Performance comparison among three different Stokes vector direct-detection receivers

Stokes vectors direct detection（SV-DD） is an effective solution for short-reach optical communications. In this Letter, we investigate two-dimensional-modulation direct-detection systems based on three Stokes vector receivers（SVRs）. The influences of three key factors including the states-of-polarization（SOP）, the splitting ratio of the coupler, and the excess loss（EL） are studied in detail. It is shown that the splitting ratio for achieving optimum performance will be changed with SOP and EL conditions. Among these SVRs, the3 × 3 coupler-based receiver with its optimal splitting ratio shows the best bit error rate performance and stability against the change of SOP.

Forward modelling of the Cotton-Mouton effect polarimetry on EAST tokamak

Measurement of plasma electron density by far-infrared laser polarimetry has become a routine and indispensable tool in magnetic confinement fusion research.This article presents the design of a Cotton-Mouton polarimeter interferometer,which provides a reliable density measurement without fringe jumps.Cotton-Mouton effect on Experimental Advanced Superconducting Tokamak(EAST)is studied by Stokes equation with three parameters(s_(1),s_(2),s_(3)).It demonstrates that under the condition of a small Cotton-Mouton effect,parameter s_(2)contains information about Cotton-Mouton effect which is proportional to the line-integrated density.For a typical EAST plasma,the magnitude of Cotton-Mouton effects is less than 2πfor laser wavelength of 432μm.Refractive effect due to density gradient is calculated to be negligible.Time modulation of Stokes parameters(s_(2),s_(3))provides heterodyne measurement.Due to the instabilities arising from laser oscillation and beam refraction in plasmas,it is necessary for the system to be insensitive to variations in the amplitude of the detection signal.Furthermore,it is shown that non-equal amplitude of X-mode and O-mode within a certain range only affects the DC offset of Stokes parameters(s_(2),s_(3))but does not greatly influence the phase measurements of Cotton-Mouton effects.

Vector Radiative Transfer in a Vertically Inhomogeneous Scattering and Emitting Atmosphere.PartⅠ:A New Discrete Ordinate Method

The original vector discrete ordinate radiative transfer(VDISORT)model takes into account Stokes radiance vector but derives its solution assuming azimuthal symmetric surface reflective matrix and atmospheric scattering phase matrix,such as the phase matrix derived from spherical particles or randomly oriented non-spherical particles.In this study,a new VDISORT is developed for general atmospheric scattering and boundary conditions.Stokes vector is decomposed into both sinusoidal and cosinusoidal harmonic modes,and the radiance at arbitrary viewing geometry is solved directly by adding two zero-weighted points in the Gaussian quadrature scheme.The complex eigenvalues in homogeneous solutions are also taken into full consideration.The accuracy of VDISORT model is comprehensively validated by four cases:Rayleigh scattering case,the spherical particle scattering case with the Legendre expansion coefficients of 0th-13th orders of the phase matrix(hereinafter L13),L13 with a polarized source,and the randomoriented oblate particle scattering case with the Legendre expansion coefficients of 0th-11th orders of the phase matrix(hereinafter L11).In all cases,the simulated radiances agree well with the benchmarks,with absolute biases less than 0.0065,0.0006,and 0.0008 for Rayleigh,unpolarized L13,and L11,respectively.Since a polarized bidirectional reflection distribution function(pBRDF)matrix is used as the lower boundary condition,VDISORT is now able to handle fully coupled atmospheric and surface polarimetric radiative transfer processes.

Novel polarization filter design for wideband radar

Usually the polarization of the interference and the target backscattering may vary constantly, so the optimal receiving polarization of the polarization filter should be recalculated, which makes the filter realization very difficult. Also the predict method of the necessary parameters is not explained in most papers, which makes the polarization filter realization impossible. A novel modi- fied interference suppression （MIS） polarization filter is proposed, which resolves these problems by a new polarization designed strategy. The computation of this polarization filter is easy in most conditions, and the necessary parameters estimation method in real time is introduced, which makes polarization filter design possible.

Restoring Polarization Angle Map for High- Fidelity Underwater Imaging

Obtaining polarization information enables researchers to enhance underwater imaging quality by removing backscattering effect and to distinguish targets of different materials.However,due to the simplified assumption of unpolarized target light,most of the existing underwater polari-metric methods lose part of the polarization information,resulting in degraded imaging quality.In this work,a novel underwater polarimetric method is reported,which obtains the angle of polariza-tion(AOP)map to improve imaging quality.Specifically,the Stokes vectors were exploited to re-move the backscattering effect by obtaining two pairs of orthogonal polarization sub-images of the underwater scene.The target reflected light and the angle between the polarization directions of the target reflected light and the backscattered light were computed through the two groups of the or-thogonal polarized sub-images.The AOP map of the target light could be derived from the Stokes vectors.Then,the transmission map of the target light was estimated by using the non-local color priorly combined with the properties of light propagating underwater.Experiments show that the reported technique enables distinguishing different targets when the colors are similar.The quantit-ative metrics validate that the reported technique produces state-of-the-art performance for under-water imaging.

Statistical characteristics of the normalized Stokes parameters

The statistical properties of the normalized Stokes parameters in a Gaussian stochastic plane wave field are described in detail. Via the expression of the three normalized Stokes parameters, the mean, variance, and high-order moments are calculated, which simplify C. Brosseau＇s results. The new dispersion, normalized contrast function, skewness, and kurtosis are defined to describe the non-Gaussian distribution characteristics, which can be applied to Gaussian wave fields relating to depolarization of light by a spatially random medium.

An analytical model for the polarization of synchrotronradiation in a soft X-ray region

Conventionally, the polarization of a synchrotron soft X-ray beam is measured through a polarimeter based on multilayer optical elements. The major drawback of the traditional approach is the difficulty in comparing different configurations due to the misalignment of each incident angle. In this paper, a new analytical model, based on the variation of reflectivity for different incident angles, is established to facilitate the extraction of important polarization-related information, i.e. angular distribution of polarization components, a tiny change of the direction of azimuth rotation axis of polarizer, etc.