旋转波片偏振仪波片方位误差研究

旋转波片Stokes偏振仪是最常用的测量光束偏振态的仪器。波片快轴方位误差是影响旋转波片Stokes偏振仪的主要误差源之一。为了研究波片方位偏差对测量精度的影响,提出了一种描述波片快轴方位误差向最终的偏振测量误差传递的数学模型,并引入协方差矩阵法表征偏振测量误差。根据这一模型,获得最优的偏振仪配置参数。在推导过程中,假设波片方位误差服从同一高斯分布。基于此误差模型,得到如下结论：(1)由波片方位误差引入的测量误差与光强测量次数N成反比;(2)测量误差独立于入射光强度,但是依赖于入射光偏振态(s₁, s₂, s₃)和波片的位相延迟量δ;(3)波片位相延迟量在(103.22°, 116.13°)范围内时波片方位误差引入的测量误差最小。最后,经过仿真实验证明,所得解析结果与仿真模拟结果相一致。     

Hybrid division of aperture/division of a focal-plane polarimeter for real-time polarization imagery without an instantaneous field-of-view error

The direct, instantaneous measurement of the Stokes parameters of optical radiation is not possible using only a single detector. To infer the Stokes parameters in an image, the optical intensity must be modulated in time, space, or spectral characteristics and multiple measurements must be made on a pixel-by-pixel basis across the scene. Most existing imaging polarimetry strategies generally suffer from either spatial or temporal misregistration. Those strategies that do not suffer from misregistration have severe restrictions placed on the spectral properties of the illumination and/or optical system. A hybrid polarimeter is proposed that can be used for broadband imaging applications that, in principle, can be made without any temporal or spatial misalignment and that does not require detailed knowledge of the spectral properties of the radiation. The strategy uses arrays of microlenses and micropolarizers to create a high-resolution spatial array of nonimaging division of aperture polarimeters.     

一种反射式扭曲向列型液晶显示优化设计的新方法

基于扭曲向列型液晶的显示器件通过调制光波的偏振态实现显示的目的,因此光波的偏振状态在其中起了极为关键的作用.本文结合琼斯矩阵和表示光波偏振态的斯托克斯参量j-circle方法,提出了一种优化反射式扭曲向列型液晶显示器件的新方法.该方法与原有的空间参量方法不同的是采用了追踪光波在传播过程中偏振态变化的办法得到反射式液晶显示器件中各光学元件的参数.该方法简单直观并且可以对多个参数同时进行优化,实现了显示性能的最优化设计并得到了新的显示模式.     

Error in determining Mueller matrix elements and its effect on solution of the inverse problem of polarimetry

We present an analysis of the errors in measurement of the Mueller matrix elements in polarimeters that are a combination of different types of Stokes polarimeters in the detection channel and controllable polarization converters in the probing channel. As polarization converters for the probing radiation, we consider a phase plate having four different angular positions in measuring the complete Mueller matrix and a linear polarizer having different angular positions in measuring the structural parts of an incomplete 4 × 3 Mueller matrix. We have shown that the error in determining the Mueller matrix elements is distributed nonuniformly over the matrix. The nature of the error distribution over the elements and its values are different for different combinations of detection and probing channels of the polarimeter, and depend on the anisotropy of the test object. The latter dictates the choice of the optimal layout for a Mueller polarimeter for studying media with the same or different types of anisotropy and the choice of Mueller matrix elements used to solve the inverse problem of determining the anisotropy parameters.     

Quantum reconstruction of an intense polarization squeezed optical state

We perform a reconstruction of the polarization sector of the density matrix of an intense polarization squeezed beam starting from a complete set of Stokes measurements. By using an appropriate quasidistribution, we map this onto the Poincaré space, providing a full quantum mechanical characterization of the measured polarization state.     

Stokes holography

A new technique, referred to as Stokes holography, is proposed and experimentally demonstrated for controlled synthesis of generalized Stokes parameters in 3D space using Stokes fringes. Stokes fringes are polarization fringes which permit to record and reconstruct complete wavefront. Full use of Stokes fringes in a single step is realized by scattering complex field and subsequently reconstructing using spatial averaging of the randomly scattered field. Mathematical formulations are derived and supported by experimental results of 3D object reconstruction in generalized Stokes parameters.     

通道调制型偏振成像系统的偏振参量重建

通道调制型偏振成像系统中,焦平面上获取的信息需要通过目标偏振参量的重建才能有效提取,因而重建是目标识别、材料分析、生物医疗等技术进一步应用的前提.为了实现在非理想情况下通道调制型偏振成像系统的偏振参量精确重建,需要解决成像系统中电荷耦合器件(CCD)采样频率与频谱位置偏移对重建的影响.本文首先详细分析了频谱不发生混叠的条件:CCD采样频率应至少为4倍基频;在偏振干涉频谱位置偏移时,使用最大频谱法确定各个偏振态的载波频率,通过频移、滤波和傅里叶变换获得目标的偏振重建二维图像;最后通过计算机模拟仿真与实验分析结合的方法验证该重建方案的可行性与有效性.模拟与实验结果表明:改进后的偏振重建法得到的偏振图像与原始输入图像的均方差在0.001以下,峰值信噪比有明显的提高,且结构相似度可达到0.9以上,表明该方法获得的二维偏振态重建图像精度高,与理论偏振解调法相比具有很大的优越性.该工作希望为后续偏振探测与分析进一步的研究提供参考.     

Least-squares analysis of the Mueller matrix

In a single-mode fiber excited by light with a fixed polarization state, the output polarizations obtained at two different optical frequencies are related by a Mueller matrix. We examine least-squares procedures for estimating this matrix from repeated measurements of the output Stokes vector for a random set of input polarization states. We then apply these methods to the determination of polarization mode dispersion and polarization-dependent loss in an optical fiber. We find that a relatively simple formalism leads to results that are comparable with those of far more involved techniques.     

Stokes parameters and polarization contrasts in Young's interference experiment

We derive a spectral interference law that governs the behavior of the four Stokes parameters in Young's two-pinhole experiment with a random electromagnetic beam. In addition to the visibility of intensity fringes, we introduce three new contrast parameters that describe the interference-induced changes in the field's state of partial polarization. The polarization modulation depends on the electric field correlations at the pinholes and is closely related to the two-point Stokes parameters. The results are expected to be particularly useful in polarization interferometry and electromagnetic coherence theory. The formalism is demonstrated with specific examples.     

基于LCTF与LCVR的偏振高光谱成像系统设计

提出一种基于液晶可调滤光片(LCTF)与两片液晶可调相位延迟器(LCVR)构成的偏振高光谱成像系统,相对于传统LCTF具有转动部件以及无法获取全部偏振态的特点,本系统能够静态凝视成像并且测量目标完整的Stokes参量。通过对两片LCVR取四组不同延迟组合,构造了一个4×4复原矩阵来获取目标的原始全偏振信息。使用干涉光强法,对两片LCVR分别进行了延迟-电压特性的精确测量;在633 nm下验证了全偏振复原算法,通过对误差分析,得到了较好的反演Stokes参数和相应的DoLP与Orient计算值,验证了复原算法的可靠性,可以为全偏振态高光谱遥感成像提供有效的数据。     

Stokes-Mueller matrix polarimetry system for glucose sensing

A Stokes-Mueller matrix polarimetry system consisting of a polarization scanning generator (PSG) and a high-accuracy Stokes polarimeter is used to sense the glucose concentration in aqueous solutions with and without scattering effects, respectively. In the proposed system, an electro-optic (EO) modulator driven by a saw-tooth waveform voltage is used to perform full state of polarization (linear/circular) scanning, while a self-built Stokes polarimeter is used to obtain dynamic measurements of the output polarized light intensity. It is shown that the measured output Stokes vectors have an accuracy of 10⁻⁴, i.e., one order higher than that of existing commercial Stokes polarimeters. The experimental results show that the optical rotation angle varies linearly with the glucose concentration over the range of 0-0.5 g/dl. Moreover, glucose sensing is successfully achieved at concentrations as low as 0.02 g/dl with a resolution of 10⁻⁶ deg/mm and an average deviation of 10⁻⁴ deg. In general, the polarimetry system proposed in this study provides a fast and reliable method for measuring the Stokes vectors, and thus has significant potential for biological sensing applications.     

Polarization controller using nematic liquid crystals

In this Letter we demonstrate a polarization controller capable of changing any state of polarization of light from one arbitrary state to another. The controller consists of a stack of three homogeneous nematic liquid-crystal cells. The polarization state is controlled by proper adjustment of the voltages applied across each of the cells. The mathematical algorithm and principles of this polarization controller are developed in the framework of the Stokes parameters, allowing easy visualization by use of a Poincaré sphere representation. The transformation functions are given for conversion of an arbitrary input state to any output state. Experiments are carried out to demonstrate arbitrary polarization transformation.     

Polarization modulated coherent optical communication systems

Polarization modulated coherent optical communication systems are interesting for low-phase noise-induced penalty and insensitivity to the fluctuations of the field state of polarization if a suitable tracking is adopted. In this paper, sever kinds of binary and multilevel polarization modulated systems are presented based c Stokes parameters detection. Quantum limit performance is determined and phase noise-induced penalty is evaluated both in the presence of a sample and hold decision device and in case of postdetection filtering.     

Far field of polarization gratings

In a recent Letter [Opt. Lett. 24, 584 (1999)], Gori analyzed polarization gratings and proposed using them as a tool to measure Stokes parameters. Most of his analysis dealt with the near field, but practical exploitation of his approach relies on the far field. A discussion focusing on the far field is presented, and recipes are suggested for actual implementations of such devices.     

基于最大和最小光强图像的偏振去雾方法

相对于传统光学探测技术,偏振探测在目标探测、识别方面有着独特的优势。针对雾、霾等天气下图像退化的问题,提出一种利用偏振信息的图像去雾方法,通过获取3个角度下目标的偏振图像,求解出场景目标的斯托克斯矢量,从斯托克斯矢量与穆勒矩阵的关系出发,分析偏振图像光强随着偏振角度的变化规律,获取最大和最小光强下的正交偏振图像,利用偏振滤波和亮通道先验方法分别估算大气光偏振度和其无穷远处大气光强值,最终重构出无雾图像。实验结果表明,在雾霾天气下,利用获取的正交偏振图像能够重构出清晰的图像,且重构图像的平均梯度和边缘强度均提升了约3倍,灰度标准差提升了约88%。     

Polarization modulated coherent optical communication systems

Abstract

Polarization modulated coherent optical communication systems are interesting for low-phase noise-induced penalty and insensitivity to the fluctuations of the field state of polarization if a suitable tracking is adopted. In this paper, sever kinds of binary and multilevel polarization modulated systems are presented based c Stokes parameters detection. Quantum limit performance is determined and phase noise-induced penalty is evaluated both in the presence of a sample and hold decision device and in case of postdetection filtering.     

The Hanle effect with partial frequency redistribution. Construction of a frequency-dependent polarization matrix and numerical solution by a PALI method

The polarized approximate lambda iteration (PALI) technique developed for the weak field Hanle effect relies on the decomposition of the Stokes parameters I, Q and U into six cylindrically symmetrical components. It has been applied to complete and partial frequency redistribution with redistribution matrices in which frequency redistribution is decoupled from scattering polarization. For partial frequency redistribution, the decoupling is obtained by an adequate decomposition of the frequency space into several domains. By angle-averaging frequency-dependent terms in the exact weak field Hanle redistribution matrix for a normal Zeeman triplet, we construct a redistribution matrix with coupling between frequency redistribution and polarization and no domain decomposition. The coupling is contained in generalized frequency redistribution functions that depend on the magnetic field. The redistribution matrix is expanded in the Landi Degl’Innocenti spherical tensors for polarimetry and the Stokes parameters are decomposed into cylindrically symmetrical components. A PALI method is set up for the calculation of these components. The Stokes parameters are calculated for different simple atmospheric models. The positive Q direction corresponds to the linear polarization perpendicular to the solar limb. It is shown that the frequency space decomposition may induce large errors on Stokes U in the transition region between line core and line wings but can safely be used for Stokes I and Q, the errors staying less than 1% at all the frequencies.     

Vector parameterization of the Lorentz group transformations and polar decomposition of Mueller matrices

It is shown that the representation of the coherence matrix (the polarization density matrix) of beams of electromagnetic waves as a biquaternion corresponding to the four-vector of a pseudo-Euclidean space whose components are the intensity and the Stokes parameters provides a possibility of introducing the group transformations of these quantities isomorphic to SO(3.1) group. These transformations are a subset of the set of Mueller polarization matrices which, generally speaking, form a semigroup. The reduction of the semigroup of Mueller matrices to the group of transformations opens the possibility to use the vector parameterization of SO(3.1) group for interpretation of the polar decomposition of Mueller matrices. In particular, in this approach, the elements of the Mueller matrices corresponding to phase elements and polarizers turn out to be most simply and naturally related to their eigenpolarizations.     

Generalized Stokes parameters and polarization behavior of flat-topped array laser beam propagating through oceanic turbulence

In present paper, the analytical expression for the cross-spectral density of the phase-locked Partially Coherent Flat-Topped (PCFT) array beams propagating through oceanic turbulence based on the extended Huygens–Fresnel integral is derived. Then, the polarization behavior and generalized Stokes parameters of the phase-locked PCFT array beam propagating through oceanic turbulence using the cross-spectral density matrix elements have been achieved. In this paper, the case of the clearwater oceanic turbulence has been considered, i.e. it has been assumed that the light wave is not affected by suspended organic and inorganic impurities. Due to the above-mentioned reason and the turbulence importance, the impacts of oceanic turbulence have been scrutinized, while the effects of absorption and scattering have been ignored. The changes in the Stokes parameters, the fluctuation of Stokes parameters, and consequently the state of polarization (including the spectral degree of polarization, the orientation angle and the degree of ellipticity) of the phase-locked PCFT array beams for different turbulence conditions upon propagation have been investigated. The results may find possible applications in underwater communication.