Polarization properties of polarized and partially coherent Electromagnetic Gaussian-Schell model pulse beams on slant path in turbulent atmosphere

This paper is based on the unified theory of coherence and polarization of stochastic electromagnetic beams and the extended Huygens–Fresnel principle, combined with the quadratic approximation of Rytov’s phase structure function and the generalized Stokes parameters. We have derived the novel expressions for the cross-spectral density matrix elements and the degree of cross-polarization of a class of elliptically polarized spatially and spectrally partially coherent Electromagnetic Gaussian-Schell model pulse (EGSMP) beams propagating through atmospheric turbulence along a slant path. Additionally, we calculate and analyze the effects of the turbulent intensity, the initial pulse duration, waist width of the beam, the spatial coherence length and temporal coherence length et al. on the polarization properties of fully polarized and partially coherent EGSMP beams. Finally, a comparison of the impact of those factors on the partially polarization beams is made. The results show that the influences of the turbulent intensity, the initial pulse duration, waist width of the beam, the spatial coherence length and temporal coherence length et al. on the polarization properties of fully polarized and partially coherent EGSMP beams are larger. While the effects of those parameters on the partially polarization and partially coherent EGSMP beams are smaller. It is noted that the results of this paper have established sound theoretical basis on the topic of improving performance of the laser system propagating through the atmospheric turbulence.     

Generalized stokes parameters of random electromagnetic beams

A generalization of the Stokes parameters of a random electromagnetic beam is introduced. Unlike the usual Stokes parameters, which depend on one spatial variable, the generalized Stokes parameters, depend on two spatial variables. They obey precise laws of propagation, both in free space and in any linear medium, whether deterministic or random. With the help of the generalized Stokes parameters, the changes in the ordinary Stokes parameters upon propagation can be determined. Numerical examples of such changes are presented. The generalized Stokes parameters contain information not only about the polarization properties of the beam but also about its coherence properties. We illustrate this fact by expressing the degree of coherence of the electromagnetic beam in terms of one of the generalized Stokes parameters.     

大气湍流中部分相干光束上行和下行传输偏振特性的比较

以部分相干的电磁高斯-谢尔模型(electromagnetic Gaussian-Schell model, EGSM) 光束为研究对象, 根据相干和偏振的统一理论以及随机光束的Stokes参量, 推导出EGSM光束在大气湍流中斜程传输时的偏振度(degree of polarization, DoP)和偏振方向角的表达式, 研究了大气湍流中上行和下行传输时EGSM光束偏振特性的不同. 研究结果表明: 在相同条件下, EGSM 光束下行传输时整个光场DoP的分布比上行传输要集中; 下行传输时轴上点的DoP达到最大值所对应的传输距离长于上行传输. 可以看出, EGSM光束沿下行路径传输时, 探测器可以接收更远距离处的波束传输信息.     

用Stokes参量法实现数字同轴偏振全息的研究

提出了一种基于Stokes参量的数字同轴偏振全息方法.在实验中用一束线偏振光和一束椭圆偏振光作为参考光, 分别与物光进行干涉,通过拍摄在两个相互垂直方向上的全息图,计算出物光在这两个方向的振幅和相位信息, 从而得到物光的Stokes参量和物体的全偏振信息,实现对各向异性物体偏振态空间分布的图像重建. 实验结果表明,该方法可用于物体的全偏振特性的测量.这种方法在求出物光Stokes参量的同时, 也可消除零级像和共轭像的干扰,因此也可用于同轴或离轴全息.     

部分相干平顶光束经光阑衍射的偏振特性

根据光束的相干-偏振矩阵和传输理论,对部分相干平顶光束经正多边形光阑衍射的偏振特性进行了系统的研究.给出了部分相干平顶光束偏振度传输公式,并将高斯-谢尔模型光束以及部分相干平顶光束在自由空间传输的偏振度作为特例统一于一般表达式中.研究表明：部分相干平顶光束经光阑衍射的偏振特性与光阑截断参数、光束的空间相干性、衍射角、传输距离、平顶光束的阶数有关. 关键词： 部分相干平顶光束 偏振特性 相干-偏振矩阵 正多边形光阑 光阑衍射     

基于声光滤光和液晶相位调谐的高光谱全偏振成像新技术

为了获取高光谱分辨率、高空间分辨率、高偏振精度、高信噪比和稳定性好的全部Stokes参量光谱图像, 考虑到声光可调谐滤光器(acousto-optical tunable filter, AOTF)的±1级衍射光的正交特性, 提出用一个AOTF滤光, 一个液晶可变延迟器(liquid crystal variable retarder, LCVR)进行相位调制和两个CCD相机分别对±1级衍射光成像的高光谱全偏振成像新技术. 从所采用的光学元件的穆勒矩阵出发, 阐述了该技术的基本工作原理; 理论分析表明, LCVR不但不会影响到第一个Stokes参量的探测精度, 而且后3个Stokes参量的相对误差分别优于0.064%, 0.31%和3.97%; 利用原理样机获取了450–700 nm、光谱带宽为10 nm的26个光谱通道的图像数据, 成像质量良好; 以工作波长为600 nm的入射光为例, 对其全部Stokes参量图像进行了具体分析讨论. 结果表明, 该新技术原理正确, 方案可行. 该研究可为光谱偏振成像技术提供新的理论和实现方案.     

部分相干平顶光束经光阑衍射的偏振特性

根据光束的相干-偏振矩阵和传输理论，对部分相干平顶光束经正多边形光阑衍射的偏振特性进行了系统的研究.给出了部分相干平顶光束偏振度传输公式，并将高斯-谢尔模型光束以及部分相干平顶光束在自由空间传输的偏振度作为特例统一于一般表达式中.研究表明：部分相干平顶光束经光阑衍射的偏振特性与光阑截断参数、光束的空间相干性、衍射角、传输距离、平顶光束的阶数有关.     

部分相干刃型位错光束的谱Stokes奇点

利用交叉谱密度函数的传输公式,推导出部分相干刃型位错光束在自由空间中传输的解析表达式.结合谱Stokes参数,详细讨论了其Stokes场的奇点变化规律.结果表明,部分相干刃型位错光束在自由空间传输过程中存在谱s12,s23和s31奇点.改变刃型位错的离轴量、斜率、空间相关长度等光束参数以及随着传输距离的变化,会有谱Stokes奇点的移动、产生和湮没,也会有V点的产生和C点旋性的反转.     

矢量光束空间偏振编码的研究

矢量光束独特的空间偏振结构使之应用于空间偏振编码成为可能。提出了一种用一阶矢量光束的偏振分布进行极角空间编码的方法。通过矢量光束生成、光束偏振分布再调制实现了空间编码光束的生成,并采用斯托克斯参数法对空间编码光束进行检测。实验结果证实了一阶矢量光束应用于极角空间偏振编码的可行性,为基于空间偏振编码的激光驾束制导提供了新方法。     

Non-linear polarization and chiral effects in birefringent solitons

Novel effects resulting from joint action of chirality and non-linearity are discussed using a basic equation describing the temporal evolution of fields in a chiral medium with Kerr non-linearity. The spatial chirality effect is characterized through the Born-Fedorov formalism. Our simulations are based on the split-step Fourier method and the solution of the Stokes parameters. The numerical results show the chiral effect on solitons with circular polarization and mixed polarization spatial solitons.     

部分相干Airy光束在湍流大气中传输时的偏振特性

研究了部分相干Airy光束在湍流大气中传输时的偏振特性,偏振保持度作为衡量偏振传输效果的一个重要参数.结果表明:部分相干Airy光束在湍流大气中传输足够远时,其偏振度会变回到初始值;而在自由空间中传输,光束的偏振度会保持在某一个特定值;在湍流大气中,当光束传输距离不是很远时,光束对称轴上的偏振度分布为Airy函数,但是当传输足够远时,该偏振度分布逐渐趋向于类高斯状;光束的束腰半径越大,相干长度越长,越有利于光束传输后偏振的保持;存在一个指数截断因子,使得光束的偏振保持度很差.这些结论对于Airy光束在通信领域中的应用具有重要的意义.     

分振幅型全Stokes同时偏振成像系统波片相位延迟误差分析

分振幅型全Stokes同时偏振成像仪具有实时性好、空间分辨率高、精度高等优点,有很高的应用价值.分振幅型全Stokes同时偏振成像系统利用偏振分束器、1/2波片和1/4波片将入射光Stokes矢量调制在4幅图像中,可解析入射光Stokes矢量. 1/2波片和1/4波片的相位延迟误差对Stokes矢量测量精度有着不可忽略的影响.建立了包含上述两种误差的Stokes矢量测量误差方程,分析了1/2波片和1/4波片相位延迟耦合误差对自然光、0°/45°线偏光、左旋圆偏光等典型基态入射光的Stokes矢量测量误差的影响,推导了任意偏振态的Stokes矢量测量误差的表征方法.在邦加球球面和球内选取不同偏振度的Stokes矢量作为入射光进行仿真.结果表明, Stokes矢量测量误差和偏振度测量误差均随着入射光偏振度的增大而增大.选取入射光偏振度为1时的偏振测量精度评估系统.为满足2%的偏振测量精度, 1/2波片相位延迟误差应在±1.6°内, 1/4波片相位延迟误差应在±0.5°内.这对提高系统的偏振测量精度具有重要意义,为系统设计和研制提供了重要的理论指导.     

Matrix treatment for partially polarized, partially coherent beams

A matrix method is outlined for dealing with quasi-monochromatic, partially polarized light when spatial coherence is not necessarily complete and propagation occurs along beams. Both spatial coherence and polarization properties are described by a single 2x2 matrix whose elements have the structure of mutual intensity functions. Through a simple example it is shown that this matrix can account for differences that would not be revealed by a scalar treatment or by a locally defined polarization matrix.     

Contrasts of Stokes parameters in Young's interference experiment and electromagnetic degree of coherence

We analyze the modulation of the Stokes parameters in Young's two-pinhole interference experiment with a random electromagnetic beam. We demonstrate that the electromagnetic (spectral) degree of coherence put forward in Opt. Lett.29, 328 (2004) [or its space-time analog in Opt. Express 11, 1137 (2003)] is physically related to the contrasts of modulation in the four Stokes parameters. More explicitly, the electromagnetic degree of coherence is a measure of both the visibility of the intensity fringes and the modulation contrasts of the three polarization Stokes parameters. We also show that by using suitable wave plates the modulation in any Stokes parameter can be transformed into the form of intensity variation, and hence the electromagnetic degree of coherence can be obtained experimentally by four visibility measurements.     

Turbulence-induced changes in degree of polarization, degree of coherence and spectrum of partially coherent electromagnetic beams

Based on a recently formulated unified theory of coherence and polarization, a method is described to study turbulence-induced changes in the polarization, the coherence and the spectrum of partially coherent electromagnetic beams on propagation. The electromagnetic Gaussian Schell-model beam is taken as a typical example of partially coherent electromagnetic beams, and the closed-form expressions for the degree of polarization, the degree of coherence and the spectrum of electromagnetic Gaussian Schell-model beams propagating through atmospheric turbulence are derived in the quadratic approximation of Rytov's phase structure function. Some interesting results are obtained, which are illustrated by numerical examples and are explained in physics.     

Generalized Stokes parameters of stochastic spatially and spectrally partially coherent electromagnetic pulsed beams

The analytical expressions for the generalized (two-point) Stokes parameters of stochastic electromagnetic Gaussian Schell-model pulsed (GSMP) beams propagating in free space are obtained. The changes in the spectral Stokes parameters in free space propagation are studied. The dependence of on-axis and transverse spectral Stokes parameters of stochastic electromagnetic GSMP beams on the pulse parameters including pulse duration and temporal coherence length is stressed and illustrated numerically. The results are interpreted physically.     

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.     

光阑对高斯谢尔模型光束偏振特性的影响

根据光束的相干-偏振矩阵理论,应用柯林公式对部分相干光经光阑衍射后的轴向、横向偏振特性从近场区到远场区的演化规律进行了详细的数值计算。经研究表明,由于光阑的衍射效应,使得高斯谢尔模型光束的偏振出现非均匀分布,光束偏振度沿轴向、横向分布出现多峰振荡现象,并且随着光阑截断参数的减小、光束空间相干长度的增大和传输距离的增大,多峰振荡逐渐增强。光束在自由空间沿轴向传输时,在近场区偏振度分布均匀,与源平面相同,随着传输距离的增大和空间相干长度的减小,偏振度沿轴向分布逐渐增大,无振荡现象。     

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.     

Cross-spectral purity of the Stokes parameters

We extend the concept of cross-spectral purity from the spectral density to the polarization properties of electromagnetic fields by considering the polarization Stokes parameters. We show that purity conditions similar to those in the case of electromagnetic cross-spectral purity can be derived for all the Stokes parameters. Furthermore, we introduce a situation of strict cross-spectral purity which leads to the equality of the degrees of coherence for electromagnetic fields in the space–time and space–frequency domains.