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1

Nonvolatile polarization control of a bistable VCSEL.  

PubMed

We report experimental evidence of nonvolatile all-optical memory operation using the two linear polarization states emitted from a GaAs oxide-confined VCSEL. The two polarization states coexist in a large range of pumping currents and substrate temperatures, and they can be controlled all-optically by exposing the device to polarization selective feedback, to crossed polarization reinjection orby injecting external light pulses. The active polarization state is recovered after powering off and on the VCSEL, while memory is lost if the substrate temperature is varied. PMID:23262865

Marconi, Mathias; Barland, Stéphane; Giudici, Massimo

2012-12-10

2

Polarization dynamics of VCSELs in external cavities  

NASA Astrophysics Data System (ADS)

We review the dynamics of VCSELs that experience both Polarization-Selective Feedback (PSF) and Crossed- Polarization Reinjection (XPR). Different regimes of regular pulsation were found. For strong enough XPR levels, the VCSEL emission in each of its linearly-polarized components displays a square-wave modulation which regularity is greatly enhanced by small levels of PSF. Such a square-wave is in antiphase for the two polarizations, and it turns out to be stable and robust over broad intervals of current. The frequency of the square-wave is determined by the length of the XPR arm. For weak levels of PSF and XPR, the VCSEL emits a regular train of short optical pulses arising from the locking of the modes in the PSF cavity. The frequency of the pulse train is stable on short time scales, but it wanders with a characteristic time scale of hundreds of roundtrips in the PSF cavity. The experimental results are successfully explained by an extension of the Spin-Flip Model that incorporates gain saturation and the effects of PSF and XPR.

Marconi, M.; Javaloyes, J.; Barland, S.; Balle, S.; Giudici, M.

2014-05-01

3

Experimental investigation of elliptically polarized injection-locked VCSELs  

NASA Astrophysics Data System (ADS)

Polarization switching (PS) between linear polarizations of a vertical-cavity surface-emitting laser (VCSEL) can appear when this device is subject to orthogonal optical injection. In this type of injection the injected field has a linear polarization orthogonal to that of the free-running VCSEL. In this situation interesting nonlinear dynamics appear, one of which is the existence of an injection-locked solution for which the two linear polarized modes of the VCSEL lock to the master laser frequency. This situation has been theoretically predicted and corresponds to an elliptically polarized injection-locked (EPIL) state. In this paper we report an experimental investigation of the dynamics of a long-wavelength single-transverse mode VCSEL subject to orthogonal optical injection. The free-running VCSEL emits a linearly polarized beam in the so called "parallel" direction. The polarization of the injected light is perpendicular to this state and is termed "orthogonal" polarization. We observe the EPIL state when the frequency of the orthogonal injected light is near the frequency of the parallel polarization. The spectral feature of the EPIL state is verified and the power of each polarization is measured. The EPIL region is measured in the frequency detuning-injected power plane. As current decreases, the frequency detuning range for the EPIL to exist is narrower and shifts toward the negative frequency detuning. Periodic dynamics in which both polarizations oscillate with a frequency very close to the relaxation oscillation frequency is found above the upper boundary of the EPIL region. Below the lower boundary of the EPIL zone, periodic dynamics is found only in the parallel polarization.

Lin, Hong; Pérez, Pablo; Valle, Angel; Pesquera, Luis

2014-05-01

4

Polarization-stable single-mode VCSELs for Cs-based MEMS atomic clock applications  

NASA Astrophysics Data System (ADS)

Vertical-cavity surface-emitting lasers (VCSELs) emitting at 894.6 nm wavelength have been fabricated for Cs-based atomic clock applications. For polarization control, a previously developed technique relying on the integration of a semiconducting surface grating in the top Bragg mirror of the VCSEL structure is employed. More specifically, we use a so-called inverted grating. The VCSELs are polarized orthogonal to the grating lines with no far-field diffraction side-lobes for sub-wavelength grating periods. Orthogonal polarization suppression ratios exceed 20 dB. The polarization stability has been investigated at different elevated substrate temperatures up to 80 °C, where the VCSEL remains polarization-stable even well above thermal roll-over. For the purpose of integration with the atomic clock microsystem, flip-chip-bondable VCSEL chips have been realized. Sub-mA threshold currents and sufficient output powers in the milliwatt range are achieved. The required modulation bandwidth of more than 5 GHz is reached at only 0.5mA bias. Maximum bandwidths above 10 GHz have been measured even at elevated temperatures up to 80 °C. Modulation current efficiency factors larger than 12 GHz/?mA are achieved at room temperature. Moreover, the intrinsic modulation characteristics of the VCSELs are investigated by precise curve fitting of measured small-signal modulation response curves and relative intensity noise spectra. A K-factor of less than 0.4 ns and a maximum 3 dB bandwidth exceeding 22 GHz are obtained.

Al-Samaneh, Ahmed; Renz, Simeon; Strodl, Andreas; Schwarz, Wolfgang; Wahl, Dietmar; Michalzik, Rainer

2010-04-01

5

Time-delay signature of chaos in 1550 nm VCSELs with variable-polarization FBG feedback.  

PubMed

Based on the framework of spin-flip model (SFM), the output characteristics of a 1550 nm vertical-cavity surface-emitting laser (VCSEL) subject to variable-polarization fiber Bragg grating (FBG) feedback (VPFBGF) have been investigated. With the aid of the self-correlation function (SF) and the permutation entropy (PE) function, the time-delay signature (TDS) of chaos in the VPFBGF-VCSEL is evaluated, and then the influences of the operation parameters on the TDS of chaos are analyzed. The results show that the TDS of chaos can be suppressed efficiently through selecting suitable coupling coefficient and feedback rate of the FBG, and is weaker than that of chaos generated by traditional variable-polarization mirror feedback VCSELs (VPMF-VCSELs) or polarization-preserved FBG feedback VCSELs (PPFBGF-VCSELs). PMID:25321044

Li, Yan; Wu, Zheng-Mao; Zhong, Zhu-Qiang; Yang, Xian-Jie; Mao, Song; Xia, Guang-Qiong

2014-08-11

6

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

7

In-line rotation sensor based on VCSEL behavior under polarization-rotating optical feedback.  

PubMed

Lasing behavior of a single-transverse-mode vertical-cavity surface-emitting laser (VCSEL) was observed while the polarization direction of an optical feedback was rotated. Optical powers of two polarization modes of a VCSEL showed sinusoidal dependences on the polarization-rotation angle. The power variation was seen when an optical feedback ratio was larger than -20 dB, though the variation depth dropped suddenly as the feedback ratio became smaller than -25 dB. An in-line type rotation sensor utilizing this behavior is proposed. The sensor system was constructed and the detection principle was demonstrated. PMID:22109394

Ura, Shogo; Shoda, Shinichiro; Nishio, Kenzo; Awatsuji, Yasuhiro

2011-11-21

8

Dual-channel chaos synchronization and communication based on unidirectionally coupled VCSELs with polarization-rotated optical feedback and polarization-rotated optical injection.  

PubMed

A novel dual-channel chaotic synchronization configuration is proposed. This system is constructed on the basis of two unidirectionally coupled vertical-cavity surface-emitting lasers (VCSELs), where a VCSEL subjected to polarization-rotated optical feedback is used as a transmitter and the other VCSEL subjected to polarization-rotated optical injection is used as a receiver. The synchronization and communication performances of such a system are numerically investigated. The results show that, similar to polarization-preserved coupled system with polarization-preserved optical feedback at the T-VCSEL port and polarization-preserved optical injection at the R-VCSEL port, such polarization-rotated coupled system can also realize complete synchronization between each pair of linear polarization (LP) modes and the total output of T-VCSEL and R-VCSEL. Compared with the polarization-preserved coupled system, this proposed system has higher tolerance to mismatched parameters. Furthermore, the average intensities of two orthogonal LP modes are almost the same so that this framework may be used to realize dual-channel chaos communication. Under the additive chaos modulation (ACM) encryption scheme, the encoded messages can be successfully extracted for both of orthogonal LP modes. PMID:19654666

Liu, Jiao; Wu, Zheng-Mao; Xia, Guang-Qiong

2009-07-20

9

VCSEL proliferation  

NASA Astrophysics Data System (ADS)

Since the commercialization of Vertical Cavity Surface Emitting Lasers (VCSELs) in 1996, Finisar's Advanced Optical Components Division has shipped well over 50 Million VCSELs. The vast majority of these were shipped into the data communications industry, which was essentially the only volume application until 2005. The driver for VCSEL manufacturing might well shift to the increasingly popular laser based optical mouse. The advantages of the laser based mouse over traditional LED mice include operation on a wider range of surfaces, higher resolution, and increased battery lifetime. What is the next application that will drive growth in VCSELs? This paper will offer a historical perspective on the emergence of VCSELs from the laboratory to reality, and the companies that have played key roles in VCSEL commercialization. Furthermore, a perspective on the market needs of future VCSEL development and applications is described.

Tatum, Jim

2007-02-01

10

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

11

Long-wavelength VCSELs for sensing applications  

NASA Astrophysics Data System (ADS)

Long-wavelength VCSELs with emission wavelengths beyond 1.3 ?m have seen a remarkable progress over the last decade. This success has been accomplished by using highly advanced device concepts which effectively overcome the fundamental technological drawbacks related with long-wavelength VCSELs such as inferior thermal properties and allow for the realization of lasers with striking device performance. In this presentation, we will give an overview on the state of the technology for long-wavelength VCSELs in conjunction with their opportunities in applications for optical sensing. While VCSELs based on InP are limited to maximum emission wavelengths around 2.3 ?m, even longer wavelengths up to the mid-infrared range beyond 3 ?m can be achieved with VCSELs based on GaSb. For near-infrared InP-based VCSELs, the output characteristics include sub-mA threshold currents, up to several milliwatts of singlemode output power and ultralow power consumption. New concepts for widely tunable VCSELs with tuning ranges up to 100 nm independent from the material system for the active region are also presented. Today, optical sensing by Tunable Diode Laser Spectroscopy is a fast emerging market. Gas sensing systems are used for a wide range of applications such as industrial process control, environmental monitoring and safety applications. With their inherent and compared to other laser types superior properties including enhanced current tuning rates, wavelength tuning ranges, modulation frequencies and power consumption, long-wavelength VCSELs are regarded as key components for TDLS applications.

Ortsiefer, M.; Rosskopf, J.; Neumeyr, C.; Gründl, T.; Grasse, C.; Chen, J.; Hangauer, A.; Strzoda, R.; Gierl, C.; Meissner, P.; Küppers, F.; Amann, M.-C.

2012-03-01

12

The design of a noble VCSEL with DOE  

NASA Astrophysics Data System (ADS)

A brand-new approach in developing VCSEL lense is presented in this paper. Using the laser process or yellow light lithography process, we can merge semiconductor laser and diffraction optics elements (DOE) to become a single semiconductor optoelectronic device. To match the surface topology of the DOE with the structure of semiconductor laser, the DOE is carved on the SiO II layer of the vertical-cavity surface-emitting laser (VCSEL). The chiseled optoelectronic semiconductor element becomes as a DOE-VCSEL device, it has the DOE function to control the emission distribution of the emitting laser.

Liang, Tsair-Chun; Chang, Sheng-Hsiung; Huang, Hsi-Shan

2007-09-01

13

1580 ELECTRONICS LETTERS 25th November 2010 Vol.46 No.24 doi: 10.1049/el.2010.9140 The first compact VCSEL with polarisation control  

E-print Network

the VCSEL suitable for low-power applications. The large extinction ratio of >21 dB is also an advantage servers or in remote sensing applications where space and energy consumption is an issue." Future-cost and high-volume solutions. New trends in VCSEL design, such as highly strained active regions (1.1 µm

Liebling, Michael

14

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

15

Dynamic Self-Locking of an OEO Containing a VCSEL  

NASA Technical Reports Server (NTRS)

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

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

2009-01-01

16

Recent Advances of VCSEL Photonics  

Microsoft Academic Search

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

Fumio Koyama

2006-01-01

17

Electrically controlling the polarizing direction of a graphene polarizer  

NASA Astrophysics Data System (ADS)

We theoretically demonstrate a polarizer with an electrically controllable polarizing direction in the far infrared range using two orthogonal periodic arrays of graphene ribbons, which have different widths and are supported on a dielectric film placed on a thick piece of metal. The operation mechanism originates from the polarization-dependent resonant absorption of the two orthogonal graphene ribbons, which can be respectively controlled with different external bias voltages. The operation wavelength can be expanded to terahertz (THz) radiation.

Zhu, Z. H.; Guo, C. C.; Liu, K.; Zhang, J. F.; Ye, W. M.; Yuan, X. D.; Qin, S. Q.

2014-09-01

18

Athermalization and on-chip multi-wavelength integration of VCSELs employing thermally actuated micromachined mirrors  

NASA Astrophysics Data System (ADS)

An athermal multi-wavelength vertical cavity surface emitting laser (VCSEL) array is demonstrated using a thermally actuated cantilever structure with different cantilever lengths. The cavity length of each VCSEL is precisely controlled via the deflection of the cantilever due to difference in the lattice constant of GaAlAs layers. Also, the thermally induced actuation of the cantilever reduces the cavity length as the ambient temperature increases, which compensates the thermal wavelength drift of the VCSEL. The wavelength drift could be reduced within ±0.017 nm/K, which is 4 times smaller than that of conventional VCSELs. The proposed multi-wavelength VCSEL array enables four wavelength channels with 2.5 nm spacing under uncooled operations.

Nakahama, M.; Sakaguchi, T.; Matsutani, A.; Koyama, F.

2014-09-01

19

Polarization dynamics in spin-polarized vertical-cavity surface-emitting lasers  

NASA Astrophysics Data System (ADS)

Spin-polarized lasers and especially spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs) are at- tractive novel spintronic devices providing functionalities and characteristics superior to their conventional purely charge-based counterparts. This applies in particular to ultrafast dynamics, modulation capability and chirp control of directly modulated lasers. Here we demonstrate that ultrafast oscillations of the circular polarization degree can be generated in VCSELs by pulsed spin injection which have the potential to reach frequencies beyond 100 GHz. These oscillations are due to the coupling of the carrier-spin-photon system via the optical birefringence for the linearly polarized laser modes in the micro-cavity and are principally decoupled from conventional relaxation oscillations of the carrier-photon system. Utilizing these polarization oscillations is a very promising path to ultrafast directly modulated spin-VCSELs in the near future as long as an effective concept can be developed to modulate or switch these polarization oscillations. After briefly reviewing the state of research in the emerging field of spin-VCSELs, we present a novel concept for controlled switching of polarization oscillations by use of multiple optical spin injection pulses. Depending on the amplitude and phase conditions of the excitation pulses, constructive or destructive interference of polarization oscillations leads to an excitation, stabilization or switch-off of these oscillations. Furthermore even short single polarization bursts can be generated with pulse widths only limited by the resonance frequency of the polarization oscillation. Consequently, this concept is an important building block for using spin controlled polarization oscillations for future communication applications.

Gerhardt, Nils C.; Höpfner, Henning; Lindemann, Markus; Hofmann, Martin R.

2014-08-01

20

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

21

Nuclear reactivity control using laser induced polarization.  

National Technical Information Service (NTIS)

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 sec...

C. D. Bowman

1989-01-01

22

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

23

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

24

Nonpolar III-nitride vertical-cavity surface emitting lasers with a polarization ratio of 100% fabricated using photoelectrochemical etching  

NASA Astrophysics Data System (ADS)

Photoelectrochemical (PEC) band gap selective undercut etching is discussed as an alternative technique to chemical-mechanical polishing and laser-lift off for substrate removal for III-nitride vertical-cavity surface-emitting lasers (VCSELs). A top-down PEC etch is also described, which offers the ability to epitaxially define an etch-stop layer, thereby achieving a high degree of cavity length control. The temperature-dependent lasing characteristics of m-plane VCSELs fabricated using PEC etching techniques are analyzed. Measurements of multiple VCSELs from the same wafer yielded lasing emission polarized along the a-direction with a polarization ratio of 100%, indicating that the entire array was uniformly polarized.

Holder, C. O.; Leonard, J. T.; Farrell, R. M.; Cohen, D. A.; Yonkee, B.; Speck, J. S.; DenBaars, S. P.; Nakamura, S.; Feezell, D. F.

2014-07-01

25

Dynamics of long-wavelength VCSELs subject to dual-beam optical injection  

NASA Astrophysics Data System (ADS)

We have studied experimentally and theoretically the nonlinear dynamics of a 1550 nm single transverse mode VCSEL subject to two-frequency orthogonal optical injection. In this type of injection both injected fields have a linear polarization that is orthogonal to that of the free-running VCSEL. We have found different behaviors that include irregular and periodic dynamics in the orthogonal polarization, periodic dynamics in both linear polarizations and a situation in which both linearly polarized modes lock to the most intense injection when its wavelength is close to the free-running laser wavelength. In this study we also analyze the generated high-frequency microwave signal found when the VCSEL is emitting only in the orthogonal polarization. The relative strength of peaks in the optical spectra at the frequencies of both master lasers depends on the behaviour of the VCSEL under single optical injection by the most intense master laser. The peak in the optical spectrum that appears at the frequency of the most intense master laser is larger than the peak that appears at the frequency of the other master laser, providing that there is stable locking when only light from the most intense laser is injected. In this case a significant emission of the VCSEL at the frequency of the most intense master laser is observed. On the contrary, if there is not stable locking when only light from the most intense laser is injected, the magnitude of both peaks becomes similar and a significant emission of the VCSEL at the frequency of the weakest master laser is observed. Good agreement is found between our experimental and theoretical results.

Pérez, Pablo; Quirce, Ana; Consoli, Antonio; Valle, Angel; Noriega, Ignacio; Pesquera, Luis; Esquivias, Ignacio

2014-05-01

26

Polarization selection and sensitivity of external cavity vertical-cavity surface-emitting laser diodes  

Microsoft Academic Search

A theoretical analysis has been undertaken of the polarization properties of birefringent vertical-cavity surface-emitting lasers (VCSELs) subject to weak optical feedback in an external cavity configuration. Attention is focussed on the competition between two orthogonal polarizations of the fundamental (LP01) transverse mode of the device. It is shown that control of the emission polarization can be exercised even for very

A. Valle; L. Pesquera; K. A. Shore

1998-01-01

27

Reliability of various size oxide aperture VCSELs  

Microsoft Academic Search

This paper presents Honeywell's most recent work on 850 nm oxide aperture vertical cavity surface emitting laser (VCSEL) reliability. The VCSELs studied have a range of aperture diameters from about 5 to 20 ?m and the reliability effect of aperture diameter is of principal interest in this paper. Larger apertures generally exhibit greater reliability. Electrostatic discharge (ESD) sensitivity thresholds of

Bobby M. Hawkins; James K. Guenter; Jim A. Tatum; J. R. Biard

2002-01-01

28

Ultrafast Directional Beam Switching in Coupled VCSELs  

NASA Technical Reports Server (NTRS)

We propose a new approach to performing ultrafast directional beam switching using two coupled Vertical-Cavity Surface-Emitting Lasers (VCSELs). The proposed strategy is demonstrated for two VCSELs of 5.6 microns in diameter placed about 1 micron apart from the edges, showing a switching speed of 42 GHz with a maximum far-field angle span of about 10 degrees.

Ning, Cun-Zheng; Goorjian, Peter

2001-01-01

29

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

30

Analysis of waveguiding properties of VCSEL structures  

SciTech Connect

In this paper, the authors explore the feasibility of using the distributed Bragg reflector, grown on the substrate for a VCSEL (Vertical Cavity Surface Emitting Laser), to provide waveguiding within the substrate. This waveguiding could serve as an interconnection among VCSELs in an array. Before determining the feasibility of waveguide interconnected VCSELs, two analysis methods are presented and evaluated for their applicability to this problem. The implementations in Mathematica of both these methods are included. Results of the analysis show that waveguiding in VCSEL structures is feasible. Some of the many possible uses of waveguide interconnected VCSELs are also briefly discussed. The tools and analysis presented in this report can be used to evaluate such system concepts and to do detailed design calculations.

Erteza, I.A. [Sandia National Labs., Albuquerque, NM (United States). Exploratory Systems Development Center

1996-09-01

31

SASE FEL Polarization Control Using Crossed Undulator  

SciTech Connect

There is a growing interest in producing intense, coherent x-ray radiation with an adjustable and arbitrary polarization state. In this paper, we study the crossed undulator scheme for rapid polarization control in a self-amplified spontaneous emission (SASE) free electron laser (FEL). Because a SASE source is a temporally chaotic light, we perform a statistical analysis on the state of polarization using FEL theory and simulations. We show that by adding a small phase shifter and a short (about 1.3 times the FEL power gain length), 90{sup o} rotated planar undulator after the main SASE planar undulator, one can obtain circularly polarized light--with over 80% polarization--near the FEL saturation.

Ding, Yuantao; Huang, Zhirong; /SLAC

2008-09-30

32

Fabrication issues of oxide-confined VCSELs  

SciTech Connect

To insert high-performance oxide-confined vertical-cavity surface- emitting lasers (VCSELs) into the manufacturing arena, we have examined the critical parameters that must be controlled to establish a repeatable and uniform wet thermal oxidation process for AlGaAs. These parameters include the AlAs mole fraction, sample temperature, carrier gas flow, and bubbler water temperature. Knowledge of these parameters has enable the compilation of oxidation rate data for AlGaAs which exhibits an Arrhenius rate dependence. The compositionally dependent activation energies for Al{sub x}Ga{sub 1-x}As layers of x=1.00, 0.98, and 0.92 are found to be 1.24, 1.75, and 1.88 eV, respectively. 7 figs, 1 tab, 14 refs.

Geib, K.M.; Choquette, K.D.; Hou, H.Q.; Hammons, B.E.

1997-04-01

33

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

34

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

35

Ultrafast Beam Switching Using Coupled VCSELs  

NASA Technical Reports Server (NTRS)

We propose a new approach to performing ultrafast beam switching using two coupled Vertical-Cavity Surface-Emitting Lasers (VCSELs). The strategy is demonstrated by numerical simulation, showing a beam switching of 10 deg at 42 GHz.

Ning, Cun-Zheng; Goorjian, Peter

2001-01-01

36

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

PubMed

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

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

2012-05-21

37

Interface control of bulk ferroelectric polarization  

SciTech Connect

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

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

2012-01-01

38

The next generation high data rate VCSEL development at SEDU  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

39

Low-Cost Optical Video Links Based on VCSELs  

NASA Astrophysics Data System (ADS)

The history of introduction and current status of VCSEL based optical video link modules which have emerged as one of the main applications of VCSELs are described. The structure and characteristics of VCSELs in optical video links are summarized. The technical issues of the next generation optical video links for the mass market are discussed.

Shin, Hyun-Kuk

40

Polarity control and growth of lateral polarity structures in AlN  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

41

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

42

RSFQ electronics for controlling superconducting polarity switches  

NASA Astrophysics Data System (ADS)

Superconducting radiation sensors are of particular interest for imaging applications in the sub-mm wavelength band because of their extraordinary sensitivity. The rising number of sensors integrated in one array entails the requirement of multiplexing techniques in order to reduce the number of wires leading into the cryogenic stage and thus reduce the thermal losses. One kind of promising code division multiplexing technique is based on a current steering switch (CSS), which is composed of two identical superconducting quantum interference devices (SQUIDs) in parallel current paths. One of them is switched from the superconducting into the normal state controlled by the applied magnetic flux. In this way the signal path can be altered and they can act as a polarity switch for analogue signals. We pursue this concept to use rapid single flux quantum (RSFQ) electronics for controlling these switches. As a first step, the SQUIDs of the CSS are inductively coupled to the storing loops of two delay flip flops (DFFs). Thus, one is able to toggle the polarity of the analogue switch by controlling the state of the DFF by RSFQ control signals. The results of simulations and measurements and also margin analyses are discussed.

Brandel, O.; Wetzstein, O.; May, T.; Toepfer, H.; Ortlepp, T.; Meyer, H.-G.

2012-12-01

43

Controlling polar molecules in optical lattices  

SciTech Connect

We theoretically investigate the interaction of polar molecules with optical lattices and microwave fields. We demonstrate the existence of frequency windows in the optical domain where the complex internal structure of the molecule does not influence the trapping potential of the lattice. In such frequency windows the Franck-Condon factors are so small that near-resonant interaction of vibrational levels of the molecule with the lattice fields have a negligible contribution to the polarizability, and light-induced decoherences are kept to a minimum. In addition, we show that microwave fields can induce a tunable dipole-dipole interaction between ground-state rotationally symmetric (J=0) molecules. A combination of a carefully chosen lattice frequency and microwave-controlled interaction between molecules will enable trapping of polar molecules in a lattice and possibly realize molecular quantum logic gates. Our results are based on ab initio relativistic electronic structure calculations of the polar KRb and RbCs molecules combined with calculations of their rovibrational motion.

Kotochigova, S. [Department of Physics, Temple University, Philadelphia, Pennsylvania 19122 (United States); National Institute of Standards and Technology, 100 Bureau Drive, Stop 8423, Gaithersburg, Maryland 20899 (United States); Tiesinga, E. [Department of Physics, Temple University, Philadelphia, Pennsylvania 19122 (United States)

2006-04-15

44

Controlling Polar Molecules in Optical Lattices  

E-print Network

We investigate theoretically the interaction of polar molecules with optical lattices and microwave fields. We demonstrate the existence of frequency windows in the optical domain where the complex internal structure of the molecule does not influence the trapping potential of the lattice. In such frequency windows the Franck-Condon factors are so small that near-resonant interaction of vibrational levels of the molecule with the lattice fields have a negligible contribution to the polarizability and light-induced decoherences are kept to a minimum. In addition, we show that microwave fields can induce a tunable dipole-dipole interaction between ground-state rotationally symmetric (J=0) molecules. A combination of a carefully chosen lattice frequency and microwave-controlled interaction between molecules will enable trapping of polar molecules in a lattice and possibly realize molecular quantum logic gates. Our results are based on ab initio relativistic electronic structure calculations of the polar KRb and RbCs molecules combined with calculations of their rovibrational motion.

S. Kotochigova; E. Tiesinga

2006-02-01

45

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

46

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

47

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

SciTech Connect

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

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

2010-05-28

48

Self-Sustained Ultrafast Pulsation in Coupled VCSELs  

NASA Technical Reports Server (NTRS)

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

Ning, Cun-Zheng

2001-01-01

49

Multiple long-wavelength VCSEL arrays for low-cost WDM  

NASA Astrophysics Data System (ADS)

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

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

1998-02-01

50

Analysis of Multi-Polarization Switching in Vertical-Cavity Surface-Emitting Lasers Using Multi-peak gain model  

NASA Astrophysics Data System (ADS)

This research investigated the mulit-polarization switching (MPS) in vertical-cavity surface-emitting lasers (VCSELs) at constant temperature by simple multi-peak gain model.In experimental results, the phenomenon of the polarization switching (PS) in the VCSEL were arduous to definite quantitative analysis. A simple multi-peak gain model which included the temperature effect and current effect was established to match the MPS in the VCSEL. Simulation results match the experimental results well and shoe that the variation of temperature is a affecting factor of MPS. Therefore, the simple multi-peak gain model contributed a good understanding of multi-polarization switching in VCSELs.

Hsu, Chuan; Chen, Yu-Fong; Chin, Pei-Hou; Quadir, Shaham; Li, Yueh-Chen; Wu, Yu-Heng; Yen, Tsu-Chiang

2013-03-01

51

Electrochemical control of cell and tissue polarity.  

PubMed

Localized ion fluxes at the plasma membrane provide electrochemical gradients at the cell surface that contribute to cell polarization, migration, and division. Ion transporters, local pH gradients, membrane potential, and organization are emerging as important factors in cell polarization mechanisms. The power of electrochemical effects is illustrated by the ability of exogenous electric fields to redirect polarization in cells ranging from bacteria, fungi, and amoebas to keratocytes and neurons. Electric fields normally surround cells and tissues and thus have been proposed to guide cell polarity in development, cancer, and wound healing. Recent studies on electric field responses in model systems and development of new biosensors provide new avenues to dissect molecular mechanisms. Here, we review recent advances that bring molecular understanding of how electrochemistry contributes to cell polarity in various contexts. PMID:25062359

Chang, Fred; Minc, Nicolas

2014-10-11

52

Fiber-tunable dilute-nitride VCSEL  

NASA Astrophysics Data System (ADS)

We report the single-mode operation and characterization of a 1.3-?m hybrid-fiber-tunable GaInNAs VCSEL. Results show that at room-temperature the device can be continuously tuned over 18.5-nm with output power up to 0.23-mW. Coupled-cavity effects were found to be a limiting factor for the tuning range. This device not only opens up potential applications in the physics of light-matter interaction, sensing and optical communications where it will, eventually, compete with InP-based VCSEL, but it is also a first step toward a tunable dilute-nitride vertical-cavity amplifier.

Laurand, N.; Calvez, S.; Dawson, M. D.; Jouhti, T.; Konttinen, J.; Pessa, M.

2005-11-01

53

Polarization controllable Fresnel lens using dye-doped liquid crystals  

E-print Network

Polarization controllable Fresnel lens using dye- doped liquid crystals Tsung-Hsien Lin,1,2 Yuhua, Florida 32816 swu@mail.ucf.edu http://lcd.creol.ucf.edu Abstract: A scattering-free, polarization controllable Fresnel zone plate lens is demonstrated using a photo-induced alignment of the dye-doped liquid

Wu, Shin-Tson

54

Advanced characterization techniques for high power VCSELs  

NASA Astrophysics Data System (ADS)

The performance of high power VCSELs in a specific application depends on the geometrical and thermal design as well as on the quality of the epitaxially grown material. Due to the relatively high heat load in densely packed high power arrays the temperature in the active zone and the DBR mirrors changes significantly with the applied current and the traditional characterization methods become less meaningful than for low power devices. This paper presents a method to measure temperature independent power curves with the help of short pulse techniques and data mapping at different heat sink temperatures. In addition the internal quantum efficiency, the transparency current and the gain coefficient are measured by a novel method which operates the VCSEL material as an edge emitter and applies a cut-back technique. The optical losses in the DBR mirrors are determined using external feedback. In summary all relevant parameters which determine the quality of an epitaxial design are measured independently and can be directly compared with modeling and help to optimize the high power VCSEL performance.

Moench, Holger; Baier, Johannes; Gronenborn, Stephan; Kolb, Johanna; Miller, Michael; Pekarski, Pavel; Schemmann, Marcel; Valster, Adriaan

2010-02-01

55

Coherent Terahertz Polarization Control through Manipulation of Electron Trajectories  

SciTech Connect

The dynamics of ionized electrons in a plasma can be controlled by synthetic optical fields composed of the fundamental and the second harmonic of femtosecond optical pulses with an arbitrary phase and polarization. We show here that the plasma-emitted half-cycle THz radiation directly reflects the two-dimensional trajectories of the electrons through polarization sensitive THz emission spectroscopy. As a result, we find that the THz polarization smoothly rotates through 2pi radians as the relative phase between the two pulses is adjusted, providing a new means of coherently controlling the polarization of light at THz frequencies.

Wen Haidan [PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, California, 94025 (United States); Lindenberg, Aaron M. [PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, California, 94025 (United States); Department of Materials Science and Engineering, Stanford University, Stanford, California, 94305 (United States)

2009-07-10

56

Coherent control of polarized neutron interferometry  

E-print Network

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

Abutaleb, Mohamed Osama

2012-01-01

57

Polarization controllable Fresnel lens using dye-doped liquid crystals  

Microsoft Academic Search

A scattering-free, polarization controllable Fresnel zone plate lens is demonstrated using a photo-induced alignment of the dye-doped liquid crystal film. This photo-aligned liquid crystal zone plate provides orthogonal polarization states for odd and even zones. The different focus orders can be separated because of their different polarization states. The fabrication process is relatively simple and the operation voltage is less

Tsung-Hsien Lin; Yuhua Huang; Andy Y. G. Fuh; Shin-Tson Wu

2006-01-01

58

New developments in 850 and 1300nm VCSELs at JDSU  

NASA Astrophysics Data System (ADS)

Results on new 850nm and 1310nm VCSEL products under development at JDSU will be presented with emphasis on reliability criteria, advances in performance, and interconnect design. An update will also be provided on JDSU's effort to introduce 10Gpbs LW VCSEL based components and modules into the marketplace.

Graham, Luke A.; Schnoes, Melinda; Maranowski, Kevin D.; Fanning, Thomas R.; Crom, Max V.; Feld, Stewart A.; Gray, Matthew H.; Bowers, Karen; Silva, Steve L.; Cook, Kirk; Schomberger, Gayle; Gable, Ben

2009-02-01

59

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

60

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

61

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

62

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

63

Spatial segregation of polarity factors into distinct cortical clusters is required for cell polarity control  

PubMed Central

Cell polarity is regulated by evolutionarily conserved polarity factors whose precise higher-order organization at the cell cortex is largely unknown. Here we image frontally the cortex of live fission yeast cells using time-lapse and super-resolution microscopy. Interestingly, we find that polarity factors are organized in discrete cortical clusters resolvable to ~50–100?nm in size, which can form and become cortically enriched by oligomerization. We show that forced co-localization of the polarity factors Tea1 and Tea3 results in polarity defects, suggesting that the maintenance of both factors in distinct clusters is required for polarity. However, during mitosis, their co-localization increases, and Tea3 helps to retain the cortical localization of the Tea1 growth landmark in preparation for growth reactivation following mitosis. Thus, regulated spatial segregation of polarity factor clusters provides a means to spatio-temporally control cell polarity at the cell cortex. We observe similar clusters in Saccharomyces cerevisiae and Caenorhabditis elegans cells, indicating this could be a universal regulatory feature. PMID:23673619

Dodgson, James; Chessel, Anatole; Yamamoto, Miki; Vaggi, Federico; Cox, Susan; Rosten, Edward; Albrecht, David; Geymonat, Marco; Csikasz-Nagy, Attila; Sato, Masamitsu; Carazo-Salas, Rafael E.

2013-01-01

64

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

65

?-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

66

28-Gbps 850-nm oxide VCSEL development and manufacturing progress at Avago  

NASA Astrophysics Data System (ADS)

Avago's 850nm VCSELs for applications requiring modulation at 25-28Gbps have been designed for -3dB bandwidths in excess of 19GHz over the extended temperature range of 0-85°C. The DBR mirrors have been optimized to minimize optical losses and thermal and electrical resistance. The active region is designed to provide superior differential gain for high optical bandwidth. In this paper we will describe the design for performance and manufacturability of Avago's high speed 25-28Gbps VCSEL. Analysis of the high-speed modulation characteristics and results of wearout reliability studies will be presented. We will also discuss the manufacturability of this next generation of high performance, reliable lasers. The challenges of epitaxial growth and wafer fabrication along with the associated process control technologies will be described.

Fanning, Thomas R.; Wang, Jingyi; Feng, Zheng-Wen; Keever, Mark; Chu, Chen; Sridhara, Aaditya; Rigo, Cesare; Yaun, Hairong; Sale, Terry; Koh, Gim-Hong; Murty, Ramana; Aboulhouda, Samir; Giovane, Laura

2014-02-01

67

A single metamaterial plate as bandpass filter, transparent wall, and polarization converter controlled by polarizations  

NASA Astrophysics Data System (ADS)

We propose an anisotropic homogeneous metamaterial flat plate having multiple functionalities under different polarizations of incident waves. From the theoretical analysis based on Maxwell's equations, we demonstrate that a single one-dimensional anisotropic metamaterial slab with the tailored constitutive parameters serves as a bandpass filter, a transparent wall, and a polarization converter under illuminations of differently polarized waves. We present a special structural unit to realize the tailored constitutive parameter tensors of the anisotropic metamaterial from which a three-dimensional metamaterial flat plate is designed and fabricated. The measured results agree very well to theoretical calculations and full-wave simulations, demonstrating the excellent performance of the polarization-controlled multiple functionalities of the single metamaterial plate.

Ma, Hui Feng; Tang, Wen Xuan; Cheng, Qiang; Cui, Tie Jun

2014-08-01

68

Directive excitation of guided electromagnetic waves through polarization control  

NASA Astrophysics Data System (ADS)

Experimental evidence is reported on the control of the directionality of guided electromagnetic microwaves by the polarization of the exciting wave. Experiments are conducted using a two-dimensional waveguide made of two parallel aluminum plates. The upper plate, which has a linear array of holes, is externally illuminated by a polarized wave whose incident wavevector is contained within the mirror-symmetry plane defined by the linear array. Surprisingly, the measurements show that the propagation inside the waveguide is highly asymmetrical, and it is controlled by the polarization of the incoming wave. This extraordinary phenomenon is explained in terms of a simple model involving a set of dipoles that are excited at the hole positions. Our finding provides a powerful method to sort different polarizations of a free-space beam to different propagation directions of guided electromagnetic waves.

Carbonell, Jorge; Rodríguez-Fortuño, Francisco J.; Díaz-Rubio, Ana; Martínez, Alejandro; Cervera, Francisco; Sánchez-Dehesa, José

2014-04-01

69

Active control of light based on polarization-coupling cascading  

NASA Astrophysics Data System (ADS)

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

Huo, Juan; Zheng, Yuanlin; Chen, Xianfeng

2014-10-01

70

Multilevel Data Storage Memory Using Deterministic Polarization Control  

SciTech Connect

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

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

2012-01-01

71

Multiexposure speckle contrast imaging using current pulsed VCSELs  

Microsoft Academic Search

We implement multiexposure contrast imaging using VCSELs to quantify cortical blood flow, towards a portable technique. Device characterization and noise compensations algorithms are used to show robustness of our technique in non ideal conditions.

Hart Levy; Dene Ringuette; Ofer Levi

2011-01-01

72

Proton implanted VCSEL's for 3 Gb\\/s data links  

Microsoft Academic Search

Transverse single-mode and multimode intensity modulated butt-coupled InGaAs vertical cavity surface emitting lasers (VCSEL)s are investigated as a light source for optical fiber communication systems. Data transmission at 3 Gb\\/s with a bit error rate (BER) of less than 10 -11 is reported for both 4.3 km of standard fiber, as well as 0.5 km of multimode graded-index fiber, 10-?m

U. Fiedler; B. Moller; G. Reiner; D. Wiedenmann; K. J. Ebeling

1995-01-01

73

Progress towards commercialization of 25-Gb/s VCSELs  

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

74

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.

75

Polarization control of electron tunneling into ferroelectric surfaces.  

PubMed

We demonstrate a highly reproducible control of local electron transport through a ferroelectric oxide via its spontaneous polarization. Electrons are injected from the tip of an atomic force microscope into a thin film of lead-zirconate titanate, Pb(Zr0.2Ti0.8)O3, in the regime of electron tunneling assisted by a high electric field (Fowler-Nordheim tunneling). The tunneling current exhibits a pronounced hysteresis with abrupt switching events that coincide, within experimental resolution, with the local switching of ferroelectric polarization. The large spontaneous polarization of the PZT film results in up to 500-fold amplification of the tunneling current upon ferroelectric switching. The magnitude of the effect is subject to electrostatic control via ferroelectric switching, suggesting possible applications in ultrahigh-density data storage and spintronics. PMID:19520954

Maksymovych, Peter; Jesse, Stephen; Yu, Pu; Ramesh, Ramamoorthy; Baddorf, Arthur P; Kalinin, Sergei V

2009-06-12

76

Microwave-band optoelectronic frequency converters based on long wavelength VCSELs  

Microsoft Academic Search

A VCSEL-based optoelectronic conversion process is investigated in details by simulation in modern OE-CAD tools and experimentally. A novel version of a VCSEL-based microwave frequency converter is proposed as well.

M. E. Belkin; L. M. Belkin; A. V. Loparev; V. Iakovlev; G. Suruceanu; A. Mereuta; A. Caliman; A. Sirbu; E. Kapon

2011-01-01

77

Piezoelectric-Potential-Controlled Polarity-Reversible Schottky Diodes and  

E-print Network

Piezoelectric-Potential-Controlled Polarity-Reversible Schottky Diodes and Switches of ZnO WiresVersity, 100084 Beijing, China Received August 14, 2008 ABSTRACT Using a two-end bonded ZnO piezoelectric-induced piezoelectric potential-drop along the PFW, which have been quantified using the thermionic emission

Wang, Zhong L.

78

Controlling attosecond electron dynamics by phase-stabilized polarization gating  

E-print Network

LETTERS Controlling attosecond electron dynamics by phase-stabilized polarization gating I. J. SOLA the signature of a single return of the electron wavepacket over a large range of energies. This temporally (low energy) and cut-off (high energy) harmonics, specific focusing conditions ensure that only

Loss, Daniel

79

Planar proton implanted VCSEL's and fiber-coupled 2-D VCSEL arrays  

Microsoft Academic Search

Efficient planar proton implanted InGaAs-GaAs MQW vertical-cavity surface-emitting laser diodes (VCSEL's) and 2-D arrays are fabricated using molecular beam epitaxy and p-type beryllium doping. Using single-step grading and modulation ?-doping in the p-type AlGaAs-GaAs Bragg reflectors top surface emitting devices with a maximum wall-plug efficiency of 17.6% and a threshold voltage of 1.8 V are demonstrated. Transverse mode behavior is

Eberhard Zeeb; Bernd Moller; C. Reiner; Manfred Ries; Thomas Hackbarth; Karl Joachim Ebeling

1995-01-01

80

Efficiency and threshold current optimization for 850 nm oxidized VCSELs using a mirror etching technique  

Microsoft Academic Search

Owing to their commercial application to data links, 850 nm VCSELs have been studied extensively to improve the efficiency and reduce the threshold current. However, there are significant tradeoffs that must be made between these two parameters in a VCSEL design. To optimize the VCSELs performance, the DBR design is optimized based on the calculated reflectivity. In this presentation, we

Chao-Kun Lin; M. H. MacDougal; A. E. Bond; P. D. Dapkus

1997-01-01

81

Feedback in close-coupled axial VCSEL-photodiode pairs  

NASA Astrophysics Data System (ADS)

We have been investigating the use of coaxial multimode VCSEL/PD (vertical cavity surface emitting laser/photodiode) pairs for positional sensing with emitter to target mirror distances on the order of 1mm. We have observed large variations in signal levels due to the strong optical feedback in these close-coupled systems, employing either heterogeneously integrated commercial components or our own monolithically integrated devices. The feedback effect is larger than anticipated due to the annular geometry of the photodetector. Even though there is very little change in the measured VCSEL total output power, the optical feedback induces variations in the transverse mode distributions in these multimode VCSELs. The higher order modes have a larger divergence angle resulting in changes in the reflected light power incident upon the active detector area for a large range of emitter/mirror separations. We will review the experimental details and provide strategies for avoiding these variations in detected power.

Geib, Kent M.; Serkland, Darwin K.; Peake, Gregory M.; Sanchez, Victoria M.

2011-03-01

82

Exploring the influence of boundary shapes on emission angular distributions and polarization states of broad-area vertical-cavity surface-emitting lasers.  

PubMed

We design the stadium-shaped and rectangular vertical-cavity surface-emitting lasers (VCSELs) to investigate the influence of boundary shapes on the emission angular distributions and polarization states. For the stadium-shaped VCSELs, the emission angular distribution prefers to be almost omnidirectional because the lasing mode with purely scarred structure is seldom to be excited. On the contrary, the rectangular VCSELs usually generate dominant lasing modes with the morphology of quasi-periodic linear ridges, which can make emission angular distribution to be concentrated on the certain direction. From the polarization-resolved light-current curves, the stadium-shaped VCSEL is quite prone to exhibit numerous abrupt changes (kinks) associated with polarization switching with increasing current, whereas for rectangular VCSEL there is no conspicuous kink to be seen during a wide range of current changing from near to far above lasing threshold. PMID:25401843

Yu, Y T; Tuan, P H; Huang, K F; Chen, Y F

2014-11-01

83

CONTROLE EM COORDENADAS POLARES DE ROBÔS MÓVEIS COM RODAS  

Microsoft Academic Search

Resumo- Sabe-se que transformações de coordenadas adequadas podem ser bastante úteis no desenvolvimento de controladores para sistemas não-holonômicos. A literatura mostra que a transformação para coordenadas polares permite o controle de robôs móveis com acionamento diferencial. No entanto, não existe um m étodo para obtenção de tais transformações. Neste artigo propõe-se transformações de variáveis adicionais que permitem a obtenção de

WALTER F. LAGES; ELDER M. HEMERLY

84

Control over topological insulator photocurrents with light polarization  

NASA Astrophysics Data System (ADS)

Three-dimensional topological insulators represent a new quantum phase of matter with spin-polarized surface states that are protected from backscattering. The static electronic properties of these surface states have been comprehensively imaged by both photoemission and tunnelling spectroscopies. Theorists have proposed that topological surface states can also exhibit novel electronic responses to light, such as topological quantum phase transitions and spin-polarized electrical currents. However, the effects of optically driving a topological insulator out of equilibrium have remained largely unexplored experimentally, and no photocurrents have been measured. Here, we show that illuminating the topological insulator Bi2Se3 with circularly polarized light generates a photocurrent that originates from topological helical Dirac fermions, and that reversing the helicity of the light reverses the direction of the photocurrent. We also observe a photocurrent that is controlled by the linear polarization of light and argue that it may also have a topological surface state origin. This approach may allow the probing of dynamic properties of topological insulators and lead to novel opto-spintronic devices.

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

2012-02-01

85

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

86

Size dependence of selectively oxidized VCSEL transverse mode structure  

SciTech Connect

The performance of vertical cavity surface emitting lasers (VCSELs) has improved greatly in recent years. Much of this improvement can be attributed to the use of native oxide layers within the laser structure, providing both electrical and optical transverse confinement. Understanding this optical confinement will be vital for the future realization of yet smaller lasers with ultralow threshold currents. Here the authors report the spectral and modal properties of small (0.5 {micro}m to 5 {micro}m current aperture) VCSELs and identify Joule heating as a dominant effect in the resonator properties of the smallest lasers.

Hegarty, S.P.; Huyet, G. [University College, Cork (Ireland). Physics Dept.; McInerney, J.G. [University College, Cork (Ireland). Physics Dept.]|[Univ. of Arizona, Tucson, AZ (United States). Optical Sciences Center; Choquette, K.D.; Hou, H.Q.; Geib, K.M. [Sandia National Labs., Albuquerque, NM (United States). Center for Compound Semiconductor Science and Technology

1998-05-01

87

Polarized Secretion of Drosophila EGFR Ligand from Photoreceptor Neurons Is Controlled by ER Localization  

E-print Network

Polarized Secretion of Drosophila EGFR Ligand from Photoreceptor Neurons Is Controlled by ER) Polarized Secretion of Drosophila EGFR Ligand from Photoreceptor Neurons Is Controlled by ER Localization exist. Abbreviations: Dac, Dachshund; DN, dominant negative; EGFR, epidermal growth factor receptor

Shilo, Benny

88

Hemin controls T cell polarization in sickle cell alloimmunization.  

PubMed

Patients with sickle cell disease (SCD) often require transfusions to treat and prevent worsening anemia and other SCD complications. However, transfusions can trigger alloimmunization against transfused RBCs with serious clinical sequelae. Risk factors for alloimmunization in SCD remain poorly understood. We recently reported altered regulatory T cell (Treg) and Th responses with higher circulating Th1 (IFN-?(+)) cytokines in chronically transfused SCD patients with alloantibodies as compared with those without alloantibodies. Because monocytes play a critical role in polarization of T cell subsets and participate in clearance of transfused RBCs, we tested the hypothesis that in response to the RBC breakdown product hemin, monocyte control of T cell polarization will differ between alloimmunized and non-alloimmunized SCD patients. Exogenous hemin induced Treg polarization in purified T cell/monocyte cocultures from healthy volunteers through the monocyte anti-inflammatory heme-degrading enzyme heme oxygenase-1. Importantly, hemin primarily through its effect on CD16+ monocytes induced an anti-inflammatory (higher Treg/lower Th1) polarization state in the non-alloimmunized SCD group, whereas it had little effect in the alloimmunized group. Non-alloimmunized SCD CD16+ monocytes expressed higher basal levels of heme oxygenase-1. Furthermore, IL-12, which contributed to a proinflammatory polarization state (low Treg/high Th1) in SCD, was dampened in hemin-treated stimulated monocytes from non-alloimmunized SCD patients, but not in the alloimmunized group. These data suggest that unlike alloimmunized patients, non-alloimmunized SCD CD16+ monocytes in response to transfused RBC breakdown products promote an anti-inflammatory state that is less conducive to alloimmunization. PMID:24879794

Zhong, Hui; Bao, Weili; Friedman, David; Yazdanbakhsh, Karina

2014-07-01

89

Polarization control of plasmonic modes in single nanoparticles and nanostructures  

NASA Astrophysics Data System (ADS)

This thesis investigates the fundamental nanoscale near-field light matter interaction between a probe tip and plasmonic antenna nanostructures. The thesis is focused on polarization control of metallic plasmon modes using scattering-type scanning near-field optical microscopy (s-SNOM). Part of the thesis is dedicated to spectroscopic near-field comparison of coated and bare single plasmonic particles in the infrared wavelength range (lambda= 9--11 microm) using s-SNOM. By tuning the wavelength of the incident light, we have acquired information on the spectral polarization dependence plasmon modes and plasmon/phonon--polariton resonant near-field interactions. The enhanced near-field coupling between the probe tip and high index Au nanostructures and Au-core thin silica coating (thickness ?10 nm) is described and quantified.

Damato, Ralph

90

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

91

Efficient 3D simulation of photonic crystal VCSELs  

Microsoft Academic Search

An efficient modular approach is used to develop components for a 3D simulator for complex semiconductor LED and laser structures. In this approach, only drift transport is simulated in bulk regions, while the active region is simulated with models of varying complexity. The approach is tested using a basic vertical-cavity surface emitting laser (VCSEL) structure, and comparisons are made with

Aditya Kulkarni; Vivek Krishnamurthy; Michael Povoloskyi; Benjamin Klein

2009-01-01

92

Synaptic polarity of the interneuron circuit controlling C. elegans locomotion  

PubMed Central

Caenorhabditis elegans is the only animal for which a detailed neural connectivity diagram has been constructed. However, synaptic polarities in this diagram, and thus, circuit functions are largely unknown. Here, we deciphered the likely polarities of seven pre-motor neurons implicated in the control of worm's locomotion, using a combination of experimental and computational tools. We performed single and multiple laser ablations in the locomotor interneuron circuit and recorded times the worms spent in forward and backward locomotion. We constructed a theoretical model of the locomotor circuit and searched its all possible synaptic polarity combinations and sensory input patterns in order to find the best match to the timing data. The optimal solution is when either all or most of the interneurons are inhibitory and forward interneurons receive the strongest input, which suggests that inhibition governs the dynamics of the locomotor interneuron circuit. From the five pre-motor interneurons, only AVB and AVD are equally likely to be excitatory, i.e., they have probably similar number of inhibitory and excitatory connections to distant targets. The method used here has a general character and thus can be also applied to other neural systems consisting of small functional networks. PMID:24106473

Rakowski, Franciszek; Srinivasan, Jagan; Sternberg, Paul W.; Karbowski, Jan

2013-01-01

93

VCSEL-based miniature laser-Doppler interferometer  

NASA Astrophysics Data System (ADS)

There are many applications for non-contact measurement of the displacement and velocity of moving objects, especially when achieved at low cost. An optical displacement sensor has been developed that can be compared to expensive laser-interferometry sensors, however at a cost compatible with requirements for consumer products. This miniature Laser-Doppler Interferometer works on all light scattering surfaces. The first large-scale application is in PC-mice. The measurement principle employs so-called "Laser Self Mixing", which occurs when laser light scattered on a surface, within the coherence length, is coupled back into the laser cavity. When the object is moving, the back-scattered light is continuously shifting in phase relative to the laser light at the laser mirror. This results in a periodic perturbation of the feedback into the laser cavity, which causes modulations of the light intensity in the cavity. The frequency of these modulations is proportional the speed of the object. A VCSEL, optimized for this application, is used as light source, a photo-diode in the sensor measures the intensity fluctuations and, finally, an integrated circuit transfers the photo-diode signal into velocity or displacement information. To determine the direction of the movement, a triangle modulation of the laser-current is used, which modulates the laser-temperature and hence the laser frequency. Next to the applications in PC-mice a much wider range of applications as input device in consumer products can be envisaged. For instance menu navigation by finger movement over a sensor in remote controls, mobile phones and lap tops. Furthermore a wide field of applications is envisaged in the manufacturing of industrial equipment, which requires non-contact measurement of the movement of materials. The small form factor of less than 0.2 cubic centimeters allows applications previously considered impossible.

Pruijmboom, Armand; Schemmann, Marcel; Hellmig, Jochen; Schutte, Jeroen; Moench, Holger; Pankert, Joseph

2008-02-01

94

Planar cell polarity genes control the connectivity of enteric neurons  

PubMed Central

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

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

2013-01-01

95

Cavity solitons in a driven VCSEL above threshold  

Microsoft Academic Search

We experimentally demonstrate the existence and the control of cavity solitons in externally driven vertical-cavity semiconductor lasers above threshold. A model including material polarization dynamics is used to predict and confirm the experimental findings.

Xavier Hachair; Francesco Pedaci; Emilie Caboche; Stphane Barland; Massimo Giudici; J. R. Tredicce; Franco Prati; Giovanna Tissoni; Reza Kheradmand; Luigi A. Lugiato; Igor Protsenko; Massimo Brambilla

2006-01-01

96

Tunable 1550nm VCSELs using high-contrast grating for next-generation networks  

NASA Astrophysics Data System (ADS)

We demonstrate wavelength-tunable SFF transceivers operating at 1550 nm using a tunable VCSEL with a high contrast grating (HCG) as the output mirror. Tunable HCG VCSELs with a ~25 nm mechanical tuning range and over 2 mW output power were realized. Error-free operation of an optical link using directly-modulated tunable HCG VCSELs transmitting at 1.25 Gbps over 18 channels spaced by 100 GHz and transmitted over 20 km of single mode fiber is demonstrated, showing the suitability of the HCG tunable VCSEL as a low cost source for next generation DWDM communications systems in access networks and data centers.

Chase, Christopher; Rao, Yi; Huang, Michael; Chang-Hasnain, Connie

2013-12-01

97

Light-by-light polarization control for telecommunication applications  

E-print Network

, polarization sensitivity of a large number of systems, such as Nonlinear Optical Loop Mirror (NOLM) [1], coherent detection [2] or optical-fiber based transmission links and associated polarization mode-fibered polarization attraction, which can occur in optical fibers at telecommunication wavelengths. More precisely, we

Paris-Sud XI, Université de

98

Effect of optical feedback on a VCSEL TDLAS  

NASA Astrophysics Data System (ADS)

This paper describes the effects of optical feedback on the sensitivity of VCSEL tunable-diode laser spectroscopy (TDLS). Three VCSELs, emitting at different wavelengths in the near-infrared, were used. A TDLS system, subjected to optical feedback, exhibited a common signal-to-noise ratio profile for all three lasers. A catastrophic degradation of TDLS sensitivity occurred when feedback exceeded a level which we associate with coherence collapse. The TDLS system had a CH4 minimum detection limit of 7.5 ppmm without optical feedback. Optical feedback of less than ten percent reduced this sensitivity by two orders of magnitude. This reduction of system sensitivity was accompanied by a second-harmonic absorption signal baseline shift which degraded the system accuracy.

Vujanic, D.; Jaeger, W.; Tulip, J.

2010-05-01

99

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

100

Compact VCSEL pumped Q-switched Nd:YAG lasers  

NASA Astrophysics Data System (ADS)

We have explored using 808nm Vertical Cavity Surface emitting laser (VCSEL) arrays for end-pumping of Nd:YAG lasers. A variety of laser designs were explored including a compact passively Q-switched lasers that produced a 22mJ pulse having a pulse width of <1.5ns, and an actively Q-switched laser that produced a 40mJ pulse having a 7 ns pulse width. The VCSEL pumped actively Q-switched laser was used as a source for sum frequency generation. Using a 2mm type II KTP and 3mm type I LBO, we generated greater than 5mJ at 355nm with a 21% THG conversion efficiency.

Cole, Brian; Hays, Alan; McIntosh, Chris; Nettleton, John; Goldberg, Lew

2012-03-01

101

Coherent Terahertz Polarization Control through Manipulation of Electron Trajectories Haidan Wen1  

E-print Network

Coherent Terahertz Polarization Control through Manipulation of Electron Trajectories Haidan Wen1 of the fundamental and the second harmonic of femtosecond optical pulses with an arbitrary phase and polarization. We trajectories of the electrons through polarization sensitive THz emission spectroscopy. As a result, we find

102

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

E-print Network

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

Paris-Sud XI, Université de

103

Butt-coupling efficiency of VCSELs into multimode fibers  

Microsoft Academic Search

We report a detailed study on butt coupling efficiencies of vertical-cavity surface-emitting lasers (VCSELs) to standard graded index multimode silica fibers. Coupling efficiency strongly depends on active laser diameter as well as index guiding and transverse mode spectrum of the laser. For typical active laser diameters of 16-20-?m coupling efficiencies of about 90% are obtained with weakly index guided proton-implanted

J. Heinrich; E. Zeeb; K. J. Ebeling

1997-01-01

104

VCSEL array-based light exposure system for laser printing  

Microsoft Academic Search

Improving the image quality and speed is an endless demand for printer applications. To meet the market requirements, we have launched the world first laser printer (DocuColor 1256 GA) introducing 780-nm single-mode 8×4 VCSEL arrays in the light exposure system in 2003. The DocuColor 1256 GA features 2400 dots per inch (dpi) resolution which is the highest in the industry

Naotaka Mukoyama; Hiromi Otoma; Jun Sakurai; Nobuaki Ueki; Hideo Nakayama

2008-01-01

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

Cavity soliton laser based on VCSEL with saturable absorber  

Microsoft Academic Search

We study theoretically a broad-area vertical cavity surface emitting laser (VCSEL) with a saturable absorber. We show numerically\\u000a the presence of cavity solitons in the system: they exist as solitary structures formed through a modulationally unstable\\u000a homogeneous lasing state that coexists with a background with zero intensity. Such a peculiar scenario endows the solitons\\u000a with unique properties compared to cavity

M. Bache; F. Prati; G. Tissoni; R. Kheradmand; L. A. Lugiato; I. Protsenko; M. Brambilla

2005-01-01

107

High volume production of single-mode VCSELs  

NASA Astrophysics Data System (ADS)

Up to now applications for singlemode VCSELs were in low volume and high prized applications like tunable diode laser absorption spectroscopy (TDLAS, [1,2]) or optical interferometers. Typical volumes for these applications are in the range of thousands of pcs per year, with pricing levels of several 100 USD/pcs. New applications for singlemode VCSELs in consumer markets require manufacturing in very high volumes and at very low cost. Examples are laser-based optical mouse sensors, optical encoders, and rubidium atomic clocks for GPS systems [3,4]. U-L-M photonics presents manufacturing aspects, device performance and reliability data for these devices. The first part of the paper is dealing with high volume manufacturing of 850 nm singlemode VCSEL chips with very high efficiency and low operation current. Special processing technologies have been developed to achieve yields on 3 inch wafers of more than 90%. Wafer qualification procedures are discussed as well. The second part of the paper covers high volume packaging in TO and SMT type packages where very high packaging yields must be achieved. In the last part of the paper reliability issues are discussed, focused on the very high susceptibility of these devices to electrostatic discharge.

Wiedenmann, Dieter; Grabherr, Martin; Jäger, Roland; King, Roger

2006-02-01

108

VCSELs and silicon light sources exploiting SOI grating mirrors  

NASA Astrophysics Data System (ADS)

In this talk, novel vertical-cavity laser structure consisting of a dielectric Bragg reflector, a III-V active region, and a high-index-contrast grating made in the Si layer of a silicon-on-insulator (SOI) wafer will be presented. In the Si light source version of this laser structure, the SOI grating works as a highly-reflective mirror as well as routes light into a Si in-plane output waveguide connected to the grating. In the vertical-cavity surface-emitting laser (VCSEL) version, there is no in-plane output waveguide connected to the grating. Thus, light is vertically emitted through the Bragg reflector. Numerical simulations show that both the silicon light source and the VCSEL exploiting SOI grating mirrors have superior performances, compared to existing silicon light sources and long wavelength VCSELs. These devices are highly adequate for chip-level optical interconnects as well as conventional short-distance optical connections. In the talk, device physics will be discussed in detail.

Chung, Il-Sug; Mørk, Jesper

2012-03-01

109

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

110

Controlling the polarization rotation of an optical field via asymmetry in electromagnetically induced transparency  

NASA Astrophysics Data System (ADS)

We propose and experimentally demonstrate a mechanism to achieve coherent control of the polarization rotation of an optical field in a multilevel electromagnetically induced transparency (EIT) system in rubidium atoms. By choosing a properly polarized coupling field and transition energy levels, the symmetry of the atomic medium to the propagation of two orthogonal polarization components of a weak linearly polarized probe field can be broken, which leads to a coherently controlled rotation of the probe field polarization. This mechanism of coherently controlled optical polarization rotation makes use of asymmetry in EIT subsystems for the two circular polarization components of the probe beam with a contribution from different transition strengths (due to different Clebsh-Gordan coefficients) in this multilevel atomic system.

Wang, Bo; Li, Shujing; Ma, Jie; Wang, Hai; Peng, K. C.; Xiao, Min

2006-05-01

111

Category # Paper # Paper Title: cw and transient characteristics of polarization switching  

E-print Network

Category # Paper # IQEC 2000 Paper Title: cw and transient characteristics of polarization Optical Phenomena #12;cw and transient characteristics of polarization switching in vertical-251-83-33513, Email: ackeman@uni-muenster.de cw and transient features of polarization switching in VCSELs

Lange, Wulfhard

112

A FOXO–Pak1 transcriptional pathway controls neuronal polarity  

PubMed Central

Neuronal polarity is essential for normal brain development and function. However, cell-intrinsic mechanisms that govern the establishment of neuronal polarity remain to be identified. Here, we report that knockdown of endogenous FOXO proteins in hippocampal and cerebellar granule neurons, including in the rat cerebellar cortex in vivo, reveals a requirement for the FOXO transcription factors in the establishment of neuronal polarity. The FOXO transcription factors, including the brain-enriched protein FOXO6, play a critical role in axo–dendritic polarization of undifferentiated neurites, and hence in a switch from unpolarized to polarized neuronal morphology. We also identify the gene encoding the protein kinase Pak1, which acts locally in neuronal processes to induce polarity, as a critical direct target gene of the FOXO transcription factors. Knockdown of endogenous Pak1 phenocopies the effect of FOXO knockdown on neuronal polarity. Importantly, exogenous expression of Pak1 in the background of FOXO knockdown in both primary neurons and postnatal rat pups in vivo restores the polarized morphology of neurons. These findings define the FOXO proteins and Pak1 as components of a cell-intrinsic transcriptional pathway that orchestrates neuronal polarity, thus identifying a novel function for the FOXO transcription factors in a unique aspect of neural development. PMID:20395366

de la Torre-Ubieta, Luis; Gaudillière, Brice; Yang, Yue; Ikeuchi, Yoshiho; Yamada, Tomoko; DiBacco, Sara; Stegmüller, Judith; Schüller, Ulrich; Salih, Dervis A.; Rowitch, David; Brunet, Anne; Bonni, Azad

2010-01-01

113

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

114

Reliability and failure mechanisms of oxide VCSELs in non-hermetic enviroments  

Microsoft Academic Search

High speed fiber optic transceiver modules using parallel optics require that oxide-confined vertical-cavity surface-emitting lasers (VCSELs) be moisture resistant in non-hermetic environments. Conventional storage 85\\/85 (85°C and 85% relative humidity) testing without a bias does not adequately characterize oxide VCSEL\\

Suning Xie; Robert W. Herrick; Gregory N. De Brabander; Wilson H. Widjaja; Uli Koelle; An-Nien Cheng; Laura M. Giovane; Frank Z. Hu; Mark R. Keever; Tim Osentowski; Scott A. McHugo; Myrna S. Mayonte; Seongsin M. Kim; Danielle R. Chamberlin; S. Jeffrey Rosner; Grant Girolami

2003-01-01

115

Albedo control of seasonal South Polar cap recession on Mars  

NASA Astrophysics Data System (ADS)

Over the last few decades, General Circulation Models (GCM) have been used to simulate the current martian climate. The calibration of these GCMs with the current seasonal cycle is a crucial step in understanding the climate history of Mars. One of the main climatic signals currently used to validate GCMs is the annual atmospheric pressure cycle. It is difficult to use changes in seasonal deposits on the surface of Mars to calibrate the GCMs given the spectral ambiguities between CO 2 and H 2O ice in the visible range. With the OMEGA imaging spectrometer covering the near infra-red range, it is now possible to monitor both types of ice at a spatial resolution of about 1 km. At global scale, we determine the change with time of the Seasonal South Polar Cap (SSPC) crocus line, defining the edge of CO 2 deposits. This crocus line is not symmetric around the geographic South Pole. At local scale, we introduce the snowdrop distance, describing the local structure of the SSPC edge. Crocus line and snowdrop distance changes can now be used to calibrate GCMs. The albedo of the seasonal deposits is usually assumed to be a uniform and constant parameter of the GCMs. In this study, albedo is found to be the main parameter controlling the SSPC recession at both global and local scale. Using a defrost mass balance model (referred to as D-frost) that incorporates the effect of shadowing induced by topography, we show that the global SSPC asymmetry in the crocus line is controlled by albedo variations. At local scale, we show that the snowdrop distance is correlated with the albedo variability. Further GCM improvements should take into account these two results. We propose several possibilities for the origin of the asymmetric albedo control. The next step will be to identify and model the physical processes that create the albedo differences.

Schmidt, Frédéric; Douté, Sylvain; Schmitt, Bernard; Vincendon, Mathieu; Bibring, Jean-Pierre; Langevin, Yves; Omega Team

2009-04-01

116

Control of polarity of heteroepitaxial ZnO films by interface engineering  

NASA Astrophysics Data System (ADS)

Control of polarity of heteroepitaxial ZnO films has been examined by interface engineering. ZnO films were grown by plasma-assisted molecular beam epitaxy on Ga-polar GaN template and c-plane sapphire substrates. Polarity of all the samples is determined by coaxial impact collision ion scattering spectroscopy. Zn- and O-polar ZnO films have successfully grown by Zn- and O-plasma pre-exposures on Ga-polar GaN templates prior to ZnO growth. High-resolution transmission electron microscopy revealed formation of a single-crystalline monoclinic Ga 2O 3 interface layer by O-plasma pre-exposure on Ga-polar GaN templates, while no interface layer was observed for Zn pre-exposed ZnO films. The polarity of ZnO films grown under oxygen ambient on c-plane sapphire with MgO buffer is revealed as O-polar. Fabrication of polarity inverted ZnO heterostructure has been studied: polarity of ZnO films on Ga-polar GaN templates was changed from Zn-polar to O-polar by inserting a MgO layer. High-resolution transmission electron microscopy revealed atomically flat interfaces at both lower and upper ZnO/MgO interfaces and no inversion domain boundaries were detected in the upper ZnO layer.

Hong, Soon-Ku; Hanada, Takashi; Chen, Yefen; Ko, Hang-Ju; Yao, Takafumi; Imai, Daisuke; Araki, Kiyoaki; Shinohara, Makoto

2002-05-01

117

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

118

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

119

Direction controllable linearly polarized laser from a dye-doped cholesteric liquid crystal  

E-print Network

Direction controllable linearly polarized laser from a dye-doped cholesteric liquid crystal Ying demonstrate a direction controllable linearly polarized laser from a dye-doped cholesteric liquid crystal (CLC codes: (230.3720) Liquid crystal devices; (160, 3710) Materials References and links 1. V. I. Kopp, Z. Q

Wu, Shin-Tson

120

Direction controllable linearly polarized laser from a dye-doped cholesteric liquid crystal  

E-print Network

Direction controllable linearly polarized laser from a dye-doped cholesteric liquid crystal Ying demonstrate a direction controllable linearly polarized laser from a dye-doped cholesteric liquid crystal (CLC codes: (230.3720) Liquid-crystal devices, (160, 3710) Materials References and links 1. V. I. Kopp, Z. Q

Wu, Shin-Tson

121

Depth-encoded all-fiber swept source polarization sensitive OCT  

PubMed Central

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

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

2014-01-01

122

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

123

Polarization-controlled Ohmic to Schottky transition at a metal/ferroelectric interface  

NASA Astrophysics Data System (ADS)

Ferroelectric polar displacements have recently been observed in conducting electron-doped BaTiO3 (n-BTO). The coexistence of a ferroelectric phase and conductivity opens the door to new functionalities that may provide a unique route for novel device applications. Using first-principles methods and electrostatic modeling, we explore the effect that the switchable polarization of n-BTO has on the electronic properties of the SrRuO3/n-BTO (001) interface. Ferroelectric polarization controls the accumulation or depletion of electron charge at the interface, and the associated bending of the n-BTO conduction band determines the transport regime across the interface. The interface exhibits a Schottky tunnel barrier for one polarization orientation, whereas an Ohmic contact is present for the opposite polarization orientation, leading to a large change in interface resistance associated with polarization reversal. Our calculations reveal a five orders of magnitude change in the interface resistance because of polarization switching.

Liu, Xiaohui; Wang, Yong; Burton, J. D.; Tsymbal, Evgeny Y.

2013-10-01

124

Challenge for Full Control of Polarization in Optical Communication Systems  

NASA Astrophysics Data System (ADS)

Countermeasures against the receiver sensitivity degradation due to the state of polarization change in single-mode fibers in coherent optical communication systems are reviewed from early efforts in 1980s to the latest research results. It is pointed out that the polarization-diversity schemes are considered to be the most promising solutions among various countermeasures for the future applications owing to its applicability to the systems with analogue as well as digital signal processing.

Ryu, Shiro

125

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

126

Distributed Algorithm for Signal Polarity Adjustment of Air-Conditioner Control Network  

NASA Astrophysics Data System (ADS)

This paper proposes a distributed algorithm for adjusting the signal polarity of the control networks for building air-conditioners. As field connection work of the two wires to the controller may be straight or cross, each controller has both plus and minus polarity circuits. It starts the algorithm in the arbitary sequence, and then negociates each other to select the plus/minus polarity circuits in order to adjust the signal polarity. A Time Petri Net model was constructed for verification of the proposed algorithm. The model describes the required specification of the system, straight/cross connection of the controller to the network bus line and the polarity adjustment algorithm. The efficient Time Petri Net verification tool made it possible to verify the model.

Ninagawa, Chuzo; Aoi, Fumio; Yokohama, Koji; Yoneda, Tomohiro

127

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

Microsoft Academic Search

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

Seiji Mita

2007-01-01

128

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

129

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

130

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

131

Apicobasal polarity controls lymphocyte adhesion to hepatic epithelial cells.  

PubMed

Loss of apicobasal polarity is a hallmark of epithelial pathologies. Leukocyte infiltration and crosstalk with dysfunctional epithelial barriers are crucial for the inflammatory response. Here, we show that apicobasal architecture regulates the adhesion between hepatic epithelial cells and lymphocytes. Polarized hepatocytes and epithelium from bile ducts segregate the intercellular adhesion molecule 1 (ICAM-1) adhesion receptor onto their apical, microvilli-rich membranes, which are less accessible by circulating immune cells. Upon cell depolarization, hepatic ICAM-1 becomes exposed and increases lymphocyte binding. Polarized hepatic cells prevent ICAM-1 exposure to lymphocytes by redirecting basolateral ICAM-1 to apical domains. Loss of ICAM-1 polarity occurs in human inflammatory liver diseases and can be induced by the inflammatory cytokine tumor necrosis factor alpha (TNF-?). We propose that adhesion receptor polarization is a parenchymal immune checkpoint that allows functional epithelium to hamper leukocyte binding. This contributes to the haptotactic guidance of leukocytes toward neighboring damaged or chronically inflamed epithelial cells that expose their adhesion machinery. PMID:25242329

Reglero-Real, Natalia; Alvarez-Varela, Adrián; Cernuda-Morollón, Eva; Feito, Jorge; Marcos-Ramiro, Beatriz; Fernández-Martín, Laura; Gómez-Lechón, Maria José; Muntané, Jordi; Sandoval, Pilar; Majano, Pedro L; Correas, Isabel; Alonso, Miguel A; Millán, Jaime

2014-09-25

132

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

NASA Astrophysics Data System (ADS)

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.

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

2014-09-01

133

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

PubMed

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

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

2014-01-01

134

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

135

482 Research Paper CDC-42 controls early cell polarity and spindle orientation  

E-print Network

482 Research Paper CDC-42 controls early cell polarity and spindle orientation in C. elegans Monica of this early E-mail: jaa@mole.bio.cam.ac.uk asymmetry. The small G protein Cdc42 is a key regulator of polarity homolog of PAR-6. The function of Cdc42 in C. elegans had not yet been Revised: 2 February 2001 Accepted

Ahringe, Julie

136

Controlling polarization of vertical-cavity surface-emitting lasers using amorphous silicon subwavelength transmission gratings  

E-print Network

device for use in integrated optoelectronic cir- cuits. In applications where polarization sensitive compo- nents are widely used, such as magneto-optic recording and coherent detection systemsControlling polarization of vertical-cavity surface-emitting lasers using amorphous silicon

137

Evolution of Developmental Control Mechanisms Long-range neural and gap junction protein-mediated cues control polarity during  

E-print Network

of stem cells to induce regeneration of specific large-scale structures would have far-mediated cues control polarity during planarian regeneration Néstor J. Oviedo a,1 , Junji Morokuma a , Peter junctions Neural signals Regeneration Polarity Planaria Having the ability to coordinate the behavior

Oviedo, Néstor J.

138

Polarization control of a high power laser by adjoint feedback control  

NASA Astrophysics Data System (ADS)

A novel technique of polarizing a high power laser with unstable resonator optics is described which places the polarizing elements in a low power feedback path external to the parent resonator structure. The technique has been used to polarize a high power industrial CO2 laser. Rejection ratios for the unwanted polarization can exceed 20 dB. The polarization vector can be rotated at will by rotating the polarizer in the low power beam path.

Blaszuk, Paul R.; Benda, John A.; Forgham, James L.; Cohen, Harold L.

1993-04-01

139

VCSEL structures used to suppress higher-order transverse modes  

NASA Astrophysics Data System (ADS)

Currently unwanted excitation of higher-order transverse modes is the most serious drawback of vertical-cavity surface-emitting diode lasers (VCSELs) limiting their possible applications. In the present paper, various methods used to suppress those modes are described and their effectiveness is compared. It is well known that, because of a nearly uniform current injection into their active regions, small-aperture VCSELs without any modification offer quite high single-fundamental-mode (SFM) output. However, their series resistance is often too high, which aggravates their high-modulation performance. Similarly uniform current injection may be also achieved with the aid of a tunnelling junction. Generally, methods suppressing higher-order modes take advantage of higher optical gain within the central part of the active region, higher radiation losses outside this region and/or higher central mirror reflectivity. Currently, applications of a tunnel junction, an impurity-induced disordering or an inverted shallow surface relief seem to be the simplest and the most effective methods. The deep etched holey structure or the ARROW structure enable obtaining similar single-mode output powers but they may be used in special cases only because of their complex technology. Photonic crystals may probably enable more advanced mechanisms of suppressing higher-order modes in future because currently their application seems to be still far from being optimised.

Nakwaski, W.

2011-03-01

140

Optical implementation of polarization-independent, bidirectional, nonblocking Clos network using polarization control technique in free space  

NASA Astrophysics Data System (ADS)

The clos network is one of the earliest multistage interconnection networks. Recently, it has been widely studied in parallel optical information processing systems, and there have been many efforts to develop this network. In this paper, a smart and compact Clos network, including Clos(2,3,2) and Clos(2,4,2), is proposed by using polarizing beam-splitters (PBS), phase spatial light modulators (PSLM), and mirrors. PBS features that are s-component (perpendicular to the incident plane) of the incident light beam is reflected, and the p-component (parallel to the incident plane) passes through it. According to switching logic, under control of external electrical signals, PSLM functions to control routing paths of the signal beams, i.e., the polarization of each optical signal is rotated or not rotated 90° by a programmable PSLM. This new type of configuration grants the features of less optical components, compact in structure, efficient in performance, and insensitive to polarization of signal beam. In addition, the straight, the exchange, and the broadcast functions of the basic switch element are implemented bidirectionally in free-space. Furthermore, the new optical experimental module of 2×3 and 2×4 optical switch is also presented by a cascading polarization-independent bidirectional 2×2 optical switch. Simultaneously, the routing state-table of 2×3 and 2×4 optical switch to perform all permutation output and nonblocking switch for the input signal beam, is achieved. Since the proposed optical setup consists of only optical polarization elements, it is compact in structure, and possesses a low energy loss, a high signal-to-ratio, and an available large number of optical channels. Finally, the discussions and the experimental results show that the Clos network proposed here should be helpful in the design of large-scale network matrix, and may be used in optical communication and optical information processing.

Yang, Junbo; Yang, Jiankun; Li, Xiujian; Chang, Shengli; Su, Xianyu; Ping, Xu

2011-04-01

141

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

142

Switching Control of Spontaneous Emission by Polarized Atoms in Two-Dimensional Photonic Crystals  

SciTech Connect

We calculate the lifetime distribution function of an assembly of polarized atoms in two-dimensional (2D) photonic crystals (PCs) at different polarization orientations of atomic dipole moments. We reveal a switching effect of atomic spontaneous emission (SE) and find a significant change of atomic lifetime, up to a factor of 33, by tuning the polarized orientation of the atoms. These observations suggest that the tuning of the polarized orientation of atoms provides a new way for the effective control of atomic SE processes in 2D PCs.

Zhou Yunsong; Wang Fuhe [Department of Physics, Capital Normal University, Beijing 100037 (China); Wang Xuehua [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Gu Benyuan [Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China)

2006-03-17

143

Controlled growth of Zn-polar ZnO epitaxial film by nitridation of sapphire substrate  

NASA Astrophysics Data System (ADS)

Surface nitridation is used to eliminate O-polar inversion domains and control the growth of single-domain Zn-polar ZnO film on sapphire (0001) substrate by rf-plasma-assisted molecular-beam epitaxy. It is found that the nitridation temperature is crucial for achieving quality AlN buffer layers and ZnO films with cation polarity, as demonstrated by ex situ transmission electron microscopy. Under optimal growth conditions, a 4×4 surface reconstruction was observed, which is confirmed to be a characteristic surface structure of the Zn-polar films, and can be used as a fingerprint to optimize the ZnO growth.

Mei, Z. X.; Du, X. L.; Wang, Y.; Ying, M. J.; Zeng, Z. Q.; Zheng, H.; Jia, J. F.; Xue, Q. K.; Zhang, Z.

2005-03-01

144

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

145

Enhanced inline conversion of fiber Bragg grating spectra based on increased polarization controllability  

NASA Astrophysics Data System (ADS)

We have demonstrated enhanced spectral conversion of a fiber Bragg grating (FBG) incorporating a polarization-diversity loop configuration (PDLC) with increased degree of freedom (DOF) in polarization control through the addition of wave plates. The proposed apparatus for spectral conversion consists of a four-port polarization beam splitter for constructing the PDLC, an FBG, and three wave plates including one half-wave and two quarter-wave plates. In the previous study using only two wave plates, slight birefringence of single-mode fibers connecting optical elements within the polarization-diversity loop induced random changes of states of polarization (SOPs), resulting in the spectral degradation. In this approach, the increased number of wave plates could complement it by providing a higher DOF in controlling SOPs and significantly improve spectral performances of the fabricated filter such as an insertion loss, side-mode suppression ratio, and band-rejection ratio.

Jang, Wook; Sung Koo, Ja; Wan Lee, Yong; Oh, Junghwan; Wook Lee, Yong

2013-04-01

146

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

147

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

148

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

E-print Network

Optical polarization control in Ti diffused channel waveguides onto LiNbO_(3) substrates have been investigated near 1530 nm wavelength regime by utilizing electro-optic effects of the substrate material. A device configuration composed of two...

Sung, Won Ju

2013-12-10

149

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

150

An optically controlled phased array antenna based on single sideband polarization modulation.  

PubMed

A novel optically controlled phased array antenna consisting a simple optical beamforming network and an N element linear patch antenna array is proposed and demonstrated. The optical beamforming network is realized by N independent phase shifters using a shared optical single sideband (OSSB) polarization modulator together with N polarization controllers (PCs), N polarization beam splitters (PBSs) and N photodetectors (PDs). An experiment is carried out. A 4-element linear patch antenna array operating at 14 GHz and a 1 × 4 optical beamforming network (OBFN) is employed to realize the phased array antenna. The radiation patterns of the phased array antenna at -30°, 0° and 30° are achieved. PMID:24663694

Zhang, Yamei; Wu, Huan; Zhu, Dan; Pan, Shilong

2014-02-24

151

Controlling Aggregation in Non-Polar Asphaltene Suspensions Through Electrostatics  

NASA Astrophysics Data System (ADS)

Asphaltenes, the most aromatic and largest molecular weight components of petroleum fluids, can undergo a liquid-liquid phase transition in conditions including highly non-polar environments. Phase separation begins with molecular association and proceeds to and through the colloidal length-scale until complete sedimentation or deposition. Non-ionic polymeric dispersants can stabilize asphaltenes at the colloidal scale in non-polar suspensions. We perform a variety of experiments which suggest that stabilization occurs by adsorption of dispersant onto the asphaltenes, truncating the progress of precipitation. In particular, dynamic light scattering (DLS) and phase-analysis light scattering (PALS) measurements indicate that electrostatic repulsion is responsible for stabilizing asphaltene colloids against further aggregation. Aggregation time increases exponentially with dispersant concentration, as expected for particles interacting through a combination of attractive dispersion forces and repulsive electrostatics. However, contrary to current understandings of electrostatic stabilization in non-polar systems, the charges in colloidal asphaltene suspensions seem to arise from the asphaltene colloids themselves rather than from dispersant micelles.

Hashmi, Sara; Firoozabadi, Abbas

2012-02-01

152

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

153

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

154

Top-emitting micromechanical VCSEL with a 31.6-nm tuning range  

Microsoft Academic Search

We report a top-emitting micromechanical vertical-cavity surface-emitting laser (VCSEL) with a continuously tunable wavelength range of 31.6 nm, the widest tuning range demonstrated by a VCSEL to date. Good laser characteristics are maintained throughout the tuning range centered at 935 nm: continuous-wave (CW) threshold occurs between 1.24.5 mA while output power at 10-mA DC bias remains between 0.5 and 1.6

Y. M. Li; W. Yuen; G. S. Li; C. J. Chang-Hasnain

1998-01-01

155

Planar Cell Polarity Acts Through Septins to Control Collective Cell Movement and Ciliogenesis  

Microsoft Academic Search

The planar cell polarity (PCP) signaling pathway governs collective cell movements during vertebrate embryogenesis, and certain PCP proteins are also implicated in the assembly of cilia. The septins are cytoskeletal proteins controlling behaviors such as cell division and migration. Here, we identified control of septin localization by the PCP protein Fritz as a crucial control point for both collective cell

Su Kyoung Kim; Asako Shindo; Tae Joo Park; Edwin C. Oh; Srimoyee Ghosh; Ryan S. Gray; Richard A. Lewis; Colin A. Johnson; Tania Attie-Bittach; Nicholas Katsanis; John B. Wallingford

2010-01-01

156

Polarization-control of the potential barrier at the electrode interfaces in epitaxial ferroelectric thin films.  

PubMed

Electrode interface is a key element in controlling the macroscopic electrical properties of the ferroelectric capacitors based on thin films. In the case of epitaxial ferroelectrics, the electrode interface is essential in controlling the leakage current and the polarization switching, two important elements in the read/write processes of nonvolatile memories. However, the relation between the polarization bound charges and the electronic properties of the electrode interfaces is not yet well understood. Here we show that polarization charges are controlling the height of the potential barriers at the electrode interfaces in the case of Pb(Zr,Ti)O3 and BaTiO3 epitaxial films. The results suggest that the height is set to a value allowing rapid compensation of the depolarization field during the polarization switching, being almost independent of the metals used for electrodes. This general behavior open a new perspective in engineering interface properties and designing new devices based on epitaxial ferroelectrics. PMID:24446901

Pintilie, Ioana; Teodorescu, Cristian Mihail; Ghica, Corneliu; Chirila, Cristina; Boni, Andra Georgia; Hrib, Luminita; Pasuk, Iuliana; Negrea, Raluca; Apostol, Nicoleta; Pintilie, Lucian

2014-02-26

157

Liquid crystals for polarization control in the MWIR  

NASA Astrophysics Data System (ADS)

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

Petrak, Erika K.; Baur, Thomas G.

2014-05-01

158

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

159

Magnetic control of electric polarization in the noncentrosymmetric compound (Cu,Ni)B2O4  

NASA Astrophysics Data System (ADS)

The weak ferromagnetic moment in Ni-doped CuB2O4 can be rotated by applying an electric field. While this implies spin-driven ferroelectricity, no direct evidence of electric polarization has been reported to date. Here we report the induction and control of polarization in the borate in the presence of an external magnetic field. Applying a magnetic field along the [110] or [11¯0] axis induces electric polarization along the [001] axis. The polarization is reversed by switching the magnetic-field direction between the [110] and [11¯0] axes. The mechanism by which electric polarization emerges can be well explained in the framework of spin-dependent metal-ligand hybridization.

Khanh, N. D.; Abe, N.; Kubo, K.; Akaki, M.; Tokunaga, M.; Sasaki, T.; Arima, T.

2013-05-01

160

Control of Fibrinogen Assembly by Changing a Polarity of Surfaces  

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

161

A 54-mW 8-Gbit/s VCSEL driver in a 65-nm CMOS technology  

NASA Astrophysics Data System (ADS)

We report a VCSEL driver ASIC designed and fabricated in a commercial 65-nm CMOS process. At 8 Gbps, the eye diagram passes the eye mask test and the bit-error-rate is less than 10-12 at the 95% confidence level. The total power consumption (including VCSEL) is about 54 mW, less than 1/4 of our previous VCSEL driver ASIC in a silicon-on-sapphire CMOS technology. The VCSEL driver has been tested in a neutron beam with the maximum energy of 800 MeV and the cross section has been estimated to be less than 3.14 × 10-11 cm2.

Liang, F.; Lu, W.; Chen, J.; Deng, B.; Gong, D.; Guo, D.; Jin, G.; Li, X.; Liang, H.; Liu, C.; Liu, G.; Wang, Z.; Xiang, A.; Xu, T.; Ye, J.; Liu, T.

2014-01-01

162

Full control of magnetism in a manganite bilayer by ferroelectric polarization  

NASA Astrophysics Data System (ADS)

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; Dagotto, Elbio

2013-10-01

163

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

164

Propagation of light in serially coupled plasmonic nanowire dimer: Geometry dependence and polarization control  

SciTech Connect

We experimentally studied plasmon-polariton-assisted light propagation in serially coupled silver nanowire (Ag-NW) dimers and probed their dependence on bending-angle between the nanowires and polarization of incident light. From the angle-dependence study, we observed that obtuse angles between the nanowires resulted in better transmission than acute angles. From the polarization studies, we inferred that light emission from junction and distal ends of Ag-NW dimers can be systematically controlled. Further, we applied this property to show light routing and polarization beam splitting in obtuse-angled Ag-NW dimer. The studied geometry can be an excellent test-bed for plasmonic circuitry.

Singh, Danveer; Raghuwanshi, Mohit; Pavan Kumar, G. V. [Photonics and Optical Nanoscopy Laboratory, Department of Physics and Department of Chemistry, Indian Institute of Science Education and Research (IISER), Pune 411008 (India)

2012-09-10

165

Controlling the chirality and polarity of vortices in magnetic tunnel junctions  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

166

Ionospheric control of polarization of low-latitude geomagnetic micropulsations at sunrise  

Microsoft Academic Search

The ionospheric control of low latitude pulsation polarization characteristics suggested by Saka et al. (1980) has been confirmed through continuous low latitude Pc3 and Pc4 geomagnetic micropulsation observations. The D-component amplitude increases as much as that of the H-component after sunrise, effecting the tilting of the major polarization ellipse axis from north to northwest. This coincides with the appearance of

O. Saka; M. Itonaga; T. Kitamura

1982-01-01

167

Control of polarized iodine atom branching ratio in NaI photodissociation  

SciTech Connect

We report branching ratios between the ground and excited states of iodine atoms in the photodissociation of sodium iodide. We employ wave packet propagation techniques to study the optimal production of polarized iodine atoms and find experimentally realizable laser parameters to control the outcome. Application of a learning algorithm shows that the product branching can be controlled by suitably varying the time delay, the chirp, and the relative phase of the pump and control laser pulses. Periodic modulation of the polarized iodine atom branching ratio as a function of the delay between the firing of the two ultrashort laser pulses provides interesting insights into the photodissociation process.

Hosseini, Babak H. [ITAMP, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138 (United States); Fakultaet fuer Physik und Astronomie, Universitaet Heidelberg, Heidelberg (Germany); Sadeghpour, H.R. [ITAMP, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138 (United States); Balakrishnan, N. [Department of Chemistry, University of Nevada Las Vegas, Las Vegas, Nevada 89154 (United States)

2005-02-01

168

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

169

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

SciTech Connect

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.

Felici, F.; Goodman, T.; Sauter, O. [Centre de Recherches en Physique des Plasmas, Association EURATOM-Suisse, Ecole Polytechnique Federale de Lausanne (EPFL), 1015 Lausanne (Switzerland); Shimozuma, T.; Ito, S.; Mizuno, Y.; Kubo, S.; Mutoh, T. [National Institite for Fusion Science (NIFS), Oroshi-cho, Toki 509-5292 (Japan)

2009-01-15

170

What controls the polarity change of decollement reflection along the Nankai Trough?  

NASA Astrophysics Data System (ADS)

Understanding of the structure and physical properties of the decollement, which is a plate boundary fault in a subduction zone, is important to elucidate a mechanism of megathrust earthquake generation. Variation of reflection polairty, which is one of the key natures of the decollement, appears to be closely related to fluid flow process in the subduction. In spite of previous seismic reflection studies to show a locality of polarity change of the decollement reflection in the Nankai Trough, its general pattern and causes are still controversial. In this study, we aim to figure out what controls the polarity change of decollement reflection along the entire Nankai Trough. We interpreted multichannel seismic reflection profiles that have been acquired in the Nankai Trough margin by Japan Agency for Marine-Earth Science and Technology (JAMSTEC) since the year of 1997. We focus on three features of the decollement reflection: regional distribution, polarity, and seismic stratigraphy. We separated the Nankai subduction zone into "stable sliding" and "stick slip" zones, based on location of the decollement step-down to the subducting oceanic crust. According to the reflection polarity (i.e., normal or reverse) of the decollement, we divided the entire Nankai subduction zone into 6 different regions along Trough. Assuming that the reflection polarity is closely related to incoming sediments, we could recognize 5 different cases in relationship between the decollement reflection polarity and seismic facies: (1) normal polarity on the top of turbidites, (2) reverse polarity in hemipelagic mud, (3) normal polarity on the volcaniclastic layer with a turbidites below, (4) reverse polarity on the volcaniclastic layer without turbidites below, and (5) normal polarity off Kumano basin. Since bedding planes of tubidites may be used as fluid paths, fluid supply to the docollement zone is quite restricted, producing the normal polarity of docollement reflection on the top of turbidites. When the decollement is developed within hemipelagic muddy sediments, it shows reverse polarity. For the vocaniclastic layer with high porosity, the decollement may be easily formed. In this talk, we will present results of the decollement reflection study, and discuss its implications for subduction processes in the Nankai Trough margin.

Lim, J.; Sasaki, T.; Higashi, M.; Park, J.

2010-12-01

171

Hybrid integration approach of VCSELs for miniaturized optical deflection of microparticles  

NASA Astrophysics Data System (ADS)

In recent years, optical manipulation has gained increasing interest, especially in combination with microfluidics. This combination offers promising tools for a fast and cost-effective sample analysis and manipulation. The contamination-free handling of micrometer-sized particles without any mechanical contact is an attractive tool for biology and medicine. VCSELs (vertical-cavity surface-emitting lasers) are an excellent choice for the trapping lasers, offering the opportunity of parallel particle manipulation by using two-dimensional VCSEL arrays, and of miniaturization by means of integration. In this paper, we present two novel concepts for the realization of the so-called integrated optical trap, resembling a strongly miniaturized version of the typically bulky setup of an optical trap. For this purpose, AlGaAs-GaAs-based VCSEL arrays with a very small device pitch were fabricated. We show the realization of integration-ready particle manipulation devices, both with top-emitting and with bottom-emitting densely packed VCSEL arrays. The smallest pitch of 18 ?m is achieved with bottom-emitting VCSEL arrays, having mesa diameters of only 16 ?m.

Bergmann, Anna; Khan, Niazul Islam; Martos Calahorro, Jose Antonio; Wahl, Dietmar; Michalzik, Rainer

2012-06-01

172

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

173

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

E-print Network

such as microelectro-mechanical systems (MEMS) VCSEL2,3 and fiber Fabry-Perot surface emitting laser (FFPSEL).4 to mechanical solutions, is the tuning response time which is close to a few 10 µs to scan the full spectral: Tunable VCSEL, Polymer Dispersed Liquid Crystal, Optical pumping, Distributed Bragg Reflector, Electro

Boyer, Edmond

174

Frequency-induced polarization bistability in vertical-cavity surface-emitting lasers with orthogonal optical injection  

SciTech Connect

We report theoretically on a pure frequency-induced polarization bistability in a vertical-cavity surface-emitting laser (VCSEL) subject to orthogonal optical injection, i.e., the master laser light polarization is orthogonal to that of the slave VCSEL. As the frequency detuning is scanned from negative to positive values and for a fixed injected power, the VCSEL exhibits two successive and possibly bistable polarization switchings. The first switching (from the slave laser polarization to the injected light polarization) exhibits a bistable region whose width is maximum for a given value of the injected power. Such a dependency of hysteresis width on the injected power is similar to that recently found experimentally by Hong et al.[Electron. Lett. 36, 2019 (2000)]. The bistability accompanying the second switching (from the injected light polarization back to the slave laser free-running polarization) exhibits, however, significantly different features related to the occurrence of optical chaos. Interestingly, the width of the bistable region can be tuned over a large range not only by modifying the injection parameters but also by modifying the device parameters, in particular the VCSEL linewidth enhancement factor.

Gatare, I. [Supelec, LMOPS CNRS UMR-7132, Unite de Recherche Commune Supelec et Universite de Metz, Rue Edouard Belin 2, F-57070 Metz (France); Department of Applied Physics and Photonics, (TW-TONA), Vrije Universiteit Brussel (VUB), Pleinlaan 2, B-1050 Brussels (Belgium); Panajotov, K. [Department of Applied Physics and Photonics, (TW-TONA), Vrije Universiteit Brussel (VUB), Pleinlaan 2, B-1050 Brussels (Belgium); Sciamanna, M. [Supelec, LMOPS CNRS UMR-7132, Unite de Recherche Commune Supelec et Universite de Metz, Rue Edouard Belin 2, F-57070 Metz (France)

2007-02-15

175

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

176

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

177

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

178

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

179

14 Climate control of biological UV exposure in polar and alpine aquatic ecosystems  

E-print Network

; Sommaruga 2001; Hessen 2002; Perin and Lean 2004) and has led to a broad range of research on UV optics14 Climate control of biological UV exposure in polar and alpine aquatic ecosystems Warwick F ozone in Antarctica over the last two decades has generated much concern about the effects of rising UV

Vincent, Warwick F.

180

Further discussion on bandwidth-enhanced chaos synchronization communication based on mutually coupled VCSELs  

NASA Astrophysics Data System (ADS)

A bandwidth-enhanced chaos synchronization communication system is proposed and its communication performance is investigated numerically. The results show that, using a bandwidth-enhanced chaotic signal from a driving vertical cavity surface-emitting laser (D-VCSEL) to drive two mutually coupled VCSELs (MC-VCSELs), the high-quality isochronal chaos synchronization with over 30GHz bandwidth between two corresponding LP modes in the two MCVCSELs can be obtained. Taking two LP modes as two different communication channels and adopting chaos masking (CMS) encryption scheme, this system can realize the bidirectional dual-channel high-speed chaos communication at 10Gbits/s transmission rate. Moreover, the parameters mismatches tolerance of this communication system and the influence of message transmission rate on the communication performance also are discussed.

Zhang, Zi-Yang; Xu, Yi-Na; Luo, Jie; He, Xiu; He, Yang; Lin, Xiao-Dong; Deng, Tao

2014-07-01

181

Phase control of semi-polar (112¯2) and non-polar (112¯0) GaN on cone shaped r-plane patterned sapphire substrates  

NASA Astrophysics Data System (ADS)

The control of formation of semi-polar (112¯2) and nonpolar a-plane (112¯0) GaN phases on r-plane cone shaped patterned sapphire substrates (CPSS) by metalorganic vapor-phase epitaxy has been investigated. With a nucleation layer grown at 535 °C and 200 mbar, only semi-polar (112¯2) GaN is formed. Increasing the nucleation layer temperature to 965 °C, only (112¯0) GaN is grown at 200 mbar. At reduced reactor pressure of 60 mbar, phase selectivity breaks down and semi-polar (112¯2) and non-polar (112¯0) GaN exist simultaneously. The crystalline quality of a-plane GaN on r-plane CPSS can be effectively improved using optimized growth direction control.

Wang, Mei-Tan; Brunner, Frank; Liao, Kuan-Yung; Li, Yun-Li; Tseng, Snow H.; Weyers, Markus

2013-05-01

182

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

183

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

184

Control of polarization and dipole moment in low-dimensional semiconductor nanostructures  

SciTech Connect

We demonstrate the control of polarization and dipole moment in semiconductor nanostructures, through nanoscale engineering of shape and composition. Rodlike nanostructures, elongated along the growth direction, are obtained by molecular beam epitaxial growth. By varying the aspect ratio and compositional contrast between the rod and the surrounding matrix, we rotate the polarization of the dominant interband transition from transverse-electric to transverse-magnetic, and modify the dipole moment producing a radical change in the voltage dependence of absorption spectra. This opens the way to the optimization of quantum dot amplifiers and electro-optical modulators.

Li, L. H.; Ridha, P. [Ecole Polytechnique Federale de Lausanne, Institute of Photonics and Quantum Electronics, Station 3, CH-1015 Lausanne (Switzerland); Mexis, M.; Smowton, P. M.; Blood, P. [Cardiff University, The Parade, Cardiff CF24 3AA (United Kingdom); Bozkurt, M.; Koenraad, P. M. [COBRA Research Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (Netherlands); Patriarche, G. [LPN/CNRS, Route de Nozay, 91460 Marcoussis (France); Fiore, A. [Ecole Polytechnique Federale de Lausanne, Institute of Photonics and Quantum Electronics, Station 3, CH-1015 Lausanne (Switzerland); COBRA Research Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (Netherlands)

2009-11-30

185

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

186

28 Gb/s 850 nm oxide VCSEL development at Avago  

NASA Astrophysics Data System (ADS)

Avago's 850nm oxide VCSEL for applications requiring modulation at 25-28G has been designed for -3dB bandwidths in excess of 18GHz over an extended temperature range of 0-85C. The VCSEL has been optimized to minimize DBR mirror thermal resistivity, electrical resistance and optical losses from free carrier absorption. The active region is designed for superior differential gain to enable high optical bandwidths. The small-signal modulation response has been characterized and the large-signal eye diagrams show excellent high-speed performance. Characterization data on other link parameters such as relative intensity noise and spectral width will also be presented.

Wang, Jingyi; Keever, Mark; Feng, Zheng-Wen; Fanning, Thomas; Chu, Chen; Sridhara, Aadi; Hopfer, Friedhelm; Sale, Terry; Cheng, An-Nien; Shao, Bing; Ding, Li; Wen, Pengyue; Chang, Hsu-Hao; Wang, Charlie; Hui, David Chak Wang; Giovane, Laura

2013-03-01

187

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

188

Chaos synchronization and encrypted communication systems as an application of VCSELs  

NASA Astrophysics Data System (ADS)

In this work we have proposed chaotic synchronization system using two identical electro-optical nonlinear delayed feedback systems (NDFS) utilizing VCSEL. This first time proposal has high potential to perform more sensitive chaotic dynamics for improvement of encrypted communications quality. In this system we have demonstrated the reduction of robustness to prevent tapping by someone else attaining higher correlation but only if the feedback gain is the same value. We have also demonstrated the variations of correlation if feedback gain has the slight difference. Moreover, we have demonstrated applications to encrypted communications using VCSEL.

Hisatomi, Masanori; Sasaki, Wakao

2014-02-01

189

Eigenmode analysis of phased-coupled VCSEL arrays using spatial coherence measurements.  

PubMed

We apply the modal coherence theory to evaluate the spatial mode structure of a 2×2 phase-coupled array of vertical cavity surface emitting lasers (VCSELs). The eigenmode structure is extracted for different pump currents by measuring the degree of spatial coherence of all VCSEL pairs in the array. The results reveal the impact of optical disorder and spatial hole burning on the modal discrimination. The approach is useful more generally for the evaluation of spatial mode content of other laser array. PMID:21808357

Lamothe, Elodie; Lundeberg, Lars D A; Kapon, Eli

2011-08-01

190

Polarity control of ZnO films grown on nitrided c-sapphire by molecular-beam epitaxy  

SciTech Connect

The polarity of molecular-beam epitaxy grown ZnO films was controlled on nitrided c-sapphire substrate by modifying the interface between the ZnO buffer layer and the nitrided sapphire. The ZnO film grown on nitrided sapphire was proven to be Zn-polar while the O-polar one was obtained by using gallium predeposition on nitrided sapphire, which was confirmed by coaxial impact collision ion scattering spectroscopy and chemical etching effect. The Zn-polar ZnO film showed higher growth rate, slightly better quality, and different surface morphology in comparison to the O-polar one.

Wang Xinqiang; Tomita, Yosuke; Roh, Ok-Hwan; Ohsugi, Masayuki; Che, Song-Bek; Ishitani, Yoshihiro; Yoshikawa, Akihiko [Center for Frontier Electronics and Photonics, Department of Electronics and Mechanical Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan)

2005-01-03

191

Polarity control of ZnO films grown on nitrided c-sapphire by molecular-beam epitaxy  

NASA Astrophysics Data System (ADS)

The polarity of molecular-beam epitaxy grown ZnO films was controlled on nitrided c-sapphire substrate by modifying the interface between the ZnO buffer layer and the nitrided sapphire. The ZnO film grown on nitrided sapphire was proven to be Zn-polar while the O-polar one was obtained by using gallium predeposition on nitrided sapphire, which was confirmed by coaxial impact collision ion scattering spectroscopy and chemical etching effect. The Zn-polar ZnO film showed higher growth rate, slightly better quality, and different surface morphology in comparison to the O-polar one.

Wang, Xinqiang; Tomita, Yosuke; Roh, Ok-Hwan; Ohsugi, Masayuki; Che, Song-Bek; Ishitani, Yoshihiro; Yoshikawa, Akihiko

2005-01-01

192

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

193

Double pass, common path method for arbitrary polarization control using a ferroelectric liquid crystal spatial light modulator.  

PubMed

We present a method for arbitrary control of the polarization of a light beam. Our method uses two holograms on a binary ferroelectric liquid crystal spatial light modulator (FLCSLM), and so has the potential to allow polarization state switching at kilohertz rates. Unlike previous methods that achieve polarization control using FLCSLMs, our method is common path and requires only the simplest optical components. For this reason, the method is very easy to setup, align, and maintain. In addition, it has the ability to modulate unpolarized input light. We demonstrate the formation of radially, azimuthally, and circularly polarized beams by imaging their focal spots formed at low numerical aperture. PMID:23546237

Clegg, James H; Neil, Mark A A

2013-04-01

194

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

195

Coupled mode theory: a powerful tool for analyzing complex VCSELs and designing advanced device features  

Microsoft Academic Search

Vertical-cavity surface-emitting lasers (VCSELs) have become leading light sources in plenty of applications due to their good characteristics and low costs. There are, however, some features that need improvements; therefore, optimized or new designs ideas are necessary. To this aim, an electromagnetic simulation tool, which is fast and precise at the same time, is desirable; to cover all the possible

Pierluigi Debernardi; Gian Paolo Bava

2003-01-01

196

Transverse Mode Dynamics of VCSELs Through Space-Time Domain Simulation  

NASA Technical Reports Server (NTRS)

Modeling and simulation are important to understand laser operation and to optimize and design device functions. Numerical simulation of VCSEL (Vertical Cavity Surface Emitting Lasers) has been largely based on solving time-independent Helmholtz equation or time dependent coupled mode equations. There are various advantages for choosing these approaches. However, the disadvantages are also apparent. The former cannot handle dynamical mode competition seen in VCSELs, while the latter assumes a given type and number of modes a priori. Furthermore, the microscopic physics of heterstructures and electron-hole plasma is very often represented by a few parameters such as linear gain coefficients and the linewidth enhancement factor. These are over simplification of space and frequency (wavelength) dependent gain and refractive index functions. When the space-time dynamical operation of VCSELs becomes important, these simple approximations become questionable. In this paper, we apply a recently developed model for edge-emitting lasers to a gain guided VCSEL for space-time domain simulation. This model takes into account the actual nonlinear dependence of gain and refractive index on frequency and carrier density within the frame work of the effective Bloch equations. The corresponding partial differential equations are solved directly by finite difference methods. Laser behavior with increasing pumping current is investigated in detail. Special attention is paid to the dynamical competition of the transverse modes.

Goorjian, Peter M.; Ning, Cun-Zheng; Saini, Subhash (Technical Monitor)

1999-01-01

197

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

198

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

SciTech Connect

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

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

1997-04-01

199

Energy-efficient oxide-confined high-speed VCSELs for optical interconnects  

NASA Astrophysics Data System (ADS)

Principles of energy-efficient high speed operation of oxide-confined VCSELs are presented. Trade-offs between oxideaperture diameter, current-density, and energy consumption per bit are demonstrated and discussed. Record energyefficient error-free data transmission up to 40 Gb/s, across up to 1000 m of multimode optical fiber and at up to 85 °C is reviewed.

Moser, Philip; Wolf, Philip; Larisch, Gunter; Li, Hui; Lott, James A.; Bimberg, Dieter

2014-02-01

200

A Mach-Zehnder interferometer for the fine control of the polarization status of a beam  

NASA Astrophysics Data System (ADS)

An optical system for the generation of a beam with a variable and controllable polarization status has been designed, realized and tested. The system is based on an interferometric set up, consisting of a splitting system, a phase delay system and a recombination system. By controlling the optical path, it is possible to obtain every polarization status: linear, elliptical and circular. The system can be realized with an all reflective scheme and it can work in a wide spectral band of the electromagnetic spectrum, from the near-infrared down to the extreme ultraviolet. The system can be integrated in different optical setups in order to enhance their versatility, such as in laser devices, optical instrumentations, synchrotron lines or free electron lasers beam transport system. Finally it can be also used to test optical device and for calibration of optical components.

Tessarolo, Enrico; Corso, Alain Jody; Bonaldo, Stefano; Zuppella, Paola; Pelizzo, Maria Guglielmina

2014-09-01

201

Injection moulding integration of a red VCSEL illuminator module for a hologram reader sensor  

NASA Astrophysics Data System (ADS)

A red VCSEL illuminator module demonstrator was manufactured by injection moulding integration. A red VCSEL chip was first attached to a simple FR4 substrate, which contains bonding pads and conducting wires for the VCSEL chip attachment and electrical driving. The substrate was then placed as an insert in an injection mould. The VCSEL chip shielding and optics formation was made in a one-step injection moulding process. The used optical thermoplastic in the processing was polycarbonate (PC). The pursued optical function of the single spherical surface attained in the moulding was to collimate the emitted red light (?=664.5 nm) from the VCSEL chip. The main critical issue related to the manufacturing of the illuminator module in the injection moulding process was the durability of bonding wire contacts. A single 25 ?m diameter gold wire was used in wire bonding in order to create the upper contact to the chip. The lower contact was processed by attaching the chip to the substrate using conductive epoxy. A test series of 20 modules using FR4 substrate materials were produced. The number of fully operative modules was 12 resulting total module yield of 60%. The main reason for a non-operative module was loosening of the bonding wire during the injection moulding process. The bonding wire durability in the moulding process can be improved by using glob-top shielding of the VCSEL device before injection moulding and using a lower holding pressure in the injection moulding process. A diamond turned insert was used in the mould in order to create a high quality lens surface on the top of the VCSEL chip. The tower average length after one iteration round by mould modification was 8.676 ?m, so the measured value was on average 20 ?m larger than nominal value. The measured RMS roughness of the processed lens surface was 5 ... 7 nm and the radius -3.23 ... 3.83 mm. The radius of the lens and the length of the tower varied depending of the used process parameters. The manufactured illumination module can be integrated with a CMOS image matrix sensor in order to form a compact hologram reader system. The injection moulding integration principle seems to be very promising method to manufacture intelligently integrated and cost-effective optoelectronic products according to experience with this demonstrator.

Keränen, Kimmo; Saastamoinen, Toni; Mäkinen, Jukka-Tapani; Silvennoinen, Mikko; Mustonen, Ilpo; Vahimaa, Pasi; Jääskeläinen, Timo; Lehto, Ari; Ojapalo, Anneli; Schorpp, Marcus; Hoskio, Pekka; Karioja, Pentti

2007-05-01

202

Polarization distribution control of parallel femtosecond pulses with spatial light modulators.  

PubMed

A parallel femtosecond pulse irradiation method using a computer-generated hologram displayed on a spatial light modulator provides the advantages of high throughput and high energy-use efficiency. Polarization control of the femtosecond pulse enables some unique properties, for example, selective excitation of an anisotropic molecule, focusing at a size beyond the diffraction limit owing to the longitudinal vector component of a radially polarized beam focused by a high-numerical-aperture objective lens, and fabrication of periodic nanostructures with femtosecond laser light. In this study, we propose a parallel femtosecond laser irradiation system with arbitrary polarization distribution control using a pair of spatial light modulators. By using the system, the interval between the diffraction spots was the closest yet reported by avoiding mutual interference among their side lobes. The interval was improved to half compared with our previous work. We also demonstrated the parallel fabrication of periodic nanostructures with orientation control, which, to our knowledge, is the first reported demonstration of its kind. PMID:23736552

Hasegawa, Satoshi; Hayasaki, Yoshio

2013-06-01

203

LKB1/AMPK and PKA control ABCB11 trafficking and polarization in hepatocytes.  

PubMed

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

204

Approach to control polarization and magnetic properties for multiferroics with Dzyaloshinskii-Moriya interaction  

NASA Astrophysics Data System (ADS)

We propose a theoretical model for one-dimensional (charge transfer magnets with Dzyaloshinskii-Moriya (DM) interaction. By using Green's function theory, we have studied the effect of DM interaction on ferroelectric and magnetic properties, where ferroelectricity is induced through symmetric mechanism. It is shown that the uniform DM interaction reduces the polarization and makes the magnetization plateau narrow down. Moreover, the transition temperature descends as the uniform DM interaction ascends, which is attributed to the decrease of the energy gap. In addition, the staggered DM interaction, which is related to intersite distance, is also discussed. It is also found that there exists a critical point, above or below which the staggered DM interaction plays different roles on the polarization, transition temperature, and magnetic behavior. As the staggered DM interaction is larger, it enhances the polarization and transition temperature and meanwhile widens the magnetization plateau, otherwise it reduces the polarization, transition temperature, and magnetization plateau. The results provide approach to control the transition temperature and physical behavior of multiferroics.

Wang, Shuling; Li, Ruixue; Fu, Hua-Hua; Ding, Linjie; Yao, Kailun

2014-07-01

205

Polarization-Controlled Switchable Multi-Wavelength Erbium-Doped Fiber Laser with Cascaded Fiber Bragg Gratings  

Microsoft Academic Search

A simple concept of switchable multiwavelength erbium-doped fiber laser is successfully proposed and demonstrated. The multiwavelengths are specified by a cascaded fiber Bragg gratings. The wavelength switching can be achieved due to the polarization dependence loss induced by proper adjustment of polarization controller in ring cavity, The experiments demonstrate that the switchable lasing operation with the random combination of three

Yang Yang; Xueguang Qiao; Jing Zhang; Rui Zhou; Ruohui Wang; Jinghua Zhang

2011-01-01

206

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

NASA Astrophysics Data System (ADS)

We demonstrate an enhanced electrical stability through a Ti oxide (TiOx) 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 TiOx thin film, resulting in oxygen cross-binding with a-IGZO surface. The electrical properties of a-IGZO thin film transistors (TFTs) with TiOx depend on the surface polarity change and electronic band structure evolution. This result indicates that TiOx 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; Choi, Yonghyuk; Jeon, Heeyoung; Shin, Seokyoon; Seo, Hyungtak; Jeon, Hyeongtag

2014-01-01

207

Controllable vector bottle-shaped fields generated by focused spatial-variant linearly polarized vector beams  

NASA Astrophysics Data System (ADS)

We demonstrate that the optical bottle-shaped fields can be controllably generated by the focused spatial-variant linearly polarized vector beams. Based on the vectorial Rayleigh-Sommerfeld formulas under the paraxial approximation, we present theoretically the analytical expression for the focused field of the vector beam and predict the evolution of the sate of polarization (SoP) in the focal region. Experimentally, we observe the vector bottle-shaped field that is in agreement with the numerical simulations. In particular, we validate that both the SoP and the size of the optical bottle field are manipulated easily by varying the azimuthal topological charge and the radial mode index.

Gu, Bing; Wu, Jia-Lu; Pan, Yang; Cui, Yiping

2013-11-01

208

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

209

Modulation and thermal properties of tunnel-coupled InAs QD 1.13mum VCSELs  

Microsoft Academic Search

Quantum dot (QD) -based vertical cavity surface emitting lasers (VCSELs) are predicted to have faster modulation response and better thermal stability as compared with quantum well (QW) VCSELs. QD size distribution, limited carrier capture and thermalization rates affect the maximum saturated gain of QD-based lasers. To address these problems, structures of tunnel coupled pairs consisting of InGaAs QW grown on

V. Tokranov; M. Yakimov; J. van Eisden; S. Oktyabrsky

2008-01-01

210

Nonclassical dual control of circularly polarized luminescence modes of binaphthyl-pyrene organic fluorophores in fluidic and glassy media.  

PubMed

The fluorescent modes and signs of the circularly polarized luminescence of an axially chiral binaphthyl-pyrene organic fluorophore were successfully controlled by changing from a fluidic chloroform solution to a glassy poly(methyl methacrylate) solid film. PMID:24934379

Nakabayashi, Kazuki; Amako, Tomoyuki; Tajima, Nobuo; Fujiki, Michiya; Imai, Yoshitane

2014-10-01

211

PKC? and GSK-3? control neuronal polarity in developing rodent enteric neurons while SMURF1 promotes neurite growth but does not influence polarity  

PubMed Central

Enteric nervous system (ENS) precursors migrate extensively before differentiating to form uniaxonal or multiaxonal neurons. ENS precursor survival, neurite growth and cell migration are all directed by Ret kinase, but downstream signaling pathways are incompletely understood. We now demonstrate that proteins regulating polarity in other cells including PAR3, PAR6, PKC?, and GSK3? are expressed in developing enteric neurons with a polarized distribution. Blocking PKC? or GSK3? reduces ENS precursor migration and induces the formation of multiaxonal neurons. Axon elongation also depends on SMURF1, an E3 ubiquitin ligase that promotes RhoA degradation and associates with polarity proteins. SMURF1 inhibition, however, does not increase the number of multiaxonal neurons in ENS precursors. These data link cell surface Ret activation with molecular machinery controlling cytoskeletal dynamics and suggest that polymorphisms influencing PKC? or GSK3? might alter Hirschsprung disease penetrance or expressivity by affecting ENS precursor migration. PMID:17728459

Vohra, Bhupinder P. S.; Fu, Ming; Heuckeroth, Robert O.

2008-01-01

212

Enhanced Scattered Light Imaging of Nanoparticles by Controlling the Polarization Distribution with Photonic Crystals  

NASA Astrophysics Data System (ADS)

An optical microscopy with a high sensitivity and resolution is required for observing semiconductor wafers and biological cells for nanotechnology and biotechnology applications. However, it is difficult to observe samples that are small compared with the optical wavelength since the signal is swamped by background noise such as dark noise and electrical noise and other signals besides that from the sample. Furthermore, light scattered from the sample cannot be focused into a spot in the image plane due to interference of polarized light, resulting in a blurred image that has a low resolution. This study proposes a method for removing the background noise and for improving the image resolution of nanoparticles by controlling the polarization direction. This method can be used to perform optical microscopy with a high sensitivity and resolution. We verify the effectiveness of this method by performing simulations and experiments. Simulations predict that the peak intensity obtained using this method will be 3.4 times higher than that obtained using a conventional microscope and that the resolution of this technique will be 0.43 times smaller than that of conventional microscopy. Experiments show that this method with a photonic crystal utilized as a radial polarization converter is capable of detecting 23-nm-diameter PSLs on a silicon wafer.

Otani, Yuko; Urano, Yuta; Honda, Toshifumi; Watanabe, Masahiro

2013-05-01

213

GDI-Mediated Cell Polarization in Yeast Provides Precise Spatial and Temporal Control of Cdc42 Signaling  

PubMed Central

Cell polarization is a prerequisite for essential processes such as cell migration, proliferation or differentiation. The yeast Saccharomyces cerevisiae under control of the GTPase Cdc42 is able to polarize without the help of cytoskeletal structures and spatial cues through a pathway depending on its guanine nucleotide dissociation inhibitor (GDI) Rdi1. To develop a fundamental understanding of yeast polarization we establish a detailed mechanistic model of GDI-mediated polarization. We show that GDI-mediated polarization provides precise spatial and temporal control of Cdc42 signaling and give experimental evidence for our findings. Cell cycle induced changes of Cdc42 regulation enhance positive feedback loops of active Cdc42 production, and thereby allow simultaneous switch-like regulation of focused polarity and Cdc42 activation. This regulation drives the direct formation of a unique polarity cluster with characteristic narrowing dynamics, as opposed to the previously proposed competition between transient clusters. As the key components of the studied system are conserved among eukaryotes, we expect our findings also to apply to cell polarization in other organisms. PMID:24348237

Wedlich-Soldner, Roland; Frey, Erwin

2013-01-01

214

Reversible control of spin-polarized supercurrents in ferromagnetic Josephson junctions  

NASA Astrophysics Data System (ADS)

Magnetic inhomogeneity at a superconductor (S)–ferromagnet (F) interface converts spin-singlet Cooper pairs into spin-one triplet pairs. These pairs are immune to the pair-breaking exchange field in F and support a long-range proximity effect. Although recent experiments have confirmed the existence of spin-polarized triplet supercurrents in S–F–S Josephson junctions, reversible control of the supercurrent has been impossible because of the robust preconfigured nature of the inhomogeneity. Here, we use a barrier comprising three F layers whose relative magnetic orientation, and hence the interfacial inhomogeneity, can be controlled by small magnetic fields; we show that this enables full control of the triplet supercurrent and, by using finite element micromagnetic simulations, we can directly relate the experimental data to the theoretical models which provide a general framework to understand the role played by magnetic states in long-range supercurrent modulation.

Banerjee, N.; Robinson, J. W. A.; Blamire, M. G.

2014-08-01

215

Planar cell polarity acts through septins to control collective cell movement and ciliogenesis.  

PubMed

The planar cell polarity (PCP) signaling pathway governs collective cell movements during vertebrate embryogenesis, and certain PCP proteins are also implicated in the assembly of cilia. The septins are cytoskeletal proteins controlling behaviors such as cell division and migration. Here, we identified control of septin localization by the PCP protein Fritz as a crucial control point for both collective cell movement and ciliogenesis in Xenopus embryos. We also linked mutations in human Fritz to Bardet-Biedl and Meckel-Gruber syndromes, a notable link given that other genes mutated in these syndromes also influence collective cell movement and ciliogenesis. These findings shed light on the mechanisms by which fundamental cellular machinery, such as the cytoskeleton, is regulated during embryonic development and human disease. PMID:20671153

Kim, Su Kyoung; Shindo, Asako; Park, Tae Joo; Oh, Edwin C; Ghosh, Srimoyee; Gray, Ryan S; Lewis, Richard A; Johnson, Colin A; Attie-Bittach, Tania; Katsanis, Nicholas; Wallingford, John B

2010-09-10

216

Complete Control of Polarization and Phase of Light with High Efficiency and Sub-wavelength Spatial Resolution  

E-print Network

Meta-surfaces are planar structures that locally change polarization, phase, and amplitude of light, thus enabling flat, lithographically patterned free-space optical components with functionalities controlled by design. Several types of meta-surfaces have been reported, but low efficiency and the inability to provide simultaneous phase and polarization control have limited their applications. Here we demonstrate a platform based on high-contrast dielectric elliptical nano-posts providing complete and efficient control of polarization and phase with sub-wavelength spatial resolution. The unprecedented freedom in manipulating light not only enables realization of conventional free-space transmissive optical elements such as phase-plates, wave-plates and beam-splitters, but also elements with novel functionalities such as general polarization switchable phase holograms and arbitrary vector beam generators which will change the design paradigms for free-space optical systems.

Arbabi, Amir; Bagheri, Mahmood; Faraon, Andrei

2014-01-01

217

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

PubMed Central

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

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

2013-01-01

218

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

NASA Astrophysics Data System (ADS)

We experimentally demonstrate space-code-division multiple access (space-CDMA) based two-dimensional (2-D) parallel optical interconnections by using image fibers and 8 × 8 vertical-cavity surface-emitting laser (VCSEL)/photo diode (PD) arrays. Two spatially encoded four-bit (2 × 2) parallel optical signals were emitted from 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 ?m for a BER performance of 10-9.

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

2002-11-01

219

QD VCSELs with InAs\\/InGaAs short period superlattice QW injector  

Microsoft Academic Search

Structures with tunnel-coupled pairs consisting of InGaAs quantum wells (QWs) grown on top of self-assembled InAs quantum dots (QDs) were used previously as a gain medium for vertical cavity surface emitting lasers (VCSELs) to eliminate problems with QD-limited maximum saturated gain. Conventional molecular beam epitaxy of tunnel-coupled QDs with slow InAs growth rate and InGaAs solid solution QW injector with

V. Tokranov; M. Yakimov; S. Oktyabrsky

2009-01-01

220

Transverse modes under external feedback and fiber coupling efficiencies of VCSEL's  

Microsoft Academic Search

We report a detailed study on the transverse mode behavior of vertical-cavity surface-emitting lasers (VCSEL's) under strong external feedback. Backreflections from a glass facet result, periodically depending on the feedback phase, in variations of the transverse mode pattern of strongly index guided multitransverse-mode-emitting lasers. As a result, butt-coupling efficiencies of these lasers strongly depend on laser-fiber distance. For typical active

J. Heinrich; H. Zeeb; K. J. Ebeling

1998-01-01

221

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

Microsoft Academic Search

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

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

1999-01-01

222

High-speed optical computing devices based on VCSEL diodes with feedback  

Microsoft Academic Search

In the present paper, we have investigated the performance of high-speed optical computing devices based on vertical-cavity-surface emitting laser (VCSEL) diodes made of GaAs with and without feedback. The characteristics of performance are the normalized transfer function of harmonic response, the gain overshoot, the resonance frequency, and the 3-dB bandwidth. The effect of the feedback regulator is deeply studied. Thermal

H. M. A. Kelash; H. S. Soror; N. F. El-Halafawy

2004-01-01

223

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

PubMed

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

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

2013-01-01

224

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

PubMed Central

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

Schnell, Michael; Savert, Alexander; Uschmann, Ingo; Reuter, Maria; Nicolai, Maria; Kampfer, Tino; Landgraf, Bjorn; Jackel, Oliver; Jansen, Oliver; Pukhov, Alexander; Kaluza, Malte Christoph; Spielmann, Christian

2013-01-01

225

Two dimensional analysis of finite size high-contrast gratings for applications in VCSELs.  

PubMed

2-dimensional simulations of high-contrast gratings (HCGs) of finite size are carried out, targeting at their applications in vertical-cavity surface-emitting lasers (VCSELs). Finite HCGs show a very different behavior from infinite grating ones. The reflectivity of a finite HCG strongly depends on the HCG size and the source size. Our simulation results predict finite reflectivity and transmission values, well consistent with reported experimental results. The band of high reflectivity (>99.5%) of finite HCGs is less broad as compared to the infinite case. Losses into a guided mode excited in the HCG plane are identified as being at the root. This guided mode is excited due to the nonzero angular components in the finite source size, and greatly enhances the transmission and the light leakage from the slab. In addition, the simulation results show that the details of the finite HCG can shape the output beam, whilst a Gaussian-like reflected wave is typically achieved. Our simulations can explain the current discrepancies between numerical predictions of reflectivities approaching 100% and working HCG-VCSELs showing finite reflectivities and nearly Gaussian-like output. Consequently, our analysis of finite HCGs is indispensable for HCG-VCSEL design. PMID:24921302

Liu, Anjin; Hofmann, Werner; Bimberg, Dieter

2014-05-19

226

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

227

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

SciTech Connect

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

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

1999-06-30

228

Controllably Interfacing with Metal: A Strategy for Enhancing CO Oxidation on Oxide Catalysts by Surface Polarization.  

PubMed

Heterogeneous catalysis often involves charge transfer from catalyst surface to adsorbed molecules, whose activity thus depends on the surface charge density of catalysts. Here, we demonstrate a unique solution-phase approach to achieve controllable interfacial lengths in oxide-metal hybrid structures. Resulting from their different work functions, surface polarization is induced by the Ag-CuO interface and acts to tailor the surface charge state of CuO. As a result, the designed hybrid catalysts exhibit enhanced intrinsic activities in catalyzing CO oxidation in terms of apparent activation energy, as compared with their counterparts. Moreover, the CO conversion rate can be enhanced by maximizing the Ag-CuO interfacial length and thus the number of active sites on the CuO. This work provides a new strategy for tuning catalytic performance by controlling interface in hybrid catalysts. PMID:25296380

Bai, Yu; Zhang, Wenhua; Zhang, Zhenhua; Zhou, Jie; Wang, Xijun; Wang, Chengming; Huang, Weixin; Jiang, Jun; Xiong, Yujie

2014-10-22

229

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

230

Polarization-Controlled Differentiation of Human Neural Stem Cells Using Synergistic Cues from the Patterns of Carbon Nanotube Monolayer Coating  

PubMed Central

We report a method for selective growth and structural-polarization-controlled neuronal differentiation of human neural stem cells (hNSCs) into neurons using carbon nanotube network patterns. The CNT patterns provide synergistic cues for the differentiation of hNSCs in physiological solution and an optimal nanotopography at the same time with good biocompatibility. We demonstrated a polarized-controlled neuronal differentiation at the level of individual NSCs. This result should provide a stable and versatile platform for controlling the hNSC growth because CNT patterns are known to be stable in time unlike commonly-used organic molecular patterns. PMID:21568294

Park, Sung Young; Choi, Dong Shin; Jin, Hye Jun; Park, Juhun; Byun, Kyung-Eun; Lee, Ki-Bum; Hong, Seunghun

2011-01-01

231

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

PubMed Central

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

Morlino, Giulia; Barreiro, Olga; Baixauli, Francesc; Robles-Valero, Javier; Gonzalez-Granado, Jose M.; Villa-Bellosta, Ricardo; Cuenca, Jesus; Sanchez-Sorzano, Carlos O.; Veiga, Esteban; Martin-Cofreces, Noa B.

2014-01-01

232

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

233

A method for polarization control and analysis on Bonse–Hart double-crystal USANS instruments  

Microsoft Academic Search

The use of polarized beams and polarization analysis is an area of increasing interest to the small-angle neutron scattering (SANS) community. Since the angular acceptance of a DCD USANS instrument is very narrow, magnetic prisms can be exploited to select polarization. We compare two schemes by which this can be accomplished and describe how this method can be adapted for

Kenneth C Littrell; Wai Tung Lee

2004-01-01

234

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

235

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

236

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

NASA Astrophysics Data System (ADS)

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.

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

2013-10-01

237

Polarity control of ZnO on sapphire by varying the MgO buffer layer thickness  

NASA Astrophysics Data System (ADS)

Polarity-controlled ZnO films with an MgO buffer layer were grown on c-plane sapphire by plasma-assisted molecular-beam epitaxy. Convergent beam electron diffraction results showed that Zn-polarity (+c) growth occurred when the MgO layer was thicker than 3 nm, whereas O-polarity (-c) growth occurred when the layer was less than 2 nm. Reflection high-energy electron diffraction results revealed that MgO growth was Stranski-Krastanov mode, and that the growth mode transition from two- to three-dimensional occurred when the layer was thicker than 1 nm. In conclusion, polarity conversion apparently occurs due to the different atomic structure between the wetting layer and islands of MgO.

Kato, Hiroyuki; Miyamoto, Kazuhiro; Sano, Michihiro; Yao, Takafumi

2004-05-01

238

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

239

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 mVpp and an extinction ratio of 4dB 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

240

0.9W compact UV pulsed lasers using high-power VCSEL array side-pumping  

NASA Astrophysics Data System (ADS)

A compact UV pulsed laser pumped by high-power two-dimensional arrays of vertical-cavity surface-emitting lasers (VCSELs) was presented. A passively Q-switched 1064-nm Nd:YAG laser was side-pumped by kW-class 808-nm VCSEL pump modules and the output pulses were frequency quadrupled to 266-nm. 10-ns, 0.68-mJ UV pulsed output was obtained at 1.33k-Hz repetition rate. The average UV power is < 0.9-W. This VCSEL pumped high power UV laser source provides a reliable, low-cost and low-profile solution for military and commercial applications including remote sensing, laser processing and spectroscopy.

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

2013-02-01

241

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

PubMed

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

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

2014-10-01

242

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

PubMed

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

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

2014-11-01

243

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

244

Calibration and Field Deployment of the NSF G-V VCSEL Hygrometer  

NASA Astrophysics Data System (ADS)

Cloud formation and dynamics have a significant influence on the Earth's radiative forcing budget, which illustrates the importance of clouds with respect to global climate. Therefore, an accurate understanding of the microscale processes dictating cloud formation is crucial for accurate computer modeling of global climate change. A critical tool for understanding these processes from an airborne platform is an instrument capable of measuring water vapor with both high accuracy and time, thus spatial, resolution. Our work focuses on an open-path, compact, vertical-cavity surface-emitting laser (VCSEL) absorption-based hygrometer, capable of 25 Hz temporal resolution, deployed on the NSF/NCAR Gulfstream-V aircraft platform. The open path nature of our instrument also helps to minimize sampling artifacts. We will discuss our efforts toward achieving within 5% accuracy over 5 orders of magnitude of water vapor concentrations. This involves an intercomparison of five independent calibration methods: ice surface saturators using an oil temperature bath, solvent slush baths (e.g. chloroform/LN2, water/ice), a research-grade frost point hygrometer, static pressure experiments, and Pt catalyzed hydrogen gas. This wide variety of available tools allows us to accurately constrain the calibrant water vapor concentrations both before and after the VCSEL hygrometer sampling chamber. For example, the mixing ratio as measured by research-grade frost point hygrometer after the VCSEL hygrometer agreed within 2% of the mixing ration expected from the water/ice bubbler source before the VCSEL over the temperature range -50°C to 20°C. Finally, due to the compact nature of our instrument, we are able to perform these calibrations simultaneously at the same temperatures (-80°C to 30°C) and pressures (150 mbar to 760 mbar) as sampled ambient air during a flight. This higher accuracy can significantly influence the science utilizing this data, which we will illustrate using preliminary data from our most recent field deployment, the NSF Deep Convective Clouds and Chemistry Experiment in May-June 2012

DiGangi, J. P.; O'Brien, A.; Diao, M.; Hamm, C.; Zhang, Q.; Beaton, S. P.; Zondlo, M. A.

2012-12-01

245

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

246

Phase-sensitive swept source OCT imaging of the human retina with a VCSEL light source  

PubMed Central

Despite the challenges in achieving high phase stability, Doppler swept source / Fourier domain OCT has advantages of less fringe washout and faster imaging speeds compared to spectral / Fourier domain detection. This manuscript demonstrates swept source OCT with a VCSEL light source at 400kHz sweep rate for phase-sensitive Doppler imaging, measuring pulsatile total retinal blood flow with high sensitivity and phase stability. A robust, simple, and computationally efficient phase stabilization approach for phase-sensitive swept source imaging is also presented. PMID:23381430

Choi, WooJhon; Potsaid, Benjamin; Jayaraman, Vijaysekhar; Baumann, Bernhard; Grulkowski, Ireneusz; Liu, Jonathan J.; Lu, Chen D.; Cable, Alex E.; Huang, David; Duker, Jay S.; Fujimoto, James G.

2013-01-01

247

Two-channels MGDM transmission over GI-MMF with using low-cost VCSEL lasers  

NASA Astrophysics Data System (ADS)

The paper presents the experimental and theoretical investigations for a 2 x 2 MIMO optical communication system based on mode group diversion multiplexing over the 200m GI-MM fiber. As light sources at the system the low-cost VCSEL lasers were used. A coupling of the optical signals into the fiber at the transmitter side was done by using only a commercial optical coupler. In analogical way a `combined' optical signal which was present on the fiber output was divided into two separate optical paths by using second optical coupler acting as a splitter.

Kowalczyk, Marcin

2014-05-01

248

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

E-print Network

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

Rappe, Andrew M.

249

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

PubMed

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. PMID:18532824

Maximov, Ivan I; Tosner, Zden?k; Nielsen, Niels Chr

2008-05-14

250

Enhanced single-fundamental LP01 mode operation of 650-nm GaAs-based GaInP/AlGaInP quantum-well VCSELs  

NASA Astrophysics Data System (ADS)

Minimal optical attenuation of plastic (polymer) optical fibres (POFs) corresponds to the 650-nm wavelength. Currently the GaInP/AlGaInP quantum-well (QW) oxide-confined (OC) vertical-cavity surface-emitting diode lasers (VCSELs) are undoubtedly the laser devices most suited to be used in 650-nm POF optical communication, for which the stable single-fundamental-mode LP01 emission (SFM) is definitely the one most desired. In the present paper, the comprehensive fully self-consistent VCSEL model is used to examine mode selectivity of the above VCSELs. An increase in the VCSEL active-region diameter leads to a gradual modification of the current injection into this region and subsequent carrier radial diffusion within it before their recombination, which is followed by an essential transformation of active-region optical-gain profiles deciding upon an excitation of successive transverse modes. In standard arsenide OC VCSELs, SFM operation is usually limited to relatively small active regions. But for a room-temperature continuous-wave operation of the GaInP/AlGaInP VCSELs, the fundamental LP01 mode remains surprisingly the lowest-threshold one up to relatively large active regions of 9-µm diameters. Nevertheless, in such VCSELs, thresholds of many LP modes become very similar to one another, which leads to their relatively poor mode selectivity and an unwanted multi-mode operation for higher output powers.

Piskorski, ?ukasz; Sarza?a, Robert P.; Nakwaski, W?odzimierz

2010-03-01

251

Organic field effect transistors with dipole-polarized polymer gate dielectrics for control of threshold voltage  

NASA Astrophysics Data System (ADS)

The authors demonstrate organic field effect transistors (OFETs) with a dipole-polarized polyurea for the gate dielectrics. In the dielectrics, the internal electric field induces the mobile charge carrier in the semiconductor layer to the semiconductor-dielectric interface. OFETs with dipole-polarized gate dielectrics exhibit lower threshold voltage. With nonpolarized gate dielectrics, the threshold voltage was -11.4V, whereas that decreased to -5.3V with polarized gate dielectrics. In addition to the threshold voltage, polarized gate dielectrics reduced subthreshold swing from 4.1to2.4V/decade at the gate voltage of -20V. These results show that dipole-polarized polyurea gate dielectrics allow us to operate OFETs with lower power consumption.

Sakai, Heisuke; Takahashi, Yoshikazu; Murata, Hideyuki

2007-09-01

252

Subwavelength polarization beam splitter with controllable splitting ratio based on surface plasmon polaritons.  

PubMed

We propose a novel V-shaped Ag nanowire structure as a subwavelength polarization beam splitter. When an incident light is focused onto the junction of the two branches, two surface plasmon polaritons (SPPs) are launched and propagate along the two branches. The polarizations of the emission light from the two ends are always parallel to the directions of the branches and the splitting ratio can be adjusted by changing the polarization of the incident light. The polarization characteristic originates from the fact that only single plasmonic waveguide mode exists in the thin nanowire and high order modes are cutoff. The near-field coupling between the two branches dominates the SPPs launching and the splitting ratio, which are very different with the single nanowire case. The V-shaped nanowire structure will have many potential applications in the integration of plasmonic devices, such as plasmonic router or polarizer. PMID:23388925

Chen, Yuanyuan; Song, Gang; Xiao, Jinghua; Yu, Li; Zhang, Jiasen

2013-01-14

253

Quantum state selection of polar molecules: Alignment, orientation and conformational control  

NASA Astrophysics Data System (ADS)

Building on ideas that go back to Stern in the 1920s we use an inhomogeneous static electric field to deflect a cold beam of polar molecules. The deflection spatially disperses the rotational quantum states of the molecules. We show that the molecules residing in the lowest-lying rotational states can be selected and used as targets for further experiments. In particular, the quantum-state-selected molecules enable unprecedented strong alignment, induced by a moderately intense laser pulse, as well as strong orientation induced by a mixed laser and static electric field. Here, alignment refers to confinement of one or more molecule-fixed axes along laboratory-fixed axes, and orientation refers to the molecular dipole moments pointing in a specific direction. Also, it is shown that the deflection enables separation of the different conformers of a single molecule. We discuss new opportunities offered by the enhanced degree of orientational control, made possibly by quantum state selection, including time resolved studies of torsion, and eventually enantiomeric conversion, of axially chiral molecules. Collaborators: J. Küpper, G. Meijer, L. B. Madsen. [4pt] [1] Laser-Induced Alignment and Orientation of Quantum-State-Selected Large Molecules, L. Holmegaard, J. H. Nielsen, I. Nevo, H. Stapelfeldt, F. Filsinger, J. Küpper, and G. Meijer, Phys. Rev. Lett. 102. 023001 (2009).

Stapelfeldt, Henrik

2009-05-01

254

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

PubMed

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

255

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

256

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

257

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

258

K-enriched WO3 nanobundles: high electrical conductivity and photocurrent with controlled polarity.  

PubMed

Potassium ions are successfully intercalated into WO3 nanobundles with the integrity of the pseudo-orthorhombic structure remaining intact. The nanobundles display a 5-fold increase in the electrical conductivity. It changes from a value of 10(-4) Sm(-1) for pure WO3 to 40 Sm(-1) upon potassium intercalation. The electrical conductivity also increases by ~200 times as temperature increases from 23 to 200 °C whereby analysis shows a thermal activation energy of ~1 eV. Density functional theory calculations show that K ions cause the reduction of the surrounding W atoms and lead to an increase in the electron population in the conduction band. Hence, the conductivity of the K-WO3 nanobundles is greatly enhanced. The calculated band structure also shows a gap of 1 eV that is consistent with the measured thermal activation energy. Upon illumination of focused laser beam, individual and isolated nanobundle displays significant photon induced current (9 nA) without external bias at low laser power (2 mW); the amplitude and polarity of photocurrent could be controlled by location of laser spot. PMID:23607498

Hu, Zhibin; Ji, Zhuan; Lim, Wilson Weicheng; Mukherjee, Bablu; Zhou, Chenggang; Tok, Eng Soon; Sow, Chorng-Haur

2013-06-12

259

Quantitative Analysis of Polarization-Controlled Tip-Enhanced Raman Imaging through the Evaluation of the Tip Dipole.  

PubMed

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

Mino, Toshihiro; Saito, Yuika; Verma, Prabhat

2014-10-28

260

Equilibrium Polarization of Ultrathin PbTiO3 with Surface Compensation Controlled by Oxygen Partial Pressure  

NASA Astrophysics Data System (ADS)

We present a synchrotron x-ray study of the equilibrium polarization structure of ultrathin PbTiO3 films on SrRuO3 electrodes epitaxially grown on SrTiO3 (001) substrates, as a function of temperature and the external oxygen partial pressure (pO2) controlling their surface charge compensation. We find that the ferroelectric Curie temperature (TC) varies with pO2 and has a minimum at the intermediate pO2, where the polarization below TC changes sign. The experiments are in qualitative agreement with a model based on Landau theory that takes into account the interaction of the phase transition with the electrochemical equilibria for charged surface species. The paraelectric phase is stabilized at intermediate pO2 when the concentrations of surface species are insufficient to compensate either polar orientation.

Highland, M. J.; Fister, T. T.; Fong, D. D.; Fuoss, P. H.; Thompson, Carol; Eastman, J. A.; Streiffer, S. K.; Stephenson, G. B.

2011-10-01

261

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

PubMed

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

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

2013-07-01

262

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

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

263

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

PubMed Central

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

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

2013-01-01

264

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

265

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

266

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

267

Energy efficiency, bit rate, and modal properties of 980 nm VCSELs for very-short-reach optical interconnects  

NASA Astrophysics Data System (ADS)

Via experimental results supported by numerical modeling we report the energy-efficiency, bit rate, and modal properties of GaAs-based 980 nm vertical cavity surface emitting lasers (VCSELs). Using our newly established Principles for the design and operation of energy-efficient VCSELs as reported in the Invited paper by Moser et al. (SPIE 9001-02 ) [1] along with our high bit rate 980 nm VCSEL epitaxial designs that include a relatively large etalonto- quantum well gain-peak wavelength detuning of about 15 nm we demonstrate record error-free (bit error ratio below 10-12) data transmission performance of 38, 40, and 42 Gbit/s at 85, 75, and 25°C, respectively. At 38 Gbit/s in a back-toback test configuration from 45 to 85°C we demonstrate a record low and highly stable dissipated energy of only ~179 to 177 fJ per transmitted bit. We conclude that our 980 nm VCSELs are especially well suited for very-short-reach and ultra-short-reach optical interconnects where the data transmission distances are about 1 m or less, and about 10 mm or less, respectively.

Li, Hui; Moser, Philip; Wolf, Philip; Larisch, Gunter; Frasunkiewicz, Leszek; Dems, Maciej; Czyszanowski, Tomasz; Lott, James A.; Bimberg, Dieter

2014-02-01

268

Route to polarization switching induced by optical injection in vertical-cavity surface-emitting lasers  

SciTech Connect

We perform a theoretical investigation of the polarization dynamics in a vertical-cavity surface-emitting laser (VCSEL) subject to orthogonal optical injection, i.e., the injected field has a linear polarization (LP) orthogonal to that of the free-running VCSEL. In agreement with previous experiments [Z. G. Pan et al., Appl. Phys. Lett. 63, 2999 (1993)], an increase of the injection strength may lead to a polarization switching accompanied by an injection locking. We find that this route to polarization switching is typically accompanied by a cascade of bifurcations to wave-mixing dynamics and time-periodic and possibly chaotic regimes. A detailed mapping of the polarization dynamics in the plane of the injection parameters (detuning, injection strength) unveils a large richness of dynamical scenarios. Of particular interest is the existence of another injection-locked solution for which the two LP modes both lock to the master laser frequency, i.e., an elliptically polarized injection-locked (EPIL) steady state. Modern continuation techniques allow us to unveil an unfolding mechanism of the EPIL solution as the detuning varies and also to link the existence of the EPIL solution to a resonance condition between the master laser frequency and the free-running frequency of the normally depressed LP mode in the slave laser. We furthermore report an additional case of bistability, in which the EPIL solution may coexist with the second injection-locked solution (the one being locked to the master polarization). This case of bistability is a result of the interaction between optical injection and the two-polarization-mode characteristics of VCSEL devices.

Sciamanna, M. [Supelec, Laboratoire Materiaux Optiques, Photonique et Systemes (LMOPS), CNRS UMR-7132, Unite de Recherche Commune Supelec et Universite de Metz, 2 Rue Edouard Belin, F-57070 Metz (France); Panajotov, K. [Department of Applied Physics and Photonics (TW-TONA), Vrije Universiteit Brussel (VUB), Pleinlaan 2, B-1050 Brussels (Belgium)

2006-02-15

269

Photoelectron emission control with polarized light in plasmonic metal random structures  

SciTech Connect

We report on the possibility of switching the emission rate of photoelectrons by polarization changes in the plasmon excitation light. Photoelectron emission is strongly enhanced in the near-field of localized surface plasmons and occurs from areas with typical diameters of 20-70 nm. The underlying physical process involves excitation of a localized surface plasmon polariton with a femtosecond laser pulse, and a subsequent multi-photon photoemission process. The non-linearity of this process leads to a sharp polarization dependence that allows efficient switching of the emission. We demonstrate that a 90 deg. polarization change can result in on/off ratios of {approx}100 for electron emission.

Word, R. C.; Fitzgerald, J.; Koenenkamp, R. [Physics Department, Portland State University, Portland, Oregon 97201 (United States)

2011-07-25

270

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

271

Differential Polarization Nonlinear Optical Microscopy with Adaptive Optics Controlled Multiplexed Beams  

PubMed Central

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

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

2013-01-01

272

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

273

Subnatural-linewidth polarization-entangled photon pairs with controllable temporal length.  

PubMed

We demonstrate an efficient experimental scheme for producing polarization-entangled photon pairs from spontaneous four-wave mixing (SFWM) in a laser-cooled (85)Rb atomic ensemble, with a bandwidth (as low as 0.8 MHz) much narrower than the rubidium atomic natural linewidth. By stabilizing the relative phase between the two SFWM paths in a Mach-Zehnder interferometer configuration, we are able to produce all four Bell states. These subnatural-linewidth photon pairs with polarization entanglement are ideal quantum information carriers for connecting remote atomic quantum nodes via efficient light-matter interaction in a photon-atom quantum network. PMID:24996089

Liao, Kaiyu; Yan, Hui; He, Junyu; Du, Shengwang; Zhang, Zhi-Ming; Zhu, Shi-Liang

2014-06-20

274

Coherent control of pump-probe signals of helical structures by adaptive pulse polarizations  

SciTech Connect

The simplification of the pump-probe spectrum of excitons by pure-phase-polarization pulse shaping is investigated by a simulation study. The state of light is manipulated by varying the phases of two perpendicular polarization components of the pump, holding its total spectral and temporal intensity profiles fixed. Genetic and iterative Fourier transform algorithms are used to search for pulse phase functions that optimize the ratio of the signal at two frequencies. New features are extracted from the congested pump-probe spectrum of a helical pentamer by selecting a combination of Liouville space pathways. Tensor components which dominate the optimized spectra are identified.

Voronine, Dmitri; Abramavicius, Darius; Mukamel, Shaul [Department of Chemistry, University of California, Irvine, California 92697-2025 (United States)

2006-01-21

275

B. Madhavan and A. F. J. Levi: `Low-power 2.5 Gbps VCSEL driver in 0.5 m CMOS technology' page 1 Electronics Letters 34, 178-179 (1998).  

E-print Network

Electronics Letters 34, 178-179 (1998). Low-power 2.5 Gbps VCSEL driver in 0.5 µm CMOS technology Bindu. F. J. Levi: `Low-power 2.5 Gbps VCSEL driver in 0.5 µm CMOS technology' page 2 Electronics LettersB. Madhavan and A. F. J. Levi: `Low-power 2.5 Gbps VCSEL driver in 0.5 µm CMOS technology' page 1

Levi, Anthony F. J.

276

Comprehensive analysis of electrically-pumped GaSb-based VCSELs  

NASA Astrophysics Data System (ADS)

This paper discusses several performance-related aspects of electrically-pumped GaSb-based buried tunnel junction VCSELs with an emission wavelength of 2.6 ?m based on theoretical and experimental results. These results allow a deeper insight into the internal device physics, such as radial diffusion of carriers, maximum continuous-wave operating temperature, diffraction loss, internal temperature, gain and loss parameters, internal quantum efficiency of the active region etc. These parameters can be taken into account while designing mid-infrared lasers which leads to an improved device performance. A simple thermal model of the devices based on the two-dimensional (2-D) finite element method using the material data from the literature is also presented. In addition, an application-based result utilizing these lasers for the measurement of absolute water vapor concentration by wavelength modulation spectroscopy (WMS) method are also described, hinting that devices are well-suited for the targeted sensing applications.

Arafin, S.; Bachmann, A.; Vizbaras, K.; Hangauer, A.; Gustavsson, J.; Bengtsson, J.; Larsson, A.; Amann, M.-C.

2011-08-01

277

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

278

Critical slowing down in polarization switching of vertical-cavity surface-emitting lasers  

NASA Astrophysics Data System (ADS)

This research investigated the critical slowing down in polarization switching (PS) of vertical-cavity surface-emitting lasers (VCSELs). The experiments were performed by step-function current injection in two types: step-up and stepdown. In the case of step-up and step-down, the relationship between relaxation time and final current in this experiment resembles critical slowing down (CSD). The critical currents of two step-function current experiment are compared. The PS in this experiment is a static case. We also find that the divergence of relaxation time follow a power law. These results contribute to the understanding of the mechanism of CSD in VCSEL's PS (VPS).

Wu, Yu-Heng; Li, Yueh-Chen; Kuo, Wang-Chuang; Yen, Tsu-Chiang

2014-05-01

279

Polarization-based all-optical logic controlled-NOT, XOR, and XNOR gates employing electro-optic effect in periodically poled lithium niobate  

NASA Astrophysics Data System (ADS)

Based on electro-optic Pockels effect of periodically poled lithium niobate, different polarization-based binary all-optical logic functions: controlled-NOT, XOR, and XNOR gates were demonstrated by altering the linear polarization state of input optical signal about 90° on the polarization plant. Because the depletion of signal intensity in polarization-based logic gates is smaller than that of digital logic signal in intensity-based logic gates and almost negligible, this scheme has potential application in realizing complex logic functions by cascading several basic gates.

Zhang, Yinxing; Chen, Yuping; Chen, Xianfeng

2011-10-01

280

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

281

Non-equilibrium spin polarization via real-time control of spin fluctuations in a semiconductor nanowire  

NASA Astrophysics Data System (ADS)

The implementation of electron spins as solid-state qubits suffers from decoherence due to its hyperfine interaction with the surrounding mesoscopic nuclear spin environment. Several methods such as complete polarization or narrowing of the nuclear spin ensemble have been proposed in order to address this issue. These proposals have been realized in quantum dots using an optical or electrical readout of the nuclear magnetic field [1, 2]. Here we demonstrate a similar control over a nanoscale ensemble of spins using the mechanical readout of magnetic resonance force microscopy (MRFM) [3]. We employ the exceptional sensitivity of MRFM to perform real-time measurement and control of an ensemble containing 10^5 nuclear spins in a semiconductor nanowire. We create hyperpolarized and narrowed nuclear spin states by harnessing the statistical fluctuations of the ensemble. Furthermore, we capture large nuclear polarization fluctuations, store them for many seconds, and read the polarization out. 1. Vink, I. T. et al. Nature Phys. 5, 764 (2009). 2. Latta, C. et al. Nature Phys. 5, 758 (2009). 3. Budakian, R. et al. Science 307, 408 (2005).

Peddibhotla, Phani; Xue, Fei; Hauge, Ikaros; Bakkers, Erik; Poggio, Martino

2013-03-01

282

Polarization control of Raman spectroscopy optimizes the assessment of bone tissue  

PubMed Central

Abstract. 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 (106?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.

2013-01-01

283

The linear dependence of polar cap index on its controlling factors in solar wind and magnetotail  

NASA Astrophysics Data System (ADS)

The solar wind is coupled to the magnetosphere-ionosphere system through various interactions, e.g., magnetic reconnection at the dayside magnetopause, and viscous interactions at the low latitude boundary layer. The polar cap, a region of open magnetic flux connecting the magnetic field of the Earth to that of the solar wind, is an ideal region in which to investigate how solar wind drives the magnetosphere-ionosphere dynamo. For such studies, the polar cap (PC) index provides a useful characterization of the state of the polar ionosphere. A previous study by Gao et al. (2012a) found that polar cap dynamics, characterized by the PC index, responds to both solar wind driving quantified by the electric field (EK-R) proposed by Kivelson and Ridley (2008) which is a representative of the electric field imposed on the ionosphere by magnetopause reconnection that takes cross polar cap potential saturation into account, and the energy release in the magnetotail, described by a modified AL index (ALU). In that study, the dependence of the PC index on EK-R and ALU was investigated assuming a linear relationship. In this study, we test the assumption that the relationship is linear by performing a similar analysis applying a more general, nonlinear model to the events of the Gao et al. (2012a) study. A nonlinear relationship can be established by use of a statistical approach referred to as the additive model. We find that the more flexible additive model outperforms the linear model. However, the improvement is small. Provided that EK-R is used to characterize the solar wind input, results obtained from the additive model are very similar to those from the linear model. This result indicates that the linear relation between the PC index and EK-R, ALU obtained by Gao et al. (2012a) represents the data within fluctuations.

Gao, Ye; Kivelson, Margaret G.; Walker, Raymond J.

2012-05-01

284

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-Sa, Eurico; Mukherjee, Avik; Lowe, Nick; St Johnston, Daniel

2014-01-01

285

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

286

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

287

Broadband femtosecond circular dichroism spectrometer with white-light polarization control.  

PubMed

A broadband, femtosecond transient circular dichroism (TRCD) spectrometer has been developed and tested in the wavelength range from 350 to 700 nm. The spectrometer uses a femtosecond probe white light with well-defined circular polarization. The latter is modulated by the polarization of a narrowband seed pulse. We have implemented a dual-beam probe geometry with phase-locked detection technique to increase the signal-to-noise ratio and to reduce optical artifacts. The spectrometer allows the acquisition of TRCD spectra with subpicosecond time resolution and typical noise levels of 10(-4) absorbance units. The performance of this instrument has been demonstrated on bis(merocyanine) nanorod aggregates in tetrahydrofurane/methylcyclohexane solution. The case study confirmed that this spectrometer is effective for the investigation of chiral properties in various molecular and nanostructural systems that have transient spectra in the UV-visible spectral range. PMID:20441322

Trifonov, Anton; Buchvarov, Ivan; Lohr, Andreas; Würthner, Frank; Fiebig, Torsten

2010-04-01

288

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

289

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

290

All-epitaxial VCSELs with tunnel QW-QD InGaAs-InAs gain medium  

Microsoft Academic Search

Quantum dot (QD) size distribution and limitations in carrier capture and thermalization rates are still limiting the maximum saturation gain in QD-based laser diodes and the utilization of QD-medium in all-epitaxial vertical cavity surface emitting lasers (VCSELs). To overcome these problems structures of tunnel coupled pairs consisting of InGaAs quantum wells grown on top of self-assembled InAs QDs (QW-on-QDs) were

V. Tokranov; M. Yakimov; J. van Eisden; S. Oktyabrsky

2007-01-01

291

Efficient phosphodiester cleaving nanozymes resulting from multivalency and local medium polarity control.  

PubMed

The self-organization of Zn(II) complexes on the surface of 1.6-nm diameter gold nanoparticles (nanozymes) allows the spontaneous formation of multiple bimetallic catalytic sites capable to promote the cleavage of a RNA model substrate. We show that by tuning the structure of the nanoparticle-coating monolayer, it is possible to decrease the polarity of the reaction site, and this in turn generates remarkable increments of the cleavage efficiency. PMID:24405094

Diez-Castellnou, Marta; Mancin, Fabrizio; Scrimin, Paolo

2014-01-29

292

Dispersion Controlling and Polarization Maintaining in a Modified Hexagonal Photonic Crystal Fiber  

Microsoft Academic Search

This paper presents a polarization maintaining modified hexagonal photonic crystal fiber (M-HPCF) with nearly zero ultra-flattened dispersion of 0plusmn0.35 ps\\/(nm-km) in the wavelength range between 1.397 mum and 1.675 mum, possessing extremely low confinement losses and birefringence of about 7.5times10-4 at lambda=1.55 mum.

S. Kaijage; Y. Namihira; N. H. Hai; F. Begum; S. M. A. Razzak; T. Kinjo; N. Zou

2007-01-01

293

Magnetic control spin-polarization reversal in a hybrid ferromagnet/semiconductor spin filter  

NASA Astrophysics Data System (ADS)

Electron spin-polarization reversal is achieved in a hybrid ferromagnet/semiconductor spin filter by introducing the third magnetic barrier and a subtle variation of its strength, and the ground or the second resonance states could be reversed separately by changing its magnetization direction. This interesting feature is believed to be of significant importance for realizing the spin switches and multiple value logic devices.

Xu, Huaizhe; Wang, Liying; Wang, Hailong; Zhang, Shichao

2014-02-01

294

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

PubMed

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

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

2012-04-01

295

Control of atomic single and double ionization dynamics using orthogonally polarized two-color laser pulses  

NASA Astrophysics Data System (ADS)

Single- and double-ionization of neon with orthogonally polarized two-color (OTC) laser fields is investigated using the COLTRIMS method. We study the influence of the long range Coulomb potential of the parent ion on the final momentum distribution of electrons emitted during single ionization. Furthermore, we investigate nonsequential double ionization in OTC fields and demonstrate that the electron-electron correlation is highly sensitive to the sub-cycle field shape of the OTC pulses, in agreement with recent theoretical predictions.

Zhang, L.; Xie, X.; Roither, S.; Kartashov, D.; Schöffler, M.; Shafir, D.; Corkum, P. B.; Baltuška, A.; Staudte, A.; Kitzler, M.

2014-04-01

296

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

297

Polarization feedback laser stabilization  

DOEpatents

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

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

1988-01-01

298

A new spore precipitator with polarized dielectric insulators for physical control of tomato powdery mildew.  

PubMed

ABSTRACT In an attempt to physically protect greenhouse tomato plants from the powdery mildew fungus Oidium neolycopersici, we developed a new electrostatic spore precipitator in which a copper wire conductor is linked to an electrostatic generator and covered with a transparent acrylic cylinder (insulator). The conductor was negatively charged by the generator, and the electrostatic field created by the conductor was used to dielectrically polarize the insulator cylinder. The dielectrically polarized cylinder also produced an electrostatic force without a spark discharge. This force was directly proportional to the potential applied to the conductor and was used to attract conidia of the pathogen. The efficacy of this spore precipitator in protecting hydroponically cultured tomato plants from powdery mildew was evaluated in the greenhouse. The hydroponic culture troughs were covered with a cubic frame installed with the spore precipitator, and the disease progress on precipitator-guarded and unguarded seedlings was traced after the conidia were disseminated mechanically from inoculum on tomato plants. Seedlings in the guarded troughs remained uninfected during the entire experiment, in spite of rapid spread of the disease to all leaves of the unguarded seedlings. PMID:18944052

Matsuda, Yoshinori; Ikeda, Hiroki; Moriura, Nobuyuki; Tanaka, Norio; Shimizu, Kunihiko; Oichi, Wataru; Nonomura, Teruo; Kakutani, Koji; Kusakari, Shin-Ichi; Higashi, Katsuhide; Toyoda, Hideyoshi

2006-09-01

299

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

300

Electro-optically generating and controlling right- and left-handed circularly polarized multiring modes of light beams.  

PubMed

We propose a simple method for generating and controlling right- and left-handed circularly polarized (RHP and LHP) multiring modes of light beams by means of Pockels effect in a single strontium barium niobate (SBN) crystal. The numerical results show that an LHP Laguerre-Gaussian LG(0l) beam, propagating along the optical axis of the crystal, will partly turn into an RHP vortex light field of order l+2. Moreover, a pair of the LHP and RHP components of the output light field is LG-like modes sharing an identically radial index, which is electro-optically controllable. The power ratio between these two components depends on the applied electric field and the mode of input beam. PMID:22825146

Zhu, Wenguo; She, Weilong

2012-07-15

301

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

302

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

SciTech Connect

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

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

2010-10-11

303

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

304

Polarization control of defect modes in three-dimensional woodpile photonic crystals.  

PubMed

The symmetry of a Fabry-Perot-like planar cavity embedded within a three-dimensional (3D) woodpile photonic crystal prevents the observation of polarization effects. In this letter we propose a geometry to break the degeneracy of the Fabry-Perot-like cavity modes by introducing asymmetry. The introduction of a one-dimensional (1D) lattice to the centre of a planar cavity allows for distinct modes parallel (TE) and perpendicular (TM) to the layer. This hybrid 3D-1D-3D lattice structure exhibits a pronounced increase in the quality-factor, and in particular shows an increase of up to 50% more than that of a planar cavity for TM modes. PMID:18545623

Ventura, Michael J; Gu, Min

2008-06-01

305

Three-dimensional simulation of 1300-nm AlGaInAs VCSEL arrays  

NASA Astrophysics Data System (ADS)

We present the optimization of the carrier injection, heat flow and optical confinement aimed for single mode operation. The analyzed structure incorporates InAlGaAs quantum wells within InP cavity. The cavity is bounded by AlGaAs/GaAs 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 used multi-physical model, which comprises three-dimensional models of optical (Plane Wave Admittance Method), thermal and electrical (Finite Element Method) phenomena. We perform the exhaustive modal analysis of the 1x3, 1x4 and 2x4 VCSEL arrays. In the analysis we investigate the influence of the distance between emitters. The analysis is performed for broad range of injected currents from threshold to the rollover. As the result we illustrate the complex competition of the modes, influence of the optical confinement on structure of the modes and determine the geometrical parameters, which favor the array modes in the considered array designs.

Czyszanowski, Tomasz; Dems, Maciej; Wasiak, Michal; Sarzala, Robert P.

2012-06-01

306

Swept source optical coherence microscopy using a 1310 nm VCSEL light source.  

PubMed

We demonstrate high speed, swept source optical coherence microscopy (OCM) using a MEMS tunable vertical cavity surface-emitting laser (VCSEL) light source. The light source had a sweep rate of 280 kHz, providing a bidirectional axial scan rate of 560 kHz. The sweep bandwidth was 117 nm centered at 1310 nm, corresponding to an axial resolution of 13.1 µm in air, corresponding to 8.1 µm (9.6 µm spectrally shaped) in tissue. Dispersion mismatch from different objectives was compensated numerically, enabling magnification and field of view to be easily changed. OCM images were acquired with transverse resolutions between 0.86 µm - 3.42 µm using interchangeable 40X, 20X and 10X objectives with ~600 µm x 600 µm, ~1 mm x 1 mm and ~2 mm x 2 mm field-of-view (FOV), respectively. Parasitic variations in path length with beam scanning were corrected numerically. These features enable swept source OCM to be integrated with a wide range of existing scanning microscopes. Large FOV mosaics were generated by serially acquiring adjacent overlapping microscopic fields and combining them in post-processing. Fresh human colon, thyroid and kidney specimens were imaged ex vivo and compared to matching histology sections, demonstrating the ability of OCM to image tissue specimens. PMID:23938673

Ahsen, Osman O; Tao, Yuankai K; Potsaid, Benjamin M; Sheikine, Yuri; Jiang, James; Grulkowski, Ireneusz; Tsai, Tsung-Han; Jayaraman, Vijaysekhar; Kraus, Martin F; Connolly, James L; Hornegger, Joachim; Cable, Alex; Fujimoto, James G

2013-07-29

307

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

308

Influence of base-region thickness on the performance of Pnp transistor-VCSEL.  

PubMed

We have recently reported a 980nm GaAs-based three terminal Pnp transistor-vertical-cavity surface-emitting laser (TVCSEL) operating at room temperature with optical power up to 1.8mW. However, the current gain ? = ?Ic/?Ib was near zero just before lasing and became negative after the lasing threshold. The main cause of the negative current gain was found to be a gradual and position-dependent forward-biasing (saturation) of the base-collector junction with increasing bias even before lasing threshold. In this article, detailed multi-physics device simulations are performed to better understand the device physics, and find ways to avoid the premature saturation of the base-collector junction. We have optimized the thickness of the base region as well as its doping concentration and the location of the quantum wells to ensure that the T-VCSEL is in the active mode throughout its range of operation. That is, the emitter-base junction is forward biased and base-collector junction is reversed biased for sweeping the excess charges out of the base region. PMID:25401889

Nadeem Akram, M; Xiang, Y; Yu, X; Zabel, Thomas; Hammar, Mattias

2014-11-01

309

Fabrication and characterization of individually addressable vertical-cavity surface-emitting laser arrays and integrated VCSEL/PIN detector arrays  

NASA Astrophysics Data System (ADS)

With the emergence of the internet, the demand for high data transmission rates in short haul area networks and fiber-to-the- desktop applications is increasing every year. Densely packed one-dimensional and two-dimensional vertical-cavity surface-emitting laser (VCSEL) arrays offer new possibilities for future short haul parallel optical links, free-space optical interconnects at the chip-to-chip, board-to-board, and on-board level. In this paper, we describe the manufacturing process of individually addressable two-dimensional VCSEL arrays, PIN detector arrays, and integrated VCSEL / PIN detector arrays. We also present measurement results of the fabricated devices and comment on the reliability.

Kasten, A. M.; Giannopoulos, A. V.; Long, C.; Chen, C.; Choquette, K. D.

2007-02-01

310

Controlling helicity-correlated beam asymmetries in a polarized electron source  

SciTech Connect

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

Kent Paschke

2007-07-01

311

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

312

Design of Control Instrumentation of a 4 meter Variable Polarization Undulator (EPU)  

SciTech Connect

The design of a high end, very sophisticated controller, that consists of an Allen Bradley ControlLogix PLC with a Kinetix servo controller for a 4.16 m EPU is presented. Four servo motors control the gap - 2 on the upper girder and 2 on the lower girder, and another 4 servos controls the phase - 2 on the upper girder inner and outer and 2 on the lower girder, inner and outer. This system is designed for The Taiwan Light Source (TLS) a synchrotron radiation machine of the National Synchrotron Radiation Research Center (NSRRC) at the energy of 1.5 GeV with electron beam current of 200 {approx} 400 mA.

Kulesza, Joe; Deyhim, Alex [Advanced Design Consulting USA, 126 Ridge Road, P.O. Box 187, Lansing, NY 14882 (United States); Fan Taiching; Chen, Jenny [National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Science-Based Industrial Park, Hsinchu 30077, Taiwan (China)

2007-01-19

313

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

314

Polar Bears  

NSDL National Science Digital Library

Use the following websites to answer questions about the rapid disappearance of polar bears in the Arctic region. Polar Bear picture Polar Bear Tracker 1: What region in the world has the fewest polar bears? 2: Using the internet as a resource, provide some reasons as to why this region is suffering from the most polar bear differences? Polar Bears Change Diet 1: Why are polar bears having to change their diets? 2: List some other factors (besides diet) in the ...

Thomas, Mr.

2010-09-27

315

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

316

Topographic control of thermohaline frontal structure in the Barents Sea Polar Front on the south flank of Spitsbergen Bank  

Microsoft Academic Search

A combination of observations and process-oriented numerical modeling is used to investigate the thermohaline structure of the Barents Sea Polar Front on the south flank of Spitsbergen Bank. The Polar Front is the boundary between warm, saline North Atlantic Water and cool, fresh Arctic Water located over the outer edge of the bank. Observations from the Barents Sea Polar Front

Glen Gawarkiewicz; Albert J. Plueddemann

1995-01-01

317

Deterministic photonic spatial-polarization hyper-controlled-not gate assisted by quantum dot inside one-side optical microcavity  

E-print Network

Up to now, all the works about constructing quantum logic gates, an essential part in quantum computing, are focused on operating on one degree of freedom (DOF) of quantum systems. Here, we investigate the possibility to achieve a scalable photonic quantum computing based on two DOFs of quantum systems and construct a deterministic hyper-controlled-not (hyper-CNOT) gate operating on both spatial-mode and polarization DOFs of a photon pair simultaneously, by using the giant optical Faraday rotation induced by a single-electron spin in a quantum dot inside a one-side optical microcavity as a result of cavity quantum electrodynamics. With this hyper-CNOT gate and linear optical elements, two-photon four-qubit cluster entangled states can be prepared and analyzed, which gives an application to manipulate more information with less resources. We analyze the experimental feasibility of this hyper-CNOT gate and show that it can be implemented with current technology.

Bao-Cang Ren; Hai-Rui Wei; Fu-Guo Deng

2013-03-01

318

Polarization-controlled TIRFM with focal drift and spatial field intensity correction.  

PubMed

Total internal reflection fluorescence microscopy (TIRFM) is becoming an increasingly common methodology to narrow the illumination excitation thickness to study cellular process such as exocytosis, endocytosis, and membrane dynamics. It is also frequently used as a method to improve signal/noise in other techniques such as in vitro single-molecule imaging, stochastic optical reconstruction microscopy/photoactivated localization microscopy imaging, and fluorescence resonance energy transfer imaging. The unique illumination geometry of TIRFM also enables a distinct method to create an excitation field for selectively exciting fluorophores that are aligned either parallel or perpendicular to the optical axis. This selectivity has been used to study orientation of cell membranes and cellular proteins. Unfortunately, the coherent nature of laser light, the typical excitation source in TIRFM, often creates spatial interference fringes across the illuminated area. These fringes are particularly problematic when imaging large cellular areas or when accurate quantification is necessary. Methods have been developed to minimize these fringes by modulating the TIRFM field during a frame capture period; however, these approaches eliminate the possibility to simultaneously excite with a specific polarization. A new, to our knowledge, technique is presented, which compensates for spatial fringes while simultaneously permitting rapid image acquisition of both parallel and perpendicular excitation directions in ~25 ms. In addition, a back reflection detection scheme was developed that enables quick and accurate alignment of the excitation laser. The detector also facilitates focus drift compensation, a common problem in TIRFM due to the narrow excitation depth, particularly when imaging over long time courses or when using a perfusion flow chamber. The capabilities of this instrument were demonstrated by imaging membrane orientation using DiO on live cells and on lipid bilayers that were supported on a glass slide (supported lipid bilayer). The use of the approach to biological problems was illustrated by examining the temporal and spatial dynamics of exocytic vesicles. PMID:24606926

Johnson, Daniel S; Toledo-Crow, Ricardo; Mattheyses, Alexa L; Simon, Sanford M

2014-03-01

319

Monolithic fabrication and performance control of multilayered, polarization sensitive, guided-mode resonance filters  

NASA Astrophysics Data System (ADS)

An efficient monolithic fabrication technique of multiple Guided-Mode Resonance Filter (GMRF) devices on a single substrate is presented. The devices consist of two crossed linear sub-wavelength grating (SWG) dielectric layers, formed by etching deposited silicon oxide films, separated by a silicon nitride waveguide. The buried SWG duty cycle is lithographically modulated to control the device resonance wavelengths, independent of the top SWG. This is because the buried SWG acts as a tunable effective index layer, controlling the waveguide mode coupling wavelength into the silicon nitride waveguide layer. The two SWG have different spatial periods, to further reduce resonance coupling between them. The fabrication is accomplished using existing photolithographic technology, and conventional PECVD coating techniques.

Poutous, Menelaos K.; Raghu Srimathi, Indumathi; Johnson, Eric G.

2012-03-01

320

Factors controlling the distribution of anaerobic methanotrophic communities in marine environments: Evidence from intact polar membrane lipids  

NASA Astrophysics Data System (ADS)

Three distinct types of microbial consortia appear to mediate the anaerobic oxidation of methane with sulfate as electron acceptor in marine sediments and are distributed ubiquitously. These consortia consist of ANerobic MEthanotrophic (ANME) archaea of the ANME-1, ANME-2 and ANME-3 clades and their sulfate-reducing bacterial partners either of the Desulfosarcina- Desulfococcus (ANME-1/DSS and ANME-2/DSS) or Desulfobulbus spp. (ANME-3/DBB) branches. Frequently one consortium type dominates the community, but the selective factors are not well constrained. Here we analyzed patterns in the composition of intact polar lipids extracted from bacterial and archaeal communities of different marine seep environments. Further, we investigated if different environmental and geographical factors were responsible for the observed patterns, and hence could be important in the selection of seep communities. Intact polar lipids (IPLs) provide a more robust distinction of the composition of extant communities than their less polar derivatives. In ANME-1/DSS-dominated communities, glycosidic- and phospho-glyceroldialkylglyceroltetraethers were abundant, while ANME-2/DSS and ANME-3/DBB-dominated communities showed abundant archaeol-based IPLs, either with glycosidic and phospho-headgroups or only phospho-headgroups, respectively. The relative proportion of bacterial IPLs varied widely from 0% to 93% and was generally lower in samples of the ANME-1 type, suggesting lower bacterial biomasses in the respective communities. In addition to these lipid signatures, distinctive features were related to the habitat characteristics of these communities: lower amounts of phosphate-based IPLs were generally observed in communities from calcified microbial mats compared to sediments, which may reflect phosphate limitation. Based on statistical analyses of IPLs and environmental data this study constrained for the first time the occurrence of three environmental factors controlling the distribution of different ANME-associated communities in a wide range of hydrocarbon seep systems. Habitats dominated by ANME-1/DSS communities were characterized by high temperature and low oxygen content in bottom waters (or even anoxia), while ANME-2/DSS and ANME-3/DBB-dominated sediments were located in settings with lower temperatures and higher oxygen content in bottom waters. Furthermore, ANME-2/DSS communities were particularly prominent in environments in which a relatively high supply of sulfate was sustained.

Rossel, Pamela E.; Elvert, Marcus; Ramette, Alban; Boetius, Antje; Hinrichs, Kai-Uwe

2011-01-01

321

Cohesin controls planar cell polarity by regulating the level of the seven-pass transmembrane cadherin Flamingo.  

PubMed

Planar cell polarity (PCP) refers to the coordination of global organ axes and individual cell polarity in vertebrate and invertebrate epithelia. Mechanisms of PCP have been best studied in the Drosophila wing, in which each epidermal cell produces a single wing hair at the distal cell edge, and this spatial specification is mediated by redistribution of the core group proteins, including the seven-pass transmembrane cadherin Flamingo/Starry night (Fmi/Stan), to selective plasma membrane domains. Through genetic screening, we found that a mutation of the SMC3 gene caused dramatic misspecification of wing hair positions. SMC3 protein is one subunit of the cohesin complex, which regulates sister chromatid cohesion and also plays a role in transcriptional control of gene expression. In the SMC3 mutant cells, Fmi appeared to be upregulated by a posttranscriptional mechanism(s), and this elevation of Fmi was at least one cause of the PCP defect. In addition to the PCP phenotype, the loss of the cohesin function affected wing morphogenesis at multiple levels: one malformation was loss of the wing margin, and this was most likely a result of downregulation of the homeodomain protein Cut. At the cellular level, apical cell size and hexagonal packing were affected in the mutant wing. Dysfunction of cohesin in humans results in Cornelia de Lange syndrome (CdLS), which is characterized by various developmental abnormalities and mental retardation. Our analysis of cohesin in epithelia may provide new insight into cellular and molecular mechanisms of CdLS. PMID:22563761

Mouri, Kousuke; Horiuchi, Shin-ya; Uemura, Tadashi

2012-06-01

322

Polar Bear Polar Bear  

NSDL National Science Digital Library

In this lesson, students will listen for key details in a nonfiction text about polar bears. They will work at completing a graphic organizer with the teacher to help organize their thinking and understanding of key details about a text. They will also complete an independent assignment where they will draw or write two things that they learned about the topic.

Burgess, Kelly

2012-09-11

323

Highly efficient active optical interconnect incorporating a partially chlorinated ribbon POF in conjunction with a visible VCSEL.  

PubMed

A low-loss 4-ch active optical interconnect (AOI) enabling passive alignment was proposed and built resorting to a transmitter (Tx) incorporating a red 680-nm VCSEL, which is linked to a receiver (Rx) module via a partially chlorinated ribbon POF. The POF was observed to exhibit an extremely low loss of ~0.24 dB/m at ? = 680 nm, in comparison to ~1.29 dB/m at ? = 850 nm, and a large numerical aperture of ~0.42. Both the Tx and Rx, which taps into a beam router based on collimated beam optics involving a pair of spherical lenses, were meant to be substantially alignment tolerant and compact. The achieved tolerance for the constructed modules was beyond 40 ?m in terms of the positioning of VCSEL and photodetector. The proposed AOI was completed by linking the Tx with the Rx via a 3-m long ribbon POF, incurring a transmission loss of as small as 3.2 dB. The AOI was practically assessed in terms of a high-speed data transmission over a wide range of temperatures and then exploited to convey full HD video signals. PMID:24921299

Lee, Hak-Soon; Lee, Sang-Shin; Kim, Bong-Seok; Son, Yung-Sung

2014-05-19

324

Cdc42 and actin control polarized expression of TI-VAMP-vesicles to neuronal growth cones and their fusion with the plasma membrane  

E-print Network

Cdc42 and actin control polarized expression of TI-VAMP-vesicles to neuronal growth cones-VAMP, but not synaptobrevin 2, concentrates in the peripheral, F-actin-rich region of the growth cones of hippocampal neurons in primary culture. Its accumulation correlates with and depends upon the presence of F-actin. Moreover

325

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

326

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

327

Simultaneous control of vortex polarity and chirality in thickness-modulated [Co/Pd]n/Ti/Ni80Fe20 disks  

NASA Astrophysics Data System (ADS)

Simultaneous vortex chirality and polarity control are observed in thickness-modulated [Co/Pd]n/Ti/Ni80Fe20 disks using magnetic force microscopy by applying a proper sequence of in-plane and out-of-plane reset fields. The thickness modulation in the NiFe layer introduces an additional shape anisotropy, which defines the vortex chirality during the in-plane reset field, while the [Co/Pd]n underlayer produces a large out-of-plane stray field, which stabilizes the vortex polarity in the NiFe layer. Micromagnetic simulations are compared with experiment results.

Shimon, G.; Ravichandar, V.; Adeyeye, A. O.; Ross, C. A.

2014-10-01

328

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

329

Cdc42-mediated MTOC polarization in dendritic cells controls targeted delivery of cytokines at the immune synapse  

PubMed Central

The immune synapse (IS) forms as dendritic cells (DCs) and T cells interact in lymph nodes during initiation of adaptive immunity. Factors that contribute to the formation and maintenance of IS stability and function have been mostly studied in T cells, whereas little is known about events occurring during synapse formation in DCs. Here, we show that DCs activated by Toll-like receptor (TLR) agonists reorient the microtubule-organizing center (MTOC) toward the interacting T cell during antigen-specific synapse formation through a mechanism that depends on the Rho GTPase Cdc42. IL-12, a pivotal cytokine produced by DCs, is found enriched around the MTOC at early time points after TLR ligation and is dragged to the DC–T cell interface in antigen-specific synapses. Synaptic delivery of IL-12 induces activation of pSTAT4 and IFN-? neosynthesis in CD8+ naive T cells engaged in antigen-specific conjugates and promotes the survival of antigen-primed T cells. We propose that DC polarization increases the local concentration of proinflammatory mediators at the IS and that this represents a new mechanism by which T cell priming is controlled. PMID:21059854

Pulecio, Julian; Petrovic, Jelena; Prete, Francesca; Chiaruttini, Giulia; Lennon-Dumenil, Ana-Maria; Desdouets, Chantal; Gasman, Stephane; Burrone, Oscar R.

2010-01-01

330

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

331

Polar Lows  

NASA Astrophysics Data System (ADS)

Providing a comprehensive review of our understanding of the small, high latitude weather systems known as polar lows, Erik Rasmussen and John Turner describe the climatological distribution of these depressions. They cover observational investigations into their structure, the operational forecasting of polar lows and the theoretical research into why they develop. They also discuss the experiments that reveal that some polar lows can be predicted. This book is of value to researchers and professional weather forecasters concerned with polar regions.

Rasmussen, Erik A.; Turner, John

2003-06-01

332

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.

333

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

2014-08-01

334

Polarizer Program  

NSDL National Science Digital Library

The Polarizer program displays the effect of a plane polarizer on an incident electromagnetic wave. The default electromagnetic wave is plane polarized but this polarization can be changed by specifying the components of the waveâs Jones vector using the input fields. The slider can be used to rotate the polarizer to change its orientation. Polarizer is an Open Source Physics program written for the teaching of optics. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the optics_polarizer.jar file will run the program if Java is installed. Other optics programs are also available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Optics.

Simov, Kiril; Christian, Wolfgang

2008-05-20

335

Analysis of anticipated performance of 650-nm GaInP/AlGaInP quantum-well GaAs-based VCSELs at elevated temperatures  

NASA Astrophysics Data System (ADS)

The possibility of application of the 650-nm oxide-confined GaInP/AlGaInP quantum-well vertical-cavity surface-emitting diode lasers (VCSELs) at elevated temperatures as sources of the carrier 650-nm wave in the fibre optical communication using POFs has been investigated with the aid of the comprehensive self-consistent model. An increase in the VCSEL threshold current at higher temperatures has been found to be mostly associated with both the carrier leakage from the valley of the Ga0.43In0.57P quantum-well material to the X-valley of the (Al0.67Ga0.33)0.52In0.48P barriers and the band-to-band absorption within the Ga0.52In0.48P layer of the band-gap comparable with the energy of emitted radiation. Nevertheless, the AlGaInP VCSELs exhibit encouraging thermal behaviour with the characteristic temperature T0 equal to as much as 134 K for the active-region temperatures up to 357 K. For the 5-?m devices, the maximal achievable output has been determined to decrease from a quite high value of 1.0 mW for 293 K to 0.6 mW for 320 K and to still high 0.33 mW for 340 K. However, an efficient operation of the above VCSEL at elevated temperatures requires still some structure modifications leading to a reduction of both the above effects, the electron leakage from the valley and the band-to-band absorption within GaInP layers.

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

2008-03-01

336

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

337

Multi-mode to single-mode switching caused by self-heating in bottom-emitting intra-cavity contacted 960 nm VCSELs  

NASA Astrophysics Data System (ADS)

Detailed investigation of anomalous modal behavior in fabricated bottom-emitting intra-cavity contacted 960 nm range vertical cavity surface emitting lasers (VCSELs) have been performed. At low currents the broad-aperture VCSELs show multi-mode operation at 945 nm via whispering gallery-like modes. Subsequent increase of pump current results in rapid increase of fundamental mode intensity and switching to a pure single transverse mode lasing regime at 960 nm with the higher slope efficiency. As a result record single transverse mode output power of 15 mW with a side-mode-suppressionratio (SMSR) above 30 dB was achieved. The observed phenomena cannot be explained by oxide-index guiding or changes in current pumping. 2D heat transport simulations show a strong temperature gradient inside the microcavity due to an effective lateral heat-sinking. This creates an effective waveguide and results in lower optical losses for the fundamental mode. At fixed pump current in pulsed regime (pulse width < 400 ns) high-order modes dominate, however the subsequent increase of pulse width leads to a rapid rise of optical power for the fundamental mode and SMSR increasing. Thus the self-heating phenomena play a crucial role in observed VCSEL unusual modal behavior.

Blokhin, Sergey A.; Maleev, Nikolai A.; Kuzmenkov, Alexander G.; Lott, James A.; Kulagina, Marina M.; Zadiranov, Yurii M.; Gladyshev, Andrey G.; Nadtochiy, Alexey M.; Nikitina, Ekaterina V.; Tikhomirov, Vladimir G.; Ledentsov, Nikolai N.; Ustinov, Viktor M.

2012-03-01

338

Direct generation of 2-ps blue pulses from gain-switched InGaN VCSEL assessed by up-conversion technique  

NASA Astrophysics Data System (ADS)

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.

Asahara, Akifumi; Chen, Shaoqiang; Ito, Takashi; Yoshita, Masahiro; Liu, Wenjie; Zhang, Baoping; Suemoto, Tohru; Akiyama, Hidefumi

2014-09-01

339

Polarization developments  

SciTech Connect

Recent developments in laser-driven photoemission sources of polarized electrons have made prospects for highly polarized electron beams in a future linear collider very promising. This talk discusses the experiences with the SLC polarized electron source, the recent progress with research into gallium arsenide and strained gallium arsenide as a photocathode material, and the suitability of these cathode materials for a future linear collider based on the parameters of the several linear collider designs that exist.

Prescott, C.Y.

1993-07-01

340

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

341

Genetic Interactions Between Leaf Polarity-Controlling Genes and ASYMMETRIC LEAVES1 and 2 in Arabidopsis Leaf Patterning  

Microsoft Academic Search

During leaf development, establishment of adaxial- abaxial polarity is essential for normal leaf morphogenesis. This process is known to be strictly regulated by several putative transcription factors, microRNA165\\/166 (miR165\\/ 166), a trans-acting short-interfering RNA (tasiR-ARF), as well as proteins involved in RNA silencing. Among the putative transcription factor genes, ASYMMETRIC LEAVES1 and 2 (AS1 and 2) facilitate the specification of

Yanlei Fu; Lin Xu; Ben Xu; Li Yang; Qihua Ling; Hua Wang; Hai Huang

2007-01-01

342

Micellar and Biochemical Properties of (Hemi)Fluorinated Surfactants Are Controlled by the Size of the Polar Head  

PubMed Central

Abstract Surfactants with fluorinated and hemifluorinated alkyl chains have yielded encouraging results in terms of membrane protein stability; however, the molecules used hitherto have either been chemically heterogeneous or formed heterogeneous micelles. A new series of surfactants whose polar head size is modulated by the presence of one, two, or three glucose moieties has been synthesized. Analytical ultracentrifugation and small-angle neutron scattering show that fluorinated surfactants whose polar head bears a single glucosyl group form very large cylindrical micelles, whereas those with two or three glucose moieties form small, homogeneous, globular micelles. We studied the homogeneity and stability of the complexes formed between membrane proteins and these surfactants by using bacteriorhodopsin and cytochrome b6f as models. Homogeneous complexes were obtained only with surfactants that form homogeneous micelles. Surfactants bearing one or two glucose moieties were found to be stabilizing, whereas those with three moieties were destabilizing. Fluorinated and hemifluorinated surfactants with a two-glucose polar head thus appear to be very promising molecules for biochemical applications and structural studies. They were successfully used for cell-free synthesis of the ion channel MscL. PMID:19686655

Breyton, Cecile; Gabel, Frank; Abla, Maher; Pierre, Yves; Lebaupain, Florence; Durand, Gregory; Popot, Jean-Luc; Ebel, Christine; Pucci, Bernard

2009-01-01

343

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.

1988-01-01

344

Polarized Sunglasses  

NSDL National Science Digital Library

When light reflects from water, asphalt, or other non-metallic surfaces, it becomes polarized. In other words, the reflected light is usually vibrating more in one direction than in others. To see how polarizing sunglasses affect this glare, check out this fun activity from the Exploratorium.

Exploratorium

2008-11-01

345

Polar Glaciology  

NASA Technical Reports Server (NTRS)

Two fields of research on polar ice sheets are likely to be of dominant interest during the 1990s. These are: the role of polar ice sheets in the hydrological cycle ocean-atmosphere-ice sheets-oceans, especially in relation to climate change; and the study and interpretation of material in deep ice cores to provide improved knowledge of past climates and of the varying levels of atmospheric constituents such as CO2, NOx, SO2, aerosols, etc., over the past 200,000 years. Both topics require a better knowledge of ice dynamics. Many of the studies that should be undertaken in polar regions by Earth Observing System require similar instruments and techniques to those used elsewhere over oceans and inland surfaces. However to study polar regions two special requirements need to be met: Earth Observing System satellite(s) need to be in a sufficiently high inclination orbit to cover most of the polar regions. Instruments must also be adapted, often by relatively limited changes, to give satisfactory data over polar ice. The observational requirements for polar ice sheets in the 1990s are summarized.

Robin, G. D.

1984-01-01

346

Quantum dot based photonic devices at 1.3 ?m: Direct modulation, mode-locking, SOAs and VCSELs  

NASA Astrophysics Data System (ADS)

We present results on directly modulated lasers with high-reflectivity coating, mode-locked lasers with a gain and absorber section, and semiconductor optical amplifiers (SOA) with anti-reflection coating, all based on InGaAs/GaAs quantum dot (QD) material emitting at 1.3 ?m. Error free 8 and 10 Gb/s data modulation is presented. 80 GHz passive mode-locking of two-section QD lasers is reported. Hybrid mode-locking was achieved at 40 GHz. The minimum pulse width at 80 GHz was 1.5 ps, with a time-bandwidth product of 1.7. QD SOAs are shown to have a chip gain larger than 26 dB. Modeling of the gain characteristics of these devices predicts 40 dB amplification under ideal biasing and input power. QD-VCSEL with 17 p-modulation doped QD layers placed in 5 field intensity antinodes and fully doped GaAs/AlGaAs DBRs show a peak multimode RT cw output power of 1.8 mW and differential efficiency of 20%. The maximum -3dB bandwidth is 3 GHz.

Laemmlin, M.; Fiol, G.; Kuntz, M.; Hopfer, F.; Mutig, A.; Ledentsov, N. N.; Kovsh, A. R.; Schubert, C.; Jacob, A.; Umbach, A.; Bimberg, D.

2006-03-01

347

Blumlein configuration for high-repetition-rate pulse generation of variable duration and polarity using synchronized switch control.  

PubMed

Blumlein generators are used in different applications such as radars, lasers, and also recently in various biomedical studies, where the effects of high-voltage nanosecond pulses on biological cells are evaluated. In these studies, it was demonstrated that by applying high-voltage nanosecond pulses to cells, plasma membrane and cell organelles are permeabilized. As suggested in a recent publication, the repetition rate and polarity of nanosecond high-voltage pulses could have an important effect on the electropermeabilization process, and consequently, on the observed phenomena. Therefore, we designed a new Blumlein configuration that enables a higher repetition rate of variable duration of either bipolar or unipolar high-voltage pulses. We achieved a maximal pulse repetition rate of 1.1 MHz. However, theoretically, this rate could be even higher. We labeled endocytotic vesicles with lucifer yellow and added propidium iodide to a cell suspension for testing the cell plasma membrane integrity, so we were able to observe the permeabilization of endocytotic vesicles and the cell plasma membrane at the same time. The new design of pulse generator was built, verified, and also tested in experiments. The resulting flexibility and variability allow further in vitro experiments to determine the importance of the pulse repetition rate and pulse polarity on membrane permeabilization -- both of the cell plasma membrane as well as of cell organelle membranes. PMID:19635688

Rebersek, Matej; Kranjc, Matej; Pavliha, Denis; Batista-Napotnik, Tina; Vrtacnik, Danilo; Amon, Slavko; Miklavcic, Damijan

2009-11-01

348

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

349

Control of membrane polar lipid composition in Acholeplasma laidlawii a by the extent of saturated fatty acid synthesis.  

PubMed

The low level of endogenous fatty acid synthesis in Acholeplasma laidlawii A strain EF22 was found to be caused by a deficiency of pantetheine in the lipid-depleted growth medium. By supplementing the oleic acid-containing medium with increasing concentrations of pantethein, saturated fatty acid synthesis was stimulated (having an apparent Km of 5 microM for pantetheine) and the incorporation of endogenously synthesized fatty acids in membrane lipids increased markedly. Furthermore, carotenoid biosynthesis was stimulated. Exogenous palmitic acid was found to inhibit partially the endogenous fatty acid synthesis. A gradual stimulation of fatty acid synthesis was accompanied by a linear increase in the molar proportion between the two dominating membrane glucolipids, monoglucosyldiacylglycerol and diglucosyldiacylglycerol. The total amount of charged membrane lipids decreased upon increasing the degree of fatty acid saturation. These regulations are discussed in terms of membrane stability, and influence of membrane molecular ordering and surface charge density on lipid polar head group synthesis. PMID:7352994

Christiansson, A; Wieslander, A

1980-01-25

350

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

351

Isolation and sequence analysis of CDC43, a gene involved in the control of cell polarity in Saccharomyces cerevisiae.  

PubMed

The Saccharomyces cerevisiae CDC43 gene product is involved in establishing cell polarity during the cell-division cycle. When grown at restrictive temperatures, temperature-sensitive cdc43 mutants are unable to form buds and display delocalized cell-surface deposition [Adams et al., J. Cell Biol. (1990) in press]. We have isolated a cdc43-complementing plasmid from a yeast genomic-DNA library and localized the CDC43 gene, by subcloning and transposon-mutagenesis experiments, to a 1.2-kb region of DNA that contained only one significant ATG-initiated open reading frame of 213 codons. The putative CDC43 gene product contains a possible nuclear-localization signal sequence, a cysteine-rich domain and a histidine-rich domain, and a region that is similar in structure to alpha-helix-turn-alpha-helix structural domains present in some prokaryotic and eukaryotic DNA-binding proteins. PMID:2199333

Johnson, D I; O'Brien, J M; Jacobs, C W

1990-05-31

352

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

353

Computer simulation of an operation of the GaInP\\/AlGaInP QW VCSELs: Excitation of various transverse LPij modes  

Microsoft Academic Search

A comprehensive fully self-consistent optical–electrical–thermal-recombination model of the 650-nm oxide-confined GaAs-based GaInP\\/AlGaInP vertical-cavity surface-emitting diode lasers (VCSELs) is used to determine their anticipated room-temperature (RT) continuous-wave (CW) performance characteristics. As expected, for the devices with very large active regions, higher-order transverse LPij modes exhibit the lowest lasing thresholds. However, the desired single fundamental LP01 mode operation remains dominating one for

Lukasz Piskorski; Robert P. Sarzala; Wlodzimierz Nakwaski

2008-01-01

354

Spectral induced polarization porosimetry  

NASA Astrophysics Data System (ADS)

Induced polarization is a geophysical method looking to image and interpret low-frequency polarization mechanisms occurring in porous media. Below 10 kHz, the quadrature conductivity of metal-free sandy and clayey materials exhibits a distribution of relaxation times, which can be related to the pore size distribution of these porous materials. When the polarization spectra are fitted with a Cole-Cole model, we first observe that the main relaxation time is controlled by the main pore size of the material and that the Cole-Cole exponent c is never much above 0.5, a value corresponding to a Warburg function. The complex conductivity is then obtained through a convolution product between the pore size distribution and such Warburg function. We also provide a way to recover the pore size distribution by performing a deconvolution of measured spectra using the Warburg function. A new dataset of mercury porosimetry and induced polarization data of six siliciclastic materials supports the hypothesis that the Cole-Cole relaxation time is strongly controlled by the pore size, and especially the characteristic pore size corresponding to the peak of the pore size distribution from mercury porosimetry. The distribution of the pore throat sizes of these materials seems fairly well recovered using the Warburg decomposition of the spectral induced polarization spectra but additional data will be needed to confirm this finding.

Revil, A.; Florsch, N.; Camerlynck, C.

2014-08-01

355

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

356

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

357

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

358

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

359

Voltage-controlled cellular viability of preosteoblasts on polarized cpTi with varying surface oxide thickness.  

PubMed

Cathodic voltage shifts of metallic biomaterials were recently shown to induce cell apoptosis in-vitro. The details of the reduction-based physico-chemical phenomena have not yet been fully elucidated. This study shows how surface oxide thickness of commercially pure titanium affects the voltage viability range, and whether anodic oxidation can extend this range. Cell viability, cytoskeletal organization, and cellular adhesion on bare and anodized Ti, at -500, -400 mV(Ag/AgCl) and open circuit potential were assessed. Surfaces were characterized using contact angle measurement and atomic force microscopy, and the observed cellular response was related to the changes in electrochemical currents, and impedance of the samples. Results show that anodization at 9 V in phosphate buffer saline generates a compact surface oxide with comparable surface roughness and energy to the starting bare surface. The anodized surface extends the viability range at 24h from -400 mV(Ag/AgCl) by about -100 mV, which corresponds to an increase in impedance of the surface from 58 k? cm(2) to 29 M? cm(2) at -400 mV(Ag/AgCl) and results in low average current densities below 0.1 ?A cm(-2). The results demonstrate that the voltage range for cell viability under cathodic polarization is expanded due to anodization of the surface oxide and lowering of cathodic currents. PMID:23810897

Haeri, Morteza; Wöllert, Torsten; Langford, George M; Gilbert, Jeremy L

2013-12-01

360

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

361

Comparison of InP- and GaSb-based VCSELs emitting at 2.3 ?m suitable for carbon monoxide detection  

NASA Astrophysics Data System (ADS)

Carbon monoxide (CO) is a prominent and toxic gas mainly generated by imperfect burning in fires or ovens. For trace gas monitoring and fire detection a compact, long term stable and calibration-free CO sensor is desirable. One very interesting measuring method is Tuneable Diode Laser Absorption Spectroscopy (TDLAS), which utilizes the unique properties of Vertical-Cavity Surface-Emitting Lasers (VCSELs). Two approaches to reach the required wavelength range for the absorption lines of CO at around 2350 nm are discussed in this paper. The first approach is an expansion of the emission wavelength range of the now well-established lasers based on InP and a second and new one is fabricating VCSELs based on GaSb. From the epitaxial point of view the gain of the active material and the realization of a tunnel junction as well as optical, thermal and electrical characteristics of the mirror materials are important issues. For a proper choice of the device design the structuring of the used materials also plays a fundamental role- in particular the substrate removal. With simultaneous considerations of all these crucial issues, devices on InP and GaSb substrates have been fabricated. Both types work in continuous-wave mode, generating light in single-mode emission at the desired wavelength of the CO absorption line, which enables CO measurements down to a concentration limit of 2 ppm.

Boehm, Gerhard; Bachmann, Alexander; Rosskopf, Jürgen; Ortsiefer, Markus; Chen, Jia; Hangauer, Andreas; Meyer, Ralf; Strzoda, Rainer; Amann, Markus-Christian

2011-05-01

362

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

363

BaCaF2/III-V semiconductor broadband distributed Bragg reflectors for long-wavelength VCSEL and SESAM devices  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

364

Polarization hologram  

NASA Astrophysics Data System (ADS)

The interaction of light with a sub-wavelength period grating can be approximated by a uniform medium with an effective refractive index. The effective index is a function of the grating structure, the indices of its composite materials and the polarization of light. In this paper we report on the design, fabrication and testing of CD, DVD polarization selective hologram gratings based upon this principle. We first describe the design, fabrication and testing of a one-layer structure. We then consider the design, fabrication and testing of a two-layer structure. We show, how the two-layer structure produces similar performance however has the lower aspect ratio. The two-layer structure is also shown to be less sensitive to off design wavelength and incident angle. Both gratings have been designed to function with the wavelengths of CD, and DVD.

Kitagawa, Seiichiro; Fujimura, Kayoko; Yamamoto, Kazuya; Okada, Makoto

2007-02-01

365

Cell polarity  

PubMed Central

Despite extensive genetic analysis of the dynamic multi-phase process that transforms a small population of lateral plate mesoderm into the mature limb skeleton, the mechanisms by which signaling pathways regulate cellular behaviors to generate morphogenetic forces are not known. Recently, a series of papers have offered the intriguing possibility that regulated cell polarity fine-tunes the morphogenetic process via orienting cell axes, division planes and cell movements. Wnt5a-mediated non-canonical signaling, which may include planar cell polarity, has emerged as a common thread in the otherwise distinct signaling networks that regulate morphogenesis in each phase of limb development. These findings position the limb as a key model to elucidate how global tissue patterning pathways direct local differences in cell behavior that, in turn, generate growth and form. PMID:22064549

Romereim, Sarah M

2011-01-01

366

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

367

Polarization Sensitivity  

NASA Astrophysics Data System (ADS)

Optical coherence tomography (OCT) (Huang et al. Science 254(5035): 1178-1181, 1991; Fercher et al. Rep Prog Phys 66:239-303, 2003; Drexler and Fujimoto Prog Retin Eye Res 27(1):45-88, 2008) is a well-established tool for high-resolution cross-sectional imaging of human ocular structures. Despite its great success in improving ocular diagnostic imaging, conventional OCT cannot directly differentiate between different tissues. However, polarization-sensitive (PS) OCT is able to generate tissue-specific contrast that can be further used to segment ocular structures and to obtain quantitative information.

Schmidt-Erfurth, U.; Schlanitz, F.; Bolz, M.; Vass, C.; Lammer, J.; Schütze, C.; Pircher, M.; Götzinger, E.; Baumann, B.; Hitzenberger, C. K.

368

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

369

Injection Electrode Polarization in Induced Polarization  

E-print Network

Injection Electrode Polarization in Induced Polarization J.B. Merriam Department of Geological-966-8593, E-mail: jim.merriam@usask.ca Polarization at the boundary between the current injection electrodes and the pore fluid occurs by a number of mechanisms. The polarization can be described as a variable contact

Merriam, James

370

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

371

Polar ozone  

NASA Technical Reports Server (NTRS)

The observation and interpretation of a large, unexpected ozone depletion over Antarctica has changed the international scientific view of stratospheric chemistry. The observations which show the veracity, seasonal nature, and vertical structure of the Antarctic ozone hole are presented. Evidence for Arctic and midlatitude ozone loss is also discussed. The chemical theory for Antarctic ozone depletion centers around the occurrence of polar stratospheric clouds (PSCs) in Antarctic winter and spring; the climatology and radiative properties of these clouds are presented. Lab studies of the physical properties of PSCs and the chemical processes that subsequently influence ozone depletion are discussed. Observations and interpretation of the chemical composition of the Antarctic stratosphere are described. It is shown that the observed, greatly enhanced abundances of chlorine monoxide in the lower stratosphere are sufficient to explain much if not all of the ozone decrease. The dynamic meteorology of both polar regions is given, interannual and interhemispheric variations in dynamical processes are outlined, and their likely roles in ozone loss are discussed.

Solomon, S.; Grose, W. L.; Jones, R. L.; Mccormick, M. P.; Molina, Mario J.; Oneill, A.; Poole, L. R.; Shine, K. P.; Plumb, R. A.; Pope, V.

1990-01-01

372

Polar Terrains  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site] Context image for PIA03577 Polar Terrains

The region surrounding the South Polar Cap contains many different terrain types. This image shows both etched terrain and a region of 'mounds'.

Image information: VIS instrument. Latitude 75S, Longitude 286.5E. 17 meter/pixel resolution.

Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

2005-01-01

373

EAT-2, a SAP-like adaptor, controls NK cell activation through phospholipase C?, Ca++, and Erk, leading to granule polarization.  

PubMed

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; Veillette, André

2014-04-01

374

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

Perez-Quintero, Luis-Alberto; Roncagalli, Romain; Guo, Huaijian; Latour, Sylvain; Davidson, Dominique

2014-01-01

375

Polarization of four-wave mixing with electromagnetically induced transparency  

NASA Astrophysics Data System (ADS)

The dependence of four-wave mixing (FWM) generated in Rubidium (Rb) vapor with electromagnetically induced transparency (EIT) window on polarizations of the incident fields is studied both theoretically and experimentally. The polarization properties of FWM signal under diverse laser polarization configurations are studied and compared. The results indicate that FWM signal is linear polarized when all incident fields are linear polarized. However, FWM becomes elliptical polarized if any incident field is elliptical polarized. Moreover, the polarizations of the incident fields also influence the dressing effect of the coupling field on FWM process. As the polarization of coupling field (or probe field) varying from linear to circular, the dressing effect gets stronger. By controlling the polarizations of the incident beams polarizations, we can manipulate the polarization state of FWM signal and the dressing effect as well.

Cheng, Xuemei; Du, Yigang; Zhang, Yanpeng; Wang, Zhiguo; Miao, Yizhu; Ren, Zhaoyu; Bai, Jintao

2012-10-01

376

Overlapping and divergent signaling pathways for ARK1 and AGD1 in the control of root hair polarity in Arabidopsis thaliana  

PubMed Central

We previously showed that seedlings harboring mutations in genes encoding ARK1, an armadillo repeat-containing kinesin, or AGD1, a class 1 ARF-GAP, have root hairs that exhibit wavy/spiral growth and two tips originating from one initiation site. These root hair defects were accompanied by bundling of endoplasmic microtubules and filamentous actin (F-actin) that extended to the extreme root hair apex. The similar phenotypes of ark1 and agd1 mutants suggest a tight coordination between the cytoskeleton and membrane trafficking in the control of root hair polarity. Indeed, cell biological and genetic studies of the agd1 mutant provided evidence that AGD1's involvement in root hair development involves cross-talk among phosphoinositides (PIs), the actin cytoskeleton and other small GTPases such as ROP2 and RABA4b. Here we show that ark1 root hairs mirror those of agd1 with regard to altered targeting of ROP2 and RABA4b, as well as abnormal tonoplast organization. Furthermore, like agd1, enhanced root hair defects in double mutants in ARK1 and genes encoding a type B phosphatidylinositol-4-phosphate 5-kinase 3 (PIP5K3), a phosphatidylinositol-4-phosphate (PI-4P) phosphatase (RHD4), a phosphatidylinositol transfer protein (COW1), and a vegetative actin isoform (ACT2), were observed. However, root hair shape of some ark1 double mutant combinations, particularly those with act2, pip5k3 and rhd4 (ark1 act2, ark1 pip5k3, ark1 rhd4), differed in some respects from agd1 act2, agd1 pip5k3, and agd1 rhd4. Taken together our results continue to point to commonalities between ARK1 and AGD1 in specifying root hair polarity, but that these two modulators of tip-growth can also regulate root hair development through divergent signaling routes with AGD1 acting predominantly during root hair initiation and ARK1 functioning primarily in sustained tip growth. PMID:24400013

Yoo, Cheol-Min; Blancaflor, Elison B.

2013-01-01

377

Adaptive shaping of femtosecond polarization profiles  

NASA Astrophysics Data System (ADS)

We report the experimental implementation of femtosecond polarization pulse shaping within an adaptive learning loop. This technique makes it possible to optimally and automatically generate light fields in which intensity, momentary frequency, and light polarization (i.e., ellipticity and orientation) change as a function of time within a single femtosecond laser pulse. By use of second-harmonic generation as a feedback signal in an evolutionary algorithm, specific phase- and polarization-modulated laser pulses are generated. Material dispersion and time-dependent modulations of the polarization state can be compensated. These experiments demonstrate the feasibility of adaptive quantum control experiments with polarization-shaped femtosecond laser pulses.

Brixner, T.; Damrauer, N. H.; Krampert, G.; Niklaus, P.; Gerber, G.

2003-05-01

378

Beyond Penguins and Polar Bears: Polar Geography  

NSDL National Science Digital Library

Our presenters provide an overview of the geography of the Arctic and Antarctic regions and featured resources from the Beyond Penguins and Polar Bears cyberzine, a resource for elementary educators. This cyberzine focuses on strategies and content to integrate science and literacy through the study of the polar regions. Recorded on May 27, 2008, Beyond Penguins and Polar Bears: Integrating Science and Literacy, Seminar 1: Polar Geography, NSDL featured our experts from The Ohio State University, Jessica Fries-Gaither, Project Director for Beyond Penguins and Polar Bears and Elementary Resource Specialist at the Ohio Resource Center and Dr. Carol Landis, Education Coordinator at the Byrd Polar Research Center.

Payo, Robert

379

Cross Polarizing Transparent Organics  

E-print Network

://upload.wikimedia.org/wikipedia/commons/f/f9/Sunglasses-1_retouch.png Slide 3: http://people.rit.edu/andpph/text-figures/polarization/polarizationCross Polarizing Transparent Organics Kenny Harvey Carleton College, Northfield MN Fleischer Group #12;Polarization #12;Advantage of Polarization Detect Residual Stresses in Transparent Plastics

Petta, Jason

380

Physics with polarized photons  

SciTech Connect

The role that polarization can play in the interaction of real and virtual photons with nuclear matter is considered. Linear, circular, and elliptical polarization are considered. Photodisintegration of the deuteron with linearly polarized photons is then examined, followed by use of circularly polarized photons with a polarized target. 30 refs., 4 figs. (LEW)

Matone, G.

1985-10-01

381

Polarization-selective grating mirrors used in the generation of radial polarization  

NASA Astrophysics Data System (ADS)

Two novel methods to control the polarization of laser radiation are presented. The discrimination between different polarization distributions isperformed with a corrugation grating in the top high-index layer of a multilayer mirror, which couples the undesired polarization into a lossy waveguidemode of the multilayer. The generation of radially polarized radiation in a laser resonator is presented as a practical verification of the principle.

Moser, T.; Glur, H.; Romano, V.; Pigeon, F.; Parriaux, O.; Ahmed, M. A.; Graf, T.

2005-05-01

382

Doppler-limited H2O and HF absorption spectroscopy by sweeping the 1,321-1,354 nm range at 55 kHz repetition rate using a single-mode MEMS-tunable VCSEL  

NASA Astrophysics Data System (ADS)

A single longitudinal mode micro-electro-mechanical system-tunable vertical cavity surface-emitting laser (VCSEL) was used to measure H2O and HF absorption spectra in the 1,321-1,354 nm range at 55 kHz repetition rate (˜ 740 MHz/ns tuning rate). Pulse delay referencing was used to achieve an absorbance noise level of 0.004 (RMS), within a factor of 2.6 of the shot noise limit. The measured linewidths approach the low-pressure feature linewidths (˜790 MHz) characteristic of the gases studied, highlighting the single-mode nature of the VCSEL throughout each rapid wavelength sweep. At even higher tuning rates, molecular features became asymmetric and broad, consistent with rapid passage and Fourier effects.

Stein, B. A.; Jayaraman, V.; Jiang, J. Y.; Cable, A.; Sanders, S. T.

2012-09-01

383

Polarization imaging apparatus  

NASA Technical Reports Server (NTRS)

A polarization imaging apparatus measures the Stokes image of a sample. The apparatus consists of an optical lens set 11, a linear polarizer 14 with its optical axis 18, a first variable phase retarder 12 with its optical axis 16 aligned 22.5.degree. to axis 18, a second variable phase retarder 13 with its optical axis 17 aligned 45.degree. to axis 18, a imaging sensor 15 for sensing the intensity images of the sample, a controller 101 and a computer 102. Two variable phase retarders 12 and 13 were controlled independently by a computer 102 through a controller unit 101 which generates a sequential of voltages to control the phase retardations of VPRs 12 and 13. A set of four intensity images, I.sub.0, I.sub.1, I.sub.2 and I.sub.3 of the sample were captured by imaging sensor 15 when the phase retardations of VPRs 12 and 13 were set at (0,0), (.pi.,0), (.pi.,.pi.) and (.pi./2,.pi.), respectively Then four Stokes components of a Stokes image, S.sub.0, S.sub.1, S.sub.2 and S.sub.3 were calculated using the four intensity images.

Zou, Yingyin Kevin (Inventor); Chen, Qiushui (Inventor); Zhao, Hongzhi (Inventor)

2010-01-01

384

Exploring Polar Oceanography  

NSDL National Science Digital Library

This activity utilizes labs, online resources, and student ideas to build an understanding of polar climates, how changes in polar oceans can affect coastal climates, and how changes in polar regions affect climates elsewhere on Earth.

Sills, Alan; Pbs

385

Polarized Light in Astronomy.  

ERIC Educational Resources Information Center

The application of very sensitive electronic detecting devices during the last decade has revolutionized and revitalized the study of polarization in celestial objects. The nature of polarization, how polaroids work, interstellar polarization, dichroic filters, polarization by scattering, and modern polarimetry are among the topics discussed. (JN)

King, D. J.

1983-01-01

386

Nondiffracting transversally polarized beam.  

PubMed

Generation of a nondiffracting transversally polarized beam by means of transmitting an azimuthally polarized beam through a multibelt spiral phase hologram and then highly focusing by a high-NA lens is presented. A relatively long depth of focus (?4.84?) of the electric field with only radial and azimuthal components is achieved. The polarization of the wavefront near the focal plane is analyzed in detail by calculating the Stokes polarization parameters. It is found that the polarization is spatially varying and entirely transversally polarized, and the polarization singularity disappears at the beam center, which makes the central bright channel possible. PMID:21886250

Yuan, G H; Wei, S B; Yuan, X-C

2011-09-01

387

WebTOP Polarization Tutorial  

NSDL National Science Digital Library

This is an interactive tutorial about Polarization based on two of the WebTOP (http://webtop.msstate.edu/) simulations, Polarization and Scattering. Covered topics include polarized and unpolarized light, waveplates, polarization by reflection and polarization by scattering.

Behringer, Ernest

2010-03-22

388

Polarization-balanced beamsplitter  

DOEpatents

A beamsplitter assembly is disclosed that includes several beamsplitter cubes arranged to define a plurality of polarization-balanced light paths. Each polarization-balanced light path contains one or more balanced pairs of light paths, where each balanced pair of light paths includes either two transmission light paths with orthogonal polarization effects or two reflection light paths with orthogonal polarization effects. The orthogonal pairing of said transmission and reflection light paths cancels polarization effects otherwise caused by beamsplitting. 10 figs.

Decker, D.E.

1998-02-17

389

Fidelity in planar cell polarity signalling  

Microsoft Academic Search

The polarity of Drosophila wing hairs displays remarkable fidelity. Each of the approximately 30,000 wing epithelial cells constructs an actin-rich prehair that protrudes from its distal vertex and points distally. The distal location and orientation of the hairs is virtually error free, thus forming a nearly perfect parallel array. This process is controlled by the planar cell polarity signalling pathway.

Dali Ma; Chung-hui Yang; Helen McNeill; Michael A. Simon; Jeffrey D. Axelrod

2003-01-01

390

8, 1103911062, 2008 Nitrate in polar ice  

E-print Network

ACPD 8, 11039­11062, 2008 Nitrate in polar ice E. W. Wolff et al. Title Page Abstract Introduction Chemistry and Physics Discussions Reassessment of the factors controlling temporal profiles of nitrate Geosciences Union. 11039 #12;ACPD 8, 11039­11062, 2008 Nitrate in polar ice E. W. Wolff et al. Title Page

Paris-Sud XI, Université de

391

Laser Polarization Effects in Supercontinuum Generation  

E-print Network

We present experimental evidence of a fourth order process in electric field in supercontinuum generation. We also show laser induced polarization preference in the supercontinuum generating media. These results have become possible through the choice of isotropic and anisotropic samples interacting with ultrashort laser pulses of changing ellipticity. Laser polarization emerges as an important control parameter for the highly nonlinear phenomenon of supercontinuum generation.

Srivastava, A; Srivastava, Alok; Goswami, Debabrata

2004-01-01

392

Laser Polarization Effects in Supercontinuum Generation  

E-print Network

We present experimental evidence of a fourth order process in electric field in supercontinuum generation. We also show laser induced polarization preference in the supercontinuum generating media. These results have become possible through the choice of isotropic and anisotropic samples interacting with ultrashort laser pulses of changing ellipticity. Laser polarization emerges as an important control parameter for the highly nonlinear phenomenon of supercontinuum generation.

Alok Srivastava; Debabrata Goswami

2004-02-22

393

Observations of the Mars Polar Vortex  

NASA Technical Reports Server (NTRS)

The winter season, westerly circumpolar flow of the Martian atmosphere, and of the terrestrial stratosphere, is concentrated into a jet whose latitude falls between 60 and 80 degrees. This jet is known as the polar vortex. The terrestrial polar vortex has been understood to be the dynamical controlling mechanism for ozone depletion in the polar stratosphere for more than a decade. More recently, the earth's stratospheric annular modes, which are essentially a weakening/strengthening oscillation of the polar vortex jet, have been shown to be coupled to and possibly even a driving mechanism for, the tropospheric Arctic Oscillation (AO) / North Atlantic Oscillation (NAO) phenomenon.

McConnochie, T. H.; Conrath, B. J.; Gierasch, P. J.; Banfield, D.; Smith, M. D.

2003-01-01

394

Polarization mode dispersion emulation using polarization maintaining fibers: Fixed root-mean-square differential group delay but varying second-order polarization mode dispersion  

Microsoft Academic Search

We report on a polarization mode dispersion (PMD) emulator with a fixed root-mean-square differential group delay (RMS-DGD) but varying second-order PMD (SO-PMD) using only a combination of polarization maintaining fibers and a polarization controller. The SO-PMD control mechanism is not completely in real time. Besides controlling the mean PMD values of the emulator, simultaneous adjustments in the maximum and minimum

Vitalis Musara; Lorinda Wu; Gaoboelwe Pelaelo; Andrew W. R. Leitch

2009-01-01

395

Controlling optical properties of periodic gold nanoparticle arrays by changing the substrate, topologic shapes of nanoparticles, and polarization direction of incident light  

NASA Astrophysics Data System (ADS)

The effects of various parameters including thickness and dielectric constants of substrates, shapes of nanoparticles, and polarization direction of incident light, on the extinction spectra of periodic gold nanoparticle arrays are investigated by the full-vectorial three-dimensional (3D) finite difference time domain (FDTD) method. The calculated results show that the substrate affects the extinction spectra by coupling the fields co-excited by the substrate and gold nanoparticles. Extinction spectra are influenced by the shapes of the nanoparticles, but there are no obvious changes in extinction spectra for similar shapes. The polarization direction of incident light has a great influence on the extinction spectra. The implications of these results are discussed.

Li, Ting; Yu, Li; Lu, Zhi-Xin; Song, Gang; Zhang, Kai

2011-08-01

396

Polarization diversity in radars  

NASA Astrophysics Data System (ADS)

Many polarization techniques, which have been proposed and analyzed to enhance radar performance, are reviewed in this paper in order to assess the possible improvement they can provide in the signal-to-disturbance ratio, target detectability, target discrimination and resolution, and target classification and identification. Some recent experimentally-based results relating to these applications are also presented. Those techniques are emphasized for which polarization-based capabilities appear sufficiently assessed, such as adaptive polarization cancellation of clutter, chaff, and jamming. Polarization Doppler processing of dual-polarization radar signals, meteorologic applications, and polarization adaptation for target detection in the clear (in free space) are also examined.

Giuli, D.

1986-02-01

397

Satellite observations of polar arcs  

NASA Astrophysics Data System (ADS)

The increased probability of observing polar arcs during periods of northward interplanetary magnetic field (IMF) has tended to obscure their significance in terms of magnetospheric topology because of the presumed 'inactive' state of the magnetosphere. However, satellite imaging has shown that these high latitude features are quite dynamic both in their intensity and spatial variations. The overall morphology of the high latitude aurora has been described by a variety of imaginative terms, but its primary optical characteristic is of a polar arc(s) extending between the dayside and nightside auroral distribution on one or both of the dawn/dusk sides of the high latitude region. This large scale morphology is controlled by the azimuth angle of the IMF and the predominant configuration is one wherein the region between the polar arc and the normal auroral distribution is filled with low intensity diffuse emission. Simultaneous particle and electric field measurements show this region exhibits a closed field line character with predominantly sunward flowing plasma. These large scale polar arcs are connected (in either a diffuse or discrete fashion) to the nightside auroral distribution with essentially equal probabilities, but exhibit a clear peak near 12 MLT. This dayside connection is commonly associated with isolated high latitude features poleward of the normal auroral distribution which probably represent processes occurring on the front surface of the magnetotail poleward of the cusp. The existence of polar arcs is not always controlled by substorm activity: polar arcs can maintain their form and position well past expansion phase suggesting that they represent a fundamental boundary in the magnetosphere which is not modified by even large substorms.

Murphree, J. S.; Austin, J. B.; Hearn, D. J.; Cogger, L. L.; Elphinstone, R. D.; Woch, J.

1994-02-01

398

Polarized Light Corridor Demonstrations.  

ERIC Educational Resources Information Center

Eleven demonstrations of light polarization are presented. Each includes a brief description of the apparatus and the effect demonstrated. Illustrated are strain patterns, reflection, scattering, the Faraday Effect, interference, double refraction, the polarizing microscope, and optical activity. (CW)

Davies, G. R.

1990-01-01

399

Our Polar Past  

NSDL National Science Digital Library

The study of polar exploration is fascinating and offers students insights into the history, culture, and politics that affect the developing sciences at the farthest ends of Earth. Therefore, the authors think there is value in incorporating polar explor

Wandersee, James; Clary, Renee

2009-12-01

400

A translational polarization rotator.  

PubMed

We explore a free-space polarization modulator in which a variable phase is introduced between the right- and left-handed circular polarization components and used to rotate the linear polarization of the outgoing beam relative to that of the incoming beam. In this device, the polarization states are separated by a circular polarizer that consists of a quarter-wave plate in combination with a wire grid. A movable mirror is positioned behind and parallel to the circular polarizer. As the polarizer-mirror distance is changed, an incident linear polarization will be rotated through an angle that is proportional to the introduced phase delay. We demonstrate a prototype device that modulates Stokes Q and U over a 20% bandwidth, from 77 to 94 GHz. PMID:23033098

Chuss, David T; Wollack, Edward J; Pisano, Giampaolo; Ackiss, Sheridan; U-Yen, Kongpop; Ng, Ming wah

2012-10-01

401

Stressed Plastics by Polarization  

NSDL National Science Digital Library

This site, by Andrew Davidhazy at the Rochester Institute of Technology, describes polarization and how it can be used to investigate transparent materials. Color photographs show examples of polarization effects, and the text explains how colors are produced.

2007-09-19

402

Polar Bears Change Diet  

NSDL National Science Digital Library

This radio broadcast from 2001 explains how polar bears have adjusted their diet due to the climate warming around Hudson Bay, Canada. The ringed seals that polar bears normally eat have been harder for polar bears to get to, due to disappearing ice. This has forced polar bears to begin eating harbor seals and bearded seals. The clip is 4 minutes and 15 seconds in length.

Schneider, Doug

2007-12-12

403

Introduction to Polarized Light  

NSDL National Science Digital Library

This item is an introductory tutorial for students of physics or optics on the topic of light polarization. It explores basic concepts, techniques in modern polarized light microscopy, historical perspectives, and applications for industrial use. Included are cross-sectional drawings of reflective and circular polarization and polarization of scattered sunlight. This item is part of a larger collection of materials for students of introductory optics and microscopy.

Davidson, Michael; Spring, Kenneth R.; Murphy, Douglas B.

2008-08-23

404

Polarization independent wavelength conversion in fibers using incoherent pumps.  

PubMed

We report polarization independent wavelength conversion based on one-pump fiber optical parametric amplifiers. A spectrum-sliced amplified spontaneous emission (ASE) light source is used to provide a non-polarized pump. The signal is coherent lights coming from a tunable laser. When adjusting the polarization of the signal using a polarization controller, the variation of wavelength conversion efficiency is less than 0.2 dB. We use the vector theory of four-wave mixing to analyze the polarization independent nature of wavelength conversion by using randomly polarized pumps. PMID:18542652

Tian, Yu; Dong, Peng; Yang, Changxi

2008-04-14

405

Polarization methods for diode laser excitation of solid state lasers  

DOEpatents

A mode-locked laser employs a coupled-polarization scheme for efficient longitudinal pumping by reshaped laser diode bars. One or more dielectric polarizers are configured to reflect a pumping wavelength having a first polarization and to reflect a lasing wavelength having a second polarization. A Yb-doped gain medium can be used that absorbs light having a first polarization and emits light having a second polarization. Using such pumping with laser cavity dispersion control, pulse durations of less than 100 fs can be achieved.

Holtom, Gary R. (Richland, WA)

2008-11-25

406

Polarization dependence of molecular adsorption on ferroelectrics.  

PubMed

The structural details of ferroelectric surfaces influence the effect of ferroelectric polarization on surface chemistry, and it is important to understand and control defect functionality as well as identify adsorption sites in ferroelectric materials. Ferroelectric domain polarization has been found to have a significant effect on surface properties and interactions. Here, both the structure and the presence of local electric fields are examined simultaneously. The surface structure and ferroelectric domain orientation are controlled while molecular adsorption effects are quantified. We use scanning tunneling microscopy (STM) to determine the surface and electronic effects of polarization-gas interactions on a model ferroelectric surface, BaTiO3 (001). PMID:23719697

Kraya, Laura Y; Kraya, Ramsey

2013-04-01

407

Calculation of polarization effects  

SciTech Connect

Basically there are two areas of accelerator applications that involve beam polarization. One is the acceleration of a polarized beam (most likely a proton beam) in a synchrotron. Another concerns polarized beams in an electron storage ring. In both areas, numerical techniques have been very useful.

Chao, A.W.

1983-09-01

408

Graphing Polar Curves  

ERIC Educational Resources Information Center

Graphing polar curves typically involves a combination of three traditional techniques, all of which can be time-consuming and tedious. However, an alternative method--graphing the polar function on a rectangular plane--simplifies graphing, increases student understanding of the polar coordinate system, and reinforces graphing techniques learned…

Lawes, Jonathan F.

2013-01-01

409

Rotation and polarization diversity  

Microsoft Academic Search

In this work, we propose and study the performance of a new transmit diversity technique called rotation and polarization diversity. In this technique, in-phase and quadrature components of the rotated symbols are transmitted over two different polarizations of polarized transmitted antenna. By this way, in-phase and quadrature components are affected by different fading coefficients. Error performance of the proposed technique

Ahmet Yilmaz; Oguz Kucur

2011-01-01

410

Circular Polarized LCD  

Microsoft Academic Search

Novel LCD, which transmits circularly polarized light, is reported. The circular polarized light enables us to see the LCD screen through polarized sunglasses. It is developed for outdoor application, such as mobile computing, car navigator, and so on. The circular light is achieved by placing additional quarter wave film upon the screen.

Hideo Takano; Yuhji Yoshida

1998-01-01

411

Bumblebees learn polarization patterns.  

PubMed

Foraging insect pollinators such as bees must find and identify flowers in a complex visual environment. Bees use skylight polarization patterns for navigation, a capacity mediated by the polarization-sensitive dorsal rim area (DRA) of their eye. While other insects use polarization sensitivity to identify appropriate habitats, oviposition sites, and food sources, to date no nonnavigational functions of polarization vision have been identified in bees. Here we investigated the ability of bumblebees (Bombus terrestris) to learn polarization patterns on artificial "flowers" in order to obtain a food reward. We show that foraging bumblebees can learn to discriminate between two differently polarized targets, but only when the target artificial "flower" is viewed from below. A context for these results is provided by polarization imaging of bee-pollinated flowers, revealing the potential for polarization patterns in real flowers. Bees may therefore have the ability to use polarization vision, possibly mediated by their polarization-sensitive DRA, both for navigation and to learn polarization patterns on flowers, the latter being the first nonnavigational function for bee polarization vision to be identified. PMID:24909321

Foster, James J; Sharkey, Camilla R; Gaworska, Alicia V A; Roberts, Nicholas W; Whitney, Heather M; Partridge, Julian C

2014-06-16

412

Playing with Polarizers.  

ERIC Educational Resources Information Center

Discussed is how polarized sunglasses block glare, help spot subtle differences in surfaces, and give a clearer view under water. Information on unpolarized and polarized light is provided. The reasons causing glare to occur and how polarizers decrease glare are discussed. (KR)

Hecht, Jeff

1991-01-01

413

Bumblebees Learn Polarization Patterns  

PubMed Central

Summary Foraging insect pollinators such as bees must find and identify flowers in a complex visual environment. Bees use skylight polarization patterns for navigation [1–3], a capacity mediated by the polarization-sensitive dorsal rim area (DRA) of their eye [4, 5]. While other insects use polarization sensitivity to identify appropriate habitats [6], oviposition sites, and food sources [7], to date no nonnavigational functions of polarization vision have been identified in bees. Here we investigated the ability of bumblebees (Bombus terrestris) to learn polarization patterns on artificial “flowers” in order to obtain a food reward. We show that foraging bumblebees can learn to discriminate between two differently polarized targets, but only when the target artificial “flower” is viewed from below. A context for these results is provided by polarization imaging of bee-pollinated flowers, revealing the potential for polarization patterns in real flowers. Bees may therefore have the ability to use polarization vision, possibly mediated by their polarization-sensitive DRA, both for navigation and to learn polarization patterns on flowers, the latter being the first nonnavigational function for bee polarization vision to be identified. PMID:24909321

Foster, James J.; Sharkey, Camilla R.; Gaworska, Alicia V.A.; Roberts, Nicholas W.; Whitney, Heather M.; Partridge, Julian C.

2014-01-01

414

Polarization attractors in harmonic mode-locked fiber laser.  

PubMed

We report on a polarimetry of harmonic mode-locked erbium-doped fiber laser with carbon nanotubes saturable absorber. We find new types of vector solitons with locked, switching and precessing states of polarization. The underlying physics presents interplay between birefringence of a laser cavity created by polarization controller along with light induced anisotropy caused by polarization hole burning. PMID:24977612

Habruseva, Tatiana; Mou, Chengbo; Rozhin, Alex; Sergeyev, Sergey V

2014-06-16

415

Hybridized nanocavities as single-polarized plasmonic antennas  

E-print Network

Hybridized nanocavities as single-polarized plasmonic antennas Ahmet Ali Yanik,1,2 Ronen Adato,1 in coherence, and act as an efficient single-polarized plasmonic nano-antenna array. We employ propagating and localized plasmons to enhance polarization control along one axis, with total suppression

416

Stable polarization-encoded quantum key distribution in fiber  

E-print Network

Polarizations of single-photon pulses have been controlled with long-term stability of more than 10 hours by using an active feedback technique for auto-compensation of unpredictable polarization scrambling in long-distance fiber. Experimental tests of long-term operations in 50, 75 and 100 km fibers demonstrated that such a single-photon polarization control supported stable polarization encoding in long-distance fibers to facilitate stable one-way fiber system for polarization-encoded quantum key distribution, providing quantum bit error rates below the absolute security threshold.

Guang Wu; Jie Chen; Yao Li; Heping Zeng

2006-06-13

417

Development of an Adaptive Polarization-Mode  

E-print Network

-mode dispersion (PMD), in single-mode optical fibers, is a phenomenon that can limit the bit-rate-distance product.2 Description of the adaptive PMD compensation system...................33 3.2.1 Block diagram of the system and control of the polarization controller........36 3.2.3 Operation and control of the variable delay line

Kansas, University of

418

ATP-binding motifs play key roles in Krp1p, kinesin-related protein 1, function for bi-polar growth control in fission yeast  

SciTech Connect

Kinesin is a microtubule-based motor protein with various functions related to the cell growth and division. It has been reported that Krp1p, kinesin-related protein 1, which belongs to the kinesin heavy chain superfamily, localizes on microtubules and may play an important role in cytokinesis. However, the function of Krp1p has not been fully elucidated. In this study, we overexpressed an intact form and three different mutant forms of Krp1p in fission yeast constructed by site-directed mutagenesis in two ATP-binding motifs or by truncation of the leucine zipper-like motif (LZiP). We observed hyper-extended microtubules and the aberrant nuclear shape in Krp1p-overexpressed fission yeast. As a functional consequence, a point mutation of ATP-binding domain 1 (G89E) in Krp1p reversed the effect of Krp1p overexpression in fission yeast, whereas the specific mutation in ATP-binding domain 2 (G238E) resulted in the altered cell polarity. Additionally, truncation of the leucine zipper-like domain (LZiP) at the C-terminal of Krp1p showed a normal nuclear division. Taken together, we suggest that krp1p is involved in regulation of cell-polarized growth through ATP-binding motifs in fission yeast.

Rhee, Dong Keun [School of Life Sciences and Biotechnology, Korea University, Seoul 136-701 (Korea, Republic of); Cho, Bon A [School of Life Sciences and Biotechnology, Korea University, Seoul 136-701 (Korea, Republic of); Kim, Hyong Bai [Department of Bioinformatics, Korea University, Yeongigun, Chungnam 339-700 (Korea, Republic of)]. E-mail: hbkim5212@hotmail.com

2005-06-03

419

Crossed Elliptical Polarization Undulator  

NASA Astrophysics Data System (ADS)

There are increasing deamands for utilizing not only the circularly polarized radition, but also the linearly polarized radiation with fast switching of polarization directions. An elliptical polarization undulator (EPU) is planned to be installed in the Advanced Light Source (ALS). Similar devices are also planned for other third-generation synchrotron radiation facilities. Those devices have a capability of generating not only the circularly polarized radiation of either right- or left-handedness, but also the linearly polarized radiation of either horizontal or vertical direction, by changing the magnet phase mechanically. However, the fast switching capability is limited, due to the magnet motion mechanism. One possibility to achieve the fast switching of polarization direction is to install two identical EPUs in series in a same straight section. By setting each EPU in a circular polarization mode in opposite handedness, one can obtain linearly polarized radiation with any required polarization direction, depending on the modulator setting between two EPUs. This scheme can be used without any major degradation of polarization degree in any low energy (less than 2 GeV) low emittance third-generation storage ring.

Sasaki, Shigemi

1997-05-01

420

Polarization effects. Volume 2  

SciTech Connect

The use of polarized proton beams in ISABELLE is important for several general reasons: (1) With a single longitudinally polarized proton beam, effects involving parity violation can be identified and hence processes involving weak interactions can be separated from those involving strong and electromagnetic interactions. (2) Spin effects are important in the strong interactions and can be useful for testing QCD. The technique for obtaining polarized proton beams in ISABELLE appears promising, particularly in view of the present development of a polarized proton beam for the AGS. Projections for the luminosity in ISABELLE for collisions of polarized protons - one or both beams polarized with longitudinal or transverse polarization - range from 1/100 to 1 times the luminosity for unpolarized protons.

Courant, E.

1981-01-01

421

Instrumentation with polarized neutrons  

NASA Astrophysics Data System (ADS)

Neutron scattering with polarization analysis is an indispensable tool for the investigation of novel materials exhibiting electronic, magnetic, and orbital degrees of freedom. In addition, polarized neutrons are necessary for neutron spin precession techniques that path the way to obtain extremely high resolution in space and time. Last but not least, polarized neutrons are being used for fundamental studies as well as very recently for neutron imaging. Many years ago, neutron beam lines were simply adapted for polarized beam applications by adding polarizing elements leading usually to unacceptable losses in neutron intensity. Recently, an increasing number of beam lines are designed such that an optimum use of polarized neutrons is facilitated. In addition, marked progress has been obtained in the technology of 3He polarizers and the reflectivity of large- m supermirrors. Therefore, if properly designed, only factors of approximately 2-3 in neutron intensity are lost. It is shown that S-benders provide neutron beams with an almost wavelength independent polarization. Using twin cavities, polarized beams with a homogeneous phase space and P>0.99 can be produced without significantly sacrificing intensity. It is argued that elliptic guides, which are coated with large m polarizing supermirrors, provide the highest flux.

Böni, P.; Münzer, W.; Ostermann, A.

2009-09-01

422

[Review] Polarization and Polarimetry  

NASA Astrophysics Data System (ADS)

Polarization is a basic property of light and is fundamentally linked to the internal geometry of a source of radiation. Polarimetry complements photometric, spectroscopic, and imaging analyses of sources of radiation and has made possible multiple astrophysical discoveries. In this article I review (i) the physical basics of polarization: electromagnetic waves, photons, and parameterizations; (ii) astrophysical sources of polarization: scattering, synchrotron radiation, active media, and the Zeeman, Goldreich-Kylafis, and Hanle effects, as well as interactions between polarization and matter (like birefringence, Faraday rotation, or the Chandrasekhar-Fermi effect); (iii) observational methodology: on-sky geometry, influence of atmosphere and instrumental polarization, polarization statistics, and observational techniques for radio, optical, and X/? wavelengths; and (iv) science cases for astronomical polarimetry: solar and stellar physics, planetary system bodies, interstellar matter, astrobiology, astronomical masers, pulsars, galactic magnetic fields, gamma-ray bursts, active galactic nuclei, and cosmic microwave background radiation.

Trippe, Sascha

2014-02-01

423

Interstellar circular polarization.  

NASA Technical Reports Server (NTRS)

This paper shows that optical observations of circular polarization produced by aligned interstellar grains could yield valuable information about the grain material. The interstellar medium is known to be linearly dichroic from observations of interstellar linear polarization. Since the same aligned grains make the medium linearly birefringent, a small component of circular polarization can result from incident linearly polarized light if the position angle of the linear polarization does not coincide with either principal axis of the medium. Calculations demonstrate that the wavelength of the circular polarization is sensitive to the imaginary part of the complex refractive index of the grain material. This provides an opportunity of investigating whether the grains are characteristically dielectric or metallic.

Martin, P. G.

1972-01-01

424

Polarization rotator-splitters in standard active silicon photonics platforms.  

PubMed

We demonstrate various silicon-on-insulator polarization management structures based on a polarization rotator-splitter that uses a bi-level taper TM0-TE1 mode converter. The designs are fully compatible with standard active silicon photonics platforms with no new levels required and were implemented in the IME baseline and IME-OpSIS silicon photonics processes. We demonstrate a polarization rotator-splitter with polarization crosstalk < -13 dB over a bandwidth of 50 nm. Then, we improve the crosstalk to < -22 dB over a bandwidth of 80 nm by integrating the polarization rotator-splitter with directional coupler polarization filters. Finally, we demonstrate a polarization controller by integrating the polarization rotator-splitters with directional couplers, thermal tuners, and PIN diode phase shifters. PMID:24663698

Sacher, Wesley D; Barwicz, Tymon; Taylor, Benjamin J F; Poon, Joyce K S

2014-02-24

425

Optical characterization of nanostructured plasmonic polarizers  

NASA Astrophysics Data System (ADS)

This thesis describes techniques involved in the optical characterization of nanostructured plasmonic devices for use as micropolarizing elements. Two types of structures were measured: (1) ultra-high extinction ratio linear micro-polarizers; and (2) the linear structures combined with circular micro-polarizers for full on-chip Stokes polarimetry. An inspection microscope was modified to perform micro-transmission and micro-reflection measurements with precise control of illumination and collection spot size, as well as control over the incident beam collimation and polarization state. The electrical response of micro-polarizing structures fabricated on photodiodes was also characterized using this system. Guidance on how to perform such measurements is presented. Simulation of the optical response was performed and agrees well with experimental results. Recommendations for future development of the equipment, methods, and structures are made.

Peltzer, Jonathan

426

Polarization tailored light driven directional optical nanobeacon.  

PubMed

We experimentally demonstrate all-optical control of the emission directivity of a dipole-like nanoparticle with spinning dipole moment sitting on the interface to an optical denser medium. The particle itself is excited by a tightly focused polarization tailored light beam under normal incidence. The position dependent local polarization of the focal field allows for tuning the dipole moment via careful positioning of the particle relative to the beam axis. As an application of this scheme, we investigate the polarization dependent coupling to a planar two-dimensional dielectric waveguide. PMID:24724814

Neugebauer, Martin; Bauer, Thomas; Banzer, Peter; Leuchs, Gerd

2014-05-14

427

Polarization at SLC  

SciTech Connect

The SLAC Linear Collider has been designed to readily accommodate polarized electron beams. Considerable effort has been made to implement a polarized source, a spin rotation system, and a system to monitor the beam polarization. Nearly all major components have been fabricated. At the current time, several source and polarimeter components have been installed. The installation and commissioning of the entire system will take place during available machine shutdown periods as the commissioning of SLC progresses. It is expected that a beam polarization of 45% will be achieved with no loss in luminosity. 13 refs., 15 figs.

Swartz, M.L.

1988-07-01

428

Polarized negative ions  

SciTech Connect

This paper presents a survey of methods, commonly in use or under development, to produce beams of polarized negative ions for injection into accelerators. A short summary recalls how the hyperfine interaction is used to obtain nuclear polarization in beams of atoms. Atomic-beam sources for light ions are discussed. If the best presently known techniques are incorporated in all stages of the source, polarized H/sup -/ and D/sup -/ beams in excess of 10 ..mu..A can probably be achieved. Production of polarized ions from fast (keV) beams of polarized atoms is treated separately for atoms in the H(25) excited state (Lamb-Shift source) and atoms in the H(1S) ground state. The negative ion beam from Lamb-Shift sources has reached a plateau just above 1 ..mu..A, but this beam current is adequate for many applications and the somewhat lower beam current is compensated by other desirable characteristics. Sources using fast polarized ground state atoms are in a stage of intense development. The next sections summarize production of polarized heavy ions by the atomic beam method, which is well established, and by optical pumping, which has recently been demonstrated to yield very large nuclear polarization. A short discussion of proposed ion sources for polarized /sup 3/He/sup -/ ions is followed by some concluding remarks.

Haeberli, W.

1981-04-01

429

Polarization independent microphotonic circuits  

E-print Network

Microphotonic circuits have been proposed for applications ranging from optical switching and routing to optical logic circuits. However many applications require microphotonic circuits to be polarization independent, a ...

Watts, Michael Robert, 1974-

2005-01-01

430

Characterization of dentin, enamel, and carious lesions by a polarization-sensitive optical coherence tomography system  

Microsoft Academic Search

Enamel and dentin are the primary components of human teeth. Both of them have a strong polarization effect. We designed a polarization-sensitive optical coherence tomography (PSOCT) system to study the spatially resolved scattering and polarization phenomena of teeth. The system is constructed in free space to avoid the complexity of polarization control in fiber-based PSOCT. The structural features of enamel

Yueli Chen; Linda Otis; Daqing Piao; Quing Zhu

2005-01-01

431

Polar Plants: Unit Outlines  

NSDL National Science Digital Library

This article assembles free resources from the Polar Plants issue of the Beyond Penguins and Polar Bears cyberzine into a unit outline based on the 5E learning cycle framework. Outlines are provided for Grades K-2 and 3-5.

Fries-Gaither, Jessica

432

TRANSVERSELY POLARIZED L PRODUCTION.  

SciTech Connect

Transversely polarized {Lambda} production in hard scattering processes is discussed in terms of a leading twist T-odd fragmentation function which describes the fragmentation of an unpolarized quark into a transversely polarized {Lambda}. We focus on the properties of this function and its relevance for the RHIC and HERMES experiments.

BORER,D.

2000-05-22

433

Polarization diversity lens  

Microsoft Academic Search

Many airborne radar systems cannot take advantage of the target signature enhancements that can be achieved by receiving two orthogonal senses of polarization from the target on a pulse to pulse basis. Planar array polarization diversity can be achieved either mechanically or electrically. The mechanical devices are bulky, heavy, and extremely slow generally taking several seconds to change state. An

L. Goldstone

1994-01-01

434