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1

VCSEL polarization control for chip-scale atomic clocks.  

SciTech Connect

Sandia National Laboratories and Mytek, LLC have collaborated to develop a monolithically-integrated vertical-cavity surface-emitting laser (VCSEL) assembly with controllable polarization states suitable for use in chip-scale atomic clocks. During the course of this work, a robust technique to provide polarization control was modeled and demonstrated. The technique uses deeply-etched surface gratings oriented at several different rotational angles to provide VCSEL polarization stability. A rigorous coupled-wave analysis (RCWA) model was used to optimize the design for high polarization selectivity and fabrication tolerance. The new approach to VCSEL polarization control may be useful in a number of defense and commercial applications, including chip-scale atomic clocks and other low-power atomic sensors.

Geib, Kent Martin; Peake, Gregory Merwin; Wendt, Joel Robert; Serkland, Darwin Keith; Keeler, Gordon Arthur

2007-01-01

2

2 VCSELS Polarization controllers Semiconductor  

E-print Network

laboratory flame, UW gas turbine engine components, Ohio pulse detonation engine, Wright- Patterson Air Force Base, Ohio rocket plume, Orbitec shock tube, UW #12;Fiber-optic access: Pulse detonation engine example 4 Pulse detonation engine at Wright-Patterson Air Force Base, OH Custom laser light distributed

Suresh, Krishnan

3

Temperature dependent polarization switch of 850-nm VCSELs with different apertures  

NASA Astrophysics Data System (ADS)

Temperature greatly affects the polarization properties of VCSELs. In this paper, these polarization properties of top-emitting 850-nm VCSELs are simulated by numerical calculation and then they are verified by experimental measurement. For a 4-?m aperture VCSEL, polarization switch current reduces from 1.4 mA to 0.4 mA as the temperature increases from 273 K to 323 K, which is caused by the change of the reflectivity of DBR and differential gain for LP01 transverse-mode. For VCSELs with 8-?m aperture, the first polarization switch current reduces from 2.1 mA to 0.8 mA as temperature increases from 273 K to 313 K. However, the second polarization switch current increases from 3.8 mA to 6.3 mA for the same increase in temperature because of the competition and polarization selection among several higher-order transverse modes. When the device aperture is further increased to 12 ?m or 16 ?m, there are several high-order transverse modes emitting even at small injection current, resulting in a serious competition and selection among themselves. This is why the polarization characteristics of VCSELs with 12 ?m or larger aperture are irregular and different from those of smaller aperture devices. Our research results provide useful guidelines for the application of VCSELs operating at different ambient temperatures.

Wang, Qiang; Guan, Baolu; Liu, Ke; Liu, Xin; Jiang, Xiaowei; Ma, Yunhua; Arafin, Shamsul; Shen, Guangdi

2014-11-01

4

1.55-?m VCSEL with polarization-independent HCG mirror on SOI.  

PubMed

We designed and fabricated a vertical-cavity surface-emitting laser (VCSEL) incorporating a polarization-independent high-index-contrast subwavelength grating (HCG) mirror on silicon-on-insulator (SOI) for a novel polarization-bistable device on a silicon substrate. The VCSEL consists of the HCG mirror, an active layer with InGaAsP quantum wells having optical gain around 1.55 ?m, and an Al0.9Ga0.1As/Al0.16Ga0.84As DBR. We used direct wafer bonding for the bonding between the active layer and the AlGaAs DBR, and benzocyclobutene (BCB) bonding for the bonding between the active layer and the polarization-independent HCG mirror. The reflectivity of the HCG embedded with BCB was measured, resulting in a 200-nm-high reflectivity band with reflectivity higher than 99% and a small polarization dependence of ± 1%. We achieved lasing of the fabricated HCG-VCSEL at 1527 nm under an optical short pulse excitation with an average power of 50 mW (~0.2 mJ/cm2) at 240 K. PMID:24514380

Tsunemi, Yoshihiro; Yokota, Nobuhide; Majima, Shota; Ikeda, Kazuhiro; Katayama, Takeo; Kawaguchi, Hitoshi

2013-11-18

5

Polarization investigation of a tunable high-speed short-wavelength bulk-micromachined MEMS-VCSEL  

NASA Astrophysics Data System (ADS)

We report the investigation of the state of polarization (SOP) of a tunable vertical-cavity surface-emitting laser (VCSEL) operating near 850 nm with a mode-hop free single-mode tuning range of about 12 nm and an amplitude modulation bandwidth of about 5 GHz. In addition, the effect of a sub-wavelength grating on the device and its influence on the polarization stability and polarization switching has been investigated. The VCSEL with an integrated sub-wavelength grating shows a stable SOP with a polarization mode suppression ratio (PMSR) more than 35 dB during the tuning.

Davani, H. A.; Kögel, B.; Debernardi, P.; Grasse, C.; Gierl, C.; Zogal, K.; Haglund, Å.; Gustavsson, J.; Westbergh, P.; Gründl, T.; Komissinskiy, P.; Bitsch, T.; Alff, L.; Küppers, F.; Larsson, A.; Amann, M.-C.; Meissner, P.

2012-03-01

6

Transverse mode control in high-contrast grating VCSELs.  

PubMed

This paper presents an extensive numerical analysis of a high-contrast grating VCSEL emitting at 0.98 ?m. Using a three-dimensional, fully vectorial optical model, we investigate the influence of a non-uniform grating with a broad range of geometrical parameters on the modal behavior of the VCSEL. Properly designed and optimized, the high-contrast grating confines the fundamental mode selectively in all three dimensions and discriminates all higher order modes by expelling them from its central region. This mechanism makes single mode operation possible under a broad range of currents and could potentially enhance the single-mode output power of such devices. The high-contrast grating design proposed here is the only design for a VCSEL with three-dimensional, selective, optical confinement that requires relatively simple fabrication. PMID:25321296

G?bski, Marcin; Kuzior, Olga; Dems, Maciej; Wasiak, Micha?; Xie, Y Y; Xu, Z J; Wang, Qi Jie; Zhang, Dao Hua; Czyszanowski, Tomasz

2014-08-25

7

High-Contrast Grating VCSELs  

NASA Astrophysics Data System (ADS)

We review a recent invention of single-layer one-dimensional high-index-contrast subwavelength grating (HCG) and its incorporation into a VCSEL structure. The HCG is approximately 50 times thinner than a conventional distributed Bragg reflector (DBR), but offers higher reflectivity with a much broader spectral width. It provides lithographically defined control of polarization, transverse mode and emission wavelength. Using this ultrathin reflector, the tunable mirror in a micro-mechanical HCG-VCSELs are fabricated with a 104 times volume reduction and more than two orders of magnitude improved tuning speed.

Chang-Hasnain, Connie J.

8

Wavelength control in fabrication of wafer fused VCSELs emitting in the 1310 nm waveband  

NASA Astrophysics Data System (ADS)

Emission wavelength setting of 1310nm-waveband VCSELs designed for coarse wavelength division multiplexing (CWDM) 4x10 Gbps fiber-optics transmission can be controlled thanks to the wafer fusion fabrication approach. This approach allows performing the cavity adjustment before bonding the distributed Bragg reflectors (DBRs) to the active cavity of the device. Cavity adjustment was performed by digital etching with nanometer precision and proves to be very effective in compensating for epitaxial growth thickness off-set relative to nominal design and thickness nonuniformity across the wafer. With this fabrication approach we reach on fused VCSEL wafers more than 90% yield of devices that fit the CWDM wavelength slots.

Sirbu, A.; Iakovlev, V.; Mereuta, A.; Caliman, A.; Suruceanu, G.; Mickovic, Z.; Kapon, Eli

2014-05-01

9

Long-haul dual-channel bidirectional chaos communication based on polarization-resolved chaos synchronization between twin 1550 nM VCSELs subject to variable-polarization optical injection  

NASA Astrophysics Data System (ADS)

Based on the polarization-resolved chaos synchronization between twin 1550 nm vertical-cavity surface-emitting lasers (VCSELs), a novel long-haul dual-channel bidirectional chaos communication system is proposed. In this system, a time delay signature (TDS)-suppressed chaotic signal, generated by a driving VCSEL (D-VCSEL) under double external cavity feedbacks (DECFs), simultaneously injects into twin VCSELs by variable-polarization optical injection (VPOI) to synchronize them and enhance the chaos output bandwidth of the two VCSELs. The simulated results show that, under proper injection parameters, high-quality polarization-resolved chaos synchronization between the twin VCSELs can be achieved; meanwhile the bandwidths of chaotic signals output from the twin VCSELs have been enhanced in comparison with that of the driven chaotic signal. Based on the high-quality polarization-resolved chaos synchronization, after adopting polarization-division-multiplexing (PDM) and chaos masking (CM) techniques, four 10 Gb/s messages hidden respectively in four chaotic carriers can be decrypted effectively after propagating 15 km in single-mode fiber (SMF) links. After adopting dispersion-shifted fibers (DSFs) as fiber links, the dual-channel bidirectional chaos communication distance can be extended to 140 km.

Wang, Ling; Wu, Zheng-Mao; Wu, Jia-Gui; Xia, Guang-Qiong

2015-01-01

10

Control of emitted light polarization in a 1310 nm dilute nitride spin-vertical cavity surface emitting laser subject to circularly polarized optical injection  

NASA Astrophysics Data System (ADS)

We experimentally demonstrate the control of the light polarization emitted by a 1310 nm dilute nitride spin-Vertical Cavity Surface Emitting Laser (VCSEL) at room temperature. This is achieved by means of a combination of polarized optical pumping and polarized optical injection. Without external injection, the polarization of the optical pump controls that of the spin-VCSEL. However, the addition of the externally injected signal polarized with either left- (LCP) or right-circular polarization (RCP) is able to control the polarization of the spin-VCSEL switching it at will to left- or right-circular polarization. A numerical model has been developed showing a very high degree of agreement with the experimental findings.

Alharthi, S. S.; Hurtado, A.; Al Seyab, R. K.; Korpijarvi, V.-M.; Guina, M.; Henning, I. D.; Adams, M. J.

2014-11-01

11

VCSELs with nematic and cholesteric liquid crystal overlays  

NASA Astrophysics Data System (ADS)

We study theoretically the spectral and polarization threshold characteristics of Vertical-Cavity Surface-Emitting Lasers with nematic and cholesteric liquid crystal overlay: LC-VCSELs. In the first case, we demonstrate the possibility of selecting between two orthogonal directions of linear polarization (LP) of the fundamental mode (x or y LP) by choosing appropriate NLC length and to achieve strong polarization discrimination: threshold gain difference as large as several times the threshold gain. We also demonstrate an active control of light polarization by electro-optically tuning the LC director and show that either polarization switching between x and y LP modes or continuous change of the LP direction is possible. For cholesteric LC-VCSEL we show that it becomes a coupled system with different spectral, threshold and polarization characteristics than the ones of the stand-alone VCSEL. Due to the existence of a band gap for circularly polarized light in the liquid crystal, lasing occurs in almost circularly polarized modes at the LC side.

Panajotov, K.; Dems, M.; Belmonte, C.; Thienpont, H.; Xie, Y.; Beeckman, J.; Neyts, K.

2013-03-01

12

An ultra-stable VCSEL light source  

NASA Astrophysics Data System (ADS)

We demonstrate a miniature VCSEL-based light source with optical power output that varies by less than 50 ppm/°C over a 40°C temperature range. This represents a ten-fold improvement in control accuracy over what is achieved by the best available light sources with semiconductor emitters. A single-mode, polarization-locked, 670-nm VCSEL (Vixar, Inc.) is used to demonstrate the feasibility of the light source. The critical component of our control system is a beamsplitter formed by a wedge of fused silica with a weakly-polarizing, interference coating. A wedge shape eliminates fluctuations in optical power caused by interference fringes and the normal incidence of the exit beam removes polarization dependency as well as the need for an anti-reflective coating. The beamsplitter is in a closed control loop that enables compensation for control errors caused by changes in photodetector responsivity, emission wavelength, and beam divergence with temperature. We also show that careful attention to optical and mechanical alignment is essential to realize the performance enhancements reported herein. Angular tolerances of +/-0.05°are required and most coating houses lack the metrology capabilities to characterize the TCB coating with such high tolerances. A discrete-wavelength reflectometer was developed for this purpose.

Downing, John; Babi?, Dubravko; Hibbs-Brenner, Mary

2013-03-01

13

VCSELs: their 30 years history and new challenges  

NASA Astrophysics Data System (ADS)

We could have the 30-year anniversary since a VCSEL was invented by Kenichi Iga. We have seen various applications including datacom, sensors, optical interconnects, spectroscopy, optical storages, printers, laser displays, laser radar, atomic clock, optical signal processing and so on. A lot of unique features have been shown, low power consumption, a wafer level testing and so on. In this paper, the brief history and our recent research activities on VCSEL photonics will be reviewed. We present the wavelength engineering of VCSEL arrays for use in high speed short-reach systems, which includes the wavelength integration and wavelength control. The joint research project on ultra-parallel optical links based on VCSEL technologies will be introduced for high speed LANs of 100Gbps or higher. The small footprint of VCSELs allows us to form a densely packed VCSEL array both in space and in wavelength. The wavelength engineering of VCSELs may open up ultra-high capacity networking. Highly controlled multi-wavelength VCSEL array and novel multi-wavelength combiners are developed toward Tera-bit/s-class ultrahigh capacity parallel optical links. In addition, the MEMS-based VCSEL technology enables widely tunable operations. We demonstrated an "athermal VCSEL" with avoiding temperature controllers for uncooled WDM applications. In addition, new functions on VCSELs for optical signal processing are addressed. We present an optical nonlinear phase shifter based on a VCSEL saturable absorber. Also, highly reflective periodic mirrors commonly used in VCSELs enables us to manipulate the speed of light. This new scheme provides us ultra-compact intensity modulators, optical switches and so on for VCSEL-based photonic integration. Also, this paper explores plasmonic VCSELs.

Koyama, Fumio

2008-11-01

14

VCSEL Applications and Simulation  

NASA Technical Reports Server (NTRS)

This viewgraph presentation gives an overview of Vertical Cavity Surface Emitting Laser (VCSEL) simulation and its applications. Details are given on the optical interconnection in information technology of VCSEL, the formulation of the simulation, its numeric algorithm, and the computational results.

Cheung, Samson; Goorjian, Peter; Ning, Cun-Zheng; Li, Jian-Zhong

2000-01-01

15

Phase-Controlled Polarization Modulators  

NASA Technical Reports Server (NTRS)

We report technology development of millimeter/submillimeter polarization modulators that operate by introducing a a variable, controlled phase delay between two orthogonal polarization states. The variable-delay polarization modulator (VPM) operates via the introduction of a variable phase delay between two linear orthogonal polarization states, resulting in a variable mapping of a single linear polarization into a combination of that Stokes parameter and circular (Stokes V) polarization. Characterization of a prototype VPM is presented at 350 and 3000 microns. We also describe a modulator in which a variable phase delay is introduced between right- and left- circular polarization states. In this architecture, linear polarization is fully modulated. Each of these devices consists of a polarization diplexer parallel to and in front of a movable mirror. Modulation involves sub-wavelength translations of the mirror that change the magnitude of the phase delay.

Chuss, D. T.; Wollack, E. J.; Novak, G.; Moseley, S. H.; Pisano, G.; Krejny, M.; U-Yen, K.

2012-01-01

16

Quasi3D Light Confinement in Double Photonic Crystal Reflectors VCSELs for CMOS-Compatible Integration  

Microsoft Academic Search

A novel architecture of one-dimensional photonic crystal membrane (PCM) reflectors embodying a heterostructure is proposed as a robust design aimed at a 3-D efficient confine- ment of light in single-mode polarization-controlled 1.55- m vertical-cavity surface-emitting laser (VCSEL) microsources for heterogeneous integration on complementary metal-oxide-semi- conductor (CMOS). On the basis of a theoretical approach, the paper focuses on the deep interweaving

Corrado Sciancalepore; Badhise Ben Bakir; Xavier Letartre; Jean-Marc Fedeli; Nicolas Olivier; Damien Bordel; Christian Seassal; Pedro Rojo-Romeo; Philippe Regreny; Pierre Viktorovitch

2011-01-01

17

Interferometric Polarization Control  

NASA Technical Reports Server (NTRS)

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.

Chuss, David T. (Inventor); Wollack, Edward J. (Inventor); Moseley, Samuel H. (Inventor); Novak, Giles A. (Inventor)

2008-01-01

18

Interferometric polarization control  

NASA Technical Reports Server (NTRS)

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.

Wollack, Edward J. (Inventor); Moseley, Samuel H. (Inventor); Novak, Giles A. (Inventor); Chuss, David T. (Inventor)

2009-01-01

19

Endless smectic A * liquid crystal polarization controller  

Microsoft Academic Search

We propose and demonstrate an endless polarization controller that uses the electroclinic effect in the smectic A* phase with homeotropic orientation. This kind of device has a great importance in optical telecommunications for polarization mode dispersion compensation, polarization multiplexing or to compensate polarization dependent losses. Its main characteristics are both high speed and endless control. To realize a liquid crystal

Laurent Dupont; Thierry Sansoni; Jean-Louis de Bougrenet de la Tocnaye

2002-01-01

20

Magnetic control of ferroelectric polarization.  

PubMed

The magnetoelectric effect--the induction of magnetization by means of an electric field and induction of polarization by means of a magnetic field--was first presumed to exist by Pierre Curie, and subsequently attracted a great deal of interest in the 1960s and 1970s (refs 2-4). More recently, related studies on magnetic ferroelectrics have signalled a revival of interest in this phenomenon. From a technological point of view, the mutual control of electric and magnetic properties is an attractive possibility, but the number of candidate materials is limited and the effects are typically too small to be useful in applications. Here we report the discovery of ferroelectricity in a perovskite manganite, TbMnO3, where the effect of spin frustration causes sinusoidal antiferromagnetic ordering. The modulated magnetic structure is accompanied by a magnetoelastically induced lattice modulation, and with the emergence of a spontaneous polarization. In the magnetic ferroelectric TbMnO3, we found gigantic magnetoelectric and magnetocapacitance effects, which can be attributed to switching of the electric polarization induced by magnetic fields. Frustrated spin systems therefore provide a new area to search for magnetoelectric media. PMID:14603314

Kimura, T; Goto, T; Shintani, H; Ishizaka, K; Arima, T; Tokura, Y

2003-11-01

21

Dynamic Self-Locking of an OEO Containing a VCSEL  

NASA Technical Reports Server (NTRS)

A method of dynamic self-locking has been demonstrated to be effective as a means of stabilizing the wavelength of light emitted by a vertical-cavity surface-emitting laser (VCSEL) that is an active element in the frequency-control loop of an optoelectronic oscillator (OEO) designed to implement an atomic clock based on an electromagnetically- induced-transparency (EIT) resonance. This scheme can be considered an alternative to the one described in Optical Injection Locking of a VCSEL in an OEO (NPO-43454), NASA Tech Briefs, Vol. 33, No. 7 (July 2009), page 33. Both schemes are expected to enable the development of small, low-power, high-stability atomic clocks that would be suitable for use in applications involving precise navigation and/or communication. To recapitulate from the cited prior article: In one essential aspect of operation of an OEO of the type described above, a microwave modulation signal is coupled into the VCSEL. Heretofore, it has been well known that the wavelength of light emitted by a VCSEL depends on its temperature and drive current, necessitating thorough stabilization of these operational parameters. Recently, it was discovered that the wavelength also depends on the microwave power coupled into the VCSEL. This concludes the background information. From the perspective that led to the conception of the optical injection-locking scheme described in the cited prior article, the variation of the VCSEL wavelength with the microwave power circulating in the frequency-control loop is regarded as a disadvantage and optical injection locking is a solution of the problem of stabilizing the wavelength in the presence of uncontrolled fluctuations in the microwave power. The present scheme for dynamic self-locking emerges from a different perspective, in which the dependence of VCSEL wavelength on microwave power is regarded as an advantageous phenomenon that can be exploited as a means of controlling the wavelength. The figure schematically depicts an atomic-clock OEO of the type in question, wherein (1) the light from the VCSEL is used to excite an EIT resonance in selected atoms in a gas cell (e.g., 87Rb atoms in a low-pressure mixture of Ar and Ne) and (2) the power supplied to the VCSEL is modulated by a microwave signal that includes components at beat frequencies among the VCSEL wavelength and modulation sidebands. As the VCSEL wavelength changes, it moves closer to or farther from a nearby absorption spectral line, and the optical power transmitted through the cell (and thus the loop gain) changes accordingly. A change in the loop gain causes a change in the microwave power and, thus, in the VCSEL wavelength. It is possible to choose a set of design and operational parameters (most importantly, the electronic part of the loop gain) such that the OEO stabilizes itself in the sense that an increase in circulating microwave power causes the VCSEL wavelength to change in a direction that results in an increase in optical absorption and thus a decrease in circulating microwave power. Typically, such an appropriate choice of operational parameters involves setting the nominal VCSEL wavelength to a point on the shorter-wavelength wing of an absorption spectral line.

Strekalov, Dmitry; Matsko, Andrey; Yu, Nan; Savchenkov, Anatoliy; Maleki, Lute

2009-01-01

22

Microprocessor-Controlled Target Polarization Monitor  

Microsoft Academic Search

The proton spin polarization of an ethylene glycol target is measured using a nuclear magnetic resonance system controlled by a DEC LSI-ll microprocessor. Programs to accomplish data acquisition and polarization computation are down-loaded via CAMAC from the host DEC 11\\/45 computer. After initialization, the Polarization Monitor operates autonomously but presents data to the host computer on demand.

J. A. Buchanan; J. M. Clement

1979-01-01

23

Reflective terahertz tunable polarization controller  

NASA Astrophysics Data System (ADS)

This paper proposes an optical device which can continuously change the polarization state of terahertz (THz) waves. The device consists of metal gate, anti-reflection coatings, liquid crystal and mirror. By changing the refractive index of liquid crystal in the interface between the metal gate and the mirror, the phase difference between two beams with orthogonal polarization is varied and a continuous phase shift is achieved. The phase shift of the device is calculated by using the finite difference time domain (FDTD) method, and the transmittance and reflectance are calculated by using the rigorous coupled wave analysis (RCWA) method. The results reveal that the structure can realize continuously tunable phase shift for THz wave at 1 THz.

Niu, Chao; Chang, Sheng-jiang

2012-07-01

24

Fast beam steering with full polarization control using a galvanometric optical scanner and polarization controller  

E-print Network

Optical beam steering is a key element in many industrial and scientific applications like in material processing, information technologies, medical imaging and laser display. Even though galvanometer-based scanners offer flexibility, speed and accuracy at a relatively low cost, they still lack the necessary control over the polarization required for certain applications. We report on the development of a polarization steerable system assembled with a fiber polarization controller and a galvanometric scanner, both controlled by a digital signal processor board. The system implements control of the polarization decoupled from the pointing direction through a feed-forward control scheme. This enables to direct optical beams to a desired direction without affecting its initial polarization state. When considering the full working field of view, we are able to compensate polarization angle errors larger than 0.2 rad, in a temporal window of less than $\\sim 20$ ms. Given the unification of components to fully cont...

Jofre, M; Steinlechner, F; Oliverio, N; Torres, J P; Pruneri, V; Mitchell, M W; 10.1364/OE.20.012247

2012-01-01

25

VCSEL collimation using self-aligned integrated polymer microlenses  

NASA Astrophysics Data System (ADS)

We report on the design and fabrication of polymer microlenses fabricated on patterned SU-8 layers in view of integrating microlenses on VCSEL arrays for laser beam shaping. For a standard top-emitting VCSEL, the lens has to be fabricated on a thick intermediate layer (pedestal) whose optimal thickness can be modelled as a function of the initial and of the aimed optical properties of the VCSEL beam. In this work, pedestals are fabricated with SU-8, which is a negative-tone photoresist transparent at the lasing wavelength. Lens deposition is realized using a robotized silicon microcantilever spotter technique after a simple SU-8 photolithography step in order to define high aspect ratio cylindrical pedestals with wide range diameters [30-140?m]. The effect of pedestal diameter on the final contact angle and curvature radius has been investigated using non contact optical profilometry and scanning electron microscopy. We show that this technique leads to a complete delimitation of the polymer droplets and to a better control of the final lens size. Moreover, lens positioning is fully ensured by the self-alignment of the droplet with the pillar center and consequently with the VCSEL source, and allows for meeting the stringent requirements on alignments.

Levallois, Christophe; Bardinal, Véronique; Vergnenègre, Corinne; Leïchlé, Thierry; Camps, Thierry; Daran, Emmanuelle; Doucet, Jean-Baptiste

2008-04-01

26

1060nm 28-Gbps VCSEL developed at Furukawa  

NASA Astrophysics Data System (ADS)

This paper presents recent development results of our 28-Gbps VCSELs featured with double intra-cavity structure and a lasing wavelength of 1060 nm. The double intra-cavity realizes very low cavity loss due to undoped semiconductor bottom DBR and dielectric top DBR layers. Compressively strained InGaAs MQW provides high differential gain that contributes to low power consumption and high reliability. Based on our 10-Gbps VCSEL structure, we carefully optimized MQW, selective oxide structure, cavity length, and doping profile in order to achieve high speed operation while maintaining high reliability and other laser performances. The developed VCSELs exhibit modulation 3 dB-bandwidth exceeding 20 GHz and D-factor of 10 GHz/(mA)1/2. Typical threshold current and slope efficiency are 0.5 mA and 0.5 W/A, respectively. The paper also discusses static and dynamic characteristics of VCSELs with various oxide aperture sizes simultaneously fabricated on the same wafer. For a longer transmission distance and better optical coupling to a multimode fiber, optical lateral confinement is precisely controlled to reduce spectral width as well as far-field pattern. Clearly opened eye diagrams are obtained at a bit rate of 28 Gbps. Bit error rate tests are also performed and 28 Gbps error free transmission has been confirmed over 300 meters of multimode-fiber optimized for 1060 nm with a PRBS pattern length of 231-1.

Suzuki, Toshihito; Funabashi, Masaki; Shimizu, Hitoshi; Nagashima, Kazuya; Kamiya, Shinichi; Kasukawa, Akihiko

2014-02-01

27

Ultrafast Narrow Band Modulation of VCSELs  

NASA Technical Reports Server (NTRS)

Multimode beating was greatly enhanced by taking output from part (e.g., half) of the output facet. Simpler sources of microwaves and millimeter waves of various frequencies were generated by varying the VCSEL diameter in a single multimode VCSEL our coupling of a few VCSELs. Breathing frequency in multi-mode operations affects modulation response and bandwidth. Optimizing RO frequency and mode beating frequency could potentially expand bandwidths suitable for wide band digital communications.

Ning, Cun-Zheng; Biegel, Bryan A. (Technical Monitor)

2002-01-01

28

VCSELs for exascale computing, computer farms, and green photonics  

NASA Astrophysics Data System (ADS)

The bandwidth-induced communication bottleneck due to the intrinsic limitations of metal interconnects is inhibiting the performance and environmental friendliness of todaýs supercomputers, data centers, and in fact all other modern electrically interconnected and interoperable networks such as data farms and "cloud" fabrics. The same is true for systems of optical interconnects (OIs), where even when the metal interconnects are replaced with OIs the systems remain limited by bandwidth, physical size, and most critically the power consumption and lifecycle operating costs. Vertical-cavity surface-emitting lasers (VCSELs) are ideally suited to solve this dilemma. Global communication providers like Google Inc., Intel Inc., HP Inc., and IBM Inc. are now producing optical interconnects based on VCSELs. The optimal bandwidth per link may be analyzed by by using Amdah?s Law and depends on the architecture of the data center and the performance of the servers within the data center. According to Google Inc., a bandwidth of 40 Gb/s has to be accommodated in the future. IBM Inc. demands 80 Tbps interconnects between solitary server chips in 2020. We recently realized ultrahigh bit rate VCSELs up to 49 Gb/s suited for such optical interconnects emitting at 980 nm. These devices show error-free transmission at temperatures up to 155°C and operate beyond 200°C. Single channel data-rates of 40 Gb/s were achieved up to 75°C. Record high energy efficiencies close to 50 fJ/bit were demonstrated for VCSELs emitting at 850 nm. Our devices are fabricated using a full three-inch wafer process, and the apertures were formed by in-situ controlled selective wet oxidation using stainless steel-based vacuum equipment of our own design. assembly, and operation. All device data are measured, recorded, and evaluated by our proprietary fully automated wafer mapping probe station. The bandwidth density of our present devices is expected to be scalable from about 100 Gbps/mm² to a physical limit of roughly 15 Tbps/mm² based on the current 12.5 Gb/s VCSEL technology. Still more energy-efficient and smaller volume laser diode devices dissipating less heat are mandatory for further up scaling of the bandwidth. Novel metal-clad VCSELs enable a reduction of the device's footprint for potentially ultrashort range interconnects by 1 to 2 orders of magnitude compared to conventional VCSELs thus enabling a similar increase of device density and bandwidth.

Hofmann, Werner; Moser, Philip; Wolf, Philip; Larisch, Gunter; Li, Hui; Li, Wei; Lott, James; Bimberg, Dieter

2012-11-01

29

An efficient electrically tunable all-fiber polarization controller  

Microsoft Academic Search

We demonstrate a novel electrically tunable all-fiber polarization controller using evaporated micro-heaters on short sections of polarization maintaining fiber. Potential applications include compact, low loss, economical polarization controllers for characterization of PDL (polarization dependent loss) or PMD (polarization mode dispersion) compensation.

E. R. Lyons; H. P. Lee

2001-01-01

30

Organic photovoltaic cells with controlled polarization sensitivity  

SciTech Connect

In this study, we demonstrate linearly polarized organic photovoltaic cells with a well-controlled level of polarization sensitivity. The polarized devices were created through the application of a large uniaxial strain to the bulk heterojunction poly(3-hexylthiophene):Phenyl-C61-butyric acid methyl ester (P3HT:PCBM) film and printing the plastically deformed active layer onto a PEDOT:PSS and indium tin oxide coated glass substrate. The P3HT:PCBM layer is processed such that it is able to accommodate high strains (over 100%) without fracture. After printing the strained films, thermal annealing is used to optimize solar cell performance while maintaining polarization sensitivity. A dichroic ratio and short circuit current ratio of ?6.1 and ?1.6 were achieved, respectively.

Awartani, Omar; O'Connor, Brendan T., E-mail: btoconno@ncsu.edu [Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Kudenov, Michael W. [Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States)

2014-03-03

31

Organic photovoltaic cells with controlled polarization sensitivity  

NASA Astrophysics Data System (ADS)

In this study, we demonstrate linearly polarized organic photovoltaic cells with a well-controlled level of polarization sensitivity. The polarized devices were created through the application of a large uniaxial strain to the bulk heterojunction poly(3-hexylthiophene):Phenyl-C61-butyric acid methyl ester (P3HT:PCBM) film and printing the plastically deformed active layer onto a PEDOT:PSS and indium tin oxide coated glass substrate. The P3HT:PCBM layer is processed such that it is able to accommodate high strains (over 100%) without fracture. After printing the strained films, thermal annealing is used to optimize solar cell performance while maintaining polarization sensitivity. A dichroic ratio and short circuit current ratio of ?6.1 and ?1.6 were achieved, respectively.

Awartani, Omar; Kudenov, Michael W.; O'Connor, Brendan T.

2014-03-01

32

Controlling Light Polarization for Attosecond Pulse Generation  

Microsoft Academic Search

We developed a technique for controlling the duration of XUV pulses by modulating the polarization of an intense short pulse\\u000a and using this pulse for high order harmonic generation. This approach allows confining the XUV emission down to the isolated\\u000a attosecond pulse level leading to the generation of broadband and tunable isolated attosecond pulses.

Eric Constant; Eric Mével

33

Fast beam steering with full polarization control using a galvanometric optical scanner and polarization controller.  

PubMed

Optical beam steering is a key element in many industrial and scientific applications like in material processing, information technologies, medical imaging and laser display. Even though galvanometer-based scanners offer flexibility, speed and accuracy at a relatively low cost, they still lack the necessary control over the polarization required for certain applications. We report on the development of a polarization steerable system assembled with a fiber polarization controller and a galvanometric scanner, both controlled by a digital signal processor board. The system implements control of the polarization decoupled from the pointing direction through a feed-forward control scheme. This enables to direct optical beams to a desired direction without affecting its initial polarization state. When considering the full working field of view, we are able to compensate polarization angle errors larger than 0.2 rad, in a temporal window of less than ? 20 ms. Given the unification of components to fully control any polarization state while steering an optical beam, the proposed system is potentially integrable and robust. PMID:22714214

Jofre, M; Anzolin, G; Steinlechner, F; Oliverio, N; Torres, J P; Pruneri, V; Mitchell, M W

2012-05-21

34

Communication using VCSEL laser array  

NASA Technical Reports Server (NTRS)

Ultrafast directional beam switching, using coupled vertical cavity surface emitting lasers (VCSELs) is combined with a light modulator to provide information transfer at bit rates of tens of GHz. This approach is demonstrated to achieve beam switching frequencies of 32-50 GHz in some embodiments and directional beam switching with angular differences of about eight degrees. This switching scheme is likely to be useful for ultrafast optical networks at frequencies much higher than achievable with other approaches. A Mach-Zehnder interferometer, a Fabry-Perot etalon, or a semiconductor-based electro-absorption transmission channel, among others, can be used as a light modulator.

Goorjian, Peter M. (Inventor)

2008-01-01

35

Interface control of bulk ferroelectric polarization  

SciTech Connect

The control of material interfaces at the atomic level has led to no- vel interfacial properties and functionalities. In particular, the study of polar discontinuities at interfaces between complex oxides lies at the frontier of modern condensed matter research. Here we em- ploy a combination of experimental measurements and theoretical calculations to demonstrate the control of a bulk property, namely ferroelectric polarization, of a heteroepitaxial bilayer by precise atomic-scale interface engineering. More specifically, the control is achieved by exploiting the interfacial valence mismatch to influence the electrostatic potential step across the interface, which manifests itself as the biased-voltage in ferroelectric hysteresis loops and determines the ferroelectric state. A broad study of diverse systems comprising different ferroelectrics and conducting perovskite un- derlayers extends the generality of this phenomenon.

Yu, P [University of California, Berkeley; Luo, Weidong [ORNL; Yi, D. [University of California, Berkeley; Zhang, J.-X. [University of California, Berkeley; Rossell, M.D. [Lawrence Berkeley National Laboratory (LBNL); Yang, C.-H. [Korea Advanced Institute of Science and Technology; You, L. [University of California, Berkeley; Singh-Bhalla, G. B. [University of California, Berkeley & LBNL; Yang, S.Y [University of California, Berkeley; He, Q [University of California, Berkeley; Ramasse, Q. M. [Lawrence Berkeley National Laboratory (LBNL); Erni, R. [Lawrence Berkeley National Laboratory (LBNL); Martin, L. W. [University of Illinois, Urbana-Champaign; Chu, Y. H. [University of California, Berkeley; Pantelides, Sokrates T [ORNL; Pennycook, Stephen J [ORNL; Ramesh, R. [University of California, Berkeley

2012-01-01

36

Interface control of bulk ferroelectric polarization  

PubMed Central

The control of material interfaces at the atomic level has led to novel interfacial properties and functionalities. In particular, the study of polar discontinuities at interfaces between complex oxides lies at the frontier of modern condensed matter research. Here we employ a combination of experimental measurements and theoretical calculations to demonstrate the control of a bulk property, namely ferroelectric polarization, of a heteroepitaxial bilayer by precise atomic-scale interface engineering. More specifically, the control is achieved by exploiting the interfacial valence mismatch to influence the electrostatic potential step across the interface, which manifests itself as the biased-voltage in ferroelectric hysteresis loops and determines the ferroelectric state. A broad study of diverse systems comprising different ferroelectrics and conducting perovskite underlayers extends the generality of this phenomenon. PMID:22647612

Yu, P.; Luo, W.; Yi, D.; Zhang, J. X.; Rossell, M. D.; Yang, C.-H.; You, L.; Singh-Bhalla, G.; Yang, S. Y.; He, Q.; Ramasse, Q. M.; Erni, R.; Martin, L. W.; Chu, Y. H.; Pantelides, S. T.; Pennycook, S. J.; Ramesh, R.

2012-01-01

37

Polarization control in spun and telecommunication optical fibers  

E-print Network

Polarization control in spun and telecommunication optical fibers Elie Assémat, Damien Dargent systems, which allows to achieve a control of the polarization state of the signal beam by adjusting the polarization of the pump. In spun fibers, all polarization states of the signal beam are attracted toward

Paris-Sud XI, Université de

38

Polarization-independent photonic switching system using fast automatic polarization controllers  

Microsoft Academic Search

A 16×16 polarization-independent photonic switching system that uses a rapidly reconfigurable, polarization-dependent switch array in combination with fast electrooptic polarization controllers, which automatically transform the arbitrary polarization states of the incoming optical signals into the desired polarization state of the lithium niobate switch array, is reported. In a 1.7-Gb\\/s fiber-optic transmission experiment, it is demonstrated that the controllers are capable

F. Heismann; A. F. Ambrose; T. O. Murphy; M. S. Whalen

1993-01-01

39

Optical fiber polarization control system based on fast locating algorithm  

NASA Astrophysics Data System (ADS)

In this thesis, the currently feedback control algorithms used in the polarization controller, including simulated annealing algorithm and gradient algorithm were analyzed. On this basis, a new method of polarization control feedback algorithm based on fast locating algorithm was proposed to solve the defects of the original algorithm, such as poor convergence and long time consuming search. It can reduce convergence time and improve the response speed of the polarization controllers. This new endless polarization control algorithm using 4-plate polarization controller was proposed and demonstrated. The results showed that the response time of the polarization controller was less than 1ms. The control of polarization was achieved and the output polarization state was stable while the light intensity fluctuated less than 2%, which could run endless reset freely.

Huang, Zhi-meng; Zhang, Da-yong; Cheng, He-ping; Luo, Yong-quan; Han, Mei; Li, Jian-feng; Liu, Cang-li

2013-09-01

40

Novel SDMA system adopting spatial and polarization control with terminal polarization assignment  

Microsoft Academic Search

This paper proposes a novel space division multiple access system that comprises base station smart antennas and mobile terminals employing a dual-polarized antenna. The smart antennas adaptively control radiation patterns and polarization using a dual-polarized antenna array. Each mobile terminal communicates with the base station by assigning polarization to minimize the interference caused by the other mobile terminals. The simulation

Kazuhiro Komiya; Kentaro Nishimori; Keiw Cho; Toshikazu Hori

2001-01-01

41

Polarity control and growth of lateral polarity structures in AlN  

NASA Astrophysics Data System (ADS)

The control of the polarity of metalorganic chemical vapor deposition grown AlN on sapphire is demonstrated. Al-polar and N-polar AlN is grown side-by-side yielding a lateral polarity structure. Scanning electron microscopy measurements reveal a smooth surface for the Al-polar and a relatively rough surface for the N-polar AlN domains. Transmission electron microscopy shows mixed edge-screw type dislocations with polarity-dependent dislocation bending. Raman spectroscopy reveals compressively strained Al-polar and relaxed N-polar domains. The near band edge luminescence consists of free and bound excitons which are broadened for the Al-polar AlN. Relaxation, better optical quality, and dislocation bending in the N-polar domains are explained by the columnar growth mode.

Kirste, Ronny; Mita, Seiji; Hussey, Lindsay; Hoffmann, Marc P.; Guo, Wei; Bryan, Isaac; Bryan, Zachary; Tweedie, James; Xie, Jinqiao; Gerhold, Michael; Collazo, Ramón; Sitar, Zlatko

2013-05-01

42

The next generation high data rate VCSEL development at SEDU  

NASA Astrophysics Data System (ADS)

In May of 2012, Emcore's VCSEL FAB and VCSEL based transceiver business joined Sumitomo Electric Device Innovations USA (SEDU). After this change of ownership, our high speed VCSEL development effort continues. In this paper, we will report the progress we made in the past year in our 25Gbps to 28Gbps VCSEL. This next generation device is targeted for EDR, 32GFC as well as other optical interconnect applications.

Xie, Chuan; Li, Neinyi; Huang, Shenghong; Liu, Chiyu; Wang, Li; Jackson, Kenneth P.

2013-03-01

43

Micromachined polarization-state controller and its application to polarization-mode dispersion compensation  

Microsoft Academic Search

We demonstrate a lightwave-micromachine-based polarization-controller and experimentally verify its operation. The results suggest that micromachines may be useful in manipulating polarization states in lightwave systems and may thus lead to smaller and cheaper polarization-mode dispersion-compensators

Lih Y. Lin; Evan L. Goldstein; Nicholas J. Frigo; Robert W. Tkac

2000-01-01

44

Advances and new functions of VCSEL photonics  

NASA Astrophysics Data System (ADS)

A vertical cavity surface emitting laser (VCSEL) was born in Japan. The 37 years' research and developments opened up various applications including datacom, sensors, optical interconnects, spectroscopy, optical storages, printers, laser displays, laser radar, atomic clock and high power sources. A lot of unique features have been already proven, such as low power consumption, a wafer level testing and so on. The market of VCSELs has been growing up rapidly and they are now key devices in local area networks based on multi-mode optical fibers. Optical interconnections in data centers and supercomputers are attracting much interest. In this paper, the advances on VCSEL photonics will be reviewed. We present the high-speed modulation of VCSELs based on a coupled cavity structure. For further increase in transmission capacity per fiber, the wavelength engineering of VCSEL arrays is discussed, which includes the wavelength stabilization and wavelength tuning based on a micro-machined cantilever structure. We also address a lateral integration platform and new functions, including high-resolution beam scanner, vortex beam creation and large-port free space wavelength selective switch with a Bragg reflector waveguide.

Koyama, Fumio

2014-11-01

45

High-power red VCSEL arrays  

NASA Astrophysics Data System (ADS)

High-power red laser sources are used in many applications such as cosmetics, cancer photodynamic therapy, and DNA sequencing in the medical field, laser-based RGB projection display, and bar-code scanning to name a few. Verticalcavity surface-emitting lasers (VCSELs) can be used as high-power laser sources, as efficient single devices can be configured into high-power two-dimensional arrays and scaled into modules of arrays. VCSELs emit in a circular, uniform beam which can greatly reduce the complexity and cost of optics. Other advantages include a narrow and stable emission spectrum, low speckle of the far-field emission, and good reliability. However, developing efficient red VCSEL sources presents some challenges because of the reduced quantum-well carrier confinement and the increased Aluminum content (to avoid absorption) which increases thermal impedance, and also decreases the DBR index contrast resulting in increased penetration length and cavity losses. We have recently developed VCSEL devices lasing in the visible 6xx nm wavelength band, and reaching 30% power conversion efficiency. We fabricated high-power 2D arrays by removing the GaAs substrate entirely and soldered the chips on high thermal conductivity submounts. Such arrays have demonstrated several Watts of output power at room temperature, in continuous-wave (CW) operation. Several tens of Watts are obtained in QCW operation. Results and challenges of these high-power visible VCSEL arrays will be discussed.

Seurin, Jean-Francois; Khalfin, Viktor; Xu, Guoyang; Miglo, Alexander; Li, Daizong; Zhou, Delai; Sundaresh, Mukta; Zou, Wei-Xiong; Lu, Chien-Yao; Wynn, James D.; Ghosh, Chuni

2013-03-01

46

Progress in extended wavelength VCSEL technology  

NASA Astrophysics Data System (ADS)

Vixar has been developing VCSELs at both shorter (680nm) and longer (1850nm) wavelengths. This paper reports on advances in technology at both of these wavelengths. 680nm VCSELs based upon the AlGaAs/AlGaInP materials system were designed and fabricated for high speed operation for plastic optical fiber (POF) based links for industrial, automotive and consumer applications. High speed testing was performed in a "back-to-back" configuration over short lengths of glass fiber, over 42 meters of POF, with and without I.C. drivers and preamps, and over temperature. Performance to 90°C, 10 Gbps and over 40 meters of plastic optical fiber has been demonstrated. Reliability testing has been performed over a range of temperatures and currents. Preliminary results predict a TT1% failure of at least 240,000 hours at 40°C and an average current modulation of 4mA. In addition, the VCSELs survive 1000 hours at 85% humidity 85°C in a non-hermetic package. 1850nm InP based VCSELs are being developed for optical neurostimulation. The goals are to optimize the output power and power conversion efficiency. 7mW of DC output power has been demonstrated at room temperature, as well as a power conversion efficiency of 12%. Devices operate to 85°C. Over 70mW of pulsed power has been achieved from a 35 VCSEL array, with a pulse width of 10?sec.

Johnson, Klein; Dummer, Matthew; Hibbs-Brenner, Mary; Hogan, William; Steidl, Charles

2013-03-01

47

Application of Twisted Retarders to a Cholesteric Liquid Crystal Polarizer for the Control of Output Polarization States  

Microsoft Academic Search

The possibility of applying twisted retarders to a cholesteric liquid crystal polarizer for the control of polarization states has been investigated. In particular, we have focused on the application of twisted retarders to the conversion of circular polarization states into linear polarization states. It has been found that circular polarization states could be converted into arbitrary linear polarization states using

Ki Cheol Yoon; Ho Cheol Yoon; Keun Young Kim; Hao Cui; Jong Rak Park; Wongun Jang

2009-01-01

48

VCSEL applications in sensors and microsystems  

NASA Astrophysics Data System (ADS)

Vertical-cavity surface-emitting lasers (VCSELs) are uniquely suited to miniaturized free-space optical systems in which surface-mounting and hybrid assembly techniques can be used to combine different technologies together. Two examples are described of such microsystems that are being developed for sensing applications. The first example is an optical position sensing system for rotating parts. Progress on fabricating similar system by flip-chip bonding techniques is then discussed. The second examples is a chemical sensing/analysis system which uses a miniature fluorescence detection model that is based on surface- mounted VCSELs and diffractive optical elements. The detection modules is integrated with a capillary electrochromatography separation system and uses substrate- mode light propagation to focus the VCSEL beam on the capillary channel.

Warren, Mial E.; Carson, Richard F.; Sweatt, William C.; Wendt, Joel R.; Nevers, J. A.; Crawford, Mary H.; Hou, Hong Q.

1998-04-01

49

VCSEL applications in sensors and microsystems  

SciTech Connect

Vertical-cavity surface-emitting lasers (VCSELs) are uniquely suited to miniaturized free-space optical systems in which surface-mounting and hybrid assembly techniques can be used to combine different technologies together. Two examples are described of such microsystems that are being developed for sensing applications. The first example is a optical position sensing system for rotating parts. Progress on fabricating similar systems by flip-chip bonding techniques is then discussed. The second example is a chemical sensing/analysis system which uses a miniature fluorescence detection module that is based on surface-mounted VCSELs and diffractive optical elements. The detection module is integrated with a capillary electrochromatography separation system and uses substrate-mode light propagation to focus the VCSEL beam on the capillary channel.

Warren, M.E.; Carson, R.F.; Sweatt, W.C.; Wendt, J.R.; Nevers, J.A.; Crawford, M.H.; Hou, H.Q.

1998-01-01

50

Process control system using polarizing interferometer  

DOEpatents

A system for nondestructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading. 38 figures.

Schultz, T.J.; Kotidis, P.A.; Woodroffe, J.A.; Rostler, P.S.

1994-02-15

51

Furnace control apparatus using polarizing interferometer  

DOEpatents

A system for nondestructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading. 38 figures.

Schultz, T.J.; Kotidis, P.A.; Woodroffe, J.A.; Rostler, P.S.

1995-03-28

52

All-optical polarization control and noise cleaning based on a nonlinear lossless polarizer  

NASA Astrophysics Data System (ADS)

We propose an all-optical fiber-based device able to accomplish both polarization control and OSNR enhancement of an amplitude modulated optical signal, affected by unpolarized additive white Gaussian noise, at the same time. The proposed noise cleaning device is made of a nonlinear lossless polarizer (NLP), that performs polarization control, followed by an ideal polarizing filter that removes the orthogonally polarized half of additive noise. The NLP transforms every input signal polarization into a unique, well defined output polarization (without any loss of signal energy) and its task is to impose a signal polarization aligned with the transparent eigenstate of the polarizing filter. In order to effectively control the polarization of the modulated signal, we show that two different NLP configurations (with counter- or co-propagating pump laser) are needed, as a function of the signal polarization coherence time. The NLP is designed so that polarization attraction is effective only on the "noiseless" (i.e., information-bearing) component of the signal and not on noise, that remains unpolarized at the NLP output. Hence, the proposed device is able to discriminate signal power (that is preserved) from in-band noise power (that is partly suppressed). Since signal repolarization is detrimental if applied to polarization-multiplexed formats, the noise cleaner application is limited here to "legacy" links, with 10 Gb/s OOK modulation, still representing the most common format in deployed networks. By employing the appropriate NLP configurations, we obtain an OSNR gain close to 3dB. Furthermore, we show how the achievable OSNR gain can be estimated theoretically.

Barozzi, Matteo; Vannucci, Armando; Picchi, Giorgio

2015-01-01

53

Nonlinear mode coupling in optical fibers and VCSELs and some applications to communication systems  

NASA Astrophysics Data System (ADS)

Nonlinear phenomena are relatively easy to observe in optical fibers and semiconductor laser cavities. In optical fibers, nonlinear effects can be seen even at low power due to the high intensities in the small fiber cores and long propagation distances possible in low loss fibers. Semiconductor lasers, in particular, vertical cavity surface emitting lasers (VCSELs), have cavities with very high Q-factors, which result in high intra cavity intensities even at low facet powers. In this thesis we will examine how these nonlinear effects are responsible for coupling between the different modes present in the medium and some applications to optical communication systems. In optical fibers, the nonlinear processes that dominate are self-phase matched processes that automatically satisfy the phase matching condition. These processes include self phase modulation (SPM) and cross phase modulation (XPM). SPM is responsible for the stability and interaction between propagating pulses known as solitons. XPM is responsible for coupling signals with different polarizations or wavelengths propagating in a fiber. In this thesis we have investigated the possibility of controlling the non-linear interaction between solitons, using XPM from another pulse and using this mechanism for pattern recognition in an optical data stream. We demonstrate high-speed (63Gb/s) recognition of 8-bit header words which is a useful function at an add- drop node in an optical network. Both SPM and XPM can be explained in terms of a nonlinear refractive index-a simplification that is made possible by the extremely fast relaxation times in silica (~40fs). In semiconductors the carriers exhibit both fast intra band (~50fs) and spin-flip relaxation (~2ps), and slow inter band dipole relaxation (~Ins). Due to this hierarchy of relaxation times, the interaction of light with the semiconductor medium cannot be described by a single effective refractive index and the carrier dynamics have to be accounted for explicitly. Using this detailed description, we have compared the contribution of spin-flip relaxation to the non-linear coupling between the polarization modes near threshold. We show that the detailed structure of the mode spectrum observed when the VCSEL cavity is probed with an injected optical field is accounted for by the slow dipole relaxation times.

Kishore, Kunal

2000-11-01

54

Full polarization control for fiber optical quantum communication systems using polarization encoding.  

PubMed

A real-time polarization control system employing two non-orthogonal reference signals multiplexed in either time or wavelength with the data signal is presented. It is shown, theoretically and experimentally, that complete control of multiple polarization states can be attained employing polarization controllers in closed-loop configuration. Experimental results on the wavelength multiplexing setup show that negligible added penalties, corresponding to an average added optical Quantum Bit Error Rate of 0.044%, can be achieved with response times smaller than 10 ms, without significant introduction of noise counts in the quantum channel. PMID:18542265

Xavier, G B; Vilela de Faria, G; Temporão, G P; von der Weid, J P

2008-02-01

55

Full polarization control for fiber optical quantum communication systems using polarization encoding  

E-print Network

A real-time polarization control system employing two nonorthogonal reference signals multiplexed in either time or wavelength with the data signal is presented. It is shown, theoretically and experimentally, that complete control of multiple polarization states can be attained employing polarization controllers in closed-loop configuration. Experimental results show that negligible added penalties, corresponding to an average added optical Quantum Bit Error Rate of 0.044%, can be achieved with response times smaller than 10 ms, without significant introduction of noise counts in the quantum channel.

G. B. Xavier; G. Vilela de Faria; G. P. Temporao; J. P. von der Weid

2007-10-22

56

Coherent control of polarized neutron interferometry  

E-print Network

In this thesis, we describe two sets of experiments using a single crystal neutron interferometer. First, we explore applications of quantum information processing (QIP) to magnetic materials characterization using polarized ...

Abutaleb, Mohamed Osama

2012-01-01

57

Single frequency stable VCSEL as a compact source for interferometry and vibrometry  

SciTech Connect

Developing an innovative PS-DAVLL (Polarization Switching DAVLL) method of frequency stabilization, which used a ferroelectric liquid crystal cell as quarter wave plate, rubidium cell and developed ultra-stable current source, allowed to obtain a frequency stability of 10{sup -9}(frequency reproducibility of 1,2centre dot10{sup -8}) and reductions in external dimensions of laser source. The total power consumption is only 1,5 Watt. Because stabilization method used in the frequency standard is insensitive to vibration, the semiconductor laser interferometer was built for measuring range over one meter, which can also be used in industry for the accurate measurement of displacements with an accuracy of 1[mum/m]. Measurements of the VCSEL laser parameters are important from the standpoint of its use in laser interferometry or vibrometry, like narrow emission line DELTAnu{sub FWHM} = 70[MHz] equivalent of this laser type and stability of linear polarization of VCSEL laser. The undoubted advantage of the constructed laser source is the lack of mode-hopping effect during continuous work of VCSEL.

Dudzik, Grzegorz; Rzepka, Janusz [Department of Field Theory, Electronic Systems and Optoelectronics, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50320 Wroclaw (Poland)

2010-05-28

58

Versatile endless optical polarization controller/tracker/demultiplexer.  

PubMed

Following an initial discussion of control error signal generation, we present new developments and applications of automatic endless optical polarization control based on a commercial electrooptic LiNbO(3) polarization transformer: (i) Fast tracking and subsequent demultiplexing of DPSK/DQPSK/QAM polarization channels was hitherto limited to a fairly fixed optical input power. With APD photoreceivers used for residual interference detection, we demonstrate here an optical level tolerance of at least 7 dB, compared to only 3 dB for PIN photoreceivers. DPSK channel polarizations are tracked at up to 40 krad/s and higher speed on the Poincaré sphere. (ii) High-order optical modulation schemes require increased accuracy of the polarization controller in the demultiplexer. This is possible at the expense of a reduced tracking speed. We achieve a mean polarization extinction ratio of >40 dB or <0.02 rad error while tracking arbitrary endless polarization changes of up to 1000 rad/s. (iii) While electronic polarization tracking in coherent receivers is currently limited to a symbol rate of about 28 GBaud we show optical polarization tracking of a signal with 1 THz bandwidth. PMID:24718201

Koch, Benjamin; Noé, Reinhold; Sandel, David; Mirvoda, Vitali

2014-04-01

59

Multiple long-wavelength VCSEL arrays for low-cost WDM  

NASA Astrophysics Data System (ADS)

Vertical-cavity surface-emitting lasers (VCSELs) emitting in the 1530-1565 nm region of flat gain in Er-doped fibers offer the potential for low-cost transmitters for wavelength division multiplexing (WDM). Methods are described to produce precisely-defined vertical-cavity surface-emitting laser arrays which: 1) efficiently utilize wafer real estate; 2) have precise and uniform wavelength distributions despite wafer thickness nonuniformity and wafer-to-wafer thickness variation; 3) are compatible with known multiplexing technologies; 4) have minimum wavelength variation with temperature. Epitaxial growth on patterned substrates with varying-size mesas has been shown to produce multiple-wavelength VCSEL arrays by Iga's group at the Tokyo Institute of Technology. This can be combined with additional refinements to fine tune the wavelengths, increase yield, and to maximize VCSEL efficiency, manufacturability and performance. Multi-wavelength VCSEL arrays represent a much lower cost, more controllable alternative to distributed-feedback laser arrays for WDM sources. The difference in laser output powers can be largely compensated via use of an Er-doped fiber amplifier within the transmitter. Reports such as that by ElectroniCast point to transmitters and receivers as being the most vital WDM components, in terms of both cost and technology.

Jewell, Jack L.; Dapkus, Paul D.; Choi, William; Lin, David; Bond, Aaron; Swirhun, Stan E.; Coleman, James J.; Jones, A. M.; West, Lawrence C.; Roberts, Charles W.

1998-02-01

60

High-speed VCSEL-based optical interconnects  

Microsoft Academic Search

Vertical Cavity Surface Emitting Lasers (VCSEL) have made significant inroads into commercial realization especially in the area of data communications. Single VCSEL devices are key components in Gb Ethernet Transceivers. A multi-element VCSEL array is the key enabling technology for high-speed multi Gb\\/s parallel optical interconnect modules. In 1996, several companies introduced a new generation of fiber optic products based

Waguih S. Ishak

2001-01-01

61

Self-Sustained Ultrafast Pulsation in Coupled VCSELs  

NASA Technical Reports Server (NTRS)

High frequency, narrow-band self-pulsating operation is demonstrated in two coupled vertical-cavity surface-emitting lasers (VCSELs). The coupled VCSELs provide an ideal source for high-repetition rate (over 40 GHz), sinusoidal-like modulated laser source with Gaussian-like near- and far-field profiles. We also show that the frequency of the modulation can be tuned by the inter-VCSEL separation or by DC-bias level.

Ning, Cun-Zheng

2001-01-01

62

A Quasioptical Vector Interferometer for Polarization Control  

NASA Technical Reports Server (NTRS)

We present a mathematical description of a Quasioptical Vector Interferometer (QVI), a device that maps an input polarization state to an output polarization state by introducing a phase delay between two linear orthogonal components of the input polarization. The advantages of such a device over a spinning wave-plate modulator for measuring astronomical polarization in the far-infrared through millimeter are: 1. The use of small, linear motions eliminates the need for cryogenic rotational bearings, 2. The phase flexibility allows measurement of Stokes V as well as Q and U, and 3. The QVI allows for both multi-wavelength and broadband modulation. We suggest two implementations of this device as an astronomical polarization modulator. The first involves two such modulators placed in series. By adjusting the two phase delays, it is possible to use such a modulator to measure Stokes Q, U, and V for passbands that are not too large. Conversely, a single QVI may be used to measure Q and V independent of frequency. In this implementation, Stokes U must be measured by rotating the instrument. We conclude this paper by presenting initial laboratory results.

Chuss, David T.; Wollack, Edward J.; Moseley, Harvey S.; Novak, Giles

2005-01-01

63

Guided-mode resonant polarization-controlled tunable color filters.  

PubMed

We demonstrate efficient guided-mode resonant polarization-controlled tunable color filters. The devices consist of subwavelength gratings that are partially etched into a thin silicon-nitride film deposited on a glass substrate. Two color filters with grating periods of 300 nm and 370 nm are designed and fabricated. The 300-nm device exhibits green and blue colors and the 370-nm device generates red and yellow colors for TE and TM polarization, respectively. The pixels have a spectral bandwidth of ~12 nm with efficiencies exceeding 90% for TE polarization and 80% for TM polarization. The devices may find application in displays, image sensors, and biomedical imaging technologies. PMID:24921349

Uddin, Mohammad Jalal; Khaleque, Tanzina; Magnusson, Robert

2014-05-19

64

Active switching in metamaterials using polarization control of light  

E-print Network

We demonstrate on-demand control of localized surface plasmons in metamaterials by means of incident light polarization. An asymmetric mode, selectively excited by s-polarized light, interfere destructively with a bright element, thereby allowing the incident light to propagate at a fairly low loss, corresponding to electromagnetically induced transparency (EIT) in an atomic system. In contrast, a symmetric mode, excited by p-polarized light, directly couples with the incident light, which is analogous to the switch-off of EIT. The light polarization-dependent excitation of asymmetric and symmetric plasmon modes holds potential for active switching applications of plasmon hybridization.

Hua Xu; Byoung Seung Ham

2010-10-11

65

VCSEL fault location apparatus and method  

DOEpatents

An apparatus for locating a fault within an optical fiber is disclosed. The apparatus, which can be formed as a part of a fiber-optic transmitter or as a stand-alone instrument, utilizes a vertical-cavity surface-emitting laser (VCSEL) to generate a test pulse of light which is coupled into an optical fiber under test. The VCSEL is subsequently reconfigured by changing a bias voltage thereto and is used as a resonant-cavity photodetector (RCPD) to detect a portion of the test light pulse which is reflected or scattered from any fault within the optical fiber. A time interval .DELTA.t between an instant in time when the test light pulse is generated and the time the reflected or scattered portion is detected can then be used to determine the location of the fault within the optical fiber.

Keeler, Gordon A. (Albuquerque, NM); Serkland, Darwin K. (Albuquerque, NM)

2007-05-15

66

Electrically pumped semiconductor laser with monolithic control of circular polarization.  

PubMed

We demonstrate surface emission of terahertz (THz) frequency radiation from a monolithic quantum cascade laser with built-in control over the degree of circular polarization by "fishbone" gratings composed of orthogonally oriented aperture antennas. Different grating concepts for circularly polarized emission are introduced along with the presentation of simulations and experimental results. Fifth-order gratings achieve a degree of circular polarization of up to 86% within a 12°-wide core region of their emission lobes in the far field. For devices based on an alternative transverse grating design, degrees of circular polarization as high as 98% are demonstrated for selected far-field regions of the outcoupled THz radiation and within a collection half-angle of about 6°. Potential and limitations of integrated antenna gratings for polarization-controlled emission are discussed. PMID:25512515

Rauter, Patrick; Lin, Jiao; Genevet, Patrice; Khanna, Suraj P; Lachab, Mohammad; Giles Davies, A; Linfield, Edmund H; Capasso, Federico

2014-12-30

67

Vergence control for robotic heads using log-polar images  

Microsoft Academic Search

This paper describes a real-time vergence control mechanism based on, log-polar images, developed for a robot head. The real-time control of active vision systems imposes strong constraints on the computational complexity of the vision algorithms. In this paper, we illustrate that vergence of a stereo head can be achieved at reduced computational cost using log-polar images. These images have higher

Alexandre Bernardino; Josh Santos-Victor

1996-01-01

68

Reliability of direct mesa flip-chip bonded VCSELs  

Microsoft Academic Search

We have demonstrated flip chip bonded vertical cavity surface emitting lasers (VCSELs) that have been bonded directly to the mesa. We have seen that flip chip bonding to the mesa has given lowered thermal impedance compared to side flip-chip and die bonded VCSELs. An array of devices has been run for 1600 hours without failure.

M. Teitelbaum; K. W. Goossen

2004-01-01

69

Statistics of transverse mode turn-on dynamics in VCSELs  

Microsoft Academic Search

The turn-on process of a multimode VCSEL is investigated from a statistical point of view. Special attention Is paid to quantities such as time jitter and bit error rate. The single-mode performance of VCSELs during current modulation is compared to that of edge-emitting lasers

J. Dellunde; M. C. Torrent; J. M. Sancho; K. A. Shore

1997-01-01

70

Polarization control in ridge-waveguide-laser diodes  

SciTech Connect

The polarization dependence of the gain/current relation and threshold current of quasi-index-guided laser diodes is analyzed for the case of lambda = 1.3 ..mu..m InGaAsP-InP ridge-waveguide lasers. Thereby it is shown that three different regimes for the stripe width and the lateral effective index discontinuity can be distinguished where one modal polarization (TE or TM) predominates. The significance of this finding on laser design and polarization control is discussed, and a comparison is performed on experimental results.

Amann, M.

1987-04-20

71

Active control of light based on polarization-coupling cascading  

NASA Astrophysics Data System (ADS)

In this letter, we proposed a novel method for optical manipulation based on polarization-coupling cascading in MgO-doped periodically poled lithium niobate crystal. Polarization-coupling cascading, a series of energy exchanges between two orthogonally polarized beams close to phase matching condition, can also lead to phase shifts, in analogy with that in cascaded second-order nonlinearities. In addition, the parameters of light such as phase, amplitude, and group velocity can be modulated by changing the relative power ratio of the incident continuous wave beams. The phase control was demonstrated by Newton's rings experiment, which was in good agreement with the theoretical prediction.

Huo, Juan; Zheng, Yuanlin; Chen, Xianfeng

2014-10-01

72

A theoretical model for ferroelectric polarization-controlled superconductor devices  

Microsoft Academic Search

Polarization-controlled superconductor devices could be used as a logic gate or other electronic units such as acoustic sensors, electro-optical transducers and image detectors. Lin and Wu (Appl. Phys. Lett. 65 (8) (1994) 1) have experimentally investigated the I–V characteristics of such a device. In this paper, we propose a theoretical model to calculate the polarization effect on the I–V curves.

J. T. Wang; F. Tang; M. Chinkhota; R. Tashakkori; D. Bagayoko

1998-01-01

73

Multilevel Data Storage Memory Using Deterministic Polarization Control  

SciTech Connect

Multilevel non-volatile memory for high-density date storage is achieved by using the deterministic control of ferroelectric polarization. In a real ferroelectric thin-film system, eight stable and reproducible polarization states are realized (i.e., 3-bit data storage) by adjusting the displacement current. This approach can be used to triple or quadruple the memory density, even at existing feature scales.

Lee, Daesu [Seoul National University; Yang, Sang Mo [Seoul National University; Kim, T. H. [Seoul National University; Jeon, B. C. [Seoul National University; Kim, Yong su [Seoul National University; Yoon, J. -G. [University of Suwon; Lee, Ho Nyung [ORNL; Baek, Seung Hyup [University of Wisconsin, Madison; Eom, Chang-Beom [University of Wisconsin, Madison; Noh, Tae Won [Seoul National University

2012-01-01

74

Multiplexed gas spectroscopy using tunable VCSELs  

NASA Astrophysics Data System (ADS)

Detection and identification of gas species using tunable laser diode laser absorption spectroscopy has been performed using vertical cavity surface emitting lasers (VCSEL). Two detection methods are compared: direct absorbance and wavelength modulation spectroscopy (WMS). In the first, the output of a DC-based laser is directly monitored to detect for any quench at the targeted specie wavelength. In the latter, the emission wavelength of the laser is modulated by applying a sinusoidal component on the drive current of frequency ?, and measuring the harmonics component (2?) of the photo-detected current. This method shows a better sensitivity measured as signal to noise ratio, and is less susceptible to interference effects such as scattering or fouling. Gas detection was initially performed at room temperature and atmospheric conditions using VCSELs of emission wavelength 763 nm for oxygen and 1392 nm for water, scanning over a range of approximately 10 nm, sufficient to cover 5-10 gas specific absorption lines that enable identification and quantization of gas composition. The amplitude and frequency modulation parameters were optimized for each detected gas species, by performing two dimensional sweeps for both tuning current and either amplitude or frequency, respectively. We found that the highest detected signal is observed for a wavelength modulation amplitude equal to the width of the gas absorbance lines, in good agreement with theoretical calculations, and for modulation frequencies below the time response of the lasers (<50KHz). In conclusion, we will discuss limit of detection studies and further implementation and packaging of VCSELs in diode arrays for continuous and simultaneous monitoring of multiple species in gaseous mixtures.

Bora, Mihail; McCarrick, James; Zumstein, Jim; Bond, Steven; Chang, Allan; Moran, Bryan; Benett, William J.; Bond, Tiziana

2012-06-01

75

Genetic Control of Organ Shape and Tissue Polarity  

PubMed Central

The mechanisms by which genes control organ shape are poorly understood. In principle, genes may control shape by modifying local rates and/or orientations of deformation. Distinguishing between these possibilities has been difficult because of interactions between patterns, orientations, and mechanical constraints during growth. Here we show how a combination of growth analysis, molecular genetics, and modelling can be used to dissect the factors contributing to shape. Using the Snapdragon (Antirrhinum) flower as an example, we show how shape development reflects local rates and orientations of tissue growth that vary spatially and temporally to form a dynamic growth field. This growth field is under the control of several dorsoventral genes that influence flower shape. The action of these genes can be modelled by assuming they modulate specified growth rates parallel or perpendicular to local orientations, established by a few key organisers of tissue polarity. Models in which dorsoventral genes only influence specified growth rates do not fully account for the observed growth fields and shapes. However, the data can be readily explained by a model in which dorsoventral genes also modify organisers of tissue polarity. In particular, genetic control of tissue polarity organisers at ventral petal junctions and distal boundaries allows both the shape and growth field of the flower to be accounted for in wild type and mutants. The results suggest that genetic control of tissue polarity organisers has played a key role in the development and evolution of shape. PMID:21085690

Green, Amelia A.; Kennaway, J. Richard; Hanna, Andrew I.; Bangham, J. Andrew; Coen, Enrico

2010-01-01

76

Polarization-insensitive and polarization-controlled dual-band absorption in metamaterials  

NASA Astrophysics Data System (ADS)

We numerically and experimentally investigated dual-band absorption of sandwich-structure metamaterials which include periodic metal coupled rings at the front separated from the metal plane at the back by a dielectric layer. The properties are demonstrated in both GHz and mid-IR regimes of electromagnetic (EM) wave. The dual-band perfect absorber with polarization independence is observed under normal incidence. In order to understand the EM properties of dual-band perfect absorber, the plasmonic excitation was clarified for both peaks. Finally, by connecting the rings, the perfect-absorption peaks can be controlled with the polarization angle of incident EM wave.

Tuong, P. V.; Park, J. W.; Rhee, J. Y.; Kim, K. W.; Jang, W. H.; Cheong, H.; Lee, Y. P.

2013-02-01

77

Numerical analysis of photonic-crystal VCSELs  

NASA Astrophysics Data System (ADS)

The introduction of a photonic-crystal to the VCSEL produces single mode emission in a very broad range of applied currents. The mechanism responsible for the discrimination of high-order modes originates from two counter-acting phenomena: 1) the PhC introduces lateral mode confinement through a strong waveguide effect and additionally by the Bragg reflections from a regular net of PhC holes 2) the holes of the PhC destroy the vertical periodicity of the DBR and contribute to the selective reduction in reflectivity of the mirror. As a result, the mode which overlaps the holes of the photonic crystal leaks through and becomes discriminated. We present numerical analysis of the influence of parameters of photonic crystal on the wavelength of emission, modal gain, slope efficiency, emitted power and tuning range in single mode VCSELs. We recognise several mechanisms determining high power emission in the single mode regime, which are: selective leakage, thermal focusing, waveguide effect induced by the photonic-crystal, gain spectrum red shift and its maximum reduction with increase of driving currents. We show that careful design of the photonic crystal allows for 10% increase in the emitted power of a singlemode regime and it allows for broad range of the steering currents from 5 to 50 mA. Such attributes support tuning of the single-mode emission over the 10 nm range of the spectrum.

Czyszanowski, Tomasz; Dems, Maciej; Sarzala, Robert P.; Panajotov, Krassimir

2013-03-01

78

Chirp and polarization control of femtosecond molecular fragmentation  

PubMed Central

We explore the simultaneous effect of chirp and polarization as the two control parameters for non-resonant photo-dissociation of n-propyl benzene. Experiments performed over a wide range of laser intensities show that these two control knobs behave mutually exclusively. Specifically, for the coherently enhanced fragments (C3H3+, C5H5+) with negatively chirped pulses and C6H5+ with positively chirped pulses, polarization effect is the same as compared to that in the case of transform-limited pulses. Though a change in polarization affects the overall fragmentation efficiency, the fragmentation pattern of n-propyl benzene molecule remains unaffected in contrast to the chirp case. PMID:24115807

Goswami, T; Das, D K; Kumar, S K Karthick; Goswami, D

2013-01-01

79

Liquid-crystal polarization controller arrays on planar waveguide circuits  

Microsoft Academic Search

In this letter, we have developed thin liquid crystal (LC) arrays for use as simple polarization-controller arrays on planar lightwave circuits (PLCs). The 30-?m thick LC arrays are vertically inserted into trenches cut across PLC substrates. Two such LC cells that are in line and parallel to each other, one of which has a direction of alignment that is rotated

Katsuhiko Hirabayashi; Chikara Amano

2002-01-01

80

Enabling quantum communications through accurate photons polarization control  

NASA Astrophysics Data System (ADS)

The rapid increase on the information sharing around the world, leads to an utmost requirement for capacity and bandwidth. However, the need for security in the transmission and storage of information is also of major importance. The use of quantum technologies provides a practical solution for secure communications systems. Quantum key distribution (QKD) was the first practical application of quantum mechanics, and nowadays it is the most developed one. In order to share secret keys between two parties can be used several methods of encoding. Due to its simplicity, the encoding into polarization is one of the most used. However, when we use optical fibers as transmission channels, the polarization suffers random rotations that may change the state of polarization (SOP) of the light initially sent to the fiber to a new one at the output. Thus, in order to enable real-time communication using this encoding method it is required the use of a dynamic control system. We describe a scheme of transmission of quantum information, which is based in the polarization encoding, and that allows to share secret keys through optical fibers without interruption. The dynamic polarization control system used in such scheme is described, both theoretically and experimentally. Their advantages and limitations for the use in quantum communications are presented and discussed.

Almeida, Álvaro J.; Muga, Nelson J.; Silva, Nuno A.; Stojanovic, Aleksandar D.; André, Paulo S.; Pinto, Armando N.; Mora, José; Capmany, José

2013-11-01

81

Fuzzy-polar control of wind-turbine generator  

SciTech Connect

This paper presents a wind-turbine blade pitch angle controller based on fuzzy polar technique. the technique takes advantage of fuzzy-linguistic modeling in expressing the natural non-linearity or imprecision of the wind-turbine system in determining pitch angles for speed and power regulation. The fuzzy-polar method presents wind-turbine state in the phase-plane in terms of its rotational speed deviation and acceleration. The state vectors thus derived serve as an indicator of the magnitude of departure from the nominal operating point. In order to shift operating state back to the phase plane origin, an acceleration or deceleration control is applied through the pitch-angle adjustment mechanism as defined by the fuzzy-linguistic control law. The performance of the pitch control design method is demonstrated on a simulated wind-turbine-driven synchronous generator.

Idowu, P. [Penn State Univ., Middletown, PA (United States)

1995-12-31

82

Polarization control of 1.3 m-wavelength vertical cavity surface emitting laser (VCSEL) fabricated by orientation-mismatched wafer bonding  

E-print Network

by orientation-mismatched wafer bonding Yae L. Okuno*, Jon Geske, Yi-Jen Chiu, Steven P. DenBaars, and John E Barbara, CA 93106 TEL: 805-893-4235 FAX: 805-893-7990 *E-mail: yae@ece.ucsb.edu Abstract A technique

Bowers, John

83

Independent control of polar and azimuthal anchoring.  

PubMed

Monte Carlo simulation, experiment, and continuum theory are used to examine the anchoring exhibited by a nematic liquid crystal at a patterned substrate comprising a periodic array of rectangles that, respectively, promote vertical and planar alignment. It is shown that the easy axis and effective anchoring energy promoted by such surfaces can be readily controlled by adjusting the design of the pattern. The calculations reveal rich behavior: for strong anchoring, as exhibited by the simulated system, for rectangle ratios ?2 the nematic aligns in the direction of the long edge of the rectangles, the azimuthal anchoring coefficient changing with pattern shape. In weak anchoring scenarios, however, including our experimental systems, preferential anchoring is degenerate between the two rectangle diagonals. Bistability between diagonally aligned and edge-aligned arrangement is predicted for intermediate combinations of anchoring coefficient and system length scale. PMID:23944468

Anquetil-Deck, C; Cleaver, D J; Bramble, J P; Atherton, T J

2013-07-01

84

Comparison of spatial anti-guided mechanism in single emitter VCSELs and VCSEL arrays  

NASA Astrophysics Data System (ADS)

We present the optimization of the carrier injection, heat flow and optical confinement aimed at single mode operation in anti-guiding long-wavelength VCSELs and VCSEL arrays. The analyzed structure incorporates InP/AlGaInAs quantum wells within an InP cavity. The cavity is bounded by GaAs/AlGaAs DBRs. The tunnel junction is responsible for carrier funneling into the active region. The air-gap etched at the interface between cavity and top DBR provides the confinement of the lateral modes. To rigorously simulate the physical phenomena taking place in the device we use a multi-physical model, which comprises three-dimensional models of optical (Plane Wave Admittance Method), thermal and electrical (Finite Element Method) phenomena. In the analysis we investigate the influence of the size of single and multiple emitters and the distance between the emitters in the case of the VCSEL arrays. As a result, we illustrate the complex competition of the modes and determine the geometrical parameters favoring specific array modes in the considered designs and compare the designs with respect to mode discrimination.

Czyszanowski, Tomasz; Dems, Maciej; Sarzala, Robert P.; Panajotov, Krassimir; Kapon, Elyahou

2014-05-01

85

Red VCSELs for POF Data Transmission and Optical Sensing Applications  

Microsoft Academic Search

We have fabricated VCSELs in the visible red spectrum. The emission wavelength ranges from approximately 650 nm to 690 nm depending on application. The devices are grown on GaAs substrates by MOVPE and processed using standard VCSEL processing technology. The active layer consists of three InGaP quantum wells. The Bragg mirrors are AlGaAs\\/AlAs multilayer structures. The bottom mirror is n-doped,

Torsten Wipiejewski; Geoffrey Duggan; Dave Barrow; Brian McGarvey; Vincent Hung; Tim Calvert; Markus Maute; John Lambkin

2007-01-01

86

Progress towards commercialization of 25-Gb/s VCSELs  

NASA Astrophysics Data System (ADS)

In this paper, we will present the development progress of 850-nm VCSELs operating at 25 Gbit/s and beyond at Sumitomo Electric Device Innovations USA. With improved growth of indium-containing quantum wells, we have demonstrated low-power-consumption VCSELs that can operate at 25 - 28 Gbit/s with reduced current density and enhanced reliability. We will also present recent progress on the improved performance of the new device in EDR cables.

Wang, Li; Xie, Chuan; Li, Neinyi; Huang, Shenghong

2014-02-01

87

Electrically-Controllable Liquid Crystal Polarizing Filter for Eliminating Reflected Light  

Microsoft Academic Search

A high-speed controllable polarizing filter has been developed to eliminate obstructive polarized light reflected from glass and watery surfaces for image pickup in video media program producing and marine dynamic remote sensing. In this device, the polarization plane of incident light is rotated through 0°, 45°, 90° or 135° by an electrically-controllable polarization rotator composed of 45° and 90° twisted

Hideo Fujikake; Kuniharu Takizawa; Tahito Aida; Hiroshi Kikuchi; Takanori Fujii; Masahiro Kawakita

1998-01-01

88

Filter control polarization mode dispersion in dispersion managed soliton systems  

NASA Astrophysics Data System (ADS)

In this paper, the dispersion managed soliton (DMS) transmission equation is built on considering the effects of polarization mode dispersion (PMD) and filter control. The DMS transmission of filtering control in constant birefringence fibers is firstly analyzed by varitional method, from which the evolving rules of characteristical DMS parameters are obtained. Secondly, the stability of DMS transmission and its timing jitter are investigated in the random varying birefringence fibers with the conventional model of PMD. The results reveal that filter control DMS system has powerful robustness to PMD effects and DMS's timing jitter can be decreased considerably with the help of filters.

Xu, Ming; Pu, Tao; Yang, Shuwen; Yang, Xianglin

2003-10-01

89

Is cell polarity under mechanical control in plants?  

PubMed

Plant cells experience a tremendous amount of mechanical stress caused by turgor pressure. Because cells are glued to their neighbors by the middle lamella, supracellular patterns of physical forces are emerging during growth, usually leading to tension in the epidermis. Cortical microtubules have been shown to reorient in response to these mechanical stresses, and to resist them, indirectly via their impact on the anisotropic structure of the cell wall. In a recent study, we show that the polar localization of the auxin efflux carrier PIN1 can also be under the control of physical forces, thus linking cell growth rate and anisotropy by a common mechanical signal. Because of the known impact of auxin on the stiffness of the cell wall, this suggests that the mechanical properties of the extracellular matrix play a crucial signaling role in morphogenesis, notably controlling the polarity of the cell, as observed in animal systems. PMID:21258209

Hamant, Olivier; Meyerowitz, Elliot M; Traas, Jan

2011-01-01

90

Remote polarization control for fiber-optic interferometers.  

PubMed

A simple method has been developed for control and prevention of polarization fade on a single output lead from a remotely located fiber-optic interferometer. The method has been demonstrated using a fiber-optic Michelson interferometer. In contrast to a previously suggested method, only a single detector is required. The technique has application for passive, remotely located sensors. Extension to balanced homodyne detection schemes and coherent communications is discussed. PMID:19738844

Wanser, K H; Safar, N H

1987-03-01

91

Control over topological insulator photocurrents with light polarization.  

PubMed

Three-dimensional topological insulators represent a new quantum phase of matter with spin-polarized surface states that are protected from backscattering. The static electronic properties of these surface states have been comprehensively imaged by both photoemission and tunnelling spectroscopies. Theorists have proposed that topological surface states can also exhibit novel electronic responses to light, such as topological quantum phase transitions and spin-polarized electrical currents. However, the effects of optically driving a topological insulator out of equilibrium have remained largely unexplored experimentally, and no photocurrents have been measured. Here, we show that illuminating the topological insulator Bi(2)Se(3) with circularly polarized light generates a photocurrent that originates from topological helical Dirac fermions, and that reversing the helicity of the light reverses the direction of the photocurrent. We also observe a photocurrent that is controlled by the linear polarization of light and argue that it may also have a topological surface state origin. This approach may allow the probing of dynamic properties of topological insulators and lead to novel opto-spintronic devices. PMID:22138862

McIver, J W; Hsieh, D; Steinberg, H; Jarillo-Herrero, P; Gedik, N

2012-02-01

92

Polarization Model and Control in Fiber-Based Bidirectional Systems with Reflections  

E-print Network

Polarization Model and Control in Fiber-Based Bidirectional Systems with Reflections by William La Polarization Model and Control in Fiber-Based Bidirectional Systems with Reflections William La Masters present, for the first time, methods to model and control the polarization of the output lightwave

Qian, Li

93

A long-range polarization-controlled optical tractor beam  

NASA Astrophysics Data System (ADS)

The laser beam has become an indispensable tool for the controllable manipulation and transport of microscopic objects in biology, physical chemistry and condensed matter physics. In particular, ‘tractor’ laser beams can draw matter towards a laser source and perform, for instance, all-optical remote sampling. Recent advances in lightwave technology have already led to small-scale experimental demonstrations of tractor beams. However, the realization of long-range tractor beams has not gone beyond the realm of theoretical investigations. Here, we demonstrate the stable transfer of gold-coated hollow glass spheres against the power flow of a single inhomogeneously polarized laser beam over tens of centimetres. Additionally, by varying the polarization state of the beam we can stop the spheres or reverse the direction of their motion at will.

Shvedov, Vladlen; Davoyan, Arthur R.; Hnatovsky, Cyril; Engheta, Nader; Krolikowski, Wieslaw

2014-11-01

94

Integrated MEMS-tunable VCSELs for reconfigurable optical interconnects  

NASA Astrophysics Data System (ADS)

A simple and low-cost technology for tunable vertical-cavity surface-emitting lasers (VCSELs) with curved movable micromirror is presented. The micro-electro-mechanical system (MEMS) is integrated with the active optical component (so-called half-VCSEL) by means of surface-micromachining using a reflown photoresist droplet as sacrificial layer. The technology is demonstrated for electrically pumped, short-wavelength (850 nm) tunable VCSELs. Fabricated devices with 10 ?m oxide aperture are singlemode with sidemode suppression >35 dB, tunable over 24 nm with output power up to 0.5mW, and have a beam divergence angle <6 °. An improved high-speed design with reduced parasitic capacitance enables direct modulation with 3dB-bandwidths up to 6GHz and error-free data transmission at 5Gbit/s. The modulation response of the MEMS under electrothermal actuation has a bandwidth of 400 Hz corresponding to switching times of about 10ms. The thermal crosstalk between MEMS and half-VCSEL is negligible and not degrading the device performance. With these characteristics the integrated MEMS-tunable VCSELs are basically suitable for use in reconfigurable optical interconnects and ready for test in a prototype system. Schemes for improving output power, tuning speed, and modulation bandwidth are briefly discussed.

Kögel, Benjamin; Debernardi, Pierluigi; Westbergh, Petter; Gustavsson, Johan S.; Haglund, Åsa; Haglund, Erik; Bengtsson, Jörgen; Larsson, Anders

2012-03-01

95

Prickle/spiny-legs isoforms control the polarity of the apical microtubule network in planar cell polarity.  

PubMed

Microtubules (MTs) are substrates upon which plus- and minus-end directed motors control the directional movement of cargos that are essential for generating cell polarity. Although centrosomal MTs are organized with plus-ends away from the MT organizing center, the regulation of non-centrosomal MT polarity is poorly understood. Increasing evidence supports the model that directional information for planar polarization is derived from the alignment of a parallel apical network of MTs and the directional MT-dependent trafficking of downstream signaling components. The Fat/Dachsous/Four-jointed (Ft/Ds/Fj) signaling system contributes to orienting those MTs. In addition to previously defined functions in promoting asymmetric subcellular localization of 'core' planar cell polarity (PCP) proteins, we find that alternative Prickle (Pk-Sple) protein isoforms control the polarity of this MT network. This function allows the isoforms of Pk-Sple to differentially determine the direction in which asymmetry is established and therefore, ultimately, the direction of tissue polarity. Oppositely oriented signals that are encoded by oppositely oriented Fj and Ds gradients produce the same polarity outcome in different tissues or compartments, and the tissue-specific activity of alternative Pk-Sple protein isoforms has been observed to rectify the interpretation of opposite upstream directional signals. The control of MT polarity, and thus the directionality of apical vesicle traffic, by Pk-Sple provides a mechanism for this rectification. PMID:25005476

Olofsson, Jessica; Sharp, Katherine A; Matis, Maja; Cho, Bomsoo; Axelrod, Jeffrey D

2014-07-01

96

Polarization State Control of Light by Single-Walled Carbon Nanotubes  

E-print Network

absorption. Fig. 2. Experimental setup for measuring polarization change induced by SWCNT film on quartz subsPolarization State Control of Light by Single-Walled Carbon Nanotubes S. Yoo, Y. Jung, D. Lee, W. T by catalytic CVD on quartz plate. We report the control of both the polarization state and transmission

Maruyama, Shigeo

97

Fast all-fiber polarization scrambling using re-entrant Lefèvre controller  

NASA Astrophysics Data System (ADS)

We demonstrate a low-cost mechanical polarization scrambler capable of near 100 kHz scrambling speed using a single modified Lefèvre controller. By reusing the same controller, many sections can be implemented and the scalability promises higher scrambling rates. The design is wideband, polarization-independent and low-loss providing a degree of polarization of <5%.

Lizé, Yannick Keith; Gomma, Robert; Kashyap, Raman; Palmer, Leigh; Willner, A. E.

2007-11-01

98

Fast all-fiber polarization scrambling using re-entrant Lefèvre controller  

Microsoft Academic Search

We demonstrate a low-cost mechanical polarization scrambler capable of near 100kHz scrambling speed using a single modified Lefèvre controller. By reusing the same controller, many sections can be implemented and the scalability promises higher scrambling rates. The design is wideband, polarization-independent and low-loss providing a degree of polarization of <5%.

Yannick Keith Lizé; Robert Gomma; Raman Kashyap; Leigh Palmer; A. E. Willner

2007-01-01

99

GaInNAs(Sb) Long-Wavelength VCSELs  

NASA Astrophysics Data System (ADS)

The push to provide high-speed optical network access directly to the end user is creating both significant pressure for the development of low-cost, high-speed access terminals as well as opportunities for development of entirely new technological approaches compared to those now used in the optical backbone networks. One of the most challenging is that of providing low-cost, long wavelength, single mode lasers that can be directly modulated at 10 Gbit/s, operate un-cooled in ambient environments and are easily packaged and coupled to fiber. Long wavelength vertical cavity surface emitting lasers (VCSELs) on GaAs certainly have the potential to meet these challenges. The development of MBE growth of GaInNAsSb on GaAs, issues of VCSEL design and successful demonstration of low threshold edge emitting lasers and the first 1530 nm monolithic VCSELs in GaInNAsSb on GaAs are described.

Harris, James S.; Bae, Hopil; Sarmiento, Tomás

100

A ferro-electric liquid crystal polarization controlled switch for WDM applications  

Microsoft Academic Search

A broadband switching using an optical switch with ferro-electric liquid crystal polarization control devices is demonstrated. The device could be available for a broadband and polarization independent switch in wavelength division multiplexing systems.

K. Nakatsuhara; T. Yamada; T. Nakagami

2003-01-01

101

Planar cell polarity genes control the connectivity of enteric neurons  

PubMed Central

A highly complex network of intrinsic enteric neurons is required for the digestive and homeostatic functions of the gut. Nevertheless, the genetic and molecular mechanisms that regulate their assembly into functional neuronal circuits are currently unknown. Here we report that the planar cell polarity (PCP) genes Celsr3 and Fzd3 are required during murine embryogenesis to specifically control the guidance and growth of enteric neuronal projections relative to the longitudinal and radial gut axes. Ablation of these genes disrupts the normal organization of nascent neuronal projections, leading to subtle changes of axonal tract configuration in the mature enteric nervous system (ENS), but profound abnormalities in gastrointestinal motility. Our data argue that PCP-dependent modules of connectivity established at early stages of enteric neurogenesis control gastrointestinal function in adult animals and provide the first evidence that developmental deficits in ENS wiring may contribute to the pathogenesis of idiopathic bowel disorders. PMID:23478408

Sasselli, Valentina; Boesmans, Werend; Vanden Berghe, Pieter; Tissir, Fadel; Goffinet, André M.; Pachnis, Vassilis

2013-01-01

102

High frequency resonance-free loss modulation in a duo-cavity VCSEL  

NASA Astrophysics Data System (ADS)

We have proposed and demonstrated the principle of optical decoupling of the AC modulation component in a lossmodulated Vertical Cavity Surface Emitting Laser (VCSEL) using a detuned duo-cavity device. This approach allows the VCSEL power to be modulated without changing the photon density in the active region. Analysis of reflectivity spectra of a Fabri-Perot cavity with absorber shows that at a certain detuning from the resonance wavelength, reflectivity is almost independent of absorption magnitude. At this spectral detuning between the active region cavity and modulator cavity, a feedback-free transmission modulation of the VCSEL output is possible. The use a multiple-double-QW (MDQW) electroabsorption modulator allows absorption swing between 0.2% and 2% per pass. Optical power modulation of transmission with contrasts up to 40% and chirp of less than 0.05 nm at 930 nm was demonstrated with our design. Initial cavity resonance detuning is controlled through growth and was determined to be ideally ~0.7 nm from analysis of stand-alone absorber cavities. Resonance coupling (splitting) was calculated to be less than 0.3 nm in case of matching resonances. Applying bias at the MDQW modulator section allows adjustment of detuning between cavities by changing the top cavity resonance wavelength mainly via Kramers-Kronig relations. The high frequency modulation characteristics can be tuned in this manner to show little or no sign of resonance, in which case the high frequency roll-off of the modulation response is entirely determined by parasitics of the modulator section. We have demonstrated a flat (+/-3db) response up to 20 GHz.

van Eisden, J.; Yakimov, M.; Tokranov, V.; Varanasi, M.; Rumyantsev, O.; Mohammed, E. M.; Young, I. A.; Oktyabrsky, S. R.

2008-02-01

103

Control of Polarization Interference in Doppler Broadened Two-Photon Resonant Four-Wave Mixing System  

NASA Astrophysics Data System (ADS)

We study two-photon resonant nondegenerate four-wave mixing (NFWM) in a Doppler broadened system. It is found that because the induced polarization is sensitive to the atomic velocity, there exists interference between polarizations of atoms with different velocities, leading to significant modification of the NFWM spectra. This polarization interference can be controlled through applying an additional coupling field.

Zuo, Zhan-Chun; Liu, Xia; Sun, Jiang; Wu, Ling-An; Fu, Pan-Ming

2006-03-01

104

Picosecond polarized supercontinuum generation controlled by intermodal four-wave mixing for  

E-print Network

Picosecond polarized supercontinuum generation controlled by intermodal four-wave mixing.druon@institutoptique.fr Abstract: We present the generation of a picosecond polarized supercontinuum in highly birefringent.4370) Nonlinear optics, fibers; (060.2420) Fibers, polarization-maintaining; (320.6629) Supercontinuum generation

Paris-Sud XI, Université de

105

Current spreading modification to enhance single-fundamental-mode VCSEL operation at higher temperatures  

NASA Astrophysics Data System (ADS)

Continuous-wave (CW) performance of modern oxide-confined (OC) vertical-cavity surface-emitting diode lasers (VCSELs) at room and elevated temperatures is investigated with the aid of the comprehensive fully self-consistent optical-electrical-thermal-gain model. A standard OC GaInNAs/GaAs double-quantum-well VCSEL emitting the 1.3-?m radiation is used as a typical modern VCSEL structure. The oxide aperture is placed at the anti-node position of an optical standing wave within a VCSEL cavity. The desired single-fundamental-mode (SFM) operation has been found to be expected only in VCSELs equipped with relatively small active regions of diameters equal or smaller than 10 ?m. Therefore a proton implantation used as an radial additional confinement of the current spreading from the upper annular contact towards the centrally located active region is proposed and its impact on the VCSEL performance is investigated. The above structure modification has been found to enable a radical improvement in the VCSEL performance. In particular, in this case, the SFM VCSEL operation is possible even in VCSELs with quite large active regions and for much wider ambient-temperature range than in the standard OC VCSELs.

Sarza?a, R. P.; Nakwaski, W.

2011-06-01

106

VCSEL-based optical trapping for microparticle manipulation  

NASA Astrophysics Data System (ADS)

In recent years, research into microfluidic devices has attracted much interest in the fields of biology and medicine, since they promise cheap and fast sample analysis with drastically reduced volume requirements. The combination of various analysis steps on one chip forms a small-sized biomedical system, where handling, fixing, and sorting of particles are major components. Here, it was demonstrated that optical manipulation is an efficient tool; in particular it is accurate, contactless, and biocompatible. However, the commonly required extensive optical setup contradicts the concept of a miniaturized system. We present a novel particle manipulation concept based on vertical-cavity surface-emitting lasers (VCSELs) as light sources. The small dimensions and the low power consumption of these devices enable a direct integration with microfluidic systems. The symmetric geometry of VCSELs leads to a high-quality, circular output beam, which we additionally shape by an etched surface relief in the laser output facet and an integrated photoresist microlens. Thus, a weakly focused output beam with a beam waist of some micrometers is generated in the microfluidic channel. With this configuration we were able to demonstrate particle deflection, trapping, and sorting with a solitary VCSEL with output powers of only 5mW. Furthermore, the surface emission of VCSELs allows a comparatively easy fabrication of two-dimensional laser arrays with arbitrary arrangement of pixels. Smart particle sorting and switching schemes can thus be realized. We have fabricated densely packed VCSEL arrays with center-to-center spacings of only 24 ?m. Equipped with integrated microlenses, these arrays are integrated with microfluidic chips based on polydimethylsiloxane (PDMS), enabling ultra-compact particle sorting and fractionation.

Michalzik, Rainer; Kroner, Andrea; Bergmann, Anna; Rinaldi, Fernando

2009-02-01

107

Investigation of a polarization controller in Ti:LiNbO3 near 1530 nm wavelength  

NASA Astrophysics Data System (ADS)

The results of analytical and experimental investigations for an electro-optic polarization controller are reported. A device configuration composed of two polarization converters with a phase shifter centered between them and all integrated over a single Ti diffused channel waveguide on LiNbO3 is used. Polarization control is achieved by applying voltages on the three integrated elements independently to adjust the phase difference between orthogonal TE and TM components of a guided optical wave as well as their relative strength. Experimental results agree with analytical predictions. For arbitrary incident polarization, endless polarization transformation can be realized at the output.

Sung, W. J.; Kim, J.; Madsen, C. K.; Eknoyan, O.

2015-01-01

108

Doubling direct-detection data rate by polarization multiplexing of 16-QAM without active polarization control.  

PubMed

We introduce and simulate a technique enabling to utilize the polarization dimension in direct-detection optical transmission, supporting polarization multiplexing (POL-MUX) over direct-detection (DD) methods previously demonstrated for a single polarization such as direct-detection OFDM. POL-MUX is currently precluded in self-coherent DD with remotely transmitted pilot, as signal x pilot components may randomly fade out. We propose POL-MUX transmission of advanced modulation formats, such as 16-QAM and higher, by means of a novel low-complexity photonic integrated optical front-end and adaptive 3x2 MIMO DSP. The principle of operation is as follows: an additional X x Y cross-polarizations signal is generated, providing three projections onto an over-complete frame of three dependent vectors. This enables to resiliently reconstruct the received state of polarization even when the remotely transmitted pilot fades along one of the received polarization axes. PMID:24514795

Nazarathy, Moshe; Agmon, Amos

2013-12-30

109

Endless polarization control algorithm using adjustable linear retarders with fixed axes  

Microsoft Academic Search

New designs are presented for polarization-transforming elements equivalent to rotating quarter-wave plates and rotating half-wave plates. These are constructed from sequences of adjustable linear retarders with fixed retardation axes, such as liquid-crystal cells (untwisted nematic) and electrooptical modulators. Then, a new endless polarization control algorithm is proposed and demonstrated. The variable linear retarders in this endless polarization controller operate over

Massimo Martinelli; Russell A. Chipman

2003-01-01

110

A Signaling Network Induced by ?2 Integrin Controls the Polarization of Lytic Granulesin Cytotoxic Cells  

PubMed Central

Cytotoxic lymphocyte skill target cells by polarized release of the content of perforin-containing granules. In natural killer cells, the binding of ?2 integrin to its ligand ICAM-1 is sufficient to promote not only adhesion but also lytic granule polarization. This provided a unique opportunity to study polarization in the absence of degranulation, and ?2 integrin signaling independently of inside-out signals from other receptors. Using an unbiased proteomics approach we identified a signaling network centered on an integrin-linked kinase (ILK)–Pyk2–Paxillin core that was required for granule polarization. Downstream of ILK, the highly conserved Cdc42–Par6 signaling pathway that controls cell polarity was activated and required for granule polarization. These results delineate two connected signaling networks induced upon ?2 integrin engagement alone, which are integrated to control polarization of the microtubule organizing center and associated lytic granules toward the site of contact with target cells during cellular cytotoxicity. PMID:25292215

Zhang, Minggang; March, Michael E.; Lane, William S.; Long, Eric O.

2014-01-01

111

Environmental Control of Cloud-to-Ground Lightning Polarity in Severe Storms  

Microsoft Academic Search

In this study, it is hypothesized that the mesoscale environment can indirectly control the cloud-to-ground (CG) lightning polarity of severe storms by directly affecting their structural, dynamical, and microphysical properties, which in turn directly control cloud electrification and ground flash polarity. A more specific hypothesis, which has been supported by past observational and laboratory charging studies, suggests that broad, strong

Lawrence D. Carey; Kurt M. Buffalo

2007-01-01

112

Controlling the polarity of the transient ferromagneticlike state in ferrimagnets  

NASA Astrophysics Data System (ADS)

It was recently observed that the two antiferromagnetically coupled sublattices of a rare earth-transition metal ferrimagnet can temporarily align ferromagnetically during femtosecond laser heating, but always with the transition metal aligning in the rare earth direction. This behavior has been attributed to the slower magnetization dynamics of the rare earth sublattice. The aim of this work was to assess how the difference in the speed of the transition metal and rare earth dynamics affects the formation of the transient ferromagneticlike state and consequently controls its formation. Our investigation was performed using extensive atomistic spin simulations and analytic micromagnetic theory of ferrimagnets, with analysis of a large area of parameter space such as initial temperature, Gd concentration, and laser fluence. Surprisingly, we found that at high temperatures, close to the Curie point, the rare earth dynamics become faster than those of the transition metal. Subsequently we show that the transient state can be formed with the opposite polarity, where the rare earth aligns in the transition metal direction. Our findings shed light on the complex behavior of this class of ferrimagnetic materials and highlight an important feature which must be considered, or even exploited, if these materials are to be used in ultrafast magnetic devices.

Atxitia, U.; Barker, J.; Chantrell, R. W.; Chubykalo-Fesenko, O.

2014-06-01

113

Laser polarization and phase control of up-conversion fluorescence in rare-earth ions.  

PubMed

We theoretically and experimentally demonstrate the up-conversion fluorescence control via resonance-mediated two-photon absorption in rare-earth ions by varying both the laser polarization and phase. We show that both the laser polarization and phase can control the up-conversion fluorescence, and the up-conversion fluorescence intensity is decreased when the laser polarization changes from linear through elliptical to circular. We also show that the laser polarization will affect the control efficiency of the up-conversion fluorescence by varying the laser phase, and the circular polarization will reduce the control efficiency. Furthermore, we suggest that the control efficiency by varying the laser polarization and the effect of the laser polarization on the control efficiency by varying the laser phase can be artificially manipulated by controlling the laser spectral bandwidth. This optical control method opens a new opportunity to control the up-conversion fluorescence of rare-earth ions, which may have significant impact on the related applications of rare-earth ions. PMID:25465401

Yao, Yunhua; Zhang, Shian; Zhang, Hui; Ding, Jingxin; Jia, Tianqing; Qiu, Jianrong; Sun, Zhenrong

2014-01-01

114

Analysis of a reset-free polarization controller for fast automatic polarization stabilization in fiber-optic transmission systems  

Microsoft Academic Search

We analyze the operation of a reset-free polarization controller comprising three endlessly rotatable wave plates: a first quarter-wave plate followed by a half-wave plate and a second quarter-wave plate, which is rotated synchronously with the first quarter-wave plate. We show that for any arbitrary angular offset between the two quarter-wave plates; the controller allows continuous, reset-free transformations from any varying

Fred Heismann

1994-01-01

115

Rapid Switching and Modulation by use of Coupled VCSELs  

NASA Technical Reports Server (NTRS)

Devices incorporating coupled vertical-cavity surface-emitting lasers (VCSELs) have been proposed as means to effect unprecedentedly rapid modulation and/or switching of light beams in advanced optical communication and information-processing systems. A basic device according to the proposal would comprise two or more VCSELs (1) positioned so close to each other that they are coupled and (2) connected to a current source that biases them at a steady current above the threshold current for lasing. The operation of VCSELs under the conditions stated above has been simulated computationally with an algorithm that solves an approximation of the Maxwell-Bloch equations. (These are nonlinear coupled partial differential equations that model the relevant aspects of the physics of semiconductor lasers.) The results of the simulations show that the intensities of the beams oscillate, out of phase relative to each other, at a frequency that is typically of the order of tens of gigahertz. In particular, one simulation was performed for two coupled VCSELs, each having a circular aperture 5.6 microns in diameter, operating at a wavelength of 980 nm. The results of the simulation showed that the intensities of the two beams oscillated in opposite phase (see Figure 1) at a frequency of 42 GHz. In the far field, the beams were found to be separated by an angle of approx.=8deg. The intensities of the beams were also found to oscillate in the near field, 90deg out of phase with the oscillation in the far field. Figure 2 depicts a simple near-field switching device in which an assembly of microlenses would couple the two oscillating beams to two receivers.

Goorjian, Peter M.; Ning, Cun-Zhen

2004-01-01

116

VCSELs Emitting in the 2–3 µm Wavelength Range  

Microsoft Academic Search

In this chapter, we tried to give a precise picture of the current state of the art of VCSEL technology in the 2–3 µm spectral\\u000a range. We described classical microcavities but also structures with external-cavity geometry which allows one to fabricate\\u000a devices with improved output beam properties (single transverse mode TEM00 operation) at high power. The electrically-pumped microcavities with highest

F. Genty; A. Garnache; L. Cerutti

117

Full control of polarization states and phase distributions of light with dual-metasurfaces  

E-print Network

Control of the phase and polarization states of light is an important goal for nearly all optical research. The development of an efficient optical component that allows the simultaneous manipulation of the polarization and phase distribution is needed. Traditional methods require the combination of multiple optical devices, and a single optical device cannot easily realize full control of light. We theoretically predict and experimentally verify that our proposed dual-metasurfaces provide an excellent means to simultaneously manipulate the phase and polarization of transmission light at the nanoscale. By introducing a phase gradient along the interface, we achieved a near-perfect anomalous refraction with controllable polarization in the near-infrared region. On the basis of these properties, we created a dual-metasurface capable of generating radially polarized beam, demonstrating the power of full control of light. This work opens exciting avenues toward improving the degrees of freedom in the manipulation...

Li, Jianxiong; Yang, Haifang; Li, Junjie; Yu, Ping; Cheng, Hua; Gu, Changzhi; Tian, Jianguo

2014-01-01

118

Electrically Controlled Diffraction Efficiency of Liquid Crystal Fresnel Lens with Polarization-Independence  

Microsoft Academic Search

We demonstrated an electrically controllable Fresnel lens with polarization-independence based on a liquid crystal. The polarization-independence of the Fresnel lens was obtained in an orthogonally aligned hybrid configuration between two adjacent zones. The Fresnel lens was fabricated using a single-masking process of the ultraviolet exposure for the photo-alignment of the LC. The polarization-independence and the electrical tunability of the Fresnel

Dong-Woo Kim; Sin-Doo Lee; Chang-Jae Yu

2007-01-01

119

1.55-m optically pumped tunable VCSEL based on a nano-polymer dispersive liquid crystal phase modulator  

E-print Network

1.55-µm optically pumped tunable VCSEL based on a nano-polymer dispersive liquid crystal phase in a n-PDLC phase layer introduced inside the VCSEL cavity. N-PDLC comprises nematic liquid crystal: Tunable VCSEL, Polymer Dispersed Liquid Crystal, Optical pumping, Distributed Bragg Reflector, Electro

Boyer, Edmond

120

Depth-encoded all-fiber swept source polarization sensitive OCT.  

PubMed

Polarization sensitive optical coherence tomography (PS-OCT) is a functional extension of conventional OCT and can assess depth-resolved tissue birefringence in addition to intensity. Most existing PS-OCT systems are relatively complex and their clinical translation remains difficult. We present a simple and robust all-fiber PS-OCT system based on swept source technology and polarization depth-encoding. Polarization multiplexing was achieved using a polarization maintaining fiber. Polarization sensitive signals were detected using fiber based polarization beam splitters and polarization controllers were used to remove the polarization ambiguity. A simplified post-processing algorithm was proposed for speckle noise reduction relaxing the demand for phase stability. We demonstrated systems design for both ophthalmic and catheter-based PS-OCT. For ophthalmic imaging, we used an optical clock frequency doubling method to extend the imaging range of a commercially available short cavity light source to improve polarization depth-encoding. For catheter based imaging, we demonstrated 200 kHz PS-OCT imaging using a MEMS-tunable vertical cavity surface emitting laser (VCSEL) and a high speed micromotor imaging catheter. The system was demonstrated in human retina, finger and lip imaging, as well as ex vivo swine esophagus and cardiovascular imaging. The all-fiber PS-OCT is easier to implement and maintain compared to previous PS-OCT systems and can be more easily translated to clinical applications due to its robust design. PMID:25401008

Wang, Zhao; Lee, Hsiang-Chieh; Ahsen, Osman Oguz; Lee, ByungKun; Choi, WooJhon; Potsaid, Benjamin; Liu, Jonathan; Jayaraman, Vijaysekhar; Cable, Alex; Kraus, Martin F; Liang, Kaicheng; Hornegger, Joachim; Fujimoto, James G

2014-09-01

121

Depth-encoded all-fiber swept source polarization sensitive OCT  

PubMed Central

Polarization sensitive optical coherence tomography (PS-OCT) is a functional extension of conventional OCT and can assess depth-resolved tissue birefringence in addition to intensity. Most existing PS-OCT systems are relatively complex and their clinical translation remains difficult. We present a simple and robust all-fiber PS-OCT system based on swept source technology and polarization depth-encoding. Polarization multiplexing was achieved using a polarization maintaining fiber. Polarization sensitive signals were detected using fiber based polarization beam splitters and polarization controllers were used to remove the polarization ambiguity. A simplified post-processing algorithm was proposed for speckle noise reduction relaxing the demand for phase stability. We demonstrated systems design for both ophthalmic and catheter-based PS-OCT. For ophthalmic imaging, we used an optical clock frequency doubling method to extend the imaging range of a commercially available short cavity light source to improve polarization depth-encoding. For catheter based imaging, we demonstrated 200 kHz PS-OCT imaging using a MEMS-tunable vertical cavity surface emitting laser (VCSEL) and a high speed micromotor imaging catheter. The system was demonstrated in human retina, finger and lip imaging, as well as ex vivo swine esophagus and cardiovascular imaging. The all-fiber PS-OCT is easier to implement and maintain compared to previous PS-OCT systems and can be more easily translated to clinical applications due to its robust design. PMID:25401008

Wang, Zhao; Lee, Hsiang-Chieh; Ahsen, Osman Oguz; Lee, ByungKun; Choi, WooJhon; Potsaid, Benjamin; Liu, Jonathan; Jayaraman, Vijaysekhar; Cable, Alex; Kraus, Martin F.; Liang, Kaicheng; Hornegger, Joachim; Fujimoto, James G.

2014-01-01

122

Independent control of differently-polarized waves using anisotropic gradient-index metamaterials  

PubMed Central

We propose a kind of anisotropic gradient-index (GRIN) metamaterials, which can be used to control differently-polarized waves independently. We show that two three- dimensional (3D) planar lenses made of such anisotropic GRIN metamaterials are able to make arbitrary beam deflections for the vertical (or horizontal) polarization but have no response to the horizontal (or vertical) polarization. Then the vertically- and horizontally-polarized waves are separated and controlled independently to deflect to arbitrarily different directions by designing the anisotropic GRIN planar lenses. We make experimental verifications of the lenses using such a special metamaterial, which has both electric and magnetic responses simultaneously to reach approximately equal permittivity and permeability. Hence excellent impedance matching is obtained between the GRIN planar lenses and the air. The measurement results demonstrate good performance on the independent controls of differently-polarized waves, as observed in the numerical simulations. PMID:25231412

Ma, Hui Feng; Wang, Gui Zhen; Jiang, Wei Xiang; Cui, Tie Jun

2014-01-01

123

Independent control of differently-polarized waves using anisotropic gradient-index metamaterials.  

PubMed

We propose a kind of anisotropic gradient-index (GRIN) metamaterials, which can be used to control differently-polarized waves independently. We show that two three- dimensional (3D) planar lenses made of such anisotropic GRIN metamaterials are able to make arbitrary beam deflections for the vertical (or horizontal) polarization but have no response to the horizontal (or vertical) polarization. Then the vertically- and horizontally-polarized waves are separated and controlled independently to deflect to arbitrarily different directions by designing the anisotropic GRIN planar lenses. We make experimental verifications of the lenses using such a special metamaterial, which has both electric and magnetic responses simultaneously to reach approximately equal permittivity and permeability. Hence excellent impedance matching is obtained between the GRIN planar lenses and the air. The measurement results demonstrate good performance on the independent controls of differently-polarized waves, as observed in the numerical simulations. PMID:25231412

Ma, Hui Feng; Wang, Gui Zhen; Jiang, Wei Xiang; Cui, Tie Jun

2014-01-01

124

Electrically-pumped directly-modulated tunable VCSEL for metro DWDM applications  

Microsoft Academic Search

We report the first electrically pumped tunable VCSELs with continuous tuning in 1530-1620 nm wavelength regime. The VCSELs are directly modulated at 2.5 Gbps (OC-48) rates and show error-free transmissions. Wavelength locking to ITU-grids are accomplished in 200 ?s

W. Yuen; G. S. Li; R. F. Nabiev; M. Jansen; D. Davis; C. J. Chang-Hasnain

2001-01-01

125

Characterizing Absorption Spectrum of Natural Rubidium by Using a Directly Modulated VCSEL  

E-print Network

Characterizing Absorption Spectrum of Natural Rubidium by Using a Directly Modulated VCSEL Ido Ben in the absorption profile of a medium containing system atoms. Moreover, the change leads to a very narrow spectra: the VCSEL output and the absorption. Two modulation side bands, separated by fhfs owe to coincide

Eisenstein, Gadi

126

IEEE PHOTONICS TECHNOLOGY LETTERS. VOL. 7, NO. 5. MAY 1995 Coherence of VCSEL's for  

E-print Network

to temperature-induced mismatch of the mirror reflectivity and gain spectra. For the 15-pmVCSEL the emission at high currents. In this letter we report a study of the coherence of the emission of gain-guided Al interconnect. The VCSEL's used in the study had an n-type mirror consisting of 32 periods of AIAs

Rocca, Jorge J.

127

VCSEL arrays for high-aggregate bandwidth of up to 1.34 Tbps  

NASA Astrophysics Data System (ADS)

Even though the lane speed of VCSEL based AOC and transceivers has reached 25 Gbps and beyond [1-7], parallel optics are getting even more important in order to meet the increasing demand for aggregate bandwidths in upcoming applications, among others, 100 Gigabit Ethernet, Infiniband EDR, or EOM (embedded optical modules). As 100 Gbps can be achieved by, e.g., 4 times 25 Gbps using standard QSFP form factor, different approaches are using large scale 2D VCSEL arrays operating at lower lane speeds. Early work on 2D VCSEL based transceivers has already been presented beginning of this century [8] and recent work also addressed the potential of this technology [9,10]. In 2013, Compass EOS has introduced a 1.34 Tbps core router solution [11,12,13] that incorporates 2D VCSEL arrays of 14x12 emitters designed and manufactured by Philips U-L-M Photonics. The VCSEL array is mounted face down onto a CMOS ASIC, directly on top of the analog area. The emission wavelength of 1000 nm allows for substrate side emission and thus for flip-chip mounting as well as the possibility of integrating 2D microlens arrays onto the stack of CMOS and VCSEL array. After briefly introducing the router with regard to the incorporated VCSEL technology we discuss the design and performance of the VCSEL array. Finally, the assembly solution for this most compact and dense transceiver solution is presented.

Grabherr, Martin; Intemann, Steffan; King, Roger; Wabra, Stefan; Jäger, Roland; Riedl, Michael

2014-02-01

128

Ultra high-speed electro-optically modulated VCSELs: modeling and experimental results  

Microsoft Academic Search

We have studied the modulation properties of a vertical cavity surface-emitting laser (VCSEL) coupled to an electrooptical modulator. It is shown that, if the modulator is placed in a resonant cavity, the modulation of the light output power is governed predominantly by electrooptic, or electrorefraction effect rather than by electroabsorption. A novel concept of electrooptically modulated (EOM) VCSEL based on

V. A. Shchukin; N. N. Ledentsov; J. A. Lott; H. Quast; F. Hopfer; L. Ya. Karachinsky; M. Kuntz; P. Moser; A. Mutig; A. Strittmatter; V. P. Kalosha; D. Bimberg

2008-01-01

129

Polarization-state control schemes for heterodyne or homodyne optical fiber communications  

Microsoft Academic Search

In heterodyne or homodyne optical fiber communications, the fluctuation of the polarization state in the fiber may deteriorate the receiver sensitivity. This paper reviews the principles and features of six polarization-state control schemes so far proposed, including two new attempts, one using Faraday rotators and the other using rotatable fiber cranks (RFC's), both of which have been proposed very recently.

Takanori Okoshi

1985-01-01

130

Blazed vector gratings fabricated using photosensitive polymer liquid crystals and control of polarization diffraction  

NASA Astrophysics Data System (ADS)

The blazed vector grating possessing antisymmetric distributions of the birefringence were fabricated by exposing the line-focused linearly polarized ultraviolet light on the photosensitive polymer liquid crystals. The polarization states of the diffraction beams can be highly and widely controlled by designing the blazed structures, and the diffraction properties were well-explained by Jones calculus.

Ono, Hiroshi; Kuzuwata, Mitsuru; Sasaki, Tomoyuki; Noda, Kohei; Kawatsuki, Nobuhiro

2014-03-01

131

Multichannel free-space optical switch using liquid-crystal polarization-control devices  

Microsoft Academic Search

This paper describes a four-channel optical switch module prototype for a reconfigurable optical interconnection network using a polarization-switched architecture and liquid crystal polarization control devices. Compact size and low insertion loss have been achieved by using integrated optical elements. The successful switching of 1 Gbps optical signals with little skew has been demonstrated.

Tsuyoshi Yamamoto; Jayantilal S. Patel; Takakiyo Nakagami

1993-01-01

132

Design and fabrication of polymer microlenses arrays for VCSELs using a cantilever based microsystem  

NASA Astrophysics Data System (ADS)

We report on the design and the fabrication of refractive microlenses using a polymer droplet deposition microsystem. The principle of this original technique consists in monomer droplets deposition using a robotized silicon-microcantilevers array. The advantages of this technique rely on the control of droplets dimensions and the positioning accuracy. Microlenses have been first modelled to optimize their geometrical parameters for VCSEL collimation. Results of lens optimization as well as the influence of the fabrication parameters fluctuations on the final divergence are detailed. First results on droplets deposition are presented, demonstrating the technique feasibility. Finally, the possibility of the modification of the surface energy to obtain the most suited contact angle before deposition is also discussed.

Bardinal, Véronique; Daran, Emmanuelle; Vergnenègre, Corinne; Leïchlé, Thierry; Segui, Yvan; Camps, Thierry; Pourciel, Jean-Bernard; Conedera, Véronique; Gavin-Djidina, Léonard; Guirardel, Mathieu

2006-04-01

133

Regulation of somatic myosin activity by Protein Phosphatase 1? controls Drosophila oocyte polarization  

PubMed Central

The Drosophila body axes are established in the oocyte during oogenesis. Oocyte polarization is initiated by Gurken, which signals from the germline through the epidermal growth factor receptor (Egfr) to the posterior follicle cells (PFCs). In response the PFCs generate an unidentified polarizing signal that regulates oocyte polarity. We have identified a loss-of-function mutation of flapwing, which encodes the catalytic subunit of Protein Phosphatase 1? (PP1?) that disrupts oocyte polarization. We show that PP1?, by regulating myosin activity, controls the generation of the polarizing signal. Excessive myosin activity in the PFCs causes oocyte mispolarization and defective Notch signaling and endocytosis in the PFCs. The integrated activation of JAK/STAT and Egfr signaling results in the sensitivity of PFCs to defective Notch. Interestingly, our results also demonstrate a role of PP1? in generating the polarizing signal independently of Notch, indicating a direct involvement of somatic myosin activity in axis formation. PMID:21490061

Sun, Yi; Yan, Yan; Denef, Natalie; Schüpbach, Trudi

2011-01-01

134

Theory of configuration control of metallic nanocomposites by light fields with designed polarization distributions  

Microsoft Academic Search

We have theoretically demonstrated the dynamics control of metallic nanoparticles by light-induced force with axially-symmetric polarized laser beam. We clarify the possibility of fabrication of metallic nanocomposite with high rotational symmetry.

Hironori Hattori; Shimpei Hidaka; Takuya Iida

2011-01-01

135

Environmental control of cloud-to-ground lightning polarity in severe storms  

E-print Network

In this study, it is hypothesized that the mesoscale environment can indirectly control the cloud-to-ground (CG) lightning polarity of severe storms by directly affecting their structural, dynamical, and microphysical properties, which in turn...

Buffalo, Kurt Matthew

2009-05-15

136

Photonic spin Hall effect in hyperbolic metamaterials for polarization-controlled routing of subwavelength modes.  

PubMed

The routing of light in a deep subwavelength regime enables a variety of important applications in photonics, quantum information technologies, imaging and biosensing. Here we describe and experimentally demonstrate the selective excitation of spatially confined, subwavelength electromagnetic modes in anisotropic metamaterials with hyperbolic dispersion. A localized, circularly polarized emitter placed at the boundary of a hyperbolic metamaterial is shown to excite extraordinary waves propagating in a prescribed direction controlled by the polarization handedness. Thus, a metamaterial slab acts as an extremely broadband, nearly ideal polarization beam splitter for circularly polarized light. We perform a proof of concept experiment with a uniaxial hyperbolic metamaterial at radio-frequencies revealing the directional routing effect and strong subwavelength ?/300 confinement. The proposed concept of metamaterial-based subwavelength interconnection and polarization-controlled signal routing is based on the photonic spin Hall effect and may serve as an ultimate platform for either conventional or quantum electromagnetic signal processing. PMID:24526135

Kapitanova, Polina V; Ginzburg, Pavel; Rodríguez-Fortuño, Francisco J; Filonov, Dmitry S; Voroshilov, Pavel M; Belov, Pavel A; Poddubny, Alexander N; Kivshar, Yuri S; Wurtz, Gregory A; Zayats, Anatoly V

2014-01-01

137

An Automatic Control System for Compensating Cross-Polarization Coupling in Frequency-Reuse Communication Systems  

Microsoft Academic Search

In frequency-reuse communication systems using orthogonally polarized waves, depolarization due mainly to rain and Faraday rotation (in satellite systems) reduces channel isolation. The control system described, incorporating a network suggested by T. S. Chu, automatically compensates for cross-polarization coupling without using iterative methods or computations. Control voltages are generated on the receive side by phase-sensitive demodulation of beacons contained in

H. Kannowade

1976-01-01

138

Environmental control of cloud-to-ground lightning polarity in severe storms  

E-print Network

ENVIRONMENTAL CONTROL OF CLOUD-TO-GROUND LIGHTNING POLARITY IN SEVERE STORMS A Thesis by KURT MATTHEW BUFFALO Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment... of the requirements for the degree of MASTER OF SCIENCE December 2007 Major Subject: Atmospheric Sciences ENVIRONMENTAL CONTROL OF CLOUD-TO-GROUND LIGHTNING POLARITY IN SEVERE STORMS A Thesis by KURT MATTHEW...

Buffalo, Kurt Matthew

2008-10-10

139

Control and characterization of multiple circularly polarized femtosecond filaments in argon.  

PubMed

We provide what is believed to be the first experimental evidence of spatial control on multiple filamentation (MF) using circularly polarized femtosecond laser pulses. The exceptional shot-to-shot reproducibility of the MF pattern allowed complete characterization of the two copropagating high-energy filaments, revealing for the first time temporal (self-) compression of circularly polarized filamenting pulses to a fifth of the initial 57 fs laser pulse duration without any sophisticated chirp control. Compared with LP MF, an enhancement in spatial stability and an increase in energy throughput are reported for circular input polarization. PMID:17572735

Trisorio, A; Hauri, C P

2007-06-15

140

Wide continuously tunable 1.55mum vertical air-cavity wavelength selective elements for filters and VCSELs using micromachined actuation (Invited Paper)  

Microsoft Academic Search

Tailored scaling allows the effectiveness of physical effects and mechanical stability to be enhanced. This is shown for micromachined 1.55mum vertical-resonator-based filters and VCSELs, capable of wide, continuous, and kink-free tuning by a single control parameter. Tuning is achieved by mechanically actuating one or several membranes in a vertical air-gap resonator including two highly reflective DBR mirrors. Electrostatically actuatable single-chip

H. Hillmer; A. Tarraf; F. Riemenschneider; S. Irmer; H. Halbritter; J. Daleiden; F. Romer; C. Prott; E. Ataro; A. Hasse; M. Strassner; S. Hansmann; P. Meissner

2005-01-01

141

Realization of microcontroller-based polarization control system with genetic algorithm  

Microsoft Academic Search

Realization of a PIC32 microcontroller-based polarization control system is described. Genetic algorithm is used for control purposes. The controller measures the signal intensity to estimate the genetic value. To reach optimum performance, the code is optimized by using the best genetic parameter to achieve the fastest execution time. This algorithm consumes low size of memory besides providing fast speed. The

Ghazaleh Mamdoohi; Aida Esmailian; Ahmad Fauzi Abas; Khairulmizam Samsudin; Ariya Hidayat; Noor Hisham Ibrahim; Mohd Adzir Mahdi

2009-01-01

142

High Efficacy Green LEDs by Polarization Controlled MOVPE  

SciTech Connect

Amazing performance in GaInN/GaN based LEDs has become possible by advanced epitaxial growth on a wide variety of substrates over the last decade. An immediate push towards product development and worldwide competition for market share have effectively reduced production cost and generated substantial primary energy savings on a worldwide scale. At all times of the development, this economic pressure forced very fundamental decisions that would shape huge industrial investment. One of those major aspects is the choice of epitaxial growth substrate. The natural questions are to what extend a decision for a certain substrate will limit the ultimate performance and to what extent, the choice of a currently more expensive substrate such as native GaN could overcome any of the remaining performance limitations. Therefore, this project has set out to explore what performance characteristic could be achieved under the utilization of bulk GaN substrate. Our work was guided by the hypotheses that line defects such as threading dislocations in the active region should be avoided and the huge piezoelectric polarization needs to be attenuated – if not turned off – for higher performing LEDs, particularly in the longer wavelength green and deep green portions of the visible spectrum. At their relatively lower performance level, deep green LEDs are a stronger indicator of relative performance improvements and seem particular sensitive to the challenges at hand. The project therefore made use of recently developed non-polar and semipolar bulk GaN substrates that were made available at Kyma Technologies by crystallographic cuts from thick polar growth of GaN. This approach naturally leads to rather small pieces of substrates, cm along the long side while mm along the short one. Small size and limited volume of sample material therefore set the limits of the ensuing development work. During the course of the project we achieved green and deep green LEDs in all those crystal growth orientations: polar c-plane, non- polar a-plane, non-polar m-plane, and semipolar planes. The active region in those structures shows dramatically reduced densities of threading dislocations unless the wavelength was extended as far as 510 nm and beyond. With the appearance of such defects, the light output power dropped precipitously supporting the necessity to avoid any and all of such defects to reach the active region. Further aspects of the non-polar growth orientation proved extremely promising for the development of such structures. Chief among them is our success to achieve extremely uniform quantum wells in these various crystal orientations that prove devoid of any alloy fluctuation beyond the theoretical limit of a binominal distribution. This became very Rensselaer Wetzel DE?EE0000627 3 directly apparent in highly advanced atom probe tomography performed in collaboration at Northwestern University. Furthermore, under reduced or absence of piezoelectric polarization, green emitters in those growth geometries exhibit an unsurpassed wavelength stability over very wide excitation and drive current ranges. Such a performance had not been possible in any polar c-plane growth and now places green LEDs in terms of wavelength stability up par with typical 450 nm blue emitters. The project also incorporated enabling opportunities in the development of micro and nano- patterned substrate technologies. Originally developped as a means to enhance generated light extraction we have demonstrated that the method of nano-patterning, in contrast to micro- patterning also results in a substantial reduction of threading dislocation generation. In green LEDs, we thereby see equal contributions of enhanced light extraction and reduced defect generation to a threefold enhancement of the green light output power. These results have opened entirely new approaches for future rapid and low cost epitaxial material development by avoidance of thick defect accommodation layers. All methods developed within this project have meanwhile widely been publicized by the members o

Wetzel, Christian

2013-03-31

143

Electrically Injected Spin Polarized Lasers  

NASA Astrophysics Data System (ADS)

The ability to electrically modulate orthogonal polarization states in spin-polarized lasers opens up avenues for a wide range of applications such as photochemical spectroscopy, optical switches, and communications with enhanced security [1]. This has motivated us to investigate the properties of quantum well (QW) [2] and quantum dot (QD) [3] spin-polarized vertical cavity surface emitting lasers (spin-VCSELs). The laser heterostructures are grown by molecular beam epitaxy (MBE). The active region consists of In0.2Ga0.8As/GaAs QWs [2] or InAs QDs [3]. VCSELs are fabricated using standard micro-fabrication techniques. The FM Schottky tunnel contact is realized with Fe or MnAs re-grown by MBE. The QW spin-VCSELs exhibit a maximum threshold current reduction of 11 % and output degree of circular polarization of 23 % at 50 K. The corresponding values observed in QD spin VCSELs at 200 K are 8 % and 14 %, respectively. Inhibition of the D'yakonov-Perel spin scattering process results in higher operating temperatures for spin-lasers with QD active region. In addition, we have demonstrated electrical modulation of the output polarization with a peak modulation index of 0.6. The spin polarization of carriers in the active region of a spin laser gives rise to large gain anisotropy at biases near threshold. As a result, the output polarization can be much larger than the spin polarization of the injected carriers. This is contrary to the linear relation between carrier spin orientations in the active region and the polarization of photons emitted upon their radiative recombination in spin light emitting diodes. The exact magnitude of the output polarization in spin lasers and the parameters upon which it depends have been analytically determined and are in excellent agreement with those obtained from measurements. These results will be described and discussed. [4pt] References: [0pt] [1] M. Holub et al., J. Phys. D. 40, R179 (2007). [0pt] [2] M. Holub et al., Phys. Rev. Lett. 98, 146603 (2007). [0pt] [3] D. Basu et al., Appl. Phys. Lett. 92, 091119 (2008). [0pt] [4] M. I. D'yakonov et al., Sov. Phys Solid State. 13, 3023 (1971)

Bhattacharya, Pallab

2009-03-01

144

Final report on LDRD project : narrow-linewidth VCSELs for atomic microsystems.  

SciTech Connect

Vertical-cavity surface-emitting lasers (VCSELs) are well suited for emerging photonic microsystems due to their low power consumption, ease of integration with other optical components, and single frequency operation. However, the typical VCSEL linewidth of 100 MHz is approximately ten times wider than the natural linewidth of atoms used in atomic beam clocks and trapped atom research, which degrades or completely destroys performance in those systems. This report documents our efforts to reduce VCSEL linewidths below 10 MHz to meet the needs of advanced sub-Doppler atomic microsystems, such as cold-atom traps. We have investigated two complementary approaches to reduce VCSEL linewidth: (A) increasing the laser-cavity quality factor, and (B) decreasing the linewidth enhancement factor (alpha) of the optical gain medium. We have developed two new VCSEL devices that achieved increased cavity quality factors: (1) all-semiconductor extended-cavity VCSELs, and (2) micro-external-cavity surface-emitting lasers (MECSELs). These new VCSEL devices have demonstrated linewidths below 10 MHz, and linewidths below 1 MHz seem feasible with further optimization.

Chow, Weng Wah; Geib, Kent Martin; Peake, Gregory Merwin; Serkland, Darwin Keith

2011-09-01

145

Final report on LDRD project :leaky-mode VCSELs for photonic logic circuits.  

SciTech Connect

This report describes the research accomplishments achieved under the LDRD Project ''Leaky-mode VCSELs for photonic logic circuits''. Leaky-mode vertical-cavity surface-emitting lasers (VCSELs) offer new possibilities for integration of microcavity lasers to create optical microsystems. A leaky-mode VCSEL output-couples light laterally, in the plane of the semiconductor wafer, which allows the light to interact with adjacent lasers, modulators, and detectors on the same wafer. The fabrication of leaky-mode VCSELs based on effective index modification was proposed and demonstrated at Sandia in 1999 but was not adequately developed for use in applications. The aim of this LDRD has been to advance the design and fabrication of leaky-mode VCSELs to the point where initial applications can be attempted. In the first and second years of this LDRD we concentrated on overcoming previous difficulties in the epitaxial growth and fabrication of these advanced VCSELs. In the third year, we focused on applications of leaky-mode VCSELs, such as all-optical processing circuits based on gain quenching.

Hargett, Terry W.; Hadley, G. Ronald; Serkland, Darwin Keith; Blansett, Ethan L.; Geib, Kent Martin; Sullivan, Charles Thomas; Keeler, Gordon Arthur; Bauer, Thomas; Ongstand, Andrea; Medrano, Melissa R.; Peake, Gregory Merwin; Montano, Victoria A.

2005-11-01

146

Fast and controllable switching the circulation and polarity of magnetic vortices  

NASA Astrophysics Data System (ADS)

We report a method to switch both the circulation and polarity of magnetic vortices in a controlled manner within a nanosecond utilizing micromagnetic simulations. The controllable switching is achieved with the combination of two different types of magnetic field pulses on submicron permalloy disks with heptagonal shape. When a magnetic field pulse of ~100 mT is applied along one of the edge directions of the heptagon, the circulation of the vortex can be manipulated according to the pulse direction. When a pair of pulses with a few tens of mT in magnitude and relative delay of about 100 ps is applied in orthogonal directions, the polarity can be further controlled without influencing the circulation. The different magnitude of switching fields allows for the combination of both types of pulses in the control of both the circulation and polarity of magnetic vortices. The switching mechanism and the controlling parameters for disks with diameters of 500 and 700 nm are discussed.

Wen, Y.; Feng, Z.; Miao, B. F.; Cao, R. X.; Sun, L.; You, B.; Wu, D.; Zhang, W.; Jiang, Z. S.; Cheng, R.; Ding, H. F.

2014-12-01

147

Liquid crystals for polarization control in the MWIR  

NASA Astrophysics Data System (ADS)

Liquid crystal (LC) technology, a critical component in a diverse range of optics for visible wavelengths, has recently been adapted into devices for the mid-wave infrared (MWIR). Optics designs, including variable retarders, attenuators, linear polarization rotators, and tunable filters, have been modified for optimal performance over the range of 3.6 to 5.7 microns. We constructed these designs using material selected for optimal optical behavior in this wavelength range. Description and characterization of these chosen component materials is included along with the performance of each device. We present design challenges, along with future plans and possibilities for MWlR LC technology.

Petrak, Erika K.; Baur, Thomas G.

2014-05-01

148

Full control of magnetism in a manganite bilayer by ferroelectric polarization  

SciTech Connect

An oxide heterostructure made of manganite bilayers and ferroelectric perovskites is predicted to lead to the full control of magnetism when switching the ferroelectric polarizations. By using asymmetric polar interfaces in the superlattices, more electrons occupy the Mn layer at the n-type interface side than at the p-type side. This charge disproportionation can be enhanced or suppressed by the ferroelectric polarization. Quantum model and density functional theory calculations reach the same conclusion: a ferromagnetic-ferrimagnetic phase transition with maximal change >90% of the total magnetization can be achieved by switching the polarization s direction. This function is robust and provides full control of the magnetization s magnitude, not only its direction, via electrical methods.

Dong, Shuai [Southeast University, Nanjing, China] [Southeast University, Nanjing, China; Dagotto, Elbio R [ORNL] [ORNL

2013-01-01

149

Magnetic control of transverse electric polarization in BiFeO3  

NASA Astrophysics Data System (ADS)

Numerous attempts have been made to realize crossed coupling between ferroelectricity and magnetism in multiferroic materials at room temperature. BiFeO3 is the most extensively studied multiferroic material that shows multiferroicity at temperatures significantly above room temperature. Here we present high-field experiments on high-quality mono-domain BiFeO3 crystals reveal substantial electric polarization orthogonal to the widely recognized one along the trigonal c axis. This novel polarization appears to couple with the domains of the cycloidal spin order and, hence, can be controlled using magnetic fields. The transverse polarization shows the non-volatile memory effect at least up to 300?K.

Tokunaga, M.; Akaki, M.; Ito, T.; Miyahara, S.; Miyake, A.; Kuwahara, H.; Furukawa, N.

2015-01-01

150

Using Polarization to Control the Phase of Spatial Modes for Application in Quantum Information  

NASA Astrophysics Data System (ADS)

Exploiting spatial modes and polarization, we experimentally demonstrate the realization of a conditional ?-phase shift. Our approach is based on an optical circuit where the polarization and transverse degrees of freedom control the Gouy phase which is applied on Hermite-Gaussian beams. Our results show good wo-qubit states has beengood agreement with the simulation of the optical circuit. As an application, we propose the implementation of a two-qubit quantum phase gate, where the qubits are encoded on the Hermite-Gaussian modes and linear polarization states.

Balthazar, W. F.; Caetano, D. P.; Souza, C. E. R.; Huguenin, J. A. O.

2014-12-01

151

Magnetic field controlled reversal of ferroelectric polarization in conical spin ordered multiferroics: Monte Carlo simulation  

NASA Astrophysics Data System (ADS)

To understand the fascinating multiferroicity observed in CoCr2O4, Monte Carlo simulation is performed on a three-dimensional spinel lattice with classical Heisenberg spins. The conical spin order is confirmed to be the origin of the peculiar magnetoelectric behavior with coexisting magnetization and ferroelectric polarization. Furthermore, the simultaneous reversals of magnetization and polarization controlled by the external magnetic field are reproduced, consisting with the experimental observation qualitatively. It is revealed that, from the microscopic structures of spins, the axis of spin cone provides a "handle," with which the magnetization and polarization can be reversed by the magnetic field easily.

Yao, Xiaoyan; Lo, Veng Cheong; Liu, Jun-Ming

2009-10-01

152

Controlling the chirality and polarity of vortices in magnetic tunnel junctions  

NASA Astrophysics Data System (ADS)

Static and dynamic control of the chirality and polarity of a magnetic vortex confined in a magnetic tunnel junction is demonstrated. The modes associated with the four chirality/polarity vortex configurations are first explored by resonant excitation with a low power rf current. When the rf power is increased, both the chirality and polarity of the vortex can be resonantly switched, which—as shown by micromagnetic simulations—involves vortex expulsion and renucleation. This tunable resonant switching of the vortex parameters are an exciting step forward for the viability of magnetic vortex-based applications.

Jenkins, A. S.; Grimaldi, E.; Bortolotti, P.; Lebrun, R.; Kubota, H.; Yakushiji, K.; Fukushima, A.; de Loubens, G.; Klein, O.; Yuasa, S.; Cros, V.

2014-10-01

153

Electric control of state of polarization in index-guiding photonic liquid crystal fibers  

NASA Astrophysics Data System (ADS)

Photonic liquid crystal fibers allow for dynamic modification of their guiding and polarization properties. In particular it is possible to dynamically tune phase delay between two orthogonal polarization of the guided mode. In this work an index-guiding photonic liquid crystal fiber with highly tunable retardation, reaching value of 15? (or 30? in terms of phase difference) is presented. Electric tuning with two sets of electrodes is also discussed and demonstrated proving that photonic liquid crystal fibers can be utilized as a all-in-fiber polarization controllers.

Ertman, Slawomir; Siarkowska, Agata; Pysz, Dariusz; Buczy?ski, Ryszard; Nowinowski-Kruszelnicki, Edward; DÄ browski, Roman; Woli?ski, Tomasz R.

2013-05-01

154

Control of Fibrinogen Assembly by Changing a Polarity of Surfaces  

NASA Astrophysics Data System (ADS)

Thrombogenesis causes various problems associated with an interruption in the blood flow (e.g., myocardial and cerebral infarction), and a hindrance to use of blood-contact vascular biomaterials (e.g., hemodialysis and cardiopulmonary bypass) with long-term patency since undesired adsorption of blood components occurs on vessels or biomaterials, such as surface-induced thrombosis. we showed that this clotting procedure can be occurred on hydrophobic polymeric surfaces without thrombin cleavage. However, the fibrinogen fibers were not formed on the polar surface such as spun-cast polymer film with pyridine and phenol groups. We also found that ?C domains play an important role in initiation of polymerization on surface. Therefore, molecular association was inhibited on the polar surfaces due to confinement of ?C chains on the surfaces. These findings were directly applied to stent surface modification. The commercial stent consist of Co-Cr alloy forms undesired fiber formation. However, PS-r-PVPh (13% phenol) coated stent surfaces completely prevent fiber formation.

Koo, Jaseung; Liu, Ying; Snow, Sara; Rambhia, Pooja; Koga, Tadanori; Rafailovich, Miriam; Galanakis, Dennis

2009-03-01

155

Magnetic field controlled reversal of ferroelectric polarization in conical spin ordered multiferroics: Monte Carlo simulation  

Microsoft Academic Search

To understand the fascinating multiferroicity observed in CoCr2O4, Monte Carlo simulation is performed on a three-dimensional spinel lattice with classical Heisenberg spins. The conical spin order is confirmed to be the origin of the peculiar magnetoelectric behavior with coexisting magnetization and ferroelectric polarization. Furthermore, the simultaneous reversals of magnetization and polarization controlled by the external magnetic field are reproduced, consisting

Xiaoyan Yao; Veng Cheong Lo; Jun-Ming Liu

2009-01-01

156

Wavelength control with grating imprinted fiber Sagnac loop mirror by polarization and strain tuning  

Microsoft Academic Search

Wavelength control by the use of fiber Bragg grating (FBG) imprinted polarization maintaining fiber (PMF) Sagnac loop mirror (SLM) is proposed and demonstrated through polarization and strain tuning. The Bragg wavelengths of the FBG in the PMF along slow or fast axis show redshifts with the increase in strain with sensitivities of 8.77×10-4 and 9.11×10-4 nm\\/mu?, respectively, whereas the interferometric

Ping Lu; Liqiu Men; Qiying Chen

2009-01-01

157

Optical Endless Polarization Stabilization at 9 krad\\/s With FPGA-Based Controller  

Microsoft Academic Search

We demonstrate endless polarization stabilization with a control speed of up to 9 krad\\/s, over random Poincare sphere trajectories. These are in total >35 Mrad long, are composed in particular of difficult-to-track circles with all radii and orientations, and thereby include all possible worst cases. The maximum polarization mismatch and relative intensity errors are 0.13 rad and 0.43%, respectively. The

Benjamin Koch; Ariya Hidayat; Hongbin Zhang; Vitali Mirvoda; Manfred Lichtinger; David Sandel; Reinhold Noe

2008-01-01

158

Coherent Terahertz Polarization Control through Manipulation of Electron Trajectories Haidan Wen1  

E-print Network

Coherent Terahertz Polarization Control through Manipulation of Electron Trajectories Haidan Wen1 radiation whose spectrum is out of the reach of conventional lasing media, methods are needed for manipulating and controlling the electron dy- namics associated with nonlinear light-matter interactions

159

All-fiber narrowband polarization controller based on coherent acousto-optic mode coupling in single-mode fiber.  

PubMed

An all-fiber, narrowband, tunable polarization controller is proposed and demonstrated. The device is based on coherent acousto-optic mode coupling induced by two orthogonal acoustic waves on a dispersion-compensating fiber. The cooperative coupling between the two polarizations of the core mode and the TE01 cladding mode through the two gratings permits indirect coupling between the two polarizations of the core mode with nearly 100% efficiency, which makes the polarization-controlling function possible. Experimental results verify the operation of the polarization controller with an insertion loss of <1 dB. PMID:15532288

Dashti, Pedram Z; Li, Qun; Lee, Henry P

2004-10-15

160

Interplanetary magnetic field control of Saturn's polar cusp aurora  

NASA Astrophysics Data System (ADS)

Dayside UV emissions in Saturn's polar ionosphere have been suggested to be the first observational evidence of the kronian "cusp" (Gérard et al., 2004). The emission has two distinct states. The first is a bright arc-like feature located in the pre-noon sector, and the second is a more diffuse "spot" of aurora which lies poleward of the general location of the main auroral oval, which may be related to different upstream interplanetary magnetic field (IMF) orientations. Here we take up the suggestion that these emissions correspond to the cusp. However, direct precipitation of electrons in the cusp regions is not capable of producing significant UV aurora. We have therefore investigated the possibility that the observed UV emissions are associated with reconnection occurring at the dayside magnetopause, possibly pulsed, akin to flux transfer events seen at the Earth. We devise a conceptual model of pulsed reconnection at the low-latitude dayside magnetopause for the case of northwards IMF which will give rise to pulsed twin-vortical flows in the magnetosphere and ionosphere in the vicinity of the open-closed field-line boundary, and hence to bi-polar field-aligned currents centred in the vortical flows. During intervals of high-latitude lobe reconnection for southward IMF, we also expect to have pulsed twin-vortical flows and corresponding bi-polar field-aligned currents. The vortical flows in this case, however, are displaced poleward of the open-closed field line boundary, and are reversed in sense, such that the field-aligned currents are also reversed. For both cases of northward and southward IMF we have also for the first time included the effects associated with the IMF By effect. We also include the modulation introduced by the structured nature of the solar wind and IMF at Saturn's orbit by developing "slow" and "fast" flow models corresponding to intermediate and high strength IMF respectively. We then consider the conditions under which the plasma populations appropriate to either sub-solar reconnection or high-latitude lobe reconnection can carry the currents indicated. We have estimated the field-aligned voltages required, the resulting precipitating particle energy fluxes, and the consequent auroral output. Overall our model of pulsed reconnection under conditions of northwards and southwards IMF, and for varying orientations of IMF By, is found to produce a range of UV emission intensities and geometries which is in good agreement with the data presented by Gérard et al. (2004). The recent HST-Cassini solar wind campaign provides a unique opportunity to test the theoretical ideas presented here.

Bunce, E. J.; Cowley, S. W. H.; Milan, S. E.

2005-06-01

161

Symmetry controlled spin polarized conductance in au nanowires.  

PubMed

The fact that the resistance of propagating electrons in solids depends on their spin orientation has led to a new field called spintronics. With the parallel advances in nanoscience, it is now possible to talk about nanospintronics. Many works have focused on the study of charge transport along nanosystems, such as carbon nanotubes, graphene nanoribbons, or metallic nanowires, and spin dependent transport properties at this scale may lead to new behaviors due to the manipulation of a small number of spins. Metal nanowires have been studied as electric contacts where atomic and molecular insertions can be constructed. Here we describe what might be considered the ultimate spin device, namely, a Au thin nanowire with one Co atom bridging its two sides. We show that this system has strong spin dependent transport properties and that its local symmetry can dramatically change them, leading to a significant spin polarized conductance. PMID:18597461

Pontes, Renato B; da Silva, E Z; Fazzio, A; da Silva, Antônio J R

2008-07-30

162

The control system of the polarized internal target of ANKE at COSY  

NASA Astrophysics Data System (ADS)

The polarized internal target for the ANKE experiment at the Cooler Synchrotron COSY of the Forschungszentrum Jülich utilizes a polarized atomic beam source to feed a storage cell with polarized hydrogen or deuterium atoms. The nuclear polarization is measured with a Lamb-shift polarimeter. For common control of the two systems, industrial equipment was selected providing reliable, long-term support and remote control of the target as well as measurement and optimization of its operating parameters. The interlock system has been implemented on the basis of SIEMENS SIMATIC S7-300 family of programmable logic controllers. In order to unify the interfacing to the control computer, all front-end equipment is connected via the PROFIBUS DP fieldbus. The process control software was implemented using the Windows-based WinCC toolkit from SIEMENS. The variety of components, to be controlled, and the logical structure of the control and interlock system are described. Finally, a number of applications derived from the present development to other, new installations are briefly mentioned.

Kleines, H.; Sarkadi, J.; Zwoll, K.; Engels, R.; Grigoryev, K.; Mikirtychyants, M.; Nekipelov, M.; Rathmann, F.; Seyfarth, H.; Kravtsov, P.; Vasilyev, A.

2006-05-01

163

Disparity estimation on log-polar images and vergence control  

Microsoft Academic Search

An important issue in the realization of an autonomous robot with stereoscopic vision is the control of vergence. Together with version, it determines uniquely the position of the fixation point in space. Vergence control is directly related to both depth perception and binocular fusion. Previous works in this field employed either a measure of correlation of stereo images or some

Riccardo Manzotti; Antonios Gasteratos; Giorgio Metta; Giulio Sandini

2001-01-01

164

High-speed ultra-broad tuning MEMS-VCSELs for imaging and spectroscopy  

E-print Network

In the last 2 years, the field of micro-electro-mechanical systems tunable vertical cavity surface-emitting lasers (MEMS-VCSELs) has seen dramatic improvements in laser tuning range and tuning speed, along with expansion ...

Jayaraman, V.

165

A passively aligned VCSEL transmitter operating at fixed current over a wide temperature range.  

PubMed

We have investigated low-current operation characteristics of a passively aligned VCSEL transmitter driven at fixed "on" and "off" current over a wide temperature range. GaAs/AlGaAs-based 850-nm oxide VCSELs with the minimum threshold current of 0.79 mA at 50 masculineC and small temperature dependence of the threshold current, d(2)I(th)/dT(2), as low as 0.114 muA/ masculineC(2) have been fabricated and used for the transmitter module. The superior temperature characteristics enable fixed-current operation of the VCSEL transmitter that complies with Gigabit Ethernet standard over a wide temperature range from -20 to 120 masculineC. This result paves the way to a VCSEL transmitter featured by low-power consumption, low-cost with a simple driving circuit and passive alignment, and a wide operation temperature range. PMID:19333278

Park, Jonghyun; Kim, Taeyong; Kim, Sung-Han; Kim, Sang-Bae

2009-03-30

166

Light-by-light polarization control and stabilization in optical fibers for telecommunication applications  

NASA Astrophysics Data System (ADS)

In this work, we experimentally demonstrate light-by-light polarization control for Telecom applications via a nonlinear interaction occurring in single mode fiber between a signal beam and a counter-propagating control pump wave. In particular, we observe an attraction and stabilization process of the state of polarization (SOP) of a 10-Gbit/s optical telecommunication signal around 1550 nm for either on/off keying (OOK) and non return-to-zero (NRZ) modulation formats. In a second section, we extend our device to 40-Gbit/s by experimentally combining an all-optical regeneration of both the polarization state and the intensity profile of a 40-Gbit/s OOK signal in a single segment of fiber. These experimental results confirm yet another fascinating way to all-optical control light features within optical fibers.

Morin, Philippe; Pitois, Stéphane; Finot, Christophe; Fatome, Julien

2012-06-01

167

Polarization-controlled diffraction from a quasicrystal nanohole array in a gold film  

NASA Astrophysics Data System (ADS)

Optical transmission and diffraction of a two-dimensional quasicrystal nanohole array in a gold film is studied. Transmission spectrum peaks are observed with strong dependence on the dispersion of the metal in the optical regime, while not coinciding exactly with the surface plasmon polariton wavevectors of the quasicrystal. The diffraction pattern from the quasicrystal shows the expected tenfold rotational symmetry. Control of the diffraction pattern orientation is achieved by rotating the polarization of the incident light. This phenomenon arises from the surface wave nature of the extraordinary transmission phenomenon. The polarization dependence can be used to analyze the polarization of the incoming beam without any moving parts, or for polarization based beam-path switching.

Marthandam, P.; Gordon, R.

2007-12-01

168

Improvement of the illumination uniformity in ICF using a random polarization control plate  

NASA Astrophysics Data System (ADS)

A random polarization control plate (RPCP) is proposed to improve the illumination uniformity in ICF. The numerical simulations show the statistical equivalenc between the intensity distribution obtained using this RPCP and that using the combination technique of a polarization control plate (PCP) and a random phase plate (RPP). However, the RPCP device employs only one plate (RPCP) which can be made by resetting the arrangement of the elements of the PCP, while the combination of PCP and RPP needs two plates (PCP and RPP). So RPCP cannot only maintain the same improving effect as the PCP+RPP, but also simplify the PCP+RPP.

Liu, Zhongyong; Zhao, Yu; Fan, Dianyuan

1998-06-01

169

Light polarization-controlled shape-memory polymer/gold nanorod composite.  

PubMed

It is demonstrated that light polarization can be used to control photothermal effect-based shape-memory polymers (SMPs). Gold nanorods (AuNRs) are embedded in poly(vinyl alcohol) (PVA) and aligned by stretching the composite film. By changing the polarization direction of the incident laser at 785 nm with respect to the film stretching direction, the magnitude of the longitudinal surface plasmon resonance of AuNRs can be varied continuously, which determines the amount of heat generated upon laser exposure and thus the local temperature rise in the composite relative to the glass transition of the PVA matrix. Consequently, the temporary-to-permanent shape recovery process of the composite can be made to occur to different extents by tuning the polarization of laser while keeping all other conditions unchanged. This finding enhances the toolbox for controlling light-triggered SMPs. PMID:24092559

Zhang, Hongji; Zhang, Jianming; Tong, Xia; Ma, Dongling; Zhao, Yue

2013-10-01

170

Use of ferroelectric liquid crystal panels to control state and degree of polarization in light beams.  

PubMed

We propose a new technique that is able to generate a light beam with a controlled state of polarization (SoP) and a customized degree of polarization (DoP). The technique relies on the fact that effective depolarization can be achieved by temporally averaging a time-dependent SoP. Our proposed setup is based on a ferroelectric liquid crystal panel of retardance ?/2, with a fast polarization switching capability (33 Hz). A mathematical basis describing the experiment is given. In addition, simulation data is discussed, showing the possibility of generating any SoP with full control of the DoP. Finally, to prove the potential of the invention proposed, experimental results are provided as well, reaching an experimental minimum DoP of 0.14. PMID:24487892

Peinado, Alba; Lizana, Angel; Campos, Juan

2014-02-01

171

Fast wavelength-swept fiber laser using electro-optic polarization controller  

Microsoft Academic Search

Fast wavelength-swept fiber laser is experimentally demonstrated using electro-optic waveguide polarization controller. Intra-cavity fiber Sagnac loop and saturable absorber filter are used to achieve fast and continuous sweeping of the single-wavelength fiber laser.

Chang-Seok Kim; Fatima Farokhrooz; Utkarsb Sharma; Jin U. Kang

2004-01-01

172

Reflectivity characteristics of the fiber loop mirror with a polarization controller  

Microsoft Academic Search

In this paper, reflectivity characteristics of a fiber loop mirror (FLM), which is formed by inserting a fiber polarization controller (PC) into the fiber loop of an ordinary FLM, are investigated in detail. A theoretical model for determining the reflectivity characteristics of the FLM is present by using the equivalent optical path technique, and the reflectivity characteristics of the FLM

Sujuan Feng; Qinghe Mao; Liang Shang; John W. Y. Lit

2007-01-01

173

Polarization control for slow and fast light in fiber optical, Raman-assisted, parametric amplification  

NASA Astrophysics Data System (ADS)

Efficient slow and fast light fiber devices based on narrow band optical parametric amplification require a strict polarization control of the waves involved in the interaction. The use of high birefringence and spun fibers is studied theoretically, possible impairments evaluated, and design parameters determined. To cite this article: M. Santagiustina et al., C. R. Physique 10 (2009).

Santagiustina, Marco; Schenato, Luca; Someda, C. G.

2009-12-01

174

Polarization control for slow and fast light in fiber optical, Raman-assisted, parametric amplification  

E-print Network

Efficient slow and fast light fiber devices based on narrow band optical parametric amplification require a strict polarization control of the waves involved in the interaction. The use of high birefringence and spun fibers is studied theoretically, possible impairments evaluated, and design parameters determined.

Santagiustina, Marco; Someda, Carlo Giacomo

2009-01-01

175

Endless fiber-to-fiber polarization controller based on ceramic programmable waveplates  

Microsoft Academic Search

In this letter, we report a fast and endless polarization controller based on lead lanthanum zirconate titanate (PLZT) ceramic programmable waveplates. A set of four volume electrodes placed in a cylindrical arrangement are drilled in an electrooptic ceramic plate. By using the Kerr effect, and taking advantage of the high electrooptic coefficient and fast response time of the PLZT, we

J. Bourderionnet; D. Dolfi; J.-P. Huignard; B. Ea-Kim; E. Corbel; D. Purer; A. Poudoulec; D. Gauden

2004-01-01

176

Polarization control of high order harmonics in the EUV photon energy  

E-print Network

Polarization control of high order harmonics in the EUV photon energy range Boris Vodungbo,1,* Anna sources renders these an ideal tool for the investigation of ultrafast magnetization dynamics now that the magnetic circular dichroism at the absorption M-edges of transition metals can be exploited. © 2011 Optical

177

Alternative 3' UTR selection controls PAR-5 homeostasis and cell polarity in C. elegans embryos.  

PubMed

Cell polarity in one-cell C. elegans embryos guides asymmetric cell division and cell-fate specification. Shortly after fertilization, embryos establish two antagonistic cortical domains of PAR proteins. Here, we find that the conserved polarity factor PAR-5 regulates PAR domain size in a dose-dependent manner. Using quantitative imaging and controlled genetic manipulation, we find that PAR-5 protein levels reflect the cumulative output of three mRNA isoforms with different translational efficiencies mediated by their 3' UTRs. 3' UTR selection is regulated, influencing PAR-5 protein abundance. Alternative splicing underlies the selection of par-5 3' UTR isoforms. 3' UTR splicing is enhanced by the SR protein kinase SPK-1, and accordingly, SPK-1 is required for wild-type PAR-5 levels and PAR domain size. Precise regulation of par-5 isoform selection is essential for polarization when the posterior PAR network is compromised. Together, strict control of PAR-5 protein levels and feedback from polarity to par-5 3' UTR selection confer robustness to embryo polarization. PMID:25199833

Mikl, Martin; Cowan, Carrie R

2014-09-11

178

Fast, high-fidelity, all-optical and dynamically-controlled polarization gate using room-temperature atomic vapor  

NASA Astrophysics Data System (ADS)

We demonstrate a fast, all-optical polarization gate in a room-temperature atomic medium. Using a Polarization-Selective-Kerr-Phase-Shift (PSKPS) technique, we selectively write a ? phase shift to one circularly-polarized component of a linearly-polarized input signal field. The output signal field maintains its original strength but acquires a 90° linear polarization rotation, demonstrating fast, high-fidelity, dynamically-controlled polarization gate operation. The intensity of the polarization-switching field used in this PKSPK-based polarization gate operation is only 2 mW/cm2, which would be equivalent to 0.5 nW of light power (? = 800 nm) confined in a typical commercial photonic hollow-core fiber. This development opens a realm of possibilities for potential future extremely low light level telecommunication and information processing systems.

Li, Runbing; Zhu, Chengjie; Deng, L.; Hagley, E. W.

2014-10-01

179

Polarization-stable vertical-cavity surface-emitting lasers with inverted grating relief for use in microscale atomic clocks  

NASA Astrophysics Data System (ADS)

Vertical-cavity surface-emitting lasers (VCSELs) with single-mode, single-polarization emission at a wavelength of 894.6 nm have become attractive light sources for miniaturized Cs-based atomic clocks. So far, VCSELs used for these applications are single-mode because of small active diameters which has the drawbacks of increased ohmic resistance and reduced lifetime. By employing surface grating reliefs, enhanced fundamental-mode emission as well as polarization-stable laser oscillation are achieved. VCSELs with 5 ?m active diameter show side-mode suppression ratios of 20 dB even at currents close to thermal roll-over with orthogonal polarization suppression ratios better than 20 dB at elevated ambient temperatures up to 100 °C.

Al-Samaneh, A.; Bou Sanayeh, M.; Miah, M. J.; Schwarz, W.; Wahl, D.; Kern, A.; Michalzik, R.

2012-10-01

180

Two-photon coherent control of atomic collisions by light with entangled polarization  

E-print Network

We describe a new method of coherent optical control of internal dynamics of atomic collisions by means of two correlated light beams having entangled polarizations. We show that if excitation of a colliding pair of atoms is by two photons having entangled polarizations, it is possible to redirect the output fragments of the collision into certain channels with a selected type of internal transition symmetry. The transition symmetry is defined in the body-fixed coordinate frame which has random and originally unknown orientation in space.

M. D. Havey; D. V. Kupriyanov; I. M. Sokolov

2015-01-21

181

Control of light polarization using optically spin-injected vertical external cavity surface emitting lasers  

SciTech Connect

We fabricated and characterized an optically pumped (100)-oriented InGaAs/GaAsP multiple quantum well Vertical External Cavity Surface Emitting Laser (VECSEL). The structure is designed to allow the integration of a Metal-Tunnel-Junction ferromagnetic spin-injector for future electrical injection. We report here the control at room temperature of the electromagnetic field polarization using optical spin injection in the active medium of the VECSEL. The switching between two highly circular polarization states had been demonstrated using an M-shaped extended cavity in multi-modes lasing. This result witnesses an efficient spin-injection in the active medium of the LASER.

Frougier, J., E-mail: julien.frougier@thalesgroup.com; Jaffrès, H.; Deranlot, C.; George, J.-M. [Unité Mixte de Physique CNRS-Thales and Université Paris Sud 11, 1 av. Fresnel, 91767 Palaiseau (France)] [Unité Mixte de Physique CNRS-Thales and Université Paris Sud 11, 1 av. Fresnel, 91767 Palaiseau (France); Baili, G.; Dolfi, D. [Thales Research and Technology, 1 av. Fresnel, 91767 Palaiseau (France)] [Thales Research and Technology, 1 av. Fresnel, 91767 Palaiseau (France); Alouini, M. [Institut de Physique de Rennes, 263 Avenue Général Leclerc, 35042 Rennes (France)] [Institut de Physique de Rennes, 263 Avenue Général Leclerc, 35042 Rennes (France); Sagnes, I. [Laboratoire de Photonique et de Nanostructures, Route de Nozay, 91460 Marcoussis (France)] [Laboratoire de Photonique et de Nanostructures, Route de Nozay, 91460 Marcoussis (France); Garnache, A. [Institut d'électronique du Sud CNRS UMR5214, Université Montpellier 2 Place Eugene Bataillon, 34095 Montpellier (France)] [Institut d'électronique du Sud CNRS UMR5214, Université Montpellier 2 Place Eugene Bataillon, 34095 Montpellier (France)

2013-12-16

182

Control of light polarization using optically spin-injected vertical external cavity surface emitting lasers  

NASA Astrophysics Data System (ADS)

We fabricated and characterized an optically pumped (100)-oriented InGaAs/GaAsP multiple quantum well Vertical External Cavity Surface Emitting Laser (VECSEL). The structure is designed to allow the integration of a Metal-Tunnel-Junction ferromagnetic spin-injector for future electrical injection. We report here the control at room temperature of the electromagnetic field polarization using optical spin injection in the active medium of the VECSEL. The switching between two highly circular polarization states had been demonstrated using an M-shaped extended cavity in multi-modes lasing. This result witnesses an efficient spin-injection in the active medium of the LASER.

Frougier, J.; Baili, G.; Alouini, M.; Sagnes, I.; Jaffrès, H.; Garnache, A.; Deranlot, C.; Dolfi, D.; George, J.-M.

2013-12-01

183

Controlling enhancement and suppression of four-wave mixing via polarized light  

SciTech Connect

We show that the four-wave mixing (FWM) processes in a multi-Zeeman level atomic system can be enhanced and suppressed by changing the polarization of one of the pump beams. Different polarization states of the pump beams will act on different transition pathways among the multi-Zeeman levels with different transition strengths, which affect the FWM efficiencies. An additional dress field applied to the adjacent transition can cause energy level splitting and therefore control the enhancement and suppression of the FWM processes in the system. The experimental results are in good agreement with our theoretical calculations.

Li Changbiao; Zhang Yanpeng; Nie Zhiqiang; Du Yigang; Wang Ruimin; Song Jianping [Key Laboratory for Physical Electronics and Devices of the Ministry of Education and Shaanxi Key Lab of Information Photonic Technique, Xi'an Jiaotong University, Xi'an 710049 (China); Xiao Min [Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701 (United States)

2010-03-15

184

Coupling strength can control the polarization twist of a plasmonic antenna.  

PubMed

The far-field polarization of the optical response of a plasmonic antenna can be tuned by subtly engineering of its geometry. In this paper, we develop design rules for nano antennas which enable the generation of circular polarized light via the excitation of circular plasmonic modes in the structure. Two initially orthogonal plasmonic modes are coupled in such a way that a rotational current is excited in the structure. Modifying this coupling strength from a weak to a strong regime controls the helicity of the scattered field. Finally, we introduce an original sensing approach that relies on the rotation of the incident polarization and demonstrates a sensitivity of 0.23 deg·nm(-1) or 33 deg·RIU(-1), related to changes of mechanical dimensions and the refractive index, respectively. PMID:23987803

Abasahl, Banafsheh; Dutta-Gupta, Shourya; Santschi, Christian; Martin, Olivier J F

2013-09-11

185

Spectral polarization and spectral phase control of time-energy entangled photons  

NASA Astrophysics Data System (ADS)

We demonstrate a scheme to spectrally manipulate a collinear, continuous stream of time and energy entangled photons to generate beamlike, bandwidth-limited fluxes of polarization-entangled photons with nearly degenerate wavelengths. Utilizing an ultrashort-pulse shaper to control the spectral phase and polarization of the photon pairs, we tailor the shape of the Hong-Ou-Mandel interference pattern, demonstrating the rules that govern the dependence of this interference pattern on the spectral phases of the photons. We then use the pulse shaper to generate all four polarization Bell states. The singlet state generated by this scheme forms a very robust decoherence-free subspace, extremely suitable for long-distance fiber-optics-based quantum communication.

Dayan, Barak; Bromberg, Yaron; Afek, Itai; Silberberg, Yaron

2007-04-01

186

Magnetic control of transverse electric polarization in BiFeO3.  

PubMed

Numerous attempts have been made to realize crossed coupling between ferroelectricity and magnetism in multiferroic materials at room temperature. BiFeO3 is the most extensively studied multiferroic material that shows multiferroicity at temperatures significantly above room temperature. Here we present high-field experiments on high-quality mono-domain BiFeO3 crystals reveal substantial electric polarization orthogonal to the widely recognized one along the trigonal c axis. This novel polarization appears to couple with the domains of the cycloidal spin order and, hence, can be controlled using magnetic fields. The transverse polarization shows the non-volatile memory effect at least up to 300?K. PMID:25575377

Tokunaga, M; Akaki, M; Ito, T; Miyahara, S; Miyake, A; Kuwahara, H; Furukawa, N

2015-01-01

187

Laser-polarization-dependent and magnetically controlled optical bistability in diamond nitrogen-vacancy centers  

NASA Astrophysics Data System (ADS)

We explore laser-polarization-dependent and magnetically controlled optical bistability (OB) in an optical ring cavity filled with diamond nitrogen-vacancy (NV) defect centers under optical excitation. The shape of the OB curve can be significantly modified in a new operating regime from the previously studied OB case, namely, by adjusting the intensity of the external magnetic field and the polarization of the control beam. The influences of the intensity of the control beam, the frequency detuning, and the cooperation parameter on the OB behavior are also discussed in detail. These results are useful in real experiments for realizing an all-optical bistate switching or coding element in a solid-state platform.

Zhang, Duo; Yu, Rong; Li, Jiahua; Ding, Chunling; Yang, Xiaoxue

2013-11-01

188

Second-Harmonic-Generation Microscopy Using Excitation Beam with Controlled Polarization Pattern to Determine Three-Dimensional Molecular Orientation  

NASA Astrophysics Data System (ADS)

We have developed a second-harmonic-generation (SHG) microscope using an excitation beam with a controlled polarization pattern in order to detect three-dimensional molecular orientation. The electric field at the focus is controlled three-dimensionally by modifying the polarization distribution with a parallel-aligned nematic-liquid-crystal spatial-light-modulator without any mechanical moving parts. We demonstrated that the SHG signal from an Achilles tendon, sliced so that collagen fibers were aligned parallel to the optical axis, excited by a radially polarized beam was higher than those excited by linearly polarized beams. The possibility of determinating three-dimensional molecular orientation was thus shown.

Yoshiki, Keisuke; Hashimoto, Mamoru; Araki, Tsutomu

2005-08-01

189

Simultaneous optical manipulation of multiple particles inside microfluidic channels using one rectangular-shaped VCSEL  

NASA Astrophysics Data System (ADS)

Optical trapping for isolation and sorting of cells and particles inside microfluidic channels is an efficient non-destructive manipulation technique in the field of biophotonics. In recent years, vertical-cavity surface-emitting lasers (VCSELs) have been proven to be excellent light sources for particle manipulation inside microfluidic channels. The small dimension and low power consumption of these devices enable direct integration with the channels. With such integration, however, the simultaneous manipulation or trapping of multiple particles require the usage of densely packed VCSEL arrays with very small device pitch, which makes the fabrication process more expensive and more complicated. We present an innovative technique for simultaneous optical multi-particle manipulation using one rectangular-shaped top-emitting AlGaAs?GaAs VCSEL resonator having an active aperture area of around 100 × 14 ?m2. The VCSEL emission wavelength is about 850 nm, which is suitable for usage in biophotonics, as biological materials present very little absorption in the near-infrared spectral range. Furthermore, this oblong VCSEL can potentially be integrated with polydimethylsiloxane (PDMS) microfluidic channels to form miniaturized optofluidic chips for ultra-compact particle handling and manipulation. We show efficient single as well as multiple polystyrene particle trapping and sorting inside PDMS microfluidic channels.

Bou Sanayeh, Marwan; Bergmann, Anna; Michalzik, Rainer

2014-05-01

190

DESIGN AND FABRICATION OF A TUNABLE INP-BASED VCSEL USING A ELECTRO-OPTIC INDEX MODULATOR  

E-print Network

. This material consists of nematic liquid crystal dispersed in a polymer material (nano-PDLC). This first VCSEL and is limited by their fragility. Furthermore, MEMS-VCSEL exhibit a relatively low switching speed which depends a liquid crystal as an electro-optic material placed inside the cavity (5). The liquid crystal (LC

Boyer, Edmond

191

Improved PHIP polarization using a precision, low noise, voltage controlled current source.  

PubMed

Existing para-hydrogen induced polarization (PHIP) instrumentation relies on magnetic fields to hyperpolarize substances. These hyperpolarized substances have enhanced magnetic resonance imaging (MRI) signals over 10,000 fold, allowing for MRI at the molecular level. Required magnetic fields are generated by energizing a solenoid coil with current produced by a voltage controlled voltage source (VCVS), also known as a power supply. A VCVS lacks the current regulation necessary to keep magnetic field fluctuations to a minimum, which results in low PHIP polarization. A voltage controlled current source (VCCS) is an electric circuit that generates a steady flow of electrons proportional to an input voltage. A low noise VCCS provides the solenoid current flow regulation necessary to generate a stable static magnetic field (Bo). We discuss the design and implementation of a low noise, high stability, VCCS for magnetic field generation with minimum variations. We show that a precision, low noise, voltage reference driving a metal oxide semiconductor field effect transistor (MOSFET) based current sink, results in the current flow control necessary for generating a low noise and high stability Bo. In addition, this work: (1) compares current stability for ideal VCVS and VCCS models using transfer functions (TF), (2) develops our VCCS design's TF, (3) measures our VCCS design's thermal & 1/f noise, and (4) measures and compares hydroxyethyl-propionate (HEP) polarization obtained using a VCVS and our VCCS. The hyperpolarization of HEP was done using a PHIP instrument developed in our lab. Using our VCCS design, HEP polarization magnitude data show a statistically significant increase in polarization over using a VCVS. Circuit schematic, bill of materials, board layout, TF derivation, and Matlab simulations code are included as supplemental files. PMID:23988431

Agraz, Jose; Grunfeld, Alexander; Cunningham, Karl; Li, Debiao; Wagner, Shawn

2013-10-01

192

Improved PHIP polarization using a precision, low noise, voltage controlled current source  

NASA Astrophysics Data System (ADS)

Existing para-hydrogen induced polarization (PHIP) instrumentation relies on magnetic fields to hyperpolarize substances. These hyperpolarized substances have enhanced magnetic resonance imaging (MRI) signals over 10,000 fold, allowing for MRI at the molecular level. Required magnetic fields are generated by energizing a solenoid coil with current produced by a voltage controlled voltage source (VCVS), also known as a power supply. A VCVS lacks the current regulation necessary to keep magnetic field fluctuations to a minimum, which results in low PHIP polarization. A voltage controlled current source (VCCS) is an electric circuit that generates a steady flow of electrons proportional to an input voltage. A low noise VCCS provides the solenoid current flow regulation necessary to generate a stable static magnetic field (Bo). We discuss the design and implementation of a low noise, high stability, VCCS for magnetic field generation with minimum variations. We show that a precision, low noise, voltage reference driving a metal oxide semiconductor field effect transistor (MOSFET) based current sink, results in the current flow control necessary for generating a low noise and high stability Bo. In addition, this work: (1) compares current stability for ideal VCVS and VCCS models using transfer functions (TF), (2) develops our VCCS design's TF, (3) measures our VCCS design's thermal & 1/f noise, and (4) measures and compares hydroxyethyl-propionate (HEP) polarization obtained using a VCVS and our VCCS. The hyperpolarization of HEP was done using a PHIP instrument developed in our lab. Using our VCCS design, HEP polarization magnitude data show a statistically significant increase in polarization over using a VCVS. Circuit schematic, bill of materials, board layout, TF derivation, and Matlab simulations code are included as supplemental files.

Agraz, Jose; Grunfeld, Alexander; Cunningham, Karl; Li, Debiao; Wagner, Shawn

2013-10-01

193

Random polarization control plate used to improve the illumination uniformity in ICF  

NASA Astrophysics Data System (ADS)

We propose the random polarization control plate (RPCP) to improve the illumination uniformity in ICF. The theoretical simulations show that the statistical characteristics of the intensity distribution created by use of the RPCP is greatly similar to that by use of combination technique of the polarization control plate (PCP) and random phase plate (RPP). This RPCP system employs only one element (RPCP), however, the combination of PCP and RPP uses two elements (PCP and RPP). Therefore this novel technique in this paper has some advantages compared with the combination technique, such as higher utilization ratio of laser energy, lower cost, easier fabrication and adjustment etc. and may become one alternative of the combination approach.

Liu, Zhongyong; Zhang, Hua; Fan, Dianyuan

1998-06-01

194

Harnessing randomness to control the polarization of light transmitted through highly scattering media.  

PubMed

We show that the multiple scattering events taking place inside a highly scattering medium, in conjunction with wavefront shaping, can be used to control the state of polarization of the light transmitted through a highly scattering medium. This control is achieved by using the intensity, phase, and polarization changing behavior of a scattering medium captured by a vector transmission matrix (VTM). We use a single beam incident upon a scattering medium to measure the absolute value of the VTM elements, in contrast to the multiple beams required in our previously reported approach. Further, the phase-only spatial light modulator based on a low-cost (< US$600) deformable micro-mirror array used in our work will make similar experiments accessible to other researchers. PMID:24663764

Tripathi, Santosh; Toussaint, Kimani C

2014-02-24

195

Wavelength control with grating imprinted fiber Sagnac loop mirror by polarization and strain tuning  

NASA Astrophysics Data System (ADS)

Wavelength control by the use of fiber Bragg grating (FBG) imprinted polarization maintaining fiber (PMF) Sagnac loop mirror (SLM) is proposed and demonstrated through polarization and strain tuning. The Bragg wavelengths of the FBG in the PMF along slow or fast axis show redshifts with the increase in strain with sensitivities of 8.77×10-4 and 9.11×10-4 nm/??, respectively, whereas the interferometric peak wavelength of the SLM exhibits a blueshift with a sensitivity of 1.9437×10-2 nm/?? for the peak with an order number of 420. The opposite strain sensitivities and the pronounced difference in the bandwidth of the FBG resonance peak and that of the SLM, together with the controllability on the wavelength spacing of the SLM neighboring transmission maxima, provide a variety of alternatives to realize wavelength tuning for many practical applications.

Lu, Ping; Men, Liqiu; Chen, Qiying

2009-07-01

196

Power-stabilized tunable narrow-band source using a VCSEL and an EDFA for FBG sensor interrogation  

NASA Astrophysics Data System (ADS)

Wavelength tuning with a current of a long-wavelength vertical-cavity surface-emitting laser (VCSEL) was studied for application to wavelength readout of fiber Bragg grating (FBG) sensors. 1.5 µm single-longitudinal-mode VCSELs with a spectral line width of 30 MHz were used. To decrease the variation in the output power with the current, saturated amplification of the VCSEL output by an erbium-doped fiber amplifier (EDFA) was proposed. In the experiment, the wavelength readout of an FBG by variation in the VCSEL current was studied first, and then amplification characteristics using a commercially available EDFA module were measured. Two VCSELs with different wavelengths and tuning ranges were used as input and compared. For a VCSEL with a wavelength tuning range of 2.5 nm, there was a threefold change in the VCSEL output power. However, the variation in the amplified output power was within ±14%. For another VCSEL with a wavelength tuning range of 3.9 nm, the variation in the amplified output power was within ±18% for variation in the VCSEL output power by 2.2 times. The power slope with respect to the wavelength was also decreased by the stabilization. Computer simulation was performed to study the wavelength shift in the measured Bragg wavelength induced by the power slope. The simulation showed that the wavelength shift can be reduced to 1/2.5-1/5 by the stabilization compared with that using a single VCSEL. Application to long-period grating sensors was also discussed.

Mizunami, Toru; Hirose, Shuji; Yoshinaga, Takeshi; Yamamoto, Ken-ichi

2013-09-01

197

Development of a liquid crystal polarization control plate aligned by photoisomerization of azo dye  

Microsoft Academic Search

We demonstrate the beam smoothing by polarization control plate (PCP) produced by liquid crystal. The liquid crystal PCP using photoisomerization of the azo-dye was developed. The PCP is constructed by 14 X 14 array of 2 mm X 2 mm square element. The damage threshold is about 12 J\\/cm2 (532 nm, 0.9 ns). The PCP suppressed the speckles produced by

Kouji Tsubakimoto; Keiichi Sueda; Noriaki Miyanaga; Takahisa Jitsuno; Masahiro Nakatsuka

1997-01-01

198

Polarization Mode Control of Two-Dimensional Photonic Crystal Laser by Unit Cell Structure Design  

Microsoft Academic Search

We demonstrate polarization mode selection in a two-dimensional (2D) photonic crystal laser by controlling the geometry of the unit cell structure. As the band diagram of the square-lattice photonic crystal is influenced by the unit cell structure, calculations reveal that changing the structure from a circular to an elliptical geometry should result in a strong modification of the electromagnetic field

Susumu Noda; Mitsuru Yokoyama; Masahiro Imada; Alongkarn Chutinan; Masamitsu Mochizuki

2001-01-01

199

LKB1/AMPK and PKA Control ABCB11 Trafficking and Polarization in Hepatocytes  

PubMed Central

Polarization of hepatocytes is manifested by bile canalicular network formation and activation of LKB1 and AMPK, which control cellular energy metabolism. The bile acid, taurocholate, also regulates development of the canalicular network through activation of AMPK. In the present study, we used collagen sandwich hepatocyte cultures from control and liver-specific LKB1 knockout mice to examine the role of LKB1 in trafficking of ABCB11, the canalicular bile acid transporter. In polarized hepatocytes, ABCB11 traffics from Golgi to the apical plasma membrane and endogenously cycles through the rab 11a-myosin Vb recycling endosomal system. LKB1 knockout mice were jaundiced, lost weight and manifested impaired bile canalicular formation and intracellular trafficking of ABCB11, and died within three weeks. Using live cell imaging, fluorescence recovery after photobleaching (FRAP), particle tracking, and biochemistry, we found that LKB1 activity is required for microtubule-dependent trafficking of ABCB11 to the canalicular membrane. In control hepatocytes, ABCB11 trafficking was accelerated by taurocholate and cAMP; however, in LKB1 knockout hepatocytes, ABCB11 trafficking to the apical membrane was greatly reduced and restored only by cAMP, but not taurocholate. cAMP acted through a PKA-mediated pathway which did not activate AMPK. Our studies establish a regulatory role for LKB1 in ABCB11 trafficking to the canalicular membrane, hepatocyte polarization, and canalicular network formation. PMID:24643070

Homolya, László; Fu, Dong; Sengupta, Prabuddha; Jarnik, Michal; Gillet, Jean-Pierre; Vitale-Cross, Lynn; Gutkind, J. Silvio; Lippincott-Schwartz, Jennifer; Arias, Irwin M.

2014-01-01

200

The actin cytoskeleton may control the polar distribution of an auxin transport protein  

NASA Technical Reports Server (NTRS)

The gravitropic bending of plants has long been linked to the changes in the transport of the plant hormone auxin. To understand the mechanism by which gravity alters auxin movement, it is critical to know how polar auxin transport is initially established. In shoots, polar auxin transport is basipetal (i.e., from the shoot apex toward the base). It is driven by the basal localization of the auxin efflux carrier complex. One mechanism for localizing this efflux carrier complex to the basal membrane may be through attachment to the actin cytoskeleton. The efflux carrier protein complex is believed to consist of several polypeptides, including a regulatory subunit that binds auxin transport inhibitors, such as naphthylphthalamic acid (NPA). Several lines of experimentation have been used to determine if the NPA binding protein interacts with actin filaments. The NPA binding protein has been shown to partition with the actin cytoskeleton during detergent extraction. Agents that specifically alter the polymerization state of the actin cytoskeleton change the amount of NPA binding protein and actin recovered in these cytoskeletal pellets. Actin-affinity columns were prepared with polymers of actin purified from zucchini hypocotyl tissue. NPA binding activity was eluted in a single peak from the actin filament column. Cytochalasin D, which fragments the actin cytoskeleton, was shown to reduce polar auxin transport in zucchini hypocotyls. The interaction of the NPA binding protein with the actin cytoskeleton may localize it in one plane of the plasma membrane, and thereby control the polarity of auxin transport.

Muday, G. K.; Hu, S.; Brady, S. R.; Davies, E. (Principal Investigator)

2000-01-01

201

40 Gbps modulation of transverse coupled cavity VCSEL with push-pull modulation scheme  

NASA Astrophysics Data System (ADS)

The push-pull modulation of a transverse coupled cavity VCSEL with a bow-tie-shaped oxide aperture is demonstrated. We experimentally show the transverse-mode switching of laterally coupled VCSELs, which potentially offers a novel push-pull modulation concept. The calculated results of small-signal responses indicate an extreme expansion of the modulation bandwidth regardless of the relaxation oscillation frequency. The small-signal response was measured by tuning the RF phase of the modulation current in one cavity. A clear eye opening up to 40 Gbps with push-pull modulation has been obtained, whereas the eye pattern with the single-cavity modulation is completely closed.

Dalir, Hamed; Koyama, Fumio

2014-09-01

202

1.5 ?m VCSEL structure optimization for high-power and high-temperature operation  

Microsoft Academic Search

MOVPE epitaxial growth and design optimisation of 1.5?m vertical cavity surface emitting lasers (VCSELs) for high power, single mode and high-temperature operation are presented. The VCSEL structure comprises a strain-compensated InAlGaAs MQW active region, a p++\\/n++ In(Al)GaAs tunnel junction and top and bottom AlGaAs\\/GaAs fused distributed Bragg reflectors. All epitaxial layers were grown by low-pressure MOVPE in nitrogen atmosphere. Excellent

A. Mereuta; A. Syrbu; V. Iakovlev; A. Rudra; A. Caliman; G. Suruceanu; C.-A. Berseth; E. Deichsel; E. Kapon

2004-01-01

203

Precise, motion-free polarization control in Second Harmonic Generation microscopy using a liquid crystal modulator in the infinity space  

PubMed Central

Second Harmonic Generation (SHG) microscopy coupled with polarization analysis has great potential for use in tissue characterization, as molecular and supramolecular structural details can be extracted. Such measurements are difficult to perform quickly and accurately. Here we present a new method that uses a liquid crystal modulator (LCM) located in the infinity space of a SHG laser scanning microscope that allows the generation of any desired linear or circular polarization state. As the device contains no moving parts, polarization can be rotated accurately and faster than by manual or motorized control. The performance in terms of polarization purity was validated using Stokes vector polarimetry, and found to have minimal residual polarization ellipticity. SHG polarization imaging characteristics were validated against well-characterized specimens having cylindrical and/or linear symmetries. The LCM has a small footprint and can be implemented easily in any standard microscope and is cost effective relative to other technologies. PMID:24156059

Lien, Chi-Hsiang; Tilbury, Karissa; Chen, Shean-Jen; Campagnola, Paul J.

2013-01-01

204

Laser heating control with polarized light in isolated multiwalled carbon nanotubes.  

PubMed

We propose a novel method of laser heating control only through change in polarization of the incident light, keeping its power density constant. The idea combines an antenna effect found in isolated multiwalled carbon nanotubes and the possibility of their heating by light illumination. To observe this we used the Raman spectroscopy technique, where the heating manifests itself in a pronounced downshift of the Raman G and 2D lines as a function of the polarization angle. Our method can be useful in field electron emission devices or in selective nanotubes heating and destruction. It can also be extended to other one dimensional nano-objects, if only certain conditions are fulfilled. PMID:23003617

Zdrojek, Mariusz; Judek, Jaros?aw; Wasik, Micha?

2012-06-01

205

Significant electrical control of amorphous oxide thin film transistors by an ultrathin Ti surface polarity modifier  

SciTech Connect

We demonstrate an enhanced electrical stability through a Ti oxide (TiO{sub x}) layer on the amorphous InGaZnO (a-IGZO) back-channel; this layer acts as a surface polarity modifier. Ultrathin Ti deposited on the a-IGZO existed as a TiO{sub x} thin film, resulting in oxygen cross-binding with a-IGZO surface. The electrical properties of a-IGZO thin film transistors (TFTs) with TiO{sub x} depend on the surface polarity change and electronic band structure evolution. This result indicates that TiO{sub x} on the back-channel serves as not only a passivation layer protecting the channel from ambient molecules or process variables but also a control layer of TFT device parameters.

Cho, Byungsu [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Samsung Display Co. Ltd., Tangjeong, Chungcheongnam-Do 336-741 (Korea, Republic of); Choi, Yonghyuk; Shin, Seokyoon [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Jeon, Heeyoung [Department of Nano-scale Semiconductor Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Seo, Hyungtak, E-mail: hseo@ajou.ac.kr [Department of Materials Science and Engineering and Energy Systems Research, Ajou University, Suwon 443-739 (Korea, Republic of); Jeon, Hyeongtag, E-mail: hjeon@hanyang.ac.kr [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Department of Nano-scale Semiconductor Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of)

2014-01-27

206

Linearly polarized single photon antibunching from a site-controlled InGaN quantum dot  

NASA Astrophysics Data System (ADS)

We report on the observation of linearly polarized single photon antibunching in the excitonic emission from a site-controlled InGaN quantum dot. The measured second order coherence function exhibits a significant dip at zero time difference, corresponding to g m 2 ( 0 ) = 0.90 under continuous laser excitation. This relatively high value of g m 2 ( 0 ) is well understood by a model as the combination of short exciton life time (320 ps), limited experimental timing resolution and the presence of an uncorrelated broadband background emission from the sample. Our result provides the first rigorous evidence of InGaN quantum dot formation on hexagonal GaN pyramids, and it highlights a great potential in these dots as fast polarized single photon emitters if the background emission can be eliminated.

Jemsson, Tomas; Machhadani, Houssaine; Karlsson, K. Fredrik; Hsu, Chih-Wei; Holtz, Per-Olof

2014-08-01

207

Dynamic control of spin wave spectra using spin-polarized currents  

SciTech Connect

We describe a method of controlling the spin wave spectra dynamically in a uniform nanostripe waveguide through spin-polarized currents. A stable periodic magnetization structure is observed when the current flows vertically through the center of nanostripe waveguide. After being excited, the spin wave is transmitted at the sides of the waveguide. Numerical simulations of spin-wave transmission and dispersion curves reveal a single, pronounced band gap. Moreover, the periodic magnetization structure can be turned on and off by the spin-polarized current. The switching process from full rejection to full transmission takes place within less than 3?ns. Thus, this type magnonic waveguide can be utilized for low-dissipation spin wave based filters.

Wang, Qi; Zhang, Huaiwu, E-mail: hwzhang@uestc.edu.cn; Tang, Xiaoli; Bai, Feiming; Zhong, Zhiyong, E-mail: zzy@uestc.edu.cn [State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054 (China); Fangohr, Hans [Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ (United Kingdom)

2014-09-15

208

Long-range Neural and Gap Junction Protein-mediated Cues Control Polarity During Planarian Regeneration  

PubMed Central

SUMMARY Having the ability to coordinate the behavior of stem cells to induce regeneration of specific large-scale structures would have far reaching consequences in the treatment of degenerative diseases, acute injury, and aging. Thus, identifying and learning to manipulate the sequential steps that determine the fate of new tissue within the overall morphogenetic program of the organism is fundamental. We identified novel early signals, mediated by the central nervous system and 3 innexin proteins, which determine the fate and axial polarity of regenerated tissue in planarians. Modulation of gap junction-dependent and neural signals specifically induces ectopic anterior regeneration blastemas in posterior and lateral wounds. These ectopic anterior blastemas differentiate new brains that establish permanent primary axes re-established during subsequent rounds of unperturbed regeneration. These data reveal powerful novel controls of pattern formation and suggest a constructive model linking nervous inputs and polarity determination in early stages of regeneration. PMID:20026026

Oviedo, Néstor J.; Morokuma, Junji; Walentek, Peter; Kema, Ido P.; Gu, Man Bock; Ahn, Joo-Myung; Hwang, Jung Shan; Gojobori, Takashi; Levin, Michael

2010-01-01

209

Polarization-resolved SHG microscopy of rat-tail tendon with controlled mechanical strain  

NASA Astrophysics Data System (ADS)

We combined polarization-resolved SHG microscopy with mechanical assays in rat-tail-tendon and measured collagen remodeling upon controlled stretching. This approach aimed to analyze the relationship between macroscopic response and sub-micrometer scale organization of collagen fibrils. We observed a straightening of the crimps followed by a sliding of the fibrils with increasing stretching of the tendon fascicles. Polarization resolution of the SHG images provided complementary information about the orientation dispersion of collagen fibrils within the focal volume and enabled monitoring of collagen remodeling at the sub-micrometer scale. Our approach can be readily generalized to other tissues and should bring new valuable information about biomechanics of microstructured tissues.

Gusachenko, I.; Goulam Houssen, Y.; Tran, V.; Allain, J.-M.; Schanne-Klein, M.-C.

2013-06-01

210

Laser trapping in anisotropic fluids and polarization-controlled particle dynamics  

PubMed Central

Anisotropic fluids are widespread, ranging from liquid crystals used in displays to ordered states of a biological cell interior. Optical trapping is potentially a powerful technique in the fundamental studies and applications of anisotropic fluids. We demonstrate that laser beams in these fluids can generate anisotropic optical trapping forces, even for particles larger than the trapping beam wavelength. Immersed colloidal particles modify the fluid's ordered molecular structures and locally distort its optic axis. This distortion produces a refractive index “corona” around the particles that depends on their surface characteristics. The laser beam can trap such particles not only at their center but also at the high-index corona. Trapping forces in the beam's lateral plane mimic the corona and are polarization-controlled. This control allows the optical forces to be reversed and cause the particle to follow a prescribed trajectory. Anisotropic particle dynamics in the trap varies with laser power because of the anisotropy of both viscous drag and trapping forces. Using thermotropic liquid crystals and biological materials, we show that these phenomena are quite general for all anisotropic fluids and impinge broadly on their quantitative studies using laser tweezers. Potential applications include modeling thermodynamic systems with anisotropic polarization-controlled potential wells, producing optically tunable photonic crystals, and fabricating light-controlled nano- and micropumps. PMID:17114287

Smalyukh, Ivan I.; Kachynski, Aliaksandr V.; Kuzmin, Andrey N.; Prasad, Paras N.

2006-01-01

211

Laser polarization dependent and magnetically control of group velocity in a dielectric medium doped with nanodiamond nitrogen vacancy centers  

NASA Astrophysics Data System (ADS)

In this paper, group velocity control of Gaussian beam in a dielectric medium doped with nanodiamond nitrogen vacancy (NV) centers under optical excitation is discussed. The shape of transmitted and reflected pulses from dielectric can be tuned by changing the intensity of magnetic field and polarization of the control beam. The effect of intensity of control beam on group velocity is also investigated.

Asadpour, Seyyed Hossein; Rahimpour Soleimani, H.

2014-03-01

212

In-situ OTDR for low-cost optical networks using a single-mode 850-nm VCSEL.  

SciTech Connect

A new approach to optical time-domain reflectometry (OTDR) is proposed that will enable distributed fault monitoring in singlemode VCSEL-based networks. In situ OTDR uses the transmitter VCSEL already resident in data transceivers as both emitter and resonant-cavity photodiode for fault location measurements. Also valuable at longer wavelengths, the concept is demonstrated here using an 850 nm oxide-confined VCSEL and simple electronics. The dead times and sensitivity obtained are adequate to detect the majority of faults anticipated in local- and metropolitan-area networks.

Geib, Kent Martin; Peake, Gregory Merwin; Serkland, Darwin Keith; Keeler, Gordon Arthur

2005-04-01

213

Modeling and characterization of VCSEL-based avionics full-duplex ethernet (AFDX) gigabit links  

Microsoft Academic Search

Low cost and intrinsic performances of 850 nm Vertical Cavity Surface Emitting Lasers (VCSELs) compared to Light Emitting Diodes make them very attractive for high speed and short distances data communication links through optical fibers. Weight saving and Electromagnetic Interference withstanding requirements have led to the need of a reliable solution to improve existing avionics high speed buses (e.g. AFDX)

Khadijetou S. Ly; A. Rissons; E. Gambardella; D. Bajon; J.-C. Mollier

2008-01-01

214

Nonlinear mode coupling in optical fibers and VCSELs and some applications to communication systems  

Microsoft Academic Search

Nonlinear phenomena are relatively easy to observe in optical fibers and semiconductor laser cavities. In optical fibers, nonlinear effects can be seen even at low power due to the high intensities in the small fiber cores and long propagation distances possible in low loss fibers. Semiconductor lasers, in particular, vertical cavity surface emitting lasers (VCSELs), have cavities with very high

Kunal Kishore

2000-01-01

215

The oxide defined VCSEL-based smart pixels for the optical database filter  

SciTech Connect

This paper presents the construction of the smart pixel arrays which perform AND and XOR functions with three-input and one-output optical signals for the application of an optical database filter. The device is based on oxide confined VCSELs bump bonded to GaAs MESFET pixels. The MSM photodetectors are monolithically integrated with MESFETs.

Pu, R.; Hayes, E.; Jurrat, R.; Stanko, P.J.; Wilmsen, C.W. [Colorado State Univ., Ft. Collins, CO (United States). Dept. of Electrical Engineering; Choquette, K.; Geib, K.; Hou, H.Q. [Sandia National Labs., Albuquerque, NM (United States)

1997-04-01

216

Servo Control of High Degree of Linear Polarization Output from Polarization-Maintaining Fiber and its Application in Fiber-Component Based Frequency Modulation Spectroscopy  

NASA Astrophysics Data System (ADS)

A novel servo control method has been developed to output a highly linear state of polarization (SOP) from a polarization-maintaining (PM) fiber. The correction signal is obtained using an SOP detection setup invented by Hänsch and Couillaud. This servo control method was then applied to fiber-component based frequency modulation spectroscopy experimentally to reduce the residual amplitude modulation (RAM) induced by nonlinear SOP incident to an electro-optic modulator. With active servo control, stable linear SOP output of PM fiber and pure frequency modulation lineshapes are obtained. Finally, long-term measurements of the dispersion background signal with feedback loop on and off are performed to evaluate the stability of RAM reduction.

Ma, Weiguang; Li, Zhixin; Tan, Wei; Zhao, Gang; Fu, Xiaofang; Zhang, Lei; Dong, Lei; Yin, Wangbao; Jia, Suotang

2013-11-01

217

In Situ Detection of PHIP at 48 mT: Demonstration Using a Centrally Controlled Polarizer  

PubMed Central

Presented here is a centrally controlled, automated parahydrogen-based polarizer with in situ detection capability. A 20% polarization, corresponding to a 5 000 000-fold signal enhancement at 48 mT, is demonstrated on 2-hydroxyethyl-1-13C-propionate-d2,3,3 using a double-tuned antenna and pulsed polarization transfer. In situ detection is a refinement of first-generation devices enabling fast calibration of rf pulses and B0, quality assurance of hyperpolarized contrast agents, and stand-alone operation without the necessity of high-field MR spectrometers. These features are essential for biomedical applications of parahydrogen-based hyperpolarization and for clinical translation. We demonstrate the flexibility of the device by recording 13C signal decay due to longitudinal relaxation of a hyperpolarized contrast agent at 48 mT corresponding to 2 MHz proton frequency. This appears to be the longest recorded T1 (101 ± 7 s) for a 13C hyperpolarized contrast agent in water. PMID:21141960

Waddell, Kevin W.; Coffey, Aaron M.; Chekmenev, Eduard Y.

2011-01-01

218

Suppressors of cytokine signaling 2 and 3 diametrically control macrophage polarization.  

PubMed

Suppressors of cytokine signaling (SOCS) are important regulators of lipopolysaccharide (LPS) and cytokine responses but their role in macrophage polarization is unknown. We have shown here that myeloid-restricted Socs3 deletion (Socs3(Lyz2cre)) resulted in resistance to LPS-induced endotoxic shock, whereas Socs2(-/-) mice were highly susceptible. We observed striking bias toward M2-like macrophages in Socs3(Lyz2cre) mice, whereas the M1-like population was enriched in Socs2(-/-) mice. Adoptive transfer experiments showed that responses to endotoxic shock and polymicrobial sepsis were transferable and macrophage dependent. Critically, this dichotomous response was associated with enhanced regulatory T (Treg) cell recruitment by Socs3(Lyz2cre) cells, whereas Treg cell recruitment was absent in the presence of Socs2(-/-) macrophages. In addition, altered polarization coincided with enhanced interferon-gamma (IFN-?)-induced signal transducer and activator of transcription-1 (STAT1) activation in Socs2(-/-) macrophages and enhanced interleukin-4 (IL-4) plus IL-13-induced STAT6 phosphorylation in Socs3(Lyz2cre) macrophages. SOCS, therefore, are essential controllers of macrophage polarization, regulating inflammatory responses. PMID:23177319

Spence, Shaun; Fitzsimons, Amy; Boyd, Caroline R; Kessler, Julia; Fitzgerald, Denise; Elliott, Joanne; Gabhann, Joan Ní; Smith, Siobhan; Sica, Antonio; Hams, Emily; Saunders, Sean P; Jefferies, Caroline A; Fallon, Padraic G; McAuley, Danny F; Kissenpfennig, Adrien; Johnston, James A

2013-01-24

219

Dynamic Control and Amplification of Molecular Chirality by Circular Polarized Light  

NASA Astrophysics Data System (ADS)

The enantiomers of a racemic photoresponsive material represent two distinct states that can be modulated with irradiation at a single wavelength by changing the handedness of the light. Dynamic control over molecular chirality was obtained by the interconversion of enantiomers of helically shaped molecules with either left or right circular polarized light (CPL). Photoresolution of the bistable compound as a dopant in a nematic liquid crystalline phase by CPL irradiation led to a chiral mesoscopic phase. The chiral information inherent to CPL is therefore transmitted to the bistable molecule, followed by amplification and macroscopic expression of the chirality.

Huck, Nina P. M.; Jager, Wolter F.; de Lange, Ben; Feringa, Ben L.

1996-09-01

220

Electro-optically modulated coupled-cavity VCSELs: electrical design optimization for high-speed operation  

NASA Astrophysics Data System (ADS)

Vertical-Cavity Surface-Emitting Lasers, due to their properties, are one of the best choices for optical communication purposes. Although direct modulated VCSELs have reached error free operation at speed of 40 Gbit/s, however, their cut-off frequency is limited by the relaxation oscillation phenomenon and is not likely to be further increased. Recently, it has been suggested that properly designed Coupled Cavity VCSEL with one cavity used as a reverse-biased Electro-Optic Modulator, can be only limited by the 3 dB electrical bandwidth cut-off frequency. Therefore, it is important to develop a high-speed electrical design for such VCSELs. In this paper we first present an analysis of an electrical equivalent circuit of EOM CC-VCSEL with lumped electrodes. We base our design on record high-speed structures reported in the literature. We optimize our structure with respect to modulator cavity length, number of top and middle distributed Bragg reflectors, doping levels of layers, radii of both mesas and non-ion implantation region in the DBR as well as the contact pad area. We show that the most influencing parameters are the mesa capacitance, series resistance and polyimide capacitance. The 3 dB bandwidth is enhanced by reducing the contact pad area and modulator cavity diameter, together with increasing the modulator cavity length. Faster operation is provided by pnp structure, instead of npn - one. A realistic structure design that is theoretically able to work with a 90 GHz modulation speed is suggested. Finally we also discuss the possibility of using a design concept of a EOM CC-VCSEL based on traveling wave electrode configuration.

Zujewski, Mateusz; Thienpont, Hugo; Panajotov, Krassimir

2012-06-01

221

Controlled polarity of sputter-deposited aluminum nitride on metals observed by aberration corrected scanning transmission electron microscopy  

SciTech Connect

The polarity determination process of sputter-deposited aluminum nitride (AlN) on metals has been analyzed using aberration corrected atomic resolution scanning transmission electron microscope. Direct growth of c-axis orientated AlN on face centered cubic metals (fcc) (111) with the local epitaxy has been observed, and the polarity was determined at the AlN/metal interface. We found that the AlN polarity can be controlled by the base metal layer: N-polarity AlN grows on Pt(111) while Al-polarity AlN forms on Al(111). Based on these results, the growth mechanism of AlN on metals is discussed.

Harumoto, T. [Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2-12-1-S8-6 O-okayama, Meguro-ku, Tokyo 152-8552 (Japan); Department of Materials Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510 (Japan); Sannomiya, T.; Matsukawa, Y.; Muraishi, S.; Shi, J.; Nakamura, Y. [Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2-12-1-S8-6 O-okayama, Meguro-ku, Tokyo 152-8552 (Japan); Sawada, H. [Japan Electron Optics Laboratory (JEOL) Ltd., 3-1-2 Musashino, Akishima, Tokyo 196-8558 (Japan); Tanaka, T.; Tanishiro, Y.; Takayanagi, K. [Department of Physics, Tokyo Institute of Technology, 2-12-1-H-51 O-okayama, Meguro-ku, Tokyo 152-8551 (Japan)

2013-02-28

222

Dynamic nuclear polarization and optimal control spatial-selective 13C MRI and MRS  

NASA Astrophysics Data System (ADS)

Aimed at 13C metabolic magnetic resonance imaging (MRI) and spectroscopy (MRS) applications, we demonstrate that dynamic nuclear polarization (DNP) may be combined with optimal control 2D spatial selection to simultaneously obtain high sensitivity and well-defined spatial restriction. This is achieved through the development of spatial-selective single-shot spiral-readout MRI and MRS experiments combined with dynamic nuclear polarization hyperpolarized [1-13C]pyruvate on a 4.7 T pre-clinical MR scanner. The method stands out from related techniques by facilitating anatomic shaped region-of-interest (ROI) single metabolite signals available for higher image resolution or single-peak spectra. The 2D spatial-selective rf pulses were designed using a novel Krotov-based optimal control approach capable of iteratively fast providing successful pulse sequences in the absence of qualified initial guesses. The technique may be important for early detection of abnormal metabolism, monitoring disease progression, and drug research.

Vinding, Mads S.; Laustsen, Christoffer; Maximov, Ivan I.; Søgaard, Lise Vejby; Ardenkjær-Larsen, Jan H.; Nielsen, Niels Chr.

2013-02-01

223

Polarity, cell division, and out-of-equilibrium dynamics control the growth of epithelial structures  

PubMed Central

The growth of a well-formed epithelial structure is governed by mechanical constraints, cellular apico-basal polarity, and spatially controlled cell division. Here we compared the predictions of a mathematical model of epithelial growth with the morphological analysis of 3D epithelial structures. In both in vitro cyst models and in developing epithelial structures in vivo, epithelial growth could take place close to or far from mechanical equilibrium, and was determined by the hierarchy of time-scales of cell division, cell–cell rearrangements, and lumen dynamics. Equilibrium properties could be inferred by the analysis of cell–cell contact topologies, and the nonequilibrium phenotype was altered by inhibiting ROCK activity. The occurrence of an aberrant multilumen phenotype was linked to fast nonequilibrium growth, even when geometric control of cell division was correctly enforced. We predicted and verified experimentally that slowing down cell division partially rescued a multilumen phenotype induced by altered polarity. These results improve our understanding of the development of epithelial organs and, ultimately, of carcinogenesis. PMID:24145168

Cerruti, Benedetta; Puliafito, Alberto; Shewan, Annette M.; Yu, Wei; Combes, Alexander N.; Little, Melissa H.; Chianale, Federica; Primo, Luca; Serini, Guido; Mostov, Keith E.; Celani, Antonio

2013-01-01

224

Optical control of hard X-ray polarization by electron injection in a laser wakefield accelerator  

NASA Astrophysics Data System (ADS)

Laser-plasma particle accelerators could provide more compact sources of high-energy radiation than conventional accelerators. Moreover, because they deliver radiation in femtosecond pulses, they could improve the time resolution of X-ray absorption techniques. Here we show that we can measure and control the polarization of ultra-short, broad-band keV photon pulses emitted from a laser-plasma-based betatron source. The electron trajectories and hence the polarization of the emitted X-rays are experimentally controlled by the pulse-front tilt of the driving laser pulses. Particle-in-cell simulations show that an asymmetric plasma wave can be driven by a tilted pulse front and a non-symmetric intensity distribution of the focal spot. Both lead to a notable off-axis electron injection followed by collective electron-betatron oscillations. We expect that our method for an all-optical steering is not only useful for plasma-based X-ray sources but also has significance for future laser-based particle accelerators.

Schnell, Michael; Sävert, Alexander; Uschmann, Ingo; Reuter, Maria; Nicolai, Maria; Kämpfer, Tino; Landgraf, Björn; Jäckel, Oliver; Jansen, Oliver; Pukhov, Alexander; Kaluza, Malte Christoph; Spielmann, Christian

2013-09-01

225

Optical control of hard X-ray polarization by electron injection in a laser wakefield accelerator.  

PubMed

Laser-plasma particle accelerators could provide more compact sources of high-energy radiation than conventional accelerators. Moreover, because they deliver radiation in femtosecond pulses, they could improve the time resolution of X-ray absorption techniques. Here we show that we can measure and control the polarization of ultra-short, broad-band keV photon pulses emitted from a laser-plasma-based betatron source. The electron trajectories and hence the polarization of the emitted X-rays are experimentally controlled by the pulse-front tilt of the driving laser pulses. Particle-in-cell simulations show that an asymmetric plasma wave can be driven by a tilted pulse front and a non-symmetric intensity distribution of the focal spot. Both lead to a notable off-axis electron injection followed by collective electron-betatron oscillations. We expect that our method for an all-optical steering is not only useful for plasma-based X-ray sources but also has significance for future laser-based particle accelerators. PMID:24026068

Schnell, Michael; Sävert, Alexander; Uschmann, Ingo; Reuter, Maria; Nicolai, Maria; Kämpfer, Tino; Landgraf, Björn; Jäckel, Oliver; Jansen, Oliver; Pukhov, Alexander; Kaluza, Malte Christoph; Spielmann, Christian

2013-01-01

226

Optical control of hard X-ray polarization by electron injection in a laser wakefield accelerator  

PubMed Central

Laser-plasma particle accelerators could provide more compact sources of high-energy radiation than conventional accelerators. Moreover, because they deliver radiation in femtosecond pulses, they could improve the time resolution of X-ray absorption techniques. Here we show that we can measure and control the polarization of ultra-short, broad-band keV photon pulses emitted from a laser-plasma-based betatron source. The electron trajectories and hence the polarization of the emitted X-rays are experimentally controlled by the pulse-front tilt of the driving laser pulses. Particle-in-cell simulations show that an asymmetric plasma wave can be driven by a tilted pulse front and a non-symmetric intensity distribution of the focal spot. Both lead to a notable off-axis electron injection followed by collective electron–betatron oscillations. We expect that our method for an all-optical steering is not only useful for plasma-based X-ray sources but also has significance for future laser-based particle accelerators. PMID:24026068

Schnell, Michael; Sävert, Alexander; Uschmann, Ingo; Reuter, Maria; Nicolai, Maria; Kämpfer, Tino; Landgraf, Björn; Jäckel, Oliver; Jansen, Oliver; Pukhov, Alexander; Kaluza, Malte Christoph; Spielmann, Christian

2013-01-01

227

Control of exciton spin statistics through spin polarization in organic optoelectronic devices  

PubMed Central

Spintronics based on organic semiconductor materials is attractive because of its rich fundamental physics and potential for device applications. Manipulating spins is obviously important for spintronics, and is usually achieved by using magnetic electrodes. Here we show a new approach where spin populations can be controlled primarily by energetics rather than kinetics. We find that exciton spin statistics can be substantially controlled by spin-polarizing carriers after injection using high magnetic fields and low temperatures, where the Zeeman energy is comparable with the thermal energy. By using this method, we demonstrate that singlet exciton formation can be suppressed by up to 53% in organic light-emitting diodes, and the dark conductance of organic photovoltaic devices can be increased by up to 45% due to enhanced formation of triplet charge-transfer states, leading to less recombination to the ground state. PMID:23149736

Wang, Jianpu; Chepelianskii, Alexei; Gao, Feng; Greenham, Neil C.

2012-01-01

228

The Rac-GAP Bcr is a novel regulator of the Par complex that controls cell polarity  

PubMed Central

Cell polarization is essential for many biological processes, including directed cell migration, and loss of polarity contributes to pathological conditions such as cancer. The Par complex (Par3, Par6, and PKC?) controls cell polarity in part by recruiting the Rac-specific guanine nucleotide exchange factor T-lymphoma invasion and metastasis 1 (Tiam1) to specialized cellular sites, where Tiam1 promotes local Rac1 activation and cytoskeletal remodeling. However, the mechanisms that restrict Par-Tiam1 complex activity to the leading edge to maintain cell polarity during migration remain unclear. We identify the Rac-specific GTPase-activating protein (GAP) breakpoint cluster region protein (Bcr) as a novel regulator of the Par-Tiam1 complex. We show that Bcr interacts with members of the Par complex and inhibits both Rac1 and PKC? signaling. Loss of Bcr results in faster, more random migration and striking polarity defects in astrocytes. These polarity defects are rescued by reducing PKC? activity or by expressing full-length Bcr, but not an N-terminal deletion mutant or the homologous Rac-GAP, Abr, both of which fail to associate with the Par complex. These results demonstrate that Bcr is an integral member of the Par-Tiam1 complex that controls polarized cell migration by locally restricting both Rac1 and PKC? function. PMID:24152735

Narayanan, Anjana S.; Reyes, Steve B.; Um, Kyongmi; McCarty, Joseph H.; Tolias, Kimberley F.

2013-01-01

229

10Gb\\/s data transmission experiments over polymeric waveguides with 850-nm wavelength multimode VCSEL array  

Microsoft Academic Search

A practical transmitter module was demonstrated, using a metal optical bench (MOB) and a tapered polymeric waveguide. The transmitter module was prepared for optical printed circuit board, which consists of the MOB, the driver chips, the vertical-cavity surface-emitting laser (VCSEL), and a tapered polymeric waveguide. We report a 10-Gb\\/s 223-1 pseudorandom bit sequence nonreturn-to-zero of data transmission from VCSEL to

Keun Byoung Yoon; In-Kui Cho; Seung-Ho Ahn

2004-01-01

230

LabVIEW-based control software for para-hydrogen induced polarization instrumentation  

NASA Astrophysics Data System (ADS)

The elucidation of cell metabolic mechanisms is the modern underpinning of the diagnosis, treatment, and in some cases the prevention of disease. Para-Hydrogen induced polarization (PHIP) enhances magnetic resonance imaging (MRI) signals over 10 000 fold, allowing for the MRI of cell metabolic mechanisms. This signal enhancement is the result of hyperpolarizing endogenous substances used as contrast agents during imaging. PHIP instrumentation hyperpolarizes Carbon-13 (13C) based substances using a process requiring control of a number of factors: chemical reaction timing, gas flow, monitoring of a static magnetic field (Bo), radio frequency (RF) irradiation timing, reaction temperature, and gas pressures. Current PHIP instruments manually control the hyperpolarization process resulting in the lack of the precise control of factors listed above, resulting in non-reproducible results. We discuss the design and implementation of a LabVIEW based computer program that automatically and precisely controls the delivery and manipulation of gases and samples, monitoring gas pressures, environmental temperature, and RF sample irradiation. We show that the automated control over the hyperpolarization process results in the hyperpolarization of hydroxyethylpropionate. The implementation of this software provides the fast prototyping of PHIP instrumentation for the evaluation of a myriad of 13C based endogenous contrast agents used in molecular imaging.

Agraz, Jose; Grunfeld, Alexander; Li, Debiao; Cunningham, Karl; Willey, Cindy; Pozos, Robert; Wagner, Shawn

2014-04-01

231

LabVIEW-based control software for para-hydrogen induced polarization instrumentation  

SciTech Connect

The elucidation of cell metabolic mechanisms is the modern underpinning of the diagnosis, treatment, and in some cases the prevention of disease. Para-Hydrogen induced polarization (PHIP) enhances magnetic resonance imaging (MRI) signals over 10 000 fold, allowing for the MRI of cell metabolic mechanisms. This signal enhancement is the result of hyperpolarizing endogenous substances used as contrast agents during imaging. PHIP instrumentation hyperpolarizes Carbon-13 ({sup 13}C) based substances using a process requiring control of a number of factors: chemical reaction timing, gas flow, monitoring of a static magnetic field (B{sub o}), radio frequency (RF) irradiation timing, reaction temperature, and gas pressures. Current PHIP instruments manually control the hyperpolarization process resulting in the lack of the precise control of factors listed above, resulting in non-reproducible results. We discuss the design and implementation of a LabVIEW based computer program that automatically and precisely controls the delivery and manipulation of gases and samples, monitoring gas pressures, environmental temperature, and RF sample irradiation. We show that the automated control over the hyperpolarization process results in the hyperpolarization of hydroxyethylpropionate. The implementation of this software provides the fast prototyping of PHIP instrumentation for the evaluation of a myriad of {sup 13}C based endogenous contrast agents used in molecular imaging.

Agraz, Jose, E-mail: joseagraz@ucla.edu; Grunfeld, Alexander; Li, Debiao [Department of Bioengineering, University of California, Los Angeles, California 91791 (United States) [Department of Bioengineering, University of California, Los Angeles, California 91791 (United States); BIRI, Cedars Sinai Medical Center, West Hollywood, California 90048 (United States); Cunningham, Karl [Ectron Corp, San Diego, California 92111 (United States)] [Ectron Corp, San Diego, California 92111 (United States); Willey, Cindy [Harris Corp, San Diego, California 92154 (United States)] [Harris Corp, San Diego, California 92154 (United States); Pozos, Robert [Department of Biology, San Diego State University, San Diego, California 92182 (United States)] [Department of Biology, San Diego State University, San Diego, California 92182 (United States); Wagner, Shawn [BIRI, Cedars Sinai Medical Center, West Hollywood, California 90048 (United States)] [BIRI, Cedars Sinai Medical Center, West Hollywood, California 90048 (United States)

2014-04-15

232

LabVIEW-based control software for para-hydrogen induced polarization instrumentation.  

PubMed

The elucidation of cell metabolic mechanisms is the modern underpinning of the diagnosis, treatment, and in some cases the prevention of disease. Para-Hydrogen induced polarization (PHIP) enhances magnetic resonance imaging (MRI) signals over 10,000 fold, allowing for the MRI of cell metabolic mechanisms. This signal enhancement is the result of hyperpolarizing endogenous substances used as contrast agents during imaging. PHIP instrumentation hyperpolarizes Carbon-13 ((13)C) based substances using a process requiring control of a number of factors: chemical reaction timing, gas flow, monitoring of a static magnetic field (Bo), radio frequency (RF) irradiation timing, reaction temperature, and gas pressures. Current PHIP instruments manually control the hyperpolarization process resulting in the lack of the precise control of factors listed above, resulting in non-reproducible results. We discuss the design and implementation of a LabVIEW based computer program that automatically and precisely controls the delivery and manipulation of gases and samples, monitoring gas pressures, environmental temperature, and RF sample irradiation. We show that the automated control over the hyperpolarization process results in the hyperpolarization of hydroxyethylpropionate. The implementation of this software provides the fast prototyping of PHIP instrumentation for the evaluation of a myriad of (13)C based endogenous contrast agents used in molecular imaging. PMID:24784636

Agraz, Jose; Grunfeld, Alexander; Li, Debiao; Cunningham, Karl; Willey, Cindy; Pozos, Robert; Wagner, Shawn

2014-04-01

233

Optically controlled polarizer using a ladder transition for high speed Stokesmetric Imaging and Quantum Zeno Effect based optical logic.  

PubMed

We demonstrate an optically controlled polarizer at ~1323 nm using a ladder transition in a Rb vapor cell. The lower leg of the 5S(1/2),F = 1->5P(1/2),F = 1,2->6S(1/2),F = 1,2 transitions is excited by a Ti:Sapphire laser locked to a saturated absorption signal, representing the control beam. A tunable fiber laser at ~1323 nm is used to excite the upper leg of the transitions, representing the signal beam. When the control beam is linearly polarized, it produces an excitation of the intermediate level with a particular orientation of the angular momentum. Under ideal conditions, this orientation is transparent to the signal beam if it has the same polarization as the control beam and is absorbed when it is polarized orthogonally. We also present numerical simulations of the system using a comprehensive model which incorporates all the relevant Zeeman sub-levels in the system, and identify means to improve the performance of the polarizer. A novel algorithm to compute the evolution of large scale quantum system enabled us to perform this computation, which may have been considered too cumbersome to carry out previously. We describe how such a polarizer may serve as a key component for high-speed Stokesmetric imaging. We also show how such a polarizer, combined with an optically controlled waveplate, recently demonstrated by us, can be used to realize a high speed optical logic gate by making use of the Quantum Zeno Effect. Finally, we describe how such a logic gate can be realized at an ultra-low power level using a tapered nanofiber embedded in a vapor cell. PMID:24150297

Krishnamurthy, Subramanian; Wang, Y; Tu, Y; Tseng, S; Shahriar, M S

2013-10-21

234

Topographical control over seasonal sublimation of the Mars North polar cap  

NASA Astrophysics Data System (ADS)

Spectroscopic analysis of the Mars permanent North polar cap (NPC) by MEX/OMEGA and MRO/CRISM instruments reveal apparent seasonal changes in the ice morphology during the summer season, implying that ice surface becomes increasingly coarse during the progression of season. This general trend is non-uniform in space, being particularly strong near inner edges of the spiral terraces. The comparison of spectroscopic data with high-resolution images returned by MRO/HiRISE camera shows that the extent of NPC apparent seasonal change revealed by NIR spectroscopy correlates with the orientation of dunes on the ice surface. In the inner edges of the spiral terraces, dunes are aligned preferentially in zonal direction, implying their formation under control of the meridional winds. In turn at the outer edges, where seasonal changes are less evident, dunes are aligned mostly in the meridional direction, assuming impact of the zonal atmospheric flow. Indeed, zonally aligned dunes have better conditions in terms of sunlight exposure, and their surface is expected to reveal faster aging. However the question arises what processes are responsible for this alignment. We hypothesize that the dunes are formed under strong control of the local meteorology, dominated with competing mesoscale zonal circulation and local katabatic winds. In most cases the latter have meridional direction and maximize near the steepest relief, i.e. southward of the boundary between neighboring terraces. In some cases katabatic winds directions are in the strong interconnection with certain local and mesoscale topography features. Thus seasonal changes of the ice surface microstructure are connected with the relief on the scale of tens of meters, which in turn may be formed under influence of the local wind pattern controlled by large-scale relief of the North polar cap.

Evdokimova, N. A.; Rodin, A. V.; Appere, T.

2012-09-01

235

Electrically controlled spin polarization and selection in a topological insulator sandwiched between ferromagnetic electrodes  

SciTech Connect

We theoretically investigate the electrically controllable spin polarization and selective efficiency of the edge state Dirac electron in a two-dimensional topological insulator (TI) sandwiched between ferromagnetic (FM) electrodes by using the method of Keldysh nonequilibrium Green's function. A nearly full spin polarization of the topological edge state with giant inversion of ?80% is observed, which is much higher than the value previously reported. Moreover, the selective efficiency for spin-up electrons under the modulation of the parallel configuration of FM electrodes has been demonstrated to be larger than 95% for the first time, while that for spin-down electrons in the antiparallel case is higher than 90% in a wide energy range, owing to the inter-edge spin tunneling induced backscattering and spin dephasing effect. The obtained results may provide a deeper understanding of the TI edge states and a valuable guidance to design spin switch and filter with high on-off speed and selective efficiency based on TIs.

Guo, Junji; Liao, Wenhu, E-mail: whliao2007@aliyun.com; Zhao, Heping [College of Physics, Mechanical and Electrical Engineering, Jishou University, Jishou 416000 (China); Zhou, Guanghui [Department of Physics and Key Laboratory for Low-Dimensional Quantum Structures and Manipulation (Ministry of Education), Hunan Normal University, Changsha 410081 (China)

2014-01-14

236

Phosphorylation of LKB1/Par-4 establishes Schwann cell polarity to initiate and control myelin extent.  

PubMed

The Schwann cell (SC)-axon interface represents a membrane specialization that integrates axonal signals to coordinate cytoskeletal dynamics resulting in myelination. Here we show that LKB1/Par-4 is asymmetrically localized to the SC-axon interface and co-localizes with the polarity protein Par-3. Using purified SCs and myelinating cocultures, we demonstrate that localization is dependent on the phosphorylation of LKB1 at serine-431. SC-specific deletion of LKB1 significantly attenuates developmental myelination, delaying the initiation and altering the myelin extent into adulthood, resulting in a 30% reduction in the conduction velocity along the adult sciatic nerves. Phosphorylation of LKB1 by protein kinase A is essential to establish the asymmetric localization of LKB1 and Par-3 and rescues the delay in myelination observed in the SC-specific knockout of LKB1. Our findings suggest that SC polarity may coordinate multiple signalling complexes that couple SC-axon contact to the redistribution of specific membrane components necessary to initiate and control myelin extent. PMID:25255972

Shen, Yun-An A; Chen, Yan; Dao, Dang Q; Mayoral, Sonia R; Wu, Laiman; Meijer, Dies; Ullian, Erik M; Chan, Jonah R; Lu, Q Richard

2014-01-01

237

Miro-1 Links Mitochondria and Microtubule Dynein Motors To Control Lymphocyte Migration and Polarity  

PubMed Central

The recruitment of leukocytes to sites of inflammation is crucial for a functional immune response. In the present work, we explored the role of mitochondria in lymphocyte adhesion, polarity, and migration. We show that during adhesion to the activated endothelium under physiological flow conditions, lymphocyte mitochondria redistribute to the adhesion zone together with the microtubule-organizing center (MTOC) in an integrin-dependent manner. Mitochondrial redistribution and efficient lymphocyte adhesion to the endothelium require the function of Miro-1, an adaptor molecule that couples mitochondria to microtubules. Our data demonstrate that Miro-1 associates with the dynein complex. Moreover, mitochondria accumulate around the MTOC in response to the chemokine CXCL12/SDF-1?; this redistribution is regulated by Miro-1. CXCL12-dependent cell polarization and migration are reduced in Miro-1-silenced cells, due to impaired myosin II activation at the cell uropod and diminished actin polymerization. These data point to a key role of Miro-1 in the control of lymphocyte adhesion and migration through the regulation of mitochondrial redistribution. PMID:24492963

Morlino, Giulia; Barreiro, Olga; Baixauli, Francesc; Robles-Valero, Javier; González-Granado, José M.; Villa-Bellosta, Ricardo; Cuenca, Jesús; Sánchez-Sorzano, Carlos O.; Veiga, Esteban; Martín-Cófreces, Noa B.

2014-01-01

238

Control of magnetic vortex chirality and polarization in indented and notched nanomagnetic disks  

NASA Astrophysics Data System (ADS)

Magnetic vortex dynamics in nanoscale structures is currently a topic of intensive research not only from a fundamental physics point of view but also for their potential use in future generation spintronics and magnetic random access memories. We propose a method, where one can independently control the magnetic vortex polarization and chirality states by a combination of fine-tuning the applied magnetic field and breaking the geometrical symmetry of the magnetic nanostructure. Numerical simulations corroborate our proposal of achieving vortex switchability for the two different geometries we investigate: the indented disk and notched disk structures. Our results suggest that the notched disk structure offers more robust vortex dynamics and better switching characteristics, which makes this geometry ideal for use as a vortex-based magnetic memory device.

El-Mezeini, Ahmed M.; Flack, Tim J.; Welland, Mark E.

2014-12-01

239

Feed-forward continuous and complete polarization control with a PLZT rotatable-variable waveplate and inline polarimeter  

Microsoft Academic Search

A Pb1-xLax(ZryTiz)1-x4\\/O3 (PLZT) electrooptic ceramic variable-rotatable waveplate and a compact inline polarimeter have been used to develop a fast feed-forward-controlled module for the continuous and complete conversion of polarization. This requires the control of only two parameters: the direction ? and strength of the applied voltage V0. Feed-forward control speed is fast, taking only 24 ?s. The chip plates were

Katsuhiko Hirabayashi; Chikara Amano

2003-01-01

240

DKIST controls model for synchronization of instrument cameras, polarization modulators, and mechanisms  

NASA Astrophysics Data System (ADS)

The Daniel K. Inouye Solar Telescope (DKIST) will include facility instruments that perform polarimetric observations of the sun. In order for an instrument to successfully perform these observations its Instrument Controller (IC) software must be able to tightly synchronize the activities of its sub-systems including polarization modulators, cameras, and mechanisms. In this paper we discuss the DKIST control model for synchronizing these sub-systems without the use of hardware trigger lines by using the DKIST Time Reference And Distribution System (TRADS) as a common time base and through sub-system control interfaces that support configuring the timing and cadence of their behavior. The DKIST Polarization Modulator Controller System (PMCS) provides an interface that allows the IC to characterize the rotation of the modulator in terms of a reference time (t0), rate, and start state. The DKIST Virtual Camera (VC) provides a complimentary interface that allows data acquisitions and accumulation sequences to be specified using a reference time (t0), rate, and execution block time slices, which are cumulative offsets from t0. Re-configuration of other instrument mechanisms such as filter, slits, or steering mirrors during the observation is the responsibility of the IC and must be carefully scheduled at known and pre-determined gaps in the VC data acquisition sequence. The DKIST TRADS provides an IEEE-1588-2008 Precision Time Protocol (PTP) service that is used to synchronize the activities of instrument sub-systems. The modulator, camera, and mechanism sub-systems subscribe to this service and can therefore perform their tasks according to a common time base. In this paper we discuss the design of the PMCS, VC, and mechanism control interfaces, and how the IC can use them to configure the behavior of these sub-systems during an observation. We also discuss the interface to TRADS and how it is used as a common time base in each of these sub-systems. We present our preliminary results of the system performance against known instrument use cases.

Ferayorni, Andrew; Beard, Andrew; Berst, Chris; Goodrich, Bret

2014-07-01

241

High-sweep-rate 1310 nm MEMS-VCSEL with 150 nm continuous tuning range.  

PubMed

Microelectromechanical-systems-based vertical-cavity surface-emitting lasers (MEMS-VCSELs) capable of a 150 nm continuous tuning range near 1310 nm are demonstrated. These devices employ a thin optically pumped active region structure with large free-spectral range, which promotes wide and continuous tuning. To achieve VCSEL emission at 1310 nm, a wide-gain-bandwidth indium phosphide-based multiple quantum well active region is combined with a wide-bandwidth fully oxidised GaAs-based mirror through wafer bonding, with tuning enabled by a suspended dielectric top mirror. These devices are capable of being scanned over the entire tuning range at frequencies up to 500 kHz, making them ideal for applications such as swept source optical coherence tomography and high-speed transient spectroscopy. PMID:23976788

Jayaraman, V; Cole, G D; Robertson, M; Uddin, A; Cable, A

2012-07-01

242

Hybrid point/ring-defect photonic crystal VCSEL with high spectral purity and high output power  

NASA Astrophysics Data System (ADS)

A hybrid point/ring-defect photonic crystal vertical-cavity surface-emitting laser (VCSEL) is presented. To analyze the possible lasing supermodes, the device is simplified to a 3 × 1 VCSEL array along any direction in plane due to the hybrid point/ring defects with approximately radial symmetry. Three supermodes are predicted based on the coupled-mode theory. In the experiment, only three supermodes appear at most over the entire current range, consistent with the theoretical predictions. The full width at half maximum of the lasing spectrum at rollover is less than 0.1 nm, and the maximum output power of the device reaches 4.3 mW.

Liu, A. J.; Chen, W.; Qu, H. W.; Zhou, W. J.; Zheng, W. H.

2011-02-01

243

Widely tunable singlemode surface micro-machined MEMS-VCSELs operating at 1.95-?m  

NASA Astrophysics Data System (ADS)

We present surface micro-machined micro-electro mechanical-system (MEMS) tunable vertical-cavity surfaceemitting lasers (VCSEL) with rectangular and triangular shaped quantum wells (QWs) emitting around 1:95 ?m predestined for broadband tunable diode laser absorption spectroscopy. The VCSELs show single-mode operation and high side-mode suppression-ratio SMSR < 50 dB within the whole tuning range of 50nm and 35 nm, the fibre-coupled optical power of 1:0mW and 1:76mW and the threshold current of 2:5mA and 2:0mA for the rectangular and triangular shaped QWs respectively. The 3 dB modulation frequency of the MEMS is 110 Hz.

Zogal, Karolina; Gruendl, Tobias; Gierl, Christian; Paul, Sujoy; Grasse, Christian; Meissner, Peter; Amann, Marcus-Christian; Kueppers, Franko

2013-03-01

244

Metamorphic DBR and tunnel-junction injection. A CW RT monolithic long-wavelength VCSEL  

Microsoft Academic Search

We present and give details about the conception and realization of the first monolithic long wavelength vertical-cavity surface-emitting laser (VCSEL) operating continuous wave at room temperature. This approach relies on two originalities: a metamorphic GaAs-AlAs distributed Bragg reflector and an injection through a reverse-biased tunnel junction. Record output powers as high as 1 mW and a maximum operating temperature of

J. Boucart; C. Starck; F. Gaborit; A. Plais; N. Bouche; E. Derouin; J. C. Remy; J. Bonnet-Gamard; L. Goldstein; C. Fortin; D. Carpentier; P. Salet; F. Brillouet; J. Jacquet

1999-01-01

245

RAB-5 Controls the Cortical Organization and Dynamics of PAR Proteins to Maintain C. elegans Early Embryonic Polarity  

PubMed Central

In all organisms, cell polarity is fundamental for most aspects of cell physiology. In many species and cell types, it is controlled by the evolutionarily conserved PAR-3, PAR-6 and aPKC proteins, which are asymmetrically localized at the cell cortex where they define specific domains. While PAR proteins define the antero-posterior axis of the early C. elegans embryo, the mechanism controlling their asymmetric localization is not fully understood. Here we studied the role of endocytic regulators in embryonic polarization and asymmetric division. We found that depleting the early endosome regulator RAB-5 results in polarity-related phenotypes in the early embryo. Using Total Internal Reflection Fluorescence (TIRF) microscopy, we observed that PAR-6 is localized at the cell cortex in highly dynamic puncta and depleting RAB-5 decreased PAR-6 cortical dynamics during the polarity maintenance phase. Depletion of RAB-5 also increased PAR-6 association with clathrin heavy chain (CHC-1) and this increase depended on the presence of the GTPase dynamin, an upstream regulator of endocytosis. Interestingly, further analysis indicated that loss of RAB-5 leads to a disorganization of the actin cytoskeleton and that this occurs independently of dynamin activity. Our results indicate that RAB-5 promotes C. elegans embryonic polarity in both dynamin-dependent and -independent manners, by controlling PAR-6 localization and cortical dynamics through the regulation of its association with the cell cortex and the organization of the actin cytoskeleton. PMID:22545101

Hyenne, Vincent; Tremblay-Boudreault, Thierry; Velmurugan, Ramraj; Grant, Barth D.; Loerke, Dinah; Labbé, Jean-Claude

2012-01-01

246

Polarization-controlled spin reorientation transition and resistive switching in ferromagnetic-ferroelectric nanostructures and tunnel junctions  

NASA Astrophysics Data System (ADS)

A spin reorientation transition (SRT) induced in a ferromagnetic nanolayer by the polarization switching in an adjoining ferroelectric film or bulk crystal is described theoretically. It is shown that such a polarization-controlled SRT can be realized in a narrow range of the nanolayer thicknesses only. Our calculations allowing for the polarization-dependent interfacial magnetic anisotropy predict that this "thickness window" is located between two threshold thicknesses, at which a size-induced SRT takes place in the ferromagnetic nanolayer at two different directions of the ferroelectric polarization. Importantly, the polarization-controlled SRT manifests itself in the resistance switching occurring in multiferroic tunnel junctions (MFTJs), where an ultrathin ferroelectric barrier is embedded between a ferromagnetic electrode with controllable magnetization and an electrode with a fixed magnetization. Using Fe/BaTiO3/Fe junctions as a representative example, we demonstrate that such MFTJs can be employed as electric-write nanoscale memory cells with reliable nondestructive readout and high thermal stability of information storage.

Pertsev, N. A.; Viaud, G.; Dkhil, B.

2014-07-01

247

Large-area high-power VCSEL pump arrays optimized for high-energy lasers  

NASA Astrophysics Data System (ADS)

Practical, large-area, high-power diode pumps for one micron (Nd, Yb) as well as eye-safer wavelengths (Er, Tm, Ho) are critical to the success of any high energy diode pumped solid state laser. Diode efficiency, brightness, availability and cost will determine how realizable a fielded high energy diode pumped solid state laser will be. 2-D Vertical-Cavity Surface-Emitting Laser (VCSEL) arrays are uniquely positioned to meet these requirements because of their unique properties, such as low divergence circular output beams, reduced wavelength drift with temperature, scalability to large 2-D arrays through low-cost and high-volume semiconductor photolithographic processes, high reliability, no catastrophic optical damage failure, and radiation and vacuum operation tolerance. Data will be presented on the status of FLIR-EOC's VCSEL pump arrays. Analysis of the key aspects of electrical, thermal and mechanical design that are critical to the design of a VCSEL pump array to achieve high power efficient array performance will be presented.

Wang, Chad; Geske, Jonathan; Garrett, Henry; Cardellino, Terri; Talantov, Fedor; Berdin, Glen; Millenheft, David; Renner, Daniel; Klemer, Daniel

2012-06-01

248

Compact VCSEL-based laser array communications systems for improved data performance in satellites  

NASA Astrophysics Data System (ADS)

Compact, radiation-hardened free-space optical data links are enabled by two-dimensional VCSEL arrays that can be modulated at high data rates while being scaled to produce high power levels. The combination of high modulation speed and scalability of power is enabled by the use of arrays which are flip-chip mounted onto sub-mounts that contain electrical strip line waveguides to provide an impedance match for the VCSELs. For laser wavelengths in the 910 nm to 1020 nm range, the lasers can be back-emitting through the GaAs substrate, which enables the use of etched microlenses to manipulate the beams from the individual elements. This approach of using VCSELs in arrays is inherently reliable and radiation-hard. The resulting free space optical data links are particularly advantageous for space-borne applications where size, weight, and power are important factors. Performance characterization of links constructed with these lasers demonstrates their suitability for short distance to medium distance data transfer at up to 10 Gb/s.

Carson, Richard F.; Warren, Mial E.; Joseph, John R.; Wilcox, Thomas; Abell, David J.; Otis, Kirk J.

2014-09-01

249

Development of a Compact Optical-MEMS Scanner with Integrated VCSEL Light Source and Diffractive Optics  

SciTech Connect

In this work the design and initial fabrication results are reported for the components of a compact optical-MEMS laser scanning system. This system integrates a silicon MEMS laser scanner, a Vertical Cavity Surface Emitting Laser (VCSEL) and passive optical components. The MEMS scanner and VCSEL are mounted onto a fused silica substrate which serves as an optical interconnect between the devices. Two Diffractive Optical Elements (DOEs) are etched into the fused silica substrate to focus the VCSEL beam and increase the scan range. The silicon MEMS scanner consists of an actuator that continuously scans the position of a large polysilicon gold-coated shuttle containing a third DOE. Interferometric measurements show that the residual stress in the 500 {micro}m x 1000 {micro}m shuttle is extremely low, with a maximum deflection of only 0.18{micro}m over an 800 {micro}m span for an unmetallized case and a deflection of 0.56{micro}m for the metallized case. A conservative estimate for the scan range is {approximately}{+-}4{degree}, with a spot size of about 0.5 mm, producing 50 resolvable spots. The basic system architecture, optical and MEMS design is reported in this paper, with an emphasis on the design and fabrication of the silicon MEMS scanner portion of the system.

Krygowski, Thomas W.; Reyes, David; Rodgers, M. Steven; Smith, James H.; Warren, Mial; Sweatt, William; Blum-Spahn, Olga; Wendt, Joel R.; Asbill, Randy

1999-06-30

250

High-speed 850 and 980 nm VCSELs for high-performance computing applications  

NASA Astrophysics Data System (ADS)

The ever growing demand for more bandwidth in high-performance computing (HPC) applications leads to a continuous replacement of traditional copper-based links by optical interconnects at ever shorter transmission distances. However, this trend results in a more stringent performance requirements for laser light sources utilized in new generations of optical interconnects in respect to single channel speed, packaging density, power consumption and temperature stability, to make the technology competitive and commercially viable. Vertical cavity surface emitting lasers operating at different wavelengths, e. g. 850 or 980 nm, represent one possible solution for the short distance high density interconnects in HPC applications. Here we present ultra-high speed highly temperature stable 980 nm VCSELs operating error-free at the record high bit rate of 44 Gbit/s at room temperature and 38 Gbit/s at 85 °C for future interand intra-chip, and module-to-module optical links. Next we present high speed extremely energy efficient 850 nm VCSELs with record low energy consumptions of only 83 fJ/bit while operating at 17 Gbit/s and of only 117 fJ/bit at 25 Gbit/s. Our VCSELs enable ecologically sound and economically practical HPC designs.

Mutig, Alex; Moser, Philip; Lott, James A.; Wolf, Philip; Hofmann, Werner; Ledentsov, Nikolay N.; Bimberg, Dieter

2011-12-01

251

Polarization controlled deep sub-wavelength periodic features written by femtosecond laser on nanodiamond thin film surface  

SciTech Connect

Deep sub-wavelength (?/??=??0.22) periodic features are induced uniformly on a nanodiamond (ND) thin film surface using femtosecond (fs) laser irradiation (pulse duration?=??110 fs and central wavelength of ?800?nm). The topography of the surface features is controlled by the laser polarization. Orientation of features is perpendicular to laser polarization. Periodicity (spatial periodicity of?polarization controlled surface plasmon-fs laser coupling mechanism prompting the interaction between fs laser and solid matter (here ND thin film) which in turn is resulting in the periodic surface features. Scanning electron microscopy in conjunction with micro Raman scattering, X-ray diffraction, and atomic force microscopy are carried out to extract surface morphology and phase information of the laser irradiated regions. This work demonstrates an easy and efficient surface fabrication technique.

Kumar Kuntumalla, Mohan; Srikanth, Vadali V. S. S., E-mail: vvsssse@uohyd.ernet.in [School of Engineering Sciences and Technology, University of Hyderabad, Hyderabad 500046 (India); Rajamudili, Kuladeep; Rao Desai, Narayana [School of Physics, University of Hyderabad, Hyderabad 500046 (India)

2014-04-21

252

Control of electron localization in the dissociation of H2+ using orthogonally polarized two-color sequential laser pulses  

NASA Astrophysics Data System (ADS)

Orthogonally polarized two-color sequential laser pulses are used to control the electron localization in the dissociation of H2+. The first single attosecond pulse, whose polarization axis is perpendicular to the molecular axis, excites H2+ from 1s?g to 2p?u, and the time-delayed infrared pulse, whose polarization axis is parallel to the molecular axis, steers the electron between two nuclei. The simulation of the time-dependent Schrödinger equation predicts the control degree of the electron localization can be up to 90% with the current laser technology. To the best of our knowledge, we first reveal that the new mechanism for this asymmetric localization is due to the mixture of 2p?g and 2p?u, instead of 1s?g and 2p?u in the previous studies.

He, Feng

2014-04-01

253

Poldip2 controls vascular smooth muscle cell migration by regulating focal adhesion turnover and force polarization.  

PubMed

Polymerase-?-interacting protein 2 (Poldip2) interacts with NADPH oxidase 4 (Nox4) and regulates migration; however, the precise underlying mechanisms are unclear. Here, we investigated the role of Poldip2 in focal adhesion turnover, as well as traction force generation and polarization. Poldip2 overexpression (AdPoldip2) in vascular smooth muscle cells (VSMCs) impairs PDGF-induced migration and induces a characteristic phenotype of long cytoplasmic extensions. AdPoldip2 also prevents the decrease in spreading and increased aspect ratio observed in response to PDGF and slightly impairs cell contraction. Moreover, AdPoldip2 blocks focal adhesion dissolution and sustains H2O2 levels in focal adhesions, whereas Poldip2 knockdown (siPoldip2) significantly decreases the number of focal adhesions. RhoA activity is unchanged when focal adhesion dissolution is stimulated in control cells but increases in AdPoldip2-treated cells. Inhibition of RhoA blocks Poldip2-mediated attenuation of focal adhesion dissolution, and overexpression of RhoA or focal adhesion kinase (FAK) reverses the loss of focal adhesions induced by siPoldip2, indicating that RhoA and FAK mediate the effect of Poldip2 on focal adhesions. Nox4 silencing prevents focal adhesion stabilization by AdPoldip2 and induces a phenotype similar to siPoldip2, suggesting a role for Nox4 in Poldip2-induced focal adhesion stability. As a consequence of impaired focal adhesion turnover, PDGF-treated AdPoldip2 cells are unable to reduce and polarize traction forces, a necessary first step in migration. These results implicate Poldip2 in VSMC migration via regulation of focal adhesion turnover and traction force generation in a Nox4/RhoA/FAK-dependent manner. PMID:25063792

Datla, Srinivasa Raju; McGrail, Daniel J; Vukelic, Sasa; Huff, Lauren P; Lyle, Alicia N; Pounkova, Lily; Lee, Minyoung; Seidel-Rogol, Bonnie; Khalil, Mazen K; Hilenski, Lula L; Terada, Lance S; Dawson, Michelle R; Lassègue, Bernard; Griendling, Kathy K

2014-10-01

254

Topographic cell instructive patterns to control cell adhesion, polarization and migration.  

PubMed

Topographic patterns are known to affect cellular processes such as adhesion, migration and differentiation. However, the optimal way to deliver topographic signals to provide cells with precise instructions has not been defined yet. In this work, we hypothesize that topographic patterns may be able to control the sensing and adhesion machinery of cells when their interval features are tuned on the characteristic lengths of filopodial probing and focal adhesions (FAs). Features separated by distance beyond the length of filopodia cannot be readily perceived; therefore, the formation of new adhesions is discouraged. If, however, topographic features are separated by a distance within the reach of filopodia extension, cells can establish contact between adjacent topographic islands. In the latter case, cell adhesion and polarization rely upon the growth of FAs occurring on a specific length scale that depends on the chemical properties of the surface. Topographic patterns and chemical properties may interfere with the growth of FAs, thus making adhesions unstable. To test this hypothesis, we fabricated different micropatterned surfaces displaying feature dimensions and adhesive properties able to interfere with the filopodial sensing and the adhesion maturation, selectively. Our data demonstrate that it is possible to exert a potent control on cell adhesion, elongation and migration by tuning topographic features' dimensions and surface chemistry. PMID:25253035

Ventre, Maurizio; Natale, Carlo Fortunato; Rianna, Carmela; Netti, Paolo Antonio

2014-11-01

255

Optically and electrically controlled circularly polarized emission from cholesteric liquid crystal materials doped with semiconductor quantum dots.  

PubMed

Novel types of electro- and photoactive quantum dot-doped cholesteric materials have been engineered. UV-irradiation or electric field application allows one to control the degree of circular polarization and intensity of fluorescence emission by prepared quantum dot-doped liquid crystal films. PMID:22972420

Bobrovsky, Alexey; Mochalov, Konstantin; Oleinikov, Vladimir; Sukhanova, Alyona; Prudnikau, Anatol; Artemyev, Mikhail; Shibaev, Valery; Nabiev, Igor

2012-12-01

256

Collective Coherent Control: Synchronization of Polarization in Ferroelectric PbTiO3 by Shaped THz Fields  

E-print Network

Collective Coherent Control: Synchronization of Polarization in Ferroelectric PbTiO3 by Shaped THz terahertz (THz) fields can be used to move ions in ferroelectric crystals from their positions in an initial structural change. We show through numerical simulations that tem- porally shaped THz fields can be used

Rappe, Andrew M.

257

Optical Control of Spatial Patterning of Nuclear Polarization in GaAs  

NASA Astrophysics Data System (ADS)

We present new results on the optical polarization of nuclear spins in gallium arsenide. Previous work has identified the contact hyperfine interaction at shallow donors as the mechanism for helicity dependent nuclear polarization. We show a new regime, where donors are only partially occupied, where nuclear quadrupolar relaxation at shallow donors is the dominant mechanism. Since quadrupolar relaxation is helicity independent, the incident light polarization may be tuned such that the two relaxation mechanisms drive the nuclear spins to opposite signs of polarization. We show that incident light wavelength and power may be tuned to create spatial patterns of varying donor occupation in a single sample, which in turn creates a pattern of positive and negative nuclear polarization. We have developed an analytical mode which accurately describes the bulk NMR signal in terms of irradiation power and wavelength. We also present stray-field NMR imaging experiments showing direct observation of the patterned nuclear polarization.

King, Jonathan; Li, Yunpu; Peng, Le; Tamargo, Maria; Meriles, Carlos; Reimer, Jeffrey

2011-03-01

258

Parametric polarization pulse shaping demonstrated for optimal control of NaK  

NASA Astrophysics Data System (ADS)

We present a routine for calculating and producing customized/parametric femtosecond laser pulses for investigating molecular processes involving the polarization. It is applied on the ionization of NaK molecules by feedback-loop optimization using the recently introduced double-pass "serial setup" that is capable of phase, amplitude, and polarization modulation. The temporal subpulse encoding uses the parameters distance, intensity, zero order spectral phase, and polarization state.

Weber, Stefan M.; Plewicki, Mateusz; Weise, Fabian; Lindinger, Albrecht

2008-05-01

259

The planar cell polarity effector protein Wdpcp (Fritz) controls epithelial cell cortex dynamics via septins and actomyosin.  

PubMed

Planar cell polarity (PCP) signaling controls polarized behaviors in diverse tissues, including the collective cell movements of gastrulation and the planar polarized beating of motile cilia. A major question in PCP signaling concerns the mechanisms linking this signaling cascade with more general cytoskeletal elements to drive polarized behavior. Previously, we reported that the PCP effector protein Wdpcp (formerly known as Fritz) interacts with septins and is critical for collective cell migration and cilia formation. Here, we report that Wdpcp is broadly involved in maintaining cortical tension in epithelial cells. In vivo 3D time-lapse imaging revealed that Wdpcp is necessary for basolateral plasma membrane stability in epithelial tissues, and we further show that Wdpcp controls cortical septin localization to maintain cortical rigidity in mucociliary epithelial cells. Finally, we show that Wdpcp acts via actomyosin to maintain balanced cortical tension in the epithelium. These data suggest that, in addition to its role in controlling plasma membrane dynamics in collective mesenchymal cell movements, Wdpcp is also essential for normal cell cortex stability during epithelial homeostasis. PMID:25436430

Park, Tae Joo; Kim, Su Kyoung; Wallingford, John B

2015-01-01

260

Environmental control of cloud-to-ground lightning polarity in severe storms  

NASA Astrophysics Data System (ADS)

The overwhelming majority of severe storms throughout the contiguous U.S. generate primarily (>75%) negative ground flashes (so-called negative storms). However, a certain subset of severe storms produces an anomalously high (> 25%) percentage of positive ground flashes (so-called positive storms). The frequency of these "anomalous" positive storms varies regionally and seasonally. In some regions (e.g., central and northern plains) and months, these positive storms are common, representing 30% or more of all severe storms. Several past studies have noted that severe storms passing through similar mesoscale regions on a given day exhibit similar cloud-to-ground (CG) lightning behavior. This repeated observation led to the idea that the local mesoscale environment indirectly influences CG lightning polarity by directly controlling storm structure, dynamics, and microphysics, which in turn control storm electrification. Although a few studies have explored this relationship, the exact conditions favoring positive storms are poorly understood. The purpose of this study is to conduct a systematic comparison of the mesoscale environments for positive and negative storms, set in the framework of a testable hypothesis. According to our hypothesis, intense updrafts and associated high liquid water contents in positive storms lead to positive charging of graupel and hail via the non-inductive charging mechanism, an enhanced lower positive charge (or inverted-polarity), and increased frequency of positive CG lightning. We have utilized abundant environmental soundings taken during the International H2O project (IHOP, May-June 2002) to document the relationship between mesoscale environment and dominant CG lightning polarity in the central plains. From hundreds of IHOP soundings, we carefully selected roughly fifty inflow proximity soundings that best represented the mesoscale environment of five (four) negative (positive) storm systems. Mean convective available potential energy (CAPE) estimated in the electrically important mixed phase zone (-10 to -40 degrees Celsius) was significantly higher in positive storms (1210 J kg-1) than in negative storms (957 J kg-1). Positive storms (14.7 m s-1) had noticeably higher mean low-level (0-3 km) shear than negative storms (10.7 m s-1). Interestingly, the mean lifting condensation level (LCL) for positive storms (2079 m) was 1.9 times higher than for negative storms (1121 m). The environmental freezing level (FL) was also lower in positive storms (3777 m) than in negative storms (4070 m). As a result, the mean warm cloud depth (FL-LCL) was dramatically larger in negative storms (2949 m) than in positive storms (1699 m). According to parcel theory, higher mixed phase CAPE directly leads to stronger updrafts and higher liquid water contents in positive storms. Larger low-level shear in positive storms aids in the development of intense low-to-mid level updrafts and enhanced liquid water contents through dynamic forcing. Higher LCL or cloud base height, which is associated with increased parcel size and decreased entrainment of dry air, in positive storms results in more efficient conversion of CAPE into kinetic energy and hence enhanced updraft strength and liquid water content. Reduced warm cloud depth in positive storms may decrease the amount of liquid water that is lost through the collision-coalescence and rainout process in a rising air parcel below the mixed phase zone, effectively increasing the amount of supercooled cloud water that is available for cloud electrification.

Carey, L. D.; Buffalo, K.

2004-12-01

261

Polarization-independent electro-optic modulator based on PMNT electrically-controlled birefringence effect and Sagnac interferometer  

NASA Astrophysics Data System (ADS)

A novel polarization-independent electro-optic modulator is proposed and investigated by using the electrically-controlled birefringence effect of transparent lead magnesium niobate titanate (PMNT) electro-optic ceramic and a Sagnac interferometer structure. The PMNT electro-optic ceramic is used as a phase retarder for two counter-propagating waves in which their polarization directions are adjusted to parallel and vertical to the electrical-field vector respectively. Then the output light intensity from the Sagnac interferometer will be modulated completely with the driven electrical signal and it is independent with the polarization direction of incident light. The extinction ratio is more than 21 dB. This modulated device will be very appropriate as a Q-switch or optical attenuator in the high power laser system.

Zhang, Xuejiao; Ye, Qing; Cai, Haiwen; Qu, Ronghui

2014-04-01

262

Quantitative analysis of polarization-controlled tip-enhanced Raman imaging through the evaluation of the tip dipole.  

PubMed

Polarization analysis in tip-enhanced Raman spectroscopy (TERS) is of tremendous advantage, as it allows one to study highly directional intrinsic properties of a sample at the nanoscale. However, neither evaluation nor control of the polarization properties of near-field light in TERS is as straightforward as in usual far-field illumination, because of the random metallic nanostructure attached to the tip apex. In this study, we have developed a method to successfully analyze the polarization of near-field light in TERS from the scattering pattern produced by the induced dipole in the metallic tip. Under dipole approximation, we measured the image of the dipole at a plane away from the focal plane, where the information about the direction of the dipole oscillation was intact. The direction of the dipole oscillation was determined from the defocused pattern, and then the polarization of near-field light was evaluated from the oscillation direction by calculating the intensity distribution of near-field light through Green's function. After evaluating the polarization of some fabricated tips, we used those tips to measure TERS images from single-walled carbon nanotubes and confirmed that the contrast of the TERS image depended on the oscillation direction of the dipole, which were also found in excellent agreement with the calculated TERS images, verifying that the polarization of the near-field was quantitatively estimated by our technique. Our technique would lead to better quantitative analysis in TERS imaging with consideration of polarization impact, giving a better understanding of the behavior of nanomaterials. PMID:25171468

Mino, Toshihiro; Saito, Yuika; Verma, Prabhat

2014-10-28

263

miR-296 regulation of a cell polarity-cell plasticity module controls tumor progression  

PubMed Central

The expression of small, non-coding RNA, or microRNAs (miR), is frequently deregulated in human cancer, but how these pathways affect disease progression is still largely elusive. Here, we report on a microRNA, miR-296, which is progressively lost during tumor progression, and correlates with metastatic disease in colorectal, breast, lung, gastric, parathyroid, liver and bile ducts cancers. Functionally, miR-296 controls a global cell motility gene signature in epithelial cells by transcriptionally repressing the cell polarity-cell plasticity module, Scrib. In turn, loss of miR-296 causes aberrantly increased and mislocalized Scrib in human tumors, resulting in exaggerated random cell migration, and tumor cell invasiveness. Re-expression of miR-296 in MDA-MB231 cells inhibits tumor growth, in vivo. Finally, miR-296 or Scrib levels predict tumor relapse in hepatocellular carcinoma patients. These data identify miR-296 as a global repressor of tumorigenicity, and uncover a previously unexplored exploitation of Scrib in tumor progression in humans. PMID:21643016

Vaira, Valentina; Faversani, Alice; Dohi, Takehiko; Montorsi, Marco; Augello, Claudia; Gatti, Stefano; Coggi, Guido; Altieri, Dario C.; Bosari, Silvano

2011-01-01

264

Reflectivity characteristics of the fiber loop mirror with a polarization controller  

NASA Astrophysics Data System (ADS)

In this paper, reflectivity characteristics of a fiber loop mirror (FLM), which is formed by inserting a fiber polarization controller (PC) into the fiber loop of an ordinary FLM, are investigated in detail. A theoretical model for determining the reflectivity characteristics of the FLM is present by using the equivalent optical path technique, and the reflectivity characteristics of the FLM are then simulated with the model. The simulation results show that, when the FLM is based on a 3 dB optical coupler (OC), the reflectivity of the FLM may be continuously adjusted to any value between 1 and 0 by changing the PC state, i.e. by either changing the fast axis orientation or the birefringence intensity of the PC alone, as well as both of them; the reflectivity spectra of the FLM are wide and flattened for any PC state, mainly limited by the operating bandwidth of the OC used. The reflectivity characteristics of the FLM are further tested experimentally. The results verify that the reflectivity of the FLM may truly be continuously adjusted between its maximum and minimum values by changing the PC state. The obtainable maximum and minimum reflectivities of the FLM are measured to be 93% and 2%, respectively. Moreover, the experimental results are in agreement with those of the simulations.

Feng, Sujuan; Mao, Qinghe; Shang, Liang; Lit, John W. Y.

2007-09-01

265

High-efficiency broadband meta-hologram with polarization-controlled dual images.  

PubMed

Holograms, the optical devices to reconstruct predesigned images, show many applications in our daily life. However, applications of hologram are still limited by the constituent materials and therefore their working range is trapped at a particular electromagnetic region. In recent years, the metasurfaces, an array of subwavelength antenna with varying sizes, show the abilities to manipulate the phase of incident electromagnetic wave from visible to microwave frequencies. Here, we present a reflective-type and high-efficiency meta-hologram fabricated by metasurface for visible wavelength. Using gold cross nanoantennas as building blocks to construct our meta-hologram devices with thickness ? ?/4, the reconstructed images of meta-hologram show polarization-controlled dual images with high contrast, functioning for both coherent and incoherent light sources within a broad spectral range and under a wide range of incidence angles. The flexibility demonstrated here for our meta-hologram paves the road to a wide range of applications related to holographic images at arbitrary electromagnetic wave region. PMID:24329425

Chen, Wei Ting; Yang, Kuang-Yu; Wang, Chih-Ming; Huang, Yao-Wei; Sun, Greg; Chiang, I-Da; Liao, Chun Yen; Hsu, Wei-Lun; Lin, Hao Tsun; Sun, Shulin; Zhou, Lei; Liu, Ai Qun; Tsai, Din Ping

2014-01-01

266

Polarized linewidth-controllable double-trapping electromagnetically induced transparency spectra in a resonant plasmon nanocavity  

PubMed Central

Surface plasmons with ultrasmall optical mode volume and strong near field enhancement can be used to realize nanoscale light-matter interaction. Combining surface plasmons with the quantum system provides the possibility of nanoscale realization of important quantum optical phenomena, including the electromagnetically induced transparency (EIT), which has many applications in nonlinear quantum optics and quantum information processing. Here, using a custom-designed resonant plasmon nanocavity, we demonstrate polarized position-dependent linewidth-controllable EIT spectra at the nanoscale. We analytically obtain the double coherent population trapping conditions in a double-? quantum system with crossing damping, which give two transparent points in the EIT spectra. The linewidths of the three peaks are extremely sensitive to the level spacing of the excited states, the Rabi frequencies and detunings of pump fields, and the Purcell factors. In particular the linewidth of the central peak is exceptionally narrow. The hybrid system may have potential applications in ultra-compact plasmon-quantum devices. PMID:24096943

Wang, Luojia; Gu, Ying; Chen, Hongyi; Zhang, Jia-Yu; Cui, Yiping; Gerardot, Brian D.; Gong, Qihuang

2013-01-01

267

Control of the Polarization of a Vacuum-Ultraviolet, High-Gain, Free-Electron Laser  

NASA Astrophysics Data System (ADS)

The two single-pass, externally seeded free-electron lasers (FELs) of the FERMI user facility are designed around Apple-II-type undulators that can operate at arbitrary polarization in the vacuum ultraviolet-to-soft x-ray spectral range. Furthermore, within each FEL tuning range, any output wavelength and polarization can be set in less than a minute of routine operations. We report the first demonstration of the full output polarization capabilities of FERMI FEL-1 in a campaign of experiments where the wavelength and nominal polarization are set to a series of representative values, and the polarization of the emitted intense pulses is thoroughly characterized by three independent instruments and methods, expressly developed for the task. The measured radiation polarization is consistently >90 % and is not significantly spoiled by the transport optics; differing, relative transport losses for horizontal and vertical polarization become more prominent at longer wavelengths and lead to a non-negligible ellipticity for an originally circularly polarized state. The results from the different polarimeter setups validate each other, allow a cross-calibration of the instruments, and constitute a benchmark for user experiments.

Allaria, Enrico; Diviacco, Bruno; Callegari, Carlo; Finetti, Paola; Mahieu, Benoît; Viefhaus, Jens; Zangrando, Marco; De Ninno, Giovanni; Lambert, Guillaume; Ferrari, Eugenio; Buck, Jens; Ilchen, Markus; Vodungbo, Boris; Mahne, Nicola; Svetina, Cristian; Spezzani, Carlo; Di Mitri, Simone; Penco, Giuseppe; Trovó, Mauro; Fawley, William M.; Rebernik, Primoz R.; Gauthier, David; Grazioli, Cesare; Coreno, Marcello; Ressel, Barbara; Kivimäki, Antti; Mazza, Tommaso; Glaser, Leif; Scholz, Frank; Seltmann, Joern; Gessler, Patrick; Grünert, Jan; De Fanis, Alberto; Meyer, Michael; Knie, André; Moeller, Stefan P.; Raimondi, Lorenzo; Capotondi, Flavio; Pedersoli, Emanuele; Plekan, Oksana; Danailov, Miltcho B.; Demidovich, Alexander; Nikolov, Ivaylo; Abrami, Alessandro; Gautier, Julien; Lüning, Jan; Zeitoun, Philippe; Giannessi, Luca

2014-10-01

268

Origins and control of polarization effects in single-mode fibers  

Microsoft Academic Search

The polarization state of light in single-mode fibers is very sensitive to any perturbation which is not symmetric about the fiber axis. While this is a source of noise, drift, or signal fading in some applications, it can also be exploited in novel guided-wave devices. The basic birefringences that couple the two modes and change the polarization state along the

S. Rashleigh

1983-01-01

269

Using a sharp metal tip to control the polarization and direction of emission from a quantum dot.  

PubMed

Optical antennas can be used to manipulate the direction and polarization of radiation from an emitter. Usually, these metallic nanostructures utilize localized plasmon resonances to generate highly directional and strongly polarized emission, which is determined predominantly by the antenna geometry alone, and is thus not easily tuned. Here we show experimentally that the emission polarization can be manipulated using a simple, nonresonant scanning probe consisting of the sharp metallic tip of an atomic force microscope; finite element simulations reveal that the emission simultaneously becomes highly directional. Together, the measurements and simulations demonstrate that interference between light emitted directly into the far field with that elastically scattered from the tip apex in the near field is responsible for this control over polarization and directionality. Due to the relatively weak emitter-tip coupling, the tip must be positioned very precisely near the emitter, but this weak coupling also leads to highly tunable emission properties with a similar degree of polarization and directionality compared to resonant antennas. PMID:25248420

Ghimire, Anil; Shafran, Eyal; Gerton, Jordan M

2014-01-01

270

Using a Sharp Metal Tip to Control the Polarization and Direction of Emission from a Quantum Dot  

NASA Astrophysics Data System (ADS)

Optical antennas can be used to manipulate the direction and polarization of radiation from an emitter. Usually, these metallic nanostructures utilize localized plasmon resonances to generate highly directional and strongly polarized emission, which is determined predominantly by the antenna geometry alone, and is thus not easily tuned. Here we show experimentally that the emission polarization can be manipulated using a simple, nonresonant scanning probe consisting of the sharp metallic tip of an atomic force microscope; finite element simulations reveal that the emission simultaneously becomes highly directional. Together, the measurements and simulations demonstrate that interference between light emitted directly into the far field with that elastically scattered from the tip apex in the near field is responsible for this control over polarization and directionality. Due to the relatively weak emitter-tip coupling, the tip must be positioned very precisely near the emitter, but this weak coupling also leads to highly tunable emission properties with a similar degree of polarization and directionality compared to resonant antennas.

Ghimire, Anil; Shafran, Eyal; Gerton, Jordan M.

2014-09-01

271

Controlled quantum key distribution with three-photon polarization-entangled states via the collective noise channel  

SciTech Connect

Using three-photon polarization-entangled GHZ states or W states, we propose controlled quantum key distribution protocols for circumventing two main types of collective noise, collective dephasing noise, or collective rotation noise. Irrespective of the number of controllers, a three-photon state can generate a one-bit secret key. The storage technique of quantum states is dispensable for the controller and the receiver, and it therefore allows performing the process in a more convenient mode. If the photon cost in a security check is disregarded, then the efficiency theoretically approaches unity.

Dong Li; Xiu Xiaoming, E-mail: xiuxiaomingdl@126.com [Dalian University of Technology, School of Physics and Optoelectronic Technology (China); Gao Yajun [Bohai University, Department of Physics, College of Mathematics and Physics (China); Yi, X. X., E-mail: yixx@dlut.edu.cn [Dalian University of Technology, School of Physics and Optoelectronic Technology (China)

2011-10-15

272

Fast deterministic switching in orthogonal spin torque devices via the control of the relative spin polarizations  

NASA Astrophysics Data System (ADS)

We model 100 ps pulse switching dynamics of orthogonal spin transfer (OST) devices that employ an out-of-plane polarizer and an in-plane polarizer. Simulation results indicate that increasing the spin polarization ratio, CP = PIPP/POPP, results in deterministic switching of the free layer without over-rotation (360° rotation). By using spin torque asymmetry to realize an enhanced effective PIPP, we experimentally demonstrate this behavior in OST devices in parallel to anti-parallel switching. Modeling predicts that decreasing the effective demagnetization field can substantially reduce the minimum CP required to attain deterministic switching, while retaining low critical switching current, Ip ˜ 500 ?A.

Park, Junbo; Ralph, D. C.; Buhrman, R. A.

2013-12-01

273

Tunable non-pixelated spatial polarization shaping including an integrated optical addressing unit  

NASA Astrophysics Data System (ADS)

We present a device for tunable spatial polarization shaping, based on a red light photo-addressable cell. Such a cell compartment is based on a bisazobenzene containing photoaligning layer and a rubbed PI aligning and is filled with the LC mixture E5. Switchable spatial addressing patterns are generated by a 200 channel micro optical addressing unit based on a red VCSEL array (? = 650 nm) and diffractive beam shapers.

Schaal, Frederik; Rutloh, Michael; Weidenfeld, Susanne; Stumpe, Joachim; Osten, Wolfgang

2014-10-01

274

SHG microscopy excited by polarization controlled beam for three-dimensional molecular orientation measurement  

NASA Astrophysics Data System (ADS)

We have developed a second-harmonic-generation (SGH) microscope to observe the three-dimensional molecular orientation with three-dimensional high spatial resolution using a polarization mode converter. The mode converter consists of a parallel-aligned nematic-liquid-crystal spatial-light-modulator (PAL-SLM) and quarter-waveplates, and converts a incident linearly polarized beam to orthogonal linearly polarized beams or radially polarized beam. We combined the mode converter with SHG microscope to obtain the local information of the three-dimensional molecular orientation. We demonstrated the detection of three-dimensional molecular orientation of collagen fiber in human Achilles' tendon. For high precision three-dimensional molecular orientation measurement, we propose a technique to calibrate the dependence of SHG detection efficiencies on molecular orientation using a liposome.

Yoshiki, K.; Hashimoto, M.; Araki, T.

2006-08-01

275

Effective all-optical polarization control induced by Raman nonlinear amplification  

Microsoft Academic Search

An effective all-optical Raman-based stabilization of any input polarization into a single state is experimentally proved exploiting an optimal combination of pump power, fibre PMD and fibre length, identified through systematic numerical simulations.

Maddalena Ferrario; Valentina Gilardone; Paolo Martelli; Lucia Marazzi; Mario Martinelli

2010-01-01

276

Defect Control for Large Remanent Polarization in Bismuth Titanate Ferroelectrics Doping Effect of Higher-Valent Cations---  

Microsoft Academic Search

The effects of concentration and distribution of defects controlled by quenching and doping of higher-valent cations on the ferroelectric properties of dense Bi4Ti3O12 ceramics were investigated. The remanent polarization (Pr) of non-doped ceramics quenched from 800°C (above the Curie temperature) was twice as large as those of samples subjected to slow cooling to 25°C and quenched from 600°C (below the

Yuji Noguchi; Ichiro Miwa; Yu Goshima; Masaru Miyayama

2000-01-01

277

Differential Polarization Nonlinear Optical Microscopy with Adaptive Optics Controlled Multiplexed Beams  

PubMed Central

Differential polarization nonlinear optical microscopy has the potential to become an indispensable tool for structural investigations of ordered biological assemblies and microcrystalline aggregates. Their microscopic organization can be probed through fast and sensitive measurements of nonlinear optical signal anisotropy, which can be achieved with microscopic spatial resolution by using time-multiplexed pulsed laser beams with perpendicular polarization orientations and photon-counting detection electronics for signal demultiplexing. In addition, deformable membrane mirrors can be used to correct for optical aberrations in the microscope and simultaneously optimize beam overlap using a genetic algorithm. The beam overlap can be achieved with better accuracy than diffraction limited point-spread function, which allows to perform polarization-resolved measurements on the pixel-by-pixel basis. We describe a newly developed differential polarization microscope and present applications of the differential microscopy technique for structural studies of collagen and cellulose. Both, second harmonic generation, and fluorescence-detected nonlinear absorption anisotropy are used in these investigations. It is shown that the orientation and structural properties of the fibers in biological tissue can be deduced and that the orientation of fluorescent molecules (Congo Red), which label the fibers, can be determined. Differential polarization microscopy sidesteps common issues such as photobleaching and sample movement. Due to tens of megahertz alternating polarization of excitation pulses fast data acquisition can be conveniently applied to measure changes in the nonlinear signal anisotropy in dynamically changing in vivo structures. PMID:24022688

Samim, Masood; Sandkuijl, Daaf; Tretyakov, Ian; Cisek, Richard; Barzda, Virginijus

2013-01-01

278

Vertical cavity surface emitting laser with nematic and chiral liquid crystals overlay  

NASA Astrophysics Data System (ADS)

A technological platform for a vertical cavity surface emitting laser (VCSEL) with tunable polarization is presented. It is realized by integrating an 850nm VCSEL chip in a liquid crystal (LC) cell that uses photo-alignment (PA) to orient the LC. Two kinds of LC are filled in and form a thin layer over the emitter of the VCSEL: nematic LC or chiral nematic LC (cLC). The VCSEL and the nematic LC layer can be electrically driven with separate electrodes. The polarization state of the laser emission can be controlled by applying an appropriate voltage over the nematic LC layer. The chiral nematic LC has a reflection band that contains the VCSEL emission wavelength, so that one circular polarized mode of the laser emission is reflected as a feedback into the VCSEL. We found that the emission from the VCSEL with cLC overlay is circularly polarized.

Xie, Y.; Beeckman, J.; Woestenborghs, W.; Panajotov, K.; Neyts, K.

2013-03-01

279

Ultrahigh speed endoscopic optical coherence tomography using micromotor imaging catheter and VCSEL technology.  

PubMed

We developed a micromotor based miniature catheter with an outer diameter of 3.2 mm for ultrahigh speed endoscopic swept source optical coherence tomography (OCT) using a vertical cavity surface-emitting laser (VCSEL) at a 1 MHz axial scan rate. The micromotor can rotate a micro-prism at several hundred frames per second with less than 5 V drive voltage to provide fast and stable scanning, which is not sensitive to the bending of the catheter. The side-viewing probe can be pulled back to acquire a three-dimensional (3D) data set covering a large area on the specimen. The VCSEL provides a high axial scan rate to support dense sampling under high frame rate operation. Using a high speed data acquisition system, in vivo 3D-OCT imaging in the rabbit GI tract and ex vivo imaging of a human colon specimen with 8 ?m axial resolution, 8 ?m lateral resolution and 1.2 mm depth range in tissue at a frame rate of 400 fps was demonstrated. PMID:23847737

Tsai, Tsung-Han; Potsaid, Benjamin; Tao, Yuankai K; Jayaraman, Vijaysekhar; Jiang, James; Heim, Peter J S; Kraus, Martin F; Zhou, Chao; Hornegger, Joachim; Mashimo, Hiroshi; Cable, Alex E; Fujimoto, James G

2013-07-01

280

Ultrahigh speed endoscopic optical coherence tomography using micromotor imaging catheter and VCSEL technology  

PubMed Central

We developed a micromotor based miniature catheter with an outer diameter of 3.2 mm for ultrahigh speed endoscopic swept source optical coherence tomography (OCT) using a vertical cavity surface-emitting laser (VCSEL) at a 1 MHz axial scan rate. The micromotor can rotate a micro-prism at several hundred frames per second with less than 5 V drive voltage to provide fast and stable scanning, which is not sensitive to the bending of the catheter. The side-viewing probe can be pulled back to acquire a three-dimensional (3D) data set covering a large area on the specimen. The VCSEL provides a high axial scan rate to support dense sampling under high frame rate operation. Using a high speed data acquisition system, in vivo 3D-OCT imaging in the rabbit GI tract and ex vivo imaging of a human colon specimen with 8 ?m axial resolution, 8 ?m lateral resolution and 1.2 mm depth range in tissue at a frame rate of 400 fps was demonstrated. PMID:23847737

Tsai, Tsung-Han; Potsaid, Benjamin; Tao, Yuankai K.; Jayaraman, Vijaysekhar; Jiang, James; Heim, Peter J. S.; Kraus, Martin F.; Zhou, Chao; Hornegger, Joachim; Mashimo, Hiroshi; Cable, Alex E.; Fujimoto, James G.

2013-01-01

281

Spatial mode discrimination in anti-guided arrays of long-wavelength VCSELs  

NASA Astrophysics Data System (ADS)

We present the optimization of the carrier injection, heat flow and optical confinement aimed at single mode operation in anti-guiding long-wavelength VCSEL arrays. The analyzed structure incorporates InP/AlGaInAs quantum wells within an InP cavity. The cavity is bounded by GaAs/AlGaAs DBRs. The tunnel junction is responsible for carrier funneling into the active region. The air-gap etched at the interface between cavity and top DBR provides the confinement of the lateral modes. To rigorously simulate the physical phenomena taking place in the device we use a multi-physical model, which comprises three-dimensional models of optical (Plane Wave Admittance Method), thermal and electrical (Finite Element Method) phenomena. We perform an exhaustive modal analysis of a 1x3 VCSEL arrays. In the analysis we investigate the influence of the size and the distance between the emitters. As the result we illustrate the complex competition of the modes and determine the geometrical parameters favoring specific array modes in the considered array designs.

Czyszanowski, Tomasz; Dems, Maciej; Sarza?a, Robert P.; Iakovlev, Vladimir; Volet, Nicolas; Kapon, Eli

2014-02-01

282

MBE growth of active regions for electrically pumped, cw-operating GaSb-based VCSELs  

NASA Astrophysics Data System (ADS)

Electrically pumped, cw-operating, single-mode GaSb-based VCSELs are attractive light sources for trace-gas sensing systems using tunable diode laser absorption spectroscopy (TDLAS) [A. Vicet, D.A. Yarekha, A. Pérona, Y. Rouillard, S. Gaillard, Spectrochimica Acta Part A 58 (2002) 2405-2412]. Only recently, the first electrically pumped (EP) devices emitting at 2.325 ?m in cw-mode at room temperature have been reported [A. Bachmann, T. Lim, K. Kashani-Shirazi, O. Dier, C. Lauer, M.-C. Amann, Electronics Letters 44(3) (2008) 202-203]. The fabrication of these devices employs the molecular beam epitaxy (MBE) growth of GaSb/AlAsSb-distributed Bragg mirrors, a multi-quantum-well active region made of AlGaAsSb/InGaAsSb and an InAsSb/GaSb-buried-tunnel junction. As VCSELs are usually driven under high injection rates, an optimum electrical design of active regions is essential for high-performance devices. In this paper we present an enhanced simulation of current flow in the active region under operation conditions. The calculation includes carrier transport by drift, diffusion and tunneling. We discuss different design criteria and material compositions for active regions. Active regions with various barrier materials were incorporated into edge emitter samples to evaluate their performance. Aluminum-containing barriers show better internal efficiency compared to active regions with GaSb as the barrier material.

Kashani-Shirazi, K.; Bachmann, A.; Boehm, G.; Ziegler, S.; Amann, M.-C.

2009-03-01

283

/III-V semiconductor broadband distributed Bragg reflectors for long-wavelength VCSEL and SESAM devices  

NASA Astrophysics Data System (ADS)

Semiconductor devices such as vertical-cavity surface-emitting lasers (VCSELs) or semiconductor-saturable absorber mirrors (SESAMs) require high-reflection mirrors. Moreover, in VCSELs, it is beneficial to have a crystalline mirror, which is as thin as possible in order to ensure a high thermal conductivity for efficient heat-sinking of the laser. On the other hand, the wavelength tuning range of a SESAM is limited by the reflection bandwidth of its distributed Bragg reflector (DBR). Thus, broadband mirrors are preferable here. This paper reports a three-pair DBR grown by molecular beam epitaxy (MBE) using BaCaF2 and GaAs on a GaAs (100) substrate. Due to the high ratio in refractive indices of GaAs and the group-IIa-fluorides, high-reflectivity mirrors and wide bandwidths can be obtained with low total thicknesses. We also investigated growth and stability of the material BaCaF2, as well as its thermal conductivity both as single layer and Bragg reflector. Observed peeling of the layers could be avoided by implementing a fluorine treatment previous to the BaCaF2 growth.

Koeninger, Anna; Boehm, Gerhard; Meyer, Ralf; Amann, Markus-Christian

2014-12-01

284

Design and analysis of high-temperature operating 795 nm VCSELs for chip-scale atomic clocks  

NASA Astrophysics Data System (ADS)

We propose a new structure design and analysis of high-temperature (>350 K) operating 795 nm vertical-cavity surface-emitting lasers (VCSELs) for 87Rb based chip-scale atomic clocks (CSACs). Compositions and thicknesses of the InAlGaAs/AlGaAs multiple quantum wells (MQWs) are optimized for high optical gain at elevated temperatures. The temperature sensitivity of the threshold current is estimated by calculating the temperature dependence of the cavity-mode gain. A self-consistent VCSEL model based on quasi-3D finite element analysis is employed to investigate the temperature distribution and output of the proposed structure. An output of 1 mW with a 3 dB bandwidth of 6 GHz is obtained from a 3 ?m aperture VCSEL under 2.4 mA current at temperature higher than 340 K. These findings indicate that high-gain QWs and gain-offset consideration are especially crucial to make high-performance VCSELs at elevated temperatures.

Zhang, Jian; Ning, Yongqiang; Zeng, Yugang; Zhang, Jianwei; Zhang, Jinlong; Fu, Xihong; Tong, Cunzhu; Wang, Lijun

2013-04-01

285

A fundamental mode Nd:GdVO4 laser pumped by a large aperture 808 nm VCSEL  

NASA Astrophysics Data System (ADS)

A fundamental mode Nd:GdVO4 laser pumped by a vertical cavity surface emitting laser (VCSEL) is experimentally demonstrated. The VCSEL has a circular output-beam which makes it easier for it to be directly coupled to a Nd:GdVO4 microcrystal. In our research, a large aperture 808 nm VCSEL, with a multi-ring-shaped aperture (MRSA) and an almost Gaussian-shaped far-field profile, is used as the pumping source. Experimental results for the Nd:GdVO4 laser pumped by the VCSEL are presented. The maximum output peak power of 0.754 W is obtained under a pump peak power of 1.3 W, and the corresponding opto-optic conversion efficiency is 58.1%. The average slope efficiency is 65.8% from the threshold pump power of 0.2 W to the pump power of 1.3 W. The laser beam quality factors are measured to be {M}x2=1.2 0 and {M}y2=1.1 5.

Hao, Y. Q.; Ma, J. L.; Yan, C. L.; Liu, G. J.; Ma, X. H.; Gong, J. F.; Feng, Y.; Wei, Z. P.; Wang, Y. X.; Zhao, Y. J.

2013-05-01

286

Carrierless amplitude phase modulation of VCSEL with 4 bit/s/Hz spectral efficiency for use in WDM-PON.  

PubMed

We experimentally demonstrate successful performance of VCSEL-based WDM link supporting advanced 16-level carrierless amplitude/phase modulation up to 1.25 Gbps, over 26 km SSMF with spectral efficiency of 4 bit/s/Hz for application in high capacity PONs. PMID:22274239

Rodes, Roberto; Wieckowski, Marcin; Pham, Thang Tien; Jensen, Jesper Bevensee; Turkiewicz, Jarek; Siuzdak, Jerzy; Monroy, Idelfonso Tafur

2011-12-19

287

Calibrations, noise, and long-term drift characteristics of the HIAPER VCSEL hygrometer  

NASA Astrophysics Data System (ADS)

Water vapor plays extremely important roles in the climate, chemistry, and dynamics of the atmosphere. Unfortunately, it is difficult to measure accurately, particularly in the upper troposphere and lower stratosphere. The NSF/NCAR Gulfstream-V HIAPER aircraft can sample in tropical moist air in the marine boundary layer to the very cold and dry air of the stratosphere. We are characterizing, testing, and calibrating a water vapor sensor to fly on HIAPER. The sensor uses a vertical cavity surface emitting laser (VCSEL) operating near 1854 nm, an open path cell with 1.9 cm diameter mirrors separated by 15 cm, and a fiber optic to deliver the infrared light. To accommodate the wide range of concentrations to be measured, the instrument can scan across two different water avpor absorption lines, a weak line at 1853.37 nm for moist air and a strong line at 1854.03 nm for dry air. Measurement specifications include 5 percent accuracy over the range from 1 ppmv at 60 mb to 4 percent mixing ratio at sea level. Initial calibrations of the instrument are being conducted by three methods: 1) comparing it with a chilled mirror hygrometer; 2) a standard dilution system of flows of nitrogen controlled by critical orifices; and 3) placing the instrument inside a vessel saturated with water vapor and immersing it in a constant, cold temperature bath. First results from the laboratory suggest that the HIAPER instrument shows excellent agreement over the chilled mirror hygrometer down to 55 C frost point. The standard dilution system of dry and saturated flows with the critical orifices also yields very good agreement with chilled mirror and HIAPER. A consistent moist offset of about 20 ppmv above the calculated frost points from the standard dilution of flows was observed until the system dried out. We have also conducted Allan variance tests to look at instrument noise and drift on 25 Hz to 2 hour timescales for constant, calibrated flows from 0.81 ppmv to 7640 ppmv. The Allan deviations show that random noise is the dominant source of noise up to ~ 80-100 s. Allan deviations for 1 Hz measurements were below 5 percent of the signal down to ~ 80 ppmv when outgassing became a more important source of noise. Long-term drift remains below the precision of the 25 Hz and 1 Hz data for up to two hours. Noise levels from the instrument are about a factor of two higher than our target specification of a minimum detectable absorbance of 1 x 10-5 at 1 Hz. However, the noise continually improves as the system dries out, and thus we suspect that at least some of this noise is related to water vapor outgassing and unrelated to optical noise from interference fringers. The drift on timescales of 1000 s is related to thermal cycling of the room temperature, and we are currently examining methods to reduce these drifts even further. Methods to truly calibrate at sub-ppmv levels as well as additional results on immersing the optical cell in a saturated, sealed chamber at low frost points (< - 40 C) will also be discussed.

Brubaker, K. A.; Paige, M. E.; Silver, J. A.; Zondlo, M. A.

2006-12-01

288

Fast deterministic switching in orthogonal spin torque devices via the control of the relative spin polarizations  

SciTech Connect

We model 100 ps pulse switching dynamics of orthogonal spin transfer (OST) devices that employ an out-of-plane polarizer and an in-plane polarizer. Simulation results indicate that increasing the spin polarization ratio, C{sub P}?=?P{sub IPP}/P{sub OPP}, results in deterministic switching of the free layer without over-rotation (360° rotation). By using spin torque asymmetry to realize an enhanced effective P{sub IPP}, we experimentally demonstrate this behavior in OST devices in parallel to anti-parallel switching. Modeling predicts that decreasing the effective demagnetization field can substantially reduce the minimum C{sub P} required to attain deterministic switching, while retaining low critical switching current, I{sub p}???500??A.

Park, Junbo; Buhrman, R. A. [Cornell University, Ithaca, New York 14853 (United States)] [Cornell University, Ithaca, New York 14853 (United States); Ralph, D. C. [Cornell University, Ithaca, New York 14853 (United States) [Cornell University, Ithaca, New York 14853 (United States); Kavli Institute at Cornell, Ithaca, New York 14853 (United States)

2013-12-16

289

Polarization dependent optical control of atomic arrangement in multilayer Ge-Sb-Te phase change materials  

NASA Astrophysics Data System (ADS)

We report the optical perturbation of atomic arrangement in the layered in GeTe/Sb2Te3 phase change memory material. To observe the structural change, the coherent A1 mode of GeTe4 local structure was investigated at various polarization angles of femtosecond pump pulses with the fluence at ?78 ?J/cm2. p-polarization found to be more effective in inducing the A1 frequency shift that can be either reversible or irreversible depending on the pump fluence. The predominant origin of this shift is attributed to rearrangement of Ge atoms driven by anisotropic dissociation of the Ge-Te bonds along the [111] axis after the p-polarized pulse irradiation.

Makino, Kotaro; Tominaga, Junji; Kolobov, Alexander V.; Fons, Paul; Hase, Muneaki

2012-12-01

290

Generation and control of polarization-entangled photons from GaAs island quantum dots by an electric field.  

PubMed

Semiconductor quantum dots are potential sources for generating polarization-entangled photons efficiently. The main prerequisite for such generation based on biexciton-exciton cascaded emission is to control the exciton fine-structure splitting. Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices. Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field. In contrast to previous studies, which were limited to In(Ga)As quantum dots, GaAs island quantum dots formed by a thickness fluctuation were used because they exhibit a larger oscillator strength and emit light with a shorter wavelength. A forward voltage was applied to a Schottky diode to control the fine-structure splitting. We observed a decrease and suppression in the fine-structure splitting of the studied single quantum dot with the field, which enabled us to generate polarization-entangled photons with a high fidelity of 0.72 ± 0.05. PMID:22314357

Ghali, Mohsen; Ohtani, Keita; Ohno, Yuzo; Ohno, Hideo

2012-01-01

291

Generation and control of polarization-entangled photons from GaAs island quantum dots by an electric field  

PubMed Central

Semiconductor quantum dots are potential sources for generating polarization-entangled photons efficiently. The main prerequisite for such generation based on biexciton–exciton cascaded emission is to control the exciton fine-structure splitting. Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices. Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field. In contrast to previous studies, which were limited to In(Ga)As quantum dots, GaAs island quantum dots formed by a thickness fluctuation were used because they exhibit a larger oscillator strength and emit light with a shorter wavelength. A forward voltage was applied to a Schottky diode to control the fine-structure splitting. We observed a decrease and suppression in the fine-structure splitting of the studied single quantum dot with the field, which enabled us to generate polarization-entangled photons with a high fidelity of 0.72±0.05. PMID:22314357

Ghali, Mohsen; Ohtani, Keita; Ohno, Yuzo; Ohno, Hideo

2012-01-01

292

A pump power controlled 1,060 nm multiwavelength fiber ring laser using nonlinear polarization rotation of SOA  

NASA Astrophysics Data System (ADS)

We propose and experimentally demonstrate a both channel spacing and wavelength-tunable 1,060 nm multiwavelength fiber laser using nonlinear polarization rotation of semiconductor optical amplifier (SOA). The SOA in the cavity can not only provide the gain but also generate a pump power controlled phase-shift between two orthogonal linear states of polarization. The experimental result shows that the fast and continuous wavelength tuning is achieved with external light injection, while the channel spacing of the multiwavelength laser can be varied by adjusting the length of polarization maintaining fiber. When an external laser source with 13 dBm power is injected into the SOA as a control pump, optically tunable operation of up to 20 wavelength channels, from 1,042 to 1,058 nm, with a wavelength spacing of 0.8 nm has been demonstrated with the signal-to-spontaneous-noise ratio over 40 dB at room temperature. The lasers are stable with a maximum power fluctuation per channel of less than 0.5 dB during 2-h test.

Liu, S.; Fu, Songnian; Tang, Ming; Shum, Perry; Liu, Deming

2013-03-01

293

Generation and control of spin-polarized photocurrents in GaMnAs heterostructures  

SciTech Connect

Photocurrents are calculated for a specially designed GaMnAs semiconductor heterostructure. The results reveal regions in the infrared range of the energy spectrum, in which the proposed structure is remarkably spin-selective. For such photon energies, the generated photocurrents are strongly spin-polarized. Application of a relatively small static bias in the growth direction of the structure is predicted to efficiently reverse the spin-polarization for some photon energies. This behavior suggests the possibility of conveniently simple switching mechanisms. The physics underlying the results is studied and understood in terms of the spin-dependent properties emerging from the particular potential profile of the structure.

Bezerra, Anibal T., E-mail: anibal@df.ufscar.br; Farinas, Paulo F.; Studart, Nelson [Departamento de Física, Universidade Federal de São Carlos, 13565-905 São Carlos, SP (Brazil); DISSE - Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutores, CNPq/MCT, Rio de Janeiro, RJ (Brazil); Castelano, Leonardo K. [Departamento de Física, Universidade Federal de São Carlos, 13565-905 São Carlos, SP (Brazil); Degani, Marcos H.; Maialle, Marcelo Z. [Faculdade de Ciências Aplicadas, Universidade Estadual de Campinas, 13484-350 Limeira, SP (Brazil); DISSE - Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutores, CNPq/MCT, Rio de Janeiro, RJ (Brazil)

2014-01-13

294

Controlling the Polarization State of Light with a Dispersion-Free Metastructure  

NASA Astrophysics Data System (ADS)

By combining the advantages of both a metallic metamaterial and a dielectric interlayer, we demonstrate the general mechanism to construct the dispersion-free metastructure, in which the intrinsic dispersion of the metallic structures is perfectly cancelled out by the thickness-dependent dispersion of the dielectric spacing layer. As examples to apply this concept, a broadband quarter-wave plate and a half-wave plate are demonstrated. By selecting the structural parameters, the polarization state of light can be freely tuned across a broad frequency range, and all of the polarization states on the Poincaré sphere can be realized dispersion free.

Jiang, Shang-Chi; Xiong, Xiang; Hu, Yuan-Sheng; Hu, Yu-Hui; Ma, Guo-Bin; Peng, Ru-Wen; Sun, Cheng; Wang, Mu

2014-04-01

295

Polarization-independent etching of fused silica based on electrons dynamics control by shaped femtosecond pulse trains for microchannel fabrication.  

PubMed

We propose an approach to realize polarization-independent etching of fused silica by using temporally shaped femtosecond pulse trains to control the localized transient electrons dynamics. Instead of nanograting formation using traditional unshaped pulses, for the pulse delay of pulse trains larger than 1 ps, coherent field-vector-related coupling is not possible and field orientation is lost. The exponential growth of the periodic structures is interrupted. In this case, disordered and interconnected nanostructures are formed, which is probably the main reason of etching independence on the laser polarization. As an application example, square-wave-shaped and arc-shaped microchannels are fabricated by using pulse trains to demonstrate the advantage of the proposed method in fabricating high-aspect-ratio and three-dimensional microchannels. PMID:25166119

Yan, X; Jiang, L; Li, X; Zhang, K; Xia, B; Liu, P; Qu, L; Lu, Y

2014-09-01

296

Control of semiconductor quantum dot emission intensity and polarization by metal nanoantennas  

NASA Astrophysics Data System (ADS)

We have studied the amplified emission properties of nanoislands with CdSe quantum dots in ZnSe/CdSe/ZnSe heterostructures surrounded by metallic antennas. It has been found that variations of the optical antenna length give rise to periodic amplification of the integral emission intensity. The period of the discovered oscillations corresponds to the wavelength of the surface plasmon-polariton mode propagating in the metallic antenna. The nature of observed periodicity was confirmed by results of numerical simulations for linear antennas. It has been established that the velocity of surface polaritons depends not only on the parameters of the dielectric constants of the metal and of the semiconductor substrate but also on the width of the metallic antenna. The influence of antenna antisymmetry (its helicity) on selective amplification of the degree of circular polarization of photoexcitation has been investigated. We found that plasmon-polariton standing waves induced in S -type (curved) antennas by circularly polarized light, which was used for quantum dot photoexcitation, result in enhanced polarization selectivity of the quantum dot emission. The selectivity of the polarization of photoexcitation is a periodic function of the helical antenna length.

Kukushkin, V. I.; Mukhametzhanov, I. M.; Kukushkin, I. V.; Kulakovskii, V. D.; Sedova, I. V.; Sorokin, S. V.; Toropov, A. A.; Ivanov, S. V.; Sobolev, A. S.

2014-12-01

297

Investigation of a Polarization Controller in Titanium Diffused Lithium Niobate Waveguide near 1530 nm Wavelength  

E-print Network

the required phase condition between them. Single mode channel waveguides were fabricated by diffusing 7?m-wide Ti stripes into the LiNbO_(3) substrate. The polarization converters and phase shifter were formed by patterning aluminum surface electrodes on top...

Sung, Won Ju

2013-12-10

298

Slmb antagonises the aPKC/Par-6 complex to control oocyte and epithelial polarity  

PubMed Central

The Drosophila anterior-posterior axis is specified when the posterior follicle cells signal to polarise the oocyte, leading to the anterior/lateral localisation of the Par-6/aPKC complex and the posterior recruitment of Par-1, which induces a microtubule reorganisation that localises bicoid and oskar mRNAs. Here we show that oocyte polarity requires Slmb, the substrate specificity subunit of the SCF E3 ubiquitin ligase that targets proteins for degradation. The Par-6/aPKC complex is ectopically localised to the posterior of slmb mutant oocytes, and Par-1 and oskar mRNA are mislocalised. Slmb appears to play a related role in epithelial follicle cells, as large slmb mutant clones disrupt epithelial organisation, whereas small clones show an expansion of the apical domain, with increased accumulation of apical polarity factors at the apical cortex. The levels of aPKC and Par-6 are significantly increased in slmb mutants, whereas Baz is slightly reduced. Thus, Slmb may induce the polarisation of the anterior-posterior axis of the oocyte by targeting the Par-6/aPKC complex for degradation at the oocyte posterior. Consistent with this, overexpression of the aPKC antagonist Lgl strongly rescues the polarity defects of slmb mutant germline clones. The role of Slmb in oocyte polarity raises an intriguing parallel with C. elegans axis formation, in which PAR-2 excludes the anterior PAR complex from the posterior cortex to induce polarity, but its function can be substituted by overexpressing Lgl. PMID:25053432

Morais-de-Sá, Eurico; Mukherjee, Avik; Lowe, Nick; St Johnston, Daniel

2014-01-01

299

PLR-1, a putative E3 ubiquitin ligase, controls cell polarity and axonal extensions in C. elegans.  

PubMed

During embryonic development neurons differentiate and extend axons and dendrites that have to reach their appropriate targets. In Caenorhabditis elegans the AVG neuron is the first neuron to extend an axon during the establishment of the ventral nerve cord, the major longitudinal axon tract in the animal. In genetic screens we isolated alleles of plr-1, which caused polarity reversals of the AVG neuron as well as outgrowth and navigation defects of the AVG axon. In addition plr-1 mutants show outgrowth defects in several other classes of neurons as well as the posterior excretory canals. plr-1 is predicted to encode a transmembrane E3 ubiquitin ligase and is widely expressed in the animal including the AVG neuron and the excretory cell. plr-1 has recently been shown to negatively regulate Wnt signalling by removing Wnt receptors from the cell surface. We observed that mutations in a gene reducing Wnt signalling as well as mutations in unc-53/NAV2 and unc-73/Trio suppress the AVG polarity defects in plr-1 mutants, but not the defects seen in other cells. This places plr-1 in a Wnt regulation pathway, but also suggests that plr-1 has Wnt independent functions and interacts with unc-53 and unc-73 to control cell polarity. PMID:25448694

Bhat, Jaffar M; Pan, Jie; Hutter, Harald

2015-02-01

300

High-Temperature Dynamics, High-Speed Modulation, and Transmission Experiments Using 1.3- InGaAs Single-Mode VCSELs  

Microsoft Academic Search

High-temperature dynamics, including small and large signal modulation response, of 1.28-?m GaAs-based vertical-cavity surface-emitting lasers (VCSELs) with highly strained InGaAs quantum wells have been investigated. The VCSELs are oxide-confined with a relatively large oxide aperture for high output power and have a surface relief for fundamental mode operation. An inverted surface relief is used to improve manufacturability and to suppress

Emma Soderberg; Johan S. Gustavsson; Peter Modh; Anders Larsson; Zhenzhong Zhang; Jesper Berggren; Mattias Hammar

2007-01-01

301

Gate-voltage-controlled spin and valley polarization transport in a normal/ferromagnetic/normal MoS? junction.  

PubMed

Two-dimensional (2D) materials are extensively explored due to the remarkable physical property and the great potential for post-silicon electronics since the landmark achievement of graphene. The monolayer (ML) MoS2 with a direct energy gap is a typical 2D material and promising candidate for a wide range of device applications. The extensive efforts so far have focused on the optical valley control applications of ML MoS2 rather than the electrical control of spin and valley transport. However, the electrical manipulation of spin injection and transport is essential to realize practical spintronics applications. Here, we theoretically demonstrated that the valley and spin transport can be electrically manipulated by a gate voltage in a normal/ferromagnetic/normal monolayer MoS2 junction device. It was found that the fully valley- and spin-polarized conductance can be achieved due to the spin-valley coupling of valence-band edges together with the exchange field, and both the amplitude and direction of the fully spin-polarized conductance can be modulated by the gate voltage. These findings not only provided deep understanding to the basic physics in the spin and valley transport of ML MoS2 but also opened an avenue for the electrical control of valley and spin transport in monolayer dichalcogenide-based devices. PMID:24417464

Li, Hai; Shao, Jianmei; Yao, Daoxin; Yang, Guowei

2014-02-12

302

Polarity of bacterial magnetotaxis is controlled by aerotaxis through a common sensory pathway.  

PubMed

Most motile bacteria navigate within gradients of external chemical stimuli by regulating the length of randomly oriented swimming episodes. Magnetotactic bacteria are characterized by chains of intracellular ferromagnetic nanoparticles and their ability to sense the geomagnetic field, which is believed to facilitate directed motion, but is not well understood at the behavioural and molecular level. Here, we show that cells of Magnetospirillum gryphiswaldense unexpectedly display swimming polarity that depends on aerotactic signal transduction through one of its four chemotaxis operons (cheOp1). Growth of cells in magnetic fields superimposed on oxygen gradients results in a gradual inherited bias of swimming runs with one of the cell poles leading, such that the resulting overall swimming direction of entire populations can be reversed by changes in oxygen concentration. These findings clearly show that there is a direct molecular link between aerotactic sensing and the determination of magnetotactic polarity, through the sensory pathway, CheOp1. PMID:25394370

Popp, Felix; Armitage, Judith P; Schüler, Dirk

2014-01-01

303

Control of Electronic Conduction at an Oxide Heterointerface using Surface Polar Adsorbates  

SciTech Connect

We study the effect of the surface adsorption of a variety of common laboratory solvents on the conductivity at the interface between LaAlO{sub 3} and SrTiO{sub 3}. This interface possesses a range of intriguing physics, notably a proposed connection between the surface state of the LaAlO{sub 3} and the conductivity buried in the SrTiO{sub 3}. We show that the application of chemicals such as acetone, ethanol, and water can induce a large change (factor of three) in the conductivity. This phenomenon is observed only for polar solvents. These data provide experimental evidence for a general polarization-facilitated electronic transfer mechanism.

Bell, Christopher

2011-08-19

304

Polarization control of ultrabroadband supercontinuum generation from midinfrared laser-induced harmonic emission  

NASA Astrophysics Data System (ADS)

We present an efficient scheme for generation of an isolated attosecond (as) pulse based on the combination of two well-known methods: polarization gating method plus a method based on using two colors (? +?/2). The first uses a pulse whose ellipticity is small within a very short time interval (called a polarization gating). By adding a second pulse whose frequency is a half-frequency (midinfrared) of the first pulse, we extend significantly the cutoff frequency, as well as the width of the supercontinuum harmonic spectrum. The high-order harmonic generation is calculated using the strong-field approximation theory. As a result, an isolated 42-as pulse is generated directly by superposing the hundreds of harmonics. To explain the mechanism of the ultrashort attosecond generation, we perform the semiclassical three-step model simulation and wavelet time-frequency transform of the harmonic spectra.

Jiao, Zhi-Hong; Wang, Guo-Li; Li, Peng-Cheng; Zhou, Xiao-Xin

2014-08-01

305

PRC1 controls spindle polarization and recruitment of cytokinetic factors during monopolar cytokinesis.  

PubMed

The central spindle is a postanaphase array of microtubules that plays an essential role in organizing the signaling machinery for cytokinesis. The model by which the central spindle organizes the cytokinetic apparatus is premised on an antiparallel arrangement of microtubules, yet cells lacking spindle bipolarity are capable of generating a distal domain of ectopic furrowing when forced into mitotic exit. Because protein regulator of cytokinesis (PRC1) and kinesin family member 4A (KIF4A) are believed to play a principal role in organizing the antiparallel midzone array, we sought to clarify their roles in monopolar cytokinesis. Although both factors localized to the distal ends of microtubules during monopolar cytokinesis, depletion of PRC1 and KIF4A displayed different phenotypes. Cells depleted of PRC1 failed to form a polarized microtubule array or ectopic furrows following mitotic exit, and recruitment of Aurora B kinase, male germ cell Rac GTPase-activating protein, and RhoA to the cortex was impaired. In contrast, KIF4A depletion impaired neither polarization nor ectopic furrowing, but it did result in elongated spindles with a diffuse distribution of cytokinetic factors. Thus, even in the absence of spindle bipolarity, PRC1 appears to be essential for polarizing parallel microtubules and concentrating the factors responsible for contractile ring assembly, whereas KIF4A is required for limiting the length of anaphase microtubules. PMID:22323288

Shrestha, Sanjay; Wilmeth, Lori Jo; Eyer, Jarrett; Shuster, Charles B

2012-04-01

306

Wnt-Planar Cell Polarity signaling controls the anterior-posterior organization of monoaminergic axons in the brainstem  

PubMed Central

Monoaminergic neurons (serotonergic (5HT) and dopaminergic (mdDA)) in the brainstem project axons along the anterior-posterior axis. Despite their important physiological functions and implication in disease, the molecular mechanisms that dictate the formation of these projections along the anterior-posterior axis remain unknown. Here we reveal a novel requirement for Wnt/planar cell polarity signaling in the anterior-posterior organization of the monoaminergic system. We find that 5HT and mdDA axons express the core planar cell polarity components Frizzled3, Celsr3 and Vangl2. In addition, monoaminergic projections show anterior-posterior guidance defects in Frizzled3, Celsr3 and Vangl2 mutant mice. The only known ligands for planar cell polarity signaling are Wnt proteins. In culture, Wnt5a attracts 5HT but repels mdDA axons and Wnt7b attracts mdDA axons. However, mdDA axons from Frizzled3 mutant mice are unresponsive to Wnt5a and Wnt7b. Both Wnts are expressed in gradients along the anterior-posterior axis, consistent with their role as directional cues. Finally, Wnt5a mutants show transient anterior-posterior guidance defects in mdDA projections. Furthermore, we observe that the cell bodies of migrating descending 5HT neurons eventually re-orient along the direction of their axons. In Frizzled3 mutants, many 5HT and mdDA neuron cell bodies are oriented abnormally along the direction of their aberrant axon projections. Overall, our data suggest that Wnt/planar cell polarity signaling may be a global anterior-posterior guidance mechanism that controls axonal and cellular organization beyond the spinal cord. PMID:21106844

Fenstermaker, Ali G.; Prasad, Asheeta A.; Bechara, Ahmad; Adolfs, Youri; Tissir, Fadel; Goffinet, Andre; Zou, Yimin; Pasterkamp, R. Jeroen

2010-01-01

307

A 1.3 Tb/s parallel optics VCSEL link  

NASA Astrophysics Data System (ADS)

A high bandwidth optical interconnect is designed based on parallel optical VCSEL links. Large matrices with 168 data channels are utilized exhibiting the highest reported full duplex aggregate bandwidth of 1.34Tb/s. Optical links of 300m are measured with BER < 10-12 while the power efficiency is 10.2 pJ/bit. The interconnect design is that of hybrid device with the III-V optoelectronics assembled directly onto the ASIC using Au/Sn eutectic bonding. Optical packaging is enabled using fiber bundle matrices whose dimensions are identical to those of the optoelectronic chips. The entire chip is assembled onto a system PCB in telecom and datacom applications. The backplane of the system becomes passive optical backplane and is entirely fiber based. The hybrid integration allows for a 3-fold increase in the number of SerDes available on a single package to about 500 lanes.

Hasharoni, Kobi; Benjamin, Shuki; Geron, Amir; Stepanov, Stanislav; Katz, Gideon; Epstein, Itai; Margalit, Niv; Chairman, David; Mesh, Michael

2014-03-01

308

VCSELs emitting in the 1310-nm waveband for novel optical communication applications  

NASA Astrophysics Data System (ADS)

High performance vertical cavity surface emitting lasers (VCSELs) emitting in the 1310 nm waveband are fabricated by bonding AlGaAs/GaAs distributed Bragg reflectors (DBRs) on both sides of a InP-based cavity containing 5 InAlGaAs quantum wells using the localized wafer fusion technique. A tunnel junction structure is used to inject carriers into the active region. Devices with 7 &mum aperture produce single mode emission with 40 dB side-mode suppression ratio. Maximum single mode output power of 1.7 mW is obtained in the temperature range of 20-70°C. Modulation capability at 3.2 Gb/s is demonstrated both at room temperature and 70°C with rise time and fall time values of eye diagrams bellow 120 ps. Overall device performance complies with the requirements of 10 GBASE-LX4 IEEE.802.3ae standard.

Syrbu, Alexei; Iakovlev, Vladimir; Suruceanu, Grigore; Caliman, Andrei; Mereuta, Alexandru; Mircea, Andrei; Berseth, Claude-Albert; Diechsel, Eckard; Boucart, Julien; Rudra, Alok; Kapon, Eli

2005-03-01

309

MIMO-OFDM WDM PON with DM-VCSEL for femtocells application.  

PubMed

We report on experimental demonstration of 2x2 MIMO-OFDM 5.6-GHz radio over fiber signaling over 20 km WDM-PON with directly modulated (DM) VCSELs for femtocells application. MIMO-OFDM algorithms effectively compensate for impairments in the wireless link. Error-free signal demodulation of 64 subcarrier 4-QAM signals modulated at 198.5 Mb/s net data rate is achieved after fiber and 2 m indoor wireless transmission. We report BER of 7x10(-3) at the receiver for 16-QAM signals modulated at 397 Mb/s after 1 m of wireless transmission. Performance dependence on different wireless transmission path lengths, antenna separation, and number of subcarriers have been investigated. PMID:22274067

Othman, M B; Deng, Lei; Pang, Xiaodan; Caminos, J; Kozuch, W; Prince, K; Yu, Xianbin; Jensen, Jesper Bevensee; Monroy, I Tafur

2011-12-12

310

Superlattices PhotoPolarization  

E-print Network

are polarization steady­state light­induced the of fall the and rise the both that show a as operated be can­­ ­­ Superlattices Asymmetric in Effect Photo­Polarization Internal Luryi Serge Liu Chun the provided effect, tangible a is superlattice the of polarization resultant field­ a of gate the control

Luryi, Serge

311

Polarization feedback laser stabilization  

DOEpatents

A system for locking two Nd:YAG laser oscillators includes an optical path for feeding the output of one laser into the other with different polarizations. Elliptical polarization is incorporated into the optical path so that the change in polarization that occurs when the frequencies coincide may be detected to provide a feedback signal to control one laser relative to the other.

Esherick, Peter (Albuquerque, NM); Owyoung, Adelbert (Albuquerque, NM)

1988-01-01

312

Highly polarized emission of the liquid crystalline conjugated polymer by controlling the surface anchoring energy  

NASA Astrophysics Data System (ADS)

We demonstrated a highly polarized organic light-emitting diode (OLED) through the enhancement of the orientational ordering of the emitting polymer with a nematic liquid crystalline (LC) phase. The highly ordered state of the conjugate polymer was obtained by thermal annealing at the nematic temperature and strong azimuthal anchoring energy of the underlying polyimide. The order parameter of the conjugate polymer was analyzed using a second-harmonic generation model and the dichroic ratio was measured to be 22 : 1. Also, we applied our optimized OLED with high optical polarizability to an effective light source for a twisted nematic LC display.

In Jo, Soo; Kim, Youngsik; Baek, Ji-Ho; Yu, Chang-Jae; Kim, Jae-Hoon

2014-01-01

313

The Hippo pathway controls border cell migration through distinct mechanisms in outer border cells and polar cells of the Drosophila ovary.  

PubMed

The Hippo pathway is a key signaling cascade in controlling organ size. The core components of this pathway are two kinases, Hippo (Hpo) and Warts (Wts), and a transcriptional coactivator, Yorkie (Yki). Yes-associated protein (YAP, a Yki homolog in mammals) promotes epithelial-mesenchymal transition and cell migration in vitro. Here, we use border cells in the Drosophila ovary as a model to study Hippo pathway functions in cell migration in vivo. During oogenesis, polar cells secrete Unpaired (Upd), which activates JAK/STAT signaling of neighboring cells and specifies them into outer border cells. The outer border cells form a cluster with polar cells and undergo migration. We find that hpo and wts are required for migration of the border cell cluster. In outer border cells, overexpression of hpo disrupts polarization of the actin cytoskeleton and attenuates migration. In polar cells, knockdown of hpo and wts or overexpression of yki impairs border cell induction and disrupts migration. These manipulations in polar cells reduce JAK/STAT activity in outer border cells. Expression of upd-lacZ is increased and decreased in yki and hpo mutant polar cells, respectively. Furthermore, forced expression of upd in polar cells rescues defects of border cell induction and migration caused by wts knockdown. These results suggest that Yki negatively regulates border cell induction by inhibiting JAK/STAT signaling. Together, our data elucidate two distinct mechanisms of the Hippo pathway in controlling border cell migration: (1) in outer border cells, it regulates polarized distribution of the actin cytoskeleton; (2) in polar cells, it regulates upd expression to control border cell induction and migration. PMID:25161211

Lin, Tzu-Huai; Yeh, Tsung-Han; Wang, Tsu-Wei; Yu, Jenn-Yah

2014-11-01

314

Effect of GaN interlayer on polarity control of epitaxial ZnO thin films grown by molecular beam epitaxy  

SciTech Connect

Epitaxial ZnO thin films were grown on nitrided (0001) sapphire substrates with an intervening GaN layer by rf-plasma-assisted molecular beam epitaxy. It was found that polarity of the ZnO epilayer could be controlled by modifying the GaN interlayer. ZnO grown on a distorted 3-nm-thick GaN interlayer has Zn-polarity while ZnO on a 20-nm-thick GaN interlayer with a high structural quality has O-polarity. High resolution transmission electron microscopy analysis indicates that the polarity of ZnO epilayer is controlled by the atomic structure of the interface between the ZnO buffer layer and the intervening GaN layer.

Wang, X. Q. [State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Sun, H. P.; Pan, X. Q. [Department of Materials Science and Engineering, The University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)

2010-10-11

315

Controllable fully spin-polarized transport in a ferromagnetically doped topological insulator junction  

NASA Astrophysics Data System (ADS)

We investigate the energy band structure and the spin-dependent transport for a normal/ferromagnetic/normal two-dimension topological insulator (TI) junction. By diagonalizing Hamiltonian for the system, the band structure shows that the edge states on two sides are coupled resulting in a gap opening due to the transverse spatial confinement. Further, the exchange field induced by magnetic impurities can also modulate the band structure with two spin degenerate bands splitting. By using the nonequilibrium Green's function method, the dependence of spin-dependent conductance and spin-polarization on the Fermi energy, the exchange field strength and the ferromagnetic TI (FTI) length are also analyzed, respectively. Interestingly, the degenerate conductance plateaus for spin-up and -down channels are broken, and both the conductances are suppressed by magnetic impurities due to the time-reversal symmetry broken and inelastic scattering. The spin-dependent conductance shows different behaviors when the Fermi energy is tuned into different ranges. Moreover, the conductance can be fully spin polarized by tuning the Fermi energy and the exchange field strength, or by tuning the Fermi energy and the FTI length. Consequently, the junction can transform from a quantum spin Hall state to a quantum anomalous Hall state, which is very important to enable dissipationless charge current for designing perfect spin filter.

Zhou, Benliang; Zhou, Benhu; Tang, Dongsheng; Zhou, Guanghui

2014-04-01

316

Specific polar subpopulations of astral microtubules control spindle orientation and symmetric neural stem cell division  

PubMed Central

Mitotic spindle orientation is crucial for symmetric vs asymmetric cell division and depends on astral microtubules. Here, we show that distinct subpopulations of astral microtubules exist, which have differential functions in regulating spindle orientation and division symmetry. Specifically, in polarized stem cells of developing mouse neocortex, astral microtubules reaching the apical and basal cell cortex, but not those reaching the central cell cortex, are more abundant in symmetrically than asymmetrically dividing cells and reduce spindle orientation variability. This promotes symmetric divisions by maintaining an apico-basal cleavage plane. The greater abundance of apical/basal astrals depends on a higher concentration, at the basal cell cortex, of LGN, a known spindle-cell cortex linker. Furthermore, newly developed specific microtubule perturbations that selectively decrease apical/basal astrals recapitulate the symmetric-to-asymmetric division switch and suffice to increase neurogenesis in vivo. Thus, our study identifies a novel link between cell polarity, astral microtubules, and spindle orientation in morphogenesis. DOI: http://dx.doi.org/10.7554/eLife.02875.001 PMID:24996848

Mora-Bermúdez, Felipe; Matsuzaki, Fumio; Huttner, Wieland B

2014-01-01

317

Controllable fully spin-polarized transport in a ferromagnetically doped topological insulator junction  

SciTech Connect

We investigate the energy band structure and the spin-dependent transport for a normal/ferromagnetic/normal two-dimension topological insulator (TI) junction. By diagonalizing Hamiltonian for the system, the band structure shows that the edge states on two sides are coupled resulting in a gap opening due to the transverse spatial confinement. Further, the exchange field induced by magnetic impurities can also modulate the band structure with two spin degenerate bands splitting. By using the nonequilibrium Green's function method, the dependence of spin-dependent conductance and spin-polarization on the Fermi energy, the exchange field strength and the ferromagnetic TI (FTI) length are also analyzed, respectively. Interestingly, the degenerate conductance plateaus for spin-up and -down channels are broken, and both the conductances are suppressed by magnetic impurities due to the time-reversal symmetry broken and inelastic scattering. The spin-dependent conductance shows different behaviors when the Fermi energy is tuned into different ranges. Moreover, the conductance can be fully spin polarized by tuning the Fermi energy and the exchange field strength, or by tuning the Fermi energy and the FTI length. Consequently, the junction can transform from a quantum spin Hall state to a quantum anomalous Hall state, which is very important to enable dissipationless charge current for designing perfect spin filter.

Zhou, Benliang; Tang, Dongsheng; Zhou, Guanghui, E-mail: ghzhou@hunnu.edu.cn [Department of Physics and Key Laboratory for Low-Dimensional Quantum Structures and Manipulation (Ministry of Education), Hunan Normal University, Changsha 410081 (China); Zhou, Benhu [Department of Physics, Shaoyang University, Shaoyang 422001 (China)

2014-04-21

318

Transmitted Light Enhancement of Electric-Field-Controlled Multidomain Vertically Aligned Liquid Crystal Displays Using Circular Polarizers and a Cholesteric Liquid Crystal Film  

Microsoft Academic Search

We have proposed two new optical configurations to improve the light transmittance of a fringing-field-controlled multidomain vertically aligned liquid crystal display (FEF-MVA-LCD). We show that, by using a MVA-LC panel sandwiched between two circular polarizers, improvement of the maximum transmittance by more than 30% is achieved in comparison to the transmittance of a conventional panel configuration using two linear polarizers.

Yoshihisa Iwamoto; Yasufumi Iimura

2003-01-01

319

A novel adaptive controller for two-degree of freedom polar robot with unknown perturbations  

NASA Astrophysics Data System (ADS)

In industrial applications, the performance of robot manipulators is always affected due to the presence of uncertainties and disturbances. This paper proposes a novel adaptive control scheme for robust control of robotic manipulators perturbed by unknown uncertainties and disturbances. First, an active sliding mode controller is designed and a sufficient condition is obtained guarantying reachability of the states to hit the sliding surface in finite time. Then, based on a Lyapunov function candidate an adaptive switching gain is derived which make the controller capable to bring the tracking error to zero without any disturbance exerted upon the stability. By virtue of this controller it can be shown that the controller can track the desired trajectories even in the presence of unknown perturbations. For the problem of determining the control parameters Particle Swarm Optimization (PSO) algorithm has been employed. Our theoretic achievements are verified by numerical simulations.

Faieghi, Mohammad Reza; Delavari, Hadi; Baleanu, Dumitru

2012-02-01

320

Image fiber optic space-CDMA parallel transmission experiment using 8 x 8 VCSEL/PD arrays.  

PubMed

We experimentally demonstrate space-code-division multiple access (space-CDMA) based twodimensional (2-D) parallel optical interconnections by using image fibers and 8 x 8 vertical-cavity surface-emitting laser (VCSEL)/photo diode (PD) arrays. Two spatially encoded four-bit (2 x 2) parallel optical signals were emitted fiom 2-D VCSEL arrays and transmitted through image fibers. The encoded signals were multiplexed by an image-fiber coupler and detected by a 2-D PD array on the receiver side. The receiver recovered the intended parallel signal by decoding the signal. The transmission speed was 64 Mbps/ch (total throughput: 512 Mbps). Bit-error-rate (BER) measurement with a laterally misaligned PD array showed the array had a misalignment tolerance of 25 microm for a BER performance of 10(-9). PMID:12440546

Nakamura, Moriya; Kitayama, Ken-ichi; Igasaki, Yasunori; Shamoto, Naoki; Kaneda, Keiji

2002-11-10

321

VCSEL-based gigabit IR-UWB link for converged communication and sensing applications in optical metro-access networks  

NASA Astrophysics Data System (ADS)

We report on experimental demonstration of an impulse radio ultrawideband (IR-UWB) based converged communication and sensing system. A 1550-nm VCSEL-generated IR-UWB signal is used for 2-Gbps wireless data distribution over 800-m and 50-km single mode fiber links which present short-range in-building and long-reach access network applications. The IR-UWB signal is also used to simultaneously measure the rotational speed of a blade spinning between 18 and 30 Hz. To the best of our knowledge, this is the very first demonstration of a simultaneous gigabit UWB telecommunication and wireless UWB sensing application, paving the way forward for the development and deployment of converged UWB VCSEL-based technologies in access and in-building networks of the future.

Pham, Tien-Thang; Braidwood Gibbon, Timothy; Tafur Monroy, Idelfonso

2012-11-01

322

Studies of VCSEL Failures in the Optical Readout Systems of the ATLAS Silicon Trackers and Liquid Argon Calorimeters  

E-print Network

The readout systems for the ATLAS silicon trackers and liquid argon calorimeters utilize vertical-cavity surface-emitting laser diodes to communicate between on and off detector readout components. A number of these VCSEL devices have failed well before their expected lifetime. We summarize the failure history and present what has been learned thus far about failure mechanisms and the dependence of the lifetime on environmental conditions.

Mark S. Cooke

2011-09-29

323

Optical control of exciton valley polarization in MoS2  

NASA Astrophysics Data System (ADS)

Atomic monolayers of transition metal dichalcogenides have emerged as an interesting class of 2-dimensional (2D) crystals beyond graphene. In particular, the isoelectronic family of MoS2, MoSe2, WS2 and WSe2 monolayers are direct band gap semiconductors.footnotetextMak, K. F., Lee, C., Hone, J., Shan, J. & Heinz, T. F. Phys Rev Lett 105, 136805 (2010); Splendiani, A. et al. Nano Lett 10, 1271-1275 (2010).^,footnotetextXiao, D., Liu, G.-B., Feng, W., Xu, X. & Yao, W. Phys Rev Lett 108, 196802 (2012); Zhu, Z. Y., Cheng, Y. C. & Schwingenschlogl, U. Phys Rev B 84, 153402 (2011). Unlike graphene, because of the lack of inversion symmetry and the presence of strong spin-orbit interactions, the fundamental energy gaps of these compounds are located at two inequivalent high-symmetry valleys in the Brillouin zone (K and K') with coupled valley and spin degrees of freedom.footnotetextIbid. This electronic property makes them unique from conventional semiconductors. In this talk, we will discuss the properties of MoS2 atomic layers as a prototype. Through characterization of the optical properties of the material as a function of thickness, we show that quantum confinement effects lead to a crossover in MoS2 from a bulk indirect gap semiconductor to a direct gap semiconductor at monolayer thickness.footnotetextMak, PRL 105, 2010 With this basic property established, we show that complete valley polarization of the excitons in monolayer MoS2 can be achieved by optical pumping with circularly polarized light.footnotetextMak, K. F., He, K., Shan, J. & Heinz, T. F. Nat Nano 7, 494-498 (2012); Zeng, H., Dai, J., Yao, W., Xiao, D., & Cui, X. Nat Nano 7, 490-493 (2012); Cao, T. et al. Nat Commun 3, 887 (2012); Sallen, G. et al. Phys Rev B 86, 081301(R) (2012). Furthermore, this polarization can be retained for longer than 1ns. Our results thus highlight the great potential of this material family for studies of valley and spin Hall physics.footnotetextXiao, D., Yao, W. & Niu, Q. Phys Rev Lett 99, 236809 (2007); Yao, W., Xiao, D. & Niu, Q. Phys Rev B 77, 235406 (2008); Xiao, D., Chang, M.-C. & Niu, Q. Rev Mod Phys 82, 1959-2007 (2010).

Mak, Kin Fai

2013-03-01

324

Controlling spin polarized band-structure by variation of vacancy intensity in nanostructures.  

PubMed

In this study, the magnetic properties of FeAl alloys with different grain sizes produced by high-pressure torsion were probed by means of magnetic Compton scattering. The measurements were performed at 300 and 10 K. Magnetic Compton profiles of nanocrystalline (35 nm) and ultrafine-grained (160 nm) FeAl alloys were analyzed in terms of the integral area, the width, and the distinctive dip intensity at low momenta. The changes in total magnetic moment and the strength of spin-polarization of itinerant electrons are assumed to be caused by vacancies induced during the preparation of the samples. Despite local disordering due to interfacial regions and deviations in perfect stoichiometry for B2 structure, the effect of vacancies is considered as the major magnetic state contributor. PMID:25646271

Kamali, S; Kilmametov, A; Ghafari, M; Itou, M; Hahn, H; Sakurai, Y

2015-02-25

325

Controlling helicity-correlated beam asymmetries in a polarized electron source  

SciTech Connect

The control of helicity-correlated changes in the electron beam is a critical issue for the next generation of parity-violating electron scattering measurements. The underlying causes and methods for controlling these changes are reviewed with reference to recent operational experience at Jefferson Lab.

Kent Paschke

2007-07-01

326

Reducing multiphoton ionization in a linearly polarized microwave field by local control  

E-print Network

We present a control procedure to reduce the stochastic ionization of hydrogen atom in a strong microwave field by adding to the original Hamiltonian a comparatively small control term which might consist of an additional set of microwave fields. This modification restores select invariant tori in the dynamics and prevents ionization. We demonstrate the procedure on the one-dimensional model of microwave ionization.

S. Huang; C. Chandre; T. Uzer

2006-10-27

327

A quantum dot single-photon source with on-the-fly all-optical polarization control and timed emission  

E-print Network

Sources of single photons are key elements in the study of basic quantum optical concepts and applications in quantum information science. Among the different sources available, semiconductor quantum dots excel with their straight forward integrability in semiconductor based on-chip solutions and the potential that photon emission can be triggered on demand. Usually, the photon emission event is part of a cascaded biexciton-exciton emission scheme. Important properties of the emitted photon such as polarization and time of emission are either probabilistic in nature or pre-determined by electronic properties of the system. In this work, we study the direct two-photon emission from the biexciton. We show that emission through this higher-order transition provides a much more versatile approach to generate a single photon. In the scheme we propose, the two-photon emission from the biexciton is enabled by a laser field (or laser pulse) driving the system into a virtual state inside the band gap. From this intermediate virtual state, the single photon of interest is then spontaneously emitted. Its properties are determined by the driving laser pulse, enabling all-optical on-the-fly control of polarization state, frequency, and time of emission of the photon.

Dirk Heinze; Artur Zrenner; Stefan Schumacher

2014-12-02

328

TDDFT study of the polarity controlled ion-pair separation in an excited-state proton transfer reaction  

NASA Astrophysics Data System (ADS)

6-Hydroxyquinoline (6HQ) is an ideal photoacid system for exploring excited-state proton transfer (ESPT) reactions. We have previously (Mahata et al. (2002) [40]) shown that the ESPT reaction between 6HQ and trimethylamine (TMA) leads to an “unusual” emission in the 440-450 nm range, containing two decay components (?5 ns and ?12 ns). The observed results suggest the presence of a contact ion-pair and a solvent separated ion-pair. In this work, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) have been employed to study the nature of the contact ion-pair formed between 6HQ and TMA and to determine why the decay component ?12 ns is absent in a non-polar solvent. Calculations of the hydrogen-bonded complexes formed between 6HQ and TMA and its ESPT reaction product, namely 6HQ-TMA and 6HQ-TMA-PT, respectively, have been carried out, both in the electronic ground and excited states. Moreover, by using the CPCM model, different dielectric constants have been introduced into the calculations. On increasing the dielectric constant, the hydrogen bond in 6HQ-TMA-PT becomes weaker and the hydrogen bond length becomes larger; this effectively facilitates the proton transfer reaction and formation of separated ion-pair. Thus, the separation and diffusion of the contact ion-pair can be controlled by changing the polarity of the surroundings.

Liu, Yu-Hui; Mehata, Mohan Singh; Lan, Sheng-Cheng

2014-07-01

329

TDDFT study of the polarity controlled ion-pair separation in an excited-state proton transfer reaction.  

PubMed

6-Hydroxyquinoline (6HQ) is an ideal photoacid system for exploring excited-state proton transfer (ESPT) reactions. We have previously (Mahata et al. (2002)) shown that the ESPT reaction between 6HQ and trimethylamine (TMA) leads to an "unusual" emission in the 440-450 nm range, containing two decay components (?5 ns and ?12 ns). The observed results suggest the presence of a contact ion-pair and a solvent separated ion-pair. In this work, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) have been employed to study the nature of the contact ion-pair formed between 6HQ and TMA and to determine why the decay component ?12 ns is absent in a non-polar solvent. Calculations of the hydrogen-bonded complexes formed between 6HQ and TMA and its ESPT reaction product, namely 6HQ-TMA and 6HQ-TMA-PT, respectively, have been carried out, both in the electronic ground and excited states. Moreover, by using the CPCM model, different dielectric constants have been introduced into the calculations. On increasing the dielectric constant, the hydrogen bond in 6HQ-TMA-PT becomes weaker and the hydrogen bond length becomes larger; this effectively facilitates the proton transfer reaction and formation of separated ion-pair. Thus, the separation and diffusion of the contact ion-pair can be controlled by changing the polarity of the surroundings. PMID:24681312

Liu, Yu-Hui; Mehata, Mohan Singh; Lan, Sheng-Cheng

2014-07-15

330

Sea ice dynamics as a control for halogen deposition in polar regions  

NASA Astrophysics Data System (ADS)

Bromine and iodine chemistry is extremely active at the sea ice margins of both polar regions, with enhanced concentrations of BrO and IO in the air column compared to the open ocean surface or snow-covered land. So-called "Bromine explosions" occur principally over first-year sea ice close to the sea ice edge, and are the major source of reactive bromine in the polar atmosphere. This results in an increase of bromide (Br-) deposited to the snowpack, compared with the Br-Na sea water mass ratio. The main source of iodine is phytoplankton, which colonize the underside of sea ice, producing iodocarbons and probably I2. Though it has been discovered that atmospheric iodine around Antarctica is produced from algae growing on the underside of the relatively thin/seasonal sea ice, satellite measurements do not show exceptional iodine activity above Arctic sea ice. However, in opposition to Antarctica, boundary layer observations show relatively small atmospheric IO concentrations downwind of ice-free open ocean, including leads and polynias. Analysis of bromine and iodine has been carried out in the Talos Dome ice core (Antarctica) which covers the last 215 ky, and in a shallow/firn core drilled at the summit of the Holtedahlfonna glacier (Northern Spitsbergen, Svalbard), covering the last 10 years. Talos Dome Br- is positively correlated with temperature and negatively correlated with sodium (Na). Based on the Br-/Na seawater ratio, bromide is depleted in the ice during glacial periods and enriched during interglacial periods. Total iodine, consisting of iodide (I-) and iodate (IO3-), peaks during glacials with lower values during interglacial periods. Although iodate is believed to be the most stable iodine species in atmospheric aerosols, it was present only in the ice core only during glacial maxima. Glacial-interglacial changes in the multi-year sea ice extent will almost certainly alter the distance between the sea ice edge and Antarctic plateau, which will influence the total bromide flux (arising both from sea salt and Br- from bromine explosions) and its ratio with sodium. A simple 1-D transport model of this scenario is able to reproduce the measured fluxes of bromine and sodium. The seasonal sea ice extent will also alter the surface area available to algal colonization, and hence iodine emission. In support of the Antarctic results, analysis of iodine and bromine in the Svalbard shallow/firn core appears to confirm the linkage between sea ice and these halogens. In particular, changes in I concentration are associated with the extent of sea ice at spring time, while Br, evaluated as enrichment relative to the Br/Na sea water mass ratio, is influenced by changes in the seasonal sea ice area. The Arctic and Antarctic ice core results suggest that sea ice dynamics are arguably the primary driver of halogen fluxes in polar regions and that both halogens could be used to understand the past variability of sea ice.

Spolaor, Andrea; Plane, John M. C.; Vallelonga, Paul; Gabrieli, Jacopo; Cozzi, Giulio; Turetta, Clara; Kohler, Jack; Isaksson, Elisabeth; Barbante, Carlo

2013-04-01

331

Ultra-fast acoustically tunable all-fiber polarization controller based on a hollow optical fiber  

Microsoft Academic Search

Local deformation of circular HOF induced by traveling acoustic wave results in a versatile control of SOP by varying frequency and voltage of RF signal. Traces of SOP on Poincare sphere are reported for various frequency and RF voltage ranges.

J. Yu; J. Lee; M. Han; S. Choi; K. Oh; S. Kim; D. Kim

2003-01-01

332

Electric- and exchange-field controlled transport through silicene barriers: Conductance gap and near-perfect spin polarization  

NASA Astrophysics Data System (ADS)

We study ballistic electron transport through silicene barriers, of width d and height U, in the presence of an exchange field M and a normal electric field Ez. Away from the Dirac point (DP), the spin- and valley-resolved conductances, as functions of U, exhibit resonances while close to it there is a pronounced dip that can be transformed into a transport gap by varying Ez. The charge conductance gc changes from oscillatory to a monotonically decreasing function of d beyond a critical Ez and this can be used to realize electric-field-controlled switching. Further, the field M splits each resonance of gc into two spin-resolved peaks. The spin polarization near the DP increases with Ez or M and becomes nearly perfect above certain of their values. Similar results hold for double barriers.

Vargiamidis, V.; Vasilopoulos, P.

2014-12-01

333

Temperature-Controlled Symmetry of Linear Polarization of Photoluminescence from InGaAs-Buried InAs/GaAs Quantum Dots  

NASA Astrophysics Data System (ADS)

We have succeeded in adjusting the symmetry of the linear polarization of exciton emission from self-assembled InAs/GaAs quantum dots by controlling the combination of temperature and composition of the InGaAs burying layer. The anisotropic shape of the Stranski-Krastanow-type quantum dot is a drawback to the generation of a polarization-entangled photon pair. We found that the polarization symmetry of the intensity and wavelength of photon emission depends on the sample temperature and the composition of the burying layer. The ground-state emission peaks in two linear polarization directions were tuned to overlap by lowering the temperature and using a high indium composition of the burying layer. Our results will aid in the development of an entangled-photon generator using the emission of exciton molecule in self-assembled quantum dots.

Mukai, Kohki; Kikushima, Kousuke; Tanaka, Tomoya; Nakashima, Seisuke

2013-06-01

334

Highly birefringent silicate glass photonic-crystal fiber with polarization-controlled frequency-shifted output: A promising fiber light source for nonlinear Raman microspectroscopy  

NASA Astrophysics Data System (ADS)

A highly birefringent silicate glass photonic-crystal fiber (PCF) is employed for polarization-controlled nonlinear-optical frequency conversion of femtosecond Cr: forsterite laser pulses with a central wavelength of 1.24 ?m to the 530--720-nm wavelength range through soliton dispersion-wave emission. The fiber exhibits a modal birefringence of 1.2·10-3 at the wavelength of 1.24 ?m due to a strong form anisotropy of its core, allowing polarization switching of the central wavelength of its blue-shifted output by 75 nm. Polarization properties and the beam quality of the blue-shifted PCF output are shown to be ideally suited for polarization-sensitive nonlinear Raman microspectroscopy.

Mitrofanov, Aleksandr V.; Linik, Yaroslav M.; Buczynski, Ryszard; Pysz, Dariusz; Lorenc, Dusan; Bugar, Ignac; Ivanov, Anatoly A.; Alfimov, Mikhail V.; Fedotov, Andrei B.; Zheltikov, Aleksei M.

2006-10-01

335

Cdc42: An Essential Rho-Type GTPase Controlling Eukaryotic Cell Polarity  

PubMed Central

Cdc42p is an essential GTPase that belongs to the Rho/Rac subfamily of Ras-like GTPases. These proteins act as molecular switches by responding to exogenous and/or endogenous signals and relaying those signals to activate downstream components of a biological pathway. The 11 current members ofthe Cdc42p family display between 75 and 100% amino acid identity and are functional as well as structural homologs. Cdc42p transduces signals to the actin cytoskeleton to initiate and maintain polarized gorwth and to mitogen-activated protein morphogenesis. In the budding yeast Saccharomyces cerevisiae, Cdc42p plays an important role in multiple actin-dependent morphogenetic events such as bud emergence, mating-projection formation, and pseudohyphal growth. In mammalian cells, Cdc42p regulates a variety of actin-dependent events and induces the JNK/SAPK protein kinase cascade, which leads to the activation of transcription factors within the nucleus. Cdc42p mediates these processes through interactions with a myriad of downstream effectors, whose number and regulation we are just starting to understand. In addition, Cdc42p has been implicated in a number of human diseases through interactions with its regulators and downstream effectors. While much is known about Cdc42p sturcture and functional interactions, little is known about the mechanism(s) by which it transduces signals within the cell. Future research sould focus on this question as well as on the detailed analysis of the interactions of Cdc42p with its regulators and downstream effectors. PMID:10066831

Johnson, Douglas I.

1999-01-01

336

Polarization-controlled TIRFM with focal drift and spatial field intensity correction.  

PubMed

Total internal reflection fluorescence microscopy (TIRFM) is becoming an increasingly common methodology to narrow the illumination excitation thickness to study cellular process such as exocytosis, endocytosis, and membrane dynamics. It is also frequently used as a method to improve signal/noise in other techniques such as in vitro single-molecule imaging, stochastic optical reconstruction microscopy/photoactivated localization microscopy imaging, and fluorescence resonance energy transfer imaging. The unique illumination geometry of TIRFM also enables a distinct method to create an excitation field for selectively exciting fluorophores that are aligned either parallel or perpendicular to the optical axis. This selectivity has been used to study orientation of cell membranes and cellular proteins. Unfortunately, the coherent nature of laser light, the typical excitation source in TIRFM, often creates spatial interference fringes across the illuminated area. These fringes are particularly problematic when imaging large cellular areas or when accurate quantification is necessary. Methods have been developed to minimize these fringes by modulating the TIRFM field during a frame capture period; however, these approaches eliminate the possibility to simultaneously excite with a specific polarization. A new, to our knowledge, technique is presented, which compensates for spatial fringes while simultaneously permitting rapid image acquisition of both parallel and perpendicular excitation directions in ~25 ms. In addition, a back reflection detection scheme was developed that enables quick and accurate alignment of the excitation laser. The detector also facilitates focus drift compensation, a common problem in TIRFM due to the narrow excitation depth, particularly when imaging over long time courses or when using a perfusion flow chamber. The capabilities of this instrument were demonstrated by imaging membrane orientation using DiO on live cells and on lipid bilayers that were supported on a glass slide (supported lipid bilayer). The use of the approach to biological problems was illustrated by examining the temporal and spatial dynamics of exocytic vesicles. PMID:24606926

Johnson, Daniel S; Toledo-Crow, Ricardo; Mattheyses, Alexa L; Simon, Sanford M

2014-03-01

337

Optimal control of vortex core polarity by resonant microwave pulses Benjamin Pigeau,1  

E-print Network

microwave magnetic field because the sense of the core rotation is linked by a right-hand rule to its, 2011) Abstract In a vortex-state magnetic nano-disk1­3, the static magnetization is curling­14 for potential application in magnetic storage devices15. Here we demonstrate coherent control of p by single

Boyer, Edmond

338

`Downward Control' of the Mean Meridional Circulation and Temperature Distribution of the Polar Winter Stratosphere  

Microsoft Academic Search

According to the `downward control' principle, the extratropical mean vertical velocity on a given pressure level is approximately proportional to the meridional gradient of the vertically integrated zonal force per unit mass exerted by waves above that level. In this paper, a simple numerical model that includes parameterizations of both planetary and gravity wave breaking is used to explore the

Rolando R. Garcia; Byron A. Boville

1994-01-01

339

Polar Bears  

NSDL National Science Digital Library

Use the following websites to answer questions about the rapid disappearance of polar bears in the Arctic region. Polar Bear picture Polar Bear Tracker 1: What region in the world has the fewest polar bears? 2: Using the internet as a resource, provide some reasons as to why this region is suffering from the most polar bear differences? Polar Bears Change Diet 1: Why are polar bears having to change their diets? 2: List some other factors (besides diet) in the ...

Thomas, Mr.

2010-09-27

340

Volumetric cutaneous microangiography of human skin in vivo by VCSEL swept-source optical coherence tomography  

PubMed Central

Three-dimensional (3D) assessment of cutaneous microcirculation in human skin is essential in the identification of disease states in skin or other organs. Few 3D imaging techniques have revealed the skin micro-vasculatures non-invasively and with sufficient imaging depth. Here, we demonstrate volumetric cutaneous microangiography of the human skin in vivo that utilizes a 1.3 µm high-speed swept-source optical coherence tomography (SS-OCT). The swept source is based on a MEMS tunable vertical cavity surface emission laser (VCSEL) that is advantageous in terms of long coherence length over 50 mm and 100 nm spectral bandwidth that enables the visualization of microstructures within a few mm from the skin surface. We show that skin microvasculature can be delineated in 3D SS-OCT images using ultrahigh-sensitive optical microangiography (UHS-OMAG) with a correlation mapping mask, providing a contrast enhanced blood perfusion map with capillary flow sensitivity. 3D microangiograms of a healthy human finger are shown with distinct cutaneous vessel architectures from different dermal layers and even within hypodermis. These findings suggest that the OCT microangiography could be a beneficial biomedical assay to assess cutaneous vascular functions in clinic.

Choi, Woo June; Wang, Ruikang K.

2015-01-01

341

3D optimization of a polymer MOEMS for active focusing of VCSEL beam  

NASA Astrophysics Data System (ADS)

We report on the optimized design of a polymer-based actuator that can be directly integrated on a VCSEL for vertical beam scanning. Its operation principle is based on the vertical displacement of a SU-8 membrane including a polymer microlens. Under an applied thermal gradient, the membrane is shifted vertically due to thermal expansion in the actuation arms induced by Joule effect. This leads to a modification of microlens position and thus to a vertical scan of the laser beam. Membrane vertical displacements as high as 8?m for only 3V applied were recently experimentally obtained. To explain these performances, we developed a comprehensive tri-dimensional thermo-mechanical model that takes into account SU-8 material properties and precise MOEMS geometry. Out-of-plane mechanical coefficients and thermal conductivity were thus integrated in our 3D model (COMSOL Multiphysics). Vertical displacements extracted from these data for different actuation powers were successfully compared to experimental values, validating this modelling tool. Thereby, it was exploited to increase MOEMS electrothermal performance by a factor higher than 5.

Abada, S.; Camps, T.; Reig, B.; Doucet, JB; Daran, E.; Bardinal, V.

2014-05-01

342

Ultrahigh speed endoscopic swept source optical coherence tomography using a VCSEL light source and micromotor catheter  

NASA Astrophysics Data System (ADS)

We developed an ultrahigh speed endoscopic swept source optical coherence tomography (OCT) system for clinical gastroenterology using a vertical-cavity surface-emitting laser (VCSEL) and micromotor based imaging catheter, which provided an imaging speed of 600 kHz axial scan rate and 8 ?m axial resolution in tissue. The micromotor catheter was 3.2 mm in diameter and could be introduced through the 3.7 mm accessory port of an endoscope. Imaging was performed at 400 frames per second with an 8 ?m spot size using a pullback to generate volumetric data over 16 mm with a pixel spacing of 5 ?m in the longitudinal direction. Three-dimensional OCT (3D-OCT) imaging was performed in patients with a cross section of pathologies undergoing standard upper and lower endoscopy at the Veterans Affairs Boston Healthcare System (VABHS). Patients with Barrett's esophagus, dysplasia, and inflammatory bowel disease were imaged. The use of distally actuated imaging catheters allowed OCT imaging with more flexibility such as volumetric imaging in the terminal ileum and the assessment of the hiatal hernia using retroflex imaging. The high rotational stability of the micromotor enabled 3D volumetric imaging with micron scale volumetric accuracy for both en face and cross-sectional imaging. The ability to perform 3D OCT imaging in the GI tract with microscopic accuracy should enable a wide range of studies to investigate the ability of OCT to detect pathology as well as assess treatment response.

Tsai, Tsung-Han; Ahsen, Osman O.; Lee, Hsiang-Chieh; Liang, Kaicheng; Giacomelli, Michael G.; Potsaid, Benjamin M.; Tao, Yuankai K.; Jayaraman, Vijaysekhar; Kraus, Martin F.; Hornegger, Joachim; Figueiredo, Marisa; Huang, Qin; Mashimo, Hiroshi; Cable, Alex E.; Fujimoto, James G.

2014-03-01

343

Factors controlling the distribution of anaerobic methanotrophic communities in marine environments: Evidence from intact polar membrane lipids  

NASA Astrophysics Data System (ADS)

Three distinct types of microbial consortia appear to mediate the anaerobic oxidation of methane with sulfate as electron acceptor in marine sediments and are distributed ubiquitously. These consortia consist of ANerobic MEthanotrophic (ANME) archaea of the ANME-1, ANME-2 and ANME-3 clades and their sulfate-reducing bacterial partners either of the Desulfosarcina- Desulfococcus (ANME-1/DSS and ANME-2/DSS) or Desulfobulbus spp. (ANME-3/DBB) branches. Frequently one consortium type dominates the community, but the selective factors are not well constrained. Here we analyzed patterns in the composition of intact polar lipids extracted from bacterial and archaeal communities of different marine seep environments. Further, we investigated if different environmental and geographical factors were responsible for the observed patterns, and hence could be important in the selection of seep communities. Intact polar lipids (IPLs) provide a more robust distinction of the composition of extant communities than their less polar derivatives. In ANME-1/DSS-dominated communities, glycosidic- and phospho-glyceroldialkylglyceroltetraethers were abundant, while ANME-2/DSS and ANME-3/DBB-dominated communities showed abundant archaeol-based IPLs, either with glycosidic and phospho-headgroups or only phospho-headgroups, respectively. The relative proportion of bacterial IPLs varied widely from 0% to 93% and was generally lower in samples of the ANME-1 type, suggesting lower bacterial biomasses in the respective communities. In addition to these lipid signatures, distinctive features were related to the habitat characteristics of these communities: lower amounts of phosphate-based IPLs were generally observed in communities from calcified microbial mats compared to sediments, which may reflect phosphate limitation. Based on statistical analyses of IPLs and environmental data this study constrained for the first time the occurrence of three environmental factors controlling the distribution of different ANME-associated communities in a wide range of hydrocarbon seep systems. Habitats dominated by ANME-1/DSS communities were characterized by high temperature and low oxygen content in bottom waters (or even anoxia), while ANME-2/DSS and ANME-3/DBB-dominated sediments were located in settings with lower temperatures and higher oxygen content in bottom waters. Furthermore, ANME-2/DSS communities were particularly prominent in environments in which a relatively high supply of sulfate was sustained.

Rossel, Pamela E.; Elvert, Marcus; Ramette, Alban; Boetius, Antje; Hinrichs, Kai-Uwe

2011-01-01

344

In-situ weak-beam and polarization control of multidimensional laser sidebands for ultrafast optical switching  

SciTech Connect

All-optical switching has myriad applications in optoelectronics, optical communications, and quantum information technology. To achieve ultrafast optical switching in a compact yet versatile setup, we demonstrate distinct sets of two-dimensional (2D) broadband up-converted multicolor arrays (BUMAs) in a thin type-I ?-barium-borate crystal with two noncollinear near-IR femtosecond pulses at various phase-matching conditions. The unique interaction mechanism is revealed as quadratic spatial solitons (QSSs)-coupled cascaded four-wave mixing (CFWM), corroborated by numerical calculations of the governing phase-matching conditions. Broad and continuous spectral-spatial tunability of the 2D BUMAs are achieved by varying the time delay between the two incident pulses that undergo CFWM interaction, rooted in the chirped nature of the weak white light and the QSSs generation of the intense fundamental beam. The control of 2D BUMAs is accomplished via seeding a weak second-harmonic pulse in situ to suppress the 2D arrays with polarization dependence on the femtosecond timescale that matches the control pulse duration of ?35 fs. A potential application is proposed on femtosecond all-optical switching in an integrated wavelength-time division multiplexing device.

Liu, Weimin; Wang, Liang; Fang, Chong, E-mail: Chong.Fang@oregonstate.edu [Department of Chemistry, Oregon State University, Corvallis, Oregon 97331 (United States)

2014-03-17

345

Adiabatic cooling for cold polar molecules on a chip using a controllable high-efficiency electrostatic surface trap  

NASA Astrophysics Data System (ADS)

We propose a controllable high-efficiency electrostatic surface trap for cold polar molecules on a chip by using two insulator-embedded charged rings and a grounded conductor plate. We calculate Stark energy structure pattern of ND3 molecules in an external electric field using the method of matrix diagonalization. We analyze how the voltages that are applied to the ring electrodes affect the depth of the efficient well and the controllability of the distance between the trap center and the surface of the chip. To obtain a better understanding, we simulate the dynamical loading and trapping processes of ND3 molecules in a |J,KM> = |1, ? 1> state by using classical Monte—Carlo method. Our study shows that the loading efficiency of our trap can reach ~ 88%. Finally, we study the adiabatic cooling of cold molecules in our surface trap by linearly lowering the potential-well depth (i.e., lowering the trapping voltage), and find that the temperature of the trapped ND3 molecules can be adiabatically cooled from 34.5 mK to ~ 5.8 mK when the trapping voltage is reduced from ?35 kV to ?3 kV.

Li, Sheng-Qiang; Xu, Liang; Xia, Yong; Wang, Hai-Ling; Yin, Jian-Ping

2014-12-01

346

Intracavity polarization control in mode-locked Er-doped fibre lasers using liquid crystals  

NASA Astrophysics Data System (ADS)

In this paper we present a novel configuration of an NPR mode-locked Er-doped laser. This new optical setup uses voltage controlled LC cells to replace standard retarders (quarter-and half-waveplates) inside the laser cavity. Using this novel, mechanical-adjustment-free setup a mode-locking was obtained with sub-500 fs pulse duration and an average power exceeding 40 mW. Presented results show that using simple LC cells, an optical layout of an NPR mode-locked laser can be greatly simplified.

Nikodem, M.; Krzempek, K.; Zygadlo, K.; Dudzik, G.; Waz, A.; Abramski, K.; Komorowska, K.

2014-06-01

347

Preservation and control of the proton and deuteron polarizations in the proposed electron-ion collider at Jefferson Lab  

SciTech Connect

We propose a scheme of preserving the proton and deuteron beam polarizations during acceleration and storage in the proposed electron-ion collider at Jefferson Lab. This scheme allows one to provide both the longitudinal and transverse polarization orientations of the proton and deuteron beams at the interaction points of the figure-8 ion collider ring. We discuss questions of matching the polarization direction at all stages of the beam transport including the pre-booster, large booster and ion collider ring.

Kondratenko, Anatoliy [Scientific and Technical Laboratory Zaryad, Novosibirsk (Russian Federation); Derbenev, Yaroslav S. [JLAB, Newport News, VA (United States); Filatov, Yury [Moscow Institute of Physics and Technology, Dolgoprudny (Russian Federation); Lin, Fanglei [JLAB, Newport News, VA (United States); Morozov, Vasiliy [JLAB, Newport News, VA (United States); Kondratenko, M. A. [Scientific and Technical Laboratory Zaryad, Novosibirsk (Russian Federation); Zhang, Yuhong [JLAB, Newport News, VA (United States)

2014-01-01

348

Stern, C.D. (1987) Control of epithelial polarity and induction in the early chick embryo. In: Mesenchymal-epithelial interactions in neural development (J.R. Wolff, J. Sievers and M.  

E-print Network

Stern, C.D. (1987) Control of epithelial polarity and induction in the early chick embryo. In and induction in the early chick embryo. In: Mesenchymal-epithelial interactions in neural development (J;Stern, C.D. (1987) Control of epithelial polarity and induction in the early chick embryo. In

Stern, Claudio

349

Simultaneous control of vortex polarity and chirality in thickness-modulated [Co/Pd]n/Ti/Ni80Fe20 disks  

NASA Astrophysics Data System (ADS)

Simultaneous vortex chirality and polarity control are observed in thickness-modulated [Co/Pd]n/Ti/Ni80Fe20 disks using magnetic force microscopy by applying a proper sequence of in-plane and out-of-plane reset fields. The thickness modulation in the NiFe layer introduces an additional shape anisotropy, which defines the vortex chirality during the in-plane reset field, while the [Co/Pd]n underlayer produces a large out-of-plane stray field, which stabilizes the vortex polarity in the NiFe layer. Micromagnetic simulations are compared with experiment results.

Shimon, G.; Ravichandar, V.; Adeyeye, A. O.; Ross, C. A.

2014-10-01

350

Quality Control and Calibration of the Dual-Polarization Radar at Kwajalein, RMI  

NASA Technical Reports Server (NTRS)

Weather radars, recording information about precipitation around the globe, will soon be significantly upgraded. Most of today s weather radars transmit and receive microwave energy with horizontal orientation only, but upgraded systems have the capability to send and receive both horizontally and vertically oriented waves. These enhanced "dual-polarimetric" (DP) radars peer into precipitation and provide information on the size, shape, phase (liquid / frozen), and concentration of the falling particles (termed hydrometeors). This information is valuable for improved rain rate estimates, and for providing data on the release and absorption of heat in the atmosphere from condensation and evaporation (phase changes). The heating profiles in the atmosphere influence global circulation, and are a vital component in studies of Earth s changing climate. However, to provide the most accurate interpretation of radar data, the radar must be properly calibrated and data must be quality controlled (cleaned) to remove non-precipitation artifacts; both of which are challenging tasks for today s weather radar. The DP capability maximizes performance of these procedures using properties of the observed precipitation. In a notable paper published in 2005, scientists from the Cooperative Institute for Mesoscale Meteorological Studies (CIMMS) at the University of Oklahoma developed a method to calibrate radars using statistically averaged DP measurements within light rain. An additional publication by one of the same scientists at the National Severe Storms Laboratory (NSSL) in Norman, Oklahoma introduced several techniques to perform quality control of radar data using DP measurements. Following their lead, the Topical Rainfall Measuring Mission (TRMM) Satellite Validation Office at NASA s Goddard Space Flight Center has fine-tuned these methods for specific application to the weather radar at Kwajalein Island in the Republic of the Marshall Islands, approximately 2100 miles southwest of Hawaii and 1400 miles east of Guam in the tropical North Pacific Ocean. This tropical oceanic location is important because the majority of rain, and therefore the majority of atmospheric heating, occurs in the tropics where limited ground-based radar data are available.

Marks, David A.; Wolff, David B.; Carey, Lawrence D.; Tokay, Ali

2010-01-01

351

Polarization feedback laser stabilization  

DOEpatents

A system for locking two Nd:YAG laser oscillators includes an optical path for feeding the output of one laser into the other with different polarizations. Elliptical polarization is incorporated into the optical path so that the change in polarization that occurs when the frequencies coincide may be detected to provide a feedback signal to control one laser relative to the other. 4 figs.

Esherick, P.; Owyoung, A.

1987-09-28

352

Polarized cells, polar actions.  

PubMed Central

The recognition of polar bacterial organization is just emerging. The examples of polar localization given here are from a variety of bacterial species and concern a disparate array of cellular functions. A number of well-characterized instances of polar localization of bacterial proteins, including the chemoreceptor complex in both C. crescentus and E. coli, the maltose-binding protein in E. coli, the B. japonicum surface attachment proteins, and the actin tail of L. monocytogenes within a mammalian cell, involve proteins or protein complexes that facilitate bacterial interaction with the environment, either the extracellular milieux or that within a plant or mammalian host. The significance of this observation remains unclear. Polarity in bacteria poses many problems, including the necessity for a mechanism for asymmetrically distributing proteins as well as a mechanism by which polar localization is maintained. Large structures, such as a flagellum, are anchored at the pole by means of the basal body that traverses the peptidoglycan wall. But for proteins and small complexes, whether in the periplasm or the membrane, one must invoke a mechanism that prevents the diffusion of these proteins away from the cell pole. Perhaps the periplasmic proteins are retained at the pole by the presence of the periseptal annulus (35). The constraining features for membrane components are not known. For large aggregates, such as the clusters of MCP, CheA, and CheW complexes, perhaps the size of the aggregate alone prevents displacement. In most cases of cellular asymmetry, bacteria are able to discriminate between the new pole and the old pole and to utilize this information for localization specificity. The maturation of new pole to old pole appears to be a common theme as well. Given numerous examples reported thus far, we propose that bacterial polarity displays specific rules and is a more general phenomenon than has been previously recognized. PMID:8226658

Maddock, J R; Alley, M R; Shapiro, L

1993-01-01

353

Solar wind density controlling penetration electric field at the equatorial ionosphere during a saturation of cross polar cap potential  

NASA Astrophysics Data System (ADS)

The most important source of electrodynamic disturbances in the equatorial ionosphere during the main phase of a storm is the prompt penetration electric field (PPEF) originating from the high-latitude region. It has been known that such an electric field is correlated with the magnetospheric convection or interplanetary electric field. Here we show a unique case, in which the electric field disturbance in the equatorial ionosphere cannot be interpreted by this concept. During the superstorm on Nov. 20-21, 2003, the cross polar cap potential (CPCP) saturated at least for 8.2 h. The CPCP reconstructed by Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure suggested that the PPEF at the equatorial ionosphere still correlated with the saturated CPCP, but the CPCP was controlled by the solar wind density instead of the interplanetary electric field. However, the predicted CPCPs by Hill-Siscoe-Ober (HSO) model and Boyle-Ridley (BR) model were not fully consistent with the AMIE result and PPEF. The PPEF also decoupled from the convection electric field in the magnetotail. Due to the decoupling, the electric field in the ring current was not able to comply with the variations of PPEF, and this resulted in a long-duration electric field penetration without shielding.

Wei, Y.; Wan, W.; Zhao, B.; Hong, M.; Ridley, A.; Ren, Z.; Fraenz, M.; Dubinin, E.; He, M.

2012-09-01

354

The ecological controls on the prevalence of candidate division TM7 in polar regions  

PubMed Central

The candidate division TM7 is ubiquitous and yet uncultured phylum of the Bacteria that encompasses a commonly environmental associated clade, TM7-1, and a “host-associated” clade, TM7-3. However, as members of the TM7 phylum have not been cultured, little is known about what differs between these two clades. We hypothesized that these clades would have different environmental niches. To test this, we used a large-scale global soil dataset, encompassing 223 soil samples, their environmental parameters and associated bacterial 16S rRNA gene sequence data. We correlated chemical, physical and biological parameters of each soil with the relative abundance of the two major classes of the phylum to deduce factors that influence the groups' seemingly ubiquitous nature. The two classes of the phylum (TM7-1 and TM7-3) were indeed distinct from each other in their habitat requirements. A key determinant of each class' prevalence appears to be the pH of the soil. The class TM7-1 displays a facultative anaerobic nature with correlations to more acidic soils with total iron, silicon, titanium and copper indicating a potential for siderophore production. However, the TM7-3 class shows a more classical oligotrophic, heterotroph nature with a preference for more alkaline soils, and a probable pathogenic role with correlations to extractable iron, sodium and phosphate. In addition, the TM7-3 was abundant in diesel contaminated soils highlighting a resilient nature along with a possible carbon source. In addition to this both classes had unique co-occurrence relationships with other bacterial phyla. In particular, both groups had opposing correlations to the Gemmatimonadetes phylum, with the TM7-3 class seemingly being outcompeted by this phylum to result in a negative correlation. These ecological controls allow the characteristics of a TM7 phylum preferred niche to be defined and give insight into possible avenues for cultivation of this previously uncultured group. PMID:25076941

Winsley, Tristrom J.; Snape, Ian; McKinlay, John; Stark, Jonny; van Dorst, Josie M.; Ji, Mukan; Ferrari, Belinda C.; Siciliano, Steven D.

2014-01-01

355

Polar Bear Polar Bear  

NSDL National Science Digital Library

In this lesson, students will listen for key details in a nonfiction text about polar bears. They will work at completing a graphic organizer with the teacher to help organize their thinking and understanding of key details about a text. They will also complete an independent assignment where they will draw or write two things that they learned about the topic.

Burgess, Kelly

2012-09-11

356

Analysis of structurally sensitive loss in GaN-based VCSEL cavities and its effect on modal discrimination.  

PubMed

Lateral loss causes optical energy to leave the laser cavity in the transverse, lateral, direction, and is sometimes neglected to simplify the numerical simulations. However, in contrast to outcoupling and absorption losses, we show that the lateral loss can change drastically with only nanometer-sized changes of the cavity structure, from being virtually zero to becoming the major source of cavity loss, since the cavity becomes antiguiding. This can be explained as the opening of a channel of efficient resonant lateral leakage of optical power at a certain oblique propagation angle. A number of different realizations of current apertures and top mirror designs in GaN-based VCSEL cavities, which have been suggested for realization of microcavity lasers emitting in the blue wavelength range, are simulated. Many of these are shown to lead to unintentional antiguiding, which can more than double the threshold gain for lasing. Notably, for strong enough antiguiding the resonant lateral leakage decreases so that the threshold gain values might again be tolerable. This regime has been suggested for robust single-mode operation since earlier predictions, building on analogies with slab waveguides, hinted at a very strong suppression of higher order modes. However, our simulations indicate that for the VCSEL cavities the derived formulas grossly overestimate the modal discrimination. PMID:24515001

Hashemi, Ehsan; Bengtsson, Jörgen; Gustavsson, Johan; Stattin, Martin; Cosendey, Gatien; Grandjean, Nicolas; Haglund, Asa

2014-01-13

357

Highly efficient active optical interconnect incorporating a partially chlorinated ribbon POF in conjunction with a visible VCSEL.  

PubMed

A low-loss 4-ch active optical interconnect (AOI) enabling passive alignment was proposed and built resorting to a transmitter (Tx) incorporating a red 680-nm VCSEL, which is linked to a receiver (Rx) module via a partially chlorinated ribbon POF. The POF was observed to exhibit an extremely low loss of ~0.24 dB/m at ? = 680 nm, in comparison to ~1.29 dB/m at ? = 850 nm, and a large numerical aperture of ~0.42. Both the Tx and Rx, which taps into a beam router based on collimated beam optics involving a pair of spherical lenses, were meant to be substantially alignment tolerant and compact. The achieved tolerance for the constructed modules was beyond 40 ?m in terms of the positioning of VCSEL and photodetector. The proposed AOI was completed by linking the Tx with the Rx via a 3-m long ribbon POF, incurring a transmission loss of as small as 3.2 dB. The AOI was practically assessed in terms of a high-speed data transmission over a wide range of temperatures and then exploited to convey full HD video signals. PMID:24921299

Lee, Hak-Soon; Lee, Sang-Shin; Kim, Bong-Seok; Son, Yung-Sung

2014-05-19

358

Tuning etch selectivity of fused silica irradiated by femtosecond laser pulses by controlling polarization of the writing pulses  

SciTech Connect

We report on experimental study on chemical etch selectivity of fused silica irradiated by femtosecond laser with either linear or circular polarization in a wide range of pulse energies. The relationships between the etch rates and pulse energies are obtained for different polarization states, which can be divided into three different regions. A drop of the etch rate for high pulse energy region is observed and the underlying mechanism is discussed. The advantage of using circularly polarized laser is justified owing to its unique capability of providing a 3D isotropic etch rate.

Yu Xiaoming; Zeng Bin [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, P. O. Box 800-211, Shanghai 201800 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100039 (China); Liao Yang; He Fei; Cheng Ya; Xu Zhizhan [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, P. O. Box 800-211, Shanghai 201800 (China); Sugioka, Koji; Midorikawa, Katsumi [Laser Technology Laboratory, RIKEN - Advanced Science Institute, Hirosawa 2-1, Wako, Saitama 351-0198 (Japan)

2011-03-01

359

1.6 Gb\\/s transmission over 1 km of 62.5 micron-core multimode fiber by subcarrier modulation of 850 nm VCSELs  

Microsoft Academic Search

We report the first subcarrier-based optical transmission of 1.6 Gbit\\/s over 1 km of standard 62.5 micron-core graded index fiber. BPSK, QPSK, and subcarrier-multiplexed BPSK are studied using 850 nm VCSEL sources

T. K. Woodward; S. Hunsche; A. J. Ritgerz; J. B. Stark

1999-01-01

360

Spin-based scheme for implementing an N-qubit tunable controlled phase gate in quantum dots by interference of polarized photons  

NASA Astrophysics Data System (ADS)

We present a scheme for direct implementation of an N-qubit tunable controlled phase gate for spin qubits in quantum dots coupled to optical cavities, resorting to spin selective dipole coupling interaction and linear optical manipulation. In the scheme, we first design a quantum entangler device to transform the operated physical qubits, which are represented by the states of the electron spins, into non-maximal hybrid entangled states with a certain probability of success via the introduction of auxiliary circularly polarized photons. Then we show that, based on this quantum entangler operation, a spin-based N-qubit tunable controlled phase gate can be probabilistically achieved by the interference and coincidence detection of polarized photons. This might lead to a useful step toward the construction of more efficient quantum circuits and quantum algorithms in solid-state qubits.

Cui, Wen-Xue; Hu, Shi; Guo, Qi; Wang, Hong-Fu; Zhang, Shou

2014-04-01

361

The effect of surface alignment on analog control of director rotation in polarization stiffened SmC* devices  

NASA Astrophysics Data System (ADS)

The effect of surface alignment on the achievement of analog ("V"-shaped) electric field control of director rotation in SmC* liquid crystal devices is investigated experimentally and through numerical modeling. Ferroelectric SmC* liquid crystals are intrinsically analog and thresholdless, i.e. the director can be rotated freely around the tilt cone. Whether or not a SmC* liquid crystal cell exhibits thresholdless switching depends strongly on the influence of the cell's alignment layers, on the magnitude of the liquid crystal's spontaneous polarization, and on whether smectic layers adopt a bookshelf or chevron configuration. To study the effect of the surface alignment layers, we have exploited a technique for the vertical (bookshelf) alignment of the smectic layers that does not depend on surface anisotropy. The alignment technique allows an experimental study of the influence of surfaces spanning a wide range of pretilt angles, azimuthal and zenithal anchoring energies. This technique is used to study the effect of surfaces on the threshold behavior of director rotation in SmC* materials under the influence of an electric field. The alignment technique also allowed us to use a high-PS liquid crystal material having an I-A-C phase sequence and reduced layer shrinkage thought to be well suited to thresholdless switching. We show that the alignment layer has a strong effect, and that excellent analog response can be achieved for the case of alignment layers which promote homeotropic director orientation. We further model and discuss the potential effect of a thin layer of nematic at the surface and the possibility of gliding of the easy axis during switching.

Reznikov, Mitya; Lopatina, Lena M.; O'Callaghan, Michael J.; Bos, Philip J.

2011-03-01

362

aPKC Phosphorylates p27Xic1, Providing a Mechanistic Link between Apicobasal Polarity and Cell-Cycle Control.  

PubMed

During the development of the nervous system, apicobasally polarized stem cells are characterized by a shorter cell cycle than nonpolar progenitors, leading to a lower differentiation potential of these cells. However, how polarization might be directly linked to the kinetics of the cell cycle is not understood. Here, we report that apicobasally polarized neuroepithelial cells in Xenopus laevis have a shorter cell cycle than nonpolar progenitors, consistent with mammalian systems. We show that the apically localized serine/threonine kinase aPKC directly phosphorylates an N-terminal site of the cell-cycle inhibitor p27Xic1 and reduces its ability to inhibit the cyclin-dependent kinase 2 (Cdk2), leading to shortening of G1 and S phases. Overexpression of activated aPKC blocks the neuronal differentiation-promoting activity of p27Xic1. These findings provide a direct mechanistic link between apicobasal polarity and the cell cycle, which may explain how proliferation is favored over differentiation in polarized neural stem cells. PMID:25490266

Sabherwal, Nitin; Thuret, Raphael; Lea, Robert; Stanley, Peter; Papalopulu, Nancy

2014-12-01

363

aPKC Phosphorylates p27Xic1, Providing a Mechanistic Link between Apicobasal Polarity and Cell-Cycle Control  

PubMed Central

Summary During the development of the nervous system, apicobasally polarized stem cells are characterized by a shorter cell cycle than nonpolar progenitors, leading to a lower differentiation potential of these cells. However, how polarization might be directly linked to the kinetics of the cell cycle is not understood. Here, we report that apicobasally polarized neuroepithelial cells in Xenopus laevis have a shorter cell cycle than nonpolar progenitors, consistent with mammalian systems. We show that the apically localized serine/threonine kinase aPKC directly phosphorylates an N-terminal site of the cell-cycle inhibitor p27Xic1 and reduces its ability to inhibit the cyclin-dependent kinase 2 (Cdk2), leading to shortening of G1 and S phases. Overexpression of activated aPKC blocks the neuronal differentiation-promoting activity of p27Xic1. These findings provide a direct mechanistic link between apicobasal polarity and the cell cycle, which may explain how proliferation is favored over differentiation in polarized neural stem cells. PMID:25490266

Sabherwal, Nitin; Thuret, Raphael; Lea, Robert; Stanley, Peter; Papalopulu, Nancy

2014-01-01

364

Polarization evolution characteristics of focused hybridly polarized vector fields  

NASA Astrophysics Data System (ADS)

We investigate the focusing property and the polarization evolution characteristics of hybridly polarized vector fields in the focal region. Three types of hybridly polarized vector fields, namely azimuthal-variant hybridly polarized vector field, radial-variant hybridly polarized vector field, and spatial-variant hybridly polarized vector field, are experimentally generated. The intensity distributions and the polarization evolution of these hybridly polarized vector fields focused under low numerical aperture (NA) are experimentally studied and good agreements with the numerical simulations are obtained. The three-dimensional (3D) state of polarization and the field distribution within the focal volume of these hybridly polarized vector fields under high-NA focusing are studied numerically. The optical curl force on Rayleigh particles induced by tightly focused hybridly polarized vector fields, which results in the orbital motion of trapped particles, is analyzed. Simulation results demonstrate that polarization-only modulation provided by the hybridly polarized vector field allows one to control both the intensity distribution and 3D elliptical polarization in the focal region, which may find interesting applications in particle trapping, manipulation, and orientation analysis.

Gu, Bing; Pan, Yang; Rui, Guanghao; Xu, Danfeng; Zhan, Qiwen; Cui, Yiping

2014-12-01

365

Polarization-controlled evolution of light transverse modes and associated Pancharatnam geometric phase in orbital angular momentum  

SciTech Connect

We present an easy, efficient, and fast method to generate arbitrary linear combinations of light orbital angular-momentum eigenstates l={+-}2 starting from a linearly polarized TEM{sub 00} laser beam. The method exploits the spin-to-orbital angular-momentum conversion capability of a liquid-crystal-based q plate and a Dove prism inserted into a Sagnac polarizing interferometer. The nominal generation efficiency is 100%, being limited only by reflection and scattering losses in the optical components. When closed paths are followed on the polarization Poincare sphere of the input beam, the associated Pancharatnam geometric phase is transferred unchanged to the orbital angular momentum state of the output beam.

Karimi, Ebrahim; Marrucci, Lorenzo [Dipartimento di Scienze Fisiche, Universita di Napoli 'Federico II', Complesso di Monte S. Angelo, I-80126 Napoli (Italy); CNR-INFM Coherentia, Complesso di Monte S. Angelo, I-80126 Napoli (Italy); Slussarenko, Sergei; Piccirillo, Bruno; Santamato, Enrico [Dipartimento di Scienze Fisiche, Universita di Napoli 'Federico II', Complesso di Monte S. Angelo, I-80126 Napoli (Italy); Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, I-80126 Napoli (Italy)

2010-05-15

366

Gravity and light control of the developmental polarity of regenerating protoplasts isolated from prothallial cells of the fern Ceratopteris richardii  

NASA Technical Reports Server (NTRS)

A procedure has been developed for isolating protoplasts from prothalli of Ceratopteris richardii which can be cultured and are capable of regeneration. Protoplasts were isolated from 2-week-old gametophytes in a medium containing wall-digesting enzymes in 0.5 M sucrose, followed by purification of the released protoplasts by floating them up into a 0.5 M sorbitol layer. Regeneration occurred over a period of 10-24 days, and, under optimal osmotic conditions, followed the developmental pattern seen during spore germination, in that the first division gave rise to a primary rhizoid. Thus, prothallial protoplasts are comparable to germinating spores as suitable models for studies of developmental polarity in single cells. As in germinating spores, the polarity of development in regenerating protoplasts is influenced by the vectors of gravity and unilateral light. However, the relative influence of light in fixing this polarity is greater in regenerating protoplasts, while in germinating spores, the influence of gravity is greater.

Edwards, E. S.; Roux, S. J.

1998-01-01

367

Polarized Sunglasses  

NSDL National Science Digital Library

In this activity, learners explore how polarizing sunglasses can help diminish road glare. By rotating a pair of polarizing sunglass lenses or other polarizing materials, learners will discover that some angles are better at reducing glare than others. Learners observe light from the sky, reflected from a mirror, or reflected from the surface of a pond. Use this activity to introduce learners to principles of light and polarization.

The Exploratorium

2011-12-05

368

Competitive photocyclization/rearrangement of 4-aryl-1,1-dicyanobutenes controlled by intramolecular charge-transfer interaction. Effect of medium polarity, temperature, pressure, excitation wavelength, and confinement.  

PubMed

A series of 4-aryl-1,1-dicyanobutenes (1a-1f) with different substituents were synthesized to control the intramolecular donor-acceptor or charge-transfer (C-T) interactions in the ground state. Photoexcitation of these C-T substrates led to competitive cyclization and rearrangement, the ratio being critically controlled by various environmental factors, such as solvent polarity, temperature and static pressure, and also by excitation wavelength and supramolecular confinement (polyethylene voids). In non-polar solvents, the rearrangement was dominant (>10 : 1) for all examined substrates, while the cyclization was favoured in polar solvents, in particular at low temperatures. Selective excitation at the C-T band further enhanced the cyclization up to >50 : 1 ratios. More importantly, the cyclization/rearrangement ratio was revealed to be a linear function of the C-T transition energy. However, the substrates with a sterically demanding or highly electron-donating substituent failed to give the cyclization product. PMID:21373708

Ito, Tadashi; Nishiuchi, Emi; Fukuhara, Gaku; Inoue, Yoshihisa; Mori, Tadashi

2011-09-01

369

RHIC Polarized proton operation  

SciTech Connect

The Relativistic Heavy Ion Collider (RHIC) operation as the polarized proton collider presents unique challenges since both luminosity(L) and spin polarization(P) are important. With longitudinally polarized beams at the experiments, the figure of merit is LP{sup 4}. A lot of upgrades and modifications have been made since last polarized proton operation. A 9 MHz rf system is installed to improve longitudinal match at injection and to increase luminosity. The beam dump was upgraded to increase bunch intensity. A vertical survey of RHIC was performed before the run to get better magnet alignment. The orbit control is also improved this year. Additional efforts are put in to improve source polarization and AGS polarization transfer efficiency. To preserve polarization on the ramp, a new working point is chosen such that the vertical tune is near a third order resonance. The overview of the changes and the operation results are presented in this paper. Siberian snakes are essential tools to preserve polarization when accelerating polarized beams to higher energy. At the same time, the higher order resonances still can cause polarization loss. As seen in RHIC, the betatron tune has to be carefully set and maintained on the ramp and during the store to avoid polarization loss. In addition, the orbit control is also critical to preserve polarization. The higher polarization during this run comes from several improvements over last run. First we have a much better orbit on the ramp. The orbit feedback brings down the vertical rms orbit error to 0.1mm, much better than the 0.5mm last run. With correct BPM offset and vertical realignment, this rms orbit error is indeed small. Second, the jump quads in the AGS improved input polarization for RHIC. Third, the vertical tune was pushed further away from 7/10 snake resonance. The tune feedback maintained the tune at the desired value through the ramp. To calibrate the analyzing power of RHIC polarimeters at any energy above injection, the polarized hydrogen jet target runs for every fill with both beams. Based on the known analyzing power, there is very little polarization loss between injection and 100 GeV. An alternative way is to measure the asymmetry at 100 GeV followed by ramping up to 250 GeV and back down to 100 GeV and then to measure the asymmetry again at 100 GeV. If the asymmetry after the down ramp is similar to the measurement before the up ramp, polarization was also preserved during the ramp to 250 GeV. The analyzing power at storage energy can then be extracted from the asymmetries measured at 100 GeV and 250 GeV. The tune and orbit feedbacks are essential for the down ramp to be possible. The polarized proton operation is still going on. We will push bunch intensity higher until reaching the beam-beam limit. The even higher intensity will have to wait for the electron lenses to compensate the beam-beam effect. To understand the details of spin dynamics in RHIC with two snakes, spin simulation with the real magnet fields have been developed recently. The study will provide guidance for possible polarization loss schemes. Further polarization gain will requires a polarized source upgrade; more careful setup jump quads in the AGS to get full benefit; and control emittance in the whole accelerator chain.

Huang, H.; Ahrens, L.; Alekseev, I.G.; Aschenauer, E.; Atoian, G.; Bai, M.; Bazilevsky, A.; Blaskiewicz, M.; Brennan, J.M.; Brown, K.A.; Bruno, D.; Connolly, R.; Dion, A.; D'Ottavio, T.; Drees, K.A.; Fischer, W.; Gardner, C.; Glenn, J.W.; Gu, X.; Harvey, M.; Hayes, T.; Hoff, L.; Hulsart, R.L.; Laster, J.; Liu, C.; Luo, Y.; MacKay, W.W.; Makdisi, Y.; Marr, G.J.; Marusic, A.; Meot, F.; Mernick, K.; Michnoff, R,; Minty, M.; Montag, C.; Morris, J.; Nemesure, S.; Poblaguev, A.; Ptitsyn, V.; Ranjibar, V.; Robert-Demolaize, G.; Roser, T.; J.; Severino, F.; Schmidke, B.; Schoefer, V.; Severino, F.; Smirnov, D.; Smith, K.; Steski, D.; Svirida, D.; Tepikian, S.; Trbojevic, D.; Tsoupas, N.; Tuozzolo, J. Wang, G.; Wilinski, M.; Yip, K.; Zaltsman, A.; Zelenski, A.; Zeno, K.; Zhang, S.Y.

2011-03-28

370

Real-time, continuous, fluorescence sensing in a freely-moving subject with an implanted hybrid VCSEL/CMOS biosensor.  

PubMed

Performance improvements in instrumentation for optical imaging have contributed greatly to molecular imaging in living subjects. In order to advance molecular imaging in freely moving, untethered subjects, we designed a miniature vertical-cavity surface-emitting laser (VCSEL)-based biosensor measuring 1cm(3) and weighing 0.7g that accurately detects both fluorophore and tumor-targeted molecular probes in small animals. We integrated a critical enabling component, a complementary metal-oxide semiconductor (CMOS) read-out integrated circuit, which digitized the fluorescence signal to achieve autofluorescence-limited sensitivity. After surgical implantation of the lightweight sensor for two weeks, we obtained continuous and dynamic fluorophore measurements while the subject was un-anesthetized and mobile. The technology demonstrated here represents a critical step in the path toward untethered optical sensing using an integrated optoelectronic implant. PMID:24009996

O'Sullivan, Thomas D; Heitz, Roxana T; Parashurama, Natesh; Barkin, David B; Wooley, Bruce A; Gambhir, Sanjiv S; Harris, James S; Levi, Ofer

2013-01-01

371

Real-time, continuous, fluorescence sensing in a freely-moving subject with an implanted hybrid VCSEL/CMOS biosensor  

PubMed Central

Performance improvements in instrumentation for optical imaging have contributed greatly to molecular imaging in living subjects. In order to advance molecular imaging in freely moving, untethered subjects, we designed a miniature vertical-cavity surface-emitting laser (VCSEL)-based biosensor measuring 1cm3 and weighing 0.7g that accurately detects both fluorophore and tumor-targeted molecular probes in small animals. We integrated a critical enabling component, a complementary metal-oxide semiconductor (CMOS) read-out integrated circuit, which digitized the fluorescence signal to achieve autofluorescence-limited sensitivity. After surgical implantation of the lightweight sensor for two weeks, we obtained continuous and dynamic fluorophore measurements while the subject was un-anesthetized and mobile. The technology demonstrated here represents a critical step in the path toward untethered optical sensing using an integrated optoelectronic implant. PMID:24009996

O’Sullivan, Thomas D.; Heitz, Roxana T.; Parashurama, Natesh; Barkin, David B.; Wooley, Bruce A.; Gambhir, Sanjiv S.; Harris, James S.; Levi, Ofer

2013-01-01

372

The VCSEL-based array optical transmitter (ATx) development towards 120-Gbps link for collider detector: development update  

NASA Astrophysics Data System (ADS)

A compact radiation-tolerant array optical transmitter module (ATx) is developed to provide data transmission up to 10Gbps per channel with 12 parallel channels for collider detector applications. The ATx integrates a Vertical Cavity Surface-Emitting Laser (VCSEL) array and driver circuitry for electrical to optical conversion, an edge warp substrate for the electrical interface and a micro-lens array for the optical interface. This paper reports the continuing development of the ATx custom package. A simple, high-accuracy and reliable active-alignment method for the optical coupling is introduced. The radiation-resistance of the optoelectronic components is evaluated and the inclusion of a custom-designed array driver is discussed.

Guo, D.; Liu, C.; Chen, J.; Chramowicz, J.; Gong, D.; Hou, S.; Huang, D.; Jin, G.; Li, X.; Liu, T.; Prosser, A.; Teng, P. K.; Ye, J.; Zhou, Y.; You, Y.; Xiang, A. C.; Liang, H.

2015-01-01

373

A multiple-input-multiple-output visible light communication system based on VCSELs and spatial light modulators.  

PubMed

A multiple-input-multiple-output (MIMO) visible light communication (VLC) system employing vertical cavity surface emitting laser (VCSEL) and spatial light modulators (SLMs) with 16-quadrature amplitude modulation (QAM)-orthogonal frequency-division multiplexing (OFDM) modulating signal is proposed and experimentally demonstrated. The transmission capacity of system is significantly increased by space-division demultiplexing scheme. With the assistance of low noise amplifier (LNA) and data comparator, good bit error rate (BER) performance, clear constellation map, and clear eye diagram are achieved for each optical channel. Such a MIMO VLC system would be attractive for providing services including data and telecommunication services. Our proposed system is suitably applicable to the lightwave communication system in wireless transmission. PMID:24663637

Lu, Hai-Han; Lin, Ying-Pyng; Wu, Po-Yi; Chen, Chia-Yi; Chen, Min-Chou; Jhang, Tai-Wei

2014-02-10

374

Controlling the delay of 100 Gb\\/s polarization division multiplexed signals through silicon photonics delay lines  

Microsoft Academic Search

We show a direct comparison between silicon reconfigurable delay lines based on coupled resonator optical waveguides and photonic crystal waveguides. The structures are used to selectively delay the two orthogonally polarized channels of a RZ-PolDM-DQPSK format at 100 Gbit\\/s.

F. Morichetti; A. Canciamilla; C. Ferrari; M. Torregiani; M. Ferrario; R. Siano; P. Boffi; L. Marazzi; P. Martelli; P. Parolari; M. Martinelli; A. Samarelli; M. Sorel; R. M. De La Rue; L. O'Faolain; D. M. Beggs; T. F. Krauss; A. Melloni

2010-01-01

375

Polarization of barcode readers  

NASA Astrophysics Data System (ADS)

In high-quality barcode readers, specular reflection from shiny barcodes is blocked by using a polarized scan laser and a crossed polarizer in front of the detector. When complex scanning geometries are required, the polarization properties of the mirrors in the system can become a limiting factor in system performance. Polarization raytracing allows systems such as barcode readers, LIDAR systems, and other polarization-critical system to be accurately characterized. Polarization raytracing often requires the use of local, ray-based coordinate system for expressing rays' polarization states, yet the choice of coordinate system can have important implications on system analysis. An example is presented in which specular reflection is controlled in a barcode reader by using reflection-enhanced coatings on only one of the four set of the mirrors in the system. The coordinate system used to express rays' polarization states in the example system provides useful lessons for other systems. The other analytical methods used in this example can be applied to a variety of scanning systems.

Reiley, Daniel J.

1998-02-01

376

Wnt4, a pleiotropic signal for controlling cell polarity, basement membrane integrity, and antimüllerian hormone expression during oocyte maturation in the female follicle.  

PubMed

Wnt4 is a key signal that channels the developmental fate of the indifferent mammalian gonad toward the ovary, but whether Wnt4 has later roles during ovary development remains unknown. To investigate this, we inactivated the Wnt4 gene by crossing Amhr2Cre and doxycycline-inducible Rosa(rtTA)-knock-in Cre mice with mice carrying a floxed Wnt4 allele and used a novel Wnt4(mCherry)-knock-in mouse. In these models, ovarian folliculogenesis was compromised, and female fertility was severely reduced, and Wnt4 deficiency eventually led to premature ovarian failure. These anomalies were associated with cell polarity defects in the follicle. Within the follicle, laminin and type IV collagen assembled ectopic basement membrane-like structures, the cell adherens junction components N-cadherin and ?-catenin lost their polarized expression pattern, and expression of the gap junction protein connexin 43 was reduced by ~30% when compared with that of the controls. Besides these changes, expression of antimüllerian hormone (Amh) was inhibited in the absence of Wnt4 signaling in vivo. Consistent with this, Wnt4 signaling up-regulated Amh gene expression in KK1 cells in vitro. Thus, Wnt4 signaling is necessary during maturation of the ovarian follicles, where it coordinates expression of Amh, cell survival, and polarized organization of the follicular cells. PMID:24371124

Prunskaite-Hyyryläinen, Renata; Shan, Jingdong; Railo, Antti; Heinonen, Krista M; Miinalainen, Ilkka; Yan, Wenying; Shen, Bairong; Perreault, Claude; Vainio, Seppo J

2014-04-01

377

Development of polarization-controlled multi-pass Thomson scattering system in the GAMMA 10 tandem mirror  

SciTech Connect

In the GAMMA 10 tandem mirror, the typical electron density is comparable to that of the peripheral plasma of torus-type fusion devices. Therefore, an effective method to increase Thomson scattering (TS) signals is required in order to improve signal quality. In GAMMA 10, the yttrium-aluminum-garnet (YAG)-TS system comprises a laser, incident optics, light collection optics, signal detection electronics, and a data recording system. We have been developing a multi-pass TS method for a polarization-based system based on the GAMMA 10 YAG TS. To evaluate the effectiveness of the polarization-based configuration, the multi-pass system was installed in the GAMMA 10 YAG-TS system, which is capable of double-pass scattering. We carried out a Rayleigh scattering experiment and applied this double-pass scattering system to the GAMMA 10 plasma. The integrated scattering signal was made about twice as large by the double-pass system.

Yoshikawa, M.; Morimoto, M.; Shima, Y.; Kohagura, J.; Sakamoto, M.; Nakashima, Y.; Imai, T. [Plasma Research Center, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577 (Japan); Yasuhara, R.; Yamada, I.; Kawahata, K.; Funaba, H. [National Institute for Fusion Science, 322-6 Oroshi-cho, Toki, Gifu 509-5292 (Japan); Minami, T. [Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan)

2012-10-15

378

Micellar and Biochemical Properties of (Hemi)Fluorinated Surfactants Are Controlled by the Size of the Polar Head  

PubMed Central

Abstract Surfactants with fluorinated and hemifluorinated alkyl chains have yielded encouraging results in terms of membrane protein stability; however, the molecules used hitherto have either been chemically heterogeneous or formed heterogeneous micelles. A new series of surfactants whose polar head size is modulated by the presence of one, two, or three glucose moieties has been synthesized. Analytical ultracentrifugation and small-angle neutron scattering show that fluorinated surfactants whose polar head bears a single glucosyl group form very large cylindrical micelles, whereas those with two or three glucose moieties form small, homogeneous, globular micelles. We studied the homogeneity and stability of the complexes formed between membrane proteins and these surfactants by using bacteriorhodopsin and cytochrome b6f as models. Homogeneous complexes were obtained only with surfactants that form homogeneous micelles. Surfactants bearing one or two glucose moieties were found to be stabilizing, whereas those with three moieties were destabilizing. Fluorinated and hemifluorinated surfactants with a two-glucose polar head thus appear to be very promising molecules for biochemical applications and structural studies. They were successfully used for cell-free synthesis of the ion channel MscL. PMID:19686655

Breyton, Cécile; Gabel, Frank; Abla, Maher; Pierre, Yves; Lebaupain, Florence; Durand, Grégory; Popot, Jean-Luc; Ebel, Christine; Pucci, Bernard

2009-01-01

379

Coherent control of polarization state rotation via Doppler broadening and Kerr nonlinearity in a spinning fast light medium  

NASA Astrophysics Data System (ADS)

We propose a four-level experimental N-type atomic configuration to observe the propagation of a light pulse in a spinning dispersive medium. In this model a fast propagating light pulse is observed in which the polarization states of the light and their transmitted images are rotated in the opposite direction to the spinning medium. We investigate the effects of Doppler broadening and Kerr nonlinearity on fast light propagation in a spinning medium. Doppler broadening and Kerr nonlinearity strongly influence the rotation of the polarization states of the light and images of fast light in a spinning medium. A pulse of group velocity ?c/2000.5 ms?1 is enhanced to ?c/80000 ms?1 due to the the Kerr effect and a significant increase is observed in the rotation of the polarization states of the light and images. At a specific parameter, a 25% fraction change is observed due to the Kerr effect. These results provide different rotation states for image coding.

Rahman, Habibur; Hizbullah; Jabar, M. S. Abdul; Khan, Anwar Ali; Ahmad, Iftikhar; Amin Bacha, Bakht

2014-11-01

380

Polarization developments  

SciTech Connect

Recent developments in laser-driven photoemission sources of polarized electrons have made prospects for highly polarized electron beams in a future linear collider very promising. This talk discusses the experiences with the SLC polarized electron source, the recent progress with research into gallium arsenide and strained gallium arsenide as a photocathode material, and the suitability of these cathode materials for a future linear collider based on the parameters of the several linear collider designs that exist.

Prescott, C.Y.

1993-07-01

381

Polarization Aberrations  

NASA Technical Reports Server (NTRS)

The analysis of the polarization characteristics displayed by optical systems can be divided into two categories: geometrical and physical. Geometrical analysis calculates the change in polarization of a wavefront between pupils in an optical instrument. Physical analysis propagates the polarized fields wherever the geometrical analysis is not valid, i.e., near the edges of stops, near images, in anisotropic media, etc. Polarization aberration theory provides a starting point for geometrical design and facilitates subsequent optimization. The polarization aberrations described arise from differences in the transmitted (or reflected) amplitudes and phases at interfaces. The polarization aberration matrix (PAM) is calculated for isotropic rotationally symmetric systems through fourth order and includes the interface phase, amplitude, linear diattenuation, and linear retardance aberrations. The exponential form of Jones matrices used are discussed. The PAM in Jones matrix is introduced. The exact calculation of polarization aberrations through polarization ray tracing is described. The report is divided into three sections: I. Rotationally Symmetric Optical Systems; II. Tilted and Decentered Optical Systems; and Polarization Analysis of LIDARs.

Mcguire, James P., Jr.; Chipman, Russell A.

1990-01-01

382

Multi-mode to single-mode switching caused by self-heating in bottom-emitting intra-cavity contacted 960 nm VCSELs  

NASA Astrophysics Data System (ADS)

Detailed investigation of anomalous modal behavior in fabricated bottom-emitting intra-cavity contacted 960 nm range vertical cavity surface emitting lasers (VCSELs) have been performed. At low currents the broad-aperture VCSELs show multi-mode operation at 945 nm via whispering gallery-like modes. Subsequent increase of pump current results in rapid increase of fundamental mode intensity and switching to a pure single transverse mode lasing regime at 960 nm with the higher slope efficiency. As a result record single transverse mode output power of 15 mW with a side-mode-suppressionratio (SMSR) above 30 dB was achieved. The observed phenomena cannot be explained by oxide-index guiding or changes in current pumping. 2D heat transport simulations show a strong temperature gradient inside the microcavity due to an effective lateral heat-sinking. This creates an effective waveguide and results in lower optical losses for the fundamental mode. At fixed pump current in pulsed regime (pulse width < 400 ns) high-order modes dominate, however the subsequent increase of pulse width leads to a rapid rise of optical power for the fundamental mode and SMSR increasing. Thus the self-heating phenomena play a crucial role in observed VCSEL unusual modal behavior.

Blokhin, Sergey A.; Maleev, Nikolai A.; Kuzmenkov, Alexander G.; Lott, James A.; Kulagina, Marina M.; Zadiranov, Yurii M.; Gladyshev, Andrey G.; Nadtochiy, Alexey M.; Nikitina, Ekaterina V.; Tikhomirov, Vladimir G.; Ledentsov, Nikolai N.; Ustinov, Viktor M.

2012-03-01

383

Direct generation of 2-ps blue pulses from gain-switched InGaN VCSEL assessed by up-conversion technique.  

PubMed

Ultra-short pulses in blue region generated from compact and low-cost semiconductor lasers have attracted much attention for a wide variety of applications. Nitride-based vertical-cavity surface-emitting lasers (VCSELs), having intrinsic high material gain and short cavities, favor the generation of ultra-short blue pulses via a simple gain-switching technique. In this study, we fabricated a single-mode InGaN VCSEL consisting of 10-period InGaN/GaN quantum wells (QWs). The output pulses were evaluated accurately with an up-conversion measurement system having time resolution of 0.12 ps. We demonstrated that ultra-short blue pulses, as short as 2.2 ps at 3.4 K and 4.0 ps at room temperature, were generated from the gain-switched InGaN VCSEL via impulsive optical pumping, without any post-processing. The gain-switched pulses we obtained should greatly promote the development of ultra-short blue pulse generation. In addition, this successful assessment demonstrates the up-conversion technique's usefulness for characterizing ultra-short blue pulses from semiconductor lasers. PMID:25236162

Asahara, Akifumi; Chen, Shaoqiang; Ito, Takashi; Yoshita, Masahiro; Liu, Wenjie; Zhang, Baoping; Suemoto, Tohru; Akiyama, Hidefumi

2014-01-01

384

Direct generation of 2-ps blue pulses from gain-switched InGaN VCSEL assessed by up-conversion technique  

PubMed Central

Ultra-short pulses in blue region generated from compact and low-cost semiconductor lasers have attracted much attention for a wide variety of applications. Nitride-based vertical-cavity surface-emitting lasers (VCSELs), having intrinsic high material gain and short cavities, favor the generation of ultra-short blue pulses via a simple gain-switching technique. In this study, we fabricated a single-mode InGaN VCSEL consisting of 10-period InGaN/GaN quantum wells (QWs). The output pulses were evaluated accurately with an up-conversion measurement system having time resolution of 0.12?ps. We demonstrated that ultra-short blue pulses, as short as 2.2?ps at 3.4?K and 4.0?ps at room temperature, were generated from the gain-switched InGaN VCSEL via impulsive optical pumping, without any post-processing. The gain-switched pulses we obtained should greatly promote the development of ultra-short blue pulse generation. In addition, this successful assessment demonstrates the up-conversion technique's usefulness for characterizing ultra-short blue pulses from semiconductor lasers. PMID:25236162

Asahara, Akifumi; Chen, Shaoqiang; Ito, Takashi; Yoshita, Masahiro; Liu, Wenjie; Zhang, Baoping; Suemoto, Tohru; Akiyama, Hidefumi

2014-01-01

385

Dynamics of vertical-cavity surface-emitting lasers in the short external cavity regime: Pulse packages and polarization mode competition  

SciTech Connect

We study the influence of delayed optical feedback from a short external cavity (EC) on the emission dynamics of vertical-cavity surface-emitting semiconductor lasers (VCSELs). We find the emergence of pulse packages (PP) exhibiting characteristics which originate from the interplay of time-delay induced dynamics and polarization mode (PM) competition. We provide detailed analysis of the polarization dynamics applying complementary cross-correlation and spectral analysis techniques. The analysis reveals an interplay of the dynamics linked to the hierarchy of time scales present in the laser system: the fast time scale of the EC delay, the slower time scale of the PP, and the slow time scale of the polarization mode competition. For an analysis of the dynamics we provide a toolbox of methods adapted to the different relevant time scales and temporal variations of the dynamics. This complementary view unveils distinct changes in the relative oscillation phase of the two PM for increasing the injection current on both the fast and the slow time scales. Our results emphasize the significance of the polarization mode competition for PP dynamics in VCSELs, contrasting the observed behavior to what was reported for edge emitters.

Tabaka, Andrzej; Thienpont, Hugo; Veretennicoff, Irina; Panajotov, Krassimir [Department of Applied Physics and Photonics (TW-TONA), Vrije Universiteit Brussel (VUB), B-1050 Brussels (Belgium); Peil, Michael; Elsaesser, Wolfgang [Institute of Applied Physics, Darmstadt University of Technology, Schlossgartenstrasse 7, 64289 Darmstadt (Germany); Sciamanna, Marc [Laboratoire Materiaux Optiques, Photonique et Systemes (LMOPS), CNRS UMR-7132, Supelec, 2 Rue Edouard Belin, F-57070 Metz (France); Fischer, Ingo [Department of Applied Physics and Photonics (TW-TONA), Vrije Universiteit Brussel (VUB), B-1050 Brussels (Belgium); Institute of Applied Physics, Darmstadt University of Technology, Schlossgartenstrasse 7, 64289 Darmstadt (Germany)

2006-01-15

386

Loop-synchronous polarization scrambling technique for simulating polarization effects using recirculating fiber loops  

Microsoft Academic Search

A loop-synchronous polarization-scrambling technique has been proposed for the purpose of simulating polarization effects in straight-line systems using recirculating loops. This technique uses a fast polarization controller within a fiber loop. The polarization controller changes its transmission matrix after each round trip of the optical signal circulating through the loop; thus, the periodic polarization transform of the loop is avoided.

Q. Yu; L.-S. Yan; S. Lee; Y. Xie; A. E. Willner

2003-01-01

387

Ultra-wideband pulse generation with flexible pulse shape and polarity control using a Sagnac-interferometer-based intensity modulator.  

PubMed

We propose a novel scheme to generate ultra-wideband (UWB) pulse by employing a Sagnac interferometer comprising a phase modulator. This structure performs a dual-input and dual-output intensity modulator (IM), ultimately resulting in the flexibility to select the shape and the polarity of the generated UWB pulse. The experiment results show a good agreement with the theoretical investigation in terms of both pulse profile and spectrum, which conforms to the definition of UWB signals by the U.S. Federal Communications Commission. Furthermore, the proposed scheme is independent of the voltage bias point. PMID:19551113

Li, Jianqiang; Xu, Kun; Fu, Songnian; Wu, Jian; Lin, Jintong; Tang, Ming; Shum, P

2007-12-24

388

Polarized Sunglasses  

NSDL National Science Digital Library

When light reflects from water, asphalt, or other non-metallic surfaces, it becomes polarized. In other words, the reflected light is usually vibrating more in one direction than in others. To see how polarizing sunglasses affect this glare, check out this fun activity from the Exploratorium.

Exploratorium

2008-11-01

389

Crossed Polarizers  

NSDL National Science Digital Library

This Hyperphysics page, from Georgia State University, describes how light behaves when passing through a pair of polarizers oriented perpendicular to each other. The website also gives an explanation of what happens when a third polarizer is added at a particular orientation between the two. Several photographs and drawings are included as well as links to related subjects for additional information.

Nave, Carl R.

2008-10-10

390

Polar Bear  

USGS Publications Warehouse

Polar bears are long-lived, late-maturing carnivores that have relatively low rates of reproduction and natural mortality. Their populations are susceptible to disturbance from human activities, such as the exploration and development of mineral resources or hunting. Polar bear populations have been an important renewable resource available to coastal communities throughout the Arctic for thousands of years.

Amstrup, S.D.; DeMaster

1988-01-01

391

Mid-IR near-perfect absorption with a SiC photonic crystal with angle-controlled polarization selectivity.  

PubMed

We theoretically investigate mid-IR absorption enhancement with a SiC one-dimensional photonic crystal (PC) microstructure at the frequency regime of the phonon-polariton band gap, where efficient absorption is unattainable in the bulk material. Our study reveals an intricate relationship between absorption efficiency and the energy velocity of light propagation, that is far more complex than hitherto believed. In particular, our findings suggest that absorption peaks away from the photonic-crystal band edge where energy velocity is minimum. While efficient absorption is still associated with a slow-light mode, the latter is faster by at least an order of magnitude in comparison to the bulk material. Moreover, our calculations suggest that absorption becomes optimal when light gradually slow downs as it enters the PC. Relying on this insight, we achieved near-perfect absorption around the phonon-polariton mid-gap frequency with a PC with a suitably terminated end face. We further demonstrate that the near-perfect absorptive property can be tuned with the incident light angle, to be polarization insensitive or polarization selective. We believe our proposed non-metallic paradigm opens up a new route for harnessing infrared absorption with semiconductor and ionic-crystal materials. PMID:22714331

Devarapu, G C R; Foteinopoulou, S

2012-06-01

392

EDITORIAL: Polarization Optics  

NASA Astrophysics Data System (ADS)

This special issue on Polarization Optics contains one review article and 23 research papers, many of which are based on presentations at the International Commission for Optics Topical Meeting on Polarization Optics, held in Polvijärvi, Finland, between 30 June and 3 July 2003. While this issue should not in any sense be considered as a `proceedings' of this meeting, the possibility of submitting papers to it was widely advertised during the meeting, which was attended by a large fraction of prominent scientists in the field of polarization optics. Thus the quality of papers in this special issue is high. In announcing both the meeting and this special issue, we emphasized that the concept of `polarization optics' should be understood in a wide sense. In fact, all contributions dealing with the vectorial nature of light were welcome. As a result, the papers included here cover a wide range of different aspects of linear and nonlinear polarization optics. Both theoretical and experimental features are discussed. We are pleased to see that the conference and this special issue both reflect the wide diversity of important and novel polarization phenomena in optics. The papers in this special issue, and other recently published works, demonstrate that even though polarization is a fundamental property of electromagnetic fields, interest in it is rapidly increasing. The fundamental relations between partial coherence and partial polarization are currently under vigorous research in electromagnetic coherence theory. In diffractive optics it has been found that the exploitation of the vectorial nature of light can be of great benefit. Fabrication of sophisticated, spatially variable polarization-control elements is becoming possible with the aid of nanolithography. Polarization singularities and the interplay of bulk properties and topology in nanoscale systems have created much enthusiasm. In nonlinear optics, the second harmonic waves generated on reflection and transmission of intense light enable research into the chirality of nanogratings. Pump-probe techniques allow one to visualize the effects of the nanostructure topology on the surface mode excitation. In quantum optics the coherent control of polarization may lead to new and fascinating applications. Some authors of invited papers at the conference have written review-type introductory sections—they were encouraged to do so—but all contributions are genuine research papers with original results, and were judged according to the normal publication criteria of the journal. It is our pleasure to thank all authors for making this a splendid special issue of Journal of Optics A: Pure and Applied Optics.

Turunen, Jari; Friesem, Asher A.; Friberg, Ari T.

2004-03-01

393

Polarity control and transport properties of Mg-doped (0001) InN by plasma-assisted molecular beam epitaxy  

SciTech Connect

The authors report on the plasma-assisted molecular beam epitaxy growth and carrier transport of Mg-doped In-face (0001) InN. The 1.2 {mu}m thick InN films were grown on GaN:Fe templates under metal rich conditions with Mg concentration from 1 Multiplication-Sign 10{sup 17}/cm{sup 3} to 3 Multiplication-Sign 10{sup 20}/cm{sup 3}. A morphological transition, associated with the formation of V-shape polarity inversion domains, was observed at Mg concentration over 7 Multiplication-Sign 10{sup 19}/cm{sup 3} by atomic force microscopy and transmission electron microscopy. Seebeck measurements indicated p-type conductivity for Mg-concentrations from 9 Multiplication-Sign 10{sup 17}/cm{sup 3} to 7 Multiplication-Sign 10{sup 19}/cm{sup 3}, i.e., as it exceeded the compensating (unintentional) donor concentration.

Choi, Soojeong; Wu Feng; Bierwagen, Oliver; Speck, James S. [Materials Department, University of California, Santa Barbara, California 93106 (United States)

2013-05-15

394

Polar Bear  

NSDL National Science Digital Library

This site from the World Wildlife Fund (WWF) International provides general information about polar bears as well as data on the movements of two radio-collared bears, along with the ice status, through a series of online maps.

2007-01-01

395

Tunable Polarization of Spin Polarized Current by Magnetic Field  

SciTech Connect

The spin polarization of a high g-factor bulk semiconductor is theoretically investigated in the presence of a magnetic field parallel to a driving electric field. Calculations have been carried out using the energy-dependent relaxation time approximation in association with spin-flip scattering. As the magnitude of the magnetic field increases, the spin-polarized current alternates between the spin-up and spin-down states for the low spin-scattering system. This implies that the current polarization can be tuned by controlling the magnetic field strength, suggesting possible applications to spintronic devices. An experimental method for investigating alternative current polarization is also considered.

Joo, S.; Kim, K.; Lee, J.; Kim, T.; Rhie, K.; Hong, J.; Shin, K-H.

2010-10-10

396

Multibeam-antenna feed system to isolate orthogonally polarized beams  

NASA Technical Reports Server (NTRS)

System is polarization tracker and comprises variable polarizer, polarization control, and receiver servo loop. System simultaneously receives desired signal and undesired signal which are approximately orthogonal. They can be either paired as left and right circular polarizations or as cross-linear polarizations.

Ohlson, J. E.; Williams, W. F.

1975-01-01

397

Kinetic Solvent Effects on the Reactions of the Cumyloxyl Radical with Tertiary Amides. Control over the Hydrogen Atom Transfer Reactivity and Selectivity through Solvent Polarity and Hydrogen Bonding.  

PubMed

A laser flash photolysis study on the role of solvent effects on hydrogen atom transfer (HAT) from the C-H bonds of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-formylpyrrolidine (FPRD), and N-acetylpyrrolidine (APRD) to the cumyloxyl radical (CumO(•)) was carried out. From large to very large increases in the HAT rate constant (kH) were measured on going from MeOH and TFE to isooctane (kH(isooctane)/kH(MeOH) = 5-12; kH(isooctane)/kH(TFE) > 80). This behavior was explained in terms of the increase in the extent of charge separation in the amides determined by polar solvents through solvent-amide dipole-dipole interactions and hydrogen bonding, where the latter interactions appear to play a major role with strong HBD solvents such as TFE. These interactions increase the electron deficiency of the amide C-H bonds, deactivating these bonds toward HAT to an electrophilic radical such as CumO(•), indicating that changes in solvent polarity and hydrogen bonding can provide a convenient method for deactivation of the C-H bond of amides toward HAT. With DMF, a solvent-induced change in HAT selectivity was observed, suggesting that solvent effects can be successfully employed to control the reaction selectivity in HAT-based procedures for the functionalization of C-H bonds. PMID:25545198

Salamone, Michela; Mangiacapra, Livia; Bietti, Massimo

2015-01-16

398

Are polar rings indeed polar?  

NASA Astrophysics Data System (ADS)

We have considered polar ring galaxy candidates, the images of which can be found in the SDSS survey. The sample of 78 galaxies includes the most reliable candidates from the SPRC and PRC catalogs, some of which already have kinematic confirmations. We analyze the distributions of studied objects by the angle between the polar ring and the central disk, and by the optical diameter of the outer ring structures. In the vast majority of cases, the outer structures lie in the plane close to polar (within 10°-20°) which indicates the stability of the corresponding orbits in the gravitational potential of the halo. Moderately inclined outer structures are observed only in about 6% of objects which probably indicates their short lifetime. In such an unstable configuration, the polar ring would often cross the disk of the galaxy, being smaller than it in the diameter. We show that the inner polar structures and outer large-scale polar rings form a single family in the distribution of diameters normalized to the optical size of the galaxy. At the same time, this distribution is bimodal, as the number of objects with d ring = (0.4-0.7) d disk is small. Such a shape of size distribution is most likely due to the fact that the stability of polar orbits in the inner regions of galaxies is maintained by the bulge or the bar, while in the outer regions it is provided by the spheroidal (or triaxial) halo.

Smirnova, K. I.; Moiseev, A. V.

2013-10-01

399

Correlation of Martian South Polar CO2 Seasonal Cap Retreat With Low Altitude Clouds: A Control On Annual Accumulation  

NASA Astrophysics Data System (ADS)

Both the north and south polar layered deposits (NPLD and SPLD) comprise the majority of surface ice on Mars and offer a historical record for understanding recent climate. Of importance, the deposits undergo seasonal variability, between winter (when CO2 ice frost covers the polar regions) and summer (when the CO2 ice has sublimed). Recent evidence has shown that winds and atmospheric deposition played major roles for forming the spiral troughs that cover the NPLD. Observations of low altitude clouds (or visible expressions of katabatic jumps), radar stratigraphy, and surface morphology, in combination with high resolution mesoscale simulations from the Laboratoire de Météorologie Dynamique, demonstrate that ice is transported across the NPLD by wind to form and modify the troughs [Smith et al., 2013]. We employ the same techniques on the SPLD to find that the processes affecting southern spiral troughs are very similar, although there is an additional seasonal component not detected on the NPLD. Clouds, as mechanisms of deposition, retreat pole-ward during southern spring and summer. The retreat is matched spatially to modeled high speed winds near the CO2 seasonal ice cap boundary. Our mesoscale simulations reveal that topographic heights of the SPLD primarily drive slope-wind (katabatic) circulations. This existing circulation is reinforced by an additional thermally-direct circulation driven by the retreating CO2 ice in proximity to nearby exposed low albedo deposits, explaining why enhanced winds (and trough clouds) are mostly found in the vicinity of the CO2 seasonal ice boundary. In one simulation, at Ls 290°, the ice line is located so that the slope winds produced by the SPLD topography are optimally enhanced (up to 20 ms-1) by thermally directed circulations caused by a nearly 100 K thermal contrast. This work, in combination with detailed stratigraphic analysis from ground penetrating radar indicates that sites of deposition and retention of ice on the pole coincide with where clouds form. Thus clouds influenced by the retreating CO2 seasonal cap tell us where annual and long-term accumulation occurs. Regions with many clouds have thicker recent deposits, while those with no clouds have little or no recent accumulation. It is possible, and eventually testable with adequate modeling, that trough morphology is dependent on a seasonal CO2 ice cap and that the troughs themselves may require a seasonal cap to initiate.

Smith, Isaac; Spiga, Aymeric

2014-05-01

400

A Bmp/Admp Regulatory Circuit Controls Maintenance and Regeneration of Dorsal-Ventral Polarity in Planarians  

E-print Network

Animal embryos have diverse anatomy and vary greatly in size. It is therefore remarkable that a common signaling pathway, BMP signaling, controls development of the dorsoventral (DV) axis throughout the Bilateria [1, 2, ...

Reddien, Peter

401

The amount and timing of precipitation control the magnitude, seasonality and sources (14C) of ecosystem respiration in a polar semi-desert, northwestern Greenland  

NASA Astrophysics Data System (ADS)

This study investigates how warming and changes in precipitation may affect the cycling of carbon (C) in tundra soils, and between high Arctic tundra and the atmosphere. We quantified ecosystem respiration (Reco) and soil pore space CO2 in a polar semi-desert in northwestern Greenland under current and future climate conditions simulated by long-term experimental warming (+2 °C, +4 °C), water addition (+50% summer precipitation), and a combination of both (+4 °C × +50% summer precipitation). We also measured the 14C content of Reco and soil CO2 to distinguish young C cycling rapidly between the atmosphere and the ecosystem from older C stored in the soil for centuries to millennia. We identified changes in the amount and timing of precipitation as a key control of the magnitude, seasonality and sources of Reco in a polar semi-desert. Throughout each summer, small (<4 mm) precipitation events during drier periods triggered the release of very old C pulses from the deep soil, while larger precipitation events (>4 mm), more winter snow and experimental irrigation were associated with higher Reco fluxes and the release of recently fixed (young) C. Warmer summers and experimental warming also resulted in higher Reco fluxes (+2 °C > +4 °C), but coincided with losses of older C. We conclude that in high Arctic, dry tundra systems, future magnitudes and patterns of old C emissions will be controlled as much by the summer precipitation regime and winter snowpack as by warming. The release of older soil C is of concern, as it may lead to net C losses from the ecosystem. Therefore, reliable predictions of precipitation amounts, frequency, and timing are required to predict the changing C cycle in the high Arctic.

Lupascu, M.; Welker, J. M.; Seibt, U.; Xu, X.; Velicogna, I.; Lindsey, D. S.; Czimczik, C. I.

2014-08-01

402

The amount and timing of precipitation control the magnitude, seasonality and sources (14C) of ecosystem respiration in a polar semi-desert, NW Greenland  

NASA Astrophysics Data System (ADS)

This study investigates how warming and changes in precipitation may affect the cycling of carbon (C) in tundra soils, and between high arctic tundra and the atmosphere. We quantified ecosystem respiration (Reco) and soil pore space CO2 in a polar semi-desert under current and future climate conditions simulated by long-term experimental warming (+2 °C, +4 °C), water addition (+50% summer precipitation) and a combination of both (+4 °C × +50% summer precipitation). We also measured the 14C content of Reco and soil CO2 to distinguish young C cycling rapidly between the atmosphere and the ecosystem from older C stored in the soil for centuries to millennia. We identified changes in the amount and timing of precipitation as a key control of the magnitude, seasonality and sources of Reco in a polar semi-desert. Throughout each summer, small (<4 mm) precipitation events during drier periods triggered the release of very old C pulses from the deep soil, while larger precipitation events (>4 mm), more winter snow and experimental irrigation were associated with higher Reco fluxes and the release of recently-fixed (young) plant C. Warmer summers and experimental warming also resulted in higher Reco fluxes (+2 °C > +4 °C), but coincided with losses of older C. We conclude that in high arctic dry tundra systems, future magnitudes and patterns of old C emissions will be controlled as much by the summer precipitation regime and winter snowpack as by warming. The release of older soil C is of concern as it may lead to net C losses from the ecosystem. Therefore, reliable predictions of precipitation amounts, frequency, and timing are required to predict the changing C cycle in the High Arctic.

Lupascu, M.; Welker, J. M.; Seibt, U.; Xu, X.; Velicogna, I.; Lindsey, D. S.; Czimczik, C. I.

2014-02-01

403

Hepatocyte Polarity  

PubMed Central

Hepatocytes, like other epithelia, are situated at the interface between the organism’s exterior and the underlying internal milieu and organize the vectorial exchange of macromolecules between these two spaces. To mediate this function, epithelial cells, including hepatocytes, are polarized with distinct luminal domains that are separated by tight junctions from lateral domains engaged in cell-cell adhesion and from basal domains that interact with the underlying extracellular matrix. Despite these universal principles, hepatocytes distinguish themselves from other nonstriated epithelia by their multipolar organization. Each hepatocyte participates in multiple, narrow lumina, the bile canaliculi, and has multiple basal surfaces that face the endothelial lining. Hepatocytes also differ in the mechanism of luminal protein trafficking from other epithelia studied. They lack polarized protein secretion to the luminal domain and target single-spanning and glycosylphosphatidylinositol-anchored bile canalicular membrane proteins via transcytosis from the basolateral domain. We compare this unique hepatic polarity phenotype with that of the more common columnar epithelial organization and review our current knowledge of the signaling mechanisms and the organization of polarized protein trafficking that govern the establishment and maintenance of hepatic polarity. The serine/threonine kinase LKB1, which is activated by the bile acid taurocholate and, in turn, activates adenosine monophosphate kinase-related kinases including AMPK1/2 and Par1 paralogues has emerged as a key determinant of hepatic polarity. We propose that the absence of a hepatocyte basal lamina and differences in cell-cell adhesion signaling that determine the positioning of tight junctions are two crucial determinants for the distinct hepatic and columnar polarity phenotypes. PMID:23720287

Treyer, Aleksandr; Müsch, Anne

2013-01-01

404

Mars south polar spring and summer behavior observed by TES: seasonal cap evolution controlled by frost grain size  

USGS Publications Warehouse

Thermal Emission Spectrometer (TES) observations of the recession phase of Mars' south polar cap are used to quantitatively map this recession in both thermal and visual appearance. Geographically nonuniform behavior interior to the cap is characterized by defining several small regions which exemplify the range of behavior. For most of the cap, while temperatures remain near the CO2 frost point, albedos slowly increase with the seasonal rise of the Sun, then drop rapidly as frost patches disappear over a period of ?20 days. A “Cryptic” region remains dark and mottled throughout its cold period. TES observations are compared with first-order theoretical spectra of solid CO2 frost with admixtures of dust and H2O. The TES spectra indicate that the Cryptic region has much larger grained solid CO2 than the rest of the cap and that the solid CO2 here may be in the form of a slab. The Mountains of Mitchel remain cold and bright well after other areas at comparable latitude, apparently as a result of unusually small size of the CO2 frost grains; we found little evidence for a significant presence of H2O. Although CO2 grain size may be the major difference between these regions, incorporated dust is also required to match the observations; a self-cleaning process carries away the smaller dust grains. Comparisons with Viking observations indicate little difference in the seasonal cycle 12 Martian years later. The observed radiation balance indicates CO2 sublimation budgets of up to 1250 kg m?2. Regional atmospheric dust is common; localized dust clouds are seen near the edge of the cap prior to the onset of a regional dust storm and interior to the cap during the storm.

Kieffer, Hugh H.; Titus, Timothy N.; Mullins, Kevin F.; Christensen, Philip R.

2000-01-01

405

Large-area arrayed polarimeters with modulated polarization state of light beam based on electrically controlling liquid crystal architecture for integrating sensor array  

NASA Astrophysics Data System (ADS)

We present an integrated polarization image sensing architecture, which can be used for measuring all the Stokes parameters, and then regulating the polarization state of light beam according to the polarization state we have known, by changing the voltage amplitude applied over the patterned electrodes. The architecture contains a liquid crystal (LC) device and an uncooled photo detector. We can calculate the polarization state of the polarized light beam by the intensities of the light passing through the different area of the LC device, and then modulate the polarization state of the light beam to other polarization state which we want by only varying the voltage amplitude of the driving signal in sub-millisecond. In this paper, we will give the simulating results of the polarimeter architecture we designed.

Tong, Qing; Zhang, Xinyu; Sang, Hongshi; Xie, Changsheng

2013-08-01

406

Polar Bear  

NSDL National Science Digital Library

In this episode of the Podcast of Life, host Ari Daniel Shapiro relates two close calls with polar bears. Listen as Heather Cray recalls how, dumped by a storm on a small Arctic island without a shotgun, she got an unexpected wake-up call. And when researcher Steve Amstrup accidentally crashed through the roof of a polar bearâs den, no one could predict what happened next. Also included is a Learn More section that provides background information on the scientists recorded in the podcast, lessons, images, and cool facts.

2009-01-01

407

Configuration Manual Polarized Proton Collider at RHIC  

SciTech Connect

In this report we present our design to accelerate and store polarized protons in RHIC, with the level of polarization, luminosity, and control of systematic errors required by the approved RHIC spin physics program. We provide an overview of the physics to be studied using RHIC with polarized proton beams, and a brief description of the accelerator systems required for the project.

Roser T.; Alekseev& #44; I.; Allgower& #44; C.; Bai& #44; M.; Batygin& #44; Y.; et al

2006-01-01

408

Polarization conversion in a silica microsphere  

E-print Network

We experimentally demonstrate controlled polarization-selective phenomena in a whispering gallery mode resonator. We observed efficient (approx. 75%) polarization conversion of light in a silica microsphere coupled to a tapered optical fiber, optimizing the polarization of the light propagating along the fiber. We present a simple model treating the microsphere as a ring resonator to explain the observed behavior.

Bianucci, P; Robertson, J W; Shvets, G; Shih, C K

2007-01-01

409

Investigation of liquid-crystal polarization-plane switches based on the twist effect and utilizing two-frequency control  

Microsoft Academic Search

An experimental investigation was made of the static and dynamic modulation characteristics and angular dependences of the contrast associated with the twist effect in nematic liquid crystals with low-frequency inversion of the sign of their dielectric anisotropy. It is shown that two-frequency control of the twist effect can be used as the basis of fairly fast wide-aperture switches of the

V V Tsvetkov; V B Fedorov; V A Tsvetkov; M N Fedorova

1980-01-01

410

Single-mode vertical-cavity surface-emitting lasers grown under accurate real-time optical control  

Microsoft Academic Search

Summary form only given. We applied an optical real-time growth control technique: TDOR (tunable dynamic optical reflectometry) to grow GaAs\\/AlGaAs-based VCSELs. TDOR control consists of exploiting reflectivity interferences measured on the growing multilayer with a tunable optical source. Prior to the growth, a set of optimal wavelengths corresponding to the successive layers to be controlled, is calculated within the tunable

F. Van Dijk; V. Bardinal; P. Dubreuil; L. Averseng; E. Bedel-Pereua; C. Fontaine; A. Munoz-Yague

2000-01-01

411

Microscope-integrated Micromanipulator based on Multiple VCSEL , Sanja Zlatanovic, Sadik C. Esener  

E-print Network

Lasers) provides them the ability to meet the demands of current biochip technologies. In earlier the demands of current biochip and lab-on-a-chip technologies, which require that the controlling devices

Esener, Sadik C.

412

Polar Connections.  

ERIC Educational Resources Information Center

Announces the theme for National Science and Technology Week (NSTW) 1998 and offers a rationale for the choice of the topic of polar connections. Suggests that the poles offer a glimpse of science as high adventure. The poles are often seen as pristine, nearly lablike environments that provide a platform for animal studies. (DDR)

Calkins, Andrew

1998-01-01

413

Controlling the stoichiometry and strand polarity of a tetramolecular G-quadruplex structure by using a DNA origami frame  

PubMed Central

Guanine-rich oligonucleotides often show a strong tendency to form supramolecular architecture, the so-called G-quadruplex structure. Because of the biological significance, it is now considered to be one of the most important conformations of DNA. Here, we describe the direct visualization and single-molecule analysis of the formation of a tetramolecular G-quadruplex in KCl solution. The conformational changes were carried out by incorporating two duplex DNAs, with G–G mismatch repeats in the middle, inside a DNA origami frame and monitoring the topology change of the strands. In the absence of KCl, incorporated duplexes had no interaction and laid parallel to each other. Addition of KCl induced the formation of a G-quadruplex structure by stably binding the duplexes to each other in the middle. Such a quadruplex formation allowed the DNA synapsis without disturbing the duplex regions of the participating sequences, and resulted in an X-shaped structure that was monitored by atomic force microscopy. Further, the G-quadruplex formation in KCl solution and its disruption in KCl-free buffer were analyzed in real-time. The orientation of the G-quadruplex is often difficult to control and investigate using traditional biochemical methods. However, our method using DNA origami could successfully control the strand orientations, topology and stoichiometry of the G-quadruplex. PMID:23863846

Rajendran, Arivazhagan; Endo, Masayuki; Hidaka, Kumi; Lan Thao Tran, Phong; Mergny, Jean-Louis; Sugiyama, Hiroshi

2013-01-01

414

Controls on Soil Moisture Wicking Extent Away From Lake Fryxell (Constant Boundary Condition) in the Dry Valleys Polar Desert, Antarctica  

NASA Astrophysics Data System (ADS)

The extreme conditions of the Antarctic Dry Valleys, are accentuated by the lack of available water across the landscape. In general, the majority of soils are wetted only briefly after infrequent, small snowfall events. However, adjacent to glacial meltwater streams and closed-basin lakes, soils wick water from these sources and wetted fronts at the soil surface are visually conspicuous, extending several meters from shoreline. We postulate that this wicking of surface water is responsible for unique solute transport and microbial diversity within the Dry Valley landscape. We performed synoptic sampling and topographic surveys around Lake Fryxell, Taylor Valley, to quantify the influence of two geomorphic controls on the scaling of these wetting fronts: 1) near-shore topography (slope), and 2) soil grain size distribution. The topographic survey was carried out with a GPS RTK unit (>10,000 points), and in the synoptic sampling campaign we collected 120 samples (4 samples from wet to dry sediments at 30 transects around the lake) for gravimetric soil moisture and particle size analysis, and made measurements of surface soil moisture, depth to permafrost at an additional 114 transects. We found that wetted fronts range in distance from 1.4 to 22.2 m and depth to resistance of penetration (taken as depth of active layer) ranged from 12 to 63.5 cm, generally decreasing with distance from shore. Our results suggest that near-lake soils are fairly homogeneous in particle size distribution; therefore slope has a greater control on wicking front distance, explaining 54% of the variance as a power-law function.

Gooseff, M. N.; Barrett, J. E.; Hill, K. R.; Bate, D. B.; Northcott, M. L.; Zeglin, L. H.; Bobb, M.; Vesbach, C. D.

2005-12-01

415

BaCaF2/III-V semiconductor broadband distributed Bragg reflectors for long-wavelength VCSEL and SESAM devices  

NASA Astrophysics Data System (ADS)

Semiconductor devices such as vertical-cavity surface-emitting lasers (VCSELs) or semiconductor-saturable absorber mirrors (SESAMs) require high-reflection mirrors. Moreover, in VCSELs, it is beneficial to have a crystalline mirror, which is as thin as possible in order to ensure a high thermal conductivity for efficient heat-sinking of the laser. On the other hand, the wavelength tuning range of a SESAM is limited by the reflection bandwidth of its distributed Bragg reflector (DBR). Thus, broadband mirrors are preferable here. This paper reports a three-pair DBR grown by molecular beam epitaxy (MBE) using BaCaF2 and GaAs on a GaAs (100) substrate. Due to the high ratio in refractive indices of GaAs and the group-IIa-fluorides, high-reflectivity mirrors and wide bandwidths can be obtained with low total thicknesses. We also investigated growth and stability of the material BaCaF2, as well as its thermal conductivity both as single layer and Bragg reflector. Observed peeling of the layers could be avoided by implementing a fluorine treatment previous to the BaCaF2 growth.

Koeninger, Anna; Boehm, Gerhard; Meyer, Ralf; Amann, Markus-Christian

2014-09-01

416

Low-Energy Electron Effects on the Polar Wind Observed by the POLAR Spacecraft  

NASA Technical Reports Server (NTRS)

Large ion outflow velocity variation at POLAR apogee have been observed. The observed H+ flow velocities were in the range of 23-110 km/s and 0+ flow velocities were in the range of 5-25 km/s. These velocity ranges lie between those predicted by simulations of the photoelectron-driven polar wind and "baseline" polar wind. The electric current contributions of the photoelectrons and polar rain are expected to control the size and altitude of an electric potential drop which accelerates the polar wind at relatively high altitudes. In this presentation, we compare polar wind characteristics observed near 5000 km and 8 RE altitudes by the Thermal Ion Dynamics Experiment (TIDE) with measurements of low-energy electrons sampled by HYDRA, both from the POLAR spacecraft, to examine possible effects of the polar rain and photoelectrons on the polar wind. Both correlations and anti-correlations are found between the polar wind velocities and the polar rain fluxes at POLAR apogee during different polar cap crossings. Also, the low-altitude upward/downward photoelectron spectra are used to estimates the potential drops above the spacecraft. We interpret these observations in terms of the effects that both photoelectrons and polar rain may have on the electric potential and polar wind acceleration along polar cap magnetic field lines.

Horwitz, J. L.; Su, Y.-J.; Dors, E. E.; Moore, Thomas E.; Giles, Barbara L.; Chandler, Michael O.; Craven, Paul D.; Chang, S.-W.; Scudder, J.

1998-01-01

417

Par proteins and neuronal polarity  

PubMed Central

A hallmark of neurons is their ability to polarize with dendrite and axon specification to allow the proper flow of information through the nervous system. Over the past decade, extensive research has been performed in an attempt to understand the molecular and cellular machinery mediating this neuronal polarization process. It has become evident that many of the critical regulators involved in establishing neuronal polarity are evolutionarily conserved proteins that had previously been implicated in controlling the polarization of other cell types. At the forefront of this research are the partition defective (Par) proteins. In this review, we will provide a commentary on the progress of work regarding the central importance of Par proteins in the establishment of neuronal polarity. PMID:21557502

Insolera, Ryan; Chen, She; Shi, Song-Hai

2011-01-01

418

Expansion of CAG Repeats in Escherichia coli Is Controlled by Single-Strand DNA Exonucleases of Both Polarities  

PubMed Central

The expansion of CAG·CTG repeat tracts is responsible for several neurodegenerative diseases, including Huntington disease and myotonic dystrophy. Understanding the molecular mechanism of CAG·CTG repeat tract expansion is therefore important if we are to develop medical interventions limiting expansion rates. Escherichia coli provides a simple and tractable model system to understand the fundamental properties of these DNA sequences, with the potential to suggest pathways that might be conserved in humans or to highlight differences in behavior that could signal the existence of human-specific factors affecting repeat array processing. We have addressed the genetics of CAG·CTG repeat expansion in E. coli and shown that these repeat arrays expand via an orientation-independent mechanism that contrasts with the orientation dependence of CAG·CTG repeat tract contraction. The helicase Rep contributes to the orientation dependence of repeat tract contraction and limits repeat tract expansion in both orientations. However, RuvAB-dependent fork reversal, which occurs in a rep mutant, is not responsible for the observed increase in expansions. The frequency of repeat tract expansion is controlled by both the 5?–3? exonuclease RecJ and the 3?–5? exonuclease ExoI, observations that suggest the importance of both 3?and 5? single-strand ends in the pathway of CAG·CTG repeat tract expansion. We discuss the relevance of our results to two competing models of repeat tract expansion. PMID:25081568

Jackson, Adam; Okely, Ewa A.

2014-01-01

419

EAT-2, a SAP-like adaptor, controls NK cell activation through phospholipase C?, Ca++, and Erk, leading to granule polarization  

PubMed Central

Ewing’s sarcoma-associated transcript 2 (EAT-2) is an Src homology 2 domain-containing intracellular adaptor related to signaling lymphocytic activation molecule (SLAM)–associated protein (SAP), the X-linked lymphoproliferative gene product. Both EAT-2 and SAP are expressed in natural killer (NK) cells, and their combined expression is essential for NK cells to kill abnormal hematopoietic cells. SAP mediates this function by coupling SLAM family receptors to the protein tyrosine kinase Fyn and the exchange factor Vav, thereby promoting conjugate formation between NK cells and target cells. We used a variety of genetic, biochemical, and imaging approaches to define the molecular and cellular mechanisms by which EAT-2 controls NK cell activation. We found that EAT-2 mediates its effects in NK cells by linking SLAM family receptors to phospholipase C?, calcium fluxes, and Erk kinase. These signals are triggered by one or two tyrosines located in the carboxyl-terminal tail of EAT-2 but not found in SAP. Unlike SAP, EAT-2 does not enhance conjugate formation. Rather, it accelerates polarization and exocytosis of cytotoxic granules toward hematopoietic target cells. Hence, EAT-2 promotes NK cell activation by molecular and cellular mechanisms distinct from those of SAP. These findings explain the cooperative and essential function of these two adaptors in NK cell activation. PMID:24687958

Pérez-Quintero, Luis-Alberto; Roncagalli, Romain; Guo, Huaijian; Latour, Sylvain; Davidson, Dominique

2014-01-01

420

Vertical-cavity surface-emitting laser with liquid crystal external cavity  

NASA Astrophysics Data System (ADS)

We have developed a technology to integrate a thin layer of liquid crystal (LC) on top of a Vertical-Cavity Surface- Emitting Laser (VCSEL). Based on this technology, we demonstrate VCSELs with a chiral liquid crystal (CLC) layer, which acts as a tuneable mirror. The reflection properties of the CLC layer are controlled by temperature. Next we demonstrate VCSEL devices with tuneable external cavity using a nematic LC layer incorporated with an additional dielectric mirror (SiO2/Ta2O5). The VCSEL and the LC layer can be electrically driven independently and the optical length in the external cavity can be tuned by the applied voltage on the LC layer. In both configurations we show that the emission properties of the VCSEL can be changed, in terms of emission wavelength, polarization state and/or lasing threshold.

Xie, Y.; Beeckman, J.; Panajotov, K.; Neyts, K.

2014-10-01

421

Overlapping and divergent signaling pathways for ARK1 and AGD1 in the control of root hair polarity in Arabidopsis thaliana  

PubMed Central

We previously showed that seedlings harboring mutations in genes encoding ARK1, an armadillo repeat-containing kinesin, or AGD1, a class 1 ARF-GAP, have root hairs that exhibit wavy/spiral growth and two tips originating from one initiation site. These root hair defects were accompanied by bundling of endoplasmic microtubules and filamentous actin (F-actin) that extended to the extreme root hair apex. The similar phenotypes of ark1 and agd1 mutants suggest a tight coordination between the cytoskeleton and membrane trafficking in the control of root hair polarity. Indeed, cell biological and genetic studies of the agd1 mutant provided evidence that AGD1's involvement in root hair development involves cross-talk among phosphoinositides (PIs), the actin cytoskeleton and other small GTPases such as ROP2 and RABA4b. Here we show that ark1 root hairs mirror those of agd1 with regard to altered targeting of ROP2 and RABA4b, as well as abnormal tonoplast organization. Furthermore, like agd1, enhanced root hair defects in double mutants in ARK1 and genes encoding a type B phosphatidylinositol-4-phosphate 5-kinase 3 (PIP5K3), a phosphatidylinositol-4-phosphate (PI-4P) phosphatase (RHD4), a phosphatidylinositol transfer protein (COW1), and a vegetative actin isoform (ACT2), were observed. However, root hair shape of some ark1 double mutant combinations, particularly those with act2, pip5k3 and rhd4 (ark1 act2, ark1 pip5k3, ark1 rhd4), differed in some respects from agd1 act2, agd1 pip5k3, and agd1 rhd4. Taken together our results continue to point to commonalities between ARK1 and AGD1 in specifying root hair polarity, but that these two modulators of tip-growth can also regulate root hair development through divergent signaling routes with AGD1 acting predominantly during root hair initiation and ARK1 functioning primarily in sustained tip growth. PMID:24400013

Yoo, Cheol-Min; Blancaflor, Elison B.

2013-01-01

422

Polarization-selective Kerr-phase-shift method for fast, all-optical polarization switching in a cold atomic medium  

NASA Astrophysics Data System (ADS)

We examine an all-optical atomic-polarization-gate scheme using a polarization-selective Kerr phase-shift technique. Using a Kerr ? -phase-shift technique, we selectively write a ? phase shift to one of the circularly polarized components of a linearly polarized signal field while leaving the other component unchanged. Upon recombination, the signal field acquires a 90? linear-polarization rotation, completing the critical polarization-gate operation. We demonstrate with numerical simulations that a special phase-control light-field detuning can be obtained which results in a complete linear-polarization rotation with a phase-control light.

Zhu, Chengjie; Deng, L.; Hagley, E. W.

2014-12-01

423

Polar Shells  

NASA Technical Reports Server (NTRS)

21 May 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows sand dunes overlain by a layer of seasonal carbon dioxide frost in the north polar region of Mars. Sunlight illuminates the scene from the lower left, but slopes facing toward the upper right seem illuminated because of the thicker accumulation of frost on the slopes facing away from the sunlight.

Location near: 76.3oN, 264.3oW Image width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Winter

2006-01-01

424

Polar ozone  

NASA Technical Reports Server (NTRS)

The observation and interpretation of a large, unexpected ozone depletion over Antarctica has changed the international scientific view of stratospheric chemistry. The observations which show the veracity, seasonal nature, and vertical structure of the Antarctic ozone hole are presented. Evidence for Arctic and midlatitude ozone loss is also discussed. The chemical theory for Antarctic ozone depletion centers around the occurrence of polar stratospheric clouds (PSCs) in Antarctic winter and spring; the climatology and radiative properties of these clouds are presented. Lab studies of the physical properties of PSCs and the chemical processes that subsequently influence ozone depletion are discussed. Observations and interpretation of the chemical composition of the Antarctic stratosphere are described. It is shown that the observed, greatly enhanced abundances of chlorine monoxide in the lower stratosphere are sufficient to explain much if not all of the ozone decrease. The dynamic meteorology of both polar regions is given, interannual and interhemispheric variations in dynamical processes are outlined, and their likely roles in ozone loss are discussed.

Solomon, S.; Grose, W. L.; Jones, R. L.; Mccormick, M. P.; Molina, Mario J.; Oneill, A.; Poole, L. R.; Shine, K. P.; Plumb, R. A.; Pope, V.

1990-01-01

425

Polar Dunes  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site]

Dunes in the Vastitas Borealis region of Mars. These sand seas migrate around the north polar cap following the strong polar vortex winds.

Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

Image information: VIS instrument. Latitude 77.3, Longitude 87.3 East (272.7 West). 19 meter/pixel resolution.

2003-01-01

426

Polar Unconformity  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site] Figure 1

19 August 2004 The arrows (see Figure 1) in this July 2004 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image indicate the location of an unconformity in the layered sequence of the martian north polar cap. An unconformity is a geologic term that indicates a break in the depositional record of a sedimentary deposit. In this case, the change is recorded by the presence of a series of polar layers that are truncated (cut off) along the line of arrows. The erosion that cut these layers along a gentle slope were later covered by a new set of layers that occur from the arrow tips upward to the top of the sequence shown here. The image is located near 85.2oN, 7.3oW. The bright features in the lower third of the image are frost-covered sand dunes. The image covers an area about 3 km (1.9 mi) across and sunlight illuminates the scene from the top/upper right.

2004-01-01

427

Magnetic control of ferroelectric polarization  

E-print Network

of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan 2 Institute of Materials Science, University of candidate materials is limited and the effects are typically too small to be useful in applications. Here we report the discovery of ferroelectricity in a perovskite manganite, TbMnO3, where the effect of spin

Chandra, Premi

428

JPL Polar Oceanography Group  

NSDL National Science Digital Library

The Jet Propulsion Laboratory's Polar Oceanography Group utilizes "satellite microwave remote sensing data and in-situ methods to understand the climate-induced variability in sea-ice and land-ice on seasonal to interannual time scales." Research conducted by the group is mainly concerned with Arctic Sea Ice, Antarctic Sea Ice, and Ice Sheets. "The principal thrust of this research is to understand the role of the polar oceans in controlling or regulating global climate." A data products section includes online data for sea ice melt detection and ice drift and ice motion data. The excellent publications section offers online copies (.pdf) of the group's work dating from 1989 to current publications that are in press. The site also provides news, contacts, and links.

429

Polarization imaging apparatus  

NASA Technical Reports Server (NTRS)

A polarization imaging apparatus measures the Stokes image of a sample. The apparatus consists of an optical lens set 11, a linear polarizer 14 with its optical axis 18, a first variable phase retarder 12 with its optical axis 16 aligned 22.5.degree. to axis 18, a second variable phase retarder 13 with its optical axis 17 aligned 45.degree. to axis 18, a imaging sensor 15 for sensing the intensity images of the sample, a controller 101 and a computer 102. Two variable phase retarders 12 and 13 were controlled independently by a computer 102 through a controller unit 101 which generates a sequential of voltages to control the phase retardations of VPRs 12 and 13. A set of four intensity images, I.sub.0, I.sub.1, I.sub.2 and I.sub.3 of the sample were captured by imaging sensor 15 when the phase retardations of VPRs 12 and 13 were set at (0,0), (.pi.,0), (.pi.,.pi.) and (.pi./2,.pi.), respectively Then four Stokes components of a Stokes image, S.sub.0, S.sub.1, S.sub.2 and S.sub.3 were calculated using the four intensity images.

Zou, Yingyin Kevin (Inventor); Chen, Qiushui (Inventor); Zhao, Hongzhi (Inventor)

2010-01-01

430

Planar polarity  

PubMed Central

The clinical burden of both adult and neonatal lung disease worldwide is substantial; in the UK alone, respiratory disease kills one in four people. It is increasingly recognized that genes and pathways that regulate lung development, may be aberrantly activated in disease and/or reactivated as part of the lungs' intrinsic repair mechanisms. Investigating the genes and signaling pathways that regulate lung growth has led to significant insights into the pathogenesis of congenital and adult lung disease. Recently, the planar cell polarity (PCP) pathway has been shown to be required for normal lung development, and data suggests that this signaling pathway is also involved in the pathogenesis of some lung diseases. In this review, we summarize current evidence indicating that the PCP pathway is required for both lung development and disease. PMID:22030785

Yates, Laura L

2011-01-01

431

Polar Plumage  

NASA Technical Reports Server (NTRS)

8 May 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows dunes in the north polar region of Mars. The dunes in this scene are covered by a layer of carbon dioxide frost that accumulated during the winter in 2005. Dark spots indicate areas where frost has begun to sublime away. In summer, the dune field will be dark, as all of the frost will be gone and the iron- and magnesium-bearing silicate sands will be exposed.

Location near: 81.9oN, 226.1oW Image width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Spring

2006-01-01

432

Polar Barchans  

NASA Technical Reports Server (NTRS)

20 July 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows dark, barchan sand dunes of the north polar region of Mars. Barchan dunes are simple, rounded forms with two horns that extend downwind. Inequalities in local wind patterns may result in one horn being extended farther than the other, as is the case for several dunes in this image. The image also shows several barchans may merge to form a long dune ridge. The horns and attendant slip faces on these dunes indicate wind transport of sand from the upper left toward the lower right. The image is located near 77.6oN, 103.6oW. The picture covers an area about 3 km (1.9 mi) wide; sunlight illuminates the scene from the lower left.

2004-01-01

433

Polarization in Interferometry  

E-print Network

Polarization in Interferometry Steven T. Myers (NRAO Socorro)(NRAO-Socorro) Twelfth Synthesis Imaging Workshop Socorro, June 8-15, 2010, , #12;Polarization in interferometry · Astrophysics of Polarization · Physics of Polarization · Antenna Response to Polarization · Interferometer Response

Myers, Steven T.

434

Beyond Penguins and Polar Bears: Polar Geography  

NSDL National Science Digital Library

Our presenters provide an overview of the geography of the Arctic and Antarctic regions and featured resources from the Beyond Penguins and Polar Bears cyberzine, a resource for elementary educators. This cyberzine focuses on strategies and content to integrate science and literacy through the study of the polar regions. Recorded on May 27, 2008, Beyond Penguins and Polar Bears: Integrating Science and Literacy, Seminar 1: Polar Geography, NSDL featured our experts from The Ohio State University, Jessica Fries-Gaither, Project Director for Beyond Penguins and Polar Bears and Elementary Resource Specialist at the Ohio Resource Center and Dr. Carol Landis, Education Coordinator at the Byrd Polar Research Center.

Payo, Robert

435

Epidermal polarity genes in health and disease.  

PubMed

The epidermis of the skin is a highly polarized, metabolic tissue with important innate immune functions. The polarity of the epidermis is, for example, reflected in controlled changes in cell shape that accompany differentiation, oriented cell division, and the planar orientation of hair follicles and cilia. The establishment and maintenance of polarity is organized by a diverse set of polarity proteins that include transmembrane adhesion proteins, cytoskeletal scaffold proteins, and kinases. Although polarity proteins have been extensively studied in cell culture and in vivo in simple epithelia of lower organisms, their role in mammalian tissue biology is only slowly evolving. This article will address the importance of polarizing processes and their molecular regulators in epidermal morphogenesis and homeostasis and discuss how alterations in polarity may contribute to skin disease. PMID:25452423

Tellkamp, Frederik; Vorhagen, Susanne; Niessen, Carien M

2014-12-01

436

Exploring Polar Oceanography  

NSDL National Science Digital Library

This activity utilizes labs, online resources, and student ideas to build an understanding of polar climates, how changes in polar oceans can affect coastal climates, and how changes in polar regions affect climates elsewhere on Earth.

Alan Sills

437

An All-fiber Tunable Polarization-Dependent Loss Element  

Microsoft Academic Search

We describe the implementation of a wavelength-tunable polarization-dependent-loss element on polarization-maintaining fiber using two independently-controlled acoustic gratings. Continuous attenuation in both fast and slow axes at the same wavelength is demonstrated.

Rong Huang; Fares Alhassen; David Tseng; Ozdal Boyraz; Henry P. Lee

2007-01-01

438

Polarized internal target apparatus  

DOEpatents

A polarized internal target apparatus with a polarized gas target of improved polarization and density achieved by mixing target gas atoms with a small amount of alkali metal gas atoms, and passing a high intensity polarized light source into the mixture to cause the alkali metal gas atoms to become polarized which interact in spin exchange collisions with target gas atoms yielding polarized target gas atoms.

Holt, Roy J. (Downers Grove, IL)

1986-01-01

439

Polarized internal target apparatus  

DOEpatents

A polarized internal target apparatus with a polarized gas target of improved