大视场偏振CCD相机的偏振特性实验标定

大视场偏振CCD相机内部的多个光学表面会改变入射光的偏振状态,并且改变的程度与入射光的偏振态、视场角和方位角等有关,影响了仪器偏振测量精度,从而制约了偏振成像遥感数据的定量化应用水平。为解决这一问题,从考虑偏振效应的大视场偏振相机响应输出模型出发,研究模型参数的标定方法,通过设计试验获取了模型参数标定数据。将经过标定的大视场偏振CCD相机测试值和可调偏振度光源预设偏振度值进行对比,结果显示偏振相机在0°、15°、25°视场角下的偏振度测量平均误差不大于1.18%,远小于光学镜头自身的起偏度。消除偏振遥感仪器自身的偏振敏感性影响,为将来我国自主星载偏振遥感图像的定量化应用奠定基础。     

偏振成像在目标探测中的应用

针对偏振度编码成像在目标探测识别中的优点,本文分析了偏振探测的消偏振机理,以及表面散射和体散射对目标偏振度的影响.利用808 nm半导体激光器照明,目标的后向散射光由卡塞格林望远镜接收,经过偏振分光棱镜成像在两个CCD上,通过一次测量获得偏振状态相互垂直的两幅图像,然后计算出目标的强度和偏振度,分别利用强度和偏振度编码成像.实验结果表明,在目标的反射率相近时,强度图像不能区分不同材料的目标,偏振度图像可以区分,融合强度和偏振度图像进行HSI伪彩色编码,可以达到目标探测、分类等目的.     

一种基于人眼视觉特性的偏振图像融合方法

根据偏振参量图像之间存在的信息冗余性和互补性,提出了一种基于人眼视觉特性的偏振图像融合方法.该方法首先对线偏振度图像和偏振角图像进行基于能量特征的融合,得到偏振特征图像;然后,利用五株采样提升小波变换实现偏振特征图像和合成强度图像的融合;最后,根据人眼对局部对比度敏感的特点,采用偏振度图像对融合结果进行对比度增强处理.实验结果表明,融合后的图像不仅突出了场景的偏振信息,而且包含了丰富的强度信息,目标与背景的对比度也得到了显著增强.     

金属板热红外偏振的方向特性研究

热红外偏振探测有利于从背景中识别金属目标.通过分析热红外偏振探测方法,根据现有条件研制了一种热红外成像偏振探测仪.利用该系统,研究了金属板热红外偏振度和观测角之间的关系.实验中采用的金属板分别为铝质和钢质,表面都进行了抛光处理.实验结果表明,金属目标板热红外偏振度和其自身的热辐射亮温值没有直接的关系.在观测角大于20°时,随着观测角度的增大,金属目标板热红外偏振度的数值也增大.但在观测角小于20°时测量,金属目标板热红外偏振度和观测角之间的关系并不遵循上述原则.     

偏振器对比较式光学电流互感器性能的影响

使用偏振态分析工具,分析了偏振器性能--偏振度、消光比的不完善以及偏置角误差等因素对比较式光学电流互感器性能的影响.结果表明,由于双输入双输出的特殊传感头结构的采用,使得比较式OCT可以有效克服偏振度和消光比的不完善带来的不利影响,但是传感头的起偏器与检偏器之间的偏置角误差会对比较式OCT的性能产生较大的影响.可以采用改进工艺精确调整偏置角、增大参考直流磁场和软件修正等措施加以改进.对改进后的比较式OCT进行了实验,实验结果表明在50℃的温度变化范围内,互感器的误差变化量仅为0.7%,较之采用比较式补偿之前的误差变化量16%,温度性能得到了显著的提高.     

基于边缘信息的偏振图像融合算法及评价

偏振遥感图像通常都采用强度、偏振度、偏振角来表征目标偏振特性.本文提出的基于边缘信息的偏振图像融合算法是将三幅偏振图像利用离散小波变换把图像分解成不同尺度的低频和高频部分,采用小波区域窗口和子区域窗口统计把小波系数分类成边缘和非边缘系数,通过这些方法进行有效的边缘细节信息提取.在融合处理中,低频图像的小波系数平均值作为融合后的低频系数,高频细节系数根据不同区域特征选择方法以及对应输入图像小波系数的窗口区域方差来确定融合后高频小波系数.仿真实验结果表明,这样使得融合后的图像细节更真实更丰富,图像的偏振特性体现更为充分,同时减少对源图像的预处理要求,使图像在整体上有较好的视觉效果.从而证明这种方法能够在保留图像微小细节方面获得满意的结果,且算法有效性优于其他的图像融合方法.     

光纤型偏振OCT系统中光偏振特性的研究

建立了偏振光在生物组织中传播的模型,并利用该模型模拟了偏振光在生物组织中传播的过程,重建了多种偏振态输入光的情况下光偏振态在生物组织中的分布及生物组织的偏振特性模型.分析了光偏振度与光被生物组织散射次数的关系,阐明了由于偏振光在组织中传播,其偏振态逐渐改变而造成的偏振OCT 干涉计两臂光束失去相干性及偏振OCT 图像质量下降现象.通过分析斯托克斯(Stokes)矢量和穆勒(Muller)矩阵在光纤型偏振OCT系统中的应用,说明Muller 矩阵不受输入光偏振态的影响,因此它比Stokes 矢量更适用于光纤型偏振OCT 系统研究.     

独立通道偏振罗盘信息检测方法及传感器设计

目前偏振光导航传感器大多以POL-神经元模型为基础,误差主要来源于通道间信号增益差异,以及检偏器阵列的相对角度误差。为了提高偏振罗盘信息的检测精度,提出了一种独立通道偏振罗盘信息检测方法。利用三个相互独立的偏振光检测通道测量大气偏振信息,获取航向角信息。并且,结合分时复用技术,设计了独立通道偏振光导航传感器,提出了相应的标定方法和误差补偿算法。实验结果表明,独立通道偏振光导航传感器能够显著降低偏振罗盘信息检测误差,补偿后传感器误差在±0.05°以内。     

基于像素偏振阵列的图像传感器航向角检测

目的:模仿昆虫的导航能力,研究基于像素偏振阵列结构图像传感器的偏振导航方法。方法:使用具有像素偏振阵列结构的芯片搭建偏振导航传感器,采用两种航向角解算方法进行导航实验。在基于图像的航向角计算方法中,以太阳子午线方向建立新的坐标体系后重绘偏振角图片,提取出所有偏振角接近90°的特征点位置进行直线拟合,结合实际太阳方位角解算出航向角。结果:两种导航方法均实现了航向角检测,基于图像的航向角解算方法精度较高,航向角测量最大误差为0.882°,误差均值为0.332°。结论:基于像素偏振阵列结构的图像传感器实现了航向角检测,精度满足导航需求。     

基于各向异性二维Ge Se的无偏振器偏振图像传感器

偏振是光的一个重要信息,偏振探测可以把信息量从三维(光强、光谱和空间)扩充到七维(光强、光谱、空间、偏振度、光偏振等),为成像物体提供关键的视觉信息(如表面粗糙度、几何形状或方向),因此偏振成像技术在目标检测等领域有着巨大的潜力.然而这些领域往往需要复杂的偏振编码,现有的复杂透镜系统和偏振器限制了集成成像传感器的小型化能力.本文通过二维各向异性α-Ge Se半导体,成功实现了无偏振器的偏振敏感可见-近红外光电探测器/成像仪.作为传感器系统的关键部件,该原型Au/GeSe/Au光电探测器具有灵敏度高、光谱响应宽、响应速度快(~10³A W^-1, 400–1050 nm, 22.7/49.5μs)等优点.此外,该器件在690–1050 nm光谱范围内表现出独特的偏振灵敏度,并且对沿y方向的偏振光吸收最强,这一点通过分析α-Ge Se的光跃迁行为也得到了证实.最后,将2D-Ge Se器件应用到成像系统中进行偏振成像,在808 nm近红外波段处,在不同的偏振方向上,辐射目标的对比度为3.45.这种成像仪在没有偏振器的情况下,能够在场景中感知双频偏振信号,为偏振成像传感器阵列的广泛应用奠定了基础.     

双拓扑绝缘体介质界面的反射波极化调控特性

本文对两种三维强拓扑绝缘体分界面的反射极化现象进行了研究,得到了线偏振光完全转化的普适性充要条件。通过分析分界面的直接反射率、交叉反射率以及极化转化率,发现该模型利用现有的拓扑绝缘体材料就可以实现线极化波的完全转变,突破了需要新的较小介电常数的拓扑绝缘体材料才能完全转化的限制。该转化过程可以利用克尔旋转角进行验证,并给出了实现超强角稳定性的极化转化器件的设计思路。这为拓扑绝缘体在极化器件方面的应用提供了理论依据。     

Influence of polarization orientation of violet light on the diffraction efficiency of bacteriorhodopsin

When a grating is recorded in a bacteriorhodopsin film by two linear parallel polarized beams together with an auxiliary violet light, the diffraction efficiency has a dependence on the polarization orientation of the violet light as well as its intensity. A method for calculating the diffraction efficiency of gratings in bacteriorhodopsin is proposed based on the two-state photochromic model, considering the saturation effect and the polarization status of all the involved lights. It is found that the polarization orientation of the violet light produces an approximate-cosine and an approximate-sine modulation on the steady-state diffraction efficiency separately at low and high intensities, respectively. The parallel polarized violet light can improve the steady-state diffraction efficiency to a larger degree than the perpendicularly polarized violet light when both are at their optimal intensities. The optimal intensity for the parallel polarized violet light is lower than that of the perpendicular polarized one. Thus, the improvement of the steady-state diffraction efficiency is less sensitive to the intensity of perpendicular polarized violet light than to that of parallel polarized violet light.     

Determining surface orientations of transparent objects based on polarization degrees in visible and infrared wavelengths

Techniques for modeling an object through observation are very important in object recognition and virtual reality. A wide variety of techniques have been developed for modeling objects with opaque surfaces, whereas less attention has been paid to objects with transparent surfaces. A transparent surface has only surface reflection; it has little body reflection. We present a new method for obtaining surface orientations of transparent surfaces through analysis of the degree of polarization in surface reflection and emission in visible and far-infrared wavelengths, respectively. This parameter, the polarization degree of reflected light at the visible wavelengths, is used for determining the surface orientation at a surface point. The polarization degree at visible wavelengths provides two possible solutions, and the proposed method uses the polarization degree at far-infrared wavelengths to resolve this ambiguity.     

Polarization changes in a partially coherent radially polarized doughnut beam through turbulent ocean

On the basis of the extended Huygens–Fresnel integral principle and unified theory of coherence and polarization of light, we studied the effects of oceanic turbulence on polarization properties of a partially coherent radially polarized doughnut (PCRPD) beam. The ocean-induced fluctuations in the refractive index are assumed be driven by temperature and salinity fluctuations. Numerical examples of changes in polarization properties, such as the degree of polarization, the degree of ellipticity, and the orientation angle in the oceanic turbulence for the PCRPD beam, are given. Our analysis demonstrates how polarization of the PCRPD beam is affected by statistical properties of the source and by several parameters of oceanic turbulence. We find that the propagation of the PCRPD beam is different from that of stochastic beams in oceanic turbulence. The degree of polarization for the PCRPD beam approaches a certain steady value, and the elliptical polarized state of the fully polarized portion of the beam will become fully linear in the far field.     

Robust and accurate estimate of the orientation of partially polarized light from a camera sensor

Polarized light carries valuable information about where the light has been and the various physical parameters that have been acting upon it. Thus there are several methods in computer vision that make it possible to obtain information on the observed object by studying the polarization of light reflected on the object. Most studies using this principle are interested in the determination of the object orientation in three-dimensional space. The basis of these studies rests on the estimate of a parameter that connects the orientation of the observed surface and the polarization of the reflected light wave. This parameter is the angle of polarization phi, also called the orientation of polarization. Generally, one using these methods estimates the phi angle by observing the reflected light wave through a linear polarizing filter and grabbing multiple frames for different angular orientations of the polarizer. So, between each acquisition, the polarizer is rotated of an angle theta relative to a horizontal reference axis. The accuracy of the phi estimate is then directly related to the positioning of the polarizer. But, in practice, it is difficult to guarantee the exact value of the rotation of this polarizer. It is all the more difficult to guarantee the reliability of positioning in time. We thus propose a robust and accurate solution, based on the self-calibration principle, for measuring the orientation of partially polarized light using CCD cameras. In contrast to methods generally discussed in computer vision journals, our estimate of the angle of polarization is independent of the reliability of the polarizer positioning.     

Liquid-crystal depolarizer consisting of randomly aligned hybrid orientation domains

A novel depolarization method for linearly polarized incident light that uses a liquid-crystal (LC) cell with randomly aligned hybrid orientation domains is theoretically described by use of Mueller matrix calculations. The depolarization effect of the incident linear polarization is confirmed with Stokes parameter measurements. The unique optical properties of the fabricated LC depolarizer are revealed; that is, the intensity of the transmitted light is independent of the rotation of the analyzer. The degree of polarization becomes zero when the retardation of the LC depolarizer coincides with a half-wavelength.     

Control of Circularly Polarized Electroluminescence in Induced Twist Structure of Conjugate Polymer

An extremely high degree of circularly polarized photoluminescence (CPPL) and electroluminescence (CPEL) (dissymmetry factor values: |g_PL| = 0.72 and |g_EL| = 1.13) are generated from twisted stacking of achiral conjugated polymer induced by nonemitting chiral dopant of high helical twisting power for the first time. Using a theoretical analysis incorporating the Stokes parameter, the twisting angle and birefringence of the aligned conjugated polymer, and the degree of linear polarization in the emitted light are found to make a roughly equal contribution to the degree of CPEL as to the degree of CPPL. Moreover, it is also found that the location of the recombination zone within the emitting layer is a crucial parameter for determining the difference in the dissymmetry factor between CPEL and CPPL. This result is applied to an organic light‐emitting display to improve the luminous efficiency by 60%.     

Measurements and simulations of polarization states of underwater light in clear oceanic waters

Polarization states of the underwater light field were measured by a hyperspectral and multiangular polarimeter and a video polarimeter under various atmospheric, surface, and water conditions, as well as solar and viewing geometries, in clear oceanic waters near Port Aransas, Texas. Some of the first comprehensive comparisons were made between the measured polarized light, including the degree and angle of linear polarization and linear Stokes parameters (Q and U), and those from Monte Carlo simulations that used concurrently measured water inherent optical properties and particle volume scattering functions as input. For selected wavelengths in the visible spectrum, measured and model-simulated polarization characteristics were found to be consistent in most cases. Measured degree and angle of linear polarization are found to be largely determined by an in-water single-scattering model. Model simulations suggest that the degree of linear polarization (DoLP) at horizontal viewing directions is highly dependent on the viewing azimuth angle for a low solar elevation. This implies that animals can use the DoLP signal for orientation.     

Application of bacteriorhodopsin film for polarization phase-shifting interferometry

Photoinduced anisotropy in bacteriorhodopsin (BR) film is based on photoanisotropic selective bleaching of BR molecules under linearly polarized excitation light. It is modulated by the polarization orientation of the linearly polarized light. The anisotropic information recorded in the BR film is read by a circularly polarized light, which is in turn converted into an elliptical polarized light by the BR film. The rotation angle and the ellipticity of the elliptical polarized light are dependent on the polarization orientation of the linearly polarized excitation light. A phase-shifting interferometer based on the photoinduced anisotropy of BR film is presented theoretically and experimentally. Phase shift is controlled by the polarization orientation of the external excitation light, thus, the phase shift can be controlled without moving parts inside the interferometer, which contributes to the mechanical stability of the system.     

Polarization separation of light in holographic grating reflection in conical mounting

Abstract

We experimentally investigate the interaction of linearly polarized light with a holographic grating in a conical mounting. Due to the periodic structure, the polarization properties of the reflected zeroth-order beam are highly sensitive to the conical angle. When a focused Gaussian beam with linear polarization impinges on an air–grating interface at an exceptional conical angle, a spatial splitting of the reflected beam is observed behind a polarizer. We find that it can be interpreted using the anisotropy of the polarization distribution in holographic grating reflection.