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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

Shallow surface gratings for high-power VCSELs with one preferred polarization for all modes  

Microsoft Academic Search

Monolithically integrated full-aperture surface gratings are shown to control the polarization of all modes of even highly multimode 850-nm oxide-confined standard industrial vertical-cavity surface-emitting lasers (VCSELs). An orthogonal polarization suppression ratio (OPSR) of more than 11 dB up to thermal rollover is achieved for an output power of 23 mW. For devices with 8-mW output power, an OPSR of more

Johannes Michael Ostermann; Pierluigi Debernardi; Christof Jalics; Rainer Michalzik

2005-01-01

3

Polymer tunable microlens arrays suitable for VCSEL beam control  

NASA Astrophysics Data System (ADS)

We report on a simple method for the collective fabrication of polymer tunable microlens arrays suitable for VCSEL active beam shaping. Its principle is based on a SU-8 suspended membrane, surmounted by a polymer microlens, and thermally actuated to achieve a vertical displacement of lens plane. SU-8 resist presents many advantages for MOEMS fabrication, as this resist allows for high aspect ratio patterns and high transparency. In addition, it exhibits a thermal expansion coefficient suitable for thermal actuation. Moreover, this kind of polymer MOEMS can be fabricated on VCSEL arrays with footprints as low as 500x500?m2 enabling a rapid, low cost and wafer-scale integration technology. We have successfully fabricated this MOEMS on a glass substrate by means of a SU-8 double exposure method and we report on a vertical displacement of 8?m under an applied power of 43mW (3V). A good agreement with the theoretical thermo-mechanical behavior is found. Moreover, optical measurements of microlens focus displacement under actuation are presented. We evaluate analytically the focus properties of the system under coherent laser illumination, using the classical ABCD matrix formalism of Gaussian transformation optics. The same approach enables one to assess its tolerance to opto-geometrical parameters, such as refractive index or dioptre curvature. As a wide range of initial gaps between the membrane and the substrate can be chosen, this MOEMS technology opens new insights for dynamic control of VCSEL beam or for tunable VCSELs fabrication.

Reig, B.; Bardinal, V.; Camps, T.; Boucher, Y. G.; Levallois, C.; Doucet, J. B.; Bourrier, D.; Daran, E.; Launay, J.

2012-06-01

4

Controlled switching of ultrafast circular polarization oscillations in spin-polarized vertical-cavity surface-emitting lasers  

SciTech Connect

We demonstrate a scheme for controlled switching of polarization oscillations in spin-polarized vertical-cavity surface-emitting lasers (spin-VCSEL). Under hybrid electrical and optical pumping conditions, our VCSEL devices show polarization oscillations with frequencies far above the VCSEL's electrical modulation bandwidth. Using multiple optical pulses, we are able to excite and amplify these polarization oscillations. When specific phase and amplitude conditions for the optical excitation pulses are met, destructive interference leads to switch-off of the polarization oscillation, enabling the generation of controlled short polarization bursts.

Höpfner, Henning, E-mail: henning.hoepfner@rub.de; Lindemann, Markus; Gerhardt, Nils C.; Hofmann, Martin R. [Photonics and Terahertz Technology, Ruhr-University Bochum, D-44780 Bochum (Germany)

2014-01-13

5

Polarization behavior and mode structure of elliptical surface relief VCSELs  

Microsoft Academic Search

Summary form only given. We investigate the polarization behavior and the mode structure of elliptical surface relief vertical-cavity surface-emitting lasers. The polarization direction is governed by the orientation of the index ellipsoid, whereas the lasing mode is determined by the losses anisotropy.

Miren Camarena; Guy Verschaffelt; Maria-Cristina Moreno; Lieven Desmet; Heiko J. Unold; Rainer Michalzik; Hugo Thienpont; Jan Danckaert; Irina Veretennicoff; Krassimir Panajotov

2003-01-01

6

Excitation of a two-mode limit cycle dynamics on the route to polarization switching in a VCSEL subject orthogonal to optical injection  

NASA Astrophysics Data System (ADS)

We experimentally and numerically report on polarization switching (PS) mechanism which involves a two-mode limit cycle dynamics in a vertical-cavity surface-emitting laser (VCSEL) subject to orthogonal optical injection from a master laser (ML). The VCSEL (slave laser, SL) emits a horizontal linearly polarized (LP) fundamental mode, without optical injection. The VCSEL is injected by a vertically polarized light from ML. Dynamical characteristics of the VCSEL are investigated as a function of optical injection parameters, i.e., injection strength and frequency detuning between master and slave lasers. We experimentally resolve an injection parameter region for which, as the injection strength is increased for fixed detunings, a limit cycle dynamics in both non-injected and injected modes is abruptly excited. For larger injection strengths, the VCSEL switches from the two-mode to a single-mode limit cycle dynamics which involves only the injected mode. Using continuation methods, we numerically identify two torus bifurcation mechanisms, namely TR I and TR II, which support such a switching scenario. We show that both TR I and TR II originate from a particular Hopf bifurcation which plays a key role in the polarization dynamics of the injected VCSEL. Furthermore, our results reveal that the newly observed switching dynamics are generic features of VCSEL two-mode systems.

Gatare, I.; Sciamanna, M.; Nizette, M.; Thienpont, H.; Panajotov, K.

2008-04-01

7

Power-induced polarization switching and bistability characteristics in 1550-nm VCSELs subjected to orthogonal optical injection  

NASA Astrophysics Data System (ADS)

The polarization switching (PS) and polarization bistability (PB) characteristics of a 1550-nm vertical-cavity surface-emitting laser (VCSEL) subjected to orthogonal optical injection are systematically investigated. The simulated results show that the PS and polarization-resolved nonlinear dynamical states of the VCSEL are critically dependent on the changing paths of the injected power. The polarization dynamics for different scanning directions of the injected power is presented to explain the polarization evolution during the formation of PS. In the case of forward scanning injected power, with the increase of frequency detuning level between the VCSEL and the injected light, the injected power required for PS gradually increases for negative frequency detuning but exhibits fluctuations for positive frequency detuning. In the case of reversely scanning injected power, the injected power required for PS displays fluctuant changes within the whole frequency detuning range. Specifically, PS may disappear under certain negative frequency detuning and large bias current. Furthermore, the hysteresis width as a function of the frequency detuning is calculated, and the regions for the appearance and disappearance of PB have been determined in the parameter space of the bias current and frequency detuning. Project supported by the National Natural Science Foundation of China (Grant Nos. 61178011, 61275116, and 61475127) and the Natural Science Foundation of Chongqing City, China (Grant No. 2012jjB40011).

Chen, Jian-Jun; Xia, Guang-Qiong; Wu, Zheng-Mao

2015-02-01

8

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

9

VCSELs at Honeywell: The story continues  

NASA Astrophysics Data System (ADS)

Honeywell continues to be the world"s leading supplier of VCSELs operating at 850 nm. This paper will cover new commercial application areas for 850-nm VCSELs, and will present new findings in VCSEL reliability science. In particular, newly-developing applications drive requirements for ever more reliable VCSEL design and fabrication, and for improvements in controls for ESD (electrostatic discharge) and EOS (electrical overstress) at manufacturing facilities both for VCSEL components and for higher-level assemblies employing VCSEL components. Honeywell efforts toward improvement of reliability and toward reduction of ESD exposure are described, as is an alternative approach to improving reliability of systems containing VCSELs without compromising their performance.

Guenter, James K.; Tatum, Jim A.; Hawthorne, Robert A., III; Hawkins, Bobby M.; Mathes, David T.

2004-06-01

10

Improved performance of polarization-stable VCSELs by monolithic sub-wavelength gratings produced by soft nano-imprint lithography.  

PubMed

We present a novel method for fabricating polarization-stable oxide-confined single-mode GaAs based vertical cavity surface emitting lasers (VCSELs) emitting at 850 nm using a new soft-lithography nano-imprint technique. A monolithic surface grating is etched in the output mirror of the laser cavity using a directly imprinted silica-based sol-gel imprint resist as an etch mask. The opto-electronic performance of these devices is compared to VCSELs fabricated by state-of-the-art electron-beam lithography. The lasers made using the soft nano-imprint technique show single-mode TM lasing at a threshold and laser slope similar to that of devices made by e-beam lithography. The soft nano-imprint technique also enables the fabrication of gratings with sub-wavelength pitch, which avoids diffraction losses in the laser cavity. The resulting single-mode VCSEL devices exhibit 29% enhanced efficiency compared to devices equipped with diffractive gratings. PMID:22107885

Verschuuren, M A; Gerlach, P; van Sprang, H A; Polman, A

2011-12-16

11

Improved performance of polarization-stable VCSELs by monolithic sub-wavelength gratings produced by soft nano-imprint lithography  

NASA Astrophysics Data System (ADS)

We present a novel method for fabricating polarization-stable oxide-confined single-mode GaAs based vertical cavity surface emitting lasers (VCSELs) emitting at 850 nm using a new soft-lithography nano-imprint technique. A monolithic surface grating is etched in the output mirror of the laser cavity using a directly imprinted silica-based sol-gel imprint resist as an etch mask. The opto-electronic performance of these devices is compared to VCSELs fabricated by state-of-the-art electron-beam lithography. The lasers made using the soft nano-imprint technique show single-mode TM lasing at a threshold and laser slope similar to that of devices made by e-beam lithography. The soft nano-imprint technique also enables the fabrication of gratings with sub-wavelength pitch, which avoids diffraction losses in the laser cavity. The resulting single-mode VCSEL devices exhibit 29% enhanced efficiency compared to devices equipped with diffractive gratings.

Verschuuren, M. A.; Gerlach, P.; van Sprang, H. A.; Polman, A.

2011-12-01

12

Recent Advances of VCSEL Photonics  

NASA Astrophysics Data System (ADS)

A vertical-cavity surface emitting laser (VCSEL) was invented 30 years ago. A lot of unique features can be expected, such as low-power consumption, wafer-level testing, small packaging capability, and so on. The market of VCSELs has been growing up rapidly in recent years, and they are now key devices in local area networks using multimode optical fibers. Also, long wavelength VCSELs are currently attracting much interest for use in single-mode fiber metropolitan area and wide area network applications. In addition, a VCSEL-based disruptive technology enables various consumer applications such as a laser mouse and laser printers. In this paper, the recent advance of VCSEL photonics will be reviewed, which include the wavelength extension of single-mode VCSELs and their wavelength integration/control. Also, this paper explores the potential and challenges for new functions of VCSELs toward optical signal processing.

Koyama, Fumio

2006-12-01

13

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

14

Evolution of VCSELs  

NASA Astrophysics Data System (ADS)

Over the last 20 years, nearly 1 billion VCSELs have been shipped, the vast majority of them emitting at 850nm using GaAs active regions, and primarily used in data communications and optical tracking applications. Looking to the future, the ever increasing speed of data communications is driving the VCSEL to evolve with more complex active regions, optical mode control, and alternate wavelengths to meet the more stringent requirements. We will discuss the current state of VCSELs for 28Gbps, and higher speeds, focusing on evolution to more complex active regions and alternate wavelength approaches, particularly as the market evolves to more active optical cables. Other high volume applications for VCSELs are driving improvements in single mode and optical power characteristics. We will present several evolving market trends and applications, and the specific VCSEL requirements that are imposed. The ubiquitous 850nm, GaAs active region VCSEL is evolving in multiple ways, and will continue to be a viable optical source well in to the future.

Tatum, Jim A.

2014-02-01

15

Control of cavity lifetime of 1.5 µm wafer-fused VCSELs by digital mirror trimming.  

PubMed

Digital chemical etching is used to trim the output mirror thickness of wafer-fused VCSELs emitting at a wavelength near 1.5µm. The fine control of the photon cavity lifetime thus achieved is employed to extract important device parameters and optimize the combination of the threshold current, output power, and direct current modulation characteristics. The fabrication process is compatible with industrial production and should help in improving device yield and in reducing manufacturing costs. PMID:25607182

Ellafi, Dalila; Iakovlev, Valdimir; Sirbu, Alexei; Suruceanu, Grigore; Mickovic, Zlatco; Caliman, Andrei; Mereuta, Alexandru; Kapon, Elyahou

2014-12-29

16

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

17

The VCSELS are coming  

NASA Astrophysics Data System (ADS)

The paper addresses the current status of 850nm VCSELs in data communications systems, and the outlook for adoption of VCSELs in other applications. In particular, recent experimental results obtained by research and development activities at Honeywell are discussed.

Tatum, Jim A.; Guenter, James K.

2003-06-01

18

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

19

VCSELs in optical networking  

NASA Astrophysics Data System (ADS)

Vertical Cavity Surface Emitting Lasers (VCSELs) are now essentially the only source used in short distance high bit rate data communications over multimode optical fiber. First commercially realized in 1996 by Honeywell, the primary application has been single channel links operating Ethernet or Fibre Channel protocols in the LAN and SAN environments. Today, the total bandwidth throughput is being raised to more than 10Gbps per channel, with the potential of several channel operation to yield more than 100Gbps. 850nm VCSELs are beginning to emerge in relatively new application arenas and wavelengths. This paper describes the market readiness for VCSELS in a wide variety of optical networking applications.

Tatum, Jim A.

2003-08-01

20

Transverse mode and polarization characteristics of AlGaInP-based VCSELs with integrated multiple oxide apertures  

NASA Astrophysics Data System (ADS)

In the current work, we show a detailed analysis of the transverse beam profile and polarization characteristics of devices with one and three oxide apertures. A Gaussian transverse beam profile is achieved with an oxide aperture diameter of less than 6 ?m. The laser light is linearly polarized with a high degree of polarization (> 97 %) in the complete current range. The stable polarization direction can be attributed to ordering effects ocurring during epitaxial growth of the GaInP material system and a reduction in crystal symmetry. Different oxide aperture diameters can be implemented in one device due to high oxidation selectivity of the AlxGa1-xAs layer depending on aluminum content. These deep oxidation layers lead to a reduction of the parasitic capacitance, while beam profile and polarization characteristics are not affected.

Weidenfeld, Susanne; Niederbracht, Hendrik; Eichfelder, Marcus; Jetter, Michael; Michler, Peter

2012-06-01

21

Computational optoelectromechanics and its application to MEMS VCSELs  

NASA Astrophysics Data System (ADS)

Vertical-cavity surface-emitting lasers (VCSELs) have been research extensively as key components for next-generation of wireless communication, computing, processing, switching and optical devices. Conventional VCSELs integrate two oppositely doped distributed Bragg reflectors (DBR) with a cavity layer between them. In the center of the cavity layer there is an active region with multiple quantum wells. Current is injected into the active region using oxide or proton-implanted apertures. Recent research and developments have been progressed to the tunable, long-wavelength, and multiple-wavelength MEMS-based electrically- and optically-pumped VCSELs. These MEMS VCSELs integrate a bottom n-DBR (for example, GaAs-AlGaAs), a cavity layer with the active region (for example, InGaAS), and a top mirror. The top mirror integrates p-DBR (oxidation and sacrificial layers, AlAs, AlGaAs) -- air gap -- top n-DBR suspended above the laser cavity and controlled (displaced or bent) by the nano- or microscale actuators. The current is fed through the p-DBR. Hence, optoelectronics and microelectromechics are examined for MEMS VCSELs. In contrast, the optically-pumped VCSLEs with membrane MEMS integrate n-DBR, cavity layer with the active region, p-DBR, sacrificial layer (for example, AlGaAs) and top mirror (quarter-wave GaAs layer). Usually, the wavelength of tunable VCSELs can be varied within 10 - 30 nm increments. To optimize MEMS VCSELs, far-reaching research and developments must be carried out. Recently, novel MEMS VCSELs topologies and configurations have been devised. These MEMS VCSELs must be modeled, analyzed, and optimized. The computer-aided-design will lead to essential improvement of lasers optimizing their performance. High-fidelity modeling, heterogeneous simulation, data-intensive analysis and synergetic design of MEMS VCSELs are part of a newly emerging field of computational optoelectromechanics. In fact, high-fidelity modeling is an important part in synthesis and design of affordable high-performance MEMS VCSELs with the desired performance and reliability. The basic equations to model VCSELs are found using the quantum mechanics, quantum electromagnetic field theory, Maxwell's and Navier-Stokes equations. To derive the equations of motion for nano- or microactuators, the functional density concept is used to find the force, and Newtonian mechanics allows one to derive the differential equations to integrate mechanical dynamics. This paper focuses on the development of the theory of computational optoelectromechanics and its application to computer-aided design of MEMS VCSELs. The modeling, simulation, analysis and design results are reported and illustrated.

Lyshevski, Sergey E.

2003-04-01

22

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

23

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

24

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

25

Optical Injection Locking of a VCSEL in an OEO  

NASA Technical Reports Server (NTRS)

Optical injection 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 opto-electronic oscillator (OEO) designed to implement an atomic clock based on an electromagnetically- induced-transparency resonance. This particular optical-injection- locking scheme is 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. 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. Inasmuch as the microwave power circulating in the frequency-control loop is a dynamic frequency-control variable (and, hence, cannot be stabilized), there arises a need for another means of stabilizing the wavelength. The present optical-injection-locking scheme satisfies the need for a means to stabilize the wavelength against microwave- power fluctuations. It is also expected to afford stabilization against temperature and current fluctuations. In an experiment performed to demonstrate this scheme, wavelength locking was observed when about 200 W of the output power of a commercial tunable diode laser was injected into a commercial VCSEL, designed to operate in the wavelength range of 795+/-3 nm, that was generating about 200 microW of optical power. (The use of relatively high injection power levels is a usual practice in injection locking of VCSELs.)

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

2009-01-01

26

High-index-contrast subwavelength grating VCSEL  

NASA Astrophysics Data System (ADS)

In this article, we report our results on 980nm high-index-contrast subwavelength grating (HCG) VCSELs for optical interconnection applications. In our structure, a thin undoped HCG layer replaces a thick p-type Bragg mirror. The HCG mirror can feasibly achieve polarization-selective reflectivities close to 100%. The investigated structure consists of a HCG mirror with an underneath ?/4-thick oxide gap, four p-type GaAlAs/GaAs pairs for current spreading, three InGaAs/GaAs quantum wells, and an n-type GaAlAs/GaAs Bragg mirror. The HCG structure was defined by e-beam lithography and dry etching. The current oxide aperture and the oxide gap underneath the HCG were simultaneously formed by the selective wet oxidation process. Compared to air-gap high contrast grating mirrors demonstrated elsewhere, our grating mirrors are particular since they are supported by thinner ?/4 aluminium oxide layer, and thus are mechanically robust and thinner than usual designs. Sub-milliamp threshold currents and single-transverse-mode operation was obtained. A hero device exhibited maximum singlemode output power of more than 4 mW at room temperature and 1 mw at 70°C, which are the highest values ever reported from the HCG structures. These results build a bridge between a standard VCSEL and a hybrid laser on silicon, making them of potential use for the realization of silicon photonics.

Gilet, Philippe; Olivier, Nicolas; Grosse, Philippe; Gilbert, Karen; Chelnokov, Alexei; Chung, Il-Sug; Mørk, Jesper

2010-02-01

27

Commercial VCSELs and VCSEL arrays designed for FDR (14 Gbps) optical links  

NASA Astrophysics Data System (ADS)

Philips recently released a new VCSEL and photodiode product family for the fast growing FDR InfiniBandTM generation. In this work we review the influence of production process variations on VCSEL characteristics, the FDR VCSEL transmission behavior as well as wear-out reliability characteristics. Data collected during an initial 15 wafers pilot production batch verify that FDR VCSEL manufacturing reached mature volume production level. The VCSEL for the next EDR (26Gbps) InfiniBandTM generation is currently being developed at Philips. The paper presents characteristics of the first EDR VCSEL iteration.

King, Roger; Intemann, Steffan; Wabra, Stefan

2012-03-01

28

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

29

Reversible Polarization Control of Single Photon Emission  

Microsoft Academic Search

We present reversible and a-priori control of the polarization of a photon emitted by a single molecule by introducing a nanoscale metal object in its near field. It is experimentally shown that, with the metal close to the emitter, the polarization ratio of the emission can be varied by a factor of 2. The tunability of polarization decays, when the

Robert J. Moerland; Tim H. Taminiau; Lukas Novotny; Hulst van Niek F; Laurens Kuipers

2008-01-01

30

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

31

Stability control of the polarization switching  

NASA Astrophysics Data System (ADS)

Pulse polarization switching is an important new method to eliminate the polarization-induced fading (PIF) in the interferometric fiber sensing system. An integrated Ti-indiffused LiNbO3 Mach-Zehnder modulator is used to achieve high-speed switch of the polarization state by switching the voltage between two appropriate voltages applied to the modulator. The stability of the polarization switching is affected by environmental factors, especially the temperature. In this paper, the stability of the polarization switching is studied. Firstly, the structure of the modulator and the principle of the polarization switching are introduced. Secondly, a feedback control method to overcome the switch instability is proposed. The output polarization state could be obtained by monitoring the intensity of the output light. Finally, the high-speed and high-accuracy stable switching between two orthogonal polarization states is realized using this method and experimentally demonstrated.

Yin, Xiaobing; Lin, Huizu; Hu, Zhengliang; Hu, Yongming

2013-08-01

32

VCSELS for high-speed data networks  

NASA Astrophysics Data System (ADS)

Applications of 850 nm VCSELs have bloomed in recent years arising from their low cost, and the ease of forming one- and two-dimensional arrays. In addition to the traditional measures of device lifetime, operation over a wide temperature range and link length, the figures of merit increasingly include power consumption (pJ/bit), footprint (bits/mm2) and cost ($/Gb/s). As 1 × 12 arrays of 10G VCSELs are widely adopted, there is a clear need for improvement along all these fronts. This is achieved through development of VCSELs operating at higher data rates, and modifications to the oxide VCSEL structure. In this paper, we discuss the development of VCSELs with electrostatic discharge protection, and high bandwidth for operation at 10 - 25 Gb/s.

Murty, M. V. Ramana; Giovane, L.; Ray, S. K.; Chew, K.-L.; Crom, M. V.; Sale, T. E.; Sridhara, A.; Zhao, C.; Chen, Chu; Fanning, T. R.

2013-03-01

33

Nuclear reactivity control using laser induced polarization  

DOEpatents

A control element for reactivity control of a fission source provides an atomic density of .sup.3 He in a control volume which is effective to control criticality as the .sup.3 He is spin-polarized. Spin-polarization of the .sup.3 He affects the cross section of the control volume for fission neutrons and hence, the reactivity. An irradiation source is directed within the .sup.3 He for spin-polarizing the .sup.3 He. An alkali-metal vapor may be included with the .sup.3 He where a laser spin-polarizes the alkali-metal atoms which in turn, spin-couple with .sup.3 He to spin-polarize the .sup.3 He atoms.

Bowman, Charles D. (Los Alamos, NM)

1991-01-01

34

Nuclear reactivity control using laser induced polarization  

DOEpatents

A control element for reactivity control of a fission source provides an atomic density of .sup.3 He in a control volume which is effective to control criticality as the .sup.3 He is spin-polarized. Spin-polarization of the .sup.3 He affects the cross section of the control volume for fission neturons and hence, the reactivity. An irradiation source is directed within the .sup.3 He for spin-polarizing the .sup.3 He. An alkali-metal vapor may be included with the .sup.3 He where a laser spin-polarizes the alkali-metal atoms which in turn, spin-couple with .sup.3 He to spin-polarize the .sup.3 He atoms.

Bowman, Charles D. (Los Alamos, NM)

1990-01-01

35

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

36

Long-wavelength VCSELs at Honeywell  

NASA Astrophysics Data System (ADS)

In this paper we describe both the 1310 and 1550 nm VCSEL development work at Honeywell using both InP and GaAs substrates, and using both MOCVD and MBE. We describe the material systems, the designs, the growth techniques, and the promising results obtained and compare them to the needs of the communications industry. InGaAsN quantum well based VCSELs have been demonstrated to 1338 nm lasing at temperatures up to 90 C. Continuous wave InP based 1550 nm VCSELs have also been demonstrated.

Johnson, Ralph H.; Blasingame, Virgil; Tatum, Jim A.; Chen, Bo-Su; Mathes, David T.; Orenstein, James D.; Wang, Tzu-Yu; Kim, Jin K.; Kwon, Ho-Ki; Ryou, Jae-Hyun; Park, Gyoungwon; Kalweit, Edith; Chanhvongsak, Helen; Ringle, Mike D.; Marta, Terry; Gieske, Joe

2003-06-01

37

Higher speed VCSELs by photon lifetime reduction  

NASA Astrophysics Data System (ADS)

The impedance characteristics and the effects of photon lifetime reduction on the performance of high-speed 850 nm VCSELs are investigated. Through S11 measurements and equivalent circuit modeling we show that the parasitic mesa capacitance can be significantly reduced by using multiple oxide layers. By performing a shallow surface etch (25 - 55 nm) on the fabricated VCSELs, we are able to reduce the photon lifetime by up to 80% and thereby significantly improve both static and dynamic properties of the VCSELs. By optimizing the photon lifetime we are able to enhance the 3dB modulation bandwidth of 7 ?m oxide aperture VCSELs from 15 GHz to 23 GHz and finally demonstrate errorfree transmission at up to 40 Gbit/s.

Westbergh, Petter; Gustavsson, Johan S.; Kögel, Benjamin; Haglund, Åsa; Larsson, Anders; Joel, Andrew

2011-03-01

38

VCSEL-Based Transceivers for Data Communications  

NASA Astrophysics Data System (ADS)

The data communications (datacom) transceiver market has experienced tremendous growth over the last fifteen years due in large part to the use of vertical-cavity surface-emitting lasers (VCSELs) and multimode optical fibers. This chapter reviews the evolution of 850 nm laser-based datacom transceivers beginning with the early use of AlGaAs edge-emitters to the adoption of VCSELs where their unique attributes have enabled significant performance enhancements and cost reductions in transceiver designs.

Jackson, Kenneth P.; Schow, Clint L.

39

Polarization-Controlled Single Photons  

Microsoft Academic Search

Vacuum-stimulated Raman transitions are driven between two magnetic substates\\u000aof a rubidium-87 atom strongly coupled to an optical cavity. A magnetic field\\u000alifts the degeneracy of these states, and the atom is alternately exposed to\\u000alaser pulses of two different frequencies. This produces a stream of single\\u000aphotons with alternating circular polarization in a predetermined\\u000aspatio-temporal mode. MHz repetition rates

T. Wilk; S. C. Webster; H. P. Specht; G. Rempe; A. Kuhn

2007-01-01

40

Polarization-controlled single photons  

E-print Network

Vacuum-stimulated Raman transitions are driven between two magnetic substates of a rubidium-87 atom strongly coupled to an optical cavity. A magnetic field lifts the degeneracy of these states, and the atom is alternately exposed to laser pulses of two different frequencies. This produces a stream of single photons with alternating circular polarization in a predetermined spatio-temporal mode. MHz repetition rates are possible as no recycling of the atom between photon generations is required. Photon indistinguishability is tested by time-resolved two-photon interference.

Wilk, T; Rempe, G; Specht, H P; Webster, S C

2006-01-01

41

Polarization-Controlled Single Photons  

NASA Astrophysics Data System (ADS)

Vacuum-stimulated Raman transitions are driven between two magnetic substates of a Rb87 atom strongly coupled to an optical cavity. A magnetic field lifts the degeneracy of these states, and the atom is alternately exposed to laser pulses of two different frequencies. This produces a stream of single photons with alternating circular polarization in a predetermined spatiotemporal mode. MHz repetition rates are possible as no recycling of the atom between photon generations is required. Photon indistinguishability is tested by time-resolved two-photon interference.

Wilk, T.; Webster, S. C.; Specht, H. P.; Rempe, G.; Kuhn, A.

2007-02-01

42

Polarization-controlled single photons  

E-print Network

Vacuum-stimulated Raman transitions are driven between two magnetic substates of a rubidium-87 atom strongly coupled to an optical cavity. A magnetic field lifts the degeneracy of these states, and the atom is alternately exposed to laser pulses of two different frequencies. This produces a stream of single photons with alternating circular polarization in a predetermined spatio-temporal mode. MHz repetition rates are possible as no recycling of the atom between photon generations is required. Photon indistinguishability is tested by time-resolved two-photon interference.

T. Wilk; S. C. Webster; H. P. Specht; G. Rempe; A. Kuhn

2006-10-26

43

Polarization-controlled single photons.  

PubMed

Vacuum-stimulated Raman transitions are driven between two magnetic substates of a 87Rb atom strongly coupled to an optical cavity. A magnetic field lifts the degeneracy of these states, and the atom is alternately exposed to laser pulses of two different frequencies. This produces a stream of single photons with alternating circular polarization in a predetermined spatiotemporal mode. MHz repetition rates are possible as no recycling of the atom between photon generations is required. Photon indistinguishability is tested by time-resolved two-photon interference. PMID:17358938

Wilk, T; Webster, S C; Specht, H P; Rempe, G; Kuhn, A

2007-02-01

44

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

45

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

46

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

47

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

48

Robust design of Si/Si3N4 high contrast grating mirror for mid-infrared VCSEL application  

E-print Network

A Si/Si3N4 high contrast grating mirror has been designed for a VCSEL integration in mid-infrared ({\\lambda} = 2.65 $\\mu$m). The use of an optimization algorithm which maximizes a VCSEL mirror quality factor allowed the adjustment of the grating parameters while keeping large and shallow grating pattern. The robustness with respect to fabrication error has been enhanced thanks to a precise study of the grating dimension tolerances. The final mirror exhibits large high reflectivity bandwidth with a polarization selectivity and several percent of tolerance on the grating dimensions.

Chevallier, Christyves; Genty, Frédéric; Jacquet, Joel

2012-01-01

49

Optical Injection-Induced Polarization Switching Dynamics in 1.5- m Wavelength Single-Mode Vertical-Cavity Surface-Emitting Lasers  

Microsoft Academic Search

We report the first experimental invetigation of the polarization-mode switching dynamics and injection-wavelength-dependent polarization-mode bistability of a 1.5-m wavelength single-mode vertical-cavity surface-emitting lasers (VCSELs) under external laser beam injection. An injection beam with polarization orthogonal to that of the stand-alone VCSEL caused polarization-mode instability and switching of the VCSEL output. By varying the optical injection detuning for fixed injection power

Kyu Hyeon Jeong; Kyong Hon Kim; Seoung Hun Lee; Min Hee Lee; Byeung-Soo Yoo; K. Alan Shore

2008-01-01

50

High-capacity free-space optical interconnects based on vertical cavity surface emitting lasers (VCSEL's)  

Microsoft Academic Search

Gaussian diffraction model is employed to analyze the optimal design of free-space optical interconnects (FSOI’s) based on the arrays of multi-tranverse mode vertical cavity surface emitting lasers (VCSEL’s), microlenses, and photodetectors. The optical channel crosstalk and the signal-to-noise ratio (SNR) are analyzed in relation to the multi-transverse mode VCSEL’s. We have found that the positioning of VCSEL’s relative to the

Rong Wang; ALEKSANDAR D. RAKIC; MARIAN L. MAJEWSKI

2000-01-01

51

Comparison of Techniques for Bonding VCSELs Directly to Ics  

SciTech Connect

This paper reports the successful bonding of 8 x 8 and 4 x 4 VCSEL arrays to Si CMOS and GaAs MESFET integrated circuits and to GaAs substrates. Three different bonding techniques are demonstrated and their electrical, optical and mechanical characteristics are compared. All three techniques remove the substrate from the VCSEL wafer, leaving individual VCSELs bonded directly to locations within the integrated circuit.

Choquette, K.D.; Geib, K.M.; Hayes, E.M. Wilmsen, C.W.; Hou, H.Q.; Pu, R.

1999-03-26

52

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

53

Development of polarization-mode controllable CARS microscope  

NASA Astrophysics Data System (ADS)

We developed a polarization-mode controllable coherent anti-Stokes Raman scattering microscope. The polarizationmode of excitations beams such as linear, radial, or azimuth polarization were switched with compact polarization mode converters made of eight-segmented liquid-crystal spatial-light-modulators. The polarization-mode of the excitation beams is electrically controllable without any mechanical operation. We demonstrated the detection of the molecular orientation of liquid crystals with the developed microscope.

Hashimoto, Mamoru; Takagi, Tatsuro; Minamikawa, Takeo; Niioka, Hirohiko; Araki, Tsutomu

2011-03-01

54

Studying the VCSEL to VCSEL injection locking for enhanced chromatic dispersion compensation  

NASA Astrophysics Data System (ADS)

In order to supply a theoretical guide for digital chaotic telecommunication, the technique of Optical injection locking (OIL) of semiconductor lasers on the chaotic communication have been investigated based on the theoretical models used to describe the dynamics of solitary VCSEL subjected to the external optical injection and signal transmission in fiber. The numerical simulation results show that, the frequency chirp and time-resolved chirp are reduced in magnitude, using a VCSEL laser as master and another VCSEL as slave, it leads to a no-penalty transmission over 50 km of uncompensated in SSMF at 10Gb/s, and it could be higher rate and more remote if there were appropriate compensation.

Li, Linfu

2010-11-01

55

Optical reversibility theorems for polarization: Application to remote control of polarization  

Microsoft Academic Search

The authors prove three optical reversibility theorems that relate the polarization ellipticity at the output of an optical system to the polarization of the retroreflected light at the input by using Jones's formalism. How these theorems can be used to measure the ellipticity of a polarization remotely and to control it remotely is described. To create a linear or a

N. Vansteenkiste; P. Vignolo; A. Aspect

1993-01-01

56

A semiconductor laser with monolithically integrated dynamic polarization control.  

PubMed

We report the first demonstration of a semiconductor laser monolithically integrated with an active polarization controller, which consists of a polarization mode converter followed by an active, differential phase shifter. High speed modulation of the device output polarization is demonstrated via current injection to the phase shifter section. PMID:23037101

Holmes, B M; Naeem, M A; Hutchings, D C; Marsh, J H; Kelly, A E

2012-08-27

57

Invited Paper Subwavelength Transmission Gratings and Their Applications in VCSELs  

E-print Network

Invited Paper Subwavelength Transmission Gratings and Their Applications in VCSELs Stephen Y. Choua of subwavelength transmission gratings (SWTGs) and their applications in vertical cavity surface emitting lasers-switching VCSEL oscillator that has a can tunable frequency up to terahertz. Keywords: subwavelength, gratings

58

Ultra-sensitive immunoassay using VCSEL detection system  

E-print Network

Ultra-sensitive immunoassay using VCSEL detection system C.F.R. Mateus, M.C.Y. Huang, C.J. Chang. In this Letter, we report the use of this system in immunoassay with a record high sensitivity to antigen be largely extended (32 nm) by using a MEMS tunable VCSEL [4]. Mouse IgG capture immunoassay: In this Letter

Cunningham, Brian

59

Prediction and evaluation of infant failures of oxide VCSELs  

NASA Astrophysics Data System (ADS)

Vertical-cavity surface-emitting lasers (VCSELs) with oxide layers introduced for modal property control are relatively weak against reliability-related damage. We propose and demonstrate a method of detecting potential damage without running a long-term burn-in test. For two damage mechanisms, chemical etching and electrostatic discharge, we found that an exceptional increase in the ideality factor ( Id V/d I) is closely related to potential damage of the device that will eventually lead to failure in the following burn-in test. The extent and the origin of the damage could also be identified by using the heights and locations of the bumps in the ideality factor curves.

Lee, Sook-Hui; Pyun, Su-Hyun; Kim, Hee Dae; Shin, Hyun Kuk; Hwang, In-Kag

2014-12-01

60

Furnace control apparatus using polarizing interferometer  

DOEpatents

A system for non-destructively 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.

Schultz, Thomas J. (Maumee, OH); Kotidis, Petros A. (Waban, MA); Woodroffe, Jaime A. (North Reading, MA); Rostler, Peter S. (Newton, MA)

1995-01-01

61

Process control system using polarizing interferometer  

DOEpatents

A system for non-destructively 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.

Schultz, Thomas J. (Maumee, OH); Kotidis, Petros A. (Waban, MA); Woodroffe, Jaime A. (North Reading, MA); Rostler, Peter S. (Newton, MA)

1994-01-01

62

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

63

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

64

Multiplexed gas spectroscopy using tunable VCSELs  

SciTech Connect

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 {omega}, and measuring the harmonics component (2{omega}) 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.

Bond, T; Bond, S; McCarrick, J; Zumstein, J; Chang, A; Moran, B; Benett, W J

2012-04-10

65

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

66

Generation of polarization-resolved wideband unpredictability-enhanced chaotic signals based on vertical-cavity surface-emitting lasers subject to chaotic optical injection.  

PubMed

A system framework is proposed and analyzed for generating polarization-resolved wideband unpredictability-enhanced chaotic signals based on a slave vertical-cavity surface-emitting laser (S-VCSEL) driven by an injected optical chaos signal from a master VCSEL (M-VCSEL) under optical feedback. After calculating the time series outputs from the M-VCSEL under optical feedback and the S-VCSEL under chaotic optical injection by using the spin-flip model (SFM), the unpredictability degree (UD) is evaluated by permutation entropy (PE), and the bandwidth of the polarization-resolved outputs from the M-VCSEL and S-VCSEL are numerically investigated. The results show that, under suitable parameters, both the bandwidth and UD of two polarization components (PCs) outputs from the S-VCSEL can be enhanced significantly compared with that of the driving chaotic signals output from the M-VCSEL. By simulating the influences of the feedback and injection parameters on the bandwidth and UD of the polarization-resolved outputs from S-VCSEL, related operating parameters can be optimized. PMID:25837062

Chen, Jian-Jun; Wu, Zheng-Mao; Tang, Xi; Deng, Tao; Fan, Li; Zhong, Zhu-Qiang; Xia, Guang-Qiong

2015-03-23

67

Optimization of polarization control schemes for QKD systems  

NASA Astrophysics Data System (ADS)

In this work we develop an analysis of polarization control schemes suitable for quantum key distribution systems. Both time division multiplexing and wavelength division multiplexing based schemes are considered. A model for the optimization of the temporal separation between reference pulses and polarization encoded photons is presented. The model accounts for the reference pulse shape, the single photon detector gate width, and the respective temporal separation between them. The theoretical results are validated through experimental measurements. These results can be used to optimize the performance of polarization control schemes and therefore to optimize the polarization encoded quantum key distribution systems.

Muga, Nelson J.; Almeida, Álvaro J.; Ferreira, Mário F.; Pinto, Armando N.

2011-05-01

68

Heat assisted magnetic recording (HAMR) with nano-aperture VCSELs for 10 Tb/in2 magnetic storage density  

NASA Astrophysics Data System (ADS)

We have conducted a thorough experimental analysis of nano-aperture VCSELs for use in heat-assisted magnetic recording (HAMR). To the best of our knowledge, this is the first study to both explore the impact of magnetic media proximity on VCSEL aperture power throughput and to use statistical methods to simultaneously characterize thousands of aperture designs. To achieve areal recording densities beyond 1 Tb/in2, high anisotropy magnetic materials are required to overcome the super-paramagnetic effect. These require high switching fields which are not conventionally available. Heat assisted magnetic recording (HAMR) is a potential technology to reduce the coercivity of the media and thus the required switching field by localized heating to enable writing of bits. The challenges being faced by this technology are to develop a precise method of delivering light to a very small, sub wavelength bit area with sufficient power through a near field aperture, and the fabrication of a laser source which can be integrated with current write heads used in hard disk drives. The focus of our work is to characterize nano-aperture VCSELs and test their potential application to HAMR. We have fabricated 850 nm VCSELs with large arrays of differently shaped nano-apertures in the gold layer on top of each VCSEL. The focusing and transmission characteristics of differently shaped nano-apertures are compared by simulations and experiments. C-shaped and H-shaped nano-apertures have also been fabricated in a gold layer deposited on a SiO2 substrate to observe the effect of close proximity of magnetic media (FePt) on the performance of nano-apertures, and polarization effects have also been characterized.

Hussain, Sajid; Kundu, Shreya; Bhatia, C. S.; Yang, Hyunsoo; Danner, Aaron J.

2013-03-01

69

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

70

Outside In: Inversion of Cell Polarity Controls Epithelial Lumen Formation  

PubMed Central

Establishment of cell polarity is important for epithelial lumen formation, and the molecular mechanisms directing this process are only partially understood. In this issue of Developmental Cell, Bryant et al. (2014) show that disassembly, membrane translocation, and reassembly of podocalyxin complexes controls epithelial cell polarization and lumen formation in 3D matrices. PMID:25373773

Davis, George E.; Cleaver, Ondine B.

2015-01-01

71

Manipulating polarization of electromagnetic waves through controllable metamaterial absorber  

Microsoft Academic Search

In this presentation, we demonstrate an approach to manipulate electromagnetic waves with different polarizations through a controllable metamaterial absorber. The metamaterial absorber designed at 3.3 GHz is proposed by properly integrating resonant unit cells with orthogonal polarization sensitivity onto a dielectric substrate and coupling the unit cells with microwave diodes. Simulation and measurement results show that through tuning the bias

Bo Zhu; Ci Huang; Junming Zhao; Tian Jiang; Yijun Feng

2010-01-01

72

A plot twist: the continuing story of VCSELs at AOC  

NASA Astrophysics Data System (ADS)

During a year of substantial consolidation in the VCSEL industry, Honeywell sold their VCSEL Optical Products Division, which has now officially changed its name to Advanced Optical Components (AOC). Both manufacture and applied research continue, however. Some of the developments of the past year are discussed in this paper. They include advances in the understanding of VCSEL degradation physics, substantial improvements in long-wavelength VCSEL performance, and continuing progress in manufacturing technology. In addition, higher speed serial communications products, at 10 gigabits and particularly at 4 gigabits per second, have shown faster than predicted growth. We place these technologies and AOC's approach to them in a market perspective, along with other emerging applications.

Guenter, James K.; Tatum, Jim A.; Hawthorne, Robert A., III; Johnson, Ralph H.; Mathes, David T.; Hawkins, Bobby M.

2005-03-01

73

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

74

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

75

Modeling of optical synchronization of chaotic external-cavity VCSELs  

Microsoft Academic Search

The performance of a master-slave configuration for effecting the synchronization of chaotic vertical-cavity surface-emitting lasers (VCSELs) is studied using numerical simulations. The dynamical evolution of optically coupled VCSELs is examined using a traveling wave model which is valid in the strong optical feedback regime. It is shown that the proposed configuration is capable of effecting synchronization in a robust manner.

P. S. Spencer; Claudio R. Mirasso; P. Colet; K. Alan Shore

1998-01-01

76

February 24, 2009 Radiation-Hardness of VCSEL/PIN  

E-print Network

February 24, 2009 Radiation-Hardness of VCSEL/PIN W. Fernando, K.K. Gan, H.P. Kagan, R.D. Kass, J Introduction Radiation hardness of PINs Radiation hardness of VCSELs Summary #12;K.K. Gan ATLAS Upgrade with 50% safety factor #12;K.K. Gan ATLAS Upgrade Week 5 K.K. Gan 5 Radiation-Hardness of Silicon PIN

Gan, K. K.

77

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

78

Circularly polarized antennas with controlled radiation patterns  

Microsoft Academic Search

Log-helix conical antennas were examined as a way to satisfy the requirement for circular polarization of antennas for spacecraft use. It was concluded that a multiple-helix antenna which allows the helix lead angle to be changed can be used when the radiation and directivity in the direction of the reception point must be changed during flight.

B. A. Prigoda; V. A. Guryev; N. S. Ulyanin; N. N. Kalugin

1974-01-01

79

Polar auxin transport: controlling where and how much  

NASA Technical Reports Server (NTRS)

Auxin is transported through plant tissues, moving from cell to cell in a unique polar manner. Polar auxin transport controls important growth and developmental processes in higher plants. Recent studies have identified several proteins that mediate polar auxin transport and have shown that some of these proteins are asymmetrically localized, paving the way for studies of the mechanisms that regulate auxin transport. New data indicate that reversible protein phosphorylation can control the amount of auxin transport, whereas protein secretion through Golgi-derived vesicles and interactions with the actin cytoskeleton might regulate the localization of auxin efflux complexes.

Muday, G. K.; DeLong, A.; Brown, C. S. (Principal Investigator)

2001-01-01

80

?-Tubulin controls neuronal microtubule polarity independently of Golgi outposts  

PubMed Central

Neurons have highly polarized arrangements of microtubules, but it is incompletely understood how microtubule polarity is controlled in either axons or dendrites. To explore whether microtubule nucleation by ?-tubulin might contribute to polarity, we analyzed neuronal microtubules in Drosophila containing gain- or loss-of-function alleles of ?-tubulin. Both increased and decreased activity of ?-tubulin, the core microtubule nucleation protein, altered microtubule polarity in axons and dendrites, suggesting a close link between regulation of nucleation and polarity. To test whether nucleation might locally regulate polarity in axons and dendrites, we examined the distribution of ?-tubulin. Consistent with local nucleation, tagged and endogenous ?-tubulins were found in specific positions in dendrites and axons. Because the Golgi complex can house nucleation sites, we explored whether microtubule nucleation might occur at dendritic Golgi outposts. However, distinct Golgi outposts were not present in all dendrites that required regulated nucleation for polarity. Moreover, when we dragged the Golgi out of dendrites with an activated kinesin, ?-tubulin remained in dendrites. We conclude that regulated microtubule nucleation controls neuronal microtubule polarity but that the Golgi complex is not directly involved in housing nucleation sites. PMID:24807906

Nguyen, Michelle M.; McCracken, Christie J.; Milner, E. S.; Goetschius, Daniel J.; Weiner, Alexis T.; Long, Melissa K.; Michael, Nick L.; Munro, Sean; Rolls, Melissa M.

2014-01-01

81

?-tubulin controls neuronal microtubule polarity independently of Golgi outposts.  

PubMed

Neurons have highly polarized arrangements of microtubules, but it is incompletely understood how microtubule polarity is controlled in either axons or dendrites. To explore whether microtubule nucleation by ?-tubulin might contribute to polarity, we analyzed neuronal microtubules in Drosophila containing gain- or loss-of-function alleles of ?-tubulin. Both increased and decreased activity of ?-tubulin, the core microtubule nucleation protein, altered microtubule polarity in axons and dendrites, suggesting a close link between regulation of nucleation and polarity. To test whether nucleation might locally regulate polarity in axons and dendrites, we examined the distribution of ?-tubulin. Consistent with local nucleation, tagged and endogenous ?-tubulins were found in specific positions in dendrites and axons. Because the Golgi complex can house nucleation sites, we explored whether microtubule nucleation might occur at dendritic Golgi outposts. However, distinct Golgi outposts were not present in all dendrites that required regulated nucleation for polarity. Moreover, when we dragged the Golgi out of dendrites with an activated kinesin, ?-tubulin remained in dendrites. We conclude that regulated microtubule nucleation controls neuronal microtubule polarity but that the Golgi complex is not directly involved in housing nucleation sites. PMID:24807906

Nguyen, Michelle M; McCracken, Christie J; Milner, E S; Goetschius, Daniel J; Weiner, Alexis T; Long, Melissa K; Michael, Nick L; Munro, Sean; Rolls, Melissa M

2014-07-01

82

Terahertz polarization pulse shaping with arbitrary field control  

NASA Astrophysics Data System (ADS)

Polarization shaping of terahertz pulses enables us to manipulate the temporal evolution of the amplitude and direction of electric-field vectors in a prescribed manner. Such arbitrary control of terahertz waves has great potential in expanding the scope of terahertz spectroscopy, the manipulation of terahertz nonlinear phenomena and coherent control. This is analogous to the use of pulse-shaping techniques for optical frequencies that involve light's polarization states as a controllable degree of freedom. Here, we propose and demonstrate a method for generating a prescribed terahertz polarization-shaped waveform by the optical rectification of a laser pulse whose instantaneous polarization state and intensity are controlled by an optical pulse shaper. We have developed a deterministic procedure to derive input parameters for the pulse shaper that are adequate to generate the desired terahertz polarization-shaped waveform, with the benefit of simple polarization selection rules for the rectification process of light waves propagating along the three-fold axis of a nonlinear optical crystal.

Sato, Masaaki; Higuchi, Takuya; Kanda, Natsuki; Konishi, Kuniaki; Yoshioka, Kosuke; Suzuki, Takayuki; Misawa, Kazuhiko; Kuwata-Gonokami, Makoto

2013-09-01

83

[Depth selectivity by using polarization-controlled spectral technique].  

PubMed

A continuous depth selectivity is examined by changing the state of polarization of the signal light, based on the orthogonal polarization spectral (OPS) microcirculation imaging system. Unlike the traditional OPS system, which could only rend a two dimensional image of a certain cross-section, the elliptically polarized light controlled by the polarizer unit and the analyzer unit could do the microscopy refocusing without mechanically scanning the sample, as a result, the tissue information at different depths could be obtained. Because the proposed system matches the emission spectrum of the light source with the absorption spectrum of the erythrocyte, it has relatively high signal-to-noise ratio, and could be used to detect microcirculation. Imaging of a pork fat with a target is acquired, and the quantitative relationship between image contrast and the state of polarization is illustrated. The results show that from linearly to circularly polarized illumination, the image contrast gradually increases, and the maximum visible depth also increases. Finally, the auricle vessel of a nude mouse was detected by this polarization-controlled spectral imaging system. Through the experiment the feasibility of depth selectivity was proved. The proposed method provides new insights to microscopy refocusing of microcirculation. PMID:24555345

Feng, Xu; Sun, Li-Qun; Zhang, En-Yao

2013-11-01

84

High-speed VCSELs for energy efficient computer interconnects  

NASA Astrophysics Data System (ADS)

State-of-the-art vertical-cavity surface-emitting laser (VCSEL) based optical interconnects for application in high performance computers and data centers are reviewed. Record energy-efficient data transmission is demonstrated with 850 nm single-mode VCSELs for multimode optical fiber lengths up to 1 km at bit rates up to 25 Gb/s. Total power consumption of less than 100 fJ/bit is demonstrated for VCSELs for the first time. Extremely temperature stable 980-nm VCSELs show lasing up to 200 °C. Error-free 44 Gb/s operation at room temperature and 38 Gb/s up to 85 °C is achieved with these devices. We present record-high bit rates in a wide temperature range of more than 160 °C. Record energy-efficient data-transmission beyond 30 Gb/s is achieved at 25 °C for this wavelength range. In view of the high speed and advanced temperature stability we suggest long wavelength VCSELs for energy-efficient short and very short-distance optical interconnects for future high performance computers.

Moser, Philip; Wolf, Philip; Lott, James A.; Larisch, Gunter; Payusov, Alexey; Mutig, Alex; Unrau, Waldemar; Ledentsov, Nikolay N.; Hofmann, Werner; Bimberg, Dieter

2012-06-01

85

Control of the polarity of magnetization vortex by torsion  

NASA Astrophysics Data System (ADS)

The switching behavior of vortex polarity in a circular ferromagnetic nanodot subjected to torsion is investigated by using a real space phase field model, which explicitly includes the coupling between magnetization and mechanical strain. It is found that the vortex polarity of the nanodot can be switched by torsion when the sign of the torsion is opposite to that of vortex chirality whereas switching does not take place if the sign of torsion is the same as that of vortex chirality. The magneto-elastic coupling and demagnetization field play a decisive role in the polarity switching, which involves an intriguing interplay of magnetization, strain, and demagnetization. The results suggest another way to control vortex polarity by mechanical torsion other than magnetic field and electric current.

Wang, Jie; Li, Gui-Ping; Shimada, Takahiro; Fang, Hui; Kitamura, Takayuki

2013-12-01

86

Stable polarization self-modulation in vertical-cavity surface-emitting lasers  

SciTech Connect

The characteristics of polarization self-modulation in a vertical-cavity surface-emitting laser (VCSEL) were studied for frequencies up to {approx}9 GHz both experimentally and theoretically. Polarization self-modulation was obtained by rotating the linearly polarized output of the VCSEL by 90{degree} and reinjecting it into the laser. Experimentally we simultaneously recorded time traces, optical and radio-frequency spectra. We found for increasing modulation frequencies that the output characteristics changed from square-wave to sinusoidal and the VCSEL system assumed new polarization eigenstates that are different from the free-running VCSEL eigenstates. We modeled polarization self-modulation as an interband process and found a good qualitative agreement between our experimental and numerical results. {copyright} {ital 1998 American Institute of Physics.}

Li, H.; Hohl, A.; Gavrielides, A. [Air Force Research Laboratory DELO, Nonlinear Optics Group, Phillips Research Site, 3550 Aberdeen Avenue, Kirtland Air Force Base, New Mexico 87117-5776 (United States)] [Air Force Research Laboratory DELO, Nonlinear Optics Group, Phillips Research Site, 3550 Aberdeen Avenue, Kirtland Air Force Base, New Mexico 87117-5776 (United States); Hou, H.; Choquette, K.D. [Center of Compound Semiconductor Science and Technology, Sandia National Laboratories MS0603, Albuquerque, New Mexico 87185-1603 (United States)] [Center of Compound Semiconductor Science and Technology, Sandia National Laboratories MS0603, Albuquerque, New Mexico 87185-1603 (United States)

1998-05-01

87

Full-field interferometric confocal microscopy using a VCSEL array  

PubMed Central

We present an interferometric confocal microscope using an array of 1200 VCSELs coupled to a multimode fiber. Spatial coherence gating provides ~18,000 continuous virtual pinholes allowing an entire en face plane to be imaged in a snapshot. This approach maintains the same optical sectioning as a scanning confocal microscope without moving parts, while the high power of the VCSEL array (~5 mW per laser) enables high-speed image acquisition with integration times as short as 100 µs. Interferometric detection also recovers the phase of the image, enabling quantitative phase measurements and improving the contrast when imaging phase objects. PMID:25078199

Redding, Brandon; Bromberg, Yaron; Choma, Michael A.; Cao, Hui

2014-01-01

88

Polarization control of single photon quantum orbital angular momentum  

E-print Network

Polarization control of single photon quantum orbital angular momentum states E. Nagali1, F, Italy Abstract: The orbital angular momentum of photons, being defined in an infinite device, the so-called "q-plate", which enables the manipulation of the photon orbital angular momentum

Roma "La Sapienza", Università di

89

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

90

Optimized design of laser range finding system using the self-mixing effect in a single-mode VCSEL  

NASA Astrophysics Data System (ADS)

An optimized design of laser range finding system using the self-mixing effect in a single-mode vertical-cavity surface-emitting laser (VCSEL) is proposed. In order to improve the ranging accuracy and expand dynamic measurement range, we apply difference frequency analog phase-locked loop (PLL) instead of fast Fourier transform (FFT) to process signal, and choose the optimum triangular wave frequency fm = 500 Hz and small modulation current 'Delta'I(p-p) = 0.28 mA to modulate single-mode VCSEL. The experiment results show that, without controlling the laser's temperature, the ranging accuracy is better than 2 mm and the measurement dynamic range is as large as 50-500 mm when the sampling time is 0.1 s and the room temperature is 0-55 Celsius degree.

Wang, Huanqin; Zhao, Tianpeng; Xu, Jun; He, Deyong; Lv, Liang; Gui, Huaqiao; Huang, Wei; Ming, Hai; Xie, Jianping

2006-02-01

91

Coherent control of optical polarization effects in metamaterials  

NASA Astrophysics Data System (ADS)

Processing of photonic information usually relies on electronics. Aiming to avoid the conversion between photonic and electronic signals, modulation of light with light based on optical nonlinearity has become a major research field and coherent optical effects on the nanoscale are emerging as new means of handling and distributing signals. Here we demonstrate that in slabs of linear material of sub-wavelength thickness optical manifestations of birefringence and optical activity (linear and circular birefringence and dichroism) can be controlled by a wave coherent with the wave probing the polarization effect. We demonstrate this in proof-of-principle experiments for chiral and anisotropic microwave metamaterials, where we show that the large parameter space of polarization characteristics may be accessed at will by coherent control. Such control can be exerted at arbitrarily low intensities, thus arguably allowing for fast handling of electromagnetic signals without facing thermal management and energy challenges.

Mousavi, Seyedmohammad A.; Plum, Eric; Shi, Jinhui; Zheludev, Nikolay I.

2015-03-01

92

Coherent control of optical polarization effects in metamaterials  

PubMed Central

Processing of photonic information usually relies on electronics. Aiming to avoid the conversion between photonic and electronic signals, modulation of light with light based on optical nonlinearity has become a major research field and coherent optical effects on the nanoscale are emerging as new means of handling and distributing signals. Here we demonstrate that in slabs of linear material of sub-wavelength thickness optical manifestations of birefringence and optical activity (linear and circular birefringence and dichroism) can be controlled by a wave coherent with the wave probing the polarization effect. We demonstrate this in proof-of-principle experiments for chiral and anisotropic microwave metamaterials, where we show that the large parameter space of polarization characteristics may be accessed at will by coherent control. Such control can be exerted at arbitrarily low intensities, thus arguably allowing for fast handling of electromagnetic signals without facing thermal management and energy challenges. PMID:25755071

Mousavi, Seyedmohammad A.; Plum, Eric; Shi, Jinhui; Zheludev, Nikolay I.

2015-01-01

93

Coherent control of optical polarization effects in metamaterials.  

PubMed

Processing of photonic information usually relies on electronics. Aiming to avoid the conversion between photonic and electronic signals, modulation of light with light based on optical nonlinearity has become a major research field and coherent optical effects on the nanoscale are emerging as new means of handling and distributing signals. Here we demonstrate that in slabs of linear material of sub-wavelength thickness optical manifestations of birefringence and optical activity (linear and circular birefringence and dichroism) can be controlled by a wave coherent with the wave probing the polarization effect. We demonstrate this in proof-of-principle experiments for chiral and anisotropic microwave metamaterials, where we show that the large parameter space of polarization characteristics may be accessed at will by coherent control. Such control can be exerted at arbitrarily low intensities, thus arguably allowing for fast handling of electromagnetic signals without facing thermal management and energy challenges. PMID:25755071

Mousavi, Seyedmohammad A; Plum, Eric; Shi, Jinhui; Zheludev, Nikolay I

2015-01-01

94

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

95

Cryogenic control system of the large COMPASS polarized target  

NASA Astrophysics Data System (ADS)

The dilution refrigerator used to cool the large COMPASS polarized target is monitored through a PC running LabVIEW TM 6.1 under Windows 2000 TM. About 60 parameters of the target (temperatures, pressures, flow rates) are continuously plotted and checked. They are periodically recorded in an Oracle TM database and in a data file. An alarm for every parameter can be individually activated and optionally connected to a GSM (Global System for Mobile Communication) delivery message system. A web server receives and publishes the online status of the target with online tables and graphics on a dedicated COMPASS polarized target information web site. A Siemens programmable logic controller (PLC) powered by an uninterruptable source keeps the cryogenic system safe and stable during the long beam periods by controlling valves and interlocks. This safety feature protects the dilution refrigerator against potential damages in case of power failure.

Gautheron, F.; Ball, J.; Baum, G.; Berglund, P.; Doshita, N.; Goertz, St.; Gustafsson, K.; Horikawa, N.; Kisselev, Y.; Koivuniemi, J.; Kondo, K.; Meyer, W.; Reicherz, G.

2004-06-01

96

Quantum phase gate and controlled entanglement with polar molecules  

SciTech Connect

We propose an alternative scenario for the generation of entanglement between rotational quantum states of two polar molecules. This entanglement arises from dipole-dipole interaction, and is controlled by a sequence of laser pulses simultaneously exciting both molecules. We study the efficiency of the process, and discuss possible experimental implementations with cold molecules trapped in optical lattices or in solid matrices. Finally, various entanglement detection procedures are presented, and their suitability for these two physical situations is analyzed.

Charron, Eric; Keller, Arne; Atabek, Osman [Laboratoire de Photophysique Moleculaire du CNRS, Universite Paris-Sud, Batiment 210, 91405 Orsay Cedex (France); Milman, Perola [Laboratoire de Photophysique Moleculaire du CNRS, Universite Paris-Sud, Batiment 210, 91405 Orsay Cedex (France); CERMICS, Ecole Nationale des Ponts et Chaussees, 6 et 8 av. Blaise Pascal, Cite Descartes, Champs-sur-Marne, 77455 Marne-la-Vallee (France)

2007-03-15

97

Polarization control at spin-driven ferroelectric domain walls.  

PubMed

Unusual electronic states arise at ferroelectric domain walls due to the local symmetry reduction, strain gradients and electrostatics. This particularly applies to improper ferroelectrics, where the polarization is induced by a structural or magnetic order parameter. Because of the subordinate nature of the polarization, the rigid mechanical and electrostatic boundary conditions that constrain domain walls in proper ferroics are lifted. Here we show that spin-driven ferroelectricity promotes the emergence of charged domain walls. This provides new degrees of flexibility for controlling domain-wall charges in a deterministic and reversible process. We create and position a domain wall by an electric field in Mn0.95Co0.05WO4. With a magnetic field we then rotate the polarization and convert neutral into charged domain walls, while its magnetic properties peg the wall to its location. Using atomistic Landau-Lifshitz-Gilbert simulations we quantify the polarization changes across the two wall types and highlight their general occurrence. PMID:25868608

Leo, Naëmi; Bergman, Anders; Cano, Andres; Poudel, Narayan; Lorenz, Bernd; Fiebig, Manfred; Meier, Dennis

2015-01-01

98

Reliability of 1.3 micron VCSELs for metro area networks  

Microsoft Academic Search

Vertical Cavity Surface Emitting Lasers (VCSELs) have been widely adopted in the 850nm data communications markets with great success. Using this technology as a basis, we have developed a 1.3 mum InGaAsN VCSEL and VCSEL Array technology for telecommunications applications. Since the reliability requirement of this market is less than 150 FITs over 20 years, we focused a great deal

Simon R. Prakash; Leo M. F. Chirovsky; Ryan L. Naone; David Galt; Dave W. Kisker; Andrew W. Jackson

2003-01-01

99

Adaptive antenna arrays with controllable spacial-polarization characteristics under conditions of the reception of partially polarized radio waves  

Microsoft Academic Search

Expressions are obtained for the optimal weight coefficient vector, radiation pattern, and maximum S\\/N ratio of an adaptive antenna array with controllable three-dimensional (directional) and polarization characteristics during steady-state operation. The signals and interference radiations are assumed to be partially polarized in the general case. The characteristics of angular and polarization signal selection in the presence of interference are investigated

L. G. Kornienko; Iu. A. Kolos

1989-01-01

100

Complete Photoionization Experiments via Ultrafast Coherent Control with Polarization Multiplexing  

NASA Astrophysics Data System (ADS)

Photoelectron angular distributions (PADs) obtained from ionization of potassium atoms using moderately intense femtosecond IR fields (˜1012 W cm-2) of various polarization states are shown to provide a route to "complete" photoionization experiments. Ionization occurs by a net three-photon absorption process, driven via the 4s?4p resonance at the one-photon level. A theoretical treatment incorporating the intrapulse electronic dynamics allows for a full set of ionization matrix elements to be extracted from 2D imaging data. 3D PADs generated from the extracted matrix elements are also compared to experimental, tomographically reconstructed, 3D photoelectron distributions, providing a sensitive test of their validity. Finally, application of the determined matrix elements to ionization via more complex, polarization-shaped, pulses is demonstrated, illustrating the utility of this methodology towards detailed understanding of complex ionization control schemes and suggesting the utility of such "multiplexed" intrapulse processes as powerful tools for measurement.

Hockett, P.; Wollenhaupt, M.; Lux, C.; Baumert, T.

2014-06-01

101

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

102

Free-Space Optical Interconnect Employing VCSEL Diodes  

NASA Technical Reports Server (NTRS)

Sensor signal processing is widely used on aircraft and spacecraft. The scheme employs multiple input/output nodes for data acquisition and CPU (central processing unit) nodes for data processing. To connect 110 nodes and CPU nodes, scalable interconnections such as backplanes are desired because the number of nodes depends on requirements of each mission. An optical backplane consisting of vertical-cavity surface-emitting lasers (VCSELs), VCSEL drivers, photodetectors, and transimpedance amplifiers is the preferred approach since it can handle several hundred megabits per second data throughput.The next generation of satellite-borne systems will require transceivers and processors that can handle several Gb/s of data. Optical interconnects have been praised for both their speed and functionality with hopes that light can relieve the electrical bottleneck predicted for the near future. Optoelectronic interconnects provide a factor of ten improvement over electrical interconnects.

Simons, Rainee N.; Savich, Gregory R.; Torres, Heidi

2009-01-01

103

VCSEL-based microsensors for photonic proximity fuzing of munitions  

Microsoft Academic Search

This paper describes technologies developed at Sandia National Laboratories to support a joint DoD\\/DoE initiative to create a compact, robust, and affordable photonic proximity sensor for munitions fuzing. The proximity fuze employs high-power vertical-cavity surface-emitting laser (VCSEL) arrays, resonant-cavity photodetectors (RCPDs), and refractive micro-optics that are integrated within a microsensor whose volume is approximately 0.01 cm3. Successful development and integration

G. A. Keeler; A. Mar; K. M. Geib; A. Y. Hsu; D. K. Serkland; G. M. Peake

2008-01-01

104

High-performance oxide-confined GaAs VCSELs  

Microsoft Academic Search

We present GaAs based selectively oxidized VCSELs with record high 57% wallplug efficiencies emitting in the 820-860-nm wavelength regime. Solid source molecular beam epitaxy with carbon as p-type dopant is used for crystal growth. Multimode devices show continuous-wave (CW) output powers up to 42 mW and stable operation from -80°C up to +185°C. Efficient single-mode output power of some milliwatts

Bernhard Weigl; Martin Grabherr; Christian Jung; R. Jager; Gernot Reiner; Rainer Michalzik; Dirk Sowada; Karl Joachim Ebeling

1997-01-01

105

Improved output performance of high-power VCSELs  

Microsoft Academic Search

The intention of this paper is to report on state-of-the-art high-power vertical-cavity surface-emitting laser diodes (VCSELs), single devices as well as two-dimensional (2-D) arrays. Both approaches are studied in terms of electrooptical characteristics, beam performance, and scaling behavior. The maximum continuous wave (CW) output power at room temperature of large-area bottom-emitting devices with active diameters up to 320 ?m is

Michael Miller; Martin Grabherr; Roger King; Roland Jäger; Rainer Michalzik; Karl Joachim Ebeling

2001-01-01

106

Comparison of fiber Fabry-Perot interferometer sensor using 850nm VCSEL vs 1300nm DFB laser as light source  

NASA Astrophysics Data System (ADS)

This research represents the first effort to apply vertical cavity surface emitting lasers (VCSELs) to the monitoring of interferometric fiber optic sensors. Spectral characteristics were measured for 850nm VCSELs to determine the combination of dc bias current, modulation current amplitude and modulation frequency for which single mode VCSEL operation and regular fringe patterns are achieved. The performance of 850nm VCSEL/FFPI systems was compared with their counterparts using 1300nm distributed feedback (DFB) lasers.

Lee, Kyungwoo; Taylor, Henry F.

2006-09-01

107

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: Tunable VCSEL, Polymer Dispersed Liquid Crystal, Optical pumping, Distributed Bragg Reflector, Electro in a n-PDLC phase layer introduced inside the VCSEL cavity. N-PDLC comprises nematic liquid crystal

Boyer, Edmond

108

Polarization control of single photon quantum orbital angular momentum states  

E-print Network

The orbital angular momentum of photons, being defined in an infinitely dimensional discrete Hilbert space, offers a promising resource for high-dimensional quantum information protocols in quantum optics. The biggest obstacle to its wider use is presently represented by the limited set of tools available for its control and manipulation. Here, we introduce and test experimentally a series of simple optical schemes for the coherent transfer of quantum information from the polarization to the orbital angular momentum of single photons and vice versa. All our schemes exploit a newly developed optical device, the so-called "q-plate", which enables the manipulation of the photon orbital angular momentum driven by the polarization degree of freedom. By stacking several q-plates in a suitable sequence, one can also access to higher-order angular momentum subspaces. In particular, we demonstrate the control of the orbital angular momentum $m$ degree of freedom within the subspaces of $|m|=2 \\hbar$ and $|m|=4\\hbar$ per photon. Our experiments prove that these schemes are reliable, efficient and have a high fidelity.

E. Nagali; F. Sciarrino; F. De Martini; B. Piccirillo; E. Karimi; L. Marrucci; E. Santamato

2009-02-04

109

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

110

VCSELs in the visible to IR as a light source for low light therapy  

NASA Astrophysics Data System (ADS)

VCSELs (Vertical Cavity Surface Emitting Lasers ) provide a very versatile optical source for Low Light Therapy applications. This talk will discuss performance characteristics and packaging demonstrations for VCSELs primarily operating in the 680nm and 850nm regimes. At 680nm individual VCSELs produce >10mW, while >0.35W can be provided from a 0.4mm2 emission area. Spectral width is typically 1-2nm even for a multi-mode or array device. At 850nm these numbers increase to >30mW and >0.8W. Even higher powers can be achieved under pulsed modulation, i.e. 0.55W for a 680nm VCSEL or 1.2W for an 850nm VCSEL. While we report on results achieved at 680nm and 850nm, extension to wavelengths ranging from 660nm to 1000nm is easily achieved. The packaging flexibility of VCSELs also makes them of significant interest to the Low Light Therapy community. We will report on the incorporation of VCSELs into surface mount packages, including typical LED packages such as the PLCC, or ceramic chip carriers. VCSELs in PLCC packages have been attached to flexible circuits to provide a broad area illumination. We will also report on a unique chip on board package which easily allows for the addition of optical elements such as diffusers, diffraction gratings or lenses. This package is 2mm on a side, sufficiently small for incorporation into catheters or implantation.

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

2014-02-01

111

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

Microsoft Academic Search

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

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

2011-01-01

112

Metrological characterization of custom-designed 894.6 nm VCSELs for miniature atomic clocks.  

PubMed

We report on the characterization and validation of custom-designed 894.6 nm vertical-cavity surface-emitting lasers (VCSELs), for use in miniature Cs atomic clocks based on coherent population trapping (CPT). The laser relative intensity noise (RIN) is measured to be 1 × 10(-11) Hz(-1) at 10 Hz Fourier frequency, for a laser power of 700 ?W. The VCSEL frequency noise is 10(13) · f(-1) Hz(2)/Hz in the 10 Hz < f < 10(5) Hz range, which is in good agreement with the VCSEL’s measured fractional frequency instability (Allan deviation) of ? 1 × 10(-8) at 1 s, and also is consistent with the VCSEL’s typical optical linewidth of 20-25 MHz. The VCSEL bias current can be directly modulated at 4.596 GHz with a microwave power of -6 to +6 dBm to generate optical sidebands for CPT excitation. With such a VCSEL, a 1.04 kHz linewidth CPT clock resonance signal is detected in a microfabricated Cs cell filled with Ne buffer gas. These results are compatible with state-of-the-art CPT-based miniature atomic clocks exhibiting a short-term frequency instability of 2-3 × 10(-11) at ? = 1 s and few 10(-12) at ? = 10(4) s integration time.. PMID:23482148

Gruet, F; Al-Samaneh, A; Kroemer, E; Bimboes, L; Miletic, D; Affolderbach, C; Wahl, D; Boudot, R; Mileti, G; Michalzik, R

2013-03-11

113

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

114

Dynamic, polarization, and transverse mode characteristics of vertical cavity surface emitting lasers  

Microsoft Academic Search

The dynamic, polarization, and transverse mode characteristics of strained InGaAs-GaAs quantum well vertical cavity surface emitting lasers (VCSELs) emitting at 0.98 ?m are investigated. The dynamic behavior of VCSELs with high and low operating voltages and series resistances is compared. A large wavelength chirp in the lasing spectrum was observed for the lasers with high voltage\\/resistance, even under low-duty-cycle pulse

Connie J. Chang-Hasnain; J. P. Harbison; Ghulam Hasnain; Ann C. Von Lehmen; L. T. Florez; N. G. Stoffel

1991-01-01

115

Optimal control of vortex core polarity by resonant microwave pulses Benjamin Pigeau,1  

E-print Network

polarity8 . Control of polarity switching can also be achieved by precise timing of non resonant magnetic, 2011) Abstract In a vortex-state magnetic nano-disk1­3, the static magnetization is curling possible stable states of opposite core polarity p. Dynamical reversal of p by large amplitude motion

Boyer, Edmond

116

Spin-orbit controlled quantum capacitance of a polar heterostructure  

NASA Astrophysics Data System (ADS)

Oxide heterostructures with polar films display special electronic properties, such as the electronic reconstruction at their internal interfaces with the formation of two-dimensional metallic states. Moreover, the electrical field from the polar layers is inversion-symmetry breaking and generates a Rashba spin-orbit coupling (RSOC) in the interfacial electronic system. We investigate the quantum capacitance of a heterostructure in which a sizable RSOC at a metallic interface is controlled by the electric field of a surface electrode. Such a structure is, for example, given by a LaAlO3 film on a SrTiO3 substrate which is gated by a top electrode. Such heterostructures can exhibit a strong enhancement of their capacitance [Li et al., Science 332, 825 (2011), 10.1126/science.1204168]. The capacitance is related to the electronic compressibility of the heterostructure, but the two quantities are not equivalent. In fact, the transfer of charge to the interface controls the relation between capacitance and compressibility. We find that, due to a strong RSOC, the quantum capacitance can be larger than the classical geometric value. However, in contrast to the results of recent investigations [Caprara et al., Phys. Rev. Lett. 109, 196401 (2012), 10.1103/PhysRevLett.109.196401;Bucheli et al., Phys. Rev. B 89, 195448 (2014), 10.1103/PhysRevB.89.195448; Seibold et al., Europhys. Lett. 109, 17006 (2015), 10.1209/0295-5075/109/17006], the compressibility does not become negative for realistic parameter values for LaAlO3/SrTiO3 and, therefore, we find that no phase-separated state is induced by the strong RSOC at these interfaces.

Steffen, Kevin; Loder, Florian; Kopp, Thilo

2015-02-01

117

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

118

Twisted hi-bi fiber distributed-feedback lasers with controllable output state of polarization.  

PubMed

We demonstrate that single polarization, hi-bi fiber DFB lasers are, in general, characterized by elliptical state of polarization (SOP), due to the in-built fiber birefringence axis rotation. Externally applied birefringence axis twist is shown to provide accurate control of the output SOP. Continuous tuning from circular to linear polarization, with polarization extinction ratio of ~40 dB, has been demonstrated. PMID:23632542

Zervas, Michalis N; Wilmshurst, Richard; Walker, Louise M B

2013-05-01

119

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

120

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

121

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

122

Transverse Mode Dynamics of VCSELs Undergoing Current Modulation  

NASA Technical Reports Server (NTRS)

Transverse mode dynamics of a 20-micron-diameter vertical-cavity surface-emitting laser (VCSEL) undergoing gain switching by deep current modulation is studied numerically. The direct current (dc) level is set slightly below threshold and is modulated by a large alternating current (ac). The resulting optical pulse train and transverse-mode patterns are obtained numerically. The ac frequency is varied from 2.5 GHz to 10 GHz, and the ac amplitude is varied from one-half to four times that of the dc level. At high modulation frequencies, a regular pulse train is not generated unless the ac amplitude is large enough. At all modulation frequencies, the transverse spatial profile switches from single-mode to multiple-mode pattern as the ac pumping level is increased. Optical pulse widths vary in the range 5-30 ps. with the pulse width decreasing when either the frequency is increased or the ac amplitude is decreased. The numerical modeling uses an approximation form of the semiconductor Maxwell-Bloch equations. Temporal evolution of the spatial profiles of the laser (and of carrier density) is determined without any assumptions about the type or number of modes. Keywords: VCSELs, current modulation, gain switching, transverse mode dynamics, computational modeling

Goorjian, Peter M.; Ning, C. Z.; Agrawal, Govind

2000-01-01

123

High-speed 850 nm VCSELs with 28 GHz modulation bandwidth for short reach communication  

NASA Astrophysics Data System (ADS)

We present results from our new generation of high performance 850 nm oxide confined vertical cavity surface-emitting lasers (VCSELs). With devices optimized for high-speed operation under direct modulation, we achieve record high 3dB modulation bandwidths of 28 GHz for ~4 ?m oxide aperture diameter VCSELs, and 27 GHz for devices with a ~7 ?m oxide aperture diameter. Combined with a high-speed photoreceiver, the ~7 ?m VCSEL enables error-free transmission at data rates up to 47 Gbit/s at room temperature, and up to 40 Gbit/s at 85°C.

Westbergh, Petter; Safaisini, Rashid; Haglund, Erik; Gustavsson, Johan S.; Larsson, Anders; Joel, Andrew

2013-03-01

124

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

125

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

126

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

127

960-km SSMF transmission of 105.7-Gb/s PDM 3-PAM using directly modulated VCSELs and coherent detection.  

PubMed

We generate a 105.7-Gb/s signal by directly modulating a 1.5-µm VCSEL with a 33.35-Gbaud 3-level signal and polarization multiplexing. By using digital coherent detection, we successfully transmit the 105.7-Gb/s line rate (88.10 Gb/s net bit rate) signal over 960-km standard single-mode-fiber (SSMF) at a 20% hard-decision forward-error correction (FEC) threshold, which is at bit-error ratio (BER) of 1.5 x 10(-2) PMID:23670015

Xie, Chongjin; Dong, Po; Winzer, Peter; Gréus, C; Ortsiefer, M; Neumeyr, C; Spiga, Silvia; Müller, Michael; Amann, M-C

2013-05-01

128

Circularly polarized microstrip antennas for frequency control with a variable reactance  

Microsoft Academic Search

This paper presents circularly polarized microstrip antennas (CP MSA) for frequency control with a variable reactance. Operating frequency of circular polarization of the proposed antennas can be controlled by the variable reactance. 8% bandwidth with axial ratio less than 3 dB and over 3 dBi gain is obtained by the proposed CP MSA. In order to enhance the CP bandwidth,

Yoshihiro Suzuki; Yuichi Kimura; Misao Haneishi

2011-01-01

129

Polar Lunar Orbits: controlling the eccentricity with low thrust propulsion  

NASA Astrophysics Data System (ADS)

Recently, several nations presented plans to reach the Moon. Satellites have been launched and many more are planned for following years. The expectations are that in the near future there will be a lunar base. The lunar poles are particularly of interest since seems to be where water can be found. Therefore, satellites in polar orbits will be needed. It is well known that lunar satellites in polar orbits suffer a high increase on the eccentricity due to the gravitational perturbation of the Earth. That effect is a natural consequence of the Kozai resonance. The final fate of such satellites is the collision with the Moon. Therefore, the control of the orbital eccentricity leads to the control of the satellite's lifetime. In the present work we study this problem and introduce an approach in order to keep the orbital eccentricity of the satellite at low values. The whole work was made considering two systems; the 3-body problem, Moon- Earth-satellite and the 4-body problem, Moon-Earth-Sun-satellite. First, we simulated the systems considering a satellite with initial eccentricity equals to 10-4 and a range of initial altitudes between 100km and 2000km. In such simulations we followed the evolution of the satellite's eccentricity. We also obtained an empirical expression for the length of time needed to occur the collision with the Moon as a function of the initial altitude. The results found for the 3-body model were not significantly different from those found for the 4-body model. Secondly, using low thrust propulsion, we introduced a correction of the eccentricity every time it reached the value 10-3 . These simulations were made considering a set of different thrust values, from 0.1N up to 1N. In each run we measured the length of time, T , needed to correct the eccentricity value (from e = 10-3 to e = 10-4 . From these results we obtained empirical expressions of T as a function of the initial altitude and as a function of the thrust value. In all these cases, the results found for the 3-body model were also not significantly different from those found for the 4-body model.

Winter, Othon; Mourão, Décio; Giuliatti Winter, Silvia Maria; Ferreira, Jose Leonardo

130

VCSEL based Faraday rotation spectroscopy at 762nm for battery powered trace molecular oxygen detection  

NASA Astrophysics Data System (ADS)

Faraday Rotation Spectroscopy (FRS) is a polarization based spectroscopic technique which can provide higher sensitivity concentration measurements of paramagnetic gases and free radicals than direct absorption spectroscopic techniques. We have developed sensor systems which require only 0.2W to perform TDLAS (tunable diode laser absorption spectroscopy), and can additionally be quickly duty cycled, enabling operation in wireless sensor networks of laser-based trace gas sensors We adapted our integrated TDLAS electronics to perform FRS in a compact and more sensitive system for quantification of molecular oxygen (O2) using a 762.3nm VCSEL in the A band. Using an AC magnetic field, we demonstrate detector noise dominated performance, achieving 2.1×10-6/Hz1/2 equivalent detectable fractional absorption and a minimum detection limit of 462 ppmv O2 in 1 second in a 15cm path. At longer paths and integration times, such a sensor will enable oxygen measurements at biotic respiration levels (<1ppmv) to measure CO2 - O2 exchange for mapping natural exchange of greenhouse gases. Potential improvement of detection limits by increasing various system performance parameters is described.

So, Stephen; Wysocki, Gerard

2010-02-01

131

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

132

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

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

133

Bianisotropic Metasurfaces for Optimal Polarization Control: Analysis and Synthesis  

NASA Astrophysics Data System (ADS)

Methods to analyze and synthesize two-dimensional, bianisotropic metamaterials (metasurfaces) are presented. First, a general bianisotropic metasurface is analyzed by using closed-form expressions that relate the reflection and transmission coefficients to its constituent surface parameters. Next, a systematic method to synthesize bianisotropic metasurfaces is outlined. It is analytically shown that bianisotropic metasurfaces can be realized by cascading anisotropic, patterned metallic sheets (electric sheet admittances). This geometry allows for straightforward design and fabrication from microwave to optical wavelengths. To demonstrate the utility of the proposed method, four devices exhibiting exotic polarization transformations are presented: a polarization rotator, an asymmetric circular polarizer, an asymmetric linear polarizer, and a symmetric circular polarizer. The optimal performance at centimeter, millimeter, and micrometer wavelengths highlights the versatility of the design process.

Pfeiffer, Carl; Grbic, Anthony

2014-10-01

134

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.

135

8-Gbps-per-channel radiation-tolerant VCSEL drivers for the LHC detector upgrade  

NASA Astrophysics Data System (ADS)

We present ASIC designs of VCSEL drivers for a single VCSEL (LOCld1), two individual VCSELs (LOCld2) and a four-channel VCSEL array (LOCld4). This work is for new detector readout systems needed in the Large Hadron Collider upgrade program. All ASICs are fabricated in a commercial 0.25-? m Silicon-on-Sapphire CMOS technology. LOCld1 and LOCld2 have passed the 8-Gbps and 10-Gbps eye mask tests. Operating at 8 Gbps data rate, the measured total jitter of LOCld1 and LOCld2 is less than 30 ps, and the power comsuption is about 200 mW per channel with 6-mA bias current and 6.4-mA modulation current. The radiation tolerance of LOCld1 has been qualified with x-ray and high-energy neutron beam test.

Li, X.; Guo, D.; Chen, J.; Gong, D.; Hou, S.; Huang, D.; Huang, G.; Liang, F.; Liu, C.; Liu, T.; Sun, X.; Teng, P.-K.; Xiang, A. C.; Ye, J.; You, Y.; Zhao, X.

2015-02-01

136

Ultrahigh speed endoscopic optical coherence tomography using micro-motor imaging catheter and VCSEL technology  

E-print Network

We developed a micro-motor based miniature catheter with an outer diameter of 3mm for ultrahigh speed endoscopic optical coherence tomography (OCT) using vertical cavity surface-emitting laser (VCSEL) at a 1MHz axial scan ...

Tsai, Tsung-Han

137

Fiber Fabry-Perot interferometer (FFPI) sensor using vertical cavity surface emitting laser (VCSEL)  

E-print Network

This research represents the first effort to apply vertical cavity surface emitting lasers (VCSELs) to the monitoring of interferometric fiber optic sensors. Modulation of the drive current causes thermal tuning of the laser light frequency...

Lee, Kyung-Woo

2006-10-30

138

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

139

Robust design of subwavelength grating mirror for mid-infrared VCSEL application  

E-print Network

Abstract--We present the design of a Si/Si3N4 subwavelength grating mirror optimized for an integration a Si/Si3N4 SGM for a VCSEL ap- plication at 2.65 µm. First, the optical properties that VCSEL mirrors, Si/Si3N4 or GaAs/AlOx. We present here a Si/Si3N4-based SGM as shown in Fig. 1. The mirror structure

Paris-Sud XI, Université de

140

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

NASA Astrophysics Data System (ADS)

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 into unexplored wavelength bands, enabling new applications. This paper describes the design and performance of high-speed ultra-broad tuning range 1050nm and 1310nm MEMS-VCSELs for medical imaging and spectroscopy. Key results include achievement of the first MEMS-VCSELs at 1050nm and 1310nm, with 100nm tuning demonstrated at 1050nm and 150nm tuning at shown at 1310nm. The latter result represents the widest tuning range of any MEMS-VCSEL at any wavelength. Wide tuning range has been achieved in conjunction with high-speed wavelength scanning at rates beyond 1 MHz. These advances, coupled with recent demonstrations of very long MEMS-VCSEL dynamic coherence length, have enabled advancements in both swept source optical coherence tomography (SS-OCT) and gas spectroscopy. VCSEL-based SS-OCT at 1050nm has enabled human eye imaging from the anterior eye through retinal and choroid layers using a single instrument for the first time. VCSEL-based SS-OCT at 1310nm has enabled real-time 3-D SS-OCT imaging of large tissue volumes in endoscopic settings. The long coherence length of the VCSEL has also enabled, for the first time, meter-scale SS-OCT applicable to industrial metrology. With respect to gas spectroscopy, narrow dynamic line-width has allowed accurate high-speed measurement of multiple water vapor and HF absorption lines in the 1310nm wavelength range, useful in gas thermometry of dynamic combustion engines.

Jayaraman, V.; Potsaid, B.; Jiang, J.; Cole, G. D.; Robertson, M. E.; Burgner, C. B.; John, D. D.; Grulkowski, I.; Choi, W.; Tsai, T. H.; Liu, J.; Stein, B. A.; Sanders, S. T.; Fujimoto, J. G.; Cable, A. E.

2013-05-01

141

Quasi-exact optical analysis of oxide-apertured microcavity VCSELs using vector finite elements  

Microsoft Academic Search

We report a new full vector finite element model for analyzing the optical properties of azimuthally symmetric oxide-apertured vertical-cavity surface emitting lasers (VCSELs). Our model allows for quasi-exact calculation of the lasing mode blueshift, threshold gain, and field profile. Through a detailed analysis of a sample VCSEL, we ascertain the physical effects which determine diffractive or parasitic mode loss. They

Michael J. Noble; James A. Lott; John P. Loehr

1998-01-01

142

Analysis of microcavity VCSEL lasing modes using a full-vector weighted index method  

Microsoft Academic Search

Presents a semi-analytic full-vector method for calculating the spatial profile, optical confinement factor resonant frequency, absorption loss, and mirror loss of lasing modes in cylindrically symmetric microcavity vertical-cavity surface-emitting lasers (VCSEL's). It can be shown that this method gives the best separable approximation for the electric and magnetic vector potentials. Our technique can model the entire VCSEL structure and can

Michael J. Noble; John P. Loehr; James A. Lott

1998-01-01

143

VCSEL-based microsensors for photonic proximity fuzing of munitions  

NASA Astrophysics Data System (ADS)

This paper describes technologies developed at Sandia National Laboratories to support a joint DoD/DoE initiative to create a compact, robust, and affordable photonic proximity sensor for munitions fuzing. The proximity fuze employs high-power vertical-cavity surface-emitting laser (VCSEL) arrays, resonant-cavity photodetectors (RCPDs), and refractive micro-optics that are integrated within a microsensor whose volume is approximately 0.01 cm3. Successful development and integration of these custom photonic components should enable a g-hard photonic proximity fuze that replaces costly assemblies of discrete lasers, photodetectors, and bulk optics. Additional applications of this technology include void sensing, ladar and short-range 3-D imaging.

Keeler, G. A.; Mar, A.; Geib, K. M.; Hsu, A. Y.; Serkland, D. K.; Peake, G. M.

2008-08-01

144

Selective area growth of well-ordered ZnO nanowire arrays with controllable polarity.  

PubMed

Controlling the polarity of ZnO nanowires in addition to the uniformity of their structural morphology in terms of position, vertical alignment, length, diameter, and period is still a technological and fundamental challenge for real-world device integration. In order to tackle this issue, we specifically combine the selective area growth on prepatterned polar c-plane ZnO single crystals using electron-beam lithography, with the chemical bath deposition. The formation of ZnO nanowires with a highly controlled structural morphology and a high optical quality is demonstrated over large surface areas on both polar c-plane ZnO single crystals. Importantly, the polarity of ZnO nanowires can be switched from O- to Zn-polar, depending on the polarity of prepatterned ZnO single crystals. This indicates that no fundamental limitations prevent ZnO nanowires from being O- or Zn-polar. In contrast to their catalyst-free growth by vapor-phase deposition techniques, the possibility to control the polarity of ZnO nanowires grown in solution is remarkable, further showing the strong interest in the chemical bath deposition and hydrothermal techniques. The single O- and Zn-polar ZnO nanowires additionally exhibit distinctive cathodoluminescence spectra. To a broader extent, these findings open the way to the ultimate fabrication of well-organized heterostructures made from ZnO nanowires, which can act as building blocks in a large number of electronic, optoelectronic, and photovoltaic devices. PMID:24720628

Consonni, Vincent; Sarigiannidou, Eirini; Appert, Estelle; Bocheux, Amandine; Guillemin, Sophie; Donatini, Fabrice; Robin, Ivan-Christophe; Kioseoglou, Joseph; Robaut, Florence

2014-05-27

145

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

146

Integrin-Mediated Activation of Cdc42 Controls Cell Polarity in Migrating Astrocytes through PKC?  

Microsoft Academic Search

We describe here a signal transduction pathway controlling the establishment of mammalian cell polarity. Scratching a confluent monolayer of primary rat astrocytes leads to polarization of cells at the leading edge. The microtubule organizing center, the microtubule cytoskeleton, and the Golgi reorganize to face the new free space, and directed cell protrusion and migration specifically occur perpendicularly to the scratch.

Sandrine Etienne-Manneville; Alan Hall

2001-01-01

147

Remote state preparation: arbitrary remote control of photon polarization Nicholas A. Peters,1  

E-print Network

Remote state preparation: arbitrary remote control of photon polarization Nicholas A. Peters,1, University of Illinois, 1110 West Green Street, Urbana, IL 61801 2 Physics Department, Truman State state preparation of arbitrary single-qubit states, encoded in the polarization of photons generated

Kwiat, Paul

148

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

149

Independent controls of differently-polarized reflected waves by anisotropic metasurfaces.  

PubMed

We propose a kind of anisotropic planar metasurface, which has capacity to manipulate the orthogonally-polarized electromagnetic waves independently in the reflection mode. The metasurface is composed of orthogonally I-shaped structures and a metal-grounded plane spaced by a dielectric isolator, with the thickness of about 1/15 wavelength. The normally incident linear-polarized waves will be totally reflected by the metal plane, but the reflected phases of x- and y-polarized waves can be controlled independently by the orthogonally I-shaped structures. Based on this principle, we design four functional devices using the anisotropic metasurfaces to realize polarization beam splitting, beam deflection, and linear-to-circular polarization conversion with a deflection angle, respectively. Good performances have been observed from both simulation and measurement results, which show good capacity of the anisotropic metasurfaces to manipulate the x- and y-polarized reflected waves independently. PMID:25873323

Ma, Hui Feng; Wang, Gui Zhen; Kong, Gu Sheng; Cui, Tie Jun

2015-01-01

150

Independent Controls of Differently-Polarized Reflected Waves by Anisotropic Metasurfaces  

PubMed Central

We propose a kind of anisotropic planar metasurface, which has capacity to manipulate the orthogonally-polarized electromagnetic waves independently in the reflection mode. The metasurface is composed of orthogonally I-shaped structures and a metal-grounded plane spaced by a dielectric isolator, with the thickness of about 1/15 wavelength. The normally incident linear-polarized waves will be totally reflected by the metal plane, but the reflected phases of x- and y-polarized waves can be controlled independently by the orthogonally I-shaped structures. Based on this principle, we design four functional devices using the anisotropic metasurfaces to realize polarization beam splitting, beam deflection, and linear-to-circular polarization conversion with a deflection angle, respectively. Good performances have been observed from both simulation and measurement results, which show good capacity of the anisotropic metasurfaces to manipulate the x- and y-polarized reflected waves independently. PMID:25873323

Ma, Hui Feng; Wang, Gui Zhen; Kong, Gu Sheng; Cui, Tie Jun

2015-01-01

151

Control of tunnel ionization in molecules by intense femtosecond laser pulses with time-dependent polarization  

NASA Astrophysics Data System (ADS)

We propose a new way of Controlling tunnel ionization in molecules by time-dependent polarization pulses. The model consists of the successful combination of the molecular ADK theory reflecting the symmetry of molecular orbitals and Landau-Zener resonances.

Kanai, Tsuneto; Minemoto, Shinichirou; Sakai, Hirofumi

152

Developing an array of site-controlled pyramidal quantum dots emitting polarization-entangled photons  

SciTech Connect

We present a site-controlled, highly symmetric quantum dot system with a density of at least 15 % of polarization-entangled photon emitters. Fidelity values of the entangled state as high as 0.721±0.043 were found.

Juska, G.; Dimastrodonato, V.; Mereni, L. O.; Gocalinska, A.; Pelucchi, E. [Tyndall National Institute, University College Cork, Lee Maltings, Cork (Ireland)

2013-12-04

153

Photoelectron spin-polarization control in the topological insulator Bi2Se3.  

PubMed

We study the manipulation of the spin polarization of photoemitted electrons in Bi2Se3 by spin- and angle-resolved photoemission spectroscopy. General rules are established that enable controlling the photoelectron spin-polarization. We demonstrate the ±?100% reversal of a single component of the measured spin-polarization vector upon the rotation of light polarization, as well as full three-dimensional manipulation by varying experimental configuration and photon energy. While a material-specific density-functional theory analysis is needed for the quantitative description, a minimal yet fully generalized two-atomic-layer model qualitatively accounts for the spin response based on the interplay of optical selection rules, photoelectron interference, and topological surface-state complex structure. It follows that photoelectron spin-polarization control is generically achievable in systems with a layer-dependent, entangled spin-orbital texture. PMID:24579623

Zhu, Z-H; Veenstra, C N; Zhdanovich, S; Schneider, M P; Okuda, T; Miyamoto, K; Zhu, S-Y; Namatame, H; Taniguchi, M; Haverkort, M W; Elfimov, I S; Damascelli, A

2014-02-21

154

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

2009-05-15

155

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

156

Polarity control in gallium nitride epilayers grown by Metalorganic Chemical Vapor Deposition  

NASA Astrophysics Data System (ADS)

Polarity control of gallium nitride (GaN) on c-plane sapphire substrate was studied via low pressure Metalorganic Chemical Vapor Deposition (MOCVD). Under mass-transport-limited growth regime with a given process supersaturation, the polarities of GaN thin films (i.e. gallium (Ga) and nitrogen (N)-polarities) depended on specific treatments of the sapphire substrate prior to GaN deposition, in addition, identical growth rates for both polar films were obtained. This ability made the fabrication of lateral polar junction (LPJ) GaN structures possible. New designs of novel device structures utilizing the resulting polarity control scheme were developed. N-polar films were consistently obtained after exposing a H2-annealed sapphire substrate to an ammonia atmosphere at temperature above 950°C. Ga-polar films were obtained either by preventing any exposure of the substrate to ammonia prior to deposition or by depositing the film on a properly annealed low temperature aluminum nitride nucleation layer (LT-AlN NL) deposited on a previously ammonia annealed sapphire substrate. As-grown Ga-polar films were generally insulating and smooth surface morphology while N-polar films exhibited n-type conductivity with carrier concentration approaching 1x1019 cm-3 and a rougher surface morphology. Following the established polarity control scheme for GaN films, LPJ structures consisting Ga-polar and N-polar domains side-by-side on a single sapphire wafer were achieved by utilizing a prior patterned AlN/bare sapphire template. The two regions were separated by an inversion domain boundary (IDB), which did not hinder the current flow across it, i.e. no energy barrier for the charge carriers. This in principle showed the possibility for the fabrication of lateral junctions and lateral based devices within the GaN technology exploiting polar doping selectivity. Understanding the doping selectivity of the two different polar domains allowed us to fabricate a lateral p/n junction in GaN by the simultaneous growth of the p- and n-type regions. Identifying the basic characteristics of a p/n junction demonstrated that the fabricated structure was a functional p/n diode. For GaN based junctions, these characteristics were: current rectification, electroluminescence and the photovoltaic effect under UV excitation.

Mita, Seiji

157

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

158

Defect-mediated polarization switching in ferroelectrics and related materials: from mesoscopic mechanisms to atomistic control  

SciTech Connect

The plethora of lattice and electronic behaviors in ferroelectric and multiferroic materials and heterostructures opens vistas into novel physical phenomena including magnetoelectric coupling and ferroelectric tunneling. The development of new classes of electronic, energy-storage, and information-technology devices depends critically on understanding and controlling field-induced polarization switching. Polarization reversal is controlled by defects that determine activation energy, critical switching bias, and the selection between thermodynamically equivalent polarization states in multiaxial ferroelectrics. Understanding and controlling defect functionality in ferroelectric materials is as critical to the future of oxide electronics and solid-state electrochemistry as defects in semiconductors are for semiconductor electronics. Here, recent advances in understanding the defect-mediated switching mechanisms, enabled by recent advances in electron and scanning probe microscopy, are discussed. The synergy between local probes and structural methods offers a pathway to decipher deterministic polarization switching mechanisms on the level of a single atomically defined defect.

Kalinin, Sergei V [ORNL; Rodriguez, Brian J [ORNL; Baddorf, Arthur P [ORNL; Balke, Nina [ORNL; Borisevich, Albina Y [ORNL; Chang, Hye Jung [ORNL; Chen, Long-Qing [Pennsylvania State University; Jesse, Stephen [ORNL; Maksymovych, Petro [ORNL; Nikiforov, Maxim [ORNL; Pennycook, Stephen J [ORNL

2010-01-01

159

Oxide confined 850-nm VCSELs for high-speed datacom applications  

NASA Astrophysics Data System (ADS)

Vertical cavity surface emitting lasers (VCSELs) are low cost and reliable light sources for high-speed local area and storage area network (LAN/SAN) optical fiber data communication systems and all other short-reach high-speed data transfer applications. The intrinsic limitations of copper-based electrical links at data rates exceeding 10 Gbit/s leads to a progressive movement wherein optical communication links replace traditional short-reach (300 m or shorter) copper interconnects. The wavelength of 850 nm is the standard for LAN/SAN applications as well as for several other evolving short-reach application areas including Fibre Channel, InfiniBand, Universal Serial Bus (optical USB), and active optical cables. Here we present our recent results on 850 nm oxide-confined VCSELs operating at data bit rates up to 40 Gbit/s at low current densities of ~10 kA/cm2 ensuring device reliability and long-term stability based on conventional industry certification specifications. The relaxation resonance frequencies, damping factors, and parasitic cut-off frequencies are determined for VCSELs with oxide-confined apertures of various diameters. At the highest optical modulation rates the VCSELs' high speed operation is limited by parasitic cut-off frequencies of 24-28 GHz. We believe that by further reducing device parasitics we will produce current modulated VCSELs with optical modulation bandwidths larger than 30 GHz and data bit rates beyond 40 Gbit/s.

Moser, Philip; Mutig, Alex; Lott, James A.; Blokhin, Sergey; Fiol, Gerrit; Nadtochiy, Alexey M.; Ledentsov, Nikolai N.; Bimberg, Dieter

2010-04-01

160

Recent advances in MEMS-VCSELs for high performance structural and functional SS-OCT imaging  

NASA Astrophysics Data System (ADS)

Since the first demonstration of swept source optical coherence tomography (SS-OCT) imaging using widely tunable micro-electromechanical systems vertical cavity surface-emitting lasers (MEMS-VCSELs) in 2011, VCSEL-based SSOCT has advanced in both device and system performance. These advances include extension of MEMS-VCSEL center wavelength to both 1060nm and 1300nm, improved tuning range and tuning speed, new SS-OCT imaging modes, and demonstration of the first electrically pumped devices. Optically pumped devices have demonstrated continuous singlemode tuning range of 150nm at 1300nm and 122nm at 1060nm, representing a fractional tuning range of 11.5%, which is nearly a factor of 3 greater than the best reported MEMS-VCSEL tuning ranges prior to 2011. These tuning ranges have also been achieved with wavelength modulation rates of >500kHz, enabling >1 MHz axial scan rates. In addition, recent electrically pumped devices have exhibited 48.5nm continuous tuning range around 1060nm with 890kHz axial scan rate, representing a factor of two increase in tuning over previously reported electrically pumped MEMS-VCSELs in this wavelength range. New imaging modes enabled by optically pumped devices at 1060nm and 1300nm include full eye length imaging, pulsatile Doppler blood flow imaging, high-speed endoscopic imaging, and hand-held wide-field retinal imaging.

Jayaraman, V.; John, D. D.; Burgner, C.; Robertson, M. E.; Potsaid, B.; Jiang, J. Y.; Tsai, T. H.; Choi, W.; Lu, C. D.; Heim, P. J. S.; Fujimoto, J. G.; Cable, A. E.

2014-03-01

161

Emcore's 1 Gb/s to 25 Gb/s VCSELs  

NASA Astrophysics Data System (ADS)

Emcore's 850 nm UltralaseTM VCSELs, operating at a data rate from 1 Gb/s to 25 Gb/s, is presented. They were based on our low-cost and hermetic-by-design chip platform which contains the same element for either singlets or arrays with a 250 ?m pitch. First, we discuss high-speed VCSEL evolutions, device designs, manufacturing processes, and device characteristics. Secondly, we present performance of Emcore's TOSAs, 40 Gb/s parallel optic modules (S12), 120 Gb/s CXP modules, active connect cables (40 Gb/s QDR and 56 Gb/s FDR), as well as comprehensive reliability qualifications of UltralaseTM VCSELs. Lastly, we briefly go over the recent progress of 20 Gb/s and 25 Gb/s VCSEL developments. We have successfully achieved a 3dB bandwidth of 15 GHz at 85°C and 8 mA for a 7.5 ?m aperture UltralaseTM VCSEL.

Li, Neinyi; Xie, Chuan; Luo, Wenlin; Helms, Chris J.; Wang, Li; Liu, Chiyu; Sun, Qi; Huang, Shenghong; Lei, Chun; Jackson, K. P.; Carson, Rich F.

2012-03-01

162

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

163

Polarization control of an X-ray free-electron laser with a diamond phase retarder.  

PubMed

A diamond phase retarder was applied to control the polarization states of a hard X-ray free-electron laser (XFEL) in the photon energy range 5-20 keV. The horizontal polarization of the XFEL beam generated from the planar undulators of the SPring-8 Angstrom Compact Free-Electron Laser (SACLA) was converted into vertical or circular polarization of either helicity by adjusting the angular offset of the diamond crystal from the exact Bragg condition. Using a 1.5 mm-thick crystal, a high degree of circular polarization, 97%, was obtained for 11.56 keV monochromatic X-rays, whereas the degree of vertical polarization was 67%, both of which agreed with the estimations including the energy bandwidth of the Si 111 beamline monochromator. PMID:24763633

Suzuki, Motohiro; Inubushi, Yuichi; Yabashi, Makina; Ishikawa, Tetsuya

2014-05-01

164

Macrophage polarization and insulin resistance: PPARgamma in control.  

PubMed

Macrophages orchestrate an inflammatory response that contributes to glucose intolerance in diet-induced obesity and plaque instability in atherosclerosis. Within this heterogeneous group of cells are proinflammatory (M1) and anti-inflammatory (M2) macrophages. Recent work has identified the nuclear hormone receptor PPARgamma as a critical signaling molecule in determining macrophage phenotype in vitro and in adipose tissue. In the current issue of Cell Metabolism, Bouhlel et al. (2007) extend this paradigm to the vessel wall by showing that both M1 and M2 macrophages are present in atherosclerotic lesions and that activation of PPARgamma polarizes circulating blood monocytes to become M2 macrophages. PMID:17681144

Charo, Israel F

2007-08-01

165

Well aligned half-V ferroelectric liquid crystal in asymmetrical surface polarity controlled alignment cells  

NASA Astrophysics Data System (ADS)

Ferroelectric liquid crystals (FLCs) were known to possess fast response time under 1 ms. The low contrast ratio yielding from defect alignment, however, limited their display application. Based on FLC elastic free energy, the asymmetrical surface polarity controlled alignment was able to suppress the horizontal chevron defects in a half Vshaped switching FLC cell. It is due to the FLC's spontaneous polarization (Ps) pointed to one direction inducing by the opposite surface polarity in asymmetrical hybrid cell. The experimental approach of different alignment materials and different strengths of surface anchoring energies were evaluated in this study. The highest contrast ratio of 780:1 at saturation voltage under 5 V was obtained. The asymmetrical surface polarity controlled alignment technique provided a promising FLC well alignment and fast switching result for TFT-LCD application.

Chen, Huang-Ming Philip; Lin, Chi-Wen

2010-08-01

166

[Study on the CNT sensor for strain measurement and its control method of Raman polarization].  

PubMed

The present paper studied the methodology of carbon nanotube (CNT) sensor applicable for the strain measurement in microscale. Based on the varieties of polarization configurations of the Raman spectrometers, a series of analytic expressions of CNT sensor were derived by applying the Raman properties of the CNT, such as the strain sensitivity and the polarization selectivity. From the viewpoint of metrology, the sensoring relationships corresponding to different polarization configurations were compared and contrasted with one another, which educed that the "bipolar homology" type is most suitable for the strain measurement where both the incident and scattered lights are continuously controllable and always remain parallel to each other. A new easy-realized control method for this configuration is introduced. The experiments proved that the method presented in this paper can effectively measure the in-plane strain components in microscale by polarized micro-Raman spectroscopy. PMID:23905328

Li, Shi-Lei; Qiu, Wei; Kang, Yi-Lan; Lei, Zhen-Kun; Li, Qiu; Deng, Wei-Lin; Gao, Di

2013-05-01

167

A Polarization Control System for Intensity-Resolved Guided Mode Resonance Sensors  

PubMed Central

In this study, a polarization-control setup for intensity-resolved guided mode resonance sensors is proposed and demonstrated experimentally. The experimental results are in good agreement with the simulation data based on rigorous coupled wave approach calculations. The proposed intensity-resolved measurement setup transfers polarization ellipses, which are produced from guided mode resonance to a linear polarization state under a buffer solution condition, and then suppresses the signals to dark using a polarization-control set. Hence, any changes in the refractive index results in an increase in the intensity signals. Furthermore, no wavelength-resolved or angular-resolved measurement is needed in this scheme. According to the experimental results, a wide linear detection range of 0.014 refractive index units is achieved and the limit of detection is 1.62E-4 RIU. PMID:24625743

Lin, Sheng-Fu; Chang, Fu-Chen; Chen, Zhi-Heng; Wang, Chih-Ming; Yang, Tsung-Hsun; Chen, Wen-Yih; Chang, Jenq-Yang

2014-01-01

168

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

169

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

170

Dynamic Control of the Polarization of Intense Laser Beams via Optical Wave Mixing in Plasmas  

NASA Astrophysics Data System (ADS)

When intense laser beams overlap in plasmas, the refractive index modulation created by the beat wave via the ponderomotive force can lead to optical wave mixing phenomena similar to those used in crystals and photorefractive materials. A new comprehensive analytical description of the modification of the polarization state of laser beams crossing at arbitrary angles in a plasma is presented. It is shown that a laser-plasma system can be used to provide full control of the polarization state of a separate "probe" laser beam; simple analytical estimates and practical considerations are provided for the design of novel photonics devices such as laser-plasma polarizers and wave plates.

Michel, P.; Divol, L.; Turnbull, D.; Moody, J. D.

2014-11-01

171

High-speed 850 nm oxide-confined VCSELs for DATACOM applications  

NASA Astrophysics Data System (ADS)

Vertical cavity surface emitting lasers (VCSELs) are low cost and reliable light sources for high-speed local area and storage area network (LAN/SAN) optical fiber data communication systems and short-reach computer interconnects. The continuing rapid increase of serial transmission data rates driven by multi-core microprocessor's bandwidth upgrades cannot be sustained via conventional copper-based links as bit rates move beyond 10 Gbit/s and distances greater than 1 m. The intrinsic limitation of copper at high single-channel data rates facilitates the need to transition to optical fiberbased links at ever shorter distances. For LAN/SAN applications the 850 nm wavelength is standard. This same wavelength is also the standard for several other evolving short-reach application areas including Fibre Channel, CEI, USB, InfiniBand, and HDMI optical link systems. Herein we present our recent results on 850 nm oxide-confined VCSELs operating at data bit rates up to 40 Gbit/s. The low operational current density in the range of ~10 kA/cm2 ensures viable device reliability and long-term stability based on well-known industry certification specifications. Key VCSEL device parameters including the relaxation resonance frequency, damping, and parasitic cut-off frequency are determined for VCSELs with oxide-confined apertures of various diameters. We find that a parasitic cut-off frequency of 24-28 GHz limits the VCSEL's high speed operation at the highest optical modulation rates. We believe that with some effort the device parasitics can be further reduced such that current modulated VCSELs can be realized with larger than 30 GHz optical modulation bandwidth and reliable and practical operation beyond 40 Gbit/s.

Mutig, Alex; Blokhin, Sergey; Nadtochiy, Alexey M.; Fiol, Gerrit; Lott, James A.; Shchukin, Vitaly A.; Ledenstov, Nikolai N.; Bimberg, Dieter

2010-02-01

172

Fiber Fabry-Perot interferometer (FFPI) sensor using vertical cavity surface emitting laser (VCSEL)  

NASA Astrophysics Data System (ADS)

This research represents the first effort to apply vertical cavity surface emitting lasers (VCSELs) to the monitoring of interferometric fiber optic sensors. Modulation of the drive current causes thermal tuning of the laser light frequency. Reflection of this frequency-modulated light from a fiber Fabry-Perot interferometer (FFPI) sensor produces fringe patterns which can be used to measure the optical path difference of the sensor. Spectral characteristics were measured for 850nm VCSELs to determine the combination of dc bias current, modulation current amplitude and modulation frequency for which single mode VCSEL operation and regular fringe patterns are achieved. The response characteristics of FFPI sensors were determined experimentally for square, triangular, saw-tooth waveforms at frequencies from 10kHz to 100kHz. The dependence of VCSEL frequency on the dc bias current was determined from spectral measurements to be ˜165GHz/mA. An independent measurement of this quantity based on counting fringes from the FFPI sensor as the laser modulated was in good agreement with this value. The effect of optical feedback into the laser was also studied. By observing the fringe shift as the FFPI sensor was heated, a fractional change in optical length with temperature of 6.95 X 10-6/°C was determined in good agreement with previous measurements on a 1300nm single mode fiber. The performance of 850nm VCSEL/FFPI systems was compared with their counterparts using 1300nm distributed feedback (DFB) lasers. The results of these experiments show that the 850nm VCSEL/FFPI combination gives regular fringe patterns at much lower bias current and modulating current amplitudes than their 1300nm DFB/FFPI counterparts.

Lee, Kyung-Woo

173

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

174

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

175

High power high repetition rate VCSEL array side-pumped pulsed blue laser  

NASA Astrophysics Data System (ADS)

High power, kW-class, 808 nm pump modules based on the vertical-cavity surface-emitting laser (VCSEL) technology were developed for side-pumping of solid-state lasers. Two 1.2 kW VCSEL pump modules were implemented in a dual side-pumped Q-switched Nd:YAG laser operating at 946 nm. The laser output was frequency doubled in a BBO crystal to produce pulsed blue light. With 125 ?s pump pulses at a 300 Hz repetition rate 6.1 W QCW 946 nm laser power was produced. The laser power was limited by thermal lensing in the Nd:YAG rod.

van Leeuwen, Robert; Zhao, Pu; Chen, Tong; Xu, Bing; Watkins, Laurence; Seurin, Jean-Francois; Xu, Guoyang; Miglo, Alexander; Wang, Qing; Ghosh, Chuni

2013-03-01

176

Polarization caging in diffusion-controlled electron transfer reactions in solution.  

PubMed

In some bimolecular diffusion-controlled electron transfer (ET) reactions such as ion recombination (IR), both solvent polarization relaxation and the mutual diffusion of the reacting ion pair may determine the rate and even the yield of the reaction. However, a full treatment with these two reaction coordinates is a challenging task and has been left mostly unsolved. In this work, we address this problem by developing a dynamic theory by combining the ideas from ET reaction literature and barrierless chemical reactions. Two-dimensional coupled Smoluchowski equations are employed to compute the time evolution of joint probability distribution for the reactant (P((1))(X,R,t)) and the product (P((2))(X,R,t)), where X, as is usual in ET reactions, describes the solvent polarization coordinate and R is the distance between the reacting ion pair. The reaction is described by a reaction line (sink) which is a function of X and R obtained by imposing a condition of equal energy on the initial and final states of a reacting ion pair. The resulting two-dimensional coupled equations of motion have been solved numerically using an alternate direction implicit (ADI) scheme (Peaceman and Rachford, J. Soc. Ind. Appl. Math. 1955, 3, 28). The results reveal interesting interplay between polarization relaxation and translational dynamics. The following new results have been obtained. (i) For solvents with slow longitudinal polarization relaxation, the escape probability decreases drastically as the polarization relaxation time increases. We attribute this to caging by polarization of the surrounding solvent. As expected, for the solvents having fast polarization relaxation, the escape probability is independent of the polarization relaxation time. (ii) In the slow relaxation limit, there is a significant dependence of escape probability and average rate on the initial solvent polarization, again displaying the effects of polarization caging. Escape probability increases, and the average rate decreases on increasing the initial polarization. Again, in the fast polarization relaxation limit, there is no effect of initial polarization on the escape probability and the average rate of IR. (iii) For normal and barrierless regions the dependence of escape probability and the rate of IR on initial polarization is stronger than in the inverted region. (iv) Because of the involvement of dynamics along R coordinate, the asymmetrical parabolic (that is, non-Marcus) energy gap dependence of the rate is observed. PMID:20809586

Singh, Rakesh Sharan; Tachiya, Masanori; Bagchi, Biman

2010-09-30

177

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

178

Real-time feedback control of millimeter-wave polarization for LHD.  

PubMed

Electron cyclotron heating (ECH) is widely used in magnetic fusion devices, and the polarization of the injected millimeter-wave beams plays a crucial role in the propagation and absorption of the beam energy by the plasma. This polarization can be adjusted by grating mirror polarizers placed in the transmission lines which carry the microwaves from the power source to the plasma. In long-pulse devices such as the Large Helical Device (LHD) and ITER, it is desirable to track changes in the plasma and adjust the polarization of the ECH in real time such as to keep the absorption as high as possible and avoid shine-through which may lead to overheating of vessel components. For this purpose a real-time feedback control scheme is envisioned in which a measure of the absorption efficiency can be used to adjust the orientation of the polarizing mirrors toward an optimum. Such a setup has been tested in a low-power test stand as preparation for future implementation in the LHD ECH system. It is shown that a simple search algorithm is efficient and can in principle be used to control either the absorption efficiency or the linear polarization angle. PMID:19191434

Felici, F; Goodman, T; Sauter, O; Shimozuma, T; Ito, S; Mizuno, Y; Kubo, S; Mutoh, T

2009-01-01

179

Polarity control of GaN thin films grown by metalorganic vapor phase epitaxy  

NASA Astrophysics Data System (ADS)

Control of the polarity of GaN thin films grown on c-plane sapphire by low-pressure metalorganic vapor phase epitaxy has been achieved. Growth of either polarity was realized by identifying and selecting appropriate substrate pre-treatments and AlN LT-buffer growth conditions. N-face (-c) GaN films were only obtained by pre-nitridation of the sapphire substrate after a H2 anneal. Smooth films of each type of polarity were obtained by using N2 as a transport and dilution gas and a V/III ratio of less than 500. The same growth rate of 1.2 ?m/h was observed for both types of polarities under the same growth conditions. Further analysis of the growth conditions demonstrated that by using N2 as the dilution gas the transport was mass-transfer limited.

Collazo, R.; Mita, S.; Schlesser, R.; Sitar, Z.

2005-05-01

180

Polarization controlled colorful images reconstructed by reflective meta-hologram  

NASA Astrophysics Data System (ADS)

Holograms, the optical devices to reconstruct pre-designed images, have been evolved dramatically since the advances in today's nanotechnology [1-4]. Metamaterials, the sub-wavelength artificial structures with tailored refraction index, enable us to design the meta-hologram working in arbitrary frequency region. Here we demonstrated the first reflective type, dual image and high efficient meta-hologram with the incident angle as well as the coherence of incident wave insensitivity in visible region at least from ? = 632.8 nm to ? = 850 nm. The meta-hologram is composed of 50-nm-thick gold cross nano-antenna coupled with 130-nm-thick gold mirror with a 50-nm-thick MgF2 as spacer. It shows different images "RCAS" and "NTU" with high image contract under x- and y-polarized illumination, respectively. Making use of the characteristic of meta-materials, these optical properties of proposed meta-hologram can be transferred to arbitrary electromagnetic region by scale-up the size of the unit cell of meta-hologram, leading to more compact, efficient and promising electromagnetic components.

Huang, Yao-Wei; Chen, Wei Ting; Yang, Kuang-Yu; Wang, Chih-Ming; Wu, Pin Chieh; Sun, Greg; Sun, Shulin; Zhou, Lei; Liu, Ai Qun; Tsai, Din Ping

2014-09-01

181

Cytokinin controls polarity of PIN1-dependent auxin transport during lateral root organogenesis.  

PubMed

The plant hormones auxin and cytokinin mutually coordinate their activities to control various aspects of development [1-9], and their crosstalk occurs at multiple levels [10, 11]. Cytokinin-mediated modulation of auxin transport provides an efficient means to regulate auxin distribution in plant organs. Here, we demonstrate that cytokinin does not merely control the overall auxin flow capacity, but might also act as a polarizing cue and control the auxin stream directionality during plant organogenesis. Cytokinin enhances the PIN-FORMED1 (PIN1) auxin transporter depletion at specific polar domains, thus rearranging the cellular PIN polarities and directly regulating the auxin flow direction. This selective cytokinin sensitivity correlates with the PIN protein phosphorylation degree. PIN1 phosphomimicking mutations, as well as enhanced phosphorylation in plants with modulated activities of PIN-specific kinases and phosphatases, desensitize PIN1 to cytokinin. Our results reveal conceptually novel, cytokinin-driven polarization mechanism that operates in developmental processes involving rapid auxin stream redirection, such as lateral root organogenesis, in which a gradual PIN polarity switch defines the growth axis of the newly formed organ. PMID:24768050

Marhavý, Peter; Duclercq, Jérôme; Weller, Benjamin; Feraru, Elena; Bielach, Agnieszka; Offringa, Remko; Friml, Ji?í; Schwechheimer, Claus; Murphy, Angus; Benková, Eva

2014-05-01

182

VCSEL electrical packaging analysis and design guidelines for multi-GHz applications  

Microsoft Academic Search

The introduction of the vertical cavity surface emitting laser (VCSEL) diode structure has created the need for enhanced performance, low cost, optical packages capable of supporting data rates as high as 5 Gb\\/s. The popular laser packages, such as the TO-46 and the TO-56 “cans”, which have been traditionally used for edge emitting laser diodes at much lower frequencies, cannot

S. H. Hall; W. L. Walters; L. F. Mattson; G. J. Fokken; B. K. Gilbert

1997-01-01

183

Assessment of VCSEL thermal rollover mechanisms from measurements and empirical modeling.  

PubMed

We use an empirical model together with experimental measurements for studying mechanisms contributing to thermal rollover in vertical-cavity surface-emitting lasers (VCSELs). The model is based on extraction of the temperature dependence of threshold current, internal quantum efficiency, internal optical loss, series resistance and thermal impedance from measurements of output power, voltage and lasing wavelength as a function of bias current over an ambient temperature range of 15-100 °C. We apply the model to an oxide-confined, 850-nm VCSEL, fabricated with a 9-?m inner-aperture diameter and optimized for high-speed operation, and show for this specific device that power dissipation due to linear power dissipation (sum total of optical absorption, carrier thermalization, carrier leakage and spontaneous carrier recombination) exceeds power dissipation across the series resistance (quadratic power dissipation) at any ambient temperature and bias current. We further show that the dominant contributors to self-heating for this particular VCSEL are quadratic power dissipation, internal optical loss, and carrier leakage. A rapid reduction of the internal quantum efficiency at high bias currents (resulting in high temperatures) is identified as being the major cause of thermal rollover. Our method is applicable to any VCSEL and is useful for identifying the mechanisms limiting the thermal performance of the device and to formulate design strategies to ameliorate them. PMID:21934912

Baveja, Prashant P; Kögel, Benjamin; Westbergh, Petter; Gustavsson, Johan S; Haglund, Åsa; Maywar, Drew N; Agrawal, Govind P; Larsson, Anders

2011-08-01

184

Design and optimization of high-performance 1.3-?m VCSELs  

NASA Astrophysics Data System (ADS)

This paper discusses the design and the internal device physics of novel high-performance vertical-cavity surface-emitting lasers (VCSELs) emitting at 1.32 ?m wavelength. Our VCSEL design features intra-cavity ring contacts, strain-compensated AlGaInAs quantum wells, and an AlInAs/InP tunnel junction. The tunnel junction is laterally confined forming an aperture for current injection and wave guiding. Undoped AlGaAs/GaAs mirrors are bonded on both sides to the InP-based active region. These devices have recently demonstrated continuous-wave (CW) lasing at stage temperatures up to 134°C, the highest temperature reported thus far for any long-wavelength VCSEL. In order to increase the single mode output power at high temperatures, we simulate, analyze, and optimize our VCSEL using advanced numerical software tools. The two-dimensional model self-consistently combines electrical, optical, thermal and gain calculations. It gives good agreement with measurements after careful calibration of material parameters. Design optimization promises single mode output power of 2mW in CW operation at 80°C ambient temperature.

Piprek, Joachim; Mehta, Manish; Jayaraman, Vijaysekhar

2004-06-01

185

Far-field emission characteristics and linewidth measurements of surface micro-machined MEMS tunable VCSELs  

NASA Astrophysics Data System (ADS)

In this paper, we demonstrate for the first time the far-field experimental results and the linewidth characteris- tics for widely tunable surface-micromachined micro-electro-mechanical system (MEMS) vertical-cavity surface- emitting lasers (VCSELs) operating at 1550 nm. The fundamental Gaussian mode emission is confirmed by optimizing the radius of curvature of top distributed Bragg reflector (DBR) membrane and by choosing an ap- propriate diameter of circular buried tunnel junctions (BTJs) so that only the fundamental Gaussian mode can sustain. For these VCSELs, a mode-hop free continuous tuning over 100 nm has already been demonstrated, which is achieved by electro-thermal tuning of the MEMS mirror. The fiber-coupled optical power of 2mW over the entire tuning range has been reported. The singlemode laser emission has more than 40 dB of side-mode suppression ratio (SMSR). The smallest linewidth achieved with these of MEMS tunable VCSELs is 98MHz which is one order of magnitude higher than that of fixed-wavelength VCSELs.

Paul, Sujoy; Gierl, Christian; Gründl, Tobias; Zogal, Karolina; Meissner, Peter; Amann, Markus-Christian; Küppers, Franko

2013-03-01

186

VCSEL Laser System for Atomic Clocks Nathan Belcher REU program, College of William and Mary  

E-print Network

VCSEL Laser System for Atomic Clocks Nathan Belcher REU program, College of William and Mary I of my project is to create a prototype atomic clock, and this summer's research has been all about modulation with rf signals, and use in miniature atomic clocks. This paper will describe the theory behind

Novikova, Irina

187

Resolution and field of view improvement in digital holography using a VCSEL source array  

Microsoft Academic Search

We describe a new implementation capable to produce superresolution (SR) and object field of view (FOV) improvement in digital lensless Fourier holography. The method provides synthetic aperture (SA) generation using angular multiplexing incoming from a Vertical Cavity Surface Emitting Laser (VCSEL) source array. SR imaging in a single exposure is obtained after proper digital processing of a multiplexed hologram coming

Luis Granero; Zeev Zalevsky; Vicente Mico

2011-01-01

188

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

189

Analysis of broadcasting satellite service feeder link power control and polarization  

NASA Technical Reports Server (NTRS)

Statistical analyses of carrier to interference power ratios (C/Is) were performed in assessing 17.5 GHz feeder links using (1) fixed power and power control, and (2) orthogonal linear and orthogonal circular polarizations. The analysis methods and attenuation/depolarization data base were based on CCIR findings to the greatest possible extent. Feeder links using adaptive power control were found to neither cause or suffer significant C/I degradation relative to that for fixed power feeder links having similar or less stringent availability objectives. The C/Is for sharing between orthogonal linearly polarized feeder links were found to be significantly higher than those for circular polarization only in links to nominally colocated satellites from nominally colocated Earth stations in high attenuation environments.

Sullivan, T. M.

1982-01-01

190

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

191

Sub-cycle control of terahertz waveform polarization using all-optically induced transient metamaterials  

E-print Network

Coherent radiation with frequencies ranging from 0.3 to 30 THz has recently become accessible by femtosecond laser technology. Terahertz (THz) waves have already found many applications in spectroscopy and imaging, and they can be manipulated using static optical elements such as lenses, polarizers, and filters. However, ultrafast modulation of THz radiation is required as well, for instance in short-range wireless communication or for preparing shaped THz transients for coherent control of numerous material excitations. Here, we demonstrate an all-optically created transient metamaterial that permits to manipulate the polarization of THz waveforms with sub-cycle precision. The polarization-modulated pulses are potentially interesting for controlling elementary motions such as vibrations of crystal lattices, rotations of molecules, and the precession of spins.

Kamaraju, N; Jian, Linke; Saha, Surajit; Venkatesan, T; Nötzold, Jan; Campen, R Kramer; Wolf, Martin; Kampfrath, Tobias

2013-01-01

192

Circular polarized electronically-controlled antenna array based on CRLH-TL  

NASA Astrophysics Data System (ADS)

In this paper, a circular polarized electronically-controlled scanning microstrip antenna array is designed, which is based on composite right left-handed transmission line (CRLH TL) and is realized by varactor diodes. Proposed electronically-controlled antenna arrays till now are always linear-polarized as the axial ratio (AR) may be spoiled by the DC feed line, especially in the CRLH TL based case. A more separated CRLH TL integrated with active lumped elements is utilized to solve the problem. The antenna array is composed of the CRLH microstrip transmission line structure and circular polarized microstrip antenna. The direction of the main lobe varies from -1° to -20 ° by continuously modifying the varactor diodes bias voltages from 0 to 20 V with 5 V as a step. The AR remains below 3 dB in the scanning range. The simulation and experimental results show a good consistence.

Fu, Jiahui; Chen, Wan; Zhou, Changfei; Zhu, Lei; Wu, Qun

2014-07-01

193

First-order polarization mode dispersion compensator using two independent feedback signals enabling separation of principal states of polarization and differential group delay controls.  

PubMed

We propose and demonstrate a novel first-order polarization mode dispersion (PMD) compensator separating principal-states-of-polarization (PSP) control from differential-group-delay (DGD) control by using two independent feedback monitoring signals. To verify the proposed operating principle, we fabricated an automatically adaptive module-type 40-Gb/s PMD compensator on printed circuit boards. The results show that unlike previous typical compensation method of controlling alternately PSP and DGD, the proposed scheme provides independent continuous PSP tracking regardless of DGD control by delay line under rapidly varying PSP condition, thus resulting in stable compensated signal with reduction in compensation time. PMID:22418113

Han, Ki Ho; Lee, Wang Joo

2012-02-13

194

Developments in Polarization and Energy Control of APPLE-II Undulators at Diamond Light Source  

NASA Astrophysics Data System (ADS)

A pair of 2m long APPLE-II type undulators have been built for the I10 BLADE beamline at Diamond Light Source. These 48mm period devices have gap as well as four moveable phase axes which provide the possibility to produce the full range of elliptical polarizations as well as linear polarization tilted through a full 180deg. The mechanical layout chosen has a 'master and slave' arrangement of the phase axes on the top and bottom. This arrangement allows the use of symmetries to provide operational ease for both changing energy using only the master phase while keeping fixed linear horizontal or circular polarization, as well as changing linear polarization angle while keeping fixed energy [1]. The design allows very fast motion of the master phase arrays, without sacrifice of accuracy, allowing the possibility of mechanical polarization switching at 1Hz for dichroism experiments. We present the mechanical design features of these devices, as well as the results of magnetic measurements and shimming from before installation. Finally, we present the results of characterization of these devices by the beamline, including polarimetry, which has been done on the various modes of motion to control energy and polarization. These modes of operation have been available to users since 2011.

Longhi, E. C.; Bencok, P.; Dobrynin, A.; Rial, E. C. M.; Rose, A.; Steadman, P.; Thompson, C.; Thomson, A.; Wang, H.

2013-03-01

195

A 3D polarizing display system base on backlight control  

NASA Astrophysics Data System (ADS)

In this paper a new three-dimensional (3D) liquid crystal display (LCD) display mode based on backlight control is presented to avoid the left and right eye images crosstalk in 3D display. There are two major issues in this new black frame 3D display mode. One is continuously playing every frame images twice. The other is controlling the backlight switch periodically. First, this paper explains the cause of the left and right eye images crosstalk, and presents a solution to avoid this problem. Then, we propose to play the entire frame images twice by repeating each frame image after it was played instead of playing the left images and the right images frame by frame alternately. Finally, the backlight is switched periodically instead of turned on all the time. The backlight is turned off while a frame of image is played for the first time, then turned on during the second time, after that it will be turned off again and run the next period with the next frame of image start to refresh. Controlling the backlight switch periodically like this is the key to achieve the black frame 3D display mode. This mode can not only achieve better 3D display effect by avoid the left and right image crosstalk, but also save the backlight power consumption. Theoretical analysis and experiments show that our method is reasonable and efficient.

Liu, Pu; Huang, Ziqiang

2011-08-01

196

Polarization State Control of Light by Single-Walled Carbon Nanotubes  

E-print Network

Society of America OCIS codes: (260.5430) Polarization; (240.0310) Thin films, (060.2340) Fiber optics components I. Introduction Single-walled carbon nano-tubes (SWCNTs) have been the subject of focused multi as saturable absorbers in mode locking of erbium doped silica fiber lasers have been reported[2,3]. Control

Maruyama, Shigeo

197

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

198

Zeno and Anti-Zeno Polarization Control of Spin Ensembles by Induced Dephasing Gonzalo A. A lvarez,1,2  

E-print Network

Zeno and Anti-Zeno Polarization Control of Spin Ensembles by Induced Dephasing Gonzalo A. A´ lvarez (polarization) control of qubits entangled with multiple spins, using induced dephasing in nuclear magnetic the bath-induced upward and downward transition rates in the qubit. By contrast, less frequent measurements

Frydman, Lucio

199

Nano-structured magnetic photonic crystals for magneto-optic polarization controllers at the communication-band wavelengths  

Microsoft Academic Search

We investigate the properties of optimized magnetic photonic crystal structures for use in integrated-optics polarization controllers. We engineer the enhancement of Faraday rotation near 1550 nm and describe a novel hysteresis-based driving scheme suitable for implementing ultra-fast polarization controllers.

M. Nur-E-Alam; Mikhail Vasiliev; Kamal Alameh

2009-01-01

200

PUBLISHED ONLINE: 31 OCTOBER 2010 | DOI: 10.1038/NPHYS1810 Optimal control of vortex-core polarity by  

E-print Network

. This distortion increases with the linear velocity of the vortex core and opposes the core polarity, until constant) is reached and the vortex-core polarity is reversed9 . In zero magnetic field, dynamical controlLETTERS PUBLISHED ONLINE: 31 OCTOBER 2010 | DOI: 10.1038/NPHYS1810 Optimal control of vortex

Loss, Daniel

201

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

202

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

203

Polarization controlled coupling and shaping of surface plasmon polaritons by nanoantenna arrays.  

PubMed

We demonstrate experimentally the use of ordered arrays of nanoantennas for polarization controlled plasmonic beam shaping and excitation. Rod- and cross-shaped nanoantennas are used as local point-like sources of surface plasmon polaritons, and the desired phase of the generated plasmonic beam is set directly through their spatial arrangement. The polarization selectivity of the optical nanoantennas allows us to further control the excitation, enabling the realization of a variety of complex and functional plasmonic beam shaping elements. We demonstrate this concept by generating plasmonic self-accelerating beams, plasmonic bottle beams, and switchable dual-focii plasmonic lenses. The freedom in the design and arrangement of these nanoantennas enables us to specifically tailor and control the shapes, wavelengths, and coupling efficiencies of complex plasmonic beams. PMID:25831374

Avayu, Ori; Epstein, Itai; Eizner, Elad; Ellenbogen, Tal

2015-04-01

204

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

205

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

206

Polarization-rotation resonances with subnatural widths using a control laser  

NASA Astrophysics Data System (ADS)

We demonstrate extremely narrow resonances for polarization rotation in an atomic vapor. The resonances are created using a strong control laser on the same transition, which polarizes the atoms due to optical pumping among the magnetic sublevels. As the power in the control laser is increased, successively higher-order nested polarization-rotation resonances are created, with progressively narrower linewidths. We study these resonances in the D2 line of Rb in a room temperature vapor cell, and demonstrate a width of 0.14~\\Gamma for the third-order rotation. The physical basis for the observed resonances is that optical pumping results in a simplified ?V-type level structure with differential dressing of the levels by the control laser, which is why the control power has to be sufficiently high for each resonance to appear. This explanation is borne out by a density-matrix analysis of the system. The dispersive lineshape and subnatural width of the resonance lends itself naturally to applications such as laser locking to atomic transitions and precision measurements.

Ranjita Chanu, Sapam; Pandey, Kanhaiya; Bharti, Vineet; Wasan, Ajay; Natarajan, Vasant

2014-05-01

207

Phase-controllable spin wave generation in iron garnet by linearly polarized light pulses  

NASA Astrophysics Data System (ADS)

A phase-controlled spin wave was non-thermally generated in bismuth-doped rare-earth iron garnet by linearly polarized light pulses. We controlled the initial phase of the spin wave continuously within a range of 180° by changing the polarization azimuth of the excitation light. The azimuth dependences of the initial phase and amplitude of the spin wave were attributed to a combination of the inverse Cotton-Mouton effect and photoinduced magnetic anisotropy. Temporally and spatially resolved spin wave propagation was observed with a CCD camera, and the waveform was in good agreement with calculations. A nonlinear effect of the spin excitation was observed for excitation fluences higher than 100 mJ/cm2.

Yoshimine, Isao; Satoh, Takuya; Iida, Ryugo; Stupakiewicz, Andrzej; Maziewski, Andrzej; Shimura, Tsutomu

2014-07-01

208

Phase-controllable spin wave generation in iron garnet by linearly polarized light pulses  

SciTech Connect

A phase-controlled spin wave was non-thermally generated in bismuth-doped rare-earth iron garnet by linearly polarized light pulses. We controlled the initial phase of the spin wave continuously within a range of 180° by changing the polarization azimuth of the excitation light. The azimuth dependences of the initial phase and amplitude of the spin wave were attributed to a combination of the inverse Cotton-Mouton effect and photoinduced magnetic anisotropy. Temporally and spatially resolved spin wave propagation was observed with a CCD camera, and the waveform was in good agreement with calculations. A nonlinear effect of the spin excitation was observed for excitation fluences higher than 100 mJ/cm{sup 2}.

Yoshimine, Isao; Iida, Ryugo; Shimura, Tsutomu [Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505 (Japan); Satoh, Takuya, E-mail: satoh@phys.kyushu-u.ac.jp [Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505 (Japan); PRESTO, Japan Science and Technology Agency, Tokyo 102-0076 (Japan); Department of Physics, Kyushu University, Fukuoka 812-8581 (Japan); Stupakiewicz, Andrzej; Maziewski, Andrzej [Laboratory of Magnetism, Faculty of Physics, University of Bialystok, Bialystok 15-424 (Poland)

2014-07-28

209

In-Line Polarization Controller Based on Liquid-Crystal Photonic Crystal Fibers  

Microsoft Academic Search

Compact polarization control elements based on index-guiding soft-glass photonic crystal fibers infiltrated with nematic liquid crystals are proposed and thoroughly studied. The nematic director profiles atthefiber'scross section are consistently calculated by solving the coupled electrostatic and elastic problem, in the context of an analysis on the tunability of liquid-crystal-in- filtrated photonic crystal fibers. The fiber's dispersive properties and light propagation

Alexandros K. Pitilakis; Dimitrios C. Zografopoulos; Emmanouil E. Kriezis

2011-01-01

210

Quantum control of molecular motion including electronic polarization effects with a two-stage toolkit  

Microsoft Academic Search

A method for incorporating strong electric field polarization effects into optimal control calculations is presented. A Born-Oppenheimer-type separation, referred to as the electric-nuclear Born-Oppenheimer (ENBO) approximation, is introduced in which variations of both the nuclear geometry and the external electric field are assumed to be slow compared with the speed at which the electronic degrees of freedom respond to these

Gabriel G. Balint-Kurti; Frederick R. Manby; Qinghua Ren; Maxim Artamonov; Tak-San Ho; Herschel Rabitz

2005-01-01

211

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

212

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

213

Group-III nitride VCSEL structures grown by molecular beam epitaxy  

Microsoft Academic Search

III-nitride VCSEL structures designed for electron-beam pumping have been grown by molecular beam epitaxy (MBE). The structures consist of a sapphire substrate on which an AlN\\/GaN distributed Bragg reflector (DBR) with peak reflectance >99% at 402 nm is deposited. The active region consists of a 2-(lambda) cavity with 25 In0.1Ga0.9N\\/GaN multiquantum wells (MQWs) whose emission coincides with the high reflectance

HockMin Ng; Theodore D. Moustakas

2000-01-01

214

Earth observing system instrument pointing control modeling for polar orbiting platforms  

NASA Astrophysics Data System (ADS)

An approach to instrument pointing control performance assessment for large multi-instrument platforms is described. First, instrument pointing requirements and reference platform control systems for the Eos Polar Platforms are reviewed. Performance modeling tools including NASTRAN models of two large platforms, a modal selection procedure utilizing a balanced realization method, and reduced order platform models with core and instrument pointing control loops added are then described. Time history simulations of instrument pointing and stability performance in response to commanded slewing of adjacent instruments demonstrates the limits of tolerable slew activity. Simplified models of rigid body responses are also developed for comparison. Instrument pointing control methods required in addition to the core platform control system to meet instrument pointing requirements are considered.

Briggs, H. C.; Kia, T.; McCabe, S. A.; Bell, C. E.

1987-01-01

215

PHYSICAL REVIEW B 84, 125305 (2011) Polarity control of carrier injection at ferroelectric/metal interfaces for electrically switchable diode  

E-print Network

/metal interfaces for electrically switchable diode and photovoltaic effects D. Lee,1 S. H. Baek,2 T. H. Kim,1 J received 9 August 2011; published 8 September 2011) We investigated a switchable ferroelectric diode effect training process to obtain ferroelectric control of the diode polarity where, by changing the polarization

Eom, Chang Beom

216

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

217

High-power single-transverse-mode holey VCSELs (Invited Paper)  

NASA Astrophysics Data System (ADS)

By introducing triangular holes into oxide confined 850nm monolithic vertical-cavity surface-emitting lasers (VCSELs), single-transverse-mode operation has been obtained for large oxide apertures of 14-15 microns. The two-dimensional triangular holes etched on the device surface were aligned circumferentially along the aperture perimeter, with their tips surrounding the device center. When the holes had a relatively large lateral penetration into the oxide aperture, the holey VCSEL lased with a single spot near field pattern with a high side-mode suppression ratio (SMSR) of 45-50dB, and an output power of 2mW. In this case, it is assumed that the triangular holes are acting as a highly mode selective loss mechanism. On the other hand, when the penetration of the holes was relatively small, an SMSR of 40dB was obtained from a large area "floral" near field pattern, with a record high single-mode output power of 7mW. The lasing spectrum and far field intensity profile of this "floral" type emission indicates that it is a somewhat deformed fundamental mode that is extending over the whole device, and oscillating in-phase. The ability of triangular holes to suppress high order modes in large area oxide confined VCSELs should be effective for systems with wavelengths other than 850nm as well.

Furukawa, Akio; Hoshi, Mitsunari; Sasaki, Satoshi; Matsuzono, Atsushi; Moritoh, Kosuke; Baba, Toshihiko

2005-04-01

218

Fabrication, Packaging, and Performance of VCSELs and Photodetectors for Space Applications  

SciTech Connect

Optocouplers are used for a variety of applications aboard spacecraft including electrical isolation, switching and power transfer. Commercially available light emitting diode (LED)-based optocouplers have experienced severe degradation of light output due to extensive displacement damage occurring in the semiconductor lattice caused by energetic proton bombardment. A new optocoupler has been designed and fabricated which utilizes vertical cavity surface emitting laser (VCSEL) and resonant cavity photodetector (RCPD) technologies for the optocoupler emitter and detector, respectively. Linear arrays of selectively oxidized GaAs/AlGaAs VCSELS and RCPDS, each designed to operate at a wavelength of 850nm, were fabricated using an airbridge contacting scheme. The airbridged contacts were designed to improve packaging yields and device reliability by eliminating the use of a polyimide planarizing layer which provided poor adhesion to the bond pad metallization. Details of the airbridged optocoupler fabrication process are reported. Discrete VCSEL and RCPD devices were characterized at temperatures between {minus}100 to 100 C. Devices were packaged in a face-to-face configuration to form a single channel optocoupler and its performance was evaluated under conditions of high-energy proton bombardment.

Armendariz, M.G.; Briggs, R.D.; Choquette, K.D.; Geib, K.M.; Serkland, D.K.

1999-03-09

219

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

220

Bidirectional hybrid PM-based RoF and VCSEL-based VLLC system.  

PubMed

A bidirectional hybrid phase modulation (PM)-based radio-over-fiber (RoF) and vertical cavity surface emitting laser (VCSEL)-based visible laser light communication (VLLC) systems employing injection-locked VCSEL-based PM-to-intensity modulation (IM) converters and optical interleavers (ILs) is proposed and demonstrated. To be the first one of using injection-locked VCSEL-based PM-to-IM converters and optical ILs in such bidirectional hybrid RoF and VLLC systems, the downstream light is successfully phase-remodulated with RoF signal for up-link transmission. Through a serious investigation in systems, bit error rate (BER) and eye diagram perform brilliantly over a 40-km single-mode fiber (SMF) transport and a 12-m free-space transmission. Such a bidirectional hybrid RoF and VLLC system would be very attractive for the integration of fiber backbone and in-door networks to provide broadband integrated services, including Internet and telecommunication services. PMID:24977870

Li, Chung-Yi; Lu, Hai-Han; Chang, Ching-Hung; Lin, Chun-Yu; Wu, Po-Yi; Zheng, Jun-Ren; Lin, Chia-Rung

2014-06-30

221

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

222

Optically controlled microwave phase shifter based on nonlinear polarization rotation in a highly nonlinear fiber.  

PubMed

This Letter reports an optically controlled microwave phase shifter with an ultra-wideband working bandwidth and a full 360° phase shifting range based on nonlinear polarization rotation (NPR) in a highly nonlinear fiber (HNLF). A continuous wave probe light is modulated by a polarization modulator (PolM) that is driven by a microwave signal to be phase shifted. The optical carrier and the first-order sidebands of the probe light experience different phase shifts due to the NPR induced by the control light in the HNLF. An optical bandpass filter is used to realize single-sideband modulation of the probe light by removing one of the first-order sidebands, as well as to reject the control light. After detecting by a photodetector, the phase of the recovered microwave signal is continuously tunable by adjusting the power of the control light. The proposed approach is theoretically analyzed and experimentally verified. A full 360° tunable phase shift is realized over an ultra-wideband frequency range from 8 to 38 GHz when the power of the control light is tuned from 0 to 570 mW. PMID:24876035

Li, Wei; Sun, Wen Hui; Wang, Wen Ting; Zhu, Ning Hua

2014-06-01

223

Theoretical study of mutual control mechanism between magnetization and polarization in multiferroic materials  

NASA Astrophysics Data System (ADS)

The mutual control mechanism between magnetization and polarization in multiferroic materials is studied. The system contains a ferromagnetic sublattice and a ferroelectric sublattice. To describe the magneto–electric coupling, we propose a linear coupling Hamiltonian between ferromagnetism and ferroelectricity without microscopic derivation. This coupling enables one to retrieve the hysteresis loops measured experimentally. The thermodynamic properties of the system are calculated, such as the temperature dependences of the magnetization, polarization, internal energy and free energy. The ferromagnetic and ferroelectric hysteresis loops driven by either a magnetic or an electric field are calculated, and the magnetic spin and pseudo-spin are always flipped synchronously under the external magnetic and electric field. Our theoretical results are in agreement with the experiments. Project supported by the National Basic Research Program of China (Grant No. 2012CB927402) and the National Natural Science Foundation of China (Grant Nos. 61275028 and 11074145).

Liu, Yu; Zhai, Liang-Jun; Wang, Huai-Yu

2015-03-01

224

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

225

Serrano (Sano) Functions with the Planar Cell Polarity Genes to Control Tracheal Tube Length  

PubMed Central

Epithelial tubes are the functional units of many organs, and proper tube geometry is crucial for organ function. Here, we characterize serrano (sano), a novel cytoplasmic protein that is apically enriched in several tube-forming epithelia in Drosophila, including the tracheal system. Loss of sano results in elongated tracheae, whereas Sano overexpression causes shortened tracheae with reduced apical boundaries. Sano overexpression during larval and pupal stages causes planar cell polarity (PCP) defects in several adult tissues. In Sano-overexpressing pupal wing cells, core PCP proteins are mislocalized and prehairs are misoriented; sano loss or overexpression in the eye disrupts ommatidial polarity and rotation. Importantly, Sano binds the PCP regulator Dishevelled (Dsh), and loss or ectopic expression of many known PCP proteins in the trachea gives rise to similar defects observed with loss or gain of sano, revealing a previously unrecognized role for PCP pathway components in tube size control. PMID:19956736

Chung, SeYeon; Vining, Melissa S.; Bradley, Pamela L.; Chan, Chih-Chiang; Wharton, Keith A.; Andrew, Deborah J.

2009-01-01

226

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

227

Nano-structured magnetic photonic crystals for magneto-optic polarization controllers at the communication-band wavelengths  

Microsoft Academic Search

We investigate the properties of optimized 1-D magnetic photonic crystal structures using doped iron garnet layers as magnetic\\u000a constituents, for use in integrated-optics polarization controllers. We engineer the enhancement of Faraday rotation near\\u000a 1,550 nm and describe a novel hysteresis-based driving scheme suitable for implementing ultra-fast polarization controllers.

Mohammad Nur-E-Alam; Mikhail Vasiliev; Kamal Alameh

2009-01-01

228

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

229

STUDY OF THE RADIATION HARDNESS OF VCSEL AND PIN K.K. GAN, W. FERNANDO, H.P. KAGAN, R.D. KASS, A. LAW,  

E-print Network

are therefore 69 and 34 Mrad, respectively. We irradiated optical modules instrumented with one silicon PIN1 STUDY OF THE RADIATION HARDNESS OF VCSEL AND PIN ARRAYS K.K. GAN, W. FERNANDO, H.P. KAGAN, R. VCSEL arrays operating at 850 nm are used to transmit optical signals while PIN arrays are used

Gan, K. K.

230

Electrically controllable in-line-type polarizer using polymer-dispersed liquid-crystal spliced optical fibers.  

PubMed

The polarization-dependent transmission of light through an electrically controllable in-line-type polarizer that is made from polymer-dispersed liquid-crystal spliced optical fibers is discussed experimentally and theoretically. This in-line-type optical splicing method has the advantage of low transmission loss when it is applied in optical fiber communication systems. An anomalous diffraction approach is used to compute the scattering cross section of polymer-dispersed liquid-crystal droplets. The experimental results are supported by a theoretical analysis. This device can be employed in electrically controllable in-line-type polarizers and has the potential to yield electrically controllable polarization-dependent loss compensators. PMID:12962378

Baek, Seungin; Jeong, Yoonchan; Kim, Hak-Rin; Lee, Sin-Doo; Lee, Byoungho

2003-09-01

231

Modelling of optical synchronization of chaotic external cavity VCSELs  

E-print Network

a significant stimulus following the publi­ cation of a chaos control technique by Ott, Grebogi, and Yorke (OGY) [1] which led to several demonstrations of the control of chaotic dynamics in a number of laser systems [2­4]. Atten­ tion is drawn, in particular, to studies of the control of chaotic dynamics

Colet, Pere

232

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

233

Universal polarization terahertz phase controllers using randomly aligned liquid crystal cells with graphene electrodes.  

PubMed

We present a universal polarization terahertz (THz) phase controller using a randomly aligned liquid crystal (LC) cell with graphene electrodes. The LC cell was fabricated using a nematic LC and two quartz substrates that were coated with a monolayer of graphene as the transparent electrode. The LC in the cell was prepared without any alignment treatments and was randomly aligned. The size of the random domains and the width of the disclination lines in the LC layer were several tens of microns. These textures disappeared when an alternating voltage was applied to the LC through the graphene layers. Using a THz time domain spectroscopic technique, we investigated the complex transmittance of the LC cell. The LC cell was highly transparent in the THz frequency range, and there was little change in the transmittance with the applied voltage. This indicated that the scattering loss originating in the randomly aligned LC molecules was small for the THz waves. We also demonstrated that the THz phase shift could be controlled by the applied voltage. The amplitude of the phase shift was explained by the ordinary and extraordinary refractive indices of the LC. These LC cells with graphene electrodes can be used to realize universal polarization THz phase controllers because of the random alignment. PMID:25831380

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

2015-04-01

234

Quantum control of molecular motion including electronic polarization effects with a two-stage toolkit.  

PubMed

A method for incorporating strong electric field polarization effects into optimal control calculations is presented. A Born-Oppenheimer-type separation, referred to as the electric-nuclear Born-Oppenheimer (ENBO) approximation, is introduced in which variations of both the nuclear geometry and the external electric field are assumed to be slow compared with the speed at which the electronic degrees of freedom respond to these changes. This assumption permits the generation of a potential energy surface that depends not only on the relative geometry of the nuclei but also on the electric field strength and on the orientation of the molecule with respect to the electric field. The range of validity of the ENBO approximation is discussed in the paper. A two-stage toolkit implementation is presented to incorporate the polarization effects and reduce the cost of the optimal control dynamics calculations. As an illustration of the method, it is applied to optimal control of vibrational excitation in a hydrogen molecule aligned along the field direction. Ab initio configuration interaction calculations with a large orbital basis set are used to compute the H-H interaction potential in the presence of the electric field. The significant computational cost reduction afforded by the toolkit implementation is demonstrated. PMID:15836023

Balint-Kurti, Gabriel G; Manby, Frederick R; Ren, Qinghua; Artamonov, Maxim; Ho, Tak-San; Rabitz, Herschel

2005-02-22

235

Controllable entanglement and polarization phase gate in coupled double quantum-well structures.  

PubMed

By analyzing the nonlinear optical response in an asymmetric coupled double quantum well structure based on the intersubband transitions, we show that a giant Kerr nonlinearity with a relatively large cross-phase modulation coefficient can be used to produce efficient photonphoton entanglement and implement an all-optical two-qubit quantum polarization phase gate. We also demonstrate that such photon-photon entanglement is practically controllable and may facilitate more practical applications in all-optical quantum information and computation. PMID:18957997

Yang, Wen-Xing; Lee, Ray-Kuang

2008-10-27

236

Low-voltage, high-speed and compact electro-absorption modulator laterally integrated with 980-nm VCSEL.  

PubMed

We present a compact electro-absorption slow-light modulator laterally-integrated with a 980-nm VCSEL. We figured out the small signal modulation response for different modulator lengths. While the 3-dB small-signal modulation bandwidth of conventional directly modulated VCSELs on the same epi-wafer structure was limited below 10 GHz, we obtained a modulation bandwidth over 21 GHz for a 30 µm long modulator. We also demonstrated large signal modulation up to 25 Gbps with a low driving voltage below 600 mV(pp) and an extinction ratio of 4 dB for the modulator length of 50 µm. Prospects of much higher speed (> 40 Gbps) were examined with reducing the size of the modulator. Also, the tapered waveguide coupling structure enables "quasi-unidirectional coupling", which reduces the optical feedback in a VCSEL from the integrated modulator. PMID:25401608

Dalir, Hamed; Takahashi, Yuta; Koyama, Fumio

2014-10-20

237

An in vitro model for immune control of chlamydial growth in polarized epithelial cells.  

PubMed Central

A polarized epithelial culture system and chlamydia-specific T-cell lines and clones were employed to investigate the ability and mechanisms by which T cells control the growth of chlamydiae in epithelial cells. Monolayers of polarized mouse epithelial cells were infected with the Chlamydia trachomatis agent of mouse pneumonitis (MoPn) and then exposed to antigen-stimulated MoPn-specific T-cell lines and clones. The results revealed that in vivo-protective MoPn-specific T-cell lines and clone 2.14-0 were capable of inhibiting the growth of MoPn in polarized epithelial cells. In contrast, the nonprotective MoPn-specific T-cell clone 2.14-3, naive splenic T cells, and a control T-cell clone could not inhibit the growth of MoPn in epithelial cells. Transmission electron microscopic analysis of infected epithelial cells which were exposed to clone 2.14-0 confirmed the absence of an established infection, as deduced from the virtual absence of inclusions in the cells. Antigen-specific activation of clone 2.14-0 was required for the MoPn-inhibitory function, since the absence of antigenic stimulation or stimulation with a heterologous chlamydial agent did not result in MoPn growth inhibition. Activation of clone 2.14-0 resulted in acquisition of the capacity to inhibit growth of both homologous (MoPn) and heterologous chlamydial agents. Close interaction between epithelial cells and clone 2.14-0 was required for the MoPn-inhibitory action, because separation of the cell types by a filter with a pore size of 0.45, 3.0, or even 8.0 microns abrogated MoPn inhibition. Protective T cells may act at close range in the epithelium to control chlamydial growth, possibly involving short-range-acting cytokines. The ability of antigen-stimulated T-cell lines and clones to inhibit chlamydial growth in polarized epithelial cultures could be a useful method for identifying protective T-cell clones and antigenic peptide fragments containing protective epitopes. Images PMID:8039923

Igietseme, J U; Wyrick, P B; Goyeau, D; Rank, R G

1994-01-01

238

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

PubMed

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; Gamba, Andrea

2013-10-28

239

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

240

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Controllable Spin Polarization of Charge Current by Rashba Spin Orbital Coupling  

NASA Astrophysics Data System (ADS)

We report a theoretic study on modulating the spin polarization of charge current in a mesoscopic four-terminal device of cross structure by using the inverse spin hall effect. The scattering region of device is a two-dimensional electron gas (2DEG) with Rashba spin orbital interaction (RSOI), one of lead is ferromagnetic metal and other three leads are spin-degenerate normal metals. By using Landauer-Büttiker formalism, we found that when a longitudinal charge current flows through 2DEG scattering region from FM lead by external bias, the transverse current can be either a pure spin current or full-polarized charge current due to the combined effect of spin hall effect and its inverse process, and the polarization of this transverse current can be easily controlled by several device parameters such as the Fermi energy, ferromagnetic magnetization, and the RSOI constant. Our method may pave a new way to control the spin polarization of a charge current.

Cui, Juan; Yang, Yong-Hong; Wang, Jun

2009-11-01

241

Muscle stem cell fate is controlled by the cell-polarity protein scrib.  

PubMed

Satellite cells are resident skeletal muscle stem cells that supply myonuclei for homeostasis, hypertrophy, and repair in adult muscle. Scrib is one of the major cell-polarity proteins, acting as a potent tumor suppressor in epithelial cells. Here, we show that Scrib also controls satellite-cell-fate decisions in adult mice. Scrib is undetectable in quiescent cells but becomes expressed during activation. Scrib is asymmetrically distributed in dividing daughter cells, with robust accumulation in cells committed to myogenic differentiation. Low Scrib expression is associated with the proliferative state and preventing self-renewal, whereas high Scrib levels reduce satellite cell proliferation. Satellite-cell-specific knockout of Scrib in mice causes a drastic and insurmountable defect in muscle regeneration. Thus, Scrib is a regulator of tissue stem cells, controlling population expansion and self-renewal with Scrib expression dynamics directing satellite cell fate. PMID:25704816

Ono, Yusuke; Urata, Yoshishige; Goto, Shinji; Nakagawa, Shunsuke; Humbert, Patrick O; Li, Tao-Sheng; Zammit, Peter S

2015-02-24

242

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

243

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

244

SC-FDE for MMF short reach optical interconnects using directly modulated 850 nm VCSELs.  

PubMed

We propose the use of single-carrier frequency-domain equalization (SC-FDE) for the compensation of modal dispersion in short distance optical links using multimode fibers and 850 nm VCSELs. By post-processing of experimental data, we demonstrate, at 7.9% overhead, the error-free transmission (over a 4 Mbit sequence) of OOK-modulated 5 Gbps over 2443 meters of OM3 fiber (with a nominal 3300 MHz×km bandwidth). The proposed solution may be applied as a low cost alternative for data center and supercomputer interconnects. PMID:23187354

Teichmann, Victor S C; Barreto, Andre N; Pham, Tien-Thang; Rodes, Roberto; Monroy, Idelfonso T; Mello, Darli A A

2012-11-01

245

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

246

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

247

Phosphorylation of LKB1/Par-4 Establishes Schwann Cell Polarity to Initiate and Control Myelin Extent  

PubMed Central

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 colocalizes 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 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 signaling 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

248

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

249

Development and characterization of controlled release polar lipid microparticles of candesartan cilexetil by solid dispersion  

PubMed Central

Candesartan cilexetil (CC) is a newer class of angiotensin II receptor antagonist used for the treatment of hypertension. The solubility of the CC is very poor and its oral bioavailability is only 15%. The controlledrelease polar lipid microparticles of CC (formulations F1, F2, F3 and F4) were prepared using variable erodible lipophilic excipients like hydrogenated castor oil, stearic acid, cetostearyl alcohol and carnauba wax by fusion method. The particle sizes of polar lipid microparticles were less than 50 microns and they were irregular in shape. Drug content ranged between 98.96 ± 2.1 and 101.9 ± 1.6% were present in all the formulations. The formulation F3 showed better drug release throughout the study period in a controlled release manner. Moreover, the in vitro release showed that all the formulations were best fitted to Higuchi model. Accelerated stability studies indicated that there was no significant changes in the chemical and physical characteristics of the formulated drug product during initial and at the end of the study period. The FTIR and DSC studies showed that there was no interaction between the drug and lipophilic excipients and no polymorphic transitions in all formulations. The X-ray diffraction peak of solid dispersion indicated that the crystalline nature of CC disappeared and no new peaks could be observed, suggesting the absence of interaction between drug and excipients. PMID:24019822

Kamalakkannan, V; Puratchikody, A; Ramanathan, L

2013-01-01

250

The RPG gene of Medicago truncatula controls Rhizobium-directed polar growth during infection  

PubMed Central

Rhizobia can infect roots of host legume plants and induce new organs called nodules, in which they fix atmospheric nitrogen. Infection generally starts with root hair curling, then proceeds inside newly formed, intracellular tubular structures called infection threads. A successful symbiotic interaction relies on infection threads advancing rapidly at their tips by polar growth through successive cell layers of the root toward developing nodule primordia. To identify a plant component that controls this tip growth process, we characterized a symbiotic mutant of Medicago truncatula, called rpg for rhizobium-directed polar growth. In this mutant, nitrogen-fixing nodules were rarely formed due to abnormally thick and slowly progressing infection threads. Root hair curling was also abnormal, indicating that the RPG gene fulfils an essential function in the process whereby rhizobia manage to dominate the process of induced tip growth for root hair infection. Map-based cloning of RPG revealed a member of a previously unknown plant-specific gene family encoding putative long coiled-coil proteins we have called RRPs (RPG-related proteins) and characterized by an “RRP domain” specific to this family. RPG expression was strongly associated with rhizobial infection, and the RPG protein showed a nuclear localization, indicating that this symbiotic gene constitutes an important component of symbiotic signaling. PMID:18621693

Arrighi, Jean-François; Godfroy, Olivier; de Billy, Françoise; Saurat, Olivier; Jauneau, Alain; Gough, Clare

2008-01-01

251

Asynchronous, self-controlled, all-optical label and payload separator using nonlinear polarization rotation in a semiconductor optical amplifier.  

PubMed

We demonstrate an all-optical label and payload separator based on nonlinear polarization rotation in a semiconductor optical amplifier (SOA). The proposed scheme uses a packet format composed of a label and payload information signal combined with a control signal by using polarization division multiplexing. The control signal is employed to separate the label from the payload signal by exploiting nonlinear polarization rotation in a SOA. Experimental results show a label from payload suppression factor of 22 dB. This scheme operates asynchronously and does not need external control signal. Clean and wide open eye diagrams are obtained for both the payload and the label signal operating at bit-rates of 10 Gbit/s and 625 Mbit/s, respectively. PMID:19483966

Vegas Olmos, J; Monroy, I; Liu, Y; Garcia Larrode, M; Turkiewicz, J; Dorren, H; Koonen, A

2004-09-01

252

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

253

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 works demonstrated the advantages of nano- polymer dispersed liquid crystal (nano-PDLC) compared a liquid crystal as an electro-optic material placed inside the cavity (5). The liquid crystal (LC

Boyer, Edmond

254

A compact, portable and low cost generic interrogation strain sensor system using an embedded VCSEL, detector and fibre Bragg grating  

NASA Astrophysics Data System (ADS)

We present a compact, portable and low cost generic interrogation strain sensor system using a fibre Bragg grating configured in transmission mode with a vertical-cavity surface-emitting laser (VCSEL) light source and a GaAs photodetector embedded in a polymer skin. The photocurrent value is read and stored by a microcontroller. In addition, the photocurrent data is sent via Bluetooth to a computer or tablet device that can present the live data in a real time graph. With a matched grating and VCSEL, the system is able to automatically scan and lock the VCSEL to the most sensitive edge of the grating. Commercially available VCSEL and photodetector chips are thinned down to 20 ?m and integrated in an ultra-thin flexible optical foil using several thin film deposition steps. A dedicated micro mirror plug is fabricated to couple the driving optoelectronics to the fibre sensors. The resulting optoelectronic package can be embedded in a thin, planar sensing sheet and the host material for this sheet is a flexible and stretchable polymer. The result is a fully embedded fibre sensing system - a photonic skin. Further investigations are currently being carried out to determine the stability and robustness of the embedded optoelectronic components.

Lee, Graham C. B.; Van Hoe, Bram; Yan, Zhijun; Maskery, Oliver; Sugden, Kate; Webb, David; Van Steenberge, Geert

2012-03-01

255

A Permanent Magnet Hall Thruster for Pulsed Orbit Control of Lunar Polar Satellites  

NASA Astrophysics Data System (ADS)

Future Moon missions devoted to Lunar surface remote sensing, for example, will require very fine and accurate orbit control. It is well known that Lunar satellites in polar orbits will suffer a high increase on the eccentricity due to the gravitational perturbation of the Earth. Without proper orbit correction the satellite lifetime will decrease and end up in a collision with the Moon surface. It is pointed out by many authors that this effect is a natural consequence of the Lidov-Kozai resonance. We studied different arcs of active lunar satellite propulsion, centered on the orbit apoapsis or periapsis, in order to be able to introduce a correction of the eccentricity at each cycle. The proposed method is based on an approach intended to keep the orbital eccentricity of the satellite at low values.

Silva Moraes, Brunno; Ferreira, José Leonardo; Soares Ferreira, Ivan; Cabo Winter, Othon; Cardozo Mourão, Décio

2014-05-01

256

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

257

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

258

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

259

Distinct Roles for Two G?–G? Interfaces in Cell Polarity Control by a Yeast Heterotrimeric G Protein  

PubMed Central

Saccharomyces cerevisiae mating pheromones trigger dissociation of a heterotrimeric G protein (G???) into G?-guanosine triphosphate (GTP) and G??. The G?? dimer regulates both mitogen-activated protein (MAP) kinase cascade signaling and cell polarization. Here, by independently activating the MAP kinase pathway, we studied the polarity role of G?? in isolation from its signaling role. MAP kinase signaling alone could induce cell asymmetry but not directional growth. Surprisingly, active G??, either alone or with G?-GTP, could not organize a persistent polarization axis. Instead, following pheromone gradients (chemotropism) or directional growth without pheromone gradients (de novo polarization) required an intact receptor–G??? module and GTP hydrolysis by G?. Our results indicate that chemoattractant-induced cell polarization requires continuous receptor–G??? communication but not modulation of MAP kinase signaling. To explore regulation of G?? by G?, we mutated G? residues in two structurally distinct G?–G? binding interfaces. Polarity control was disrupted only by mutations in the N-terminal interface, and not the Switch interface. Incorporation of these mutations into a G?–G? fusion protein, which enforces subunit proximity, revealed that Switch interface dissociation regulates signaling, whereas the N-terminal interface may govern receptor–G??? coupling. These findings raise the possibility that the G??? heterotrimer can function in a partially dissociated state, tethered by the N-terminal interface. PMID:17978098

Strickfaden, Shelly C.

2008-01-01

260

High-speed 850-nm VCSELs for 40-Gb/s transmission  

NASA Astrophysics Data System (ADS)

We have explored the possibility to extend the data transmission rate for standard 850-nm GaAs-based VCSELs beyond the 10 Gbit/s limit of today's commercially available directly-modulated devices. By sophisticated tailoring of the design for high-speed performance we demonstrate that 10 Gb/s is far from the upper limit. For example, the thermal conductivity of the bottom mirror is improved by the use of binary compounds, and the electrical parasitics are kept at a minimum by incorporating a large diameter double layered oxide aperture in the design. We also show that the intrinsic high speed performance is significantly improved by replacing the traditional GaAs QWs with strained InGaAs QWs in the active region. The best overall performance is achieved for a device with a 9 ?m diameter oxide aperture, having in a threshold current of 0.6 mA, a maximum output power of 9 mW, a thermal resistance of 1.9 °C/mW, and a differential resistance of 80 ?. The measured 3dB bandwidth exceeds 20 GHz, and we experimentally demonstrate that the device is capable of error-free transmission (BER<10-12) under direct modulation at a record-high bit-rate of 32 Gb/s over 50 m of OM3 fiber at room temperature, and at 25 Gb/s over 100 m of OM3 fiber at 85 °C. We also demonstrate transmission at 40 Gb/s over 200 m of OM3+ fiber at room temperature using a subcarrier multiplexing scheme with a spectrally efficient 16 QAM modulation format. All transmission results were obtained with the VCSEL biased at current densities between 11-14 kA/cm2, which is close to the 10 kA/cm2 industry benchmark for reliability. Finally, we show that by a further reduction of the oxide capacitance and by reducing the photon lifetime using a shallow surface etch, a record bandwidth of 23 GHz for 850 nm VCSELs can be reached.

Gustavsson, Johan; Westbergh, Petter; Szczerba, Krzysztof; Haglund, Åsa; Larsson, Anders; Karlsson, Magnus; Andrekson, Peter; Hopfer, Friedhelm; Fiol, Gerrit; Bimberg, Dieter; Olsson, Bengt-Erik; Kristiansson, A.; Healy, Sorcha; O'Reilly, Eoin; Joel, Andrew

2010-04-01

261

TRULY ENDLESS POLARIZATION CONTROL WITH I&Q MODE CONVERTERS IN X-CUT, Y-PROPAGATION LITHIUM NIOBATE  

E-print Network

endless polarization control even under worst case conditions. Several such systems can be cascaded on one with one suitable extra degree-of-freedom [1]. Experiments of this kind have been published-propagation LiNbO3 waveplates [1]. The latter suffer from DC drift and will not stay calibrated stably enough

Noé, Reinhold

262

Polarization control of high order harmonics in the EUV photon energy range.  

PubMed

We report the generation of circularly polarized high order harmonics in the extreme ultraviolet range (18-27 nm) from a linearly polarized infrared laser (40 fs, 0.25 TW) focused into a neon filled gas cell. To circularly polarize the initially linearly polarized harmonics we have implemented a four-reflector phase-shifter. Fully circularly polarized radiation has been obtained with an efficiency of a few percents, thus being significantly more efficient than currently demonstrated direct generation of elliptically polarized harmonics. This demonstration opens up new experimental capabilities based on high order harmonics, for example, in biology and materials science. The inherent femtosecond time resolution of high order harmonic generating table top laser 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. PMID:21369265

Vodungbo, Boris; Barszczak Sardinha, Anna; Gautier, Julien; Lambert, Guillaume; Valentin, Constance; Lozano, Magali; Iaquaniello, Grégory; Delmotte, Franck; Sebban, Stéphane; Lüning, Jan; Zeitoun, Philippe

2011-02-28

263

Catalyst-site-controlled coordination polymerization of polar vinyl monomers to highly syndiotactic polymers.  

PubMed

This contribution reports a combined synthetic, kinetic, mechanistic, and theoretical/computational study of the recently discovered catalyst-site-controlled coordination polymerization of polar vinyl monomers [such as methyl methacrylate (MMA) and N,N-dimethylacrylamide (DMAA)] into highly syndiotactic polymers. Among the 12 C(s)-ligated ansa-cyclopentadienyl (Cp)-R(2)E(C,Si)-fluorenyl (Flu) group 4 metallocene catalyst systems examined-which varied in metal center, anion structure, bridging atom and substituents, and ligand substitution pattern-cationic ansa-metallocene ester enolate catalyst 6(+)[B(C(6)F(5))(4)](-), derived from the activation of the precatalyst [Ph(2)C(Cp)(2,7-(t)Bu(2)-Flu)]Zr[OC(O(i)Pr)=CMe(2)](2) with [Ph(3)C][B(C(6)F(5))(4)], stood out as the best catalyst in all aspects of the MMA polymerization at room temperature, including the highest activity (1554 h(-1) TOF), efficiency (98% I*), syndiotacticity (94% rr), and control (predicted number-average molecular weight and 1.14 molecular weight distribution). Kinetic and mechanistic results are consistent with a catalyst-site-controlled, monometallic coordination-addition mechanism, involving fast intramolecular addition within the catalyst-monomer complex leading to the resting eight-membered ester enolate chelate, followed by the rate-limiting ring-opening of the chelate to regenerate the active species. This work has also uncovered several unique features of this polymerization system that are in marked contrast to the propylene polymerization by analogous C(s)-ligated cationic alkyl catalysts: a constant syndiotacticity of PMMA produced over a wide polymerization temperature range (i.e., from 0 degrees C, 94% rr to 25 degrees C, 94% rr to 50 degrees C, 93% rr); insensitivity of its high activity, degree of control, and stereoselectivity to solvent polarity and structure of weakly coordinating anions; and deviation from a pure site-control mechanism at high [MMA]/[catalyst] ratios. Computational results provide theoretical support for the proposed monomer-assisted, catalyst-site epimerization, after an enantiofacial mistake, to a thermodynamically more stable resting state, which accounts for the observed higher than expected [mr] contents based on a pure site-controlled mechanism. DFT calculations rationalize why the Ph(2)C< bridged catalyst 6 exhibits higher stereoselectivity than other catalysts with the Me(2)C< or Me(2)Si< bridge: the bridge rigidity pushes the eta(3)-bound Flu ligand closer to the growing chain and the monomer, thereby increasing DeltaE(stereo) between the competing transition states for the addition of a monomer molecule to the opposite (correct and wrong) enantiofaces of the enolate growing chain. The relative polymerization activity of this catalyst series is shown to correlate with the relative energetics of the back-biting of the penultimate unit and ion-pair formation. PMID:20121281

Zhang, Yuetao; Ning, Yalan; Caporaso, Lucia; Cavallo, Luigi; Chen, Eugene Y-X

2010-03-01

264

Optimal control design of NMR and dynamic nuclear polarization experiments using monotonically convergent algorithms  

NASA Astrophysics Data System (ADS)

Optimal control theory has recently been introduced to nuclear magnetic resonance (NMR) spectroscopy as a means to systematically design and optimize pulse sequences for liquid- and solid-state applications. This has so far primarily involved numerical optimization using gradient-based methods, which allow for the optimization of a large number of pulse sequence parameters in a concerted way to maximize the efficiency of transfer between given spin states or shape the nuclear spin Hamiltonian to a particular form, both within a given period of time. Using such tools, a variety of new pulse sequences with improved performance have been developed, and the NMR spin engineers have been challenged to consider alternative routes for analytical experiment design to meet similar performance. In addition, it has lead to increasing demands to the numerical procedures used in the optimization process in terms of computational speed and fast convergence. With the latter aspect in mind, here we introduce an alternative approach to numerical experiment design based on the Krotov formulation of optimal control theory. For practical reasons, the overall radio frequency power delivered to the sample should be minimized to facilitate experimental implementation and avoid excessive sample heating. The presented algorithm makes explicit use of this requirement and iteratively solves the stationary conditions making sure that the maximum of the objective is reached. It is shown that this method is faster per iteration and takes different paths within a control space than gradient-based methods. In the present work, the Krotov approach is demonstrated by the optimization of NMR and dynamic nuclear polarization experiments for various spin systems and using different constraints with respect to radio frequency and microwave power consumption.

Maximov, Ivan I.; Tošner, Zden?k; Nielsen, Niels Chr.

2008-05-01

265

Optimal oxide-aperture for improving the power conversion efficiency of VCSEL arrays  

NASA Astrophysics Data System (ADS)

The maximum power conversion efficiencies of the top-emitting, oxide-confined, two-dimensional integrated 2×2 and 4×4 vertical-cavity surface-emitting laser (VCSEL) arrays with the oxide-apertures of 6 ?m, 16 ?m, 19 ?m, 26 ?m, 29 ?m, 36 ?m, 39 ?m, and 46 ?m are fabricated and characterized, respectively. The maximum power conversion efficiencies increase rapidly with the augment of oxide-aperture at the beginning and then decrease slowly. A maximum value of 27.91% at an oxide-aperture of 18.6 ?m is achieved by simulation. The experimental data are well consistent with the simulation results, which are analyzed by utilizing an empirical model. Project supported by the National Natural Science Foundation of China (Grant Nos. 61222501 and 61335004) and the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20111103110019)

Wang, Wen-Juan; Li, Chong; Zhou, Hong-Yi; Wu, Hua; Luan, Xin-Xin; Shi, Lei; Guo, Xia

2015-02-01

266

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

267

Volumetric cutaneous microangiography of human skin in vivo by VCSEL swept-source optical coherence tomography  

NASA Astrophysics Data System (ADS)

We demonstrate volumetric cutaneous microangiography of the human skin in vivo that utilises 1.3-?m high-speed sweptsource optical coherence tomography (SS-OCT). The swept source is based on a micro-electro-mechanical (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, which enables the visualisation of microstructures within a few mm from the skin surface. We show that the 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, R. K.

2014-08-01

268

Local control of spin polarization in a semiconductor by microscale current loops  

NASA Astrophysics Data System (ADS)

We demonstrate a method to electrically manipulate the spin polarization in a semiconductor on a micrometer length scale and a submicrosecond time scale. A variable magnetic field induced by a microscale current loop magnetizes the Mn2+ ions in a CdMnTe/CdMgTe diluted magnetic semiconductor quantum well, and via sp-d exchange interaction polarizes photogenerated electron-hole pairs. A maximum spin polarization degree of ±8.5% is obtained at 4.2 K without external magnetic field. The induced carrier spin polarization and the thermal heating of Mn2+ spins are resolved spatially and temporally by microphotoluminescence measurements.

Chen, Y. S.; Halm, S.; Neshataeva, E.; Kümmell, T.; Bacher, G.; Wiater, M.; Wojtowicz, T.; Karczewski, G.

2008-10-01

269

Selectively oxidized patterned InP-based vertical-cavity surface-emitting lasers and VCSEL arrays  

NASA Astrophysics Data System (ADS)

It is possible to grow defect-free strained layers on patterned substrates (mesas or grooves) up to thicknesses far exceeding the critical thickness. Defect nucleation and propagation are inhibited in such growth. This property was exploited to design, fabricate and characterize a novel 1.55?m InP-based patterned VCSEL with lattice-mismatched GaAs/AlGaAs top Distributed Bragg Reflectors (DBR), with defect density less than 104 cm -2. TEM and photoluminescence studies were used to evaluate the optical quality of the grown material. Lasers were designed and fabricated with InP/InGaAsP bottom mirrors, laterally oxidized InAlAs current confining layers, and a short-stack, high-contrast GaAs/AlxO top DBR mirrors. 8-40?m diameter VCSELs have been characterized. A threshold current of 5mA is observed at 15°C for an 8?m diameter device; and up to 60?W of light output was recorded. The oxidation of InAlAs in InP-based heterostructures was studied for long wavelength VCSEL applications. The dependence on adjacent layer composition, thickness and doping were investigated. Several key contributions were made in this area, including: the characterization of the process at lower temperatures reduces substrate damage, observation of a dependence on adjacent layer composition resulting in the highest oxidation rate for InAlAs, and the first demonstration of an oxide-confined InP-based VCSEL. GaAs-based VCSEL arrays with AlGaAs/InGaAs active region for high power applications were designed and fabricated using a planar. Individual devices as well as arrays of varying size were characterized and operated with maximum conversion efficiencies of 5%. Good uniformity in threshold current and scalable power were obtained for a variety of arrays. 10 x 10 arrays, operating with 3.5% conversion efficiency, gave powers in excess of 60mW (limited by the current supply). The thermal crosstalk in 4 x 4 VCSEL arrays was also investigated. A thermal isolation of 2mW/K was recorded for devices separated by 50?m and a conductivity is 0.057W/cm-K is extracted from the data. The ouput power of the lasers is temperature-insensitive under constant voltage operation. The multi-transverse mode behavior of a 2 x 2 array was studied. We believe that spatial hole burning and non- uniform current injection are the mechanisms responsible for the multi-mode characteristic of the arrays.

Gebretsadik, Herte

270

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

271

Corticosteroid solubility and lipid polarity control release from solid lipid nanoparticles.  

PubMed

Solid lipid nanoparticles (SLN) show promise as a drug delivery system for skin administration. The solid state of the lipid particle enables efficient drug encapsulation and controlled drug release. The present study addresses the influence of lipid composition and drug substance lipid solubility on the in vitro release profile of corticosteroids from SLN for topical administration. Firstly, the effect of lipid composition on the lipid solubility and in vitro release of betamethasone-17-valerate (BMV) was determined by varying the lipid monoglyceride content and the chain length of the fatty acid moiety. Secondly, the effect of drug substance physicochemical properties was determined by studying five different corticosteroid derivatives with different lipophilicity. A high concentration of monoglyceride in SLN increased the amount of BMV released. The corticosteroid release rate depended on the drug substance lipophilicity and it was clear that the release profiles depended on drug partitioning to the aqueous phase as indicated by zero order kinetics. The results emphasize that the corticosteroid solubility in the lipid phase greatly influence drug distribution in the lipid particles and release properties. Thus knowledge of drug substance solubility and lipid polarity contributes to optimize SLN release properties. PMID:19836439

Jensen, Louise B; Magnussson, Emily; Gunnarsson, Linda; Vermehren, Charlotte; Nielsen, Hanne M; Petersson, Karsten

2010-05-01

272

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

273

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

274

Distinct Roles for Two GG Interfaces in Cell Polarity Control by a Yeast Heterotrimeric G Protein  

Microsoft Academic Search

Saccharomyces cerevisiae mating pheromones trigger dissociation of a heterotrimeric G protein (G) into G- guanosine triphosphate (GTP) and G. The G dimer regulates both mitogen-activated protein (MAP) kinase cascade signaling and cell polarization. Here, by independently activating the MAP kinase pathway, we studied the polarity role of G in isolation from its signaling role. MAP kinase signaling alone could induce

Shelly C. Strickfaden; Peter M. Pryciak

2008-01-01

275

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

276

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

277

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

PubMed Central

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

278

Polarization control of quantum dot emission by chiral photonic crystal slabs  

E-print Network

We investigate theoretically the polarization properties of the quantum dot's optical emission from chiral photonic crystal structures made of achiral materials in the absence of external magnetic field at room temperature. The mirror symmetry of the local electromagnetic field is broken in this system due to the decreased symmetry of the chiral modulated layer. As a result, the radiation of randomly polarized quantum dots normal to the structure becomes partially circularly polarized. The sign and degree of circular polarization are determined by the geometry of the chiral modulated structure and depend on the radiation frequency. A degree of circular polarization up to 99% can be achieved for randomly distributed quantum dots, and can be close to 100% for some single quantum dots.

Lobanov, Sergey V; Gippius, Nikolay A; Tikhodeev, Sergei G; Kulakovskii, Vladimir D; Konishi, Kuniaki; Kuwata-Gonokami, Makoto

2014-01-01

279

Polarization control of quantum dot emission by chiral photonic crystal slabs.  

PubMed

We investigate theoretically the polarization properties of the quantum dot's (QDs) optical emission from chiral photonic crystal structures made of achiral materials in the absence of external magnetic field at room temperature. The mirror symmetry of the local electromagnetic field is broken in this system due to the decreased symmetry of the chiral modulated layer. As a result, the radiation of randomly polarized QDs normal to the structure becomes partially circularly polarized. The sign and degree of circular polarization are determined by the geometry of the chiral modulated structure and depend on the radiation frequency. A degree of circular polarization up to 99% can be achieved for randomly distributed QDs, and can be close to 100% for some single QDs. PMID:25831376

Lobanov, Sergey V; Weiss, Thomas; Gippius, Nikolay A; Tikhodeev, Sergei G; Kulakovskii, Vladimir D; Konishi, Kuniaki; Kuwata-Gonokami, Makoto

2015-04-01

280

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

281

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

282

VCSEL-based, high-speed, in situ TDLAS for in-cylinder water vapor measurements in IC engines.  

PubMed

We report the first application of a vertical-cavity surfaceemitting laser (VCSEL) for calibration- and sampling-free, high-speed, in situ H2O concentration measurements in IC engines using direct TDLAS (tunable diode laser absorption spectroscopy). Measurements were performed in a single-cylinder research engine operated under motored conditions with a time resolution down to 100 ?s (i.e., 1.2 crank angle degrees at 2000 rpm). Signal-to-noise ratios (1?) up to 29 were achieved, corresponding to a H2O precision of 0.046 vol.% H2O or 39 ppm · m. The modulation frequency dependence of the performance was investigated at different engine operating points in order to quantify the advantages of VCSEL against DFB lasers. PMID:24105541

Witzel, O; Klein, A; Meffert, C; Wagner, S; Kaiser, S; Schulz, C; Ebert, V

2013-08-26

283

Controlled lateral packing of insulin monolayers influences neuron polarization in solid-supported cultures.  

PubMed

Neurons are highly polarized cells, composed of one axon and several branching dendrites. One important issue in neurobiology is to understand the molecular factors that determine the neuron to develop polarized structures. A particularly early event, in neurons still lacking a discernible axon, is the segregation of IGF-1 (Insulin like Growth Factor-1) receptors in one neurite. This receptor can be activated by insulin in bulk, but, it is not known if changes of insulin organization as a monomolecular film may affect neuron polarization. To this end, in this work we developed solid-supported Langmuir-Blodgett films of insulin with different surface packing density. Hyppocampal pyramidal neurons, in early stage of differentiation, were cultured onto those substrates and polarization was studied after 24 h by confocal microscopy. Also we used surface reflection interference contrast microscopy and confocal microscopy to study attachment patterns and morphology of growth cones. We observed that insulin films packed at 14 mN/m induced polarization in a similar manner to high insulin concentration in bulk, but insulin packed at 44 mN/m did not induce polarization. Our results provide novel evidence that the neuron polarization through IGF-1 receptor activation can be selectively modulated by the lateral packing of insulin organized as a monomolecular surface for cell growth. PMID:23466543

Grasso, E J; Oliveira, R G; Oksdath, M; Quiroga, S; Maggio, B

2013-07-01

284

Applications of 1.55 ?m optically injection-locked VCSELs in wavelength division multiplexed passive optical networks  

NASA Astrophysics Data System (ADS)

In this paper, we will discuss the utilization of optically injection-locked (OIL) 1.55 ?m vertical-cavity surface-emitting lasers (VCSELs) for operation as low-cost, stable, directly modulated, and potentially uncooled transmitters, whereby the injection-locking master source is furnished by modulated downstream signals. Such a transmitter will find useful application in wavelength division multiplexed passive optical networks (WDM-PONs) which is actively being developed to meet the ever-increasing bandwidth demands of end users. Our scheme eliminates the need for external injection locking optical sources, external modulators, and wavelength stabilization circuitry. We show through experiments that the injection-locked VCSEL favors low injection powers and responds only strongly to the carrier but not the modulated data of the downstream signal. Further, we will discuss results from experimental studies performed on the dependence of OIL-VCSELs in bidirectional networks on the degree of Rayleigh backscattered signal and extinction ratio. We show that error-free upstream performance can be achieved when the upstream signal to Rayleigh backscattering ratio is greater than 13.4 dB, and with minimal dependence on the downstream extinction ratio. We will also review a fault monitoring and localization scheme based on a highly-sensitive yet low-cost monitor comprising a low output power broadband source and low bandwidth detectors. The proposed scheme benefits from the high reflectivity top distributed Bragg reflector mirror of the OIL-VCSEL, incurring only a minimal penalty on the upstream transmissions of the existing infrastructure. Such a scheme provides fault monitoring without having to further invest in the upgrade of customer premises.

Wong, Elaine; Zhao, Xiaoxue; Chang-Hasnain, Connie J.; Hofmann, Werner; Amann, Marcus C.

2007-11-01

285

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

286

Bidirectional reflectance distribution function of thermal control coatings and heat-shielding materials illuminated by polarized light  

NASA Astrophysics Data System (ADS)

Stokes parameters were measured for radiation reflected in the range 5° to 80° by silver-colored, white, and black thermal control coatings deposited on an aluminum alloy substrate, by green paint on a phenolic plastic surface, and by uncoated carbon-fiber reinforced plastic illuminated by linearly polarized He-Ne laser radiation at an incident angle of -5°. The bidirectional reflectance distribution function of the investigated samples was determined as a function of the view zenith angle.

Voschula, I. V.; Dlugunovich, V. A.; Zhumar, A. Yu.

2013-05-01

287

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

288

Flamingo, a Seven-Pass Transmembrane Cadherin, Regulates Planar Cell Polarity under the Control of Frizzled  

Microsoft Academic Search

We identified a seven-pass transmembrane receptor of the cadherin superfamily, designated Flamingo (Fmi), localized at cell–cell boundaries in the Drosophila wing. In the absence of Fmi, planar polarity was distorted. Before morphological polarization of wing cells along the proximal-distal (P-D) axis, Fmi was redistributed predominantly to proximal and distal cell edges. This biased localization of Fmi appears to be driven

Tadao Usui; Yasuyuki Shima; Yuko Shimada; Shinji Hirano; Robert W. Burgess; Thomas L. Schwarz; Masatoshi Takeichi; Tadashi Uemura

1999-01-01

289

1550 nm VCSEL-based 0.48 Tb/s transmission scheme employing PAM-4 and WDM for active optical cables  

NASA Astrophysics Data System (ADS)

With this paper we investigate the system-level performance of VCSELs, parameterized with true experimental LI-VI data and dynamic characteristics of state-of-the-art VCSELs with 3 dB modulation bandwidth at 15 GHz, and propose their deployment as high-speed multi-level optical sources in a mid-range active optical cable (AOC) model for performance prediction of a rack-to-rack interconnection. The AOC architecture combines a 6-element 1550 nm VCSEL array, each directly modulated with 40 Gbaud PAM-4 data, with a wavelength division multiplexer (WDM), in order to implement a parallel link with aggregate traffic of 0.48 Tb/s. Transmission reach exceeded 300 m by deploying a two-tap feed forward equalizer filter at the electrical VCSEL driver. Bit Error Rate (BER) measurements and analysis were carried out in MATLAB. In practice, the thermal behavior and basic operational characteristics of the VCSELs fabricated by the Technische Universität München (TUM) were used to study the thermal performance and operational range of the complete AOC model. The VCSELs were initially operated at 20°C and BER measurements showed power penalties of 1.7 dB and 3.5 dB at 300 m and 500 m of transmission distance respectively for all 6 data channels. System performance was also investigated for elevated operating temperatures of the VCSEL module and the additional system degradation and BER penalties introduced by operation at 50°C and 65°C were also investigated for transmission distances of 300 m and 500 m.

Markou, S.; Dris, S.; Kalavrouziotis, D.; Avramopoulos, H.; Pleros, N.; Tsiokos, Dimitris M.

2014-05-01

290

Linearly polarized emission from an embedded quantum dot using nanowire morphology control.  

PubMed

GaAs nanowires with elongated cross sections are formed using a catalyst-free growth technique. This is achieved by patterning elongated nanoscale openings within a silicon dioxide growth mask on a (111)B GaAs substrate. It is observed that MOVPE-grown vertical nanowires with cross section elongated in the [21?1?] and [1?12] directions remain faithful to the geometry of the openings. An InGaAs quantum dot with weak radial confinement is realized within each nanowire by briefly introducing indium into the reactor during nanowire growth. Photoluminescence emission from an embedded nanowire quantum dot is strongly linearly polarized (typically >90%) with the polarization direction coincident with the axis of elongation. Linearly polarized PL emission is a result of embedding the quantum dot in an anisotropic nanowire structure that supports a single strongly confined, linearly polarized optical mode. This research provides a route to the bottom-up growth of linearly polarized single photon sources of interest for quantum information applications. PMID:25674919

Foster, Andrew P; Bradley, John P; Gardner, Kirsty; Krysa, Andrey B; Royall, Ben; Skolnick, Maurice S; Wilson, Luke R

2015-03-11

291

MEMS tunable VCSEL light source for ultrahigh speed 60kHz - 1MHz axial scan rate and long range centimeter class OCT imaging  

NASA Astrophysics Data System (ADS)

This paper demonstrates new wavelength swept light source technology, MEMS tunable VCSELs, for OCT imaging. The VCSEL achieves a combination of ultrahigh sweep speeds, wide spectral tuning range, flexibility in sweep trajectory, and extremely long coherence length, which cannot be simultaneously achieved with other technologies. A second generation prototype VCSEL is optically pumped at 980nm and a low mass electrostatically tunable mirror enables high speed wavelength tuning centered at ~1310nm with ~110nm of tunable bandwidth. Record coherence length >100mm enables extremely long imaging range. By changing the drive waveform, a single 1310nm VCSEL was driven to sweep at speeds from 100kHz to 1.2MHz axial scan rate with unidirectional and bidirectional high duty cycle sweeps. We demonstrate long range and high resolution 1310nm OCT imaging of the human anterior eye at 100kHz axial scan rate and imaging of biological samples at speeds of 60kHz - 1MHz. A first generation 1050nm device is shown to sweep over 100nm. The results of this study suggest that MEMS based VCSEL swept light source technology has unique performance characteristics and will be a critical technology for future ultrahigh speed and long depth range OCT imaging.

Potsaid, Benjamin; Jayaraman, Vijaysekhar; Fujimoto, James G.; Jiang, James; Heim, Peter J. S.; Cable, Alex E.

2012-01-01

292

Controlled synthesis and size-dependent polarization domain structure of colloidal germanium telluride nanocrystals.  

PubMed

Germanium telluride (GeTe) exhibits interesting materials properties, including a reversible amorphous-to-crystalline phase transition and a room-temperature ferroelectric distortion, and has demonstrated potential for nonvolatile memory applications. Here, a colloidal approach to the synthesis of GeTe nanocrystals over a wide range of sizes is demonstrated. These nanocrystals have size distributions of 10-20% and exist in the rhombohedral structure characteristic of the low-temperature polar phase. The production of nanocrystals of widely varying sizes is facilitated by the use of Ge(II) precursors with different reactivities. A transition from a monodomain state to a state with multiple polarization domains is observed with increasing size, leading to the formation of richly faceted nanostructures. These results provide a starting point for deeper investigation into the size-scaling and fundamental nature of polar-ordering and phase-change processes in nanoscale systems. PMID:21280629

Polking, Mark J; Zheng, Haimei; Ramesh, Ramamoorthy; Alivisatos, A Paul

2011-02-23

293

Defect control for polarization switching in Bi2WO6-based single crystals  

NASA Astrophysics Data System (ADS)

The authors have investigated the leakage current mechanism and polarization properties of Bi2WO6 single crystals along the a axis at 25°C. High-pressure oxygen annealing led to a decrease in leakage current, showing that electron is a detrimental carrier of the leakage current property. It is demonstrated that 2mol% Mn substitution at the W site is effective for decreasing the leakage current density to the order of 10-8A/cm2. Mn-doped crystals show a saturated polarization hysteresis loop with a remanent polarization of 50?C/cm2. Electron spin resonance analysis suggests that Mn3+ acts as an electron acceptor for reducing the leakage current in the Bi2WO6 system.

Noguchi, Yuji; Murata, Koichiro; Miyayama, Masaru

2006-12-01

294

Eukaryotic Chemotaxis: A Network of Signaling Pathways Controls Motility, Directional Sensing, and Polarity  

PubMed Central

Chemotaxis, the directed migration of cells in chemical gradients, is a vital process in normal physiology and in the pathogenesis of many diseases. Chemotactic cells display motility, directional sensing, and polarity. Motility refers to the random extension of pseudopodia, which may be driven by spontaneous actin waves that propagate through the cytoskeleton. Directional sensing is mediated by a system that detects temporal and spatial stimuli and biases motility toward the gradient. Polarity gives cells morphologically and functionally distinct leading and lagging edges by relocating proteins or their activities selectively to the poles. By exploiting the genetic advantages of Dictyostelium, investigators are working out the complex network of interactions between the proteins that have been implicated in the chemotactic processes of motility, directional sensing, and polarity. PMID:20192768

Swaney, Kristen F.; Huang, Chuan-Hsiang; Devreotes, Peter N.

2015-01-01

295

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

296

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

297

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

298

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. PMID:25635163

Choi, Woo June; Wang, Ruikang K.

2015-01-01

299

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

300

Polarization control of Raman spectroscopy optimizes the assessment of bone tissue.  

PubMed

There is potential for Raman spectroscopy (RS) to complement tools for bone diagnosis due to its ability to assess compositional and organizational characteristics of both collagen and mineral. To aid this potential, the present study assessed specificity of RS peaks to the composition of bone, a birefringent material, for different degrees of instrument polarization. Specifically, relative changes in peaks were quantified as the incident light rotated relative to the orientation of osteonal and interstitial tissue, acquired from cadaveric femurs. In a highly polarized instrument (10(6)?1 extinction ratio), the most prominent mineral peak (?1 Phosphate at 961 cm(-1)) displayed phase similarity with the Proline peak at 856 cm(-1). This sensitivity to relative orientation between bone and light observed in the highly polarized regime persisted for certain sensitive peaks (e.g., Amide I at 1666? cm(-1)) in unaltered instrumentation (200?1 extinction ratio). Though Proline intensity changed with bone rotation, the phase of Proline matched that of ?1 Phosphate. Moreover, when mapping ?1 Phosphate/Proline across osteonal-interstitial borders, the mineralization difference between the tissue types was evident whether using a 20x or 50x objectives. Thus, the polarization bias inherent in commercial RS systems does not preclude the assessment of bone composition when using phase-matched peaks. PMID:23708192

Makowski, Alexander J; Patil, Chetan A; Mahadevan-Jansen, Anita; Nyman, Jeffry S

2013-05-01

301

Deterministic control of nanooptical excitations in plasmonic nanostructures using ultrashort polarization-shaped laser pulses  

E-print Network

core-level dynamics in the layered charge-density-wave compound 1T­TaS2 in response to impulsive as to extrinsic pump-laser induced vacuum space-charge effects. Reversible Switching in Self-assembled Monolayers ultrashort polarization-shaped laser pulses M. Aeschlimann, M. Bauer, D. Bayer, T. Brixner, S. Cunovic, A

Bauer, Michael

302

The Zebrafish Glypican Knypek Controls Cell Polarity during Gastrulation Movements of Convergent Extension  

Microsoft Academic Search

Mutations in the zebrafish knypek locus impair gastrulation movements of convergent extension that narrow embryonic body and elongate it from head to tail. We demonstrate that knypek regulates cellular movements but not cell fate specification. Convergent extension movement defects in knypek are associated with abnormal cell polarity, as mutant cells fail to elongate and align medio-laterally. Positional cloning reveals that

Jacek Topczewski; Diane S. Sepich; Dina C. Myers; Charline Walker; Angel Amores; Zsolt Lele; Matthias Hammerschmidt; John Postlethwait; Lilianna Solnica-Krezel

2001-01-01

303

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

304

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

305

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

PubMed

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

2014-08-01

306

First Step Toward Ultrafast Nuclear-Spin Polarization: All-optical Control and Direct Detection of Ultrafast Electron-Spin Polarization Using Femtosecond Laser Pulses  

SciTech Connect

We demonstrate the first experimental observation of ultrafast electron-spin polarization upon photoionization using femtosecond and nanosecond lasers. For the optical detection of electron-spin polarization we measure the laser-induced fluorescence of photoions. The experimental results agree well with our theoretical results obtained by solving the time-dependent Schroedinger equations.

Nakajima, Takashi [Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); RIKEN - Institute of Physical and Chemical Research, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Matsuo, Yukari; Kobayashi, Tohru [RIKEN - Institute of Physical and Chemical Research, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan)

2009-08-04

307

Temperature dependent investigation of carrier transport, injection, and densities in 808 nm AlGaAs multi-quantum-well active layers for VCSELs  

NASA Astrophysics Data System (ADS)

The electro-optical efficiency of semiconductor vertical-cavity surface-emitting lasers (VCSELs) strongly depends on the efficient carrier injection into the quantum wells (QWs) in the laser active region. However, carrier injection degrades with increasing temperature which limits the VCSEL performance particularly in high power applications where self heating imposes high temperatures in operation. By simulation we investigate the transport of charge carriers in 808 nm AlGaAs multi-quantum-well active layers with special attention to the temperature dependence of carrier injection into the QWs. Experimental reference data was extracted from oxide-confined, top-emitting VCSELs. The transport simulations follow a drift-diffusion-model complemented by a customized, energy-resolved, semi-classical carrier capture theory. QW gain was calculated in the screened Hartree-Fock approximation with band structures from 8x8 k.p-theory. Using the gain data and by setting losses and the optical confinement factor according to experimental reference results, the appropriate threshold condition and threshold carrier densities in the QWs for a VCSEL are established in simulation for all transport considerations. With the combination of gain and transport model, we can explain experimental reference data for the injection efficiency and threshold current density. Our simulations show that the decreasing injection efficiency with temperature is not solely due to increased thermionic escape of carriers from the QWs. Carrier injection is also hampered by state filling in the QWs initiated from higher threshold carrier densities with temperature. Consequently, VCSEL properties not directly related to the active layer design like optical out-coupling or internal losses link the temperature dependent carrier injection to VCSEL mirror design.

Engelhardt, Andreas P.; Kolb, Johanna S.; Römer, Friedhard; Weichmann, Ulrich; Moench, Holger; Witzigmann, Bernd

2014-05-01

308

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

309

Growth control of nonpolar and polar ZnO/MgxZnO quantum wells by pulsed-laser deposition  

NASA Astrophysics Data System (ADS)

Growth control of nonpolar and polar ZnO/MgxZnO quantum wells (QWs) is demonstrated by in situ RHEED during the pulsed laser deposition process. Nonpolar QWs were grown homoepitaxially on m-plane and on a-plane ZnO single crystals. For m-plane (101¯0) ZnO QWs we report a change of growth mode from a two dimensional layer by layer growth evidenced by RHEED oscillations to the formation of surface nanostripes as observed by atomic force microscopy. The aspect ratio of the self organized nanostripes depends on the oxygen partial pressure. a-lane (112¯0) ZnO QW-structures show a smooth surface with a rms-roughness of 0.3 nm. Homoepitaxial nonpolar QWs do not show the quantum-confined Stark effect while polar quantum wells on a-plane sapphire does with an internal electric field of approximately 0.53 MV/cm. Furthermore, by implementing a low temperature MgxZnO buffer layer, the interface quality of heteroepitaxially grown polar ZnO/MgxZnO QWs on a-plane sapphire substrates is considerably improved. RHEED oscillations were observed during the whole growth of such QWs.

Zippel, J.; Lorenz, M.; Lange, M.; Stölzel, M.; Benndorf, G.; Grundmann, M.

2013-02-01

310

Author's personal copy Single transverse mode control of VCSEL by photonic crystal and  

E-print Network

a Microelectronics & Nanotechnology Program, Telekom Malaysia Research & Development (TMR&D), Lingkaran Teknokrat St., Bldg. E, Vancouver, WA 98665, USA d Electrical & Computer Engineering Department, University, and introduce high resistance which reduces the high speed capability. Recently, various methods are reported

Choquette, Kent

311

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

312

Off-resonant polarized light-controlled thermoelectric transport in ultrathin topological insulators  

NASA Astrophysics Data System (ADS)

We study thermoelectric transport in ultrathin topological insulators under the application of circularly polarized off-resonant light of frequency ? and amplitude A . We derive analytical expressions for the band structure, orbital magnetization Morb, and the thermal (?x y) and Nernst (?x y) conductivities. Reversing the light polarization from right to left leads to an exchange of the conduction and valence bands of the symmetric and antisymmetric surface states and to a sign change in Morb,?x y, and ?x y. Varying the sample thickness or A /? leads to a strong enhancement of Morb and ?x y. These effects, accessible to experiments, open the possibility for selective, state-exchanged excitations under light and the conversion of heat to electric energy.

Tahir, M.; Vasilopoulos, P.

2015-03-01

313

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

314

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

315

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

316

Microbial Competition in Polar Soils: A Review of an Understudied but Potentially Important Control on Productivity  

PubMed Central

Intermicrobial competition is known to occur in many natural environments, and can result from direct conflict between organisms, or from differential rates of growth, colonization, and/or nutrient acquisition. It has been difficult to extensively examine intermicrobial competition in situ, but these interactions may play an important role in the regulation of the many biogeochemical processes that are tied to microbial communities in polar soils. A greater understanding of how competition influences productivity will improve projections of gas and nutrient flux as the poles warm, may provide biotechnological opportunities for increasing the degradation of contaminants in polar soil, and will help to predict changes in communities of higher organisms, such as plants. PMID:24832797

Bell, Terrence H.; Callender, Katrina L.; Whyte, Lyle G.; Greer, Charles W.

2013-01-01

317

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

PubMed Central

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.

2012-01-01

318

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

319

The heparan sulfate-modifying enzyme glucuronyl C5-epimerase HSE-5 controls Caenorhabditis elegans Q neuroblast polarization during migration.  

PubMed

Directional cell migration is fundamental for neural development, and extracellular factors are pivotal for this process. Heparan sulfate proteoglycans (HSPGs) that carry long chains of differentially modified sugar residues contribute to extracellular matrix; however, the functions of HSPG in guiding cell migration remain elusive. Here, we used the Caenorhabditis elegans mutant pool from the Million Mutation Project and isolated a mutant allele of the heparan sulfate-modifying enzyme glucuronyl C5-epimerase HSE-5. Loss-of-function of this enzyme resulted in defective Q neuroblast migration. We showed that hse-5 controlled Q cell migration in a cell non-autonomous manner. By performing live cell imaging in hse-5 mutant animals, we found that hse-5 controlled initial polarization during Q neuroblast migration. Furthermore, our genetic epistasis analysis demonstrated that lon-2 might act downstream of hse-5. Finally, rescue of the hse-5 mutant phenotype by expression of human and mouse hse-5 homologs suggested a conserved function for this gene in neural development. Taken together, our results indicated that proper HSPG modification in the extracellular matrix by HSE-5 is essential for neuroblast polarity during migration. PMID:25614236

Wang, Xiangming; Liu, Jianhong; Zhu, Zhiwen; Ou, Guangshuo

2015-03-15

320

Position- and orientation-controlled polarized light interaction of individual indium tin oxide nanorods  

SciTech Connect

We have systematically investigated the position, orientation, and polarization angle dependence of scattered light from well-characterized, indium tin oxide nanorods (ITO NRs) upon illumination with monochromatic light. Scattering signals from individual ITO NRs of horizontal and vertical configurations are probed quantitatively by examining signal response with respect to the analyzer angle and position along the length of the NR. Our efforts can be highly beneficial in providing fundamental understanding for the light interaction behavior of ITO NRs. Our results can provide valuable bases for comprehending optical emission from individual NRs, with their ever-growing applications in optoelectronics, photonics, and biosensing.

Choi, Daniel S.; Joh, Daniel Y.; Lee, Thomas; Milchak, Marissa; Zhou, Hebing; Kang, Yongkoo; Hahm, Jong-in, E-mail: jh583@georgetown.edu [Department of Chemistry, Georgetown University, 37th and O Sts. N.W., Washington, DC 20057 (United States)

2014-02-24

321

Plasmonic Nanoantennas for Efficient Control of Polarization-Entangled Photon Pairs  

E-print Network

We suggest a novel source of polarization-entangled photon pairs based on a cross-shaped plasmonic nanoantenna driven by a single quantum dot. The integration of the nanoantenna with a metal mirror overcomes the fundamental tradeoff between the spontaneous emission (SE) enhancement and the extraction efficiency typical of microcavity and nanowire-based architectures. With a very-high extraction efficiency of entangled photons (~90%) at 1.55 um and large SE enhancement (~90) over a broad 330 nm spectral range, the proposed design will pave the way toward reliable integrated sources of nonclassical light.

Ivan S. Maksymov; Andrey E. Miroshnichenko; Yuri S. Kivshar

2012-06-22

322

Growth Control by Committee – Intercellular Junctions, Cell Polarity, and the Cytoskeleton Regulate Hippo Signaling  

PubMed Central

Summary Over the past decade, the Hippo tumor suppressor pathway has emerged as a central regulator of growth in epithelial tissues. Research in Drosophila and in mammals has shown that this kinase signaling cascade regulates the activity of the transcriptional coactivator and oncoprotein Yorkie/Yap. In this review, we discuss recent findings that emphasize the cell cortex - specifically the actin cytoskeleton, intercellular junctions and the protein complexes determine cell polarity - as a key site for Hippo pathway regulation. We also highlight where additional research is needed to integrate known functional interactions between Hippo pathway components. PMID:22516196

Boggiano, Julian C.; Fehon, Richard G.

2012-01-01

323

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

NASA Astrophysics Data System (ADS)

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.; Sun, H. P.; Pan, X. Q.

2010-10-01

324

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

325

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

326

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

327

Control of vibrational states by spin-polarized transport in a carbon nanotube resonator  

NASA Astrophysics Data System (ADS)

We study spin-dependent transport in a suspended carbon nanotube quantum dot in contact with two ferromagnetic leads and with the dot's spin coupled to the flexural mechanical modes. The spin-vibration interaction induces spin-flip processes between the two energy levels of the dot. This interaction arises from the spin-orbit coupling or a magnetic field gradient. The inelastic vibration-assisted spin flips give rise to a mechanical damping and, for an applied bias voltage, to a steady nonequilibrium occupation of the harmonic oscillator. We analyze these effects as function of the energy-level separation of the dot and the magnetic polarization of the leads. Depending on the magnetic configuration and the bias-voltage polarity, we can strongly cool a single mode or pump energy into it. In the latter case, we find that within our approximation, the system approaches eventually a regime of mechanical instability. Furthermore, owing to the sensitivity of the electron transport to the spin orientation, we find signatures of the nanomechanical motion in the current-voltage characteristic. Hence, the vibrational state can be read out in transport measurements.

Stadler, P.; Belzig, W.; Rastelli, G.

2015-02-01

328

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

329

Quantum control of molecular vibrational and rotational excitations in a homonuclear diatomic molecule: A full three-dimensional treatment with polarization forces  

Microsoft Academic Search

The optimal control of the vibrational excitation of the hydrogen molecule [Balint-Kurti et al., J. Chem. Phys. 122, 084110 (2005)] utilizing polarization forces is extended to three dimensions. The polarizability of the molecule, to first and higher orders, is accounted for using explicit ab initio calculations of the molecular electronic energy in the presence of an electric field. Optimal control

Qinghua Ren; Gabriel G. Balint-Kurti; Frederick R. Manby; Maxim Artamonov; Tak-San Ho; Herschel Rabitz

2006-01-01

330

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

331

Bandwidths of Micro Twisted-Pair Cables and Fusion Spliced SIMM-GRIN Fiber and Radiation Hardness of PIN/VCSEL Arrays  

E-print Network

of PIN/VCSEL Arrays K.K. Gana , W. Fernandoa , H.P. Kagana , R.D. Kassa , A. Lawa , M.R.M. Lebbaib , P optical link architecture. The electrical signals between the current pixel modules and the optical modules are transmitted via micro-twisted cables. The optical signals between the optical modules

Gan, K. K.

332

120Gb\\/s 100-m transmission in a single multicore multimode fiber containing six cores interfaced with a matching VCSEL array  

Microsoft Academic Search

Over 100 Gb\\/s is carried across a single 100-m strand of multicore multimode fiber. A custom VCSEL array transmits 16.7 to 20 Gb\\/s\\/channel into six cores housed within a 125-?m cladding. Negligible crosstalk is observed.

B. G. Lee; D. M. Kuchta; F. E. Doany; C. L. Schow; C. Baks; R. John; P. Pepeljugoski; T. F. Taunay; B. Zhu; M. F. Yan; G. E. Oulundsen; D. S. Vaidya; W. Luo; N. Li

2010-01-01

333

Invisible code display for robots' eye communication using polarization control by LCD panel  

NASA Astrophysics Data System (ADS)

An invisible code is one of the useful technologies for a computer interaction. In this paper, we propose a method to display invisible codes using LCD panels and to detect a polarized symbol image with a conventional CCD camera. The authors have been developing the mobile robots which can cooperation between robots. The robots should communicate with each other in order to cooperate together. Therefore, the communication between robots is very important problem to be solved. These robots generally utilize wireless transmission system. The transmission sets send and receive on the same frequency or channel to establish the radio communication. This is called working simplex. The robots cannot start communication if both sets use different frequency channels. It is important to perform an initial configuration for establishing the radio signal transmission at a first contact among strange mobile robots. To solve this problem, this paper describes an information transmission system using an invisible code on displays which show an expression of robot's eyes.

Sakamoto, Kunio; Furukawa, Takeru

2010-11-01

334

Controlling energy level offsets in organic/organic heterostructures using intramolecular polar bonds  

NASA Astrophysics Data System (ADS)

The impact of intramolecular polar bonds (IPBs) on the energy level alignment in layered systems of rodlike conjugated molecules standing on the substrate was investigated for pentacene (PEN) and perfluoropentacene (PFP) on SiO2 using ultraviolet photoelectron spectroscopy. A remarkably large energy offset of 1.75 eV was found between the highest occupied molecular orbital (HOMO) levels of PEN and PFP caused by IPBs at the surface of standing PFP layers. This large HOMO-level offset results in a narrow intermolecular energy gap of approximately 0.4 eV at the interface between PEN and PFP layers. However, the absence of significant spatial overlap of PEN and PFP electron wave functions across the layers suppresses interlayer optical transitions.

Duhm, Steffen; Salzmann, Ingo; Heimel, Georg; Oehzelt, Martin; Haase, Anja; Johnson, Robert L.; Rabe, Jürgen P.; Koch, Norbert

2009-01-01

335

Planar cell polarity and the developmental control of cell behavior in vertebrate embryos.  

PubMed

Planar cell polarity (PCP), the orientation and alignment of cells within a sheet, is a ubiquitous cellular property that is commonly governed by the conserved set of proteins encoded by so-called PCP genes. The PCP proteins coordinate developmental signaling cues with individual cell behaviors in a wildly diverse array of tissues. Consequently, disruptions of PCP protein functions are linked to defects in axis elongation, inner ear patterning, neural tube closure, directed ciliary beating, and left/right patterning, to name only a few. This review attempts to synthesize what is known about PCP and the PCP proteins in vertebrate animals, with a particular focus on the mechanisms by which individual cells respond to PCP cues in order to execute specific cellular behaviors. PMID:22905955

Wallingford, John B

2012-01-01

336

Control of vertebrate intraflagellar transport by the planar cell polarity effector Fuz  

PubMed Central

Cilia play key roles in development and homeostasis, and defects in cilia structure or function lead to an array of human diseases. Ciliogenesis is accomplished by the intraflagellar transport (IFT) system, a set of proteins governing bidirectional transport of cargoes within ciliary axonemes. In this paper, we present a novel platform for in vivo analysis of vertebrate IFT dynamics. Using this platform, we show that the planar cell polarity (PCP) effector Fuz was required for normal IFT dynamics in vertebrate cilia, the first evidence directly linking PCP to the core machinery of ciliogenesis. Further, we show that Fuz played a specific role in trafficking of retrograde, but not anterograde, IFT proteins. These data place Fuz in the small group of known IFT effectors outside the core machinery and, additionally, identify Fuz as a novel cytoplasmic effector that differentiates between the retrograde and anterograde IFT complexes. PMID:22778277

Brooks, Eric R.

2012-01-01

337

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

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

338

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

339

Control of vertebrate intraflagellar transport by the planar cell polarity effector Fuz.  

PubMed

Cilia play key roles in development and homeostasis, and defects in cilia structure or function lead to an array of human diseases. Ciliogenesis is accomplished by the intraflagellar transport (IFT) system, a set of proteins governing bidirectional transport of cargoes within ciliary axonemes. In this paper, we present a novel platform for in vivo analysis of vertebrate IFT dynamics. Using this platform, we show that the planar cell polarity (PCP) effector Fuz was required for normal IFT dynamics in vertebrate cilia, the first evidence directly linking PCP to the core machinery of ciliogenesis. Further, we show that Fuz played a specific role in trafficking of retrograde, but not anterograde, IFT proteins. These data place Fuz in the small group of known IFT effectors outside the core machinery and, additionally, identify Fuz as a novel cytoplasmic effector that differentiates between the retrograde and anterograde IFT complexes. PMID:22778277

Brooks, Eric R; Wallingford, John B

2012-07-01

340

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

341

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

342

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

343

Control of the Martian Water Cycle by the Northern Polar Ice Cap  

NASA Astrophysics Data System (ADS)

In order to undertake credible studies of the Martian climate at other epochs, one requirement is a mechanistic understanding of the processes controlling the water cycle. This need arises from the increasing role of atmospheric water ice and vapour as radiatively active species as global atmospheric water abundances increase. Further, a key motivation for modeling past climates is the need to understand temporal variations in the amounts, state, and locations of water. We have investigated the processes controlling the water cycle with the Geophysical Fluid Dynamics Laboratory (GFDL) Mars General Circulation Model (GCM). These simulations suggest that primary parameters controlling current global atmospheric water abundance are the albedo and thermal inertia of the northern residual water ice cap, which in turn will be controlled by the macro- and microphysical properties of the ice. Additional information is contained in the original extended abstract.

Richardson, M. I.; Wilson, R. J.

2000-08-01

344

Par6–aPKC uncouples ErbB2 induced disruption of polarized epithelial organization from proliferation control  

Microsoft Academic Search

The polarized glandular organization of epithelial cells is frequently lost during development of carcinoma. However, the specific oncogene targets responsible for polarity disruption have not been identified. Here, we demonstrate that activation of ErbB2 disrupts apical–basal polarity by associating with Par6–aPKC, components of the Par polarity complex. Inhibition of interaction between Par6 and aPKC blocked the ability of ErbB2 to

Victoria Aranda; Teresa Haire; Marissa E. Nolan; Joseph P. Calarco; Avi Z. Rosenberg; James P. Fawcett; Tony Pawson; Senthil K. Muthuswamy

2006-01-01

345

Planar cell polarity controls directional Notch signaling in the Drosophila leg  

PubMed Central

The generation of functional structures during development requires tight spatial regulation of signaling pathways. Thus, in Drosophila legs, in which Notch pathway activity is required to specify joints, only cells distal to ligand-producing cells are capable of responding. Here, we show that the asymmetric distribution of planar cell polarity (PCP) proteins correlates with this spatial restriction of Notch activation. Frizzled and Dishevelled are enriched at distal sides of each cell and hence localize at the interface with ligand-expressing cells in the non-responding cells. Elimination of PCP gene function in cells proximal to ligand-expressing cells is sufficient to alleviate the repression, resulting in ectopic Notch activity and ectopic joint formation. Mutations that compromise a direct interaction between Dishevelled and Notch reduce the efficacy of repression. Likewise, increased Rab5 levels or dominant-negative Deltex can suppress the ectopic joints. Together, these results suggest that PCP coordinates the spatial activity of the Notch pathway by regulating endocytic trafficking of the receptor. PMID:22736244

Capilla, Amalia; Johnson, Ruth; Daniels, Maki; Benavente, María; Bray, Sarah J.; Galindo, Máximo Ibo

2012-01-01

346

Polarization-Controlled TIRFM with Focal Drift and Spatial Field Intensity Correction  

PubMed Central

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.

2014-01-01

347

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

348

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 ...

Mr. Thomas

2010-09-27

349

Polar-localised poplar K + channel capable of controlling electrical properties of wood-forming cells  

Microsoft Academic Search

In previous studies, we have shown that annual expression profiles of cambial and wood tissue with respect to the Shaker K+ channel PTORK correlate with cambial activity. To follow PTORK-gene activity on the cellular level, we isolated the respective promoter regions and generated transgenic Arabidopsis plants expressing the GUS gene under the control of the PTORK promoter. Cross-sections of petioles

Matthias Arend; Andrea Stinzing; Christa Wind; Katharina Langer; Andreas Latz; Peter Ache; Jörg Fromm; Rainer Hedrich

2005-01-01

350

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

E-print Network

Control Arthur Year Structure Material H. Shimizu K. Kaede [13] 1988 QWP-HWP LiNbO3 R. Noeet al. [14] 1988 3 or 4 retarders Fiber squeezers F. Heismann [15, 16] 1989, 1990 Multiple sets of a retarder and a coupler LiNbO3 L. Moller [17] 2001 2...

Sung, Won Ju

2013-12-10

351

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

352

Surface micromachined tunable 1.55 ?m-VCSEL with 102 nm continuous single-mode tuning  

NASA Astrophysics Data System (ADS)

For the first time a vertical-cavity surface-emitting laser (VCSEL) with a single-mode wavelength-tuning over 102nm in the range of 1550nm is demonstrated. The fiber-coupled optical output power has a maximum of 3.5mW and is > 2mW over the entire tuning range. The sidemode suppression ratios are > 45dB. The wavelength tuning is achieved with the micro-electro mechanical actuation of a mirror membrane fabricated with surface micro-machining for on-wafer mass production. The mirror membrane consists of low cost dielectric materials (SiOx/SiNy) deposited with low temperature (< 100°C) Plasma Enhanced Chemical Vapor Deposition (PECVD).

Gierl, C.; Gruendl, T.; Debernardi, P.; Zogal, K.; Grasse, C.; Davani, H. A.; Böhm, G.; Jatta, S.; Küppers, F.; Meißner, P.; Amann, M.-C.

2011-08-01

353

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

354

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

355

The proto-oncoprotein SYT (SS18) controls ATP release and regulates cyst formation by polarized MDCK cells.  

PubMed

The SYT proto-oncoprotein (also known as SS18) is a gene expression regulator conserved across species. Although its biological function is still unknown, the importance of SYT as a housekeeping protein is illustrated by the lethal phenotype of SYT-null embryos. Notably, SYT is a component of the synovial sarcoma-associated translocation product, the SYT-SSX oncogene. SYT was previously reported as a mediator of cell adhesion. In the present study we show that SYT possesses distinct domains that control MDCK cyst formation in three-dimensional collagen cultures. While the carboxy-half of SYT, the QPGY domain, is required for cyst growth, the amino-terminal region appears to exert on this process a regulatory effect. Further analysis suggested that the purinergic G protein-coupled P2Y receptor signaling is involved in SYT-induced cystogenesis. Activation of this cascade is due to facilitation of ATP release in the extracellular space of polarized MDCK cells by SYT. These studies allow us to begin to understand the vital role of SYT in controlling epithelial morphogenesis and might explain the lethality of its loss in the developing embryo. PMID:18835266

Chittezhath, Manesh; Frump, Andrea L; Jourquin, Jerome; Lobdell, Nichole; Eid, Josiane E

2008-11-15

356

The proto-oncoprotein SYT (SS18) controls ATP release and regulates cyst formation by polarized MDCK cells  

PubMed Central

The SYT proto-oncoprotein (also known as SS18) is a gene expression regulator conserved across species. Although its biological function is still unknown, the importance of SYT as a housekeeping protein is illustrated by the lethal phenotype of SYT-null embryos. Notably, SYT is a component of the synovial sarcoma-associated translocation product, the SYT-SSX oncogene. SYT was previously reported as a mediator of cell adhesion. In the present study we show that SYT possesses distinct domains that control MDCK cyst formation in three-dimensional collagen cultures. While the carboxy-half of SYT, the QPGY domain, is required for cyst growth, the amino-terminal region appears to exert on this process a regulatory effect. Further analysis suggested that the purinergic G protein-coupled P2Y receptor signaling is involved in SYT-induced cystogenesis. Activation of this cascade is due to facilitation of ATP release in the extracellular space of polarized MDCK cells by SYT. These studies allow us to begin to understand the vital role of SYT in controlling epithelial morphogenesis and might explain the lethality of its loss in the developing embryo. PMID:18835266

Chittezhath, Manesh; Frump, Andrea L; Jourquin, Jerome; Lobdell, Nichole; Eid, Josiane E

2008-01-01

357

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

358

In-situ weak-beam and polarization control of multidimensional laser sidebands for ultrafast optical switching  

NASA Astrophysics Data System (ADS)

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

2014-03-01

359

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

1987-01-01

360

Effects of maneuver dynamics on drag polars of the X-29A forward-swept-wing aircraft with automatic wing camber control  

NASA Technical Reports Server (NTRS)

The camber control loop of the X-29A FSW aircraft was designed to furnish the optimum L/D for trimmed, stabilized flight. A marked difference was noted between automatic wing camber control loop behavior in dynamic maneuvers and in stabilized flight conditions, which in turn affected subsonic aerodynamic performance. The degree of drag level increase was a direct function of maneuver rate. Attention is given to the aircraft flight drag polar effects of maneuver dynamics in light of wing camber control loop schedule. The effect of changing camber scheduling to better track the optimum automatic camber control L/D schedule is discussed.

Hicks, John W.; Moulton, Bryan J.

1988-01-01

361

Polarity Therapy for Cancer-Related Fatigue in Patients With Breast Cancer Receiving Radiation Therapy: A Randomized Controlled Pilot Study  

PubMed Central

Background Cancer-related fatigue (CRF) is the most frequently reported side effect of cancer and its treatment. In previous research, Polarity Therapy (PT), an energy therapy, was shown to reduce CRF in patients receiving radiation. This study reports on a small randomized clinical trial designed to collect preliminary data on the efficacy of PT compared with an active control (massage) and passive control (standard care) for CRF among cancer patients receiving radiation therapy. Methods Forty-five women undergoing radiation therapy for breast cancer were randomized to I of 3 weekly treatment conditions. Patients received standard clinical care, 3 modified massages, or 3 PT treatments. CRF and healthrelated quality of life (HRQL) were assessed during baseline and the 3 intervention weeks. Results TResults show CRF ratings were reduced after PT. The effect sizes for PT versus modified massage and versus standard care were small when using the primary measure of CRF (Brief Fatigue Inventory) and large when using the secondary measure of CRF (Daily CRF Diaries).The effect size was medium when assessing the benefit of PT on maintaining HRQL compared with standard care with very little difference between the PT and modified massage conditions. Patients’ feedback showed that both the modified massage and PT treatments were deemed useful by radiation patients. Conclusion. The present pilot randomized clinical trial supports previous experimental research showing that PT, a noninvasive and gentle energy therapy, may be effective in controlling CRF. Further confirmatory studies as well as investigations of the possible mechanisms of PT are warranted. PMID:21382958

Mustian, Karen M.; Roscoe, Joseph A.; Palesh, Oxana G.; Sprod, Lisa K.; Heckler, Charles E.; Peppone, Luke J.; Usuki, Kenneth Y.; Ling, Marilyn N.; Brasacchio, Ralph A.; Morrow, Gary R.

2011-01-01

362

Controlled suppression of superconductivity by the generation of polarized Cooper pairs in spin-valve structures  

NASA Astrophysics Data System (ADS)

Transport measurements are presented on thin-film superconducting spin-valve systems, where the controlled noncollinear arrangement of two ferromagnetic Co layers can be used to influence the superconducting state of Nb. We observe a very clear oscillation of the superconducting transition temperature with the relative orientation of the two ferromagnetic layers. Our measurements allow us to distinguish between the competing influences of domain averaging, stray dipolar fields, and the formation of superconducting spin triplets. Domain averaging is shown to lead to a weak enhancement of transition temperature for the antiparallel configuration of exchange fields, while much larger changes are observed for other configurations, which can be attributed to drainage currents due to spin triplet formation.

Flokstra, M. G.; Cunningham, T. C.; Kim, J.; Satchell, N.; Burnell, G.; Curran, P. J.; Bending, S. J.; Kinane, C. J.; Cooper, J. F. K.; Langridge, S.; Isidori, A.; Pugach, N.; Eschrig, M.; Lee, S. L.

2015-02-01

363

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

364

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

365

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.

Kelly Burgess

2012-09-11

366

Finite difference analysis of thermal characteristics of continuous wave operation 850 nm lateral current injection and implant-apertured VCSEL with flip-chip bond design  

Microsoft Academic Search

Summary form only given. The VCSELs of this work are based on an implanted-aperture, index-guided, lateral current injected, top dielectric mirror GaAs quantum well 850 nm design. The thermal simulation employs quasi-three dimensional finite difference analysis to calculate the temperature, thermal resistance and the rise time of temperature at a fixed bias to calculate the nonuniform heat source distribution.

R. Mehandru; G. Dang; B. Luo; S. Kim; F. Ren; S. J. Pearton; W. S. Hobson; J. Lopata; M. Tayahi; W. Chang; H. Shen

2002-01-01

367

Finite difference analysis of thermal characteristics of CW operation 850 nm lateral current injection and implant-apertured VCSEL with flip-chip bond design  

Microsoft Academic Search

The finite difference method was used to analyze the thermal characteristics of continuous wave 850 nm AlGaAs\\/GaAs implant-apertured vertical-cavity surface-emitting lasers (VCSELs). A novel flip-chip design was used to enhance the heat dissipation. The temperature rise in the active can be maintained below 40 °C at 4 mW output power with 10 mA current bias. By contrast, the temperature rise

R. Mehandru; G. Dang; S. Kim; F. Ren; W. S. Hobson; J. Lopata; S. J. Pearton; W. Chang; H. Shen

2002-01-01

368

Performance comparison of 850-nm and 1550-nm VCSELs exploiting OOK, OFDM, and 4-PAM over SMF/MMF links for low-cost optical interconnects  

NASA Astrophysics Data System (ADS)

We experimentally compare the performance of two commercially available vertical-cavity surface-emitting laser diodes (VCSELs), a multi-mode 850-nm and a single-mode 1550-nm, exploiting on-off keying/direct detection (OOK/DD), and orthogonal frequency division multiplexed (OFDM) quadrature phase-shift keying (QPSK)/16-ary quadrature amplitude modulation (16QAM) with direct detection, over SMF (100 m and 5 km) and MMF (100 m and 1 km) short-range links, for their potential application in low-cost rack-to-rack optical interconnects. Moreover, we assess the performance of quaternary-pulse amplitude modulation (4-PAM), for the 1550-nm transmitter over SMF and MMF links and we compare it to the data-rate equivalent NRZ-OOK. The extensive performance comparison under various transmission scenarios shows the superiority of 1550-nm single-mode VCSEL compared to its multi-mode 850-nm counterpart. Moreover, OFDM/DD and 4-PAM in conjunction with low-cost, inexpensive VCSELs as transmitters prove to be an enabling technology for next-generation WDM, point-to-point, short-reach, SMF/MMF optical interconnects and potential candidates to substitute NRZ-OOK. Nevertheless, the sensitivity requirements are higher in that case, whereas these advanced, spectrally-efficient modulation formats become severely degraded when transmitted over MMF links, especially, when employing the inexpensive 850-nm VCSELs as transmitter. Finally, we compare the performance of the point-to-point links under investigation to the performance of a semiconductor optical amplifier (SOA)- based, scalable permutation switch fabric, the Optical Shared MemOry Supercomputer Interconnect System (OSMOSIS).

Karinou, Fotini; Deng, Lei; Lopez, Roberto Rodes; Prince, Kamau; Jensen, Jesper Bevensee; Monroy, Idelfonso Tafur

2013-06-01

369

Cell polarity and hyphal morphogenesis are controlled by multiple rho-protein modules in the filamentous ascomycete Ashbya gossypii.  

PubMed Central

Polarized cell growth requires a polarized organization of the actin cytoskeleton. Small GTP-binding proteins of the Rho-family have been shown to be involved in the regulation of actin polarization as well as other processes. Hyphal growth in filamentous fungi represents an ideal model to investigate mechanisms involved in generating cell polarity and establishing polarized cell growth. Since a potential role of Rho-proteins has not been studied so far in filamentous fungi we isolated and characterized the Ashbya gossypii homologs of the Saccharomyces cerevisiae CDC42, CDC24, RHO1, and RHO3 genes. The AgCDC42 and AgCDC24 genes can both complement conditional mutations in the S. cerevisiae CDC42 and CDC24 genes and both proteins are required for the establishment of actin polarization in A. gossypii germ cells. Agrho1 mutants show a cell lysis phenotype. Null mutant strains of Agrho3 show periodic swelling of hyphal tips that is overcome by repolarization and polar hyphal growth in a manner resembling the germination pattern of spores. Thus different Rho-protein modules are required for distinct steps during polarized hyphal growth of A. gossypii. PMID:11156982

Wendland, J; Philippsen, P

2001-01-01

370

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

371

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

372

Phosphatidylinositol 4,5-Bisphosphate Influences PIN Polarization by Controlling Clathrin-Mediated Membrane Trafficking in Arabidopsis[C][W  

PubMed Central

The functions of the minor phospholipid phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P2] during vegetative plant growth remain obscure. Here, we targeted two related phosphatidylinositol 4-phosphate 5-kinases (PI4P 5-kinases) PIP5K1 and PIP5K2, which are expressed ubiquitously in Arabidopsis thaliana. A pip5k1 pip5k2 double mutant with reduced PtdIns(4,5)P2 levels showed dwarf stature and phenotypes suggesting defects in auxin distribution. The roots of the pip5k1 pip5k2 double mutant had normal auxin levels but reduced auxin transport and altered distribution. Fluorescence-tagged auxin efflux carriers PIN-FORMED (PIN1)–green fluorescent protein (GFP) and PIN2-GFP displayed abnormal, partially apolar distribution. Furthermore, fewer brefeldin A–induced endosomal bodies decorated by PIN1-GFP or PIN2-GFP formed in pip5k1 pip5k2 mutants. Inducible overexpressor lines for PIP5K1 or PIP5K2 also exhibited phenotypes indicating misregulation of auxin-dependent processes, and immunolocalization showed reduced membrane association of PIN1 and PIN2. PIN cycling and polarization require clathrin-mediated endocytosis and labeled clathrin light chain also displayed altered localization patterns in the pip5k1 pip5k2 double mutant, consistent with a role for PtdIns(4,5)P2 in the regulation of clathrin-mediated endocytosis. Further biochemical tests on subcellular fractions enriched for clathrin-coated vesicles (CCVs) indicated that pip5k1 and pip5k2 mutants have reduced CCV-associated PI4P 5-kinase activity. Together, the data indicate an important role for PtdIns(4,5)P2 in the control of clathrin dynamics and in auxin distribution in Arabidopsis. PMID:24326589

Ischebeck, Till; Werner, Stephanie; Krishnamoorthy, Praveen; Lerche, Jennifer; Meijón, Mónica; Stenzel, Irene; Löfke, Christian; Wiessner, Theresa; Im, Yang Ju; Perera, Imara Y.; Iven, Tim; Feussner, Ivo; Busch, Wolfgang; Boss, Wendy F.; Teichmann, Thomas; Hause, Bettina; Persson, Staffan; Heilmann, Ingo

2013-01-01

373

Applying the data fusion method to evaluation of the performance of two control signals in monitoring polarization mode dispersion effects in fiber optic links  

NASA Astrophysics Data System (ADS)

With increasing distance and bit rate in fiber optic links the effects of polarization mode dispersion (PMD) have been highlighted. Since PMD has a statistical nature, using a control signal that can provide accurate information to dynamically tune a PMD compensator is of great importance. In this paper, we apply the data fusion method with the aim of introducing a method that can be used to evaluate more accurately the performance of control signals before applying them in a PMD compensation system. Firstly, the minimum and average degree of polarization (DOP_min and DOP_ave respectively) as control signals in monitoring differential group delay (DGD) for a system including all-order PMD are calculated. Then, features including the amounts of sensitivity and ambiguity in DGD monitoring are calculated for NRZ data format as DGD to bit time (DGD/T) varies. It is shown that each of the control signals mentioned has both positive and negative features for efficient DGD monitoring. Therefore, in order to evaluate features concurrently and increase reliability, we employ data fusion to fuse features of each control signal, which makes evaluating and predicting the performance of control signals possible, before applying them in a real PMD compensation system. Finally, the reliability of the results obtained from data fusion is tested in a typical PMD compensator.

Dashtbani Moghari, M.; Rezaei, P.; Habibalahi, A.

2015-02-01

374

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

375

Parallel pipeline networking and signal processing with field-programmable gate arrays (FPGAs) and VCSEL-MSM smart pixels  

NASA Astrophysics Data System (ADS)

We present a networking and signal processing architecture called Transpar-TR (Translucent Smart Pixel Array-Token- Ring) that utilizes smart pixel technology to perform 2D parallel optical data transfer between digital processing nodes. Transpar-TR moves data through the network in the form of 3D packets (2D spatial and 1D time). By utilizing many spatial parallel channels, Transpar-TR can achieve high throughput, low latency communication between nodes, even with each channel operating at moderate data rates. The 2D array of optical channels is created by an array of smart pixels, each with an optical input and optical output. Each smart pixel consists of two sections, an optical network interface and ALU-based processor with local memory. The optical network interface is responsible for transmitting and receiving optical data packets using a slotted token ring network protocol. The smart pixel array operates as a single-instruction multiple-data processor when processing data. The Transpar-TR network, consisting of networked smart pixel arrays, can perform pipelined parallel processing very efficiently on 2D data structures such as images and video. This paper discusses the Transpar-TR implementation in which each node is the printed circuit board integration of a VCSEL-MSM chip, a transimpedance receiver array chip and an FPGA chip.

Kuznia, C. B.; Sawchuk, Alexander A.; Zhang, Liping; Hoanca, Bogdan; Hong, Sunkwang; Min, Chris; Pansatiankul, Dhawat E.; Alpaslan, Zahir Y.

2000-05-01

376

Polar Coordinates  

NSDL National Science Digital Library

This activity allows the user to explore the polar coordinate system. The applet is similar to GraphIt, but instead allows users to explore the representation of a function in the polar coordinate system.

377

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.

2011-12-05

378

Polar Projection  

NSDL National Science Digital Library

This online demonstration shows students how a polar projection map is created. A brief overview discusses the way some map projections can distort the polar regions, making them appear much larger than they really are.The short animation shows how mapmakers transform the round Earth into an accurate polar projection map.

379

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

380

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

381

Broadband composite polarization rotator  

NASA Astrophysics Data System (ADS)

We describe a broadband optical device that is capable of rotating the polarization plane of a linearly polarized light at any desired angle over a wide range of wavelengths. The device is composed of a sequence of half-wave plates rotated at specific angles with respect to their fast-polarization axes. This design draws on an analogy with composite pulses, which is a well-known control technique from quantum physics. We derive the solutions for the rotation angles of the single half-wave plates depending on the desired polarization rotation angle. We show that the broadband polarization rotator is robust against variations of the parameters of both the crystal and the light field.

Rangelov, Andon A.; Kyoseva, Elica

2015-03-01

382

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

383

Dynamics of voltage polarity reversal as the controlling factor in space-charge induced breakdown of insulating polymers  

Microsoft Academic Search

Our investigation is focused on the understanding of high-field phenomena in polymers. In highly insulating materials such as polyethylene, space charge has a strong influence on both the short and long term breakdown strengths. The aim of this report is to demonstrate and discuss the importance of the dynamics of voltage polarity reversal at the injecting needle electrode on space

M. Mammeri; C. Laurent; M. Nedjar

1997-01-01

384

Flamingo controls the planar polarity of sensory bristles and asymmetric division of sensory organ precursors in Drosophila  

Microsoft Academic Search

The sensory bristles of the fruit fly Drosophila are organized in a polarized fashion such that bristles on the thorax point posteriorly. These bristles are derived from asymmetric division of sensory organ precursors (SOPs). The Numb protein, which is localized asymmetrically in a cortical crescent in each SOP, segregates into only one of the two daughter cells during cell division,

Bingwei Lu; Tadao Usui; Tadashi Uemura; Lily Jan; Yuh-Nung Jan

1999-01-01

385

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

386

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

387

High-power Yb-fiber comb with feed-forward control of nonlinear-polarization-rotation mode-locking and large-mode-area fiber amplification.  

PubMed

We report on a simple scheme to precisely control carrier-envelope phase of a nonlinear-polarization-rotation mode-locked self-started Yb-fiber laser system with an average output power of ?7??W and a pulse width of 130 fs. The offset frequency was locked to the repetition rate of ?64.5??MHz with a relative linewidth of ?1.4??MHz by using a self-referenced feed-forward scheme based on an acousto-optic frequency shifter. The phase noise and timing jitter were calculated to be 370 mrad and 120 as, respectively. PMID:22555721

Yan, Ming; Li, Wenxue; Yang, Kangwen; Zhou, Hui; Shen, Xuling; Zhou, Qian; Ru, Qitian; Bai, Dongbi; Zeng, Heping

2012-05-01

388

120 Gbit/s, polarization-multiplexed 10 Gsymbol/s, 64 QAM coherent transmission over 150 km using an optical voltage controlled oscillator.  

PubMed

We report a polarization-multiplexed, 10 Gsymbol/s 64 QAM coherent transmission over 150 km using an optical voltage controlled oscillator (OVCO). The OVCO enables us to realize a low phase noise optical phase-locked loop (OPLL) due to its wideband operation independent of the frequency modulation (FM) bandwidth of an LD. As a result, 120 Gbit/s, 64 QAM data were successfully transmitted over 150 km with a power penalty as low as 1 dB. PMID:24514339

Wang, Yixin; Kasai, Keisuke; Omiya, Tatsunori; Nakazawa, Masataka

2013-11-18

389

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

390

Single-mode electrically pumped GaSb-based VCSELs emitting continuous-wave at 2.4 and 2.6 ?m  

NASA Astrophysics Data System (ADS)

Vertical-cavity surface-emitting lasers (VCSELs) are perfect light sources for spectroscopic applications, where properties such as continuous-wave (cw) operation, single-mode emission, high lifetime and often low power consumption are crucial. For applications such as tunable diode laser absorption spectroscopy (TDLAS), there is a growing interest in laser devices emitting in the near- to mid-infrared wavelength range, where many environmentally and technologically important gases show strong absorption lines. The (AlGaIn)(AsSb) material system based on GaSb is the material of choice for covering the 2.0-3.3 ?m range. In this paper, we report on electrically pumped single-mode VCSELs with emission wavelengths of 2.4 and 2.6 ?m, operating cw at room temperature and beyond. By (electro-) thermal tuning, the emission wavelength can be tuned mode-hop free over a range of several nanometers. In addition, low threshold currents of several milliamperes promise mobile application. In the devices, a structured buried tunnel junction with subsequent overgrowth has been used in order to achieve efficient current confinement, reduced optical losses and increased electrical conductivity. Furthermore, strong optical confinement is introduced in the lasers due to laterally differing cavity lengths.

Bachmann, Alexander; Arafin, Shamsul; Kashani-Shirazi, Kaveh

2009-12-01

391

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

392

Electrical control of valley and spin polarized current and tunneling magnetoresistance in a silicene-based magnetic tunnel junction  

NASA Astrophysics Data System (ADS)

We investigate the electronic transport in a silicene-based ferromagnetic metal/ferromagnetic insulator/ferromagnetic metal tunnel junction. The results show that the valley and spin transports are strongly dependent on local application of a vertical electric field and effective magnetization configurations of the ferromagnetic layers. In particular, it is found that the fully valley and spin polarized currents can be realized by tuning the external electric field. Furthermore, we also demonstrate that the tunneling magnetoresistance ratio in such a full magnetic junction of silicene is very sensitive to the electric field modulation.

Wang, Dali; Jin, Guojun

2014-07-01

393

Robust real-time 15.125 Gb/s adaptive optical OFDM transmissions over 100 m OM2 MMFs utilizing directly modulated VCSELs subject to optical injection locking.  

PubMed

Optical injection locking (OIL) is an effective approach for significantly enhancing the modulation bandwidths of VCSELs. The frequency responses of OIL-VCSELs are, however, very sensitive to the applied OIL conditions. This brings about strong difficulties in practically utilizing the OIL-enhanced modulation bandwidths to achieve highly robust transmission performances of directly modulated OIL-VCSEL-based multi-mode fibre (MMF) links for cost-sensitive application scenarios such as data-centers. In this paper, directly modulated OIL-VCSEL-based real-time dual-band optical OFDM (OOFDM) transceivers with tunability in both the electrical and optical domains are experimentally demonstrated, for the first time, utilizing DACs/ADCs at sampling speeds as low as 4GS/s. The transceivers can support 15.125 Gb/s adaptive OOFDM transmissions over 100 m OM2 MMF links based on intensity modulation and direct detection. More importantly, the adaptability and tunability of the demonstrated transceivers enable the achievement of excellent robustness of the aggregated OOFDM transmission capacity to OIL condition variations. It is shown that, over a large diversity of OIL conditions that give rise to significantly different system frequency responses, the aggregated OOFDM transmission capacity only vary by <11% in the aforementioned transmission link. PMID:24515076

Zhang, H B; Yi, X W; Zhang, Q W; Ling, Y; Deng, M L; Hugues-Salas, E; Giddings, R P; Hong, Y; Wang, M; Tang, J M

2014-01-13

394

Development of polarization-controlled multi-pass Thomson scattering system in the GAMMA 10 tandem mirror.  

PubMed

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. PMID:23126991

Yoshikawa, M; Yasuhara, R; Morimoto, M; Shima, Y; Kohagura, J; Sakamoto, M; Nakashima, Y; Imai, T; Yamada, I; Kawahata, K; Funaba, H; Minami, T

2012-10-01

395

Epidermal Growth Factor Signalling Controls Myosin II Planar Polarity to Orchestrate Convergent Extension Movements during Drosophila Tubulogenesis  

PubMed Central

Most epithelial tubes arise as small buds and elongate by regulated morphogenetic processes including oriented cell division, cell rearrangements, and changes in cell shape. Through live analysis of Drosophila renal tubule morphogenesis we show that tissue elongation results from polarised cell intercalations around the tubule circumference, producing convergent-extension tissue movements. Using genetic techniques, we demonstrate that the vector of cell movement is regulated by localised epidermal growth factor (EGF) signalling from the distally placed tip cell lineage, which sets up a distal-to-proximal gradient of pathway activation to planar polarise cells, without the involvement for PCP gene activity. Time-lapse imaging at subcellular resolution shows that the acquisition of planar polarity leads to asymmetric pulsatile Myosin II accumulation in the basal, proximal cortex of tubule cells, resulting in repeated, transient shortening of their circumferential length. This repeated bias in the polarity of cell contraction allows cells to move relative to each other, leading to a reduction in cell number around the lumen and an increase in tubule length. Physiological analysis demonstrates that animals whose tubules fail to elongate exhibit abnormal excretory function, defective osmoregulation, and lethality. PMID:25460353

Bunt, Stephanie; Bischoff, Marcus; VijayRaghavan, Krishnaswamy; Skaer, Helen

2014-01-01

396

Epidermal growth factor signalling controls myosin II planar polarity to orchestrate convergent extension movements during Drosophila tubulogenesis.  

PubMed

Most epithelial tubes arise as small buds and elongate by regulated morphogenetic processes including oriented cell division, cell rearrangements, and changes in cell shape. Through live analysis of Drosophila renal tubule morphogenesis we show that tissue elongation results from polarised cell intercalations around the tubule circumference, producing convergent-extension tissue movements. Using genetic techniques, we demonstrate that the vector of cell movement is regulated by localised epidermal growth factor (EGF) signalling from the distally placed tip cell lineage, which sets up a distal-to-proximal gradient of pathway activation to planar polarise cells, without the involvement for PCP gene activity. Time-lapse imaging at subcellular resolution shows that the acquisition of planar polarity leads to asymmetric pulsatile Myosin II accumulation in the basal, proximal cortex of tubule cells, resulting in repeated, transient shortening of their circumferential length. This repeated bias in the polarity of cell contraction allows cells to move relative to each other, leading to a reduction in cell number around the lumen and an increase in tubule length. Physiological analysis demonstrates that animals whose tubules fail to elongate exhibit abnormal excretory function, defective osmoregulation, and lethality. PMID:25460353

Saxena, Aditya; Denholm, Barry; Bunt, Stephanie; Bischoff, Marcus; VijayRaghavan, Krishnaswamy; Skaer, Helen

2014-12-01

397

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

398

Polarization Imaging Apparatus  

NASA Technical Reports Server (NTRS)

A polarization imaging apparatus has shown promise as a prototype of instruments for medical imaging with contrast greater than that achievable by use of non-polarized light. The underlying principles of design and operation are derived from observations that light interacts with tissue ultrastructures that affect reflectance, scattering, absorption, and polarization of light. The apparatus utilizes high-speed electro-optical components for generating light properties and acquiring polarization images through aligned polarizers. These components include phase retarders made of OptoCeramic (registered TradeMark) material - a ceramic that has a high electro-optical coefficient. The apparatus includes a computer running a program that implements a novel algorithm for controlling the phase retarders, capturing image data, and computing the Stokes polarization images. Potential applications include imaging of superficial cancers and other skin lesions, early detection of diseased cells, and microscopic analysis of tissues. The high imaging speed of this apparatus could be beneficial for observing live cells or tissues, and could enable rapid identification of moving targets in astronomy and national defense. The apparatus could also be used as an analysis tool in material research and industrial processing.

Zou, Yingyin K.; Chen, Qiushui

2010-01-01

399

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

400

Normalized Polarization Ratios for the Analysis of Cell Polarity  

PubMed Central

The quantification and analysis of molecular localization in living cells is increasingly important for elucidating biological pathways, and new methods are rapidly emerging. The quantification of cell polarity has generated much interest recently, and ratiometric analysis of fluorescence microscopy images provides one means to quantify cell polarity. However, detection of fluorescence, and the ratiometric measurement, is likely to be sensitive to acquisition settings and image processing parameters. Using imaging of EGFP-expressing cells and computer simulations of variations in fluorescence ratios, we characterized the dependence of ratiometric measurements on processing parameters. This analysis showed that image settings alter polarization measurements; and that clustered localization is more susceptible to artifacts than homogeneous localization. To correct for such inconsistencies, we developed and validated a method for choosing the most appropriate analysis settings, and for incorporating internal controls to ensure fidelity of polarity measurements. This approach is applicable to testing polarity in all cells where the axis of polarity is known. PMID:24963926

Shimoni, Raz; Pham, Kim; Yassin, Mohammed; Ludford-Menting, Mandy J.; Gu, Min; Russell, Sarah M.

2014-01-01

401

Control of the recombination rate by changing the polarity of the electrolyte in dye-sensitized solar cells.  

PubMed

Recombination in Dye-sensitized Solar Cells (DSCs) is an electron transfer process critical for high efficiency. The chemical nature of the electron acceptor is known to have an important impact on recombination and, hence, limits the choice of hole conductors in DSCs and related solar cells. In this respect, Room Temperature Ionic liquids (RTILs) have been recognized as an alternative to volatile organic solvents due to their negligible vapor pressure, which offers the chance for long-term stability. However, RTIL-based electrolytes lead to lower performance, a feature that has been attributed to the high viscosity of ionic liquids and the mass-transport limitation associated with it. In this work we show that the origin of the lower performance is also related to an increase in the recombination loss due to the polar nature of the RTIL and the influence of the reorganization energy of the electron acceptor in a polar environment. To investigate this chemical effect, different mixing ratios of RTILs and an organic solvent (acetonitrile) have been considered. The fabricated devices have been characterized by small-perturbation techniques (Impedance Electrochemical Spectroscopy and Intensity-Modulated Photovoltage and Photocurrent Spectroscopies) and Open-Circuit Voltage Decay measurements, which have been used to extract electron lifetimes at different applied voltages. Two different ruthenium dyes (hydrophilic N719 and hydrophobic Z907) and two different cations in the RTIL (imidazolium- and pyrrolidinium-based) have been considered. The results obtained show that for pure ionic liquids the lifetime-voltage curve is exponential, which is a signature of large reorganization energies for electron transfer. In contrast, pure acetonitrile exhibits a non-exponential behavior, which is consistent with relatively low reorganization energy. Interestingly, and as a general rule, we find that recombination is faster in systems with higher reorganization energies. This is interpreted as a consequence of the availability of more acceptor states for electron transfer. In addition, it is found that mixing RTILs and acetonitrile is an interesting strategy to increase the stability of DSCs without significant recombination losses, provided that the right dye and RTIL, in particular, a pyrrolidinium component, are used. PMID:25184736

Idigoras, Jesús; Tena-Zaera, Ramón; Anta, Juan A

2014-10-21

402

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

403

Controlling interface oxygen for forming Ag ohmic contact to semi-polar (1 1 -2 2) plane p-type GaN  

NASA Astrophysics Data System (ADS)

Low-resistance Ag ohmic contacts to semi-polar (1 1 -2 2) p-GaN were developed by controlling interfacial oxide using a Zn layer. The 300 °C-annealed Zn/Ag samples showed ohmic behavior with a contact resistivity of 6.0 × 10-4 ? cm2 better than that of Ag-only contacts (1.0 × 10-3 ? cm2). The X-ray photoemission spectroscopy (XPS) results showed that annealing caused the indiffusion of oxygen at the contact/GaN interface, resulting in the formation of different types of interfacial oxides, viz. Ga-oxide and Ga-doped ZnO. Based on the XPS and electrical results, the possible mechanisms underlying the improved electrical properties of the Zn/Ag samples are discussed.

Park, Jae-Seong; Han, Jaecheon; Seong, Tae-Yeon

2014-11-01

404

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

405

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

406

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

407

Reduction of phase-induced intensity noise in a fiber-based coherent Doppler lidar using polarization control.  

PubMed

Optimization of signal-to-noise ratio is an important aspect in the design of optical heterodyne detection systems such as a coherent Doppler lidar (CDL). In a CDL, optimal performance is achieved when the noise in the detector signal is dominated by local oscillator shot-noise. Most modern CDL systems are built using rugged and cost-efficient fiber optic components. Unfortunately, leakage signals such as residual reflections inherent within fiber components (e.g. circulator) can introduce phase-induced intensity noise (PIIN) to the Doppler spectrum in a CDL. Such excess noise may be a few orders of magnitude above the shot-noise level within the relevant CDL frequency bandwidth--corrupting the measurement of typically weak backscattered signals. In this study, observation of PIIN in a fiber-based CDL with a master-oscillator power-amplifier tapered semiconductor laser source is reported. Furthermore, we experimentally demonstrate what we believe is a newly proposed method using a simple polarization scheme to reduce PIIN by more than an order of magnitude. PMID:20389545

Rodrigo, Peter John; Pedersen, Christian

2010-03-01

408

An ultra-bright white LED based non-contact skin cancer imaging system with polarization control  

NASA Astrophysics Data System (ADS)

Early detection and excision of melanoma skin cancer is crucial for a successful therapy. Dermoscopy in direct contact with the skin is routinely used for inspection, but screening is time consuming for high-risk patients with a large number of nevi. Features like symmetry, border, color and most importantly changes like growth or depigmentation of a nevus may indicate malignancy. We present a non-contact remote imaging system for human melanocytic nevi with homogenous illumination by an ultra-bright white LED. The advantage compared to established dermoscopy systems requiring direct skin contact is that deformation of raised nevi is avoided and full-body scans of the patients may time-efficiently be obtained while they are in a lying, comfortable position. This will ultimately allow for automated screening in the future. In addition, calibration of true color rendering, which is essential for distinguishing between benign and malignant lesions and to ensure reproducibility and comparison between individual check-ups in order to follow nevi evolution is implemented as well as suppression of specular highlights on the skin surface by integration of polarizing filters. Important features of the system which will be crucial for future integration into automated systems are the possibility to record images without artifacts in combination with short exposure times which both reduce image blurring caused by patient motion.

Günther, A.; Basu, C.; Roth, B.; Meinhardt-Wollweber, M.

2013-06-01

409

Isotropically Polarized Speckle Patterns  

NASA Astrophysics Data System (ADS)

The polarization of the light scattered by an optically dense and random solution of dielectric nanoparticles shows peculiar properties when the scatterers exhibit strong electric and magnetic polarizabilities. While the distribution of the scattering intensity in these systems shows the typical irregular speckle patterns, the helicity of the incident light can be fully conserved when the electric and magnetic polarizabilities of the scatterers are equal. We show that the multiple scattering of helical beams by a random dispersion of "dual" dipolar nanospheres leads to a speckle pattern exhibiting a perfect isotropic constant polarization, a situation that could be useful in coherent control of light as well as in lasing in random media.

Schmidt, Mikolaj K.; Aizpurua, Javier; Zambrana-Puyalto, Xavier; Vidal, Xavier; Molina-Terriza, Gabriel; Sáenz, Juan José

2015-03-01

410

480 Mbit/s UWB bi-directional radio over fiber CWDM PON using ultra-low cost and power VCSELs.  

PubMed

Radio-over-fiber (RoF) schemes offer the possibility of permitting direct access to native format services for the domestic user. A low power requirement and cost effectiveness are crucial to both the service provider and the end user. Here, we present an ultra-low cost and power RoF scheme using direct modulation of commercially-available 1344 nm and 1547 nm VCSELs by band-group 1 UWB wireless signals (ECMA-368) at near broadcast power levels. As a result, greatly simplified electrical-optical-electrical conversion is accomplished. A successful demonstration over a transmission distance of 20.1 km is described using a SSMF, CWDM optical network. EVMs of better than -18.3 dB were achieved. PMID:22274019

Quinlan, Terence; Morant, Maria; Dudley, Sandra; Llorente, Roberto; Walker, Stuart

2011-12-12

411

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

412

Polarization Considerations  

NASA Technical Reports Server (NTRS)

As light passes through a optical system the reflections and refractions will in general change the polarization state of the light. If we assume that all of the materials in the thin film coatings and substrate are isotropic and homogeneous then calculating the amount of "instrumental" polarization is a relatively straight forward task. In the following sections we will present a of the steps required to perform a 'polarization ray trace' calculation for a single ray and monochromatic and hence polarized light. The thin film portion of the calculation is also shown. The reason for explicitly showing the thin film equations is that there are sign conventions imposed on the boundary value equations by the orientation and handedness of the various coordinate frames which are attached to the geometric rays. The attenuation of light through a optical system, is relatively simple, and requires at the very least a lens (average) reflectivity or transmissivity. Determining the polarization sensitivity of a optical system is still relatively straight forward requiring at least a knowledge of the behavior of the "s" and "p" components at each interface for the chief ray. Determining the thin film induced aberrations of a optical system are somewhat more demanding. Questions about the arithmetic sign of the phase factors and how this relates to the overall "OPD" of a ray are ubiquitous. Many rays are required to construct a wavefront. Thin film codes which modify the OPD's of rays are a requirement for this last mentioned computation. This requires a consistent scheme of coordinate frames and sign conventions and is probably the most demanding task of a polarization ray trace. Only the electric field will used in the discussion. This is not a restriction as the Stokes parameters are functions of the electric field. The following does not attempt to explain, but only to present all of the required concepts and formulas.

Waluschka, Eugene

1998-01-01

413

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

414

CONFIGURATION MANUAL POLARIZED PROTON COLLIDER AT RHIC.  

SciTech Connect

In this report, the authors present their 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. They 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.; MACKAY,W.W.; ALEKSEEV,I.; BAI,M.; BROWN,K.; BUNCE,G.; CAMERON,P.; COURANT,E.; ET AL.

2001-03-01

415

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, I.; Allgower, C.; Bai, M.; Batygin, Y.; et al

2006-01-01

416

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 bear’s 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

417

Turning on and off the Immunological Switch: Immune Response Polarization and Its Control by IL10 and STAT3  

Microsoft Academic Search

\\u000a The innate and immunologic arms of host resistance to pathogenic infections use distinct patterns of cytokine production to\\u000a direct appropriate tissue responses. This chapter discusses how this “Immunological Switch” is coordinated by distinct T helper\\u000a cell lineages and how IL-10 and STAT3 signaling controls the inflammatory response. A particular emphasis is given to the\\u000a role of IL-10 and STAT3 in

C. Andrew Stewart; Giorgio Trinchieri

418

INJECTION ELECTRODE POLARIZATION RESISTIVITY AND INDUCED POLARIZATION  

E-print Network

INJECTION ELECTRODE POLARIZATION IN RESISTIVITY AND INDUCED POLARIZATION J.B. Merriam University.merriam@usask.ca Abstract Polarization of injection electrodes in resistivity and induced polarization may reach several will only be a problem if the received signal is very much smaller than the polarization. In induced

Merriam, James

419

Uniformly elliptically-polarized vector optical fields  

NASA Astrophysics Data System (ADS)

We present a modified, more universal scheme for generating vector fields. Here we design in principle and experimentally generate a new kind of uniformly elliptically polarized vector field, which has the same ellipticity and sense of local elliptic polarization at any location and also has a flexibly designable distribution of orientation of the elliptic polarization. An introduced additional degree of freedom is used to flexibly change the ellipticity. In particular, the ellipticity and the orientation of polarization can be independently controlled by two parameters. This makes it easier to both control the spatial structure of the polarization and to engineer the focusing field.

Pan, Yue; Ren, Zhi-Cheng; Qian, Sheng-Xia; Gao, Xu-Zhen; Li, Yongnan; Tu, Chenghou; Wang, Hui-Tian

2015-03-01

420

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

421

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

422

Dynamic nuclear polarization from current-induced electron spin polarization  

NASA Astrophysics Data System (ADS)

Current-induced electron spin polarization is shown to produce nuclear hyperpolarization through dynamic nuclear polarization. Saturated fields of several millitesla are generated upon the application of an electric field over a time scale of 100 s in InGaAs epilayers and measured using optical Larmor magnetometry. We show that, in contrast to previous demonstrations of current-induced dynamic nuclear polarization, the direction of the current relative to the crystal axis and external magnetic field may be used to control the magnitude and direction of the saturation nuclear field.

Trowbridge, C. J.; Norman, B. M.; Kato, Y. K.; Awschalom, D. D.; Sih, V.

2014-08-01

423

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

424

Differential expression control and polarized distribution of plasma membrane-resident SYP1 SNAREs in Arabidopsis thaliana.  

PubMed

Membrane trafficking to the plasma membrane (PM) is a highly organized process which enables plant cells to build up their bodies. SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) genes, which encode the proteins involved in membrane trafficking, are much more abundant in the Arabidopsis genome than in that of any other eukaryote. We have previously shown that a large number of SNARE molecules in the Arabidopsis cell are localized predominantly on the PM. In the present study, in order to elucidate the physiological function of each PM-localized SNARE, we analyzed the spatiotemporal expression profiling of nine SYP1s that are resident in the PM of Arabidopsis, and used the information thus acquired to generate transgenic Arabidopsis plants expressing green fluorescent protein-fused Qa-SNAREs under control of their authentic promoters. Among the nine SYP1s, only SYP132 is expressed ubiquitously in all tissues throughout plant development. The expression patterns of the other SYP1s, in contrast, are tissue specific, and all different from one another. A particularly noteworthy example is SYP123, which is predominantly expressed in root hair cells during root development, and shows a focal accumulation pattern at the tip region of root hairs. These results suggest that SYP132 is involved in constitutive membrane trafficking to the PM throughout plant development, while the other SYP1s are involved in membrane trafficking events such as root formation or tip growth of root hair, with some redundancy. PMID:19098073

Enami, Kazuhiko; Ichikawa, Mie; Uemura, Tomohiro; Kutsuna, Natsumaro; Hasezawa, Seiichiro; Nakagawa, Tsuyoshi; Nakano, Akihiko; Sato, Masa H

2009-02-01

425

A 10 GHz polarization scanning reference source  

NASA Astrophysics Data System (ADS)

Amplitude and phase control of two orthogonal linear polarized RF waves provide a very versatile means for producing a time varying linear polarization scanning reference source. Dynamic control of the state of polarization of the radiated EM wave offers unique scan patterns, which lead to robust recovery of attitude angular information of various flying platforms, such as unmanned aerial vehicles. Data taken in an anechoic chamber confirms the efficacy of the technique.

Dhadwal, Harbans S.; Rastegar, Jahangir

2014-06-01

426

Focusing through turbid media by polarization modulation  

E-print Network

We demonstrate that polarization modulation of an illumination beam can effectively control the spatial profile of the light transmitted through turbid media. Since the transmitted electric fields are completely mingled in turbid media, polarization states of an illumination beam can be effectively used to control the propagation of light through turbid media. Numerical simulations were performed which agree with experimental results obtained using a commercial in-plane switching liquid-crystal display for modulating the input polarization states.

Park, Jongchan; Yu, Hyeonseung; Park, YongKeun

2015-01-01

427

Control of the Polarity of the Interplanetary Magnetic Field on the Dawn-Dusk Symmetry of the Magnetopause  

NASA Astrophysics Data System (ADS)

The solar wind dynamic pressure is reduced when the solar wind flows around the magnetosphere due to the diversion of the flows. The magnetopause is the boundary where the reduced dynamic pressure is balanced with the magnetic pressure of the compressed magnetosphere by the solar wind. The size and shape of the magnetopause have long been considered among the most important parameters in Solar Terrestrial physics. Previous models of the size and shape of the magnetopause often assumed the axis- symmetry of the magnetopause with respect to the Sun-Earth line. With a large number of magnetopause crossings by ISEE-1 and -2, AMPTE/IRM, Hawkeye, Geotail, Interball-1, and Magion-4, we are able to consider the asymmetry of the magnetopuase. In the Shue et al. [1997] model, the magnetopause was modeled by two parameters, r0 and alpha, representing the subsolar standoff distance and the flaring level of the magnetopause, respectively. Parameter alpha was assumed to be independent of phi in the Shue et al. [1997] model, where phi is the angle between the Z axis and the mapping of the radial vector of the magnetopause on the YZ plane. In the present study we allow alpha to be a function of phi. We separate crossings with different phis and fit them in each bin to the new functional form proposed by Shue et al. [1997]. We find that the magnetopause is symmetric in the dawn-dusk direction for northward IMF. However, its size on the dawnside becomes larger when the IMF is southward. The function of alpha in terms of phi can be combined with the 2-D Shue et al. [1997] model into a 3-D magnetopause model. (Shue, J.-H., J. K. Chao, H. C. Fu, C. T. Russell, P. Song, K. K. Khurana, and H. J. Singer, A new functional form to study the solar wind control of the magnetopause size and shape, J. Geophys. Res., 102, 9497, 1997.)

Shue, J.; Jhuang, B.; Song, P.; Safrankova, J.; Nemecek, Z.; Russell, C. T.; Chen, S.

2008-12-01

428

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

429

Evolution of an N-level system via automated vectorization of the Liouville equations and application to optically controlled polarization rotation  

E-print Network

The Liouville equation governing the evolution of the density matrix for an atomic/molecular system is expressed in terms of a commutator between the density matrix and the Hamiltonian, along with terms that account for decay and redistribution. For finding solutions of this equation, it is convenient first to reformulate the Liouville equation by defining a vector corresponding to the elements of the density operator, and determining the corresponding time-evolution matrix. For a system of N energy levels, the size of the evolution matrix is N2xN2. When N is very large, evaluating the elements of these matrices becomes very cumbersome. We describe a novel algorithm that can produce the evolution matrix in an automated fashion for an arbitrary value of N. As a non-trivial example, we apply this algorithm to a fifteen-level atomic system used for producing optically controlled polarization rotation. We also point out how such a code can be extended for use in an atomic system with arbitrary number of energy le...

Shahriar, M S; Krishnamurthy, Subramanian; Tu, Y; Pati, G S; Tseng, S

2013-01-01

430

Evolution of an N-level system via automated vectorization of the Liouville equations and application to optically controlled polarization rotation  

E-print Network

The Liouville equation governing the evolution of the density matrix for an atomic/molecular system is expressed in terms of a commutator between the density matrix and the Hamiltonian, along with terms that account for decay and redistribution. For finding solutions of this equation, it is convenient first to reformulate the Liouville equation by defining a vector corresponding to the elements of the density operator, and determining the corresponding time-evolution matrix. For a system of N energy levels, the size of the evolution matrix is N2xN2. When N is very large, evaluating the elements of these matrices becomes very cumbersome. We describe a novel algorithm that can produce the evolution matrix in an automated fashion for an arbitrary value of N. As a non-trivial example, we apply this algorithm to a fifteen-level atomic system used for producing optically controlled polarization rotation. We also point out how such a code can be extended for use in an atomic system with arbitrary number of energy levels.

M. S. Shahriar; Ye Wang; Subramanian Krishnamurthy; Y. Tu; G. S. Pati; S. Tseng

2013-09-04

431

Anisotropic photo-control of spontaneous polarization in BiFeO3 thin films: Indications of photo-assisted magnetoelectric effect  

NASA Astrophysics Data System (ADS)

The terahertz (THz) emission from multiferroic BiFeO3 (BFO) due to ultra-fast depolarization of electric order helps in evaluating its ferroelectric behavior [1]. In this work, we investigate THz-emission in BFO films on (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) substrates along (100), (110) and (111) directions. THz emission amplitude (ETHz) and its electric field dependence are similar in BFO (100) and BFO (110); ETHz as function of electric field translates to ferroelectric-like hysteresis loop, and sign and amplitude of THz-emission are commensurate with the applied electric field. On the contrary, in BFO (111) the hysteretic loop is absent, ETHz varies linearly with electric field and the polarity of THz-emission is opposite to that of the electric field. These results suggest that THz-emission is mainly a result of ultrafast depolarization but with a superimposed character of ultrafast reorientation or demagnetization of antiferromagnetic (AFM) order. Though AFM order in BFO makes the determination of magnetoelectric (ME) coupling rather difficult, the photo-assisted electric field control of AFM order shown in the present work is suggestive of photo-assisted ME effect. 1. K. Takahashi et al., Phys. Rev. Lett. 96, 117402 (2006).

Rana, D. S.; Kawayama, I.; Murakami, H.; Tonouchi, M.

2008-03-01