Showing papers on "Optical polarization published in 2008"
TL;DR: High-resolution radio images and optical polarization measurements of the blazar BL Lacertae reveal a bright feature in the jet that causes a double flare of radiation from optical frequencies to TeV γ-ray energies, as well as a delayed outburst at radio wavelengths that is identified with the acceleration and collimation zone predicted by the theories.
Abstract: Blazars are the most extreme active galactic nuclei. They possess oppositely directed plasma jets emanating at near light speeds from accreting supermassive black holes. According to theoretical models, such jets are propelled by magnetic fields twisted by differential rotation of the black hole's accretion disk or inertial-frame-dragging ergosphere1, 2, 3. The flow velocity increases outward along the jet in an acceleration and collimation zone containing a coiled magnetic field4, 5. Detailed observations of outbursts of electromagnetic radiation, for which blazars are famous, can potentially probe the zone. It has hitherto not been possible to either specify the location of the outbursts or verify the general picture of jet formation. Here we report sequences of high-resolution radio images and optical polarization measurements of the blazar BL Lacertae. The data reveal a bright feature in the jet that causes a double flare of radiation from optical frequencies to TeV -ray energies, as well as a delayed outburst at radio wavelengths. We conclude that the event starts in a region with a helical magnetic field that we identify with the acceleration and collimation zone predicted by the theories. The feature brightens again when it crosses a standing shock wave corresponding to the bright 'core' seen on the images.
783 citations
TL;DR: In this paper, the authors exploit the idea of a half-wave Hertz dipole antenna at near-infrared wavelengths to concentrate radiation into a nanometre-scale germanium photodetector.
Abstract: A critical challenge for the convergence of optics and electronics is that the micrometre scale of optics is significantly larger than the nanometre scale of modern electronic devices. In the conversion from photons to electrons by photodetectors, this size incompatibility often leads to substantial penalties in power dissipation, area, latency and noise1,2,3,4. A photodetector can be made smaller by using a subwavelength active region; however, this can result in very low responsivity because of the diffraction limit of the light. Here we exploit the idea of a half-wave Hertz dipole antenna (length ∼ 380 nm) from radio waves, but at near-infrared wavelengths (length ∼ 1.3 µm), to concentrate radiation into a nanometre-scale germanium photodetector. This gives a polarization contrast of a factor of 20 in the resulting photocurrent in the subwavelength germanium element, which has an active volume of 0.00072 µm3, a size that is two orders of magnitude smaller than previously demonstrated detectors at such wavelengths. By scaling down device size, the principles of radio antennas can be used in the optical regime. These optical antennas act as a bridge between optics and electronics, collecting and enhancing light to enable the creation of tiny semiconductor photodetectors.
692 citations
TL;DR: A broadband, thin-film, polarizing beam splitter based on an anisotropic diffraction grating composed of reactive mesogens (polymerizable liquid crystals) that manifests high diffraction efficiency and high extinction ratio in both theory and experiment.
Abstract: We demonstrate a broadband, thin-film, polarizing beam splitter based on an anisotropic diffraction grating composed of reactive mesogens (polymerizable liquid crystals). This achromatic polarization grating (PG) manifests high diffraction efficiency (~100%) and high extinction ratio (⩾1000:1) in both theory and experiment. We show an operational bandwidth Δλ/λ0~56% (roughly spanning visible wavelength range) that represents more than a fourfold increase of bandwidth over conventional PGs (and significantly larger than any other grating). The diffraction angle and operational region (visible, near-infrared, midwave infrared, and ultraviolet wavelengths) may be easily tailored during fabrication. The essence of the achromatic design is a stack of two chiral PGs with an opposite twist sense and employs the principle of retardation compensation. We fully characterize its optical properties and derive the theoretical diffraction behavior.
344 citations
TL;DR: A review of acoustic and ultrasonic optical fiber sensors (OFSs) is given in this article, which covers optical fiber sensing methods for detecting dynamic strain signals, including general sound and acoustic signals, high-frequency signals, and other signals such as acoustic emissions, and impact induced dynamic strain.
Abstract: This paper gives a review of acoustic and ultrasonic optical fiber sensors (OFSs). The review covers optical fiber sensing methods for detecting dynamic strain signals, including general sound and acoustic signals, high-frequency signals, i.e., ultrasonic/ultrasound, and other signals such as acoustic emissions, and impact induced dynamic strain. Several optical fiber sensing methods are included, in an attempted to summarize the majority of optical fiber sensing methods used to date. The OFS include single fiber sensors and optical fiber devices, fiber-optic interferometers, and fiber Bragg gratings (FBGs). The single fiber and fiber device sensors include optical fiber couplers, microbend sensors, refraction-based sensors, and other extrinsic intensity sensors. The optical fiber interferometers include Michelson, Mach-Zehnder, Fabry-Perot, Sagnac interferometers, as well as polarization and model interference. The specific applications addressed in this review include optical fiber hydrophones, biomedical sensors, and sensors for nondestructive evaluation and structural health monitoring. Future directions are outlined and proposed for acousto-ultrasonic OFS.
309 citations
TL;DR: This paper presents the modeling of an underwater wireless optical communication channel using the vector radiative transfer theory, and investigates the polarization behavior of light in the underwater environment, showing the significance of the cross-polarization component when the light encounters more scattering.
Abstract: This paper presents the modeling of an underwater wireless optical communication channel using the vector radiative transfer theory. The vector radiative transfer equation captures the multiple scattering nature of natural water, and also includes the polarization behavior of light. Light propagation in an underwater environment encounters scattering effect creating dispersion which introduces inter-symbol-interference to the data communication. The attenuation effect further reduces the signal to noise ratio. Both scattering and absorption have adverse effects on underwater data communication. Using a channel model based on radiative transfer theory, we can quantify the scattering effect as a function of distance and bit rate by numerical Monte Carlo simulations. We also investigate the polarization behavior of light in the underwater environment, showing the significance of the cross-polarization component when the light encounters more scattering.
280 citations
TL;DR: This letter explores the Gram-Schmidt orthogonalization procedure (GSOP) for compensation of quadrature imbalance in an optical 90deg hybrid and demonstrates the improvement which can be achieved using the GSOP, including the impact of quantization in the digital coherent receiver.
Abstract: This letter explores the Gram-Schmidt orthogonalization procedure (GSOP) for compensation of quadrature imbalance in an optical 90deg hybrid. We present computer simulations for an optical QPSK communication system using a digital coherent receiver and investigate the impact of quadrature imbalance on the required optical signal-to-noise ratio for the receiver and the frequency estimation algorithm. We then demonstrate the improvement which can be achieved using the GSOP, including the impact of quantization in the digital coherent receiver. Finally, we show that the GSOP can equally be applied to polarization-division multiplexed systems, applying the GSOP in conjunction with the constant modulus algorithm to demultiplex a PDM-QPSK signal.
272 citations
TL;DR: In this article, a moving acoustic grating is generated by stimulated Brillouin scattering between writing beams in one polarization and used to reflect an orthogonally polarized reading beam at different wavelengths.
Abstract: We report a novel kind of all-optical dynamic grating based on Brillouin scattering in a polarization maintaining fiber (PMF). A moving acoustic grating is generated by stimulated Brillouin scattering between writing beams in one polarization and used to reflect an orthogonally polarized reading beam at different wavelengths. The center wavelength of the grating is controllable by detuning the writing beams, and the 3 dB bandwidth of approximately 80 MHz is observed with the tunable reflectance of up to 4% in a 30 m PMF.
246 citations
TL;DR: The ability of this approach to extract the individual intrinsic polarimetry characteristics should prove valuable in diagnostic photomedicine in quantifying the small optical rotations due to the presence of glucose in tissue and for monitoring changes in tissue birefringence as a signature of tissue abnormality.
Abstract: Linear birefringence and optical activity are two common optical polarization effects present in biological tissue, and determi- nation of these properties has useful biomedical applications. How- ever, measurement and unique interpretation of these parameters in tissue is hindered by strong multiple scattering effects and by the fact that these and other polarization effects are often present simulta- neously. We have investigated the efficacy of a Mueller matrix decom- position methodology to extract the individual intrinsic polarimetry characteristics linear retardance and optical rotation , in particu- lar from a multiply scattering medium exhibiting simultaneous linear birefringence and optical activity. In the experimental studies, a pho- toelastic modulation polarimeter was used to record Mueller matrices from polyacrylamide phantoms having strain-induced birefringence, sucrose-induced optical activity, and polystyrene microspheres- induced scattering. Decomposition of the Mueller matrices recorded in the forward detection geometry from these phantoms with con- trolled polarization properties yielded reasonable estimates for and parameters. The confounding effects of scattering, the propagation path of multiple scattered photons, and detection geometry on the estimated values for and were further investigated using polarization-sensitive Monte Carlo simulations. The results show that in the forward detection geometry, the effects of scattering induced linear retardance and diattenuation are weak, and the decomposition of the Mueller matrix can retrieve the intrinsic values for and with reasonable accuracy. The ability of this approach to extract the indi- vidual intrinsic polarimetry characteristics should prove valuable in diagnostic photomedicine, for example, in quantifying the small opti- cal rotations due to the presence of glucose in tissue and for monitor- ing changes in tissue birefringence as a signature of tissue abnormality. © 2008 Society of Photo-Optical Instrumentation Engineers. DOI: 10.1117/1.2960934
231 citations
TL;DR: In this paper, the authors investigated the degree and angle of velocity anisotropy induced by MHD turbulence using computational simulations and molecular line observations of the Taurus molecular cloud.
Abstract: Velocity anisotropy induced by MHD turbulence is investigated using computational simulations and molecular line observations of the Taurus molecular cloud. A new analysis method is presented to evaluate the degree and angle of velocity anisotropy using spectroscopic imaging data of interstellar clouds. The efficacy of this method is demonstrated on model observations derived from three-dimensional velocity and density fields from the set of numerical MHD simulations that span a range of magnetic field strengths. The analysis is applied to 12CO J = 1–0 imaging of a subfield within the Taurus molecular cloud. Velocity anisotropy is identified that is aligned within ~10° of the mean local magnetic field direction derived from optical polarization measurements. Estimated values of the field strength based on velocity anisotropy are consistent with results from other methods. When combined with new column density measurements for Taurus, our magnetic field strength estimate indicates that the envelope of the cloud is magnetically subcritical. These observations favor strong MHD turbulence within the low-density, subcritical, molecular gas substrate of the Taurus cloud.
171 citations
01 Jan 2008
TL;DR: In this article, the performance of different electronic equalization and processing schemes for 40 and 10-Gb/s optical transmission over single-mode fiber (SMF) is discussed, from the point of their ability to compensate chromatic dispersion (CD) and polarization mode dispersion(PMD).
Abstract: The performance of different electronic equalization and processing schemes for 40- and 10-Gb/s optical transmission over single-mode fiber (SMF) are discussed, from the point of their ability to compensate chromatic dispersion (CD) and polarization mode dispersion (PMD). In addition, the impact of fiber nonlinearity and modulation format on equalization is also investigated. The main objective of this paper is to present an overview and a comparison of the performances rather than a detailed explanation of the principles of the different equalization schemes. The equalizers which will be covered are analog equalizer (feedforward and decision feedback type), maximum likelihood sequence estimator (MLSE), electronic precompensation, coherent/intradyne detection with digital signal processing (DSP) equalization, DSP-based optical orthogonal frequency division multiplexing (OFDM), and turbo equalization.
170 citations
TL;DR: The SPHERE project as mentioned in this paper is an exo-solar planet imager, which aims to detect giant exosolar planets in the vicinity of bright stars and to characterize them through spectroscopic and polarimetric observations.
Abstract: The SPHERE is an exo-solar planet imager, which goal is to detect giant exo-solar planets in the vicinity of bright stars
and to characterize them through spectroscopic and polarimetric observations. It is a complete system with a core made
of an extreme-Adaptive Optics (AO) wavefront correction, a pupil tracker and diffraction suppression through a variety
of coronagraphs. At its back end, a differential dual imaging camera and an integral field spectrograph (IFS) work in the
Near Infrared (NIR) Y, J, H and Ks bands (0.95 - 2.32μm), and a high resolution polarization camera covers the optical
range (0.6 - 0.9 μm). The IFS is a low resolution spectrograph (R~50) working in the near IR (0.95-1.65 microns), an
ideal wavelength range for the detection of giant planet features. In our baseline design the IFU is a new philosophy
microlens array of about 145x145 elements designed to reduce as much as possible the cross talk when working at
diffraction limit. The IFU will cover a field of view of about 1.7 x 1.7 square arcsecs reaching a contrast of 10 -7 ,
providing a high contrast and high spatial resolution "imager" able to search for planet well inside the star PSF.
Pulkovo Observatory1, Saint Petersburg State University2, Boston University3, INAF4, Spanish National Research Council5, University of Michigan6, Academy of Sciences of Uzbekistan7, Max Planck Society8, Bulgarian Academy of Sciences9, University of Turku10, Ohio University11, Centre national de la recherche scientifique12, National Central University13, Moscow State University14, Isaac Newton Institute15, Aarhus University16, Ariès17, Chinese Academy of Sciences18, Harvard University19, Osaka Kyoiku University20, Lebedev Physical Institute21, Abastumani Astrophysical Observatory22, Helsinki University of Technology23, Korea Astronomy and Space Science Institute24, University of Southampton25, Special Astrophysical Observatory26, Cardiff University27, University of Colorado Denver28, Cork Institute of Technology29, ASTRON30
TL;DR: In this article, the authors present radio-to-optical data taken by the WEBT, supplemented by our VLBA and RXTE observations, of 3C 279.
Abstract: Context. The quasar 3C 279 is among the most extreme blazars in terms of luminosity and variability of flux at all wavebands. Its vari ations in flux and polarization are quite complex and therefore require intensive monitoring observations at multiple wavebands to characterise and interpret the observed changes. Aims. In this paper, we present radio-to-optical data taken by the WEBT, supplemented by our VLBA and RXTE observations, of 3C 279. Our goal is to use this extensive database to draw inferences regarding the physics of the relativistic jet. Methods. We assemble multifrequency light curves with data from 30 ground-based observatories and the space-based instruments SWIFT (UVOT) and RXTE, along with linear polarization vs. time in the optical R band. In addition, we present a sequence of 22 images (with polarization vectors) at 43 GHz at resolution 0.15 milliarcse c, obtained with the VLBA. We analyse the light curves and polarization, as well as the spectral energy distributions at different epochs, corresponding to different brightness states. Results. We find that the IR-optical-UV continuum spectrum of the vari able component corresponds to a power law with a constant slope of−1.6, while in the 2.4‐10 keV X-ray band it varies in slope from−1.1 to−1.6. The steepest X-ray spectrum occurs at a flux minimum. Durin g a decline in flux from maximum in late 2006, the optical and 43 GHz core po larization vectors rotate by∼ 300 ◦ . Conclusions. The continuum spectrum agrees with steady injection of relativistic electrons with a power-law energy distribution of slope−3.2 that is steepened to−4.2 at high energies by radiative losses. The X-ray emission at flux minimum comes most likely from a new component that starts in an upstream section of the jet where inverse Compton scattering of seed photons from outside the jet is important. The rotation of the polarization vector implies that the jet contains a helical magnetic field that extends ∼ 20 pc past the 43 GHz core.
TL;DR: In this paper, an urban 86 km fiber has been demonstrated with a resolution of 2×10-18 at one day measuring time using an optical compensator, with a reference carrier frequency of 1 GHz and a rapid scrambling of the polarisation state of the input light in order to reduce the sensitivity to polarisation mode dispersion in the fibre.
Abstract: RF frequency transfer over an urban 86 km fibre has
been demonstrated with a resolution of 2×10-18 at one day
measuring time using an optical compensator. This result is obtained with a
reference carrier frequency of 1 GHz, and a rapid scrambling of the
polarisation state of the input light in order to reduce the sensitivity to
the polarisation mode dispersion in the fibre. The limitation due to the
fibre chromatic dispersion associated with the laser frequency fluctuations
is highlighted and analyzed. A preliminary test of an extended compensated
link over 186 km using optical amplifiers gives a resolution below
10-17 at 1 day.
TL;DR: In this article, a novel gain media based on staggered InGaN quantum wells (QWs) grown by metal-organic chemical vapor deposition was demonstrated as improved active region for visible light emitters.
Abstract: A novel gain media based on staggered InGaN quantum wells (QWs) grown by metal-organic chemical vapor deposition was demonstrated as improved active region for visible light emitters. Fermi's golden rule indicates that InGaN QW with step-function like In content in the well leads to significantly improved radiative recombination rate and optical gain due to increased electron-hole wavefunction overlap, in comparison to that of conventional InGaN QW. Spontaneous emission spectra of both conventional and staggered InGaN QW were calculated based on energy dispersion and transition matrix element obtained by 6-band k middotp formalism for wurtzite semiconductor, taking into account valence-band-states mixing, strain effects, and polarization-induced electric fields. The calculated spectra for the staggered InGaN QW showed enhancement of radiative recombination rate, which is in good agreement with photoluminescence and cathodoluminescence measurements at emission wavelength regime of 425 and 500 nm. Experimental results of light-emitting diode (LED) structures utilizing staggered InGaN QW also show significant improvement in output power. Staggered InGaN QW allows polarization engineering leading to improved luminescence intensity and LED output power as a result of enhanced radiative recombination rate.
TL;DR: In this paper, a spatially variable retardation (SVR) plate was used to transform a linearly-polarized Gaussian beam to a radially or an azimuthally polarized doughnut (0, 1) ∗ Laguerre Gaussian (LG) beam.
TL;DR: The behavior of the scintillation index of a wide-sense statistically stationary, quasi-monochromatic, electromagnetic beam propagating in a homogeneous isotropic medium is studied in this paper.
TL;DR: In this article, the authors investigated the sensitivity of the digital coherent receiver both theoretically and experimentally, and showed that the receiver sensitivity close to the shot-noise limit is achieved in the 10-Gbit/s binary phase-shift keying system with the help of a lownoise optical preamplifier.
Abstract: In this paper, we investigate the sensitivity of the digital coherent receiver both theoretically and experimentally. The receiver sensitivity close to the shot-noise limit is demonstrated in the 10-Gbit/s binary phase-shift keying system with the help of a low-noise optical preamplifier. We also introduce polarization diversity into our receiver. Maximal-ratio polarization combining in the digital domain makes the receiver sensitivity independent of the state of polarization of the incoming signal without power penalty.
TL;DR: In this article, the results of fabrication of sub-50nm features on a 100nm pitch by the PDL-spacer DP process using 0.85 NA dry ArF lithography are reported.
Abstract: A double patterning (DP) process is introduced with application for advanced technology nodes. This DP technique is enabled by a novel low-temperature pulsed deposition layer (PDL TM ) oxide film which is deposited directly on patterned photoresist. In this article, we will report the results of fabrication of sub-50nm features on a 100nm pitch by the PDL-spacer DP process using 0.85 NA dry ArF lithography. This result represents the potential of the PDL-based DP to significantly enhance the resolution of the patterning process beyond the limits of optical lithography. Components of CD variance for this spacer DP scheme will be discussed.
TL;DR: In this paper, a novel technique to realize frequency quadrupling and upconversion in a radio over fiber (RoF) link is proposed and experimentally demonstrated by using two cascaded Mach-Zehnder modulators (MZMs) that are biased at the minimum transmission point, with a tunable optical delay line placed between the MZMs.
Abstract: In this paper, a novel technique to realize frequency quadrupling and upconversion in a radio over fiber (RoF) link is proposed and experimentally demonstrated. The frequency quadrupling is achieved by using two cascaded Mach-Zehnder modulators (MZMs) that are biased at the minimum transmission point, with a tunable optical delay line placed between the MZMs. By properly adjusting the time delay between the two MZMs, a pair of optical wavelengths with a wavelength spacing corresponding to four times the frequency of the microwave drive signal is generated. The two wavelengths are then sent to a third MZM to which an intermediate-frequency (IF) signal is applied. At the output of the third MZM, a frequency-upconverted signal at the millimeter-wave (mm-wave) band is obtained. The advantages of the technique are that a relatively low-frequency local oscillator (LO) signal is used to generate a high-frequency LO signal and the upconverted signal is more tolerant to the dispersion-induced power fading compared with a conventional RoF link based on double-sideband (DSB) modulation. Experiments are performed to verify the technique.
TL;DR: In this paper, a non-destructive, highly precise optical metrology system for measuring the average refractive index of a liquid solution such that its glucose concentration can be derived is presented.
Patent•
12 Feb 2008TL;DR: In this article, a nonpolar or semipolar Group-III nitride diode laser is controlled by orienting an axis of light propagation in relation to an optical polarization direction or crystallographic orientation.
Abstract: Optical gain of a nonpolar or semipolar Group-III nitride diode laser is controlled by orienting an axis of light propagation in relation to an optical polarization direction or crystallographic orientation of the diode laser. The axis of light propagation is substantially perpendicular to the mirror facets of the diode laser, and the optical polarization direction is determined by the crystallographic orientation of the diode laser. To maximize optical gain, the axis of light propagation is oriented substantially perpendicular to the optical polarization direction or crystallographic orientation.
TL;DR: The results of polarimetric (R-band) and multicolor photometric (BH RI J H K) observations of the blazar AO 0235+16 during an outburst in 2006 December were presented in this article.
Abstract: We present the results of polarimetric (R-band) and multicolor photometric (BH RI J H K) observations of the blazar AO 0235+16 during an outburst in 2006 December. The data reveal a short timescale of variability (several hours), which increases from optical to near-IR wavelengths; even shorter variations are detected in polarization. The flux density correlates with the degree of polarization, and at the maximum degree of polarization the electric vector tends to align with the parsec-scale jet direction. We find that a variable component with a steady power-law spectral energy distribution and very high optical polarization (30%-50%) is responsible for the variability. We interpret these properties of the blazar within a model of a transverse shock propagating down the jet. In this case a small change in the viewing angle of the jet, by 1°, and a decrease in the shocked plasma compression by a factor of ~1.5 are sufficient to account for the variability.
TL;DR: In this paper, the authors describe the BMV (Birefringence Magnetique du Vide) experiment, a novel apparatus to study the propagation of light in a transverse magnetic field.
Abstract: In this paper, we describe in detail the BMV (Birefringence Magnetique du Vide) experiment, a novel apparatus to study the propagation of light in a transverse magnetic field. It is based on a very high finesse Fabry-Perot cavity and on pulsed magnets specially designed for this purpose. We justify our technical choices and we present the current status and perspectives.
23 Jun 2008
TL;DR: This paper proposes a two- pass separation method exploiting high frequency patterns in two-dimensions that can filter out the global components much more completely than traditional one-pass separation methods.
Abstract: We present a new 3D scanning method using modulated phase-shifting. Optical scanning of complex objects or scenes with significant global light transport, such as subsurface scattering, interreflections, volumetric scattering, etc. is a difficult task since the direct surface reflection will be mixed with the global illumination. The direct and global components can be effficiently separated using high frequency illumination which to some extend is done in traditional phase-shifting for 3D scanning. In this paper we introduce the concept of modulation based separation where a high frequency signal is multiplied on top of other signal. The modulated signal inherits the good separation properties of the high frequency signal and allows for removing artifacts due to global illumination. This technique can be used to clean up arbitrary projected signals, e.g. photographs as well as the sinusoid patterns used for phase-shifting. For the modulated phase-shifting, we propose a two-pass separation method exploiting high frequency patterns in two-dimensions that can filter out the global components much more completely than traditional one-pass separation methods. We demonstrate the effectiveness of our approach on a couple of scenes with significant subsurface scattering and interreflections.
04 May 2008
TL;DR: By using extreme numerical-aperture solid-immersion microscopy at 1553 nm, this paper demonstrated, under certain circumstances, polarization-sensitive imaging with resolution values approaching 100 nm which substantially surpass the classical scalar diffraction-limit embodied by Sparrowpsilas resolution criterion.
Abstract: By using extreme numerical-aperture solid-immersion microscopy at 1553 nm we demonstrate, under certain circumstances, polarization-sensitive imaging with resolution values approaching 100 nm which substantially surpass the classical scalar diffraction-limit embodied by Sparrowpsilas resolution criterion.
TL;DR: A survey of non-polar surfaces of nitride materials and devices can be found in this article, where the main properties of the materials grown in nonpolar directions are discussed with emphasis on the deviations from those of nitrides grown along the polar direction.
Abstract: The quest to use nonpolar surfaces of nitride materials and devices started a few years ago with the aim to avoid the strong internal electric fields in active regions of optoelec-tronic devices and to improve their efficiency. Starting with the growth optimizations, the progression via thorough understanding of new physical properties of the materials has led to significant improvement of device performance and to novel device concepts. In this review a historical survey of nonpolar nitride growth achievements is made. Along the way new challenges in material growth and characterization have been encountered and more sophisticated methods have been developed, which are briefly summarized. The main properties of the nitride materials grown in nonpolar directions are discussed with emphasis on the deviations from those of nitrides grown along the polar direction. Physical phenomena such as inherently present anisotropic in-plane strain and optical polarization anisotropy have been proposed for the realization of novel polarized light-emitting diodes, polarization-sensitive detectors and modulators. The present status of the nitride devices with nonpolar and semipolar surfaces is discussed, and an outlook of the future trends is presented. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, isolated points of circular polarization in transverse fields of varying polarization are classified morphologically into three distinct types known as lemons, stars, and monstars, and these morphologies are interpreted here according to two natural parameters associated with the singularity, namely, the anisotropy of the C point and the polarization azimuth.
Abstract: C points, that is, isolated points of circular polarization in transverse fields of varying polarization, are classified morphologically into three distinct types known as lemons, stars, and monstars. These morphologies are interpreted here according to two natural parameters associated with the singularity, namely, the anisotropy of the C point and the polarization azimuth on the anisotropy axis. In addition to providing insight into singularity morphology, this observation applies to the densities of the various morphologies in isotropic random polarization speckle fields.
TL;DR: In this paper, the authors present an analysis of radio spectral properties in total intensity and polarization, size, optical identifications and redshift distribution of the BSS sources, showing spectral curvature in most sources with spectral steepening that increases at higher frequencies.
Abstract: The Australia Telescope 20-GHz (AT20G) Survey is a blind survey of the whole southern sky at 20GHz (with follow-up observations at 4.8 and 8.6 GHz) carried out with the Australia Telescope Compact Array from 2004 to 2007. The Bright Source Sample (BSS) is a complete flux-limited subsample of the AT20G Survey catalogue comprising 320 extragalactic (|b| > 1°.5) radio sources south of δ = -15° with S 20GHz > 0.50 Jy. Of these, 218 have near simultaneous observations at 8 and 5 GHz. In this paper we present an analysis of radio spectral properties in total intensity and polarization, size, optical identifications and redshift distribution of the BSS sources. The analysis of the spectral behaviour shows spectral curvature in most sources with spectral steepening that increases at higher frequencies (the median spectral index a, assuming S oc v α , decreases from α 8.6 4.8 = 0.11 between 4.8 and 8.6 GHz to α 20 8.6 = -0.16 between 8.6 and 20 GHz), even if the sample is dominated by flat spectra sources (85 per cent of the sample has α 20 8.6 > -0.5). The almost simultaneous spectra in total intensity and polarization allowed us a comparison of the polarized and total intensity spectra: polarized fraction slightly increases with frequency, but the shapes of the spectra have little correlation. Optical identifications provided an estimation of redshift for 186 sources with a median value of 1.20 and 0.13, respectively, for QSO and galaxies.
TL;DR: A Feussner-type terahertz polarizer with a nematic liquid crystal (NLC) layer between two fused-silica prisms is demonstrated.
Abstract: A Feussner-type terahertz polarizer with a nematic liquid crystal (NLC) layer between two fused-silica prisms is demonstrated. The polarization factor and extinction ratio of the NLC-based terahertz polarizer can exceed 0.99 and 10−5, respectively.
TL;DR: In this article, the potential of electronic dispersion compensation (EDC) in amplified multispan 111-Gb/s wavelength division multiplexed systems based on polarization-multiplexed quadrature phase-shift keying modulation with coherent detection was investigated.
Abstract: We carried out an extensive simulative analysis to investigate in depth the potential of electronic dispersion compensation (EDC) in amplified multispan 111-Gb/s wavelength- division-multiplexed systems based on polarization-multiplexed quadrature phase-shift keying modulation with coherent detection, also in the presence of substantial fiber nonlinearity. For typical single-mode and nonzero dispersion-shifted fibers, our results show that the use of inline optical dispersion management is always suboptimal versus using EDC at the receiver.