capabilities are theoretically investigated using the photorefractive dynamics described in previous chapters of the dissertation. The implementation of the feed-forward image compression network with 900 input and 9 output neurons with 6-bit interconnection accuracy is experimentally demonstrated. Learning of the Perceptron network that determines sex based on input face images of 900 pixels is also successfully demonstrated.

Laser Radar Study Using Resonance Absorption for Remote Detection Of Air Pollutants

NASA Technical Reports Server (NTRS)

Igarashi, Takashi

1973-01-01

A laser radar using resonance absorption has an advantage of increased detection range and sensitivity compared with that achieved by Raman or resonance back scattering. In this paper, new laser radar system using resonance absorption is proposed and results obtained from this laser radar system are discussed. NO2, SO2 gas has an absorption spectrum at 4500 A and 3000 A respectively as shown in Fig. 1. A laser light including at least a set of an absorption peak (lambda)1 and a valley (lambda)2 is emitted into a pollutant atmosphere. The light reflected with a topographical reflector or an atmospheric Mie scattering as distributed reflectors is received and divided into two wavelength components (lambda)1 and (lambda)2. The laser radar system used in the investigation is shown in Fig', 2 and consists of a dye laser transmitter, an optical receiver with a special monochrometer and a digital processer. Table 1 shows the molecular constants of NO2, and SO2 and the dye laser used in this experiment. In this system, the absolute concentration of the pollutant gas can be measured in comparison with a standard gas cell. The concentration of NO2, SO2 as low as 0.1 ppm have been measured at 100 m depth resolution. For a 1 mJ laser output, the observable range of this system achieved up to 300 m using the distributed Mie reflector. The capability and technical limitation of the system will be discussed in detail.

A Simple Ultra-Wideband Magneto-Electric Dipole Antenna With High Gain

NASA Astrophysics Data System (ADS)

Shuai, Chen-yang; Wang, Guang-ming

2017-12-01

A simple ultra-wideband magneto-electric dipole antenna utilizing a differential-fed structure is designed. The antenna mainly comprises three parts, including a novel circular horned reflector, two vertical semicircular shorted patches as a magnetic dipole, and a horizontal U-shaped semicircular electric dipole. A differential feeding structure working as a perfect balun excites the designed antenna. The results of simulation have a good match with the ones of measurement. Results indicate that the designed antenna achieves a wide frequency bandwidth of 107 % which is 3.19 10.61 GHz, when VSWR is below 2. Via introducing the circular horned reflector, the designed antenna attains a steady and high gain of 12±1.5dBi. Moreover, settled broadside direction main beam, high front-to-back ratio, low cross polarization, and the symmetrical and relatively stable radiation patterns in the E-and H-plane are gotten in the impedance bandwidth range. In the practical applications, the proposed antenna that is dc grounded and has a simple structure satisfies the requirement of many outdoor antennas.

Resonant-enhanced full-color emission of quantum-dot-based micro LED display technology.

PubMed

Han, Hau-Vei; Lin, Huang-Yu; Lin, Chien-Chung; Chong, Wing-Cheung; Li, Jie-Ru; Chen, Kuo-Ju; Yu, Peichen; Chen, Teng-Ming; Chen, Huang-Ming; Lau, Kei-May; Kuo, Hao-Chung

2015-12-14

Colloidal quantum dots which can emit red, green, and blue colors are incorporated with a micro-LED array to demonstrate a feasible choice for future display technology. The pitch of the micro-LED array is 40 μm, which is sufficient for high-resolution screen applications. The method that was used to spray the quantum dots in such tight space is called Aerosol Jet technology which uses atomizer and gas flow control to obtain uniform and controlled narrow spots. The ultra-violet LEDs are used in the array to excite the red, green and blue quantum dots on the top surface. To increase the utilization of the UV photons, a layer of distributed Bragg reflector was laid down on the device to reflect most of the leaked UV photons back to the quantum dot layers. With this mechanism, the enhanced luminous flux is 194% (blue), 173% (green) and 183% (red) more than that of the samples without the reflector. The luminous efficacy of radiation (LER) was measured under various currents and a value of 165 lm/Watt was recorded.

Ductile extension of syn-magmatic lower crusts, with application to volcanic passive margins: the Ivrea Zone (Southern Alps, Italy)

NASA Astrophysics Data System (ADS)

Bidault, Marie; Geoffroy, Laurent; Arbaret, Laurent; Aubourg, Charles

2017-04-01

Deep seismic reflection profiles of present-day volcanic passive margins often show a 2-layered lower crust, from top to bottom: an apparently ductile 12 km-thick middle-lower layer (LC1) of strong folded reflectors and a 4 km-thick supra-Moho layer (LC2) of horizontal and parallel reflectors. Those layers appear to be structurally disconnected and to develop at the early stages of margins evolution. A magmatic origin has been suggested by several studies to explain those strong reflectors, favoring mafic sills intrusion hypothesis. Overlying mafic and acidic extrusives (Seaward Dipping Reflectors sequences) are bounded by continentward-dipping detachment faults rooting in, and co-structurated with, the ductile part of the lower crust (LC1). Consequently the syn-rift to post-rift evolution of volcanic passive margins (and passive margins in general) largely depends on the nature and the properties of the lower crust, yet poorly understood. We propose to investigate the properties and rheology of a magma-injected extensional lower crust with a field analogue, the Ivrea Zone (Southern Alps, Italy). The Ivrea Zone displays a complete back-thrusted section of a Variscan continental lower crust that first underwent gravitational collapse, and then lithospheric extension. This Late Paleozoic extension was apparently associated with the continuous intrusion of a large volume of mafic to acid magma. Both the magma timing and volume, and the structure of the Ivrea lower crust suggest that this section represents an adequate analogue of a syn-magmatic in-extension mafic rift zone which aborted at the end of the Permian. Notably, we may recognize the 2 layers LC1 and LC2. From a number of tectonic observations, we reconstitute the whole tectonic history of the area, focusing on the strain field evolution with time, in connection with mafic magma injection. We compare those results with available data from extensional mafic lower crusts at rifts and margins.

Feasibility study of a synthesis procedure for array feeds to improve radiation performance of large distorted reflector antennas

NASA Technical Reports Server (NTRS)

Stutzman, W. L.; Takamizawa, K.; Werntz, P.; Lapean, J.; Barts, R.

1991-01-01

The following subject areas are covered: General Reflector Antenna Systems Program version 7(GRASP7); Multiple Reflector Analysis Program for Cylindrical Antennas (MRAPCA); Tri-Reflector 2D Synthesis Code (TRTDS); a geometrical optics and a physical optics synthesis techniques; beam scanning reflector, the type 2 and 6 reflectors, spherical reflector, and multiple reflector imaging systems; and radiometric array design.

Design, Fabrication and Characterization of Micro Opto-Electro-Mechanical Systems.

DTIC Science & Technology

1995-12-01

interference problems (see Fig. 3-6). Improvements in the lithography of the MCNC process would allow for grating spaces of less than 2 gm and therefore...A micro-spectrometer has been fabricated using LIGA, an acronym for lithography , electroforming, and micromolding (the acronym came from the German...location for test samples and an adjustable mirror. The beams are brought back together to form an interference pattern. At an observation screen the

All-reflective optical target illumination system with high numerical aperture

DOEpatents

Sigler, Robert D.

1978-01-01

An all-reflective optical system for providing illumination of a target focal region at high numerical aperture from a pair of co-axially, confluent collimated light beams. A target cavity is defined by a pair of opposed inner ellipsoidal reflectors having respective first focal points within a target region and second focal points at a vertex opening in the opposing reflector. Outwardly of each inner reflector is the opposed combination of a spherical reflector, and an outer generally ellipsoidal reflector having an aberrated first focal point coincident with the focus of the opposing spherical reflector and a second focal point coincident with the second focal point of the opposing inner ellipsoidal reflector through a vertex opening in the spherical reflector. The confluent collimated beams are incident through vertex openings in the outer ellipsoidal reflectors onto respective opposing spherical reflectors. Each beam is reflected by the associated spherical reflector onto the opposing outer ellipsoidal reflector and focused thereby onto the opposing inner ellipsoidal reflector, and then onto the target region.

EXPERIMENTAL AND ANALYTICAL STUDIES OF REFLECTRO CONTROL FOR THE ADVANCED ENGINEERING TEST REACTOR. PART A. EXPERIMENTAL STUDIES WITH THE REFLECTOR CONTROL SYSTEM MODEL. PART B. ANALYTICAL STUDIES OF REFLECTOR CONTROL

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

Bertelson, P.C.; Francis, T.L.

1959-10-21

Studies of reflector control for the Advanced Engineering Test Reactor were made. The performance of various parts of the reflector control system model such as the safety reflector and the water jet educator, boric acid injection, and demineralizer systems is discussed. The experimental methods and results obtained are discussed. Four reflector control schemes were studied. The schemes were a single-region and three-region reflector schemes two separate reflectors, and two connected reflectors. Calculations were made of shim and safety reflector worth for a variety of parameters. Safety reflector thickness was varied from 7.75 to 0 inches, with and without boron. Boricmore » acid concentration was varied from 100 to 2% of saturation in the shim reflectors. Neutron flux plots are presented (C.J.G.)« less

Reflector system for a lighting fixture

DOEpatents

Siminovitch, Michael J.; Page, Erik; Gould, Carl T.

1998-01-01

Disclosed herein is a reflector system for a lighting fixture having a illumination source surrounded by an envelope. The reflector system includes a first reflector surrounding the illumination source. The reflector system also includes a second reflector which is non-contiguous with the first reflector and which surrounds the illumination source. The illumination source creates light rays which are reflected by the first and second reflectors. The first reflector directs light rays toward the center line of the fixture. However, the reflected rays despite being so reflected do not substantially intersect the envelope. The reflected light rays from the second reflector being directed so that they diverge from the center line of the fixture avoiding intersection with the semi-transparent envelope.

Reflector system for a lighting fixture

DOEpatents

Siminovitch, Michael J.; Page, Erik; Gould, Carl T.

2001-01-01

Disclosed herein is a reflector system for a lighting fixture having a illumination source surrounded by an envelope. The reflector system includes a first reflector surrounding the illumination source. The reflector system also includes a second reflector which is non-contiguous with the first reflector and which surrounds the illumination source. The illumination source creates light rays which are reflected by the first and second reflectors. The first reflector directs light rays toward the center line of the fixture. However, the reflected rays despite being so reflected do not substantially intersect the envelope. The reflected light rays from the second reflector being directed so that they diverge from the center line of the fixture avoiding intersection with the semi-transparent envelope.

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

Dewani, Aliya A., E-mail: a.ashraf@griffith.edu.au; O’Keefe, Steven G.; Thiel, David V.

A novel 2D simple low cost frequency selective surface was screen printed on thin (0.21 mm), flexible transparent plastic substrate (relative permittivity 3.2). It was designed, fabricated and tested in the frequency range 10-20 GHz. The plane wave transmission and reflection coefficients agreed with numerical modelling. The effective permittivity and thickness of the backing sheet has a significant effect on the frequency characteristics. The stop band frequency reduced from 15GHz (no backing) to 12.5GHz with polycarbonate. The plastic substrate thickness beyond 1.8mm has minimal effect on the resonant frequency. While the inner element spacing controls the stop-band frequency, the substratemore » thickness controls the bandwidth. The screen printing technique provided a simple, low cost FSS fabrication method to produce flexible, conformal, optically transparent and bio-degradable FSS structures which can find their use in electromagnetic shielding and filtering applications in radomes, reflector antennas, beam splitters and polarizers.« less

Optically transparent frequency selective surfaces on flexible thin plastic substrates

NASA Astrophysics Data System (ADS)

Dewani, Aliya A.; O'Keefe, Steven G.; Thiel, David V.; Galehdar, Amir

2015-02-01

A novel 2D simple low cost frequency selective surface was screen printed on thin (0.21 mm), flexible transparent plastic substrate (relative permittivity 3.2). It was designed, fabricated and tested in the frequency range 10-20 GHz. The plane wave transmission and reflection coefficients agreed with numerical modelling. The effective permittivity and thickness of the backing sheet has a significant effect on the frequency characteristics. The stop band frequency reduced from 15GHz (no backing) to 12.5GHz with polycarbonate. The plastic substrate thickness beyond 1.8mm has minimal effect on the resonant frequency. While the inner element spacing controls the stop-band frequency, the substrate thickness controls the bandwidth. The screen printing technique provided a simple, low cost FSS fabrication method to produce flexible, conformal, optically transparent and bio-degradable FSS structures which can find their use in electromagnetic shielding and filtering applications in radomes, reflector antennas, beam splitters and polarizers.

Structured FBG filters for 10-Gb/s DPSK signal demodulation in single ended applications

NASA Astrophysics Data System (ADS)

Marazzi, L.; Boffi, P.; Parolari, P.; Martinelli, M.; Gatti, D.; Coluccelli, N.; Longhi, S.

2011-05-01

Differential phase-shift keying (DPSK) demodulations operated by a structured fiber Bragg grating (FBG) filter and by a Mach-Zehnder delay interferometer (MZDI) in a single-ended configuration are compared. Experimental measurements at 10 Gb/s demonstrate that a specially designed FBG outperforms an integrated-optic MZDI of ˜4 dB and ˜3.5 dB in back-to-back and after 25-km propagation, respectively. Both demodulators show low polarization sensitivity and signal frequency detuning dependence, but only MZDI operating point requires a thermal control. FBG filter proves an interesting solution for DPSK demodulation in low-cost applications and, moreover, can be designed to match colorless requirements of wave division multiplexed passive optical network (WDM-PON) applications.

AWG-based WDM-PON monitoring system using an optical switch and a WDM filter

NASA Astrophysics Data System (ADS)

Liaw, S.-K.; Lai, Y.-T.; Chang, C.-L.; Shung, O.

2008-09-01

A new WDM-PON scheme with real-time monitoring based on a time-sharing method is proposed. It uses an optical time domain reflectometer (OTDR) to monitor multiple ports by integrating an optical switch (OSW) with a dense wavelength division multiplexer (DWDM) at the optical line terminal (OLT) site. Each downstream signal and its corresponding monitoring signal are separated by m times the free-space range (FSR) of an array waveguide grating (AWG). A bit error rate (BER) test in 2.5 Gb/s × 27 km is performed with and without turning on the OTDR. A small power penalty of 0.7 dB is observed compared to the back-to-back measurement.

Reflector system for a lighting fixture

DOEpatents

Siminovitch, M.J.; Page, E.; Gould, C.T.

1998-09-08

Disclosed herein is a reflector system for a lighting fixture having a illumination source surrounded by an envelope. The reflector system includes a first reflector surrounding the illumination source. The reflector system also includes a second reflector which is non-contiguous with the first reflector and which surrounds the illumination source. The illumination source creates light rays which are reflected by the first and second reflectors. The first reflector directs light rays toward the center line of the fixture. However, the reflected rays despite being so reflected do not substantially intersect the envelope. The reflected light rays from the second reflector being directed so that they diverge from the center line of the fixture avoiding intersection with the semi-transparent envelope. 5 figs.

Design and optimization of the plasmonic graphene/InP thin-film solar-cell structure

NASA Astrophysics Data System (ADS)

Nematpour, Abedin; Nikoufard, Mahmoud; Mehragha, Rouholla

2018-06-01

In this paper, a graphene/InP thin-film Schottky-junction solar cell with a periodic array of plasmonic back-reflector is proposed. In this structure, a single-layer graphene sheet is deposited on the surface of the InP to form a Schottky junction. Then, the layer stack of the proposed solar-cell is optimized to have a maximum optical absorption of 〈A W〉  =  0.985 (98.5%) and short-circuit current density of J sc  =  33.01 mA cm‑2.

Understanding temperature tuning of the all polymer co-extruded laser

NASA Astrophysics Data System (ADS)

Crescimanno, Michael; Andrews, Jim; Aviles, Michael; Dawson, Nathan; Petrus, Joshua; Mazzocco, Anthony; Singer, Ken; Baer, Eric; Song, Hyunmin

2012-10-01

We investigate the effects of elevated temperatures on a few types of all-polymer multilayer films that were fabricated using a co-extrusion melt-process technique. We report on the anisotropic thermal expansion of the multilayer films, which affects the photonic crystal structure via constituent wise induced anisotropic strains and a change in the relative refractive indices. In addition to the characterization of these films in the temperature range of approximately 20-95 degrees C, we show the application to non-contact temperature sensing and wavelength tuning of all polymer Distributed FeedBack (DFB) lasers and Distributed Bragg Reflector (DBR) lasers.

In0.53Ga0.47As/InP conventional and inverted thermophotovoltaic cells with back surface reflector

NASA Astrophysics Data System (ADS)

Karlina, L. B.; Kulagina, M. M.; Timoshina, N. Kh.; Vlasov, A. S.; Andreev, V. M.

2007-02-01

Characteristics of conventional and inverted InGaAs/InP thermophotovoltaic (TPV) cells with a back surface reflector (BSR) fabricated on electrically active n-type InP substrates are presented. Thermophotovoltaic cells based on lattice matched InP-In0.53Ga0.47As heterostructures were fabricated with the use of LPE and Zn,P diffusion technologies. In the p-n TPV cells (conventional type, spectral range 600÷1800 nm) with a frontal p-InGaAs layer, BSR was made on a n-InP substrate. In the n-p structure (inverted type, spectral range1000-1800 nm) with a frontal bulk n-InP-window-substrate, BSR was formed on a p-InGaAs layer. Antireflection coating (ARC) on the frontal cell surface consists of ZnS/MgF2 layers. Results of investigation of sub-bangap photons reflection from InP substrates with a backside MgF2/Au mirror in the range of 1800÷2000nm are described. The reflection of BSR for InP samples with the doping level in the range of 1×1017÷6×1018cm-3 evidenced a weak dependence on their thickness and doping level. A reflection of 86÷90% has been measured for substrates 100μm thick and 80% for ones 400μm thick with ARC. Study of sub-bandgap photon reflection of p-InGaAs (Zn,P) layers with surface concentration of 1÷3×1019cm-3 has been also carried out. A reflection of 68÷77% for 2÷4μm layers with "hybrid" (ohmic contact plus mirror) back-surface reflector consisted of deposited Cr/Au layers was measured. It was found, that p-n and n-p thermophotovoltaic 1×1cm2 cells with identical grid design reveal similar parameters for up to 1A/cm2 current density (VOC=465mV and FF=64%) and the 76÷80% reflection of the sub-bandgap photons for wavelengths longer than 1.86μm. The developed inverted InGaAs TPV cells have been tested under illumination of silicon carbide high temperature emitter. The photocurrent density Jsc=7A/cm2, open circuit voltage Voc=0.476V and fill factor FF=0.691 have been measured in the inverted (without BSR) InGaAs cell under SiC emitter heated to the temperature of about 1550°C. Both types of devices can successfully be used as TPV cells for conversion of radiation in the range of 1500-1900K, with 14-15% efficiency.

Room temperature continuous wave, monolithic tunable THz sources based on highly efficient mid-infrared quantum cascade lasers

PubMed Central

Lu, Quanyong; Wu, Donghai; Sengupta, Saumya; Slivken, Steven; Razeghi, Manijeh

2016-01-01

A compact, high power, room temperature continuous wave terahertz source emitting in a wide frequency range (ν ~ 1–5 THz) is of great importance to terahertz system development for applications in spectroscopy, communication, sensing, and imaging. Here, we present a strong-coupled strain-balanced quantum cascade laser design for efficient THz generation based on intracavity difference frequency generation. Room temperature continuous wave emission at 3.41 THz with a side-mode suppression ratio of 30 dB and output power up to 14 μW is achieved with a wall-plug efficiency about one order of magnitude higher than previous demonstrations. With this highly efficient design, continuous wave, single mode THz emissions with a wide frequency tuning range of 2.06–4.35 THz and an output power up to 4.2 μW are demonstrated at room temperature from two monolithic three-section sampled grating distributed feedback-distributed Bragg reflector lasers. PMID:27009375

Electroabsorption-modulated widely tunable DBR laser transmitter for WDM-PONs.

PubMed

Han, Liangshun; Liang, Song; Wang, Huitao; Qiao, Lijun; Xu, Junjie; Zhao, Lingjuan; Zhu, Hongliang; Wang, Baojun; Wang, Wei

2014-12-01

We present an InP based distributed Bragg reflector (DBR) laser transmitter which has a wide wavelength tuning range and a high chip output power for wavelength division multiplexing passive optical network (WDM-PON) applications. By butt-jointing InGaAsP with 1.45 µm emission wavelength as the material of the grating section, the laser wavelength can be tuned for over 13 nm by the DBR current. Accompanied by varying the chip temperature, the tuning range can be further enlarged to 16 nm. With the help of the integrated semiconductor optical amplifier (SOA), the largest chip output power is over 30 mW. The electroabsorption modulator (EAM) is integrated into the device by the selective-area growth (SAG) technique. The 3 dB small signal modulation bandwidth of the EAM is over 13 GHz. The device has both a simple tuning scheme and a simple fabrication procedure, making it suitable for low cost massive production which is desirable for WDM-PON uses.

Room temperature continuous wave, monolithic tunable THz sources based on highly efficient mid-infrared quantum cascade lasers.

PubMed

Lu, Quanyong; Wu, Donghai; Sengupta, Saumya; Slivken, Steven; Razeghi, Manijeh

2016-03-24

A compact, high power, room temperature continuous wave terahertz source emitting in a wide frequency range (ν~1-5 THz) is of great importance to terahertz system development for applications in spectroscopy, communication, sensing, and imaging. Here, we present a strong-coupled strain-balanced quantum cascade laser design for efficient THz generation based on intracavity difference frequency generation. Room temperature continuous wave emission at 3.41 THz with a side-mode suppression ratio of 30 dB and output power up to 14 μW is achieved with a wall-plug efficiency about one order of magnitude higher than previous demonstrations. With this highly efficient design, continuous wave, single mode THz emissions with a wide frequency tuning range of 2.06-4.35 THz and an output power up to 4.2 μW are demonstrated at room temperature from two monolithic three-section sampled grating distributed feedback-distributed Bragg reflector lasers.

Cross-sectional imaging of extracted jawbone of a pig by optical coherence tomography

NASA Astrophysics Data System (ADS)

Tachikawa, Noriko; Yoshimura, Reiko; Ohbayashi, Kohji

2011-03-01

Dental implantation has become popular in dental treatments. Although careful planning is made to identify vital structures such as the inferior alveolar nerve or the sinus, as well as dimensions of the bone, prior to commencement of surgery, dental implantation is not fully free from risks. If a diagnostic tool is available to objectively measure bone feature before surgery and dimensions during surgery, considerable fraction of the risks may be avoided. Optical coherence tomography (OCT) is a candidate for the purpose, which enables cross-sectional imaging of bone. In this work, we performed in vitro cross-sectional imaging of extracted pig's jawbone with swept source OCT using superstructure-grating distributed Bragg reflector (SSG-DBR) laser as the source. The relatively long wavelength range of 1600nm of the laser is suitable for deeper bone imaging. We confirmed an image penetration depth of about 3 mm in physical length, which satisfies one of the criterions to apply OCT for in vivo diagnosis of bone during surgery.

Switchable dual-wavelength SOA-based fiber laser with continuous tunability over the C-band at room-temperature.

PubMed

Ummy, M A; Madamopoulos, N; Razani, M; Hossain, A; Dorsinville, R

2012-10-08

We propose and demonstrate a simple compact, inexpensive, SOA-based, dual-wavelength tunable fiber laser, that can potentially be used for photoconductive mixing and generation of waves in the microwave and THz regions. A C-band semiconductor optical amplifier (SOA) is placed inside a linear cavity with two Sagnac loop mirrors at its either ends, which act as both reflectors and output ports. The selectivity of dual wavelengths and the tunability of the wavelength difference (Δλ) between them is accomplished by placing a narrow bandwidth (e.g., 0.3 nm) tunable thin film-based filter and a fiber Bragg grating (with bandwidth 0.28 nm) inside the loop mirror that operates as the output port. A total output power of + 6.9 dBm for the two wavelengths is measured and the potential for higher output powers is discussed. Optical power and wavelength stability are measured at 0.33 dB and 0.014 nm, respectively.

The interstellar D1 line at high resolution

NASA Technical Reports Server (NTRS)

Hobbs, L. M.; Welty, D. E.

1990-01-01

Observations at a resolving power or a velocity resolution are reported of the interstellar D(sub 1) line of Na I in the spectra of gamma Cas, delta Ori, epsilon Ori, pi Sco, delta Cyg, and alpha Cyg. An echelle grating was used in a double-pass configuration with a CCD detector in the coude spectrograph of the 2.7 m reflector at McDonald Observatory. At least 42 kinematically distinct clouds are detected along the light paths to the five more distant stars, in addition to a single cloud seen toward delta Cyg. The absorption lines arising in 13 of the clouds are sufficiently narrow and unblended to reveal clearly resolved hyperfine structure components split by 1.05 km/s. An additional 13 clouds apparently show comparably narrow, but more strongly blended, lines. For each individual cloud, upper limits T(sub max) and (v sub t)(sub max) on the temperature and the turbulent velocity, respectively, are derived by fitting the observed lines with theoretical absorption profiles.

Bifocal reflector for electrohydraulic lithotripters.

PubMed

Prieto, F E; Loske, A M

1999-03-01

To describe the design and construction of a bifocal reflector that could be used in electrohydraulic extracorporeal shockwave lithotripters in order to increase their efficiency. The new reflector is obtained by joining two sectors of two rotationally symmetric ellipsoidal reflectors having different distances between their foci, which results in a bifocal composite reflector with the F1 foci in coincidence and the two F2 foci separated by a certain distance. As in conventional reflectors, shockwaves are generated by the electrical breakdown of water between two electrodes, located at the focus (F1) closest to the reflector. A prototype was constructed and tested in an experimental shockwave generator of our own make, using two different types of kidney-stone models, one to test the stone fragmentation abilities, and the other to test the stone pitting abilities. Fragmentation data for the new reflector were compared with those of a conventional ellipsoidal reflector tested on the same device. The new design appeared to be more efficient in breaking up both types of kidney-stone models than the conventional reflector. Pressure measurements were obtained with both reflectors using needle hydrophones. The physical background of shockwave reflection on both reflectors is also explained. With this new reflector, it could be possible, in principle, to reduce the treatment time of extracorporeal shockwave lithotripsy.

Silicon photonic resonator sensors and devices

NASA Astrophysics Data System (ADS)

Chrostowski, Lukas; Grist, Samantha; Flueckiger, Jonas; Shi, Wei; Wang, Xu; Ouellet, Eric; Yun, Han; Webb, Mitch; Nie, Ben; Liang, Zhen; Cheung, Karen C.; Schmidt, Shon A.; Ratner, Daniel M.; Jaeger, Nicolas A. F.

2012-02-01

Silicon photonic resonators, implemented using silicon-on-insulator substrates, are promising for numerous applications. The most commonly studied resonators are ring/racetrack resonators. We have fabricated these and other resonators including disk resonators, waveguide-grating resonators, ring resonator reflectors, contra-directional grating-coupler ring resonators, and racetrack-based multiplexer/demultiplexers. While numerous resonators have been demonstrated for sensing purposes, it remains unclear as to which structures provide the highest sensitivity and best limit of detection; for example, disc resonators and slot-waveguide-based ring resonators have been conjectured to provide an improved limit of detection. Here, we compare various resonators in terms of sensor metrics for label-free bio-sensing in a micro-fluidic environment. We have integrated resonator arrays with PDMS micro-fluidics for real-time detection of biomolecules in experiments such as antigen-antibody binding reaction experiments using Human Factor IX proteins. Numerous resonators are fabricated on the same wafer and experimentally compared. We identify that, while evanescent-field sensors all operate on the principle that the analyte's refractive index shifts the resonant frequency, there are important differences between implementations that lie in the relationship between the optical field overlap with the analyte and the relative contributions of the various loss mechanisms. The chips were fabricated in the context of the CMC-UBC Silicon Nanophotonics Fabrication course and workshop. This yearlong, design-based, graduate training program is offered to students from across Canada and, over the last four years, has attracted participants from nearly every Canadian university involved in photonics research. The course takes students through a full design cycle of a photonic circuit, including theory, modelling, design, and experimentation.

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.

Imaging of sound speed using reflection ultrasound tomography.

PubMed

Nebeker, Jakob; Nelson, Thomas R

2012-09-01

The goal of this work was to obtain and evaluate measurements of tissue sound speed in the breast, particularly dense breasts, using backscatter ultrasound tomography. An automated volumetric breast ultrasound scanner was constructed for imaging the prone patient. A 5- to 7-MHz linear array transducer acquired 17,920 radiofrequency pulse echo A-lines from the breast, and a back-wall reflector rotated over 360° in 25 seconds. Sound speed images used reflector echoes that after preprocessing were uploaded into a graphics processing unit for filtered back-projection reconstruction. A velocimeter also was constructed to measure the sound speed and attenuation for comparison to scanner performance. Measurements were made using the following: (1) deionized water from 22°C to 90°C; (2) various fluids with sound speeds from 1240 to 1904 m/s; (3) acrylamide gel test objects with features from 1 to 15 mm in diameter; and (4) healthy volunteers. The mean error ± SD between sound speed reference and image data was -0.48% ± 9.1%, and the error between reference and velocimeter measurements was -1.78% ± 6.50%. Sound speed image and velocimeter measurements showed a difference of 0.10% ± 4.04%. Temperature data showed a difference between theory and imaging performance of -0.28% ± 0.22%. Images of polyacrylamide test objects showed detectability of an approximately 1% sound speed difference in a 2.4-mm cylindrical inclusion with a contrast to noise ratio of 7.9 dB. An automated breast scanner offers the potential to make consistent automated tomographic images of breast backscatter, sound speed, and attenuation, potentially improving diagnosis, particularly in dense breasts.

Extreme Precision Antenna Reflector Study Results

NASA Technical Reports Server (NTRS)

Sharp, G. R.; Gilger, L. D.; Ard, K. E.

1985-01-01

Thermal and mechanical distortion degrade the RF performance of antennas. The complexity of future communications antennas requires accurate, dimensionally stable antenna reflectors and structures built from materials other than those currently used. The advantages and disadvantages of using carbon fibers in an epoxy matrix are reviewed as well as current reflector fabrications technology and adjustment. The manufacturing sequence and coefficient of thermal expansion of carbon fiber/borosilicate glass composites is described. The construction of a parabolic reflector from this material and the assembling of both reflector and antenna are described. A 3M-aperture-diameter carbon/glass reflector that can be used as a subassembly for large reflectors is depicted. The deployment sequence for a 10.5M-aperture-diameter antenna, final reflector adjustment, and the deployment sequence for large reflectors are also illustrated.

Dual annular rotating "windowed" nuclear reflector reactor control system

DOEpatents

Jacox, Michael G.; Drexler, Robert L.; Hunt, Robert N. M.; Lake, James A.

1994-01-01

A nuclear reactor control system is provided in a nuclear reactor having a core operating in the fast neutron energy spectrum where criticality control is achieved by neutron leakage. The control system includes dual annular, rotatable reflector rings. There are two reflector rings: an inner reflector ring and an outer reflector ring. The reflectors are concentrically assembled, surround the reactor core, and each reflector ring includes a plurality of openings. The openings in each ring are capable of being aligned or non-aligned with each other. Independent driving means for each of the annular reflector rings is provided so that reactor criticality can be initiated and controlled by rotation of either reflector ring such that the extent of alignment of the openings in each ring controls the reflection of neutrons from the core.

Computer prediction of dual reflector antenna radiation properties

NASA Technical Reports Server (NTRS)

Christodoulou, C.

1981-01-01

A program for calculating radiation patterns for reflector antennas with either smooth analytic surfaces or with surfaces composed of a number of panels. Techniques based on the geometrical optics (GO) approach were used in tracing rays over the following regions: from a feed antenna to the first reflector surface (subreflector); from this reflector to a larger reflector surface (main reflector); and from the main reflector to a mathematical plane (aperture plane) in front of the main reflector. The equations of GO were also used to calculate the reflected field components for each ray making use of the feed radiation pattern and the parameters defining the surfaces of the two reflectors. These resulting fields form an aperture distribution which is integrated numerically to compute the radiation pattern for a specified set of angles.

Micron-scale channel formation by the release and bond-back of pre-stressed thin films: A finite element analysis

NASA Astrophysics Data System (ADS)

Annabattula, R. K.; Huck, W. T. S.; Onck, P. R.

2010-04-01

Buckling of thin films on a rigid substrate during use or fabrication is a well-known but unwanted phenomenon. However, this phenomenon can also be exploited to generate well-controlled patterns at the micro and nano-scale. These patterned surfaces find various technological applications such as optical gratings or micro/nano-fluidic channels. In this article, we present a numerical model that accounts for the buckling-up of pre-strained thin films by a reduction of the interface toughness and the subsequent bond-back. Channels are formed whose dimensions can be controlled by tuning the film dimensions, film thickness and stiffness, the eigenstrain in the film and the cohesive interface energy between the film and the substrate. We will show how the buckling-up and draping back processes can be captured in terms of a limited set of dimensionless parameters, providing quantitative insight on how these parameters should be tuned to generate a specified channel geometry.

Computer simulation of ion beam analysis of laterally inhomogeneous materials

NASA Astrophysics Data System (ADS)

Mayer, M.

2016-03-01

The program STRUCTNRA for the simulation of ion beam analysis charged particle spectra from arbitrary two-dimensional distributions of materials is described. The code is validated by comparison to experimental backscattering data from a silicon grating on tantalum at different orientations and incident angles. Simulated spectra for several types of rough thin layers and a chessboard-like arrangement of materials as example for a multi-phase agglomerate material are presented. Ambiguities between back-scattering spectra from two-dimensional and one-dimensional sample structures are discussed.

A Wafer-Bonded, Floating Element Shear-Stress Sensor Using a Geometric Moire Optical Transduction Technique

NASA Technical Reports Server (NTRS)

Horowitz, Stephen; Chen, Tai-An; Chandrasekaran, Venkataraman; Tedjojuwono, Ken; Cattafesta, Louis; Nishida, Toshikazu; Sheplak, Mark

2004-01-01

This paper presents a geometric Moir optical-based floating-element shear stress sensor for wind tunnel turbulence measurements. The sensor was fabricated using an aligned wafer-bond/thin-back process producing optical gratings on the backside of a floating element and on the top surface of the support wafer. Measured results indicate a static sensitivity of 0.26 microns/Pa, a resonant frequency of 1.7 kHz, and a noise floor of 6.2 mPa/(square root)Hz.

JPRS Report Science & Technology Japan 16th International Congress of the International Society for Photogrammetry and Remote Sensing Volume 1

DTIC Science & Technology

1989-01-24

coherent noise . To overcome this disadvantages, a new holographic inverse filtering system has been developed by the authors. The inverse filter is...beam is blocked. The deblurred aerial image is formed in the image plane IP (the back focal plane of L2). The frequency of the grating used in this... impulse response of the optical system. For certain types of blurs, which include linear motion of the camera under the assumption that the picture

Dynamic fiber Bragg gratings based health monitoring system of composite aerospace structures

NASA Astrophysics Data System (ADS)

Panopoulou, A.; Loutas, T.; Roulias, D.; Fransen, S.; Kostopoulos, V.

2011-09-01

The main purpose of the current work is to develop a new system for structural health monitoring of composite aerospace structures based on real-time dynamic measurements, in order to identify the structural state condition. Long-gauge Fibre Bragg Grating (FBG) optical sensors were used for monitoring the dynamic response of the composite structure. The algorithm that was developed for structural damage detection utilizes the collected dynamic response data, analyzes them in various ways and through an artificial neural network identifies the damage state and its location. Damage was simulated by slightly varying locally the mass of the structure (by adding a known mass) at different zones of the structure. Lumped masses in different locations upon the structure alter the eigen-frequencies in a way similar to actual damage. The structural dynamic behaviour has been numerically simulated and experimentally verified by means of modal testing on two different composite aerospace structures. Advanced digital signal processing techniques, e.g. the wavelet transform (WT), were used for the analysis of the dynamic response for feature extraction. WT's capability of separating the different frequency components in the time domain without loosing frequency information makes it a versatile tool for demanding signal processing applications. The use of WT is also suggested by the no-stationary nature of dynamic response signals and the opportunity of evaluating the temporal evolution of their frequency contents. Feature extraction is the first step of the procedure. The extracted features are effective indices of damage size and location. The classification step comprises of a feed-forward back propagation network, whose output determines the simulated damage location. Finally, dedicated training and validation activities were carried out by means of numerical simulations and experimental procedures. Experimental validation was performed initially on a flat stiffened panel, representing a section of a typical aeronautical structure, manufactured and tested in the lab and, as a second step, on a scaled up space oriented structure, which is a composite honeycomb plate, used as a deployment base for antenna arrays. An integrated FBG sensor network, based on the advantage of multiplexing, was mounted on both structures and different excitation positions and boundary conditions were used. The analysis of operational dynamic responses was employed to identify both the damage and its position. The system that was designed and tested initially on the thin composite panel, was successfully validated on the larger honeycomb structure. Numerical simulation of both structures was used as a support tool at all the steps of the work providing among others the location of the optical sensors used. The proposed work will be the base for the whole system qualification and validation on an antenna reflector in future work.

Dual annular rotating [open quotes]windowed[close quotes] nuclear reflector reactor control system

DOEpatents

Jacox, M.G.; Drexler, R.L.; Hunt, R.N.M.; Lake, J.A.

1994-03-29

A nuclear reactor control system is provided in a nuclear reactor having a core operating in the fast neutron energy spectrum where criticality control is achieved by neutron leakage. The control system includes dual annular, rotatable reflector rings. There are two reflector rings: an inner reflector ring and an outer reflector ring. The reflectors are concentrically assembled, surround the reactor core, and each reflector ring includes a plurality of openings. The openings in each ring are capable of being aligned or non-aligned with each other. Independent driving means for each of the annular reflector rings is provided so that reactor criticality can be initiated and controlled by rotation of either reflector ring such that the extent of alignment of the openings in each ring controls the reflection of neutrons from the core. 4 figures.

Reoptimization of the Ohio State University radio telescope for the NASA SETI program

NASA Technical Reports Server (NTRS)

Dixon, R. S.

1991-01-01

The Ohio State University radiotelescope is the second largest radio telescope in the United States, equivalent in collecting area (2200 sq m) to a 175-foot diameter dish. For the past 17 years it has been dedicated fulltime to SETI, and it is now being considered by NASA for selection as the NASA dedicated SETI observatory. The telescope was originally designed, optimized, and used as an all-sky survey instrument to create detailed maps and catalogs of the radio astronomical sky. For the SETI Program, some re-optimizations are required. Right ascension tracking for one to two hours (depending on the declination) was achieved by exploiting the exceptionally large f/d ratio of the telescope. The feed horns were mounted on a large moveable, rubber-tired cart which is capable of a total motion of 100 feet. The cart can carry many horns, making possible simultaneous observations at many sky directions and frequency ranges. Rapid declination movement and its automation will be accomplished through simplification of the existing braking system, and replacement of older mechanical sensors by modern electronic inclinometers and proximity detectors. Circular polarization capability will be achieved through an increase in the number of horizontal wires in the reflector mesh, or addition of a finer mesh on top of the existing one. The telescope has great inherent resistance to radio frequency interference, due to its ground-mounted feed horns and shielding by the large reflectors of half the horizon. The resistance was recently increased further by installation of rolled-edges and diffraction-trapping gratings on the feed horns. If further shielding should be required, inexpensive side shields could be added to the telescope, making it a totally closed structure on all four sides.

Study on the fabrication of back surface reflectors in nano-crystalline silicon thin-film solar cells by using random texturing aluminum anodization

NASA Astrophysics Data System (ADS)

Shin, Kang Sik; Jang, Eunseok; Cho, Jun-Sik; Yoo, Jinsu; Park, Joo Hyung; Byungsung, O.

2015-09-01

In recent decades, researchers have improved the efficiency of amorphous silicon solar cells in many ways. One of the easiest and most practical methods to improve solar-cell efficiency is adopting a back surface reflector (BSR) as the bottom layer or as the substrate. The BSR reflects the incident light back to the absorber layer in a solar cell, thus elongating the light path and causing the so-called "light trapping effect". The elongation of the light path in certain wavelength ranges can be enhanced with the proper scale of BSR surface structure or morphology. An aluminum substrate with a surface modified by aluminum anodizing is used to improve the optical properties for applications in amorphous silicon solar cells as a BSR in this research due to the high reflectivity and the low material cost. The solar cells with a BSR were formed and analyzed by using the following procedures: First, the surface of the aluminum substrate was degreased by using acetone, ethanol and distilled water, and it was chemically polished in a dilute alkali solution. After the cleaning process, the aluminum surface's morphology was modified by using a controlled anodization in a dilute acid solution to form oxide on the surface. The oxidized film was etched off by using an alkali solution to leave an aluminum surface with randomly-ordered dimple-patterns of approximately one micrometer in size. The anodizing conditions and the anodized aluminum surfaces after the oxide layer had been removed were systematically investigated according to the applied voltage. Finally, amorphous silicon solar cells were deposited on a modified aluminum plate by using dc magnetron sputtering. The surfaces of the anodized aluminum were observed by using field-emission scanning electron microscopy. The total and the diffuse reflectances of the surface-modified aluminum sheets were measured by using UV spectroscopy. We observed that the diffuse reflectances increased with increasing anodizing voltage. The properties of the solar cells on anodized aluminum substrates were analyzed by using a solar simulator.

THERMAL NEUTRONIC REACTOR

DOEpatents

Spinrad, B.I.

1960-01-12

A novel thermal reactor was designed in which a first reflector formed from a high atomic weight, nonmoderating material is disposed immediately adjacent to the reactor core. A second reflector composed of a moderating material is disposed outwardly of the first reflector. The advantage of this novel reflector arrangement is that the first reflector provides a high slow neutron flux in the second reflector, where irradiation experiments may be conducted with a small effect on reactor reactivity.

Prospects for Geostationary Doppler Weather Radar

NASA Technical Reports Server (NTRS)

Tanelli, Simone; Fang, Houfei; Durden, Stephen L.; Im, Eastwood; Rhamat-Samii, Yahya

2009-01-01

A novel mission concept, namely NEXRAD in Space (NIS), was developed for detailed monitoring of hurricanes, cyclones, and severe storms from a geostationary orbit. This mission concept requires a space deployable 35-m diameter reflector that operates at 35-GHz with a surface figure accuracy requirement of 0.21 mm RMS. This reflector is well beyond the current state-of-the-art. To implement this mission concept, several potential technologies associated with large, lightweight, spaceborne reflectors have been investigated by this study. These spaceborne reflector technologies include mesh reflector technology, inflatable membrane reflector technology and Shape Memory Polymer reflector technology.

Laser beam alignment system

DOEpatents

Kasner, William H.; Racki, Daniel J.; Swenson, Clark E.

1984-01-01

A plurality of pivotal reflectors direct a high-power laser beam onto a workpiece, and a rotatable reflector is movable to a position wherein it intercepts the beam and deflects a major portion thereof away from its normal path, the remainder of the beam passing to the pivotal reflectors through an aperture in the rotating reflector. A plurality of targets are movable to positions intercepting the path of light traveling to the pivotal reflectors, and a preliminary adjustment of the latter is made by use of a low-power laser beam reflected from the rotating reflector, after which the same targets are used to make a final adjustment of the pivotal reflectors with the portion of the high-power laser beam passed through the rotating reflector.

Fusion reactor pumped laser

DOEpatents

Jassby, D.L.

1987-09-04

A nuclear pumped laser capable of producing long pulses of very high power laser radiation is provided. A toroidal fusion reactor provides energetic neutrons which are slowed down by a moderator. The moderated neutrons are converted to energetic particles capable of pumping a lasing medium. The lasing medium is housed in an annular cell surrounding the reactor. The cell includes an annular reflecting mirror at the bottom and an annular output window at the top. A neutron reflector is disposed around the cell to reflect escaping neutrons back into the cell. The laser radiation from the annular window is focused onto a beam compactor which generates a single coherent output laser beam. 10 figs.

Fusion reactor pumped laser

DOEpatents

Jassby, Daniel L.

1988-01-01

A nuclear pumped laser capable of producing long pulses of very high power laser radiation is provided. A toroidal fusion reactor provides energetic neutrons which are slowed down by a moderator. The moderated neutrons are converted to energetic particles capable of pumping a lasing medium. The lasing medium is housed in an annular cell surrounding the reactor. The cell includes an annular reflecting mirror at the bottom and an annular output window at the top. A neutron reflector is disposed around the cell to reflect escaping neutrons back into the cell. The laser radiation from the annular window is focused onto a beam compactor which generates a single coherent output laser beam.

Off-axis reflective optical apparatus

NASA Technical Reports Server (NTRS)

Ames, Lawrence L. (Inventor); Leary, David F. (Inventor); Mammini, Paul V. (Inventor)

2005-01-01

Embodiments of the present invention are directed to a simple apparatus and a convenient and accurate method of mounting the components to form an off-axis reflective optical apparatus such as a collimator. In one embodiment, an off-axis reflective optical apparatus comprises a mounting block having a ferrule holder support surface and an off-axis reflector support surface which is generally perpendicular to the ferrule holder support surface. An optical reflector is mounted on the off-axis reflector support surface and has a reflected beam centerline. The optical reflector has a conic reflective surface and a conic center. A ferrule holder is mounted on the ferrule holder support surface. The ferrule holder provides a ferrule for coupling to an optical fiber and orienting a fiber tip of the optical fiber along a fiber axis toward the optical reflector. The fiber axis is nonparallel to the reflected beam centerline. Prior to mounting the optical reflector to the off-axis reflector support surface and prior to mounting the ferrule holder to the ferrule holder support surface, the optical reflector is movable on the off-axis reflector surface and the ferrule holder is movable on the ferrule holder support surface to align the conic center of the optical reflector with respect to the fiber tip of the optical fiber, and the apparatus has at least one of the following features: (1) the optical reflector is movable on the off-axis reflector support surface to adjust a focus of the fiber tip with respect to the optical reflector, and (2) the ferrule holder is movable on the ferrule holder support surface to adjust the focus of the fiber tip with respect to the optical reflector.

Walter Baade and the Southern Hemisphere

NASA Astrophysics Data System (ADS)

Osterbrock, D. E.

1993-12-01

The inception of the European Southern Observatory is generally traced to Walter Baade's discussions with Jan Oort during his visit to Leiden in the spring of 1953. However, these discussions had certainly been underway between them previously, during Oort's visit to Pasadena in early 1952. Furthermore, Baade's great interest in southern-hemisphere astronomy and his strong desire to observe there can be traced far back in his career. In 1927, after his return to Germany from a year in the U.S. under a Rockefeller fellowship, Baade reported that his country had no chance to catch up with American astronomy in the northern hemisphere. He advocated moving the Hamburg 1-meter reflector to the southern hemisphere to get in ahead of the U.S. with an effective telescope there. Baade emphasized the research that could be done on high-luminosity and variable stars in the Magellanic Clouds. Later, after he had joined the Mount Wilson staff, his early attempts to locate the center of our Galaxy and globular clusters near it (in 1937) and his observational study (with Edwin Hubble) of the Sculptor and Fornax dwarf galaxies (in 1939) re-emphasized to him the need for a southern observatory. During and soon after World War II he made many suggestions on a search for ``cluster-type variables'' in the Magellanic Clouds to Enrique Gaviola, director of the new 1.5-meter Bosque Alegre reflector in Argentina. Baade wanted to go there to observe with it himself, but his German citizenship prevented him from leaving the U.S.. Finally, in the last year of his life, he was able to observe NGC 6522 (the globular cluster in ``his'' window), with the Mount Stromlo 1.9-meter reflector.

Laser interrogation techniques for high-sensitivity strain sensing by fiber-Bragg-grating structures

NASA Astrophysics Data System (ADS)

Gagliardi, G.; Salza, M.; Ferraro, P.; De Natale, P.

2017-11-01

Novel interrogation methods for static and dynamic measurements of mechanical deformations by fiber Bragg-gratings (FBGs) structures are presented. The sensor-reflected radiation gives information on suffered strain, with a sensitivity dependent on the interrogation setup. Different approaches have been carried out, based on laser-frequency modulation techniques and near-IR lasers, to measure strain in single-FBG and in resonant high-reflectivity FBG arrays. In particular, for the fiber resonator, the laser frequency is actively locked to the cavity resonances by the Pound-Drever-Hall technique, thus tracking any frequency change due to deformations. The loop error and correction signals fed back to the laser are used as strain monitor. Sensitivity limits vary between 200 nɛ/√Hz in the quasi-static domain (0.5÷2 Hz), and between 1 and 4 nɛ/√Hz in the 0.4-1 kHz range for the single-FBG scheme, while strain down to 50 pɛ can be detected by using the laser-cavity-locked method.

Tracking the photodissociation dynamics of liquid nitromethane at 266 nm by femtosecond time-resolved broadband transient grating spectroscopy

NASA Astrophysics Data System (ADS)

Wu, Honglin; Song, Yunfei; Yu, Guoyang; Wang, Yang; Wang, Chang; Yang, Yanqiang

2016-05-01

Femtosecond time-resolved transient grating (TG) technique was employed to get insight into the photodissociation mechanism of liquid nitromethane (NM). Broadband white-light continuum was introduced as the probe to observe the evolution of electronic excited states of NM molecules and the formation of photodissociation products simultaneously. The reaction channel of liquid NM under 266 nm excitation was obtained that NM molecules in excited state S2 relax through two channels: about 73% relax to low lying S1 state through S2/S1 internal conversion with a time constant of 0.24 ps and then go back to the ground state through S1/S0 internal conversion; the other 27% will dissociate with a time constant of 2.56 ps. NO2 was found to be one of the products from the experimental TG spectra, which confirmed that C-N bond rupture was the primary dissociation channel of liquid NM.

Fiber Optic Bragg Grating Sensors for Thermographic Detection of Subsurface Anomalies

NASA Technical Reports Server (NTRS)

Allison, Sidney G.; Winfree, William P.; Wu, Meng-Chou

2009-01-01

Conventional thermography with an infrared imager has been shown to be an extremely viable technique for nondestructively detecting subsurface anomalies such as thickness variations due to corrosion. A recently developed technique using fiber optic sensors to measure temperature holds potential for performing similar inspections without requiring an infrared imager. The structure is heated using a heat source such as a quartz lamp with fiber Bragg grating (FBG) sensors at the surface of the structure to detect temperature. Investigated structures include a stainless steel plate with thickness variations simulated by small platelets attached to the back side using thermal grease. A relationship is shown between the FBG sensor thermal response and variations in material thickness. For comparison, finite element modeling was performed and found to agree closely with the fiber optic thermography results. This technique shows potential for applications where FBG sensors are already bonded to structures for Integrated Vehicle Health Monitoring (IVHM) strain measurements and can serve dual-use by also performing thermographic detection of subsurface anomalies.

A new fabrication method for precision antenna reflectors for space flight and ground test

NASA Technical Reports Server (NTRS)

Sharp, G. Richard; Wanhainen, Joyce S.; Ketelsen, Dean A.

1991-01-01

Communications satellites are using increasingly higher frequencies that require increasingly precise antenna reflectors for use in space. Traditional industry fabrication methods for space antenna reflectors employ successive modeling techniques using high- and low-temperature molds for reflector face sheets and then a final fit-up of the completed honeycomb sandwich panel antenna reflector to a master pattern. However, as new missions are planned at much higher frequencies, greater accuracies will be necessary than are achievable using these present methods. A new approach for the fabrication of ground-test solid-surface antenna reflectors is to build a rigid support structure with an easy-to-machine surface. This surface is subsequently machined to the desired reflector contour and coated with a radio-frequency-reflective surface. This method was used to fabricate a 2.7-m-diameter ground-test antenna reflector to an accuracy of better than 0.013 mm (0.0005 in.) rms. A similar reflector for use on spacecraft would be constructed in a similar manner but with space-qualified materials. The design, analysis, and fabrication of the 2.7-m-diameter precision antenna reflector for antenna ground tests and the extension of this technology to precision, space-based antenna reflectors are described.

A Wideband Corner-Reflector Antenna for 240 to 400 MHz.

DTIC Science & Technology

1983-09-19

8217 .; ,:,:. .-.:.,.;.. - -... - .- . -.. .-- v...- ..... .-. .-.- 1,.:..- FIGURES 1. Corner Reflector with Open-Sleeve Dipole Feed ............ ...... 7 2...Open-Sleeve Dipole Feed for Corner Reflector, 240-400 MHz........ 8 3. Closeup Photo of Open-Sleeve Dpole ..................... ...... 8 4. VSWR of...4-ft Corner Reflector, Open-Sleeve Dipole Feed .......... 9 5. Gain of Corner Reflector............ .............. . ....... 9 6. Measured E- and H

Feasibility study of a synthesis procedure for array feeds to improve radiation performance of large distorted reflector antennas

NASA Technical Reports Server (NTRS)

Stutzman, W. L.; Takamizawa, K.; Werntz, P.; Lapean, J.; Barts, R.; Shen, B.; Dunn, D.

1992-01-01

The topics covered include the following: (1) performance analysis of the Gregorian tri-reflector; (2) design and performance of the type 6 reflector antenna; (3) a new spherical main reflector system design; (4) optimization of reflector configurations using physical optics; (5) radiometric array design; and (7) beam efficiency studies.

Pressure-release versus rigid reflector for extracorporeal shockwave lithotripsy.

PubMed

Loske, Achim M; Prieto, Fernando E

2002-06-01

To evaluate the advantages and disadvantages of using a pressure-release reflector instead of a rigid reflector to concentrate shockwaves for extracorporeal shockwave lithotripsy (SWL). As in all electrohydraulic lithotripters, shockwaves were generated by electrical breakdown of water between two electrodes, located at the focus (F1) closest to a paraellipsoidal reflector. A pressure-release reflector, made out of polyurethane foam, was constructed and tested on a research lithotripter using kidney stone models. Fragmentation data and pressure measurements were compared with those of a conventional rigid reflector tested on the same device. The weight of stone model fragments remaining after shockwave exposure was less with the pressure-release reflector after screening through a 3.0 x 3.0-mm mesh. The residual fragment weight was less with the rigid reflector using 1.0 x 1.0- and 0.6 x 0.6-mm meshes. Pressure-release reflectors may maintain acceptable stone fragmentation while offering improved patient safety and should be considered for SWL.

Lamp method and apparatus using multiple reflections

DOEpatents

MacLennan, Donald A.; Turner, Brian P.

2001-01-01

An electrodeless microwave discharge lamp includes an envelope with a discharge forming fill disposed therein which emits light, the fill being capable of absorbing light at one wavelength and re-emitting the absorbed light at a different wavelength, the light emitted from the fill having a first spectral power distribution in the absence of reflection of light back into the fill, a source of microwave energy coupled to the fill to excite the fill and cause the fill to emit light, and a reflector disposed within the microwave cavity and configured to reflect at least some of the light emitted by the fill back into the fill while allowing some light to exit, the exiting light having a second spectral power distribution with proportionately more light in the visible region as compared to the first spectral power distribution, wherein the light re-emitted by the fill is shifted in wavelength with respect to the absorbed light and the magnitude of the shift is in relation to an effective optical path length.

Temporal dynamics of frequency-tunable graphene-based plasmonic grating structures for ultra-broadband terahertz communication

NASA Astrophysics Data System (ADS)

Jornet, Josep Miquel; Thawdar, Ngwe; Woo, Ethan; Andrello, Michael A.

2017-05-01

Terahertz (THz) communication is envisioned as a key wireless technology to satisfy the need for 1000x faster wireless data rates. To date, major progress on both electronic and photonic technologies are finally closing the so-called THz gap. Among others, graphene-based plasmonic nano-devices have been proposed as a way to enable ultra-broadband communications above 1THz. The unique dynamic complex conductivity of graphene enables the propagation of Surface Plasmon Polariton (SPP) waves at THz frequencies. In addition, the conductivity of graphene and, thus, the SPP propagation properties, can be dynamically tuned by means of electrostatic biasing or material doping. This result opens the door to frequency-tunable devices for THz communications. In this paper, the temporal dynamics of graphene-enhanced metallic grating structures used for excitation and detection of SPP waves at THz frequencies are analytically and numerically modeled. More specifically, the response of a metallic grating structure built on top of a graphene-based heterostructure is analyzed by taking into account the grating period and duty cycle and the Fermi energy of the graphene layer. Then, the interfacial charge transfer between a metallic back-gate and the graphene layer in a metal/dielectric/graphene stack is analytically modeled, and the range of achievable Fermi energies is determined. Finally, the rate at which the Fermi energy in graphene can be tuned is estimated starting from the transmission line model of graphene. Extensive numerical and simulation results with COMSOL Multi-physics are provided. The results show that the proposed structure enables dynamic frequency systems with THz bandwidths, thus, enabling resilient communication techniques such as time-hopping THz modulations.

Polycrystalline Silicon Thin-film Solar cells with Plasmonic-enhanced Light-trapping

PubMed Central

Varlamov, Sergey; Rao, Jing; Soderstrom, Thomas

2012-01-01

One of major approaches to cheaper solar cells is reducing the amount of semiconductor material used for their fabrication and making cells thinner. To compensate for lower light absorption such physically thin devices have to incorporate light-trapping which increases their optical thickness. Light scattering by textured surfaces is a common technique but it cannot be universally applied to all solar cell technologies. Some cells, for example those made of evaporated silicon, are planar as produced and they require an alternative light-trapping means suitable for planar devices. Metal nanoparticles formed on planar silicon cell surface and capable of light scattering due to surface plasmon resonance is an effective approach. The paper presents a fabrication procedure of evaporated polycrystalline silicon solar cells with plasmonic light-trapping and demonstrates how the cell quantum efficiency improves due to presence of metal nanoparticles. To fabricate the cells a film consisting of alternative boron and phosphorous doped silicon layers is deposited on glass substrate by electron beam evaporation. An Initially amorphous film is crystallised and electronic defects are mitigated by annealing and hydrogen passivation. Metal grid contacts are applied to the layers of opposite polarity to extract electricity generated by the cell. Typically, such a ~2 μm thick cell has a short-circuit current density (Jsc) of 14-16 mA/cm2, which can be increased up to 17-18 mA/cm2 (~25% higher) after application of a simple diffuse back reflector made of a white paint. To implement plasmonic light-trapping a silver nanoparticle array is formed on the metallised cell silicon surface. A precursor silver film is deposited on the cell by thermal evaporation and annealed at 23°C to form silver nanoparticles. Nanoparticle size and coverage, which affect plasmonic light-scattering, can be tuned for enhanced cell performance by varying the precursor film thickness and its annealing conditions. An optimised nanoparticle array alone results in cell Jsc enhancement of about 28%, similar to the effect of the diffuse reflector. The photocurrent can be further increased by coating the nanoparticles by a low refractive index dielectric, like MgF2, and applying the diffused reflector. The complete plasmonic cell structure comprises the polycrystalline silicon film, a silver nanoparticle array, a layer of MgF2, and a diffuse reflector. The Jsc for such cell is 21-23 mA/cm2, up to 45% higher than Jsc of the original cell without light-trapping or ~25% higher than Jsc for the cell with the diffuse reflector only. Introduction Light-trapping in silicon solar cells is commonly achieved via light scattering at textured interfaces. Scattered light travels through a cell at oblique angles for a longer distance and when such angles exceed the critical angle at the cell interfaces the light is permanently trapped in the cell by total internal reflection (Animation 1: Light-trapping). Although this scheme works well for most solar cells, there are developing technologies where ultra-thin Si layers are produced planar (e.g. layer-transfer technologies and epitaxial c-Si layers) 1 and or when such layers are not compatible with textures substrates (e.g. evaporated silicon) 2. For such originally planar Si layer alternative light trapping approaches, such as diffuse white paint reflector 3, silicon plasma texturing 4 or high refractive index nanoparticle reflector 5 have been suggested. Metal nanoparticles can effectively scatter incident light into a higher refractive index material, like silicon, due to the surface plasmon resonance effect 6. They also can be easily formed on the planar silicon cell surface thus offering a light-trapping approach alternative to texturing. For a nanoparticle located at the air-silicon interface the scattered light fraction coupled into silicon exceeds 95% and a large faction of that light is scattered at angles above critical providing nearly ideal light-trapping condition (Animation 2: Plasmons on NP). The resonance can be tuned to the wavelength region, which is most important for a particular cell material and design, by varying the nanoparticle average size, surface coverage and local dielectric environment 6,7. Theoretical design principles of plasmonic nanoparticle solar cells have been suggested 8. In practice, Ag nanoparticle array is an ideal light-trapping partner for poly-Si thin-film solar cells because most of these design principle are naturally met. The simplest way of forming nanoparticles by thermal annealing of a thin precursor Ag film results in a random array with a relatively wide size and shape distribution, which is particularly suitable for light-trapping because such an array has a wide resonance peak, covering the wavelength range of 700-900 nm, important for poly-Si solar cell performance. The nanoparticle array can only be located on the rear poly-Si cell surface thus avoiding destructive interference between incident and scattered light which occurs for front-located nanoparticles 9. Moreover, poly-Si thin-film cells do not requires a passivating layer and the flat base-shaped nanoparticles (that naturally result from thermal annealing of a metal film) can be directly placed on silicon further increases plasmonic scattering efficiency due to surface plasmon-polariton resonance 10. The cell with the plasmonic nanoparticle array as described above can have a photocurrent about 28% higher than the original cell. However, the array still transmits a significant amount of light which escapes through the rear of the cell and does not contribute into the current. This loss can be mitigated by adding a rear reflector to allow catching transmitted light and re-directing it back to the cell. Providing sufficient distance between the reflector and the nanoparticles (a few hundred nanometers) the reflected light will then experience one more plasmonic scattering event while passing through the nanoparticle array on re-entering the cell and the reflector itself can be made diffuse - both effects further facilitating light scattering and hence light-trapping. Importantly, the Ag nanoparticles have to be encapsulated with an inert and low refractive index dielectric, like MgF2 or SiO2, from the rear reflector to avoid mechanical and chemical damage 7. Low refractive index for this cladding layer is required to maintain a high coupling fraction into silicon and larger scattering angles, which are ensured by the high optical contrast between the media on both sides of the nanoparticle, silicon and dielectric 6. The photocurrent of the plasmonic cell with the diffuse rear reflector can be up to 45% higher than the current of the original cell or up to 25% higher than the current of an equivalent cell with the diffuse reflector only. PMID:22805108

Effects of deterministic surface distortions on reflector antenna performance

NASA Technical Reports Server (NTRS)

Rahmat-Samii, Y.

1985-01-01

Systematic distortions of reflector antenna surfaces can cause antenna radiation patterns to be undesirably different from those of perfectly smooth reflector surfaces. In this paper, a simulation model for systematic distortions is described which permits an efficient computation of the effects of distortions in the reflector pattern. The model uses a vector diffraction physical optics analysis for the determination of both the co-polar and cross-polar fields. An interpolation scheme is also presented for the description of reflector surfaces which are prescribed by discrete points. Representative numerical results are presented for reflectors with sinusoidally and thermally distorted surfaces. Finally, comparisons are made between the measured and calculated patterns of a slowly-varying distorted offset parabolic reflector.

Demonstration of a Single-Crystal Reflector-Filter for Enhancing Slow Neutron Beams

DOE PAGES

Muhrer, Guenter; Schönfeldt, Troels; Iverson, Erik B.; ...

2016-06-14

The cold polycrystalline beryllium reflector-filter concept has been used to enhance the cold neutron emission of cryogenic hydrogen moderators, while suppressing the intermediate wavelength and fast neutron emission at the same time. While suppressing the fast neutron emission is often desired, the suppression of intermediate wavelength neutrons is often unwelcome. It has been hypothesized that replacing the polycrystalline reflector-filter concept with a single-crystal reflector-filter concept would overcome the suppression of intermediate wavelength neutrons and thereby extend the usability of the reflector-filter concept to shorter but still important wavelengths. In this paper we present the first experimental data on a single-crystalmore » reflector-filter and compare experimental results with hypothesized performance. We find that a single-crystal reflector-filter retains the long-wavelength benefit of the polycrystalline reflector-filter, without suffering the same loss of important intermediate wavelength neutrons. Ultimately, this finding extends the applicability of the reflector-filter concept to intermediate wavelengths, and furthermore indicates that the reflector-filter benefits arise from its interaction with fast (background) neutrons, not with intermediate wavelength neutrons of potential interest in many types of neutron scattering.« less

Acoustic Levitation System

NASA Technical Reports Server (NTRS)

Gammell, P. M.; Wang, T. G.; Croonquist, A.; Lee, M. C.

1985-01-01

Dense materials, such as steel balls, continuously levitated with energy provided by efficient high-powered siren in combination with shaped reflector. Reflector system, consisting of curved top reflector and flat lower reflector, eliminates instability in spatial positioning of sample.

Development of two-channel prototype ITER vacuum ultraviolet spectrometer with back-illuminated charge-coupled device and microchannel plate detectors.

PubMed

Seon, C R; Choi, S H; Cheon, M S; Pak, S; Lee, H G; Biel, W; Barnsley, R

2010-10-01

A vacuum ultraviolet (VUV) spectrometer of a five-channel spectral system is designed for ITER main plasma impurity measurement. To develop and verify the system design, a two-channel prototype system is fabricated with No. 3 (14.4-31.8 nm) and No. 4 (29.0-60.0 nm) among the five channels. The optical system consists of a collimating mirror to collect the light from source to slit, two holographic diffraction gratings with toroidal geometry, and two different electronic detectors. For the test of the prototype system, a hollow cathode lamp is used as a light source. To find the appropriate detector for ITER VUV system, two kinds of detectors of the back-illuminated charge-coupled device and the microchannel plate electron multiplier are tested, and their performance has been investigated.

Development of the tongue coating analyzer based on concave grating monochrometer and virtual instrument

NASA Astrophysics Data System (ADS)

Ren, Zhong; Liu, Guodong; Zeng, Lvming; Huang, Zhen; Zeng, Wenping

2010-10-01

The tongue coating diagnosis is an important part in tongue diagnosis of traditional Chinese medicine (TCM).The change of the thickness and color of the tongue coating can reflect the pathological state for the patient. By observing the tongue coating, a Chinese doctor can determine the nature or severity of disease. Because some limitations existed in the tongue diagnosis method of TCM and the method based on the digital image processing, a novel tongue coating analyzer(TCA) based on the concave grating monochrometer and virtual instrument is developed in this paper. This analyzer consists of the light source system, check cavity, optical fiber probe, concave grating monochrometer, spectrum detector system based on CCD and data acquisition (DAQ) card, signal processing circuit system, computer and data analysis software based on LabVIEW, etc. Experimental results show that the novel TCA's spectral range can reach 300-1000 nm, its wavelength resolution can reach 1nm, and this TCA uses the back-split-light technology and multi-channel parallel analysis. Compared with the TCA based on the image processing technology, this TCA has many advantages, such as, compact volume, simpler algorithm, faster processing speed, higher accuracy, cheaper cost and real-time handle data and display the result, etc. Therefore, it has the greatly potential values in the fields of the tongue coating diagnosis for TCM.

Concepts and analysis for precision segmented reflector and feed support structures

NASA Technical Reports Server (NTRS)

Miller, Richard K.; Thomson, Mark W.; Hedgepeth, John M.

1990-01-01

Several issues surrounding the design of a large (20-meter diameter) Precision Segmented Reflector are investigated. The concerns include development of a reflector support truss geometry that will permit deployment into the required doubly-curved shape without significant member strains. For deployable and erectable reflector support trusses, the reduction of structural redundancy was analyzed to achieve reduced weight and complexity for the designs. The stiffness and accuracy of such reduced member trusses, however, were found to be affected to a degree that is unexpected. The Precision Segmented Reflector designs were developed with performance requirements that represent the Reflector application. A novel deployable sunshade concept was developed, and a detailed parametric study of various feed support structural concepts was performed. The results of the detailed study reveal what may be the most desirable feed support structure geometry for Precision Segmented Reflector/Large Deployable Reflector applications.

Reflectivity Spectra for Commonly Used Reflectors

NASA Astrophysics Data System (ADS)

Janecek, Martin

2012-06-01

Monte Carlo simulations play an important role in developing and evaluating the performance of radiation detection systems. To accurately model a reflector in an optical Monte Carlo simulation, the reflector's spectral response has to be known. We have measured the reflection coefficient for many commonly used reflectors for wavelengths from 250 nm to 800 nm. The reflectors were also screened for fluorescence and angular distribution changes with wavelength. The reflectors examined in this work include several polytetrafluoroethylene (PTFE) reflectors, Spectralon, GORE diffuse reflector, titanium dioxide paint, magnesium oxide, nitrocellulose filter paper, Tyvek paper, Lumirror, Melinex, ESR films, and aluminum foil. All PTFE films exhibited decreasing reflectivity with longer wavelengths due to transmission. To achieve >;0.95 reflectivity in the 380 to 500 nm range, the PTFE films have to be at least 0.5 mm thick-nitrocellulose is a good alternative if a thin diffuse reflector is needed. Several of the reflectors have sharp declines in reflectivity below a cut-off wavelength, including TiO2 (420 nm), ESR film (395 nm), nitrocellulose (330 nm), Lumirror (325 nm), and Melinex (325 nm). PTFE-like reflectors were the only examined reflectors that had reflectivity above 0.90 for wavelengths below 300 nm. Lumirror, Melinex, and ESR film exhibited fluorescence. Lumirror and Melinex are excited by wavelengths between 320 and 420 nm and have their emission peaks located at 440 nm, while ESR film is excited by wavelengths below 400 nm and the emission peak is located at 430 nm. Lumirror and Melinex also exhibited changing angular distributions with wavelength.

Deployable reflector structure

NASA Technical Reports Server (NTRS)

Mikulas, Martin, Jr. (Inventor); Hoberman, Charles (Inventor)

1993-01-01

A deployable reflector structure is presented. The structure has a number of movable reflector panels pivotably supported on rigid arms. Several such arms are pivotably connected to a central structure. The arm can move in starburst fashion from a packaged stage, where all arms are vertical, to a deployed stage, where all arms are horizontal. All of the movable reflector panels are maintained at a predetermined angle to an axis of the reflector structure when the arms are pivoted. The reflector panels are stacked tightly on top of each other in the packaged state of the reflector structure. Simple mechanisms are used for avoiding interference between panels on different arms in the packaged stage and for fitting the movable panels together like tiles in the deployed stage.

Evaluation of deer warning reflectors in Virginia.

DOT National Transportation Integrated Search

2003-01-01

A deer warning reflector consists of a red, double-sided reflector mounted on posts, similar to those used for roadside delineators along roadways. As vehicles approach and move through the road section, it is purported that the reflector reflects th...

Experimental study of an adaptive CFRC reflector for high order wave-front error correction

NASA Astrophysics Data System (ADS)

Lan, Lan; Fang, Houfei; Wu, Ke; Jiang, Shuidong; Zhou, Yang

2018-03-01

The recent radio frequency communication system developments are generating the need for creating space antennas with lightweight and high precision. The carbon fiber reinforced composite (CFRC) materials have been used to manufacture the high precision reflector. The wave-front errors caused by fabrication and on-orbit distortion are inevitable. The adaptive CFRC reflector has received much attention to do the wave-front error correction. Due to uneven stress distribution that is introduced by actuation force and fabrication, the high order wave-front errors such as print-through error is found on the reflector surface. However, the adaptive CFRC reflector with PZT actuators basically has no control authority over the high order wave-front errors. A new design architecture assembled secondary ribs at the weak triangular surfaces is presented in this paper. The virtual experimental study of the new adaptive CFRC reflector has conducted. The controllability of the original adaptive CFRC reflector and the new adaptive CFRC reflector with secondary ribs are investigated. The virtual experimental investigation shows that the new adaptive CFRC reflector is feasible and efficient to diminish the high order wave-front error.

Extended-bandwidth frequency sweeps of a distributed feedback laser using combined injection current and temperature modulation

NASA Astrophysics Data System (ADS)

Hefferman, Gerald; Chen, Zhen; Wei, Tao

2017-07-01

This article details the generation of an extended-bandwidth frequency sweep using a single, communication grade distributed feedback (DFB) laser. The frequency sweep is generated using a two-step technique. In the first step, injection current modulation is employed as a means of varying the output frequency of a DFB laser over a bandwidth of 99.26 GHz. A digital optical phase lock loop is used to lock the frequency sweep speed during current modulation, resulting in a linear frequency chirp. In the second step, the temperature of the DFB laser is modulated, resulting in a shifted starting laser output frequency. A laser frequency chirp is again generated beginning at this shifted starting frequency, resulting in a frequency-shifted spectrum relative to the first recorded data. This process is then repeated across a range of starting temperatures, resulting in a series of partially overlapping, frequency-shifted spectra. These spectra are then aligned using cross-correlation and combined using averaging to form a single, broadband spectrum with a total bandwidth of 510.9 GHz. In order to investigate the utility of this technique, experimental testing was performed in which the approach was used as the swept-frequency source of a coherent optical frequency domain reflectometry system. This system was used to interrogate an optical fiber containing a 20 point, 1-mm pitch length fiber Bragg grating, corresponding to a period of 100 GHz. Using this technique, both the periodicity of the grating in the frequency domain and the individual reflector elements of the structure in the time domain were resolved, demonstrating the technique's potential as a method of extending the sweeping bandwidth of semiconductor lasers for frequency-based sensing applications.

Optimisation of a polygon mirror-based spectral filter for swept source optical coherence tomography (SS-OCT)

NASA Astrophysics Data System (ADS)

Everson, Michael; Duma, Virgil-Florin; Dobre, George

2018-03-01

Medical imaging using Optical Coherence Tomography (OCT) provides clinicians with 3D, high resolution reconstructions of microscopic structures, in depth. It has been initially developed for ophthalmology, in order to scan the retinas of patients to diagnose illness. The quality of the images depends upon their axial and lateral resolutions and the properties of the light being used. Research using a polygon mirror (PM) as a spectral filter in Swept Source OCT (SS-OCT) has resulted in a variety of different experimental arrangements. Although the application of PM-based SS-OCT sources has been successfully demonstrated, the combination of their components' fundamental properties and the overall impact they have on imaging performance is rarely reported. A more detailed examination of these properties would lead to a full description of their operation and to the best methods to employ if system performance is to be maximised. This work presents our current findings of on-going research into the optimisation of PM-based SS-OCT systems. A swept source spectral filter, consisting of a collimator, a transmission grating, a two-lens telescope and an off-axis PM with an end reflector mirror has been evaluated experimentally and compared with theoretical predictions. The system's performance has been compared for two different fibre collimators. Although the beam width on the grating is different for each of the two collimators, the spot size at the PM facet is made the same by selecting appropriate focal lengths. An improvement in the signal roll-off at the interferometer output of 1.0 dB/mm was obtained when using a 3.4 mm collimator compared to a 1.5 mm collimator.

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.

Extended-bandwidth frequency sweeps of a distributed feedback laser using combined injection current and temperature modulation.

PubMed

Hefferman, Gerald; Chen, Zhen; Wei, Tao

2017-07-01

This article details the generation of an extended-bandwidth frequency sweep using a single, communication grade distributed feedback (DFB) laser. The frequency sweep is generated using a two-step technique. In the first step, injection current modulation is employed as a means of varying the output frequency of a DFB laser over a bandwidth of 99.26 GHz. A digital optical phase lock loop is used to lock the frequency sweep speed during current modulation, resulting in a linear frequency chirp. In the second step, the temperature of the DFB laser is modulated, resulting in a shifted starting laser output frequency. A laser frequency chirp is again generated beginning at this shifted starting frequency, resulting in a frequency-shifted spectrum relative to the first recorded data. This process is then repeated across a range of starting temperatures, resulting in a series of partially overlapping, frequency-shifted spectra. These spectra are then aligned using cross-correlation and combined using averaging to form a single, broadband spectrum with a total bandwidth of 510.9 GHz. In order to investigate the utility of this technique, experimental testing was performed in which the approach was used as the swept-frequency source of a coherent optical frequency domain reflectometry system. This system was used to interrogate an optical fiber containing a 20 point, 1-mm pitch length fiber Bragg grating, corresponding to a period of 100 GHz. Using this technique, both the periodicity of the grating in the frequency domain and the individual reflector elements of the structure in the time domain were resolved, demonstrating the technique's potential as a method of extending the sweeping bandwidth of semiconductor lasers for frequency-based sensing applications.

Quasi-interferometric scheme improved by fiber Bragg grating written on macrostructure defect in silica multimode optical fiber operating in a few-mode regime

NASA Astrophysics Data System (ADS)

Evtushenko, Alexander S.; Faskhutdinov, Lenar M.; Kafarova, Anastasia M.; Kuznetzov, Artem A.; Minaeva, Alina Yu.; Sevruk, Nikita L.; Nureev, Ilnur I.; Vasilets, Alexander A.; Andreev, Vladimir A.; Morozov, Oleg G.; Burdin, Vladimir A.; Bourdine, Anton V.

2017-04-01

This work presents results of experimental approbation of earlier on proposed modified fiber optic stress sensor based on a few-mode effects occurring during laser-excited optical signal propagation over silica multimode optical fiber (MMF). Modification is concerned with a passage to quasi-interferometric scheme realized by two multimode Y-couplers with equalized arm lengths improved by fiber Bragg grating (FBG) written on preliminary formed precision macrostructure defects in silica multimode graded-index optical fibers and special offset launching conditions providing laser-based excitation of higher-order modes. The "arms" of quasi-interferometer are two equalized lengths of MMF Cat. OM2 with great central dip of refractive index profile and strong pulse splitting due to high differential mode delay (DMD). We tested FBGs with Bragg wavelength both 1310 nm and 1550 nm written over tapers or up-tapers preliminary formed in short pieces of MMF Cat. OM2+/OM3 and further jointed to the end of one of the arms before output Y-coupler. Researches were focused on comparison analysis of pulse responses under changing of selected excited mode mixing and power diffusion processes due to stress distributed action to sensor fiber depending. Here we considered FBGs not only as particular wavelength reflector during spectral response measurement but also as local periodic microstructure defect which strongly effects on few-mode signal components mixing process also improved by combination with macro-defect like taper or up-taper that should provide response variation. Some results pulse response measurements produced for different scheme configuration and their comparison analysis are represented.

A Nonlinear Dynamic Model and Free Vibration Analysis of Deployable Mesh Reflectors

NASA Technical Reports Server (NTRS)

Shi, H.; Yang, B.; Thomson, M.; Fang, H.

2011-01-01

This paper presents a dynamic model of deployable mesh reflectors, in which geometric and material nonlinearities of such a space structure are fully described. Then, by linearization around an equilibrium configuration of the reflector structure, a linearized model is obtained. With this linearized model, the natural frequencies and mode shapes of a reflector can be computed. The nonlinear dynamic model of deployable mesh reflectors is verified by using commercial finite element software in numerical simulation. As shall be seen, the proposed nonlinear model is useful for shape (surface) control of deployable mesh reflectors under thermal loads.

A Micromachined Geometric Moire Interferometric Floating-Element Shear Stress Sensor

NASA Technical Reports Server (NTRS)

Horowitz, S.; Chen, T.; Chandrasekaran, V.; Tedjojuwono, K.; Nishida, T.; Cattafesta, L.; Sheplak, M.

2004-01-01

This paper presents the development of a floating-element shear stress sensor that permits the direct measurement of skin friction based on geometric Moir interferometry. The sensor was fabricated using an aligned wafer-bond/thin-back process producing optical gratings on the backside of a floating element and on the top surface of the support wafer. Experimental characterization indicates a static sensitivity of 0.26 microns/Pa, a resonant frequency of 1.7 kHz, and a noise floor of 6.2 mPa/(square root)Hz.

Reflector control technology in space laser communication

NASA Astrophysics Data System (ADS)

Xie, Meilin; Ma, Caiwen; Yao, Cheng; Huang, Wei; Lian, Xuezheng; Feng, Xubin; Jing, Feng

2017-11-01

The optical frequencies band is used as information carrier to realize laser communication between two low-orbit micro-satellites in space which equipped with inter-satellite laser communication terminals, optical switches, space routers and other payload. The laser communication terminal adopts a two-dimensional turntable with a single mirror structure. In this paper, the perturbation model of satellite platform is established in this paper. The relationship between the coupling and coordinate transformation of satellite disturbance is analyzed and the laser pointing vector is deduced. Using the tracking differentiator to speed up the circular grating angle information constitute speed loop feedback, which avoids the problem of error amplification caused by the high frequency of the conventional difference algorithm. Finally, the suppression ability of the satellite platform disturbance and the tracking accuracy of the tracking system are simulated and analyzed. The results show that the tracking accuracy of the whole system is 10μrad in the case of satellite vibration, which provides the basis for the optimization of the performance of the space-borne laser communication control system.

Numerical simulation studies of nano-scale surface plasmon components: waveguides, splitters, and filters

NASA Astrophysics Data System (ADS)

Lin, Xian-Shi; Huang, Xu-Guang

2008-12-01

In this paper, we theoretically and numerically demonstrate a two-dimensional Metal-Dielectric-Metal (MDM) waveguide based on finite-difference time-domain simulation of the propagation characteristics of surface plasmon polaritons (SPPs). For practical applications, we propose a plasmonic Y-branch waveguide based on MDM structure for high integration. The simulation results show that the Y-branch waveguide proposed here makes optical splitter with large branching angle (~180 degree) come true. We also introduce a finite array of periodic tooth structure on one surface of the MDM waveguide which is in a similar way as FBGs or Bragg reflectors, potentially as filters for WDM applications. Our results show that the novel structure not only can realize filtering function of wavelength with a high transmittance over 92%, but also with an ultra-compact size in the length of a few hundred nanometers, in comparison with other grating-like SPPs filters. The MDM waveguide splitters and filters could be utilized to achieve ultra-compact photonic filtering devices for high integration in SPPs-based flat metallic surfaces.

2.3 µm range InP-based type-II quantum well Fabry-Perot lasers heterogeneously integrated on a silicon photonic integrated circuit.

PubMed

Wang, Ruijun; Sprengel, Stephan; Boehm, Gerhard; Muneeb, Muhammad; Baets, Roel; Amann, Markus-Christian; Roelkens, Gunther

2016-09-05

Heterogeneously integrated InP-based type-II quantum well Fabry-Perot lasers on a silicon waveguide circuit emitting in the 2.3 µm wavelength range are demonstrated. The devices consist of a "W"-shaped InGaAs/GaAsSb multi-quantum-well gain section, III-V/silicon spot size converters and two silicon Bragg grating reflectors to form the laser cavity. In continuous-wave (CW) operation, we obtain a threshold current density of 2.7 kA/cm² and output power of 1.3 mW at 5 °C for 2.35 μm lasers. The lasers emit over 3.7 mW of peak power with a threshold current density of 1.6 kA/cm² in pulsed regime at room temperature. This demonstration of heterogeneously integrated lasers indicates that the material system and heterogeneous integration method are promising to realize fully integrated III-V/silicon photonics spectroscopic sensors in the 2 µm wavelength range.

A high-performance lab-on-a-chip liquid sensor employing surface acoustic wave resonance

NASA Astrophysics Data System (ADS)

Kustanovich, K.; Yantchev, V.; Kirejev, V.; Jeffries, G. D. M.; Lobovkina, T.; Jesorka, A.

2017-11-01

We demonstrate herein a new concept for lab-on-a-chip in-liquid sensing, through integration of surface acoustic wave resonance (SAR) in a one-port configuration with a soft polymer microfluidic delivery system. In this concept, the reflective gratings of a one-port surface acoustic wave (SAW) resonator are employed as mass loading-sensing elements, while the SAW transducer is protected from the measurement environment. We describe the design, fabrication, implementation, and characterization using liquid medium. The sensor operates at a frequency of 185 MHz and has demonstrated a comparable sensitivity to other SAW in-liquid sensors, while offering quality factor (Q) value in water of about 250, low impedance and fairly low susceptibility to viscous damping. For proof of principle, sensing performance was evaluated by means of binding 40 nm neutravidin-coated SiO2 nanoparticles to a biotin-labeled lipid bilayer deposited over the reflectors. Frequency shifts were determined for every step of the affinity assay. Demonstration of this integrated technology highlights the potential of SAR technology for in-liquid sensing.

A new approach for shaping of dual-reflector antennas

NASA Technical Reports Server (NTRS)

Lee, Teh-Hong; Burnside, W. D.; Rudduck, Roger C.

1987-01-01

The shaping of 2-D dual-reflector antenna systems to generate a prescribed distribution with uniform phase at the aperture of the second reflector is examined. This method is based on the geometrical nature of Cassegrain and Gregorian dual-reflector antennas. The method of syntheses satisfies the principles of geometrical optics which are the foundations of dual-reflector designs. Instead of setting up differential equations or heuristically designing the subreflector, a set of algebraic equations is formulated and solved numerically to obtain the desired surfaces. The caustics of the reflected rays from the subreflector can be obtained and examined. Several examples of 2-D dual-reflector shaping are shown to validate the study. Geometrical optics and physical optics are used to calculate the scattered fields from the reflectors.

16 CFR 1512.16 - Requirements for reflectors.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 1512.16 Commercial Practices CONSUMER PRODUCT SAFETY COMMISSION FEDERAL HAZARDOUS SUBSTANCES ACT... vehicle headlamps. The use of reflector combinations off the center plane of the bicycle (defined in...) Front reflector. The reflector or mount shall not contact the ground plane when the bicycle is resting...

Reducing Operating Temperature in Photovoltaic Modules

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

Silverman, Timothy J.; Deceglie, Michael G.; Subedi, Indra

Reducing the operating temperature of photovoltaic modules increases their efficiency and lifetime. This can be achieved by reducing the production of waste heat or by improving the rejection of waste heat. We tested, using a combination of simulation and experiment, several thermal modifications in each category. To predict operating temperature and energy yield changes in response to changes to the module, we implemented a physics-based transient simulation framework based almost entirely on measured properties. The most effective thermal modifications reduced the production of waste heat by reflecting unusable light from the cell or the module. Consistent with previous results andmore » verified in this work through year-long simulations, the ideal reflector resulted in an annual irradiance-weighted temperature reduction of 3.8 K for crystalline silicon (c-Si). Our results illustrate that more realistic reflector concepts must balance detrimental optical effects with the intended thermal effects to realize the optimal energy production advantage. Methods improving thermal conductivity or back-side emissivity showed only modest improvements of less than 1 K. We also studied a GaAs module, which uses high-efficiency and high-subbandgap reflectivity to operate at an annual irradiance-weighted temperature 12 K cooler than that of a c-Si module under the same conditions.« less

Reducing Operating Temperature in Photovoltaic Modules

DOE PAGES

Silverman, Timothy J.; Deceglie, Michael G.; Subedi, Indra; ...

2018-01-09

Reducing the operating temperature of photovoltaic modules increases their efficiency and lifetime. This can be achieved by reducing the production of waste heat or by improving the rejection of waste heat. We tested, using a combination of simulation and experiment, several thermal modifications in each category. To predict operating temperature and energy yield changes in response to changes to the module, we implemented a physics-based transient simulation framework based almost entirely on measured properties. The most effective thermal modifications reduced the production of waste heat by reflecting unusable light from the cell or the module. Consistent with previous results andmore » verified in this work through year-long simulations, the ideal reflector resulted in an annual irradiance-weighted temperature reduction of 3.8 K for crystalline silicon (c-Si). Our results illustrate that more realistic reflector concepts must balance detrimental optical effects with the intended thermal effects to realize the optimal energy production advantage. Methods improving thermal conductivity or back-side emissivity showed only modest improvements of less than 1 K. We also studied a GaAs module, which uses high-efficiency and high-subbandgap reflectivity to operate at an annual irradiance-weighted temperature 12 K cooler than that of a c-Si module under the same conditions.« less

Origin of the Reflectin Gene and Hierarchical Assembly of Its Protein.

PubMed

Guan, Zhe; Cai, Tiantian; Liu, Zhongmin; Dou, Yunfeng; Hu, Xuesong; Zhang, Peng; Sun, Xin; Li, Hongwei; Kuang, Yao; Zhai, Qiran; Ruan, Hao; Li, Xuanxuan; Li, Zeyang; Zhu, Qihui; Mai, Jingeng; Wang, Qining; Lai, Luhua; Ji, Jianguo; Liu, Haiguang; Xia, Bin; Jiang, Taijiao; Luo, Shu-Jin; Wang, Hong-Wei; Xie, Can

2017-09-25

Cephalopods, the group of animals including octopus, squid, and cuttlefish, have remarkable ability to instantly modulate body coloration and patterns so as to blend into surrounding environments [1, 2] or send warning signals to other animals [3]. Reflectin is expressed exclusively in cephalopods, filling the lamellae of intracellular Bragg reflectors that exhibit dynamic iridescence and structural color change [4]. Here, we trace the possible origin of the reflectin gene back to a transposon from the symbiotic bioluminescent bacterium Vibrio fischeri and report the hierarchical structural architecture of reflectin protein. Intrinsic self-assembly, and higher-order assembly tightly modulated by aromatic compounds, provide insights into the formation of multilayer reflectors in iridophores and spherical microparticles in leucophores and may form the basis of structural color change in cephalopods. Self-assembly and higher-order assembly in reflectin originated from a core repeating octapeptide (here named protopeptide), which may be from the same symbiotic bacteria. The origin of the reflectin gene and assembly features of reflectin protein are of considerable biological interest. The hierarchical structural architecture of reflectin and its domain and protopeptide not only provide insights for bioinspired photonic materials but also serve as unique "assembly tags" and feasible molecular platforms in biotechnology. Copyright © 2017 Elsevier Ltd. All rights reserved.

Large area low-cost space solar cell development

NASA Technical Reports Server (NTRS)

Baraona, C. R.; Cioni, J. L.

1982-01-01

A development program to produce large-area (5.9 x 5.9 cm) space quality silicon solar cells with a cost goal of 30 $/watt is descibed. Five cell types under investigation include wraparound dielectric, mechanical wraparound and conventional contact configurations with combinations of 2 or 10 ohm-cm resistivity, back surface reflectors and/or fields, and diffused or ion implanted junctions. A single step process to cut cell and cover-glass simultaneously is being developed. A description of cell developments by Applied Solar Energy Corp., Spectrolab and Spire is included. Results are given for cell and array tests, performed by Lockheed, TRW and NASA. Future large solar arrays that might use cells of this type are discussed.

Hubble Space Telescope electrical power system

NASA Technical Reports Server (NTRS)

Whitt, Thomas H.; Bush, John R., Jr.

1990-01-01

The Hubble Space Telescope (HST) electrical power system (EPS) is supplying between 2000 and 2400 W of continuous power to the electrical loads. The major components of the EPS are the 5000-W back surface field reflector solar array, the six nickel-hydrogen (NiH2) 22-cell 88-Ah batteries, and the charge current controllers, which, in conjunction with the flight computer, control battery charging. The operation of the HST EPS and the results of the HST NiH2 six-battery test are discussed, and preliminary flight data are reviewed. The HST NiH2 six-battery test is a breadboard of the HST EPS on test at Marshall Space Flight Center.

Incorporating photon recycling into the analytical drift-diffusion model of high efficiency solar cells

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

Lumb, Matthew P.; Naval Research Laboratory, Washington, DC 20375; Steiner, Myles A.

The analytical drift-diffusion formalism is able to accurately simulate a wide range of solar cell architectures and was recently extended to include those with back surface reflectors. However, as solar cells approach the limits of material quality, photon recycling effects become increasingly important in predicting the behavior of these cells. In particular, the minority carrier diffusion length is significantly affected by the photon recycling, with consequences for the solar cell performance. In this paper, we outline an approach to account for photon recycling in the analytical Hovel model and compare analytical model predictions to GaAs-based experimental devices operating close tomore » the fundamental efficiency limit.« less

Solar energy collection system

NASA Technical Reports Server (NTRS)

Miller, C. G.; Stephens, J. B. (Inventor)

1979-01-01

A fixed, linear, ground-based primary reflector having an extended curved sawtooth-contoured surface covered with a metalized polymeric reflecting material, reflects solar energy to a movably supported collector that is kept at the concentrated line focus reflector primary. The primary reflector may be constructed by a process utilizing well known freeway paving machinery. The solar energy absorber is preferably a fluid transporting pipe. Efficient utilization leading to high temperatures from the reflected solar energy is obtained by cylindrical shaped secondary reflectors that direct off-angle energy to the absorber pipe. A seriatim arrangement of cylindrical secondary reflector stages and spot-forming reflector stages produces a high temperature solar energy collection system of greater efficiency.

Theoretical modeling of the dynamics of a semiconductor laser subject to double-reflector optical feedback

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

Bakry, A.; Abdulrhmann, S.; Ahmed, M., E-mail: mostafa.farghal@mu.edu.eg

2016-06-15

We theoretically model the dynamics of semiconductor lasers subject to the double-reflector feedback. The proposed model is a new modification of the time-delay rate equations of semiconductor lasers under the optical feedback to account for this type of the double-reflector feedback. We examine the influence of adding the second reflector to dynamical states induced by the single-reflector feedback: periodic oscillations, period doubling, and chaos. Regimes of both short and long external cavities are considered. The present analyses are done using the bifurcation diagram, temporal trajectory, phase portrait, and fast Fourier transform of the laser intensity. We show that adding themore » second reflector attracts the periodic and perioddoubling oscillations, and chaos induced by the first reflector to a route-to-continuous-wave operation. During this operation, the periodic-oscillation frequency increases with strengthening the optical feedback. We show that the chaos induced by the double-reflector feedback is more irregular than that induced by the single-reflector feedback. The power spectrum of this chaos state does not reflect information on the geometry of the optical system, which then has potential for use in chaotic (secure) optical data encryption.« less

Special test equipment and fixturing for MSAT reflector assembly alignment

NASA Technical Reports Server (NTRS)

Young, Jeffrey A.; Zinn, Michael R.; Mccarten, David R.

1994-01-01

The MSAT Reflector Assembly is a state of the art subsystem for Mobile Satellite (MSAT), a geosynchronous-based commercial mobile telecommunication satellite program serving North America. The Reflector Assembly consisted of a deployable, three-hinge, folding-segment Boom, deployable 5.7 x 5.3-meter 16-rib Wrap-Rib Reflector, and a Reflector Pointing Mechanism (RPM). The MSAT spacecraft was based on a Hughes HS601 spacecraft bus carrying two Reflector Assemblies independently dedicated for L-band transmit and receive operations. Lockheed Missiles and Space Company (LMSC) designed and built the Reflector Assembly for MSAT under contract to SPAR Aerospace Ltd. Two MSAT satellites were built jointly by SPAR Aerospace Ltd. and Hughes Space and Communications Co. for this program, the first scheduled for launch in 1994. When scaled for wavelength, the assembly and alignment requirements for the Reflector Assembly were in many instances equivalent to or exceeded that of a diffraction-limited visible light optical system. Combined with logistical constraints inherent to large, compliant, lightweight structures; 'bolt-on' alignment; and remote, indirect spacecraft access; the technical challenges were formidable. This document describes the alignment methods, the special test equipment, and fixturing for Reflector Assembly assembly and alignment.

78 FR 14357 - Certain Compact Fluorescent Reflector Lamps, Products Containing Same and Components Thereof...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-03-05

... Reflector Lamps, Products Containing Same and Components Thereof; Institution of Investigation AGENCY: U.S... fluorescent reflector lamps, products containing same and components thereof by reason of infringement of... compact fluorescent reflector lamps, products containing same and components thereof by reason of...

Solar thermal collectors using planar reflector

NASA Technical Reports Server (NTRS)

Espy, P. N.

1978-01-01

Specular reflectors have been used successfully with flat-plate collectors to achieve exceptionally high operating temperatures and high delivered energy per unit collector area. Optimal orientation of collectors and reflectors can result in even higher performance with an improved relationship between energy demand and supply. This paper reports on a study providing first order optimization of collector-reflector arrays in which single- and multiple-faceted reflectors in fixed or singly adjustable configurations provide delivered energy maxima in either summer or winter.

Photogrammetry research for FAST eleven-meter reflector panel surface shape measurement

NASA Astrophysics Data System (ADS)

Zhou, Rongwei; Zhu, Lichun; Li, Weimin; Hu, Jingwen; Zhai, Xuebing

2010-10-01

In order to design and manufacture the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) active reflector measuring equipment, measurement on each reflector panel surface shape was presented, static measurement of the whole neutral spherical network of nodes was performed, real-time dynamic measurement at the cable network dynamic deformation was undertaken. In the implementation process of the FAST, reflector panel surface shape detection was completed before eleven-meter reflector panel installation. Binocular vision system was constructed based on the method of binocular stereo vision in machine vision, eleven-meter reflector panel surface shape was measured with photogrammetry method. Cameras were calibrated with the feature points. Under the linearity camera model, the lighting spot array was used as calibration standard pattern, and the intrinsic and extrinsic parameters were acquired. The images were collected for digital image processing and analyzing with two cameras, feature points were extracted with the detection algorithm of characteristic points, and those characteristic points were matched based on epipolar constraint method. Three-dimensional reconstruction coordinates of feature points were analyzed and reflective panel surface shape structure was established by curve and surface fitting method. The error of reflector panel surface shape was calculated to realize automatic measurement on reflector panel surface shape. The results show that unit reflector panel surface inspection accuracy was 2.30mm, within the standard deviation error of 5.00mm. Compared with the requirement of reflector panel machining precision, photogrammetry has fine precision and operation feasibility on eleven-meter reflector panel surface shape measurement for FAST.

33 CFR 118.120 - Radar reflectors and racons.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Radar reflectors and racons. 118... BRIDGES BRIDGE LIGHTING AND OTHER SIGNALS § 118.120 Radar reflectors and racons. The District Commander may require or authorize the installation of radar reflectors and racons on bridge structures, stakes...

46 CFR 169.726 - Radar reflector.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 46 Shipping 7 2011-10-01 2011-10-01 false Radar reflector. 169.726 Section 169.726 Shipping COAST... Control, Miscellaneous Systems, and Equipment § 169.726 Radar reflector. Each nonmetallic vessel less than 90 feet in length must exhibit a radar reflector of suitable size and design while underway. Markings ...

33 CFR 118.120 - Radar reflectors and racons.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 33 Navigation and Navigable Waters 1 2011-07-01 2011-07-01 false Radar reflectors and racons. 118... BRIDGES BRIDGE LIGHTING AND OTHER SIGNALS § 118.120 Radar reflectors and racons. The District Commander may require or authorize the installation of radar reflectors and racons on bridge structures, stakes...

46 CFR 169.726 - Radar reflector.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 46 Shipping 7 2010-10-01 2010-10-01 false Radar reflector. 169.726 Section 169.726 Shipping COAST... Control, Miscellaneous Systems, and Equipment § 169.726 Radar reflector. Each nonmetallic vessel less than 90 feet in length must exhibit a radar reflector of suitable size and design while underway. Markings ...

46 CFR 169.726 - Radar reflector.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 46 Shipping 7 2012-10-01 2012-10-01 false Radar reflector. 169.726 Section 169.726 Shipping COAST... Control, Miscellaneous Systems, and Equipment § 169.726 Radar reflector. Each nonmetallic vessel less than 90 feet in length must exhibit a radar reflector of suitable size and design while underway. Markings ...

33 CFR 118.120 - Radar reflectors and racons.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 33 Navigation and Navigable Waters 1 2014-07-01 2014-07-01 false Radar reflectors and racons. 118... BRIDGES BRIDGE LIGHTING AND OTHER SIGNALS § 118.120 Radar reflectors and racons. The District Commander may require or authorize the installation of radar reflectors and racons on bridge structures, stakes...

46 CFR 169.726 - Radar reflector.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 46 Shipping 7 2014-10-01 2014-10-01 false Radar reflector. 169.726 Section 169.726 Shipping COAST... Control, Miscellaneous Systems, and Equipment § 169.726 Radar reflector. Each nonmetallic vessel less than 90 feet in length must exhibit a radar reflector of suitable size and design while underway. Markings ...

33 CFR 118.120 - Radar reflectors and racons.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 33 Navigation and Navigable Waters 1 2012-07-01 2012-07-01 false Radar reflectors and racons. 118... BRIDGES BRIDGE LIGHTING AND OTHER SIGNALS § 118.120 Radar reflectors and racons. The District Commander may require or authorize the installation of radar reflectors and racons on bridge structures, stakes...

46 CFR 169.726 - Radar reflector.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 46 Shipping 7 2013-10-01 2013-10-01 false Radar reflector. 169.726 Section 169.726 Shipping COAST... Control, Miscellaneous Systems, and Equipment § 169.726 Radar reflector. Each nonmetallic vessel less than 90 feet in length must exhibit a radar reflector of suitable size and design while underway. Markings ...

33 CFR 118.120 - Radar reflectors and racons.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 33 Navigation and Navigable Waters 1 2013-07-01 2013-07-01 false Radar reflectors and racons. 118... BRIDGES BRIDGE LIGHTING AND OTHER SIGNALS § 118.120 Radar reflectors and racons. The District Commander may require or authorize the installation of radar reflectors and racons on bridge structures, stakes...

Single-ended retroreflection sensors for absorption spectroscopy in high-temperature environments

NASA Astrophysics Data System (ADS)

Melin, Scott T.; Wang, Ze; Neal, Nicholas J.; Rothamer, David A.; Sanders, Scott T.

2017-04-01

Novel single-ended sensor arrangements are demonstrated for in situ absorption spectroscopy in combustion and related test articles. A single-ended optical access technique based on back-reflection from a polished test article surface is presented. H2O vapor absorption spectra were measured at 10 kHz in a homogeneous-charge compression-ignition engine using a sensor of this design collecting back-reflection from a polished piston surface. The measured spectra show promise for high-repetition-rate measurements in practical combustion devices. A second sensor was demonstrated based on a modification to this optical access technique. The sensor incorporates a nickel retroreflective surface as back-reflector to reduce sensitivity to beam steering and misalignment. In a propane-fired furnace, H2O vapor absorption spectra were obtained over the range 7315-7550 cm- 1 at atmospheric pressure and temperatures up to 775 K at 20 Hz using an external-cavity diode laser spectrometer. Gas properties of temperature and mole fraction were obtained from this furnace data using a band-shape spectral fitting technique. The temperature accuracy of the band-shape fitting was demonstrated to be ±1.3 K for furnace measurements at atmospheric pressure. These results should extend the range of applications in which absorption spectroscopy sensors are attractive candidates.

Toward Directly-Deposited Optical Blocking Filters for High-performance, Back-illuminated Imaging X-ray Detectors

NASA Astrophysics Data System (ADS)

Bautz, Mark W.; Kissel, S. E.; Ryu, K.; Suntharalingam, V.

2014-01-01

Silicon X-ray detectors require optical blocking filters to prevent out-of-band (UV, visible and near-IR) radiation from corrupting the X-ray signal. Traditionally, blocking filters have been deposited on thin, free-standing membranes suspended over the detector. Free-standing filters are fragile, however, and in past instruments have required heavy and complex vacuum housings to protect them from acoustic loads during ground operations and launch. A directly-deposited blocking filter greatly simplifies the instrument and in principle permits better soft X-ray detection efficiency than a traditional free-standing filter. Directly-deposited filters have flown in previous generation instruments (e.g. the XMM/Newton Reflection Grating Spectrometer) but none has yet been demonstrated on a modern, high-performance back-illuminated X-ray CCD. We report here on the status of our NASA-funded Strategic Astrophysics Technology program to demonstrate such filters.

Electrically switchable polymer stabilised broadband infrared reflectors and their potential as smart windows for energy saving in buildings.

PubMed

Khandelwal, Hitesh; Loonen, Roel C G M; Hensen, Jan L M; Debije, Michael G; Schenning, Albertus P H J

2015-07-01

Electrically switchable broadband infrared reflectors that are relatively transparent in the visible region have been fabricated using polymer stabilised cholesteric liquid crystals. The IR reflectors can change their reflection/transmission properties by applying a voltage in response to changes in environmental conditions. Simulations predict that a significant amount of energy can be saved on heating, cooling and lighting of buildings in places such as Madrid by using this switchable IR reflector. We have also fabricated a switchable IR reflector which can also generate electricity. These polymer based switchable IR reflectors are of high potential as windows of automobiles and buildings to control interior temperatures and save energy.

Reflectors with directional-mixed reflection properties for application in luminaries with high-power LED diodes

NASA Astrophysics Data System (ADS)

Zaremba, Krzysztof

2008-06-01

Application of directional-mixed reflectors results in a luminance decrease of the apparent image of light emitting diodes (LEDs), which is advantageous as far as glare reduction is concerned. On the other hand, reflectors have a negative impact on luminous intensity curves of the luminaries. This work analyzes an impact of surfaces with directional-mixed reflection properties in a mirror reflector designed for a luminary equipped with high-power LEDs. We present an algorithm used to determine the shape of the reflector of the surface with small scattering, where the axis twist angle for a parabolic reflector varies in a predefined range and follows a power function.

Electrically switchable polymer stabilised broadband infrared reflectors and their potential as smart windows for energy saving in buildings

PubMed Central

Khandelwal, Hitesh; Loonen, Roel C. G. M.; Hensen, Jan L. M.; Debije, Michael G.; Schenning, Albertus P. H. J.

2015-01-01

Electrically switchable broadband infrared reflectors that are relatively transparent in the visible region have been fabricated using polymer stabilised cholesteric liquid crystals. The IR reflectors can change their reflection/transmission properties by applying a voltage in response to changes in environmental conditions. Simulations predict that a significant amount of energy can be saved on heating, cooling and lighting of buildings in places such as Madrid by using this switchable IR reflector. We have also fabricated a switchable IR reflector which can also generate electricity. These polymer based switchable IR reflectors are of high potential as windows of automobiles and buildings to control interior temperatures and save energy. PMID:26132328

System concept for a moderate cost Large Deployable Reflector (LDR)

NASA Technical Reports Server (NTRS)

Swanson, P. N.; Breckinridge, J. B.; Diner, A.; Freeland, R. E.; Irace, W. R.; Mcelroy, P. M.; Meinel, A. B.; Tolivar, A. F.

1986-01-01

A study was carried out at JPL during the first quarter of 1985 to develop a system concept for NASA's LDR. Major features of the concept are a four-mirror, two-stage optical system; a lightweight structural composite segmented primary reflector; and a deployable truss backup structure with integral thermal shield. The two-stage optics uses active figure control at the quaternary reflector located at the primary reflector exit pupil, allowing the large primary to be passive. The lightweight composite reflector panels limit the short-wavelength operation to approximately 30 microns but reduce the total primary reflector weight by a factor of 3 to 4 over competing technologies. On-orbit thermal analysis indicates a primary reflector equilibrium temperature of less than 200 K with a maximum gradient of about 5 C across the 20-m aperture. Weight and volume estimates are consistent with a single Shuttle launch, and are based on Space Station assembly and checkout.

75 FR 34656 - Energy Conservation Program for Consumer Products: Energy Conservation Standards for Certain...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-06-18

... diameter, elliptical reflector (ER), and bulged reflector (BR) incandescent reflector lamps. In that... document or any other aspect of the rulemaking for certain small diameter, ER, and BR incandescent..., ER, and BR incandescent reflector lamps, and provide docket number EERE-2010- BT-STD-0005 and/or RIN...

Corrosion protection for silver reflectors

DOEpatents

Arendt, Paul N.; Scott, Marion L.

1991-12-31

A method of protecting silver reflectors from damage caused by contact with gaseous substances which are often present in the atmosphere and a silver reflector which is so protected. The inventive method comprises at least partially coating a reflector with a metal oxide such as aluminum oxide to a thickness of 15 .ANG. or less.

Lightweight composite reflectors for space optics

NASA Astrophysics Data System (ADS)

Williams, Brian E.; McNeal, Shawn R.; Ono, Russell M.

1998-01-01

The primary goal of this work was to advance the state of the art in lightweight, high optical quality reflectors for space- and Earth-based telescopes. This was accomplished through the combination of a precision silicon carbide (SiC) reflector surface and a high specific strength, low-mass SiC structural support. Reducing the mass of components launched into space can lead to substantial cost savings, but an even greater benefit of lightweight reflectors for both space- and Earth-based optics applications is the fact that they require far less complex and less expensive positioning systems. While Ultramet is not the first company to produce SiC by chemical vapor deposition (CVD) for reflector surfaces, it is the first to propose and demonstrate a lightweight, open-cell SiC structural foam that can support a thin layer of the highly desirable polished SiC reflector material. SiC foam provides a substantial structural and mass advantage over conventional honeycomb supports and alternative finned structures. The result is a reflector component that meets or exceeds the optical properties of current high-quality glass, ceramic, and metal reflectors while maintaining a substantially lower areal density.

Shape adjustment optimization and experiment of cable-membrane reflectors

NASA Astrophysics Data System (ADS)

Du, Jingli; Gu, Yongzhen; Bao, Hong; Wang, Congsi; Chen, Xiaofeng

2018-05-01

Cable-membrane structures are widely employed for large space reflectors due to their lightweight, compact and easy package. In these structures, membranes are attached to cable net, serving as reflectors themselves or as supporting structures for other reflective surface. The cable length and membrane shape have to be carefully designed and fabricated to guarantee the desired reflector surface shape. However, due to inevitable error in cable length and membrane shape during the manufacture and assembly of cable-membrane reflectors, some cables have to be designed to be capable of length adjustment. By carefully adjusting the length of these cables, the degeneration in reflector shape precision due to this inevitable error can be effectively reduced. In the paper a shape adjustment algorithm for cable-membrane reflectors is proposed. Meanwhile, model updating is employed during shape adjustment to decrease the discrepancy of the numerical model with respect to the actual reflector. This discrepancy has to be considered because during attaching membranes to cable net, the accuracy of the membrane shape is hard to guarantee. Numerical examples and experimental results demonstrate the proposed method.

Out-of-Plane Seismic Reflections Beneath the Pacific and Their Geophysical Implications

NASA Astrophysics Data System (ADS)

Schumacher, Lina; Thomas, Christine; Abreu, Rafael

2018-03-01

We detect seismic P wave arrivals that reach the surface from a different horizontal direction than the theoretical back azimuth of the earthquake. Slowness, back azimuth, and traveltime of observed out-of-plane signals are measured with array methods in relation to the main phases that travel along the great circle path. This directivity information is used to back trace the wave through a 1-D velocity model to its scattering or reflection location. The focus of this study lies on out-of-plane signals reflected once beneath the Pacific at a depth greater than 800 km. Data analysis is carried out for a broad frequency range (band-pass filter with corner periods of 0.5-5 s up to 5-50 s) to enable the detection of different structures and heterogeneities. In addition to mapping seismic heterogeneities in the lower mantle, we also qualitatively analyze waveforms and polarities of these signals to understand the nature of the structure. The observed 21 reflections with a reflection depth between 800 and 2,200 km illuminate heterogeneities in the mid- and lower mantle. Back-traced locations show shallowest depths around Hawaii and increase in depth to the north and southwest. Analysis of the polarities indicates low velocities for the imaged structure, and complexity of waveforms argues for a likely thermochemical origin. Additional 11 deep reflections/scatterers with depth larger than 2,200 km suggest internal heterogeneities or a presence of the D'' reflector.

Evaluation of Hardware and Procedures for Astronaut Assembly and Repair of Large Precision Reflectors

NASA Technical Reports Server (NTRS)

Lake, Mark S.; Heard, Walter L., Jr.; Watson, Judith J.; Collins, Timothy J.

2000-01-01

A detailed procedure is presented that enables astronauts in extravehicular activity (EVA) to efficiently assemble and repair large (i.e., greater than 10m-diameter) segmented reflectors, supported by a truss, for space-based optical or radio-frequency science instruments. The procedure, estimated timelines, and reflector hardware performance are verified in simulated 0-g (neutral buoyancy) assembly tests of a 14m-diameter, offset-focus, reflector test article. The test article includes a near-flight-quality, 315-member, doubly curved support truss and 7 mockup reflector panels (roughly 2m in diameter) representing a portion of the 37 total panels needed to fully populate the reflector. Data from the tests indicate that a flight version of the design (including all reflector panels) could be assembled in less than 5 hours - less than the 6 hours normally permitted for a single EVA. This assembly rate essentially matches pre-test predictions that were based on a vast amount of historical data on EVA assembly of structures produced by NASA Langley Research Center. Furthermore, procedures and a tool for the removal and replacement of a damaged reflector panel were evaluated, and it was shown that EVA repair of this type of reflector is feasible with the use of appropriate EVA crew aids.

Baseline monitoring using aircraft laser ranging. [spaceborne laser simulation and aircraft laser tracking

NASA Technical Reports Server (NTRS)

Krabill, W. B.; Hoge, F. E.; Martin, C. F.

1982-01-01

The use of aircraft laser ranging for the determination of baselines between ground based retroreflectors was investigated via simulations and with tests at Wallops Flight Center using the Airborne Oceanographic Lidar (AOL) on the Wallops C-54 aircraft ranging to a reflector array deployed around one of the Wallops runways. The aircraft altitude and reflector spacing were chosen on the basis of scaled down modeling of spacecraft tracking from 1000 km of reflectors separated by some 52 km, or of high altitude (10 km) aircraft tracking of reflectors separated by some 500 m. Aircraft altitudes flown for different passes across the runway reflector array varied from 800 m to 1350 m, with 32 reflectors deployed over an approximtely 300 m x 500 m ground pattern. The AOL transmitted 400 pulses/sec with a scan rate of 5/sec in a near circular pattern, so that the majority of the pulses were reflected by the runway surface or its environs rather than by retroreflectors. The return pulse characteristics clearly showed the high reflectivity of portions of the runway, with several returns indistinguishable in amplitude from reflector returns. For each pass across the reflector field, typically six to ten reflector hits were identified, consistent with that predicted by simulations and the observed transmitted elliptical pulse size.

Tracking reflector assembly for a skylight

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

Dominquez, R.L.

1984-02-07

A tracking reflector assembly for a skylight includes a ring-shaped base member rotatably supported above the skylight by a plurality of rollers which engage a channel formed within an annular wall of the ring. A reflector is pivotally coupled to the ring for reflecting light into the skylight to supplement light which strikes the skylight directly. A vertical drive motor operates in response to a pair of photosensors for raising and lowering the reflector to follow changes in the angular elevation of the sun. The ring-shaped base member includes a toothed lower surface engaged by a gear coupled to amore » horizontal drive motor for rotating the ring-shaped base member in response to a third photosensor for following east-to-west movement of the sun. Each of the aforementioned photosensors is normally shaded and actuates the associated drive motor only when being struck by direct sunlight. A vertical limit switch limits the amount by which the reflector may be pivotally raised to avoid reflecting midday summer sunlight into the skylight. Another switch is responsive to closure of the reflector over the base member for preventing the vertical drive motor from attempting to further pivot the reflector downwardly. A fourth photosensor senses darkness resulting from sunset or heavy overcast conditions for pivoting the reflector downwardly and returning the base member and reflector to an easterly direction. A limit switch senses the return of the base member to the full east position for terminating actuation of the horizontal drive motor. A user operated switch selectively enables the tracking reflector assembly to operate automatically or causes the reflector to be lowered and the base member to be returned to the full east position until the user again enables the automatic control circuitry.« less

Deployment simulation of a deployable reflector for earth science application

NASA Astrophysics Data System (ADS)

Wang, Xiaokai; Fang, Houfei; Cai, Bei; Ma, Xiaofei

2015-10-01

A novel mission concept namely NEXRAD-In-Space (NIS) has been developed for monitoring hurricanes, cyclones and other severe storms from a geostationary orbit. It requires a space deployable 35-meter diameter Ka-band (35 GHz) reflector. NIS can measure hurricane precipitation intensity, dynamics and its life cycle. These information is necessary for predicting the track, intensity, rain rate and hurricane-induced floods. To meet the requirements of the radar system, a Membrane Shell Reflector Segment (MSRS) reflector technology has been developed and several technologies have been evaluated. However, the deployment analysis of this large size and high-precision reflector has not been investigated. For a pre-studies, a scaled tetrahedral truss reflector with spring driving deployment system has been made and tested, deployment dynamics analysis of this scaled reflector has been performed using ADAMS to understand its deployment dynamic behaviors. Eliminating the redundant constraints in the reflector system with a large number of moving parts is a challenging issue. A primitive joint and flexible struts were introduced to the analytical model and they can effectively eliminate over constraints of the model. By using a high-speed camera and a force transducer, a deployment experiment of a single-bay tetrahedral module has been conducted. With the tested results, an optimization process has been performed by using the parameter optimization module of ADAMS to obtain the parameters of the analytical model. These parameters were incorporated to the analytical model of the whole reflector. It is observed from the analysis results that the deployment process of the reflector with a fixed boundary experiences three stages. These stages are rapid deployment stage, slow deployment stage and impact stage. The insight of the force peak distributions of the reflector can help the optimization design of the structure.

Criticality Safety Analysis on the Mixed Be, Nat-U, and C (Graphite) Reflectors in 55-Gallon Waste Drums and Their Equivalents for HWM Applications

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

Chou, P

The objective of this analysis is to develop and establish the technical basis on the criticality safety controls for the storage of mixed beryllium (Be), natural uranium (Nat-U), and carbon (C)/graphite reflectors in 55-gallon waste containers and/or their equivalents in Hazardous Waste Management (HWM) facilities. Based on the criticality safety limits and controls outlined in Section 3.0, the operations involving the use of mixed-reflector drums satisfy the double-contingency principle as required by DOE Order 420.1 and are therefore criticality safe. The mixed-reflector mass limit is 120 grams for each 55-gallon drum or its equivalent. a reflector waiver of 50 gramsmore » is allowed for Be, Nat-U, or C/graphite combined. The waived reflectors may be excluded from the reflector mass calculations when determining if a drum is compliant. The mixed-reflector drums are allowed to mix with the typical 55-gallon one-reflector drums with a Pu mass limit of 120 grams. The fissile mass limit for the mixed-reflector container is 65 grams of Pu equivalent each. The corresponding reflector mass limits are 300 grams of Be, and/or 100 kilograms of Nat-U, and/or 110 kilograms of C/graphite for each container. All other unaffected control parameters for the one-reflector containers remain in effect for the mixed-reflector drums. For instance, Superior moderators, such as TrimSol, Superla white mineral oil No. 9, paraffin, and polyethylene, are allowed in unlimited quantities. Hydrogenous materials with a hydrogen density greater than 0.133 gram/cc are not allowed. Also, an isolation separation of no less than 76.2 cm (30-inch) is required between a mixed array and any other array. Waste containers in the action of being transported are exempted from this 76.2-cm (30-inch) separation requirement. All deviations from the CS controls and mass limits listed in Section 3.0 will require individual criticality safety analyses on a case-by-case basis for each of them to confirm their criticality safety prior to their deployment and implementation.« less

Suppression of large intraluminal bubble expansion in shock wave lithotripsy without compromising stone comminution: Methodology and in vitro experiments

NASA Astrophysics Data System (ADS)

Zhong, Pei; Zhou, Yufeng

2001-12-01

To reduce the potential of vascular injury without compromising the stone comminution capability of a Dornier HM-3 lithotripter, we have devised a method to suppress intraluminal bubble expansion via in situ pulse superposition. A thin shell ellipsoidal reflector insert was designed and fabricated to fit snugly into the original reflector of an HM-3 lithotripter. The inner surface of the reflector insert shares the same first focus with the original HM-3 reflector, but has its second focus located 5 mm proximal to the generator than that of the HM-3 reflector. With this modification, the original lithotripter shock wave is partitioned into a leading lithotripter pulse (peak positive pressure of 46 MPa and positive pulse duration of 1 μs at 24 kV) and an ensuing second compressive wave of 10 MPa peak pressure and 2 μs pulse duration, separated from each other by about 4 μs. Superposition of the two waves leads to a selective truncation of the trailing tensile component of the lithotripter shock wave, and consequently, a reduction in the maximum bubble expansion up to 41% compared to that produced by the original reflector. The pulse amplitude and -6 dB beam width of the leading lithotripter shock wave from the upgraded reflector at 24 kV are comparable to that produced by the original HM-3 reflector at 20 kV. At the lithotripter focus, while only about 30 shocks are needed to cause a rupture of a blood vessel phantom made of cellulose hollow fiber (i.d.=0.2 mm) using the original HM-3 reflector at 20 kV, no rupture could be produced after 200 shocks using the upgraded reflector at 24 kV. On the other hand, after 100 shocks the upgraded reflector at 24 kV can achieve a stone comminution efficiency of 22%, which is better than the 18% efficiency produced by the original reflector at 20 kV (p=0.043). All together, it has been shown in vitro that the upgraded reflector can produce satisfactory stone comminution while significantly reducing the potential for vessel rupture in shock wave lithotripsy.

Planar shock reflection on a wedged concave reflector

NASA Astrophysics Data System (ADS)

Yu, Fan-Ming; Sheu, Kuen-Dong

2001-04-01

The investigation of shock reflection and shock diffraction phenomena upon a wedged concave reflector produced by a planar incident shock wave has been done in the shock tube facility of Institute of Aeronautics and Astronautics, National Cheng- Kung University. The experiment proceeds upon three wedged concave reflectors models the upper and lower wedge angles arrangement of them are (50 degrees, 50 degrees) - 35 degrees, 35 degrees) and (50 degrees, 35 degrees), respectively. They were tested at Mach numbers of 1.2 - 1.65 and 2.0. On the first reflector, following the regular reflection on the 50 degree-wedged surface by the incident shock wave, a Mach shock diffraction behavior has been observed as shock moves outward from the apex of the reflector. On the apex of the reflector, it behaviors as a sector of the blast shock moving on a diverging channel. On the shadowgraph pictures it has been observed there exists a pattern of gas dynamics focus upon the second reflector. The Mach reflection from the 35 degree- wedged surface as being generated by the planar incident shock wave, on which the overlapping of the two triple points from both wedged surface offers the focusing mechanism. The shock interference, which proceeds by the Mach shock reflection and the regular shock diffraction from the reflector, generates a very complicate rolling-up of slip lines system. On the third reflector, the mixed shock interference behavior has been observed of which two diffraction shocks from concave 50 degree-wedged surface and 35 degree-wedged surface interfere with each other. The measurement of the peak pressure along a ray from the model apex parallel to incident shock direction indicates that the measured maximum pressure rising is larger near the apex of the reflector. Considering the measured maximum pressure increment due to the reflection shocks indicate that the wave strength upon large apex angle reflector is greater than it is upon small apex angle reflector. However, as considering the measured maximum pressure increment following the diffraction shocks, the results show that due to the focusing process upon (35 degree, 35 degree) reflector, it is of the largest increment.

10 CFR 429.35 - Bare or covered (no reflector) medium base compact fluorescent lamps.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 10 Energy 3 2012-01-01 2012-01-01 false Bare or covered (no reflector) medium base compact....35 Bare or covered (no reflector) medium base compact fluorescent lamps. (a) Sampling plan for... reflector) medium base compact fluorescent lamps; and (2) For each basic model of bare or covered (no...

10 CFR 429.35 - Bare or covered (no reflector) medium base compact fluorescent lamps.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 10 Energy 3 2014-01-01 2014-01-01 false Bare or covered (no reflector) medium base compact....35 Bare or covered (no reflector) medium base compact fluorescent lamps. (a) Sampling plan for... reflector) medium base compact fluorescent lamps; and (2) For each basic model of bare or covered (no...

10 CFR 429.35 - Bare or covered (no reflector) medium base compact fluorescent lamps.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 10 Energy 3 2013-01-01 2013-01-01 false Bare or covered (no reflector) medium base compact....35 Bare or covered (no reflector) medium base compact fluorescent lamps. (a) Sampling plan for... reflector) medium base compact fluorescent lamps; and (2) For each basic model of bare or covered (no...

43 CFR 2806.43 - How does BLM calculate rent for passive reflectors and local exchange networks?

Code of Federal Regulations, 2011 CFR

2011-10-01

... reflectors and local exchange networks? 2806.43 Section 2806.43 Public Lands: Interior Regulations Relating...-Of-Way § 2806.43 How does BLM calculate rent for passive reflectors and local exchange networks? (a) BLM calculates rent for passive reflectors and local exchange networks by using the same rent...

Surface measuring technique. [using a laser to scan the surface of a reflector

NASA Technical Reports Server (NTRS)

Spiers, R. B., Jr.

1980-01-01

Measurement of the surface contour of a large electrostatically formed concave reflector using a modified Foucault or knife edge test is described. The curve of the actual electrostatically formed reflector surface is compared to a curve representing a reference sphere. Measurements of surface slope and deviation are calculated every 15 cm along the reflector's horizontal and vertical diameters. Characterization of surface roughness on a small scale compared to the laser spot size at the reflector are obtained from the increased laser spot size at a distant projection screen.

Interpreting Radar View near Mars' South Pole, Orbit 1334

NASA Technical Reports Server (NTRS)

2006-01-01

A radargram from the Shallow Subsurface Radar instrument (SHARAD) on NASA's Mars Reconnaissance Orbiter is shown in the upper-right panel and reveals detailed structure in the polar layered deposits of the south pole of Mars.

The sounding radar collected the data presented here during orbit 1334 of the mission, on Nov. 8, 2006.

The horizontal scale in the radargram is distance along the ground track. It can be referenced to the ground track map shown in the lower right. The radar traversed from about 75 to 85 degrees south latitude, or about 590 kilometers (370 miles). The ground track map shows elevation measured by the Mars Orbiter Laser Altimeter on NASA's Mars Global Surveyor orbiter. Green indicates low elevation; reddish-white indicates higher elevation. The traverse proceeds up onto a plateau formed by the layers.

The vertical scale on the radargram is time delay of the radar signals reflected back to Mars Reconnaissance Orbiter from the surface and subsurface. For reference, using an assumed velocity of the radar waves in the subsurface, time is converted to depth below the surface at one place: about 1,500 meters (5,000 feet) to one of the deeper subsurface reflectors. The color scale varies from black for weak reflections to white for strong reflections.

The middle panel shows mapping of the major subsurface reflectors, some of which can be traced for a distance of 100 kilometers (60 miles) or more. The layers are not all horizontal and the reflectors are not always parallel to one another. Some of this is due to variations in surface elevation, which produce differing velocity path lengths for different reflector depths. However, some of this behavior is due to spatial variations in the deposition and removal of material in the layered deposits, a result of the recent climate history of Mars.

The Shallow Subsurface Radar was provided by the Italian Space Agency (ASI). Its operations are led by the University of Rome and its data are analyzed by a joint U.S.-Italian science team. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages the Mars Reconnaissance Orbiter for the NASA Science Mission Directorate, Washington.

Corner reflector SAR interferometry as an element of a landslide early warning system

NASA Astrophysics Data System (ADS)

Singer, J.; Riedmann, M.; Lang, O.; Anderssohn, J.; Thuro, K.; Wunderlich, Th.; Heunecke, O.; Minet, Ch.

2012-04-01

The development of efficient and cost-effective landslide monitoring techniques is the central aim of the alpEWAS research project (www.alpewas.de). Within the scope of the project a terrestrial geosensor network on a landslide site in the Bavarian Alps has been set up, consisting of low cost GNSS with subcentimeter precision, time domain reflectometry (TDR) and video tacheometry (VTPS). To increase the spatial sampling, 16 low-cost Radar Corner Reflectors (CRs) were installed on the site in 2011. The CRs are to reflect radar signals back to the TerraSAR-X radar satellite, allowing for precise displacement measurements. The subject of this study is the application of the CR SAR Interferometry (CRInSAR) technique, and the integration of the derived motion field into an early warning system for landslide monitoring based on terrestrial measurements. An accurate validation data set is realized independently of the monitoring network using millimeter precision GNSS and tacheometer measurements. The 12 CRs from Astrium Geo-Information Services employed over the test site were specifically designed for TerraSAR-X satellite passes. They are made of concrete with integrated metal plates weighing about 80 to 100 kg. They are of triangular trihedral shape with minimal dimensions to obtain a Radar Cross Section 100 times stronger than that of the surrounding area. The concrete guarantees stability against harsh weather conditions, and robustness with respect to vandalism or theft. In addition, the Technical University of Munich (TUM) and the German Aerospace Center (DLR) installed another four CRs made entirely out of aluminum, with the TUM reflectors being of similar minimum size than the Astrium reflectors. Three CRs were placed on assumed stable ground outside the slope area and shall act as reference reflectors. Since the installation date of most CRs (25/08/2011), TerraSAR-X HighResolution SpotLight data have been repeatedly acquired from ascending orbit over the test site with an incidence angle of 25.73°. The ascending orbit was chosen for the satellite to look on the backslope of the mountain, minimizing foreshortening effects. The datasets have a spatial resolution of about one meter and VV polarization, and have been processed with precise Scientific Orbits. In a first step, the sub-pixel position of the CR, as well as its intensity are characterized. The phase values for each image are then extracted for each CR and a differential interferometric phase with respect to a single master is calculated using a Digital Elevation Model. These phases are then unwrapped in the temporal domain and transformed to displacements. The redundant displacement results stemming from the use of three different reference reflectors are adjusted and an error is estimated. To integrate the result into the early warning system, datum corrections are necessary, as the InSAR displacement measurement is relative to the reference point(s) and reference time. In addition, the line-of-sight measurement is transformed with respect to coordinate system of the alpEWAS measurement system. Both the InSAR and terrestrial landslide movement measurements are then cross-checked with the validation high precision GNSS and tacheometer measurements.

Near ultraviolet InGaN/AlGaN-based light-emitting diodes with highly reflective tin-doped indium oxide/Al-based reflectors.

PubMed

Choi, Chang-Hoon; Han, Jaecheon; Park, Jae-Seong; Seong, Tae-Yeon

2013-11-04

The enhanced light output power of a InGaN/AlGaN-based light-emitting diodes (LEDs) using three different types of highly reflective Sn-doped indium oxide (ITO)/Al-based p-type reflectors, namely, ITO/Al, Cu-doped indium oxide (CIO)/s-ITO(sputtered)/Al, and Ag nano-dots(n-Ag)/CIO/s-ITO/Al, is presented. The ITO/Al-based reflectors exhibit lower reflectance (76 - 84% at 365 nm) than Al only reflector (91.1%). However, unlike Al only n-type contact, the ITO/Al-based contacts to p-GaN show good ohmic characteristics. Near-UV (365 nm) InGaN/AlGaN-based LEDs with ITO/Al, CIO/s-ITO/Al, and n-Ag/CIO/s-ITO/Al reflectors exhibit forward-bias voltages of 3.55, 3.48, and 3.34 V at 20 mA, respectively. The LEDs with the ITO/Al and CIO/s-ITO/Al reflectors exhibit 9.5% and 13.5% higher light output power (at 20 mA), respectively, than the LEDs with the n-Ag/CIO/s-ITO/Al reflector. The improved performance of near UV LEDs is attributed to the high reflectance and low contact resistivity of the ITO/Al-based reflectors, which are better than those of conventional Al-based reflectors.

Conformal Membrane Reflectors for Deployable Optics

NASA Technical Reports Server (NTRS)

Hood, Patrick J.; Keys, Andrew S. (Technical Monitor)

2002-01-01

This presentation reports the Phase I results on NASA's Gossamer Spacecraft Exploratory Research and Technology Program. Cornerstone Research Group, Inc., the University of Rochester, and International Photonics Consultants collaborated to investigate the feasibility of free-standing, liquid-crystal-polymer (LCP) reflectors for integration into space-based optical systems. The goal of the program was to achieve large-diameter, broadband. reflective membranes that are resistant to the effects of space, specifically cryogenic environments and gamma-ray irradiation. Additionally, we assessed the applicability of utilizing the technology as tight sails, since, by their very nature, these films offer high-reflectivity at specified wavelengths. Previous research programs have demonstrated all-polymer, narrow-band Specular reflectors and diffuse membrane reflectors. The feasibility of fabricating an all-polymer broadband specular reflector and a narrow-band specular membrane reflector was assessed in the Phase I Gossamer program. In addition, preliminary gamma irradiation studies were conducted to determine the stability of the polymer reflectors to radiation. Materials and process technology were developed to fabricate coupon-scale reflectors of both broad- and narrow-band specular reflectors in Phase 1. This presentation will report the results of these studies, including, the performance of a narrow-band specular membrane. Gamma irradiation exposures indicate limited impact on the optical performance although additional exposure studies are warranted. Plans to scale up the membrane fabrication process will be presented.

76 FR 56678 - Energy Efficiency Program for Consumer Products: Public Meeting and Availability of the Framework...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-09-14

... reflector (ER) and bulged reflector (BR) bulb shapes, and with diameters of 2.75 inches or less. Therefore....25 and 2.75 inches, as well as lamps with ER, BR, bulged parabolic aluminized reflector (BPAR), or... certain reflector (R), ER and BR IRLs. DOE has concluded, for the reasons that follow, that it has the...

Primary reflector for solar energy collection systems

NASA Technical Reports Server (NTRS)

Miller, C. G. (Inventor); Stephens, J. B.

1978-01-01

A fixed, linear, ground-based primary reflector is disclosed which has an extended curved sawtooth-contoured surface covered with a metalized polymeric reflecting material. The device reflects solar energy to a movably supported collector that is kept at the concentrated line focus of the reflector primary. The primary reflector may be constructed by a process utilizing well-known freeway paving machinery.

Primary reflector for solar energy collection systems and method of making same

NASA Technical Reports Server (NTRS)

Miller, C. G.; Stephens, J. B. (Inventor)

1979-01-01

Solar energy is reflected to a movably supported collector that is kept at the concentrated line focus of the reflector primary by a fixed, linear, ground-based primary reflector having an extended curved sawtooth contoured surface covered with a metalized polymeric reflecting material. The primary reflector was constructed by a process utilizing well-known freeway paving machinery.

Space Optical Communications Using Laser Beam Amplification

NASA Technical Reports Server (NTRS)

Agrawal, Govind

2015-01-01

The Space Optical Communications Using Laser Beam Amplification (SOCLBA) project will provide a capability to amplify a laser beam that is received in a modulating retro-reflector (MRR) located in a satellite in low Earth orbit. It will also improve the pointing procedure between Earth and spacecraft terminals. The technology uses laser arrays to strengthen the reflected laser beam from the spacecraft. The results of first year's work (2014) show amplification factors of 60 times the power of the signal beam. MMRs are mirrors that reflect light beams back to the source. In space optical communications, a high-powered laser interrogator beam is directed from the ground to a satellite. Within the satellite, the beam is redirected back to ground using the MMR. In the MMR, the beam passes through modulators, which encode a data signal onto the returning beam. MMRs can be used in small spacecraft for optical communications. The SOCLBA project is significant to NASA and small spacecraft due to its application to CubeSats for optical data transmission to ground stations, as well as possible application to spacecraft for optical data transmission.

Design method of LED rear fog lamp based on freeform micro-surface reflectors

NASA Astrophysics Data System (ADS)

Yu, Jindong; Wu, Heng

2017-11-01

We propose a practical method for the design of a light-emitting diode (LED) rear fog lamp based on freeform micro-surface reflectors. The lamp consists of nine LEDs and each of them has a freeform micro-surface reflector correspondingly. The micro-surface reflector design includes three steps. An initial freeform reflector is first built based on the light energy maps. The micro-surface reflector is then constructed on the bias of the initial one. Finally, a two-step method is designed to optimize the micro-surface reflector. With the proposed method, a module is designed and LCW DURIS E5 LED source whose emitting surface is 5.7 mm × 3.0 mm is adopted for simulation. A prototype is also assembled and fabricated to verify the real performance. Both the simulation and experimental results demonstrate that the luminous intensity distribution can well fulfill the requirements of ECE No.38 regulation. Furthermore, more than 79% energy can be saved when compared with the rear fog lamps using conventional sources.

Wide scanning spherical antenna

NASA Technical Reports Server (NTRS)

Shen, Bing (Inventor); Stutzman, Warren L. (Inventor)

1995-01-01

A novel method for calculating the surface shapes for subreflectors in a suboptic assembly of a tri-reflector spherical antenna system is introduced, modeled from a generalization of Galindo-Israel's method of solving partial differential equations to correct for spherical aberration and provide uniform feed to aperture mapping. In a first embodiment, the suboptic assembly moves as a single unit to achieve scan while the main reflector remains stationary. A feed horn is tilted during scan to maintain the illuminated area on the main spherical reflector fixed throughout the scan thereby eliminating the need to oversize the main spherical reflector. In an alternate embodiment, both the main spherical reflector and the suboptic assembly are fixed. A flat mirror is used to create a virtual image of the suboptic assembly. Scan is achieved by rotating the mirror about the spherical center of the main reflector. The feed horn is tilted during scan to maintain the illuminated area on the main spherical reflector fixed throughout the scan.

Huss Receives 2013 Cryosphere Young Investigator Award: Citation: Response

NASA Astrophysics Data System (ADS)

Huss, Matthias

2014-07-01

I would like to thank the AGU Cryosphere focus group for this award. Gaining such an important recognition at this stage of a scientific career is indeed both a great honor and a motivation to me. I was a little child when I first stepped onto a glacier. There was an unforgettable sensation of attraction and interest that touched me—one might call it a magic moment. Back then, I would never have imagined being a glaciologist one day. But it feels right, and I am grateful to have received the opportunity of exploring this wonderful element of nature.

Feasibility Study of Graphite Epoxy Antenna for a Microwave Limb Sounder Radiometer (MLSR)

NASA Technical Reports Server (NTRS)

1979-01-01

Results are presented of a feasibility study to design graphite epoxy antenna reflectors for a jet propulsion laboratory microwave limb sounder instrument (MLSR). Two general configurations of the offset elliptic parabolic reflectors are presented that will meet the requirements on geometry and reflector accuracy. The designs consist of sandwich construction for the primary reflectors, secondary reflector support structure and cross-tie members between reflector pairs. Graphite epoxy materials of 3 and 6 plies are used in the facesheets of the sandwich. An aluminum honeycomb is used for the core. A built-in adjustment system is proposed to reduce surface distortions during assembly. The manufacturing and environmental effects are expected to result in surface distortions less than .0015 inch and pointing errors less than .002 degree.

Reflector and Protections in a Sodium-cooled Fast Reactor: Modelling and Optimization

NASA Astrophysics Data System (ADS)

Blanchet, David; Fontaine, Bruno

2017-09-01

The ASTRID project (Advanced Sodium Technological Reactor for Industrial Demonstration) is a Generation IV nuclear reactor concept under development in France [1]. In this frame, studies are underway to optimize radial reflectors and protections. Considering radial protections made in natural boron carbide, this study is conducted to assess the neutronic performances of the MgO as the reference choice for reflector material, in comparison with other possible materials including a more conventional stainless steel. The analysis is based upon a simplified 1-D and 2-D deterministic modelling of the reactor, providing simplified interfaces between core, reflector and protections. Such models allow examining detailed reaction rate distributions; they also provide physical insights into local spectral effects occurring at the Core-Reflector and at the Reflector-Protection interfaces.

Interaction of acoustic levitation field with liquid reflecting surface

NASA Astrophysics Data System (ADS)

Hong, Z. Y.; Xie, W. J.; Wei, B.

2010-01-01

Single-axis acoustic levitation of substances, such as foam, water, polymer, and aluminum, is achieved by employing various liquids as the sound reflectors. The interaction of acoustic levitation field with liquid reflecting surface is investigated theoretically by considering the deformation of the liquid surface under acoustic radiation pressure. Numerical calculations indicate that the deformation degree of the reflecting surface shows a direct proportion to the acoustic radiation power. Appropriate deformation is beneficial whereas excessive deformation is unfavorable to enhance the levitation capability. Typically, the levitation capability with water reflector is smaller than that with the concave rigid reflector but slightly larger than that with the planar rigid reflector at low emitter vibration intensity. Liquid reflectors with larger surface tension and higher density behave more closely to the planar rigid reflector.

Nuclear reactor reflector

DOEpatents

Hopkins, Ronald J.; Land, John T.; Misvel, Michael C.

1994-01-01

A nuclear reactor reflector is disclosed that comprises a stack of reflector blocks with vertical water flow passages to cool the reflector. The interface between blocks is opposite support points for reactor fuel rods. Water flows between the reflector and the reactor barrel from passages in a bottom block. The top block contains a flange to limit this flow and the flange has a slot to receive an alignment pin that is welded to the barrel. The pin is held in the slot by two removable shims. Alignment bars extend the length of the stack in slots machined in each block when the stack is assembled.

Nuclear reactor reflector

DOEpatents

Hopkins, R.J.; Land, J.T.; Misvel, M.C.

1994-06-07

A nuclear reactor reflector is disclosed that comprises a stack of reflector blocks with vertical water flow passages to cool the reflector. The interface between blocks is opposite support points for reactor fuel rods. Water flows between the reflector and the reactor barrel from passages in a bottom block. The top block contains a flange to limit this flow and the flange has a slot to receive an alignment pin that is welded to the barrel. The pin is held in the slot by two removable shims. Alignment bars extend the length of the stack in slots machined in each block when the stack is assembled. 12 figs.

Tailored reflectors for illumination.

PubMed

Jenkins, D; Winston, R

1996-04-01

We report on tailored reflector design methods that allow the placement of general illumination patterns onto a target plane. The use of a new integral design method based on the edge-ray principle of nonimaging optics gives much more compact reflector shapes by eliminating the need for a gap between the source and the reflector profile. In addition, the reflectivity of the reflector is incorporated as a design parameter. We show the performance of design for constant irradiance on a distant plane, and we show how a leading-edge-ray method may be used to achieve general illumination patterns on nearby targets.

Gravity deformation measurements of 70m reflector surfaces

NASA Technical Reports Server (NTRS)

Brenner, Michael; Imbriale, William A.; Britcliffe, Michael K.

2001-01-01

Two of NASA's Deep Space Network (DSN) 70-meter reflectors are measured using a Leica TDM-5000 theodolite. The main reflector surface was measured at five elevation angles so that a gravity deformation model could be derived that described the main reflector distortions over the entire range of elevation angles. The report describes the measurement equipment and accuracy and the results derived from the data.

Enhanced linearly polarized lasing emission from nanoimprinted surface-emitting distributed feedback laser based on polymeric liquid crystals

NASA Astrophysics Data System (ADS)

Jeong, Soon Moon; Ha, Na Young; Chee, Mu Guen; Araoka, Fumito; Ishikawa, Ken; Takezoe, Hideo; Nishimura, Suzushi; Suzaki, Goro

2008-12-01

The authors have demonstrated the enhancement of linearly polarized lasing emission intensity using a structure made by a simple fabrication process. The enhanced lasing is achieved using a nanoimprinted distributed feedback structure together with spin-coated polymeric liquid crystals. The backward linearly TE-polarized lasing emission is transformed to left-handed circularly polarized light (L-CPL) by employing a dye-doped polymeric nematic liquid crystal (PNLC) film as a (-1/4)λ[=(3/4)λ] plate. The L-CPL is effectively reflected by a L-polymeric cholesteric liquid crystal film as a reflector and transformed back to TE-polarized light by the PNLC film; as a result one-directional emission intensity is enhanced.

High power and single mode quantum cascade lasers.

PubMed

Bismuto, Alfredo; Bidaux, Yves; Blaser, Stéphane; Terazzi, Romain; Gresch, Tobias; Rochat, Michel; Muller, Antoine; Bonzon, Christopher; Faist, Jerome

2016-05-16

We present a single mode quantum cascade laser with nearly 1 W optical power. A buried distributed feedback reflector is used on the back section for wavelength selection. The laser is 6 mm long, 3.5 μm wide, mounted episide-up and the laser facets are left uncoated. Laser emission is centered at 4.68 μm. Single-mode operation with a side mode suppression ratio of more than 30 dB is obtained in whole range of operation. Farfield measurements prove a symmetric, single transverse-mode emission in TM00-mode with typical divergences of 41° and 33° in the vertical and horizontal direction respectively. This work shows the potential for simple fabrication of high power lasers compatible with standard DFB processing.

Impact of HFIR LEU Conversion on Beryllium Reflector Degradation Factors

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

Ilas, Dan

2013-10-01

An assessment of the impact of low enriched uranium (LEU) conversion on the factors that may cause the degradation of the beryllium reflector is performed for the High Flux Isotope Reactor (HFIR). The computational methods, models, and tools, comparisons with previous work, along with the results obtained are documented and discussed in this report. The report documents the results for the gas and neutronic poison production, and the heating in the beryllium reflector for both the highly enriched uranium (HEU) and LEU HFIR configurations, and discusses the impact that the conversion to LEU may have on these quantities. A time-averagingmore » procedure was developed to calculate the isotopic (gas and poisons) production in reflector. The sensitivity of this approach to different approximations is gauged and documented. The results show that the gas is produced in the beryllium reflector at a total rate of 0.304 g/cycle for the HEU configuration; this rate increases by ~12% for the LEU case. The total tritium production rate in reflector is 0.098 g/cycle for the HEU core and approximately 11% higher for the LEU core. A significant increase (up to ~25%) in the neutronic poisons production in the reflector during the operation cycles is observed for the LEU core, compared to the HEU case, for regions close to the core s horizontal midplane. The poisoning level of the reflector may increase by more than two orders of magnitude during long periods of downtime. The heating rate in the reflector is estimated to be approximately 20% lower for the LEU core than for the HEU core. The decrease is due to a significantly lower contribution of the heating produced by the gamma radiation for the LEU core. Both the isotopic (gas and neutronic poisons) production and the heating rates are spatially non-uniform throughout the beryllium reflector volume. The maximum values typically occur in the removable reflector and close to the midplane.« less

Broadband direction-dependent transmission of light with photonic crystal heterostructure grating

NASA Astrophysics Data System (ADS)

Yilmaz, D.; Giden, I. H.; Kurt, H.

2018-01-01

Direction-dependent light transmission is a remarkable phenomenon owing to its great potential to be used in optical communication processing systems such as optical diodes, isolators and rectifiers. All these applications require optical reciprocity breaking mechanisms such as magneto-optical effect. Keeping the reciprocity intact, it is possible to manipulate the amount and spatial form of the two oppositely propagating lights exiting from a passive photonic medium. In this paper, a photonic crystal diffraction grating (PCDG) configuration is studied for the investigation of asymmetric light transport due to the spatial inversion symmetry breaking in the designed compact all-dielectric PC heterostructure. Thanks to the periodic corrugations at the back-surface of the designed structure, the backward transmission of the zero-order diffracted wave is notably suppressed while the efficient unidirectional forward transmission is achieved. Numerical calculations show that up to 73% of the incoming electromagnetic energy is transmitted in the forward illumination whereas it reduces down to a value of 6% (which corresponds to 10.85 dB beam suppression) in the case of backward illumination. That asymmetric light transmission leads to a contrast ratio (CR) of above 0.55 (CR  =  (T +x   -  T -x )/(T +x   +  T -x ), in which T -x and T +x are the transmission efficiencies in the  -x and  +x directions, respectively). The highest contrast ratio of CR  =  0.99 is calculated at the incident frequency of a/λ  =  0.5338 having the forward and backward transmissions of {T +x ,T -x }  =  {42%,0.1%}, which corresponds to the beam suppression of 26.23 dB. Furthermore, the proposed PCDG exhibits the diffraction grating effect at the considerable range of angle of incidence up to  ±20° at certain frequencies indicating that the proposed grating system is durable to source misalignments.

Detection of reflector surface from near field phase measurements

NASA Technical Reports Server (NTRS)

Ida, Nathan

1991-01-01

The deviation of a reflector antenna surface from a perfect parabolic shape causes degradation of the performance of the antenna. The problem of determining the shape of the reflector surface in a reflector antenna using near field phase measurements is not a new one. A recent issue of the IEEE tansactions on Antennas and Propagation (June 1988) contained numerous descriptions of the use of these measurements: holographic reconstruction or inverse Fourier transform. Holographic reconstruction makes use of measurement of the far field of the reflector and then applies the Fourier transform relationship between the far field and the current distribution on the reflector surface. Inverse Fourier transformation uses the phase measurements to determine the far field pattern using the method of Kerns. After the far field pattern is established, an inverse Fourier transform is used to determine the phases in a plane between the reflector surface and the plane in which the near field measurements were taken. These calculations are time consuming since they involve a relatively large number of operations. A much faster method can be used to determine the position of the reflector. This method makes use of simple geometric optics to determine the path length of the ray from the feed to the reflector and from the reflector to the measurement point. For small physical objects and low frequencies, diffraction effects have a major effect on the error, and the algorithm provides incorrect results. It is believed that the effect is less noticeable for large distortions such as antenna warping, and more noticeable for small, localized distortions such as bumps and depressions such as might be caused by impact damage.

The effect of reflector geometry on the acoustic field and bubble dynamics produced by an electrohydraulic shock wave lithotripter.

PubMed

Zhou, Yufeng; Zhong, Pei

2006-06-01

A theoretical model for the propagation of shock wave from an axisymmetric reflector was developed by modifying the initial conditions for the conventional solution of a nonlinear parabolic wave equation (i.e., the Khokhlov-Zabolotskaya-Kuznestsov equation). The ellipsoidal reflector of an HM-3 lithotripter is modeled equivalently as a self-focusing spherically distributed pressure source. The pressure wave form generated by the spark discharge of the HM-3 electrode was measured by a fiber optic probe hydrophone and used as source conditions in the numerical calculation. The simulated pressure wave forms, accounting for the effects of diffraction, nonlinearity, and thermoviscous absorption in wave propagation and focusing, were compared with the measured results and a reasonably good agreement was found. Furthermore, the primary characteristics in the pressure wave forms produced by different reflector geometries, such as that produced by a reflector insert, can also be predicted by this model. It is interesting to note that when the interpulse delay time calculated by linear geometric model is less than about 1.5 micros, two pulses from the reflector insert and the uncovered bottom of the original HM-3 reflector will merge together. Coupling the simulated pressure wave form with the Gilmore model was carried out to evaluate the effect of reflector geometry on resultant bubble dynamics in a lithotripter field. Altogether, the equivalent reflector model was found to provide a useful tool for the prediction of pressure wave form generated in a lithotripter field. This model may be used to guide the design optimization of reflector geometries for improving the performance and safety of clinical lithotripters.

The effect of reflector geometry on the acoustic field and bubble dynamics produced by an electrohydraulic shock wave lithotripter

PubMed Central

Zhou, Yufeng; Zhong, Pei

2007-01-01

A theoretical model for the propagation of shock wave from an axisymmetric reflector was developed by modifying the initial conditions for the conventional solution of a nonlinear parabolic wave equation (i.e., the Khokhlov–Zabolotskaya–Kuznestsov equation). The ellipsoidal reflector of an HM-3 lithotripter is modeled equivalently as a self-focusing spherically distributed pressure source. The pressure wave form generated by the spark discharge of the HM-3 electrode was measured by a fiber optic probe hydrophone and used as source conditions in the numerical calculation. The simulated pressure wave forms, accounting for the effects of diffraction, nonlinearity, and thermoviscous absorption in wave propagation and focusing, were compared with the measured results and a reasonably good agreement was found. Furthermore, the primary characteristics in the pressure wave forms produced by different reflector geometries, such as that produced by a reflector insert, can also be predicted by this model. It is interesting to note that when the interpulse delay time calculated by linear geometric model is less than about 1.5 μs, two pulses from the reflector insert and the uncovered bottom of the original HM-3 reflector will merge together. Coupling the simulated pressure wave form with the Gilmore model was carried out to evaluate the effect of reflector geometry on resultant bubble dynamics in a lithotripter field. Altogether, the equivalent reflector model was found to provide a useful tool for the prediction of pressure wave form generated in a lithotripter field. This model may be used to guide the design optimization of reflector geometries for improving the performance and safety of clinical lithotripters. PMID:16838506

Interpreting Radar View near Mars' South Pole, Orbit 1360

NASA Technical Reports Server (NTRS)

2006-01-01

A radargram from the Shallow Subsurface Radar instrument (SHARAD) on NASA's Mars Reconnaissance Orbiter is shown in the upper-right panel and reveals detailed structure in the polar layered deposits of the south pole of Mars.

The sounding radar collected the data presented here during orbit 1360 of the mission, on Nov. 10, 2006.

The horizontal scale in the radargram is distance along the ground track. It can be referenced to the ground track map shown in the lower right. The radar traversed from about 74 degrees to 85 degrees south latitude, or about 650 kilometers (400 miles). The ground track map shows elevation measured by the Mars Orbiter Laser Altimeter on NASA's Mars Global Surveyor orbiter. Green indicates low elevation; reddish-white indicates higher elevation. The traverse proceeds up onto a plateau formed by the layers.

The vertical scale on the radargram is time delay of the radar signals reflected back to Mars Reconnaissance Orbiter from the surface and subsurface. For reference, using an assumed velocity of the radar waves in the subsurface, time is converted to depth below the surface at one place: about 800 meters (2,600 feet) to one of the strongest subsurface reflectors. This reflector marks the base of the polar layered deposits. The color scale varies from black for weak reflections to white for strong reflections.

The middle panel shows mapping of the major subsurface reflectors, some of which can be traced for a distance of 100 kilometers (60 miles) or more. The layering manifests the recent climate history of Mars, recorded by the deposition and removal of ice and dust.

The Shallow Subsurface Radar was provided by the Italian Space Agency (ASI). Its operations are led by the University of Rome and its data are analyzed by a joint U.S.-Italian science team. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages the Mars Reconnaissance Orbiter for the NASA Science Mission Directorate, Washington.

Reflector for efficient coupling of a laser beam to air or other fluids

DOEpatents

Kare, Jordin T.

1992-01-01

A reflector array is disclosed herein that provides a controlled region or regions of plasma breakdowns from a laser beam produced at a remotely-based laser source. The plasma may be applied to produce thrust to propel a spacecraft, or to diagnose a laser beam, or to produce shockwaves. The spacecraft propulsion system comprises a reflector array attached to the vehicle. The reflector array comprises a plurality of reflectors spaced apart on a reflective surface, with each reflector acting as an independent focusing mirror. The reflectors are spaced closely together to form a continuous or partially-continuous surface. The reflector array may be formed from a sheet of reflective material, such as copper or aluminum. In operation, a beam of electromagnetic energy, such as a laser beam, is directed at the reflectors which focus the reflected electromagnetic energy at a plurality of regions off the surface. The energy concentrated in the focal region causes a breakdown of the air or other fluid in the focal region, creating a plasma. Electromagnetic energy is absorbed in the plasma and it grows in volume, compressing and heating the adjacent fluid thereby providing thrust. Laser pulses may be applied repetitively. After each such thrust pulse, fresh air can be introduced next to the surface either laterally, or through a perforated surface. If air or some other gas or vapor is supplied, for example from a tank carried on board a vehicle, this invention may also be used to provide thrust in a vacuum environment.

Analysis of a generalized dual reflector antenna system using physical optics

NASA Technical Reports Server (NTRS)

Acosta, Roberto J.; Lagin, Alan R.

1992-01-01

Reflector antennas are widely used in communication satellite systems because they provide high gain at low cost. Offset-fed single paraboloids and dual reflector offset Cassegrain and Gregorian antennas with multiple focal region feeds provide a simple, blockage-free means of forming multiple, shaped, and isolated beams with low sidelobes. Such antennas are applicable to communications satellite frequency reuse systems and earth stations requiring access to several satellites. While the single offset paraboloid has been the most extensively used configuration for the satellite multiple-beam antenna, the trend toward large apertures requiring minimum scanned beam degradation over the field of view 18 degrees for full earth coverage from geostationary orbit may lead to impractically long focal length and large feed arrays. Dual reflector antennas offer packaging advantages and more degrees of design freedom to improve beam scanning and cross-polarization properties. The Cassegrain and Gregorian antennas are the most commonly used dual reflector antennas. A computer program for calculating the secondary pattern and directivity of a generalized dual reflector antenna system was developed and implemented at LeRC. The theoretical foundation for this program is based on the use of physical optics methodology for describing the induced currents on the sub-reflector and main reflector. The resulting induced currents on the main reflector are integrated to obtain the antenna far-zone electric fields. The computer program is verified with other physical optics programs and with measured antenna patterns. The comparison shows good agreement in far-field sidelobe reproduction and directivity.

Two-dimensional displacement measurement based on two parallel gratings

NASA Astrophysics Data System (ADS)

Wei, Peipei; Lu, Xi; Qiao, Decheng; Zou, Limin; Huang, Xiangdong; Tan, Jiubin; Lu, Zhengang

2018-06-01

In this paper, a two-dimensional (2-D) planar encoder based on two parallel gratings, which includes a scanning grating and scale grating, is presented. The scanning grating is a combined transmission rectangular grating comprised of a 2-D grating located at the center and two one-dimensional (1-D) gratings located at the sides. The grating lines of the two 1-D gratings are perpendicular to each other and parallel with the 2-D grating lines. The scale grating is a 2-D reflective-type rectangular grating placed in parallel with the scanning grating, and there is an angular difference of 45° between the grating lines of the two 2-D gratings. With the special structural design of the scanning grating, the encoder can measure the 2-D displacement in the grating plane simultaneously, and the measured interference signals in the two directions are uncoupled. Moreover, by utilizing the scanning grating to modulate the phase of the interference signals instead of the prisms, the structure of the encoder is compact. Experiments were implemented, and the results demonstrate the validity of the 2-D planar grating encoder.

Bragg Reflector-Induced Increased Nonradiative Lifetime in Gallium Arsenide (GaAs)/Aluminum Gallium Arsenide (AlGaAs) Double Heterostructures

DTIC Science & Technology

2015-09-01

ARL-TR-7473 ● SEP 2015 US Army Research Laboratory Bragg Reflector-Induced Increased Nonradiative Lifetime in Gallium Arsenide...return it to the originator. ARL-TR-7473 ● SEP 2015 US Army Research Laboratory Bragg Reflector-Induced Increased Nonradiative ...3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE Bragg Reflector-Induced Increased Nonradiative Lifetime in Gallium Arsenide (GaAs)/Aluminum

The DART Cylindrical, Infrared, 1 Meter Membrane Reflector

NASA Technical Reports Server (NTRS)

Morgan, Rhonda M.; Agnes, Greg S.; Barber, Dan; Dooley, Jennifer; Dragovan, Mark; Hatheway, Al E.; Marcin, Marty

2004-01-01

The Dual Anamorphic Reflector Telescopes (DART) is an architecture for large aperture space telescopes that enables the use of membranes. A membrane can be readily shaped in one direction of curvature using a combination of boundary control and tensioning, yielding a cylindrical reflector. Two cylindrical reflectors (orthogonal and confocal) comprise the 'primary mirror' of the telescope system. The aperture is completely unobstructed and ideal for infrared and high contrast observations.

Coaxial Virtual Cathode Enhancement

DTIC Science & Technology

2004-10-20

need more solid evidence to clarify them. Table 2. Frequency list for geometries without reflectors, showing the microwave frequencies based on their...frequency. V. The Functions of the Reflectors Table 3 is a frequency list with the donut reflector at different positions. From Table 3, we can see that...both cases. We do observe that the microwave power generally is decreased by the donut reflector. Table 3. Frequency list for geometries with a donut

Fabrication of Spherical Reflectors in Outer Space

NASA Technical Reports Server (NTRS)

Wang, Yu; Dooley, Jennifer; Dragovan, Mark; Serivens, Wally

2005-01-01

A process is proposed for fabrication of lightweight spherical reflectors in outer space for telescopes, radio antennas, and light collectors that would be operated there. The process would obviate the relatively massive substrates and frames needed to support such reflectors in normal Earth gravitation. According to the proposal, fabrication of a reflector would begin with blowing of a bubble to the specified reflector radius. Taking advantage of the outer-space vacuum as a suitable environment for evaporative deposition of metal, a metal-evaporation source would be turned on and moved around the bubble to deposit a reflective metal film over the specified reflector area to a thickness of several microns. Then the source would be moved and aimed to deposit more metal around the edge of the reflector area, increasing the thickness there to approximately equal to 100 micron to form a frame. Then the bubble would be deflated and peeled off the metal, leaving a thin-film spherical mirror having an integral frame. The mirror would then be mounted for use. The feasibility of this technology has been proved by fabricating a prototype at JPL. As shown in the figure, a 2-in. (.5-cm) diameter hemispherical prototype reflector was made from a polymer bubble coated with silver, forming a very smooth surface.

A method to design blended rolled edges for compact range reflectors

NASA Technical Reports Server (NTRS)

Gupta, Inder J.; Burnside, Walter D.

1989-01-01

A method to design blended rolled edges for arbitrary rim shape compact range reflectors is presented. The reflectors may be center-fed or offset-fed. The method leads to rolled edges with minimal surface discontinuities. It is shown that the reflectors designed using the prescribed method can be defined analytically using simple expressions. A procedure to obtain optimum rolled edges parameter is also presented. The procedure leads to blended rolled edges that minimize the diffracted fields emanating from the junction between the paraboloid and the rolled edge surface while satisfying certain constraints regarding the reflector size and the minimum operating frequency of the system.

The development of composite materials for spacecraft precision reflector panels

NASA Technical Reports Server (NTRS)

Tompkins, Stephen S.; Bowles, David E.; Funk, Joan G.; Towell, Timothy W.; Lavoie, J. A.

1990-01-01

One of the critical technology needs for large precision reflectors required for future astrophysics and optical communications is in the area of structural materials. Therefore, a major area of the Precision Segmented Reflector Program at NASA is to develop lightweight composite reflector panels with durable, space environmentally stable materials which maintain both surface figure and required surface accuracy necessary for space telescope applications. Results from the materials research and development program at NASA Langley Research Center are discussed. Advanced materials that meet the reflector panel requirements are identified. Thermal, mechanical and durability properties of candidate materials after exposure to simulated space environments are compared to the baseline material.

A Method for Producing a Shaped Contour Radiation Pattern Using a Single Shaped Reflector and a Single Feed

NASA Technical Reports Server (NTRS)

Cherrette, A. R.; Lee, S. W.; Acosta, R. J.

1988-01-01

Eliminating the corporate feed network in shaped contour beam antennas will reduce the expense, weight, and RF loss of the antenna system. One way of producing a shaped contour beam without using a feed network is to use a single shaped reflector with a single feed element. For a prescribed contour beam and feed, an optimization method for designing the reflector shape is given. As a design example, a shaped reflector is designed to produce a continental U.S. coverage (CONUS) beam. The RF performance of the shaped reflector is then verified by physical optics.

A method to design blended rolled edges for compact range reflectors

NASA Technical Reports Server (NTRS)

Gupta, Inder J.; Ericksen, Kurt P.; Burnside, Walter D.

1990-01-01

A method to design blended rolled edges for arbitrary rim shape compact range reflectors is presented. The reflectors may be center-fed or offset-fed. The method leads to rolled edges with minimal surface discontinuities. It is shown that the reflectors designed using the prescribed method can be defined analytically using simple expressions. A procedure to obtain optimum rolled edges parameters is also presented. The procedure leads to blended rolled edges that minimize the diffracted fields emanating from the junction between the paraboloid and the rolled edge surface while satisfying certain constraints regarding the reflector size and the minimum operating frequency of the system.

The novel support structure design of high stability for space borne primary reflector

NASA Astrophysics Data System (ADS)

Yu, Fei; Ding, Lin; Tan, Ting; Pei, Jing-yang.; Zhao, Xue-min; Bai, Shao-jun

2018-01-01

The novel support structure design of high stability for space borne primary mirror is presented. The structure is supported by a ball head support rod, for statically determinate support of reflector. The ball head assembly includes the supporting rod, nesting, bushing and other important parts. The liner bushing of the resistant material is used to fit for ball head approximated with the reflector material, and then the bad impact of thermal mismatch could be minimized to minimum. In order to ensure that the structure of the support will not be damaged, the glue spots for limitation is added around the reflector, for position stability of reflector. Through analysis and calculation, it can be seen that the novel support structure would not transfer the external stresses to the reflector, and the external stresses usually result from thermal mismatch and assembly misalignment. The novel method is useful for solving the problem of the bad influence form thermal stress and assembly force. In this paper, the supporting structure is introduced and analyzed in detail. The simulation results show that the ball head support reflector works more stably.

Analytical approximation of a distorted reflector surface defined by a discrete set of points

NASA Technical Reports Server (NTRS)

Acosta, Roberto J.; Zaman, Afroz A.

1988-01-01

Reflector antennas on Earth orbiting spacecrafts generally cannot be described analytically. The reflector surface is subjected to a large temperature fluctuation and gradients, and is thus warped from its true geometrical shape. Aside from distortion by thermal stresses, reflector surfaces are often purposely shaped to minimize phase aberrations and scanning losses. To analyze distorted reflector antennas defined by discrete surface points, a numerical technique must be applied to compute an interpolatory surface passing through a grid of discrete points. In this paper, the distorted reflector surface points are approximated by two analytical components: an undistorted surface component and a surface error component. The undistorted surface component is a best fit paraboloid polynomial for the given set of points and the surface error component is a Fourier series expansion of the deviation of the actual surface points, from the best fit paraboloid. By applying the numerical technique to approximate the surface normals of the distorted reflector surface, the induced surface current can be obtained using physical optics technique. These surface currents are integrated to find the far field radiation pattern.

Scanning properties of large dual-shaped offset and symmetric reflector antennas

NASA Astrophysics Data System (ADS)

Galindo-Israel, Victor; Veruttipong, Watt; Norrod, Roger D.; Imbriale, William A.

1992-04-01

Several characteristics of dual offset (DOSR) and symmetric shaped reflectors are examined. Among these is the amelioration of the added cost of manufacturing a shaped reflector antenna, particularly a doubly curved surface for the DOSR, if adjustable panels, which may be necessary for correction of gravity and wind distortions, are also used for improving gain by shaping. The scanning properties of shaped reflectors, both offset and circularly symmetric, are examined and compared to conic section scanning characteristics. Scanning of the pencil beam is obtained by lateral and axial translation of a single point-source feed. The feed is kept pointed toward the center of the subreflector. The effects of power spillover and aperture phase error as a function of beam scanning is examined for several different types of large reflector designs including DOSR, circularly symmetric large f/D and smaller f/D dual reflector antenna systems. It is graphically illustrated that the Abbe-sine condition for improving scanning of an optical system cannot, inherently, be satisfied in a dual-shaped reflector system shaped for high gain and low feed spillover.

Steam Rankine Solar Receiver, phase 2

NASA Technical Reports Server (NTRS)

Deanda, L. E.; Faust, M.

1981-01-01

A steam rankine solar receiver (SRSR) based on a tubular concept was designed and developed. The SRSR is an insulated, cylindrical coiled tube boiler which is mounted at the focal plane of a fully tracking parabolic solar reflector. The concentrated solar energy received at the focal plane is then transformed to thermal energy through steam generation. The steam is used in a small Rankine cycle heat engine to drive a generator for the production of electrical energy. The SRSR was designed to have a dual mode capability, performing as a once through boiler with and without reheat. This was achieved by means of two coils which constitute the boiler. The boiler core size of the SRSR is 17.0 inches in diameter and 21.5 inches long. The tube size is 7/16 inch I.D. by 0.070 inch wall for the primary, and 3/4 inch I.D. by 0.125 inch wall for the reheat section. The materials used were corrosion resistant steel (CRES) type 321 and type 347 stainless steel. The core is insulated with 6 inches of cerablanket insulation wrapped around the outer wall. The aperture end and the reflector back plate at the closed end section are made of silicon carbide. The SRSR accepts 85 kwth and has a design life of 10,000 hrs when producing steam at 1400 F and 2550 psig.

Wearable sensors in intelligent clothing for measuring human body temperature based on optical fiber Bragg grating.

PubMed

Li, Hongqiang; Yang, Haijing; Li, Enbang; Liu, Zhihui; Wei, Kejia

2012-05-21

Measuring body temperature is considerably important to physiological studies as well as clinical investigations. In recent years, numerous observations have been reported and various methods of measurement have been employed. The present paper introduces a novel wearable sensor in intelligent clothing for human body temperature measurement. The objective is the integration of optical fiber Bragg grating (FBG)-based sensors into functional textiles to extend the capabilities of wearable solutions for body temperature monitoring. In addition, the temperature sensitivity is 150 pm/°C, which is almost 15 times higher than that of a bare FBG. This study combines large and small pipes during fabrication to implant FBG sensors into the fabric. The law of energy conservation of the human body is considered in determining heat transfer between the body and its clothing. The mathematical model of heat transmission between the body and clothed FBG sensors is studied, and the steady-state thermal analysis is presented. The simulation results show the capability of the material to correct the actual body temperature. Based on the skin temperature obtained by the weighted average method, this paper presents the five points weighted coefficients model using both sides of the chest, armpits, and the upper back for the intelligent clothing. The weighted coefficients of 0.0826 for the left chest, 0.3706 for the left armpit, 0.3706 for the right armpit, 0.0936 for the upper back, and 0.0826 for the right chest were obtained using Cramer's Rule. Using the weighting coefficient, the deviation of the experimental result was ± 0.18 °C, which favors the use for clinical armpit temperature monitoring. Moreover, in special cases when several FBG sensors are broken, the weighted coefficients of the other sensors could be changed to obtain accurate body temperature.

Materials and process optimization for dual-shell satellite antenna reflectors

NASA Astrophysics Data System (ADS)

Balaski, Darcy R.; van Oyen, Hans J.; Nissan, Sorin J.

A comprehensive, design-optimization test program was conducted for satellite antenna reflectors composed of two offset paraboloidal Kevlar-reinforced sandwich shells separated by a circular sandwich structure. In addition to standard mechanical properties testing, coefficient of thermal expansion and hygroscopic tests were conducted to predict reflector surface accuracy in the thermal cycling environment of orbital space. Attention was given to the relative placement of components during assembly, in view of reflector surface measurements.

Lamp with a truncated reflector cup

DOEpatents

Li, Ming; Allen, Steven C.; Bazydola, Sarah; Ghiu, Camil-Daniel

2013-10-15

A lamp assembly, and method for making same. The lamp assembly includes first and second truncated reflector cups. The lamp assembly also includes at least one base plate disposed between the first and second truncated reflector cups, and a light engine disposed on a top surface of the at least one base plate. The light engine is configured to emit light to be reflected by one of the first and second truncated reflector cups.

Terrestrial Laser Scanner Two-Face Measurements for Analyzing the Elevation-Dependent Deformation of the Onsala Space Observatory 20-m Radio Telescope's Main Reflector in a Bundle Adjustment.

PubMed

Holst, Christoph; Schunck, David; Nothnagel, Axel; Haas, Rüdiger; Wennerbäck, Lars; Olofsson, Henrik; Hammargren, Roger; Kuhlmann, Heiner

2017-08-09

For accurate astronomic and geodetic observations based on radio telescopes, the elevation-dependent deformation of the radio telescopes' main reflectors should be known. Terrestrial laser scanning has been used for determining the corresponding changes of focal lengths and areal reflector deformations at several occasions before. New in this publication is the situation in which we minimize systematic measurement errors by an improved measurement and data-processing concept: Sampling the main reflector in both faces of the laser scanner and calibrating the laser scanner in situ in a bundle adjustment. This concept is applied to the Onsala Space Observatory 20-m radio telescope: The focal length of the main reflector decreases by 9.6 mm from 85 ∘ to 5 ∘ elevation angle. Further local deformations of the main reflector are not detected.

Graphical method to design multilayer phase retarders.

PubMed

Apfel, J H

1981-03-15

When multilayer reflectors are used at nonnormal incidence, the two planes of polarization generally have different phase shifts. This difference, known as phase retardance, depends on the multilayer design, the incidence angle, and the wavelength. Heretofore, the design of reflectors with specific phase retardance has been carried out by computer optimization except for the case of a single layer on a metal substrate. A graph of phase retardance D vs the average phase shift A as a function of layer thickness provides a means for visualization that is useful in reflector designs. A D-A graph predicts the phase properties of a reflector as a function of the index and thickness of an added layer. Graphs of phase retardance vs average phase for two different materials can be superposed to predict the composite performance of a multilayer reflector. This graphical technique is employed to design and analyze reflectors with specified phase retardance.

Main-Reflector Manufacturing Technology for the Deep Space Optical Communications Ground Station

NASA Technical Reports Server (NTRS)

Britcliffe, M. J.; Hoppe, D. J.

2001-01-01

The Deep Space Network (DSN) has plans to develop a 10-m-diameter optical communications receiving station. The system uses the direct detection technique, which has much different requirements from a typical astronomical telescope. The receiver must operate in daylight and nighttime conditions. This imposes special requirements on the optical system to reject stray light from the Sun and other sources. One of the biggest challenges is designing a main-reflector surface that meets these requirements and can be produced at a reasonable cost. The requirements for the performance of the reflector are presented. To date, an aspherical primary reflector has been assumed. A reflector with a spherical reflector has a major cost advantage over an aspherical design, with no sacrifice in performance. A survey of current manufacturing techniques for optical mirrors of this type was performed. Techniques including solid glass, lightweight glass, diamond-turned aluminum, and composite mirrors were investigated.

State-of-the-art low-cost solar reflector materials

NASA Astrophysics Data System (ADS)

Kennedy, C.; Jorgensen, G.

1994-11-01

Solar thermal technologies generate power by concentrating sunlight with large mirrors. The National Renewable Energy Laboratory (NREL) is working with industrial partners to develop the optical reflector materials needed for the successful deployment of this technology. The reflector materials must be low in cost and maintain high specular reflectance for extended lifetimes in severe outdoor environments. Currently, the best candidate materials for solar mirrors are silver-coated low-iron glass and silvered polymer films. Polymer reflectors are lighter in weight, offer greater flexibility in system design, and have the potential for lower cost than glass mirrors. In parallel with collaborative activities, several innovative candidate reflector-material constructions were investigated at NREL. The low-cost material requirement necessitates manufacturing compatible with mass-production techniques. Future cooperative efforts with the web-coating industry offers the promise of exciting new alternative materials and the potential for dramatic cost savings in developing advanced solar reflector materials.

Interferometric Polarization Control

NASA Technical Reports Server (NTRS)

Wollack, Edward J. (Inventor); Moseley, Samuel H. (Inventor); Chuss, David T. (Inventor); Novak, Giles A. (Inventor)

2008-01-01

A signal conditioning module provides a polarimeter capability in a photometric system. The module may include multiple variable delay polarization modulators. Each modulator may include an input port, and a first arm formed to include a first reflector and first rooftop mirror arranged in opposed relationship. The first reflector may direct an input radiation signal to the first rooftop mirror. Each modulator also may include an output port and a second arm formed to include a second reflector and second rooftop mirror arranged in opposed relationship. The second reflector can guide a signal from the second rooftop mirror towards the output port to provide an output radiation signal. A beamsplitting grid may be placed between the first reflector and the first rooftop mirror, and also between the second reflector and the second rooftop mirror. A translation apparatus can provide adjustment relative to optical path length vis-a-vis the first arm, the second arm and the grid.

Interferometric polarization control

NASA Technical Reports Server (NTRS)

Wollack, Edward J. (Inventor); Novak, Giles A. (Inventor); Moseley, Samuel H. (Inventor); Chuss, David T. (Inventor)

2009-01-01

A signal conditioning module provides a polarimeter capability in a photometric system. The module may include multiple variable delay polarization modulators. Each modulator may include an input port, and a first arm formed to include a first reflector and first rooftop mirror arranged in opposed relationship. The first reflector may direct an input radiation signal to the first rooftop mirror. Each modulator also may include an output port and a second arm formed to include a second reflector and second rooftop mirror arranged in opposed relationship. The second reflector can guide a signal from the second rooftop mirror towards the output port to provide an output radiation signal. A beamsplitting grid may be placed between the first reflector and the first rooftop mirror, and also between the second reflector and the second rooftop mirror. A translation apparatus can provide adjustment relative to optical path length vis-a-vis the first arm, the second arm and the grid.

Terrestrial Laser Scanner Two-Face Measurements for Analyzing the Elevation-Dependent Deformation of the Onsala Space Observatory 20-m Radio Telescope’s Main Reflector in a Bundle Adjustment

PubMed Central

Schunck, David; Nothnagel, Axel; Haas, Rüdiger; Wennerbäck, Lars; Olofsson, Henrik; Hammargren, Roger; Kuhlmann, Heiner

2017-01-01

For accurate astronomic and geodetic observations based on radio telescopes, the elevation-dependent deformation of the radio telescopes’ main reflectors should be known. Terrestrial laser scanning has been used for determining the corresponding changes of focal lengths and areal reflector deformations at several occasions before. New in this publication is the situation in which we minimize systematic measurement errors by an improved measurement and data-processing concept: Sampling the main reflector in both faces of the laser scanner and calibrating the laser scanner in situ in a bundle adjustment. This concept is applied to the Onsala Space Observatory 20-m radio telescope: The focal length of the main reflector decreases by 9.6 mm from 85∘ to 5∘ elevation angle. Further local deformations of the main reflector are not detected. PMID:28792449

Beyond Wires and Seeds: Reflector-guided Breast Lesion Localization and Excision.

PubMed

Mango, Victoria L; Wynn, Ralph T; Feldman, Sheldon; Friedlander, Lauren; Desperito, Elise; Patel, Sejal N; Gomberawalla, Ameer; Ha, Richard

2017-08-01

Purpose To evaluate outcomes of Savi Scout (Cianna Medical, Aliso Viejo, Calif) reflector-guided localization and excision of breast lesions by analyzing reflector placement, localization, and removal, along with target excision and rates of repeat excision (referred to as re-excision). Materials and Methods A single-institution retrospective review of 100 women who underwent breast lesion localization and excision by using the Savi Scout surgical guidance system from June 2015 to May 2016 was performed. By using image guidance 0-8 days before surgery, 123 nonradioactive, infrared-activated, electromagnetic wave reflectors were percutaneously inserted adjacent to or within 111 breast targets. Twenty patients had two or three reflectors placed for bracketing or for localizing multiple lesions, and when ipsilateral, they were placed as close as 2.6 cm apart. Target and reflector were localized intraoperatively by one of two breast surgeons who used a handpiece that emitted infrared light and electromagnetic waves. Radiographs of the specimen and pathologic analysis helped verify target and reflector removal. Target to reflector distance was measured on the mammogram and radiograph of the specimen, and reflector depth was measured on the mammogram. Pathologic analysis was reviewed. Re-excision rates and complications were recorded. By using statistics software, descriptive statistics were generated with 95% confidence intervals (CIs) calculated. Results By using sonographic (40 of 123; 32.5%; 95% CI: 24.9%, 41.2%) or mammographic (83 of 123; 67.5%; 95% CI: 58.8% 75.1%) guidance, 123 (100%; 95% CI: 96.4%, 100%) reflectors were placed. Mean mammographic target to reflector distance was 0.3 cm. All 123 (100%; 95% CI: 96.4%, 100%) targets and reflectors were excised. Pathologic analysis yielded 54 of 110 malignancies (49.1%; 95% CI: 39.9%, 58.3%; average, 1.0 cm; range, 0.1-5 cm), 32 high-risk lesions (29.1%; 95% CI: 21.4%, 38.2%), and 24 benign lesions (21.8%; 95% CI: 115.1%, 30.4%). Four of 54 malignant cases (7.4%; 95% CI: 2.4%, 18.1%) demonstrated margins positive for cancer that required re-excision. Five of 110 radiographs of the specimen (4.5%; 95% CI: 1.7%, 10.4%) demonstrated increased distance between the target and reflector distance of greater than 1.0 cm (range, 1.1-2.6 cm) compared with postprocedure mammogram the day of placement, three of five were associated with hematomas, two of five migrated without identifiable cause. No related postoperative complications were identified. Conclusion Savi Scout is an accurate, reliable method to localize and excise breast lesions with acceptable margin positivity and re-excision rates. Bracketing is possible with reflectors as close as 2.6 cm. Savi Scout overcomes many limitations of other localization methods, which warrants further study. © RSNA, 2017.

Reflector for efficient coupling of a laser beam to air or other fluids

DOEpatents

Kare, J.T.

1992-10-06

A reflector array is disclosed herein that provides a controlled region or regions of plasma breakdowns from a laser beam produced at a remotely-based laser source. The plasma may be applied to produce thrust to propel a spacecraft, or to diagnose a laser beam, or to produce shock waves. The spacecraft propulsion system comprises a reflector array attached to the vehicle. The reflector array comprises a plurality of reflectors spaced apart on a reflective surface, with each reflector acting as an independent focusing mirror. The reflectors are spaced closely together to form a continuous or partially-continuous surface. The reflector array may be formed from a sheet of reflective material, such as copper or aluminum. In operation, a beam of electromagnetic energy, such as a laser beam, is directed at the reflectors which focus the reflected electromagnetic energy at a plurality of regions off the surface. The energy concentrated in the focal region causes a breakdown of the air or other fluid in the focal region, creating a plasma. Electromagnetic energy is absorbed in the plasma and it grows in volume, compressing and heating the adjacent fluid thereby providing thrust. Laser pulses may be applied repetitively. After each such thrust pulse, fresh air can be introduced next to the surface either laterally, or through a perforated surface. If air or some other gas or vapor is supplied, for example from a tank carried on board a vehicle, this invention may also be used to provide thrust in a vacuum environment. 10 figs.

Preliminary design approach for large high precision segmented reflectors

NASA Technical Reports Server (NTRS)

Mikulas, Martin M., Jr.; Collins, Timothy J.; Hedgepeth, John M.

1990-01-01

A simplified preliminary design capability for erectable precision segmented reflectors is presented. This design capability permits a rapid assessment of a wide range of reflector parameters as well as new structural concepts and materials. The preliminary design approach was applied to a range of precision reflectors from 10 meters to 100 meters in diameter while considering standard design drivers. The design drivers considered were: weight, fundamental frequency, launch packaging volume, part count, and on-orbit assembly time. For the range of parameters considered, on-orbit assembly time was identified as the major design driver. A family of modular panels is introduced which can significantly reduce the number of reflector parts and the on-orbit assembly time.

Optical properties of nonimaging concentrators with corrugated reflectors

NASA Astrophysics Data System (ADS)

Roennelid, Mats; Perers, Bengt; Karlsson, Bjorn

1994-09-01

A ray tracing study has been performed on the optical properties of cylindrical nonimaging concentrators with linear corrugated reflectors. The corrugations are assumed to be V-formed and to have an extension parallel to the meridian plane of the concentrators. It is shown that the acceptance angle for radiation incident in the meridian plane can be increased for moderate corrugations. This increased acceptance is balanced by a decreased acceptance of radiation from other directions. Calculations of angular acceptance for a 2X compound parabolic concentrator is presented. It is shown that the annual irradiation on a solar collector with booster reflector can be increased if corrugated reflectors are used instead of smooth reflectors.

Long-reach transmission experiment of a wavelength division multiplexed-passive optical networks transmitter based on reflective semiconductor optical amplifiers

NASA Astrophysics Data System (ADS)

Jeon, Sie-Wook; Kim, Youngbok; Park, Chang-Soo

2012-01-01

We propose and demonstrate a long-reach wavelength division multiplexed-passive optical networks (WDM-PON) based on reflective semiconductor optical amplifiers (RSOAs) with easy maintenance of the optical source. Unlike previous studies the proposed WDM-PON uses two RSOAs: one for wavelength-selected light generation to provide a constant seed light to the second RSOA, the other for active external modulation. This method is free from intensity-fluctuated power penalties inherent to directly modulated single-RSOA sources, making long-reach transmission possible. Also, the wavelength of the modulated signal can easily be changed for the same RSOA by replacing the external feedback reflector, such as a fiber Bragg grating, or via thermal tuning. The seed light has a high-side-mode suppression ratio (SMSR) of 45 dB, and the bit error rate (BER) curve reveals that the upstream 1.25-Gb/s nonreturn-to-zero (NRZ) signal with a pseudo-random binary sequence (PRBS) of length of 215-1 has power penalties of 0.22 and 0.69 dB at BERs of 10-9 after 55-km and 110-km transmission due to fiber dispersion, respectively.

Electrically driven hybrid Si/III-V Fabry-Pérot lasers based on adiabatic mode transformers.

PubMed

Ben Bakir, B; Descos, A; Olivier, N; Bordel, D; Grosse, P; Augendre, E; Fulbert, L; Fedeli, J M

2011-05-23

We report the first demonstration of an electrically driven hybrid silicon/III-V laser based on adiabatic mode transformers. The hybrid structure is formed by two vertically superimposed waveguides separated by a 100-nm-thick SiO2 layer. The top waveguide, fabricated in an InP/InGaAsP-based heterostructure, serves to provide optical gain. The bottom Si-waveguides system, which supports all optical functions, is constituted by two tapered rib-waveguides (mode transformers), two distributed Bragg reflectors (DBRs) and a surface-grating coupler. The supermodes of this hybrid structure are controlled by an appropriate design of the tapers located at the edges of the gain region. In the middle part of the device almost all the field resides in the III-V waveguide so that the optical mode experiences maximal gain, while in regions near the III-V facets, mode transformers ensure an efficient transfer of the power flow towards Si-waveguides. The investigated device operates under quasi-continuous wave regime. The room temperature threshold current is 100 mA, the side-mode suppression ratio is as high as 20 dB, and the fiber-coupled output power is ~7 mW.

Extraordinary capabilities of optical devices incorporating guided-mode resonance gratings: application summary and recent examples

NASA Astrophysics Data System (ADS)

Magnusson, Robert; Yoon, Jae Woong; Amin, Mohammad Shyiq; Khaleque, Tanzina; Uddin, Mohammad Jalal

2014-03-01

For selected device concepts that are members of an evolving class of photonic devices enabled by guided-mode resonance (GMR) effects, we review physics of operation, design, fabrication, and characterization. We summarize the application potential of this field and provide new and emerging aspects. Our chosen examples include resonance elements with extremely wide reflection bands. Thus, in a multilevel structure with conformal germanium (Ge) films, reflectance exceeds 99% for spectral widths approaching 1100 nm. A simpler design, incorporating a partially etched single Ge layer on a glass substrate, exhibits a high-reflectance bandwidth close to 900 nm. We present a couple of interesting new device concepts enabled by GMRs coexisting with the Rayleigh anomaly. Our example Rayleigh reflector exhibits a wideband high-efficiency flattop spectrum and extremely rapid angular transitions. Moreover, we show that it is possible to fashion transmission filters by excitation of leaky resonant modes at the Rayleigh anomaly in a subwavelength nanograting. A unique transmission spectrum results, which is tightly delimited in angle and wavelength as experimentally demonstrated. We update our application list with new developments including GMR-based coherent perfect absorbers, multiparametric biosensors, and omnidirectional wideband absorbers.

Frequency stability of a dual wavelength quantum cascade laser.

PubMed

Sergachev, Ilia; Maulini, Richard; Gresch, Tobias; Blaser, Stéphane; Bismuto, Alfredo; Müller, Antoine; Bidaux, Yves; Südmeyer, Thomas; Schilt, Stéphane

2017-05-15

We characterized the dual wavelength operation of a distributed Bragg reflector (DBR) quantum cascade laser (QCL) operating at 4.5 μm using two independent optical frequency discriminators. The QCL emits up to 150 mW fairly evenly distributed between two adjacent Fabry-Perot modes separated by ≈11.6 GHz. We show a strong correlation between the instantaneous optical frequencies of the two lasing modes, characterized by a Pearson correlation coefficient of 0.96. As a result, we stabilized one laser mode of the QCL to a N 2 O transition using a side-of-fringe locking technique, reducing its linewidth by a factor 6.2, from 406 kHz in free-running operation down to 65 kHz (at 1-ms observation time), and observed a simultaneous reduction of the frequency fluctuations of the second mode by a similar amount, resulting in a linewidth narrowing by a factor 5.4, from 380 kHz to 70 kHz. This proof-of-principle demonstration was performed with a standard DBR QCL that was not deliberately designed for dual-mode operation. These promising results open the door to the fabrication of more flexible dual-mode QCLs with the use of specifically designed gratings in the future.

Methodes d'optimisation des parametres 2D du reflecteur dans un reacteur a eau pressurisee

NASA Astrophysics Data System (ADS)

Clerc, Thomas

With a third of the reactors in activity, the Pressurized Water Reactor (PWR) is today the most used reactor design in the world. This technology equips all the 19 EDF power plants. PWRs fit into the category of thermal reactors, because it is mainly the thermal neutrons that contribute to the fission reaction. The pressurized light water is both used as the moderator of the reaction and as the coolant. The active part of the core is composed of uranium, slightly enriched in uranium 235. The reflector is a region surrounding the active core, and containing mostly water and stainless steel. The purpose of the reflector is to protect the vessel from radiations, and also to slow down the neutrons and reflect them into the core. Given that the neutrons participate to the reaction of fission, the study of their behavior within the core is capital to understand the general functioning of how the reactor works. The neutrons behavior is ruled by the transport equation, which is very complex to solve numerically, and requires very long calculation. This is the reason why the core codes that will be used in this study solve simplified equations to approach the neutrons behavior in the core, in an acceptable calculation time. In particular, we will focus our study on the diffusion equation and approximated transport equations, such as SPN or S N equations. The physical properties of the reflector are radically different from those of the fissile core, and this structural change causes important tilt in the neutron flux at the core/reflector interface. This is why it is very important to accurately design the reflector, in order to precisely recover the neutrons behavior over the whole core. Existing reflector calculation techniques are based on the Lefebvre-Lebigot method. This method is only valid if the energy continuum of the neutrons is discretized in two energy groups, and if the diffusion equation is used. The method leads to the calculation of a homogeneous reflector. The aim of this study is to create a computational scheme able to compute the parameters of heterogeneous, multi-group reflectors, with both diffusion and SPN/SN operators. For this purpose, two computational schemes are designed to perform such a reflector calculation. The strategy used in both schemes is to minimize the discrepancies between a power distribution computed with a core code and a reference distribution, which will be obtained with an APOLLO2 calculation based on the method Method Of Characteristics (MOC). In both computational schemes, the optimization parameters, also called control variables, are the diffusion coefficients in each zone of the reflector, for diffusion calculations, and the P-1 corrected macroscopic total cross-sections in each zone of the reflector, for SPN/SN calculations (or correction factors on these parameters). After a first validation of our computational schemes, the results are computed, always by optimizing the fast diffusion coefficient for each zone of the reflector. All the tools of the data assimilation have been used to reflect the different behavior of the solvers in the different parts of the core. Moreover, the reflector is refined in six separated zones, corresponding to the physical structure of the reflector. There will be then six control variables for the optimization algorithms. [special characters omitted]. Our computational schemes are then able to compute heterogeneous, 2-group or multi-group reflectors, using diffusion or SPN/SN operators. The optimization performed reduces the discrepancies distribution between the power computed with the core codes and the reference power. However, there are two main limitations to this study: first the homogeneous modeling of the reflector assemblies doesn't allow to properly describe its physical structure near the core/reflector interface. Moreover, the fissile assemblies are modeled in infinite medium, and this model reaches its limit at the core/reflector interface. These two problems should be tackled in future studies. (Abstract shortened by UMI.).

SELF-REGULATING BOILING-WATER NUCLEAR REACTORS

DOEpatents

Ransohoff, J.A.; Plawchan, J.D.

1960-08-16

A boiling-water reactor was designed which comprises a pressure vessel containing a mass of water, a reactor core submerged within the water, a reflector tank disposed within the reactor, the reflector tank being open at the top to the interior of the pressure vessel, and a surge tank connected to the reflector tank. In operation the reflector level changes as a function of the pressure witoin the reactor so that the reactivity of the reactor is automatically controlled.

Integrated reflector antenna design and analysis

NASA Technical Reports Server (NTRS)

Zimmerman, M. L.; Lee, S. W.; Ni, S.; Christensen, M.; Wang, Y. M.

1993-01-01

Reflector antenna design is a mature field and most aspects were studied. However, of that most previous work is distinguished by the fact that it is narrow in scope, analyzing only a particular problem under certain conditions. Methods of analysis of this type are not useful for working on real-life problems since they can not handle the many and various types of perturbations of basic antenna design. The idea of an integrated design and analysis is proposed. By broadening the scope of the analysis, it becomes possible to deal with the intricacies attendant with modem reflector antenna design problems. The concept of integrated reflector antenna design is put forward. A number of electromagnetic problems related to reflector antenna design are investigated. Some of these show how tools for reflector antenna design are created. In particular, a method for estimating spillover loss for open-ended waveguide feeds is examined. The problem of calculating and optimizing beam efficiency (an important figure of merit in radiometry applications) is also solved. Other chapters deal with applications of this general analysis. The wide angle scan abilities of reflector antennas is examined and a design is proposed for the ATDRSS triband reflector antenna. The development of a general phased-array pattern computation program is discussed and how the concept of integrated design can be extended to other types of antennas is shown. The conclusions are contained in the final chapter.

Light-Output Enhancement of GaN-Based Light-Emitting Diodes with Three-Dimensional Backside Reflectors Patterned by Microscale Cone Array

PubMed Central

Hu, Jinyong; Wang, Hong

2014-01-01

Three-dimensional (3D) backside reflector, compared with flat reflectors, can improve the probability of finding the escape cone for reflecting lights and thus enhance the light-extraction efficiency (LEE) for GaN-based light-emitting diode (LED) chips. A triangle-lattice of microscale SiO2 cone array followed by a 16-pair Ti3O5/SiO2 distributed Bragg reflector (16-DBR) was proposed to be attached on the backside of sapphire substrate, and the light-output enhancement was demonstrated by numerical simulation and experiments. The LED chips with flat reflectors or 3D reflectors were simulated using Monte Carlo ray tracing method. It is shown that the LEE increases as the reflectivity of backside reflector increases, and the light-output can be significantly improved by 3D reflectors compared to flat counterparts. It can also be observed that the LEE decreases as the refractive index of the cone material increases. The 3D 16-DBR patterned by microscale SiO2 cone array benefits large enhancement of LEE. This microscale pattern was prepared by standard photolithography and wet-etching technique. Measurement results show that the 3D 16-DBR can provide 12.1% enhancement of wall-plug efficiency, which is consistent with the simulated value of 11.73% for the enhancement of LEE. PMID:25133262

From rifting to spreading - seismic structure of the rifted western Mariana extinct arc and the ParceVela back-arc basin

NASA Astrophysics Data System (ADS)

Grevemeyer, Ingo; Kodaira, Shuichi; Fujie, Gou; Takahashi, Narumi

2017-04-01

The proto Izu-Ogasawara (Bonin)-Mariana (IBM) Island arc was created when subduction of the Pacific plate began during the Eocene. Today, the Kyushu-Palau Ridge (KPR) at the centre of the Philippine Sea and the western Mariana Ridge (WMR) are considered to be a remnant of the proto IBM Island arc. The KPR and WMR were separated when back-arc spreading began at 30 to 29 Ma in the Shikoku Basin and ParceVela Basin (PVB). Volcanic activity along the arcs diminished at 27 Ma and there is little evidence of volcanic activity between 23-17 Ma. Arc volcanism was reactivated at 15 Ma, when the opening of the Shikoku Basin and PVB ceased. At about 5 Ma the Mariana Basin opened, rifting the WMR from the Mariana arc. Here, we report results from the seismic refraction and wide-angle profile MR101c shot in summer of 2003 by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) aboard the RV KAIYO during the cruise KY03-06, extending from the PVB across the WMR and terminating just to the east of the WMR. Along MR101c 46 OBS recorded shots from an airgun array of 12,000 cubic inches (197 litres); 44 OBS provided excellent P-wave data, including arrivals sampling the crust (Pg), the crust/mantle boundary (PmP), the uppermost mantle (Pn) and a deep reflection (PnP) under the WMR. To yield the seismic velocity structure, we used a joint reflection and refraction tomography, revealing the crustal and mantle P-wave velocity structure, the seismic Moho, and a deep-seated reflector. Distinct features are a 14 km thick crust forming the WMR, a high-velocity lower crust in both transition zones to the ParceVela Basin and Mariana Basin, and a reflector at 24 km depth, which shallows to 18 km in the transition zone to the Mariana Basin, perhaps reflecting rifting-related thinning of the entire lithosphere. The deep-reflector, however, did not occur under the PVB. Upper mantle velocity below the WMR is <7.5 km/s. High velocities of the lower crust of the WMR flanking the adjacent basins mimic the structure found in the Lau Basin - Tonga Arc system, perhaps indicating entrainment of hydrous melts from the adjacent arc governing early seafloor spreading when the spreading centre was at close distant to the volcanic arc. Upper mantle below the PVB shows typical mantle properties, supporting a P-wave velocity of >8 km/s. However, with respect to oceanic crust sampled in the Pacific Basin, PVB crust is with 5 km thinner and seismic velocities in the lower crust are with 6.7 km/s much lower.

New core-reflector boundary conditions for transient nodal reactor calculations

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

Lee, E.K.; Kim, C.H.; Joo, H.K.

1995-09-01

New core-reflector boundary conditions designed for the exclusion of the reflector region in transient nodal reactor calculations are formulated. Spatially flat frequency approximations for the temporal neutron behavior and two types of transverse leakage approximations in the reflector region are introduced to solve the transverse-integrated time-dependent one-dimensional diffusion equation and then to obtain relationships between net current and flux at the core-reflector interfaces. To examine the effectiveness of new core-reflector boundary conditions in transient nodal reactor computations, nodal expansion method (NEM) computations with and without explicit representation of the reflector are performed for Laboratorium fuer Reaktorregelung und Anlagen (LRA) boilingmore » water reactor (BWR) and Nuclear Energy Agency Committee on Reactor Physics (NEACRP) pressurized water reactor (PWR) rod ejection kinetics benchmark problems. Good agreement between two NEM computations is demonstrated in all the important transient parameters of two benchmark problems. A significant amount of CPU time saving is also demonstrated with the boundary condition model with transverse leakage (BCMTL) approximations in the reflector region. In the three-dimensional LRA BWR, the BCMTL and the explicit reflector model computations differ by {approximately}4% in transient peak power density while the BCMTL results in >40% of CPU time saving by excluding both the axial and the radial reflector regions from explicit computational nodes. In the NEACRP PWR problem, which includes six different transient cases, the largest difference is 24.4% in the transient maximum power in the one-node-per-assembly B1 transient results. This difference in the transient maximum power of the B1 case is shown to reduce to 11.7% in the four-node-per-assembly computations. As for the computing time, BCMTL is shown to reduce the CPU time >20% in all six transient cases of the NEACRP PWR.« less

Offset truss hex solar concentrator

NASA Technical Reports Server (NTRS)

White, John E. (Inventor); Sturgis, James D. (Inventor); Erikson, Raymond J. (Inventor); Waligroski, Gregg A. (Inventor); Scott, Michael A. (Inventor)

1991-01-01

A solar energy concentrator system comprises an offset reflector structure made up of a plurality of solar energy reflector panel sections interconnected with one another to form a piecewise approximation of a portion of a (parabolic) surface of revolution rotated about a prescribed focal axis. Each panel section is comprised of a plurality of reflector facets whose reflective surfaces effectively focus reflected light to preselected surface portions of the interior sidewall of a cylindrically shaped solar energy receiver. The longitudinal axis of the receiver is tilted at an acute angle with respect to the optical axis such that the distribution of focussed solar energy over the interior surface of the solar engine is optimized for dynamic solar energy conversion. Each reflector panel section comprises a flat, hexagonally shaped truss support framework and a plurality of beam members interconnecting diametrically opposed corners of the hexagonal framework recessed within which a plurality of (spherically) contoured reflector facets is disposed. The depth of the framework and the beam members is greater than the thickness of a reflector facet such that a reflector facet may be tilted (for controlling the effective focus of its reflected light through the receiver aperture) without protruding from the panel section.

Structural-electromagnetic bidirectional coupling analysis of space large film reflector antennas

NASA Astrophysics Data System (ADS)

Zhang, Xinghua; Zhang, Shuxin; Cheng, ZhengAi; Duan, Baoyan; Yang, Chen; Li, Meng; Hou, Xinbin; Li, Xun

2017-10-01

As used for energy transmission, a space large film reflector antenna (SLFRA) is characterized by large size and enduring high power density. The structural flexibility and the microwave radiation pressure (MRP) will lead to the phenomenon of structural-electromagnetic bidirectional coupling (SEBC). In this paper, the SEBC model of SLFRA is presented, then the deformation induced by the MRP and the corresponding far field pattern deterioration are simulated. Results show that, the direction of the MRP is identical to the normal of the reflector surface, and the magnitude is proportional to the power density and the square of cosine incident angle. For a typical cosine function distributed electric field, the MRP is a square of cosine distributed across the diameter. The maximum deflections of SLFRA linearly increase with the increasing microwave power densities and the square of the reflector diameters, and vary inversely with the film thicknesses. When the reflector diameter becomes 100 m large and the microwave power density exceeds 102 W/cm2, the gain loss of the 6.3 μm-thick reflector goes beyond 0.75 dB. When the MRP-induced deflection degrades the reflector performance, the SEBC should be taken into account.

Design of reflector contours to satisfy photometric criteria using physically realizable light sources

NASA Astrophysics Data System (ADS)

Spencer, Domina E.

2001-11-01

Traditionally reflector design has been confined to the use of surfaces defined in terms of conic sections, assuming that all light sources can be considered to be point sources. In the middle of the twentieth century, it was recognized that major improvements could be made if the shape of the reflector was designed to produce a desired distribution of light form an actual light source. Cylindrical reflectors were created which illuminated airport runways using fluorescent lamps in such a way that pilots could make visual landings safely even in fog. These reflector contours were called macrofocal parabolic cylinders. Other new reflector contours introduced were macrofocal elliptic cylinders which confined the light to long rectangles. Surfaces of revolution the fourth degree were also developed which made possible uniform floodlighting of a circular region. These were called horned and peaked quartics. The optimum solution of the automotive head lighting problem has not yet been found. The paper concludes with a discussion of the possibility of developing reflectors which are neither cylindrical nor rotational but will produce the optimum field of view for the automobile driver both in clear weather and in fog.

Disordered animal multilayer reflectors and the localization of light

PubMed Central

Jordan, T. M.; Partridge, J. C.; Roberts, N. W.

2014-01-01

Multilayer optical reflectors constructed from ‘stacks’ of alternating layers of high and low refractive index dielectric materials are present in many animals. For example, stacks of guanine crystals with cytoplasm gaps occur within the skin and scales of fish, and stacks of protein platelets with cytoplasm gaps occur within the iridophores of cephalopods. Common to all these animal multilayer reflectors are different degrees of random variation in the thicknesses of the individual layers in the stack, ranging from highly periodic structures to strongly disordered systems. However, previous discussions of the optical effects of such thickness disorder have been made without quantitative reference to the propagation of light within the reflector. Here, we demonstrate that Anderson localization provides a general theoretical framework to explain the common coherent interference and optical properties of these biological reflectors. Firstly, we illustrate how the localization length enables the spectral properties of the reflections from more weakly disordered ‘coloured’ and more strongly disordered ‘silvery’ reflectors to be explained by the same physical process. Secondly, we show how the polarization properties of reflection can be controlled within guanine–cytoplasm reflectors, with an interplay of birefringence and thickness disorder explaining the origin of broadband polarization-insensitive reflectivity. PMID:25339688

Bandwidth Study of the Microwave Reflectors with Rectangular Corrugations

NASA Astrophysics Data System (ADS)

Zhang, Liang; He, Wenlong; Donaldson, Craig R.; Cross, Adrian W.

2016-09-01

The mode-selective microwave reflector with periodic rectangular corrugations in the inner surface of a circular metallic waveguide is studied in this paper. The relations between the bandwidth and reflection coefficient for different numbers of corrugation sections were studied through a global optimization method. Two types of reflectors were investigated. One does not consider the phase response and the other does. Both types of broadband reflectors operating at W-band were machined and measured to verify the numerical simulations.

Distributed Bragg Reflectors With Reduced Optical Absorption

DOEpatents

Klem, John F.

2005-08-16

A new class of distributed Bragg reflectors has been developed. These distributed Bragg reflectors comprise interlayers positioned between sets of high-index and low-index quarter-wave plates. The presence of these interlayers is to reduce photon absorption resulting from spatially indirect photon-assisted electronic transitions between the high-index and low-index quarter wave plates. The distributed Bragg reflectors have applications for use in vertical-cavity surface-emitting lasers for use at 1.55 .mu.m and at other wavelengths of interest.

Durability of reflector materials in the space environment

NASA Technical Reports Server (NTRS)

Whitaker, Ann F.; Finckenor, Miria M.; Edwards, David; Kamenetzky, Rachel R.; Linton, Roger C.

1995-01-01

Various reflector configurations were flown as part of the Long Duration Exposure Facility (LDEF) A0171 experiment. These reflectors consisted of nickel substrates with aluminum, enhanced aluminum (multiple layers of aluminum and silver), silver, and silver alloy coatings with glassy ceramic overcoatings. These samples have been evaluated for changes in reflectance due to 5.8 years in the space environment. The reflector materials have also been evaluated using angstrometer, Rutherford backscattering (RBS), and electron spectroscopy for chemical analysis (ESCA) techniques.

Bifacial PV cell with reflector for stand-alone mast for sensor powering purposes

NASA Astrophysics Data System (ADS)

Jakobsen, Michael L.; Thorsteinsson, Sune; Poulsen, Peter B.; Riedel, N.; Rødder, Peter M.; Rødder, Kristin

2017-09-01

Reflectors to bifacial PV-cells are simulated and prototyped in this work. The aim is to optimize the reflector to specific latitudes, and particularly northern latitudes. Specifically, by using minimum semiconductor area the reflector must be able to deliver the electrical power required at the condition of minimum solar travel above the horizon, worst weather condition etc. We will test a bifacial PV-module with a retroreflector, and compare the output with simulations combined with local solar data.

Wavelength-controlled external-cavity laser with a silicon photonic crystal resonant reflector

NASA Astrophysics Data System (ADS)

Gonzalez-Fernandez, A. A.; Liles, Alexandros A.; Persheyev, Saydulla; Debnath, Kapil; O'Faolain, Liam

2016-03-01

We report the experimental demonstration of an alternative design of external-cavity hybrid lasers consisting of a III-V Semiconductor Optical Amplifier with fiber reflector and a Photonic Crystal (PhC) based resonant reflector on SOI. The Silicon reflector comprises a polymer (SU8) bus waveguide vertically coupled to a PhC cavity and provides a wavelength-selective optical feedback to the laser cavity. This device exhibits milliwatt-level output power and sidemode suppression ratio of more than 25 dB.

Projections of limiting states for load-bearing structures of reflectors made of polymer composites

NASA Astrophysics Data System (ADS)

Doronin, S. V.

2017-12-01

This paper deals with limiting states typical for reflector antennas for terrestrial satellite communication systems. Reflectors made of polymer composites are studied. These limiting states are projected by results of the numerical analysis of the stress and strain states. The analysis is executed for reflectors under conditions of static and dynamic loading. It takes into account both overshoot of the state variables of allowed level and the processes of long-term structural material degradation.

A soft actuation system for segmented reflector articulation and isolation

NASA Technical Reports Server (NTRS)

Agronin, Michael L.; Jandura, Louise

1990-01-01

Segmented reflectors have been proposed for space based applications such as optical communication and large diameter telescopes. An actuation system for mirrors in a space based segmented mirror array was developed as part of NASA's Precision Segmented Reflector program. The actuation system, called the Articulated Panel Module (APM), provides 3 degrees of freedom mirror articulation, gives isolation from structural motion, and simplifies space assembly of the mirrors to the reflector backup truss. A breadboard of the APM was built and is described.

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.

[Why does our heart fibrillate?- or what goats can teach us].

PubMed

Eckstein, Jens

2014-07-23

Our present knowledge about cardiac electrophysiology is based on numerous experiments and discoveries going back to the Greek antique and ancient Egypt. Exploration of cardiac anatomy was followed by the description of circulation and cardiac physiology in the 17th century. In the early 20th century cardiac electrophysiology became the new field of interest and was studied with the help of numerous animal experiments (squid, rays, dogs, goats, mice and other species). We ought to be grateful for the knowledge and possibilities in modern medicine that were made possible by the great number of researchers, patients and animals that contributed to this.

Orbital radar evidence for lunar subsurface layering in Maria Serenitatis and Crisium

NASA Technical Reports Server (NTRS)

Peeples, W. J.; Sill, W. R.; May, T. W.; Ward, S. H.; Phillips, R. J.; Jordan, R. L.; Abbott, E. A.; Killpack, T. J.

1978-01-01

Data from the lunar-orbiting Apollo 17 radar sounding experiment (60-m wavelength) have been examined in both digital and holographic formats, and it is concluded that there are two subsurface radar reflectors below the surface in Mare Serenitatis and one reflector below the surface in Mare Crisium. The mean apparent depths of the reflectors below the surface of the former Mare are 0.9 and 1.6 km, while the reflector below the surface of the latter Mare has a mean depth of 1.4 km. These reflectors represent basin-wide subsurface interfaces. Techniques for reducing surface backscatter (clutter) in the data are described, and reasons for thinking that the distinct alignments in radar returns represent subsurface reflecting horizons are explained

Strategy for reflector pattern calculation - Let the computer do the work

NASA Technical Reports Server (NTRS)

Lam, P. T.; Lee, S.-W.; Hung, C. C.; Acosta, R.

1986-01-01

Using high frequency approximations, the secondary pattern of a reflector antenna can be calculated by numerically evaluating a radiation integral I(u,v). In recent years, tremendous effort has been expended to reducing I(u,v) to Fourier integrals. These reduction schemes are invariably reflector geometry dependent. Hence, different analyses/computer software development must be carried out for different reflector shapes/boundaries. It is pointed out, that, as the computer power improves, these reduction schemes are no longer necessary. Comparable accuracy and computation time can be achieved by evaluating I(u,v) by a brute force FFT described in this note. Furthermore, there is virtually no restriction on the reflector geometry by using the brute force FFT.

Acoustic suspension system

NASA Technical Reports Server (NTRS)

Lee, M. C.; Wang, T. G. (Inventor)

1983-01-01

An acoustic levitation system is described, with single acoustic source and a small reflector to stably levitate a small object while the object is processed as by coating or heating it. The system includes a concave acoustic source which has locations on opposite sides of its axis that vibrate towards and away from a focal point to generate a converging acoustic field. A small reflector is located near the focal point, and preferably slightly beyond it, to create an intense acoustic field that stably supports a small object near the reflector. The reflector is located about one-half wavelength from the focal point and is concavely curved to a radius of curvature (L) of about one-half the wavelength, to stably support an object one-quarter wavelength (N) from the reflector.

Preliminary design considerations for 10 to 40 meter-diameter precision truss reflectors

NASA Technical Reports Server (NTRS)

Mikulas, Martin M., Jr.; Collins, Timothy J.; Hedgepeth, John M.

1990-01-01

A simplified preliminary design capability for erectable precision segmented reflectors is presented. This design capability permits a rapid assessment of a wide range of reflector parameters as well as new structural concepts and materials. The preliminary design approach was applied to a range of precision reflectors from 10 meters to 100 meters in diameter while considering standard design drivers. The design drivers considered were: weight, fundamental frequency, launch packaging volume, part count, and on-orbit assembly time. For the range of parameters considered, on-orbit assembly time was identified as the major design driver. A family of modular panels is introduced which can significantly reduce the number of reflector parts and the on-orbit assembly time.

Strategy for reflector pattern calculation: Let the computer do the work

NASA Technical Reports Server (NTRS)

Lam, P. T.; Lee, S. W.; Hung, C. C.; Acousta, R.

1985-01-01

Using high frequency approximations, the secondary pattern of a reflector antenna can be calculated by numerically evaluating a radiation integral I(u,v). In recent years, tremendous effort has been expended to reducing I(u,v) to Fourier integrals. These reduction schemes are invariably reflector geometry dependent. Hence, different analyses/computer software development must be carried out for different reflector shapes/boundaries. it is pointed out, that, as the computer power improves, these reduction schemes are no longer necessary. Comparable accuracy and computation time can be achieved by evaluating I(u,v) by a brute force FFT described in this note. Furthermore, there is virtually no restriction on the reflector geometry by using the brute force FFT.

Adaptive Nulling in Hybrid Reflector Antennas

DTIC Science & Technology

1992-09-01

correction of reflector distortion and vernier beamsteering, MEEE Trans. Antennas Propagat, 36:1351-1358. 4 Cherrette , A.R., et al (1989) Compensation of...Propagat, 36:1351-1358. 4. Cherrette , A.R., et al (1989) Compensation of reflector antenna surface distortion using an array feed,IEEE Trans. Antennas

A comparison of reflector antenna designs for wide-angle scanning

NASA Technical Reports Server (NTRS)

Zimmerman, M.; Lee, S. W.; Houshmand, B.; Rahmatsamii, Y.; Acosta, R. J.

1989-01-01

Conventional reflector antennas are typically designed for up to + or - 20 beamwidths scan. An attempt was made to stretch this scan range to some + or - 300 beamwidths. Six single and dual reflector antennas were compared. It is found that a symmetrical parabolic reflector with f/D = 2 and a single circular waveguide feed has the minimum scan loss (only 0.6 dB at Theta sub 0 = 8 deg, or a 114 beamwidths scan). The scan is achieved by tilting the parabolic reflector by an angle equal to the half-scan angle. The f/D may be shortened if a cluster 7 to 19 elements instead of one element is used for the feed. The cluster excitation is adjusted for each new beam scan direction to compensate for the imperfect field distribution over the reflector aperture. The antenna can be folded into a Cassegrain configuration except that, due to spillover and blockage considerations, the amount of folding achievable is small.

Active feed array compensation for reflector antenna surface distortions. Ph.D. Thesis - Akron Univ., Ohio

NASA Technical Reports Server (NTRS)

Acosta, Roberto J.

1988-01-01

The feasibility of electromagnetic compensation for reflector antenna surface distortions is investigated. The performance characteristics of large satellite communication reflector antenna systems degrade as the reflector surface distorts, mainly due to thermal effects from solar radiation. The technique developed can be used to maintain the antenna boresight directivity and sidelobe level independent of thermal effects on the reflector surface. With the advent of monolithic microwave integrated circuits (MMIC), a greater flexibility in array fed reflector antenna systems can be achieved. MMIC arrays provide independent control of amplitude and phase for each of the many radiating elements in the feed array. By assuming a known surface distortion profile, a simulation study is carried out to examine the antenna performance as a function of feed array size and number of elements. Results indicate that the compensation technique can effectively control boresight directivity and sidelobe level under peak surface distortion in the order of tenth of a wavelength.

Numerical form-finding method for large mesh reflectors with elastic rim trusses

NASA Astrophysics Data System (ADS)

Yang, Dongwu; Zhang, Yiqun; Li, Peng; Du, Jingli

2018-06-01

Traditional methods for designing a mesh reflector usually treat the rim truss as rigid. Due to large aperture, light weight and high accuracy requirements on spaceborne reflectors, the rim truss deformation is indeed not negligible. In order to design a cable net with asymmetric boundaries for the front and rear nets, a cable-net form-finding method is firstly introduced. Then, the form-finding method is embedded into an iterative approach for designing a mesh reflector considering the elasticity of the supporting rim truss. By iterations on form-findings of the cable-net based on the updated boundary conditions due to the rim truss deformation, a mesh reflector with a fairly uniform tension distribution in its equilibrium state could be finally designed. Applications on offset mesh reflectors with both circular and elliptical rim trusses are illustrated. The numerical results show the effectiveness of the proposed approach and that a circular rim truss is more stable than an elliptical rim truss.

InGaAs multiple quantum well modulating retro-reflector for free-space optical communications

NASA Astrophysics Data System (ADS)

Rabinovich, William S.; Gilbreath, G. Charmaine; Goetz, Peter G.; Mahon, Rita; Katzer, D. Scott; Ikossi-Anastasiou, Kiki; Binari, Steven C.; Meehan, Timothy J.; Stell, Mena F.; Sokolsky, Ilene; Vasquez, John A.; Vilcheck, Michael J.

2002-01-01

Modulating retro-reflectors provide means for free space optical communication without the need for a laser, telescope or pointer tracker on one end of the link. These systems work by coupling a retro-reflector with an electro- optic shutter. The modulating retro-reflector is then interrogated by a cw laser beam from a conventional optical communications system and returns a modulated signal beam to the interrogator. Over the last few years the Naval Research Laboratory has developed modulating retro-reflector based on corner cubes and large area Transmissive InGaAs multiple quantum well modulators. These devices can allow optical links at speeds up to about 10 Mbps. We will discuss the critical performance characteristics of such systems including modulating rate, power consumption, optical contrast ratio and operating wavelength. In addition a new modulating retro-reflector architecture based upon cat s eye retroreflectors will be discussed. This architecture has the possibility for data rates of hundreds of megabits per second at power consumptions below 100 mW.

Towards a sub 15-dBA optical micromachined microphone

PubMed Central

Kim, Donghwan; Hall, Neal A.

2014-01-01

Micromachined microphones with grating-based optical-interferometric readout have been demonstrated previously. These microphones are similar in construction to bottom-inlet capacitive microelectromechanical-system (MEMS) microphones, with the exception that optoelectronic emitters and detectors are placed inside the microphone's front or back cavity. A potential advantage of optical microphones in designing for low noise level is the use of highly-perforated microphone backplates to enable low-damping and low thermal-mechanical noise levels. This work presents an experimental study of a microphone diaphragm and backplate designed for optical readout and low thermal-mechanical noise. The backplate is 1 mm × 1 mm and is fabricated in a 2-μm-thick epitaxial silicon layer of a silicon-on-insulator wafer and contains a diffraction grating with 4-μm pitch etched at the center. The presented system has a measured thermal-mechanical noise level equal to 22.6 dBA. Through measurement of the electrostatic frequency response and measured noise spectra, a device model for the microphone system is verified. The model is in-turn used to identify design paths towards MEMS microphones with sub 15-dBA noise floors. PMID:24815250

Convergence studies of deterministic methods for LWR explicit reflector methodology

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

Canepa, S.; Hursin, M.; Ferroukhi, H.

2013-07-01

The standard approach in modem 3-D core simulators, employed either for steady-state or transient simulations, is to use Albedo coefficients or explicit reflectors at the core axial and radial boundaries. In the latter approach, few-group homogenized nuclear data are a priori produced with lattice transport codes using 2-D reflector models. Recently, the explicit reflector methodology of the deterministic CASMO-4/SIMULATE-3 code system was identified to potentially constitute one of the main sources of errors for core analyses of the Swiss operating LWRs, which are all belonging to GII design. Considering that some of the new GIII designs will rely on verymore » different reflector concepts, a review and assessment of the reflector methodology for various LWR designs appeared as relevant. Therefore, the purpose of this paper is to first recall the concepts of the explicit reflector modelling approach as employed by CASMO/SIMULATE. Then, for selected reflector configurations representative of both GII and GUI designs, a benchmarking of the few-group nuclear data produced with the deterministic lattice code CASMO-4 and its successor CASMO-5, is conducted. On this basis, a convergence study with regards to geometrical requirements when using deterministic methods with 2-D homogenous models is conducted and the effect on the downstream 3-D core analysis accuracy is evaluated for a typical GII deflector design in order to assess the results against available plant measurements. (authors)« less

KSC00pp0823

NASA Image and Video Library

2000-06-30

At dawn on Launch Pad 36A, Cape Canaveral Air Force Station, an Atlas IIA/Centaur rocket is fueled for launch of NASA’s Tracking and Data Relay Satellite (TDRS-H). One of three satellites (labeled H, I and J) being built by the Hughes Space and Communications Company, the latest TDRS uses an innovative springback antenna design. A pair of 15-foot-diameter, flexible mesh antenna reflectors fold up for launch, then spring back into their original cupped circular shape on orbit. The new satellites will augment the TDRS system’s existing Sand Ku-band frequencies by adding Ka-band capability. TDRS will serve as the sole means of continuous, high-data-rate communication with the Space Shuttle, with the International Space Station upon its completion, and with dozens of unmanned scientific satellites in low earth orbit

KSC-00pp0823

NASA Image and Video Library

2000-06-30

At dawn on Launch Pad 36A, Cape Canaveral Air Force Station, an Atlas IIA/Centaur rocket is fueled for launch of NASA’s Tracking and Data Relay Satellite (TDRS-H). One of three satellites (labeled H, I and J) being built by the Hughes Space and Communications Company, the latest TDRS uses an innovative springback antenna design. A pair of 15-foot-diameter, flexible mesh antenna reflectors fold up for launch, then spring back into their original cupped circular shape on orbit. The new satellites will augment the TDRS system’s existing Sand Ku-band frequencies by adding Ka-band capability. TDRS will serve as the sole means of continuous, high-data-rate communication with the Space Shuttle, with the International Space Station upon its completion, and with dozens of unmanned scientific satellites in low earth orbit

KSC00pp0819

NASA Image and Video Library

2000-06-30

NASA’s Tracking and Data Relay Satellite (TDRS-H) sits poised on Launch Pad 36A, Cape Canaveral Air Force Station, before its scheduled launch aboard an Atlas IIA/Centaur rocket. One of three satellites (labeled H, I and J) being built by the Hughes Space and Communications Company, the latest TDRS uses an innovative springback antenna design. A pair of 15-foot-diameter, flexible mesh antenna reflectors fold up for launch, then spring back into their original cupped circular shape on orbit. The new satellites will augment the TDRS system’s existing Sand Ku-band frequencies by adding Ka-band capability. TDRS will serve as the sole means of continuous, high-data-rate communication with the space shuttle, with the International Space Station upon its completion, and with dozens of unmanned scientific satellites in low earth orbit

KSC-00pp0819

NASA Image and Video Library

2000-06-30

NASA’s Tracking and Data Relay Satellite (TDRS-H) sits poised on Launch Pad 36A, Cape Canaveral Air Force Station, before its scheduled launch aboard an Atlas IIA/Centaur rocket. One of three satellites (labeled H, I and J) being built by the Hughes Space and Communications Company, the latest TDRS uses an innovative springback antenna design. A pair of 15-foot-diameter, flexible mesh antenna reflectors fold up for launch, then spring back into their original cupped circular shape on orbit. The new satellites will augment the TDRS system’s existing Sand Ku-band frequencies by adding Ka-band capability. TDRS will serve as the sole means of continuous, high-data-rate communication with the space shuttle, with the International Space Station upon its completion, and with dozens of unmanned scientific satellites in low earth orbit

Iris as a reflector for differential absorption low-coherence interferometry to measure glucose level in the anterior chamber

PubMed Central

Zhou, Yong; Zeng, Nan; Ji, Yanhong; Li, Yao; Dai, Xiangsong; Li, Peng; Duan, Lian; Ma, Hui; He, Yonghong

2011-01-01

We present a method of glucose concentration detection in the anterior chamber with a differential absorption optical low-coherent interferometry (LCI) technique. Back-reflected light from the iris, passing through the anterior chamber twice, was selectively obtained with the LCI technique. Two light sources, one centered within (1625 nm) and the other centered outside (1310 nm) of a glucose absorption band were used for differential absorption measurement. In the eye model and pig eye experiments, we obtained a resolution glucose level of 26.8 mg/dL and 69.6 mg/dL, respectively. This method has a potential application for noninvasive detection of glucose concentration in aqueous humor, which is related to the glucose concentration in blood. PMID:21280906

Anisotropy of the permittivity field inferred from aspect-sensitive radar echoes

NASA Technical Reports Server (NTRS)

Waterman, A. T.

1984-01-01

An attempt is made to draw some quantitative conclusions regarding the anisotropy of the clear-air back-scattering mechanism based on the measured variation of echo power with zenith angle. The measurements were made by the SOUSY group of the Max Planck Institute for Aeronomy at Lindau, FRG. They installed their 47-MHz transmitter and antenna feed in the 300-meter diameter reflector at Arecibo. The resulting 1.7-degree beam was stepped successively through seven 1.7-degree intervals from 1.7 to 11.7 degrees in zenith angle, obtaining about four minutes of data at each setting. This procedure was carried out in an eastward pointing azimuth and in a northward pointing azimuth, the entire set of measurements consuming an hour and twenty minutes. Range resolution was 150 meters.

LDR structural technology activities at JPL

NASA Technical Reports Server (NTRS)

Wada, Ben

1988-01-01

The status of the Large Deployable Reflector (LDR) technology requirements and the availability of that technology in the next few years are summarized. The research efforts at JPL related to these technology needs are also discussed. LDR requires that a large and relatively stiff truss-type backup structure have a surface accurate to 100 microns in space (initial position with thermal distortions) and the dynamic characteristics predictable and/or measurable by on-orbit system identification for micron level motion. This motion may result from the excitation of the lower modes or from wave-type motions. It is also assumed that the LDR structure can be ground tested to validate its ability to meet mission requirements. No program manager will commit a structural design based solely on analysis, unless the analysis is backed by a validation test program.

Graphene as a transparent electrode for amorphous silicon-based solar cells

NASA Astrophysics Data System (ADS)

Vaianella, F.; Rosolen, G.; Maes, B.

2015-06-01

The properties of graphene in terms of transparency and conductivity make it an ideal candidate to replace indium tin oxide (ITO) in a transparent conducting electrode. However, graphene is not always as good as ITO for some applications, due to a non-negligible absorption. For amorphous silicon photovoltaics, we have identified a useful case with a graphene-silica front electrode that improves upon ITO. For both electrode technologies, we simulate the weighted absorption in the active layer of planar amorphous silicon-based solar cells with a silver back-reflector. The graphene device shows a significantly increased absorbance compared to ITO-based cells for a large range of silicon thicknesses (34.4% versus 30.9% for a 300 nm thick silicon layer), and this result persists over a wide range of incidence angles.

Open cycle gas core nuclear rockets

NASA Technical Reports Server (NTRS)

Ragsdale, Robert

1991-01-01

The open cycle gas core engine is a nuclear propulsion device. Propulsion is provided by hot hydrogen which is heated directly by thermal radiation from the nuclear fuel. Critical mass is sustained in the uranium plasma in the center. It has typically 30 to 50 kg of fuel. It is a thermal reactor in the sense that fissions are caused by absorption of thermal neutrons. The fast neutrons go out to an external moderator/reflector material and, by collision, slow down to thermal energy levels, and then come back in and cause fission. The hydrogen propellant is stored in a tank. The advantage of the concept is very high specific impulse because you can take the plasma to any temperature desired by increasing the fission level by withdrawing or turning control rods or control drums.

Steep and flat bandpass filter using linearly chirped and apodized fiber Bragg grating

NASA Astrophysics Data System (ADS)

Wu, Xunqi; Jacquet, Jo"l.; Duan, Guanghua

2010-02-01

The development of new optical systems requires the design of novel components that fulfill the market constraints. In particular, low loss, high optical rejection and low cost narrowband filters can play an important role for the introduction of the Wavelength Division Multiplexing (WDM) technology in the local network. So, a novel fiber filter is proposed in this article, with a special combined apodized Linearly Chirped Fiber Bragg Grating (LCFBG) which presents the preferable flat-top and steep-edge characteristics. In the design, we use a continuum cavity condition which is obtained when the effective round-trip phase of oscillated wavelength band is kept identical over the whole Bragg wavelength range. And the transmission spectra are calculated by the reconstruction of the matrixes with the continuum oscillation condition. Therefore, our works show that the ideal square shaped filter is obtained with a lower chirp value relatively together with symmetric reflectivity on both mirrors. The coupling coefficient of the FBG is adjusted to get the same reflectivity values and then to get a transmission filter close to unity. We have then introduced an apodization function of the filter to get a flatter transfer function. Various apodizations schemes have been tested. In this paper, we design and analyze a type of continuum fiber filter with the cavity formed between mirror and apodized LCFBG as reflectors. We calculate firstly the reflectivity, the transmissivity and the group time delay of LCFBG modeled by a simple and practical Transfer Matrix Method (TMM), and then the cavity is reconstructed by TMM, the length of the oscillated cavity is calculated by the continuum oscillation condition, so the output of transmission from the side of LCFBG is continuous in the corresponded reflected bandwidth of LCFBG. We obtain the results and discuss some characteristics of this type of continuum fiber filter.

47 CFR 25.201 - Definitions.

Code of Federal Regulations, 2013 CFR

2013-10-01

... reflector. When non-reflector or non-circular aperture antennas are employed, an equivalent diameter can be.... Earth Station on Vessel (“ESV”). An ESV is an earth station onboard a craft designed for traveling on... Internet or World Wide Web on-line filing forms. Equivalent diameter. When circular aperture reflector...

Feasibility evaluation of a neutron grating interferometer with an analyzer grating based on a structured scintillator.

PubMed

Kim, Youngju; Kim, Jongyul; Kim, Daeseung; Hussey, Daniel S; Lee, Seung Wook

2018-03-01

We introduce an analyzer grating based on a structured scintillator fabricated by a gadolinium oxysulfide powder filling method for a symmetric Talbot-Lau neutron grating interferometer. This is an alternative way to analyze the Talbot self-image of a grating interferometer without using an absorption grating to block neutrons. Since the structured scintillator analyzer grating itself generates the signal for neutron detection, we do not need an additional scintillator screen as an absorption analyzer grating. We have developed and tested an analyzer grating based on a structured scintillator in our symmetric Talbot-Lau neutron grating interferometer to produce high fidelity absorption, differential phase, and dark-field contrast images. The acquired images have been compared to results of a grating interferometer utilizing a typical absorption analyzer grating with two commercial scintillation screens. The analyzer grating based on the structured scintillator enhances interference fringe visibility and shows a great potential for economical fabrication, compact system design, and so on. We report the performance of the analyzer grating based on a structured scintillator and evaluate its feasibility for the neutron grating interferometer.

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

Feasibility evaluation of a neutron grating interferometer with an analyzer grating based on a structured scintillator

NASA Astrophysics Data System (ADS)

Kim, Youngju; Kim, Jongyul; Kim, Daeseung; Hussey, Daniel. S.; Lee, Seung Wook

2018-03-01

We introduce an analyzer grating based on a structured scintillator fabricated by a gadolinium oxysulfide powder filling method for a symmetric Talbot-Lau neutron grating interferometer. This is an alternative way to analyze the Talbot self-image of a grating interferometer without using an absorption grating to block neutrons. Since the structured scintillator analyzer grating itself generates the signal for neutron detection, we do not need an additional scintillator screen as an absorption analyzer grating. We have developed and tested an analyzer grating based on a structured scintillator in our symmetric Talbot-Lau neutron grating interferometer to produce high fidelity absorption, differential phase, and dark-field contrast images. The acquired images have been compared to results of a grating interferometer utilizing a typical absorption analyzer grating with two commercial scintillation screens. The analyzer grating based on the structured scintillator enhances interference fringe visibility and shows a great potential for economical fabrication, compact system design, and so on. We report the performance of the analyzer grating based on a structured scintillator and evaluate its feasibility for the neutron grating interferometer.

16 CFR 1512.16 - Requirements for reflectors.

Code of Federal Regulations, 2011 CFR

2011-01-01

..., preferred assembly method that shall insure that the reflector meets the optical requirements of this...(m)(2). The reflectors and/or mounts shall incorporate a distinct, preferred assembly method that... on the rim. (2) If the retroreflective material is applied to the rim in the form of a self-adhesive...

49 CFR Appendix B to Part 224 - Reflectorization Implementation Compliance Report

Code of Federal Regulations, 2012 CFR

2012-10-01

... 49 Transportation 4 2012-10-01 2012-10-01 false Reflectorization Implementation Compliance Report B Appendix B to Part 224 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL RAILROAD ADMINISTRATION, DEPARTMENT OF TRANSPORTATION REFLECTORIZATION OF RAIL FREIGHT ROLLING STOCK Pt. 224, App. B Appendix B to Part 224...

Concentrating Solar Power Projects - Puerto Errado 2 Thermosolar Power

Science.gov Websites

linear Fresnel reflector system. Status Date: April 26, 2013 Project Overview Project Name: Puerto Errado . (Novatec Biosol AG) (15%) Technology: Linear Fresnel reflector Turbine Capacity: Net: 30.0 MW Gross: 30.0 ? Background Technology: Linear Fresnel reflector Status: Operational Country: Spain City: Calasparra Region