Continuous-wave backreflection measurement of polarization modedispersion

Experimental results of continuous-wave polarization mode dispersion (PMD) measurements are presented. The proposed technique is based on the backscattered signal given by the Fresnel reflection at the fiber far-end. Experimental statistical distribution of the differential group delay of the round-trip is reported. It presents a Rayleigh distribution whose mean value is simply related to the fiber mean differential group delay. Finally, the statistical distribution of the round-trip dispersion vector is found experimentally and numerically. The proposed method can be easily used for one-end measurement of PMD in installed optical cables     

Self-consistency of polarization diversity measurement of rainfall

Polarization diversity measurements of rainfall, namely the reflectivity factor, differential reflectivity, and specific differential propagation phase, vary in a constrained three-dimensional space. Algorithms are derived to quantify this self-consistency of measurements. In particular, estimation of the specific differential propagation phase shift based on reflectivity and differential reflectivity is analyzed in detail. Theoretical simulation as well as radar observations of rainfall at S (CSU-CHILL) and C (Polar 55C) bands are used to demonstrate that the range profiles of differential propagation shift can be constructed from measurements of reflectivity and differential reflectivity     

斯托克斯光偏振态测量系统的优化

为了满足光偏振态分振幅测量模块（DOAP）对分光棱镜复杂且严格的加工要求,采用在经典DOAP透射光路及反射光路各引入一块波片的方法,组成改进后的光偏振态测量模块。推导了新的仪器矩阵表达式,通过分析波片参量对仪器矩阵条件数的影响,得到了最佳波片的参量及其关系。结果表明,优化后的斯托克斯椭偏仪测量薄膜样品的厚度和折射率的标准差分别为0.1nm和0.001。通过选择波片的最佳方位角或相位延迟量可以实现斯托克斯椭偏仪仪器矩阵的优化,从而提高系统的测量稳定性及可靠性。     

保偏光纤拍长的测量方法

介绍了保偏光纤拍长测量的几种常用方法,就其测量原理,试验装置及优缺点分别进行了较为详细的分析和说明.并就目前多数测量方法适用于高双折射光纤的不足,介绍了一种较好的测量低双折射光纤拍长的方法.     

光束会聚对光学偏振探测影响的分析

为了得到由于偏振成像系统自身的光束会聚现象导致仪器偏振测量产生误差的规律,采用空间偏振光束追击矩阵理论,对平行于光轴方向振动的透射光强对偏振测量精度的影响进行了理论分析.结果表明,偏振光束会聚导致实际测量的偏振度小于光束真实的偏振度;光束会聚程度越高,测量的偏振度与光束真实偏振度的误差越大;在光束会聚状态和偏振测量条件...     

CLASSIFICATION OF MULTI-LOOK POLARIMETRIC SAR IMAGERY AND POLARIZATION CHANNEL OPTIMIZATION

In this paper, a new maximum likelihood (ML) classification algorithm is proposed to classify the multi-look polarimetric synthetic aperture radar (SAR) imagery. Experimental results with the NASA/JPL airborne L-band polarimetric SAR data demonstrate the effectiveness of the new algorithm. Furthermore, when using the algorithm in the classifications with subsets of the multi-look polarimetric SAR data, the polarization-channel optimization for the terrain type classification is implemented.     

Long-term measurement of PMD and polarization drift in installedfibers

We report the most detailed long-term measurement of polarization mode dispersion (PMD) made to date. We measured two separate fibers under the same time period, which makes it possible to compare the drift properties of two similar fibers in the same environment. The measured Jones matrices suffers from both random and systematic errors, a generic problem which we discuss in detail and solve. The results confirmed the well-known statistical properties of the PMD-vector. Furthermore, the drift averaged over wavelength is very well (96%) correlated between the two fibers. We finally quantified the temporal drift by computing the autocorrelation function of the PMD-vector analytically, both with respect to wavelength and to drift time. The analytical theory shows good agreement with the measurements     

Two-states method for polarization dependent loss measurement

We report a two-states method for measuring polarization dependent loss (PDL) in an optical fiber system. Based on the property that the Mueller matrix governing the transmission property of any linear, time-invariant optical system with birefringence and PDL satisfies Lorentz transformation, we prove that PDL depends on the first column of the Mueller matrix. Hence only two orthogonal input polarization states are required to explicitly determine PDL. Experiment results show the agreement of our method with previously reported methods.     

偏振度测试方法的研究

偏振度（DOP）是描述光速性能的一个物理量,其测量具有重要意义。文章详细分析了偏振仪法、偏振扰码法和极值搜索法测试DOP的原理、实现方法及其优缺点,对DOP的不同计算方法进行了讨论,提出了适用于偏振模色散（PMD）补偿的高精度、快速的DOP测试方案。     

大气偏振中性点的便携式测量

为了避免常用的天空光偏振模式测量仪器中鱼眼镜头所引起的图像边缘区域扭曲的缺点,采用手机相机和线性偏振片相结合的方法,进行了理论分析和实际验证,得到了大气偏振模式的分布情况和中性点位置的数据。结果表明,实际测量的中性点区域与理论仿真的结果间高度角的偏差为2.4°±2.6°, 方位角的偏差为1.4°±0.8°,证明了测量方法的可行性;随着天空中云层的增加,天空光偏振分布图像会发生扭曲,但仍然可以确定中性点位置,为天空光偏振仿生导航提供了参考。该研究可用来确定太阳位置、实现自身定向及导航定位,并且具有易操作、便携等优点,在一定程度上降低了天空光偏振仿生导航的成本,提高了民用价值。     

Frequency dependence on polarization switching measurement in ferroelectric capacitors

Ferroelectric hysteresis loop measurement under high driving frequency generally faces great challenges.Parasitic factors in testing circuits such as leakage current and RC delay could result in abnormal hysteresis loops with erroneous rem-nant polarization(P_r)and coercive field(E_c).In this study,positive-up-negative-down(PUND)measurement under a wide fre-quency range was performed on a 10-nm thick Hf_0.5Zr_0.5O₂ ferroelectric film.Detailed analysis on the leakage current and RC delay was conducted as the polarization switching occurs in the FE capacitor.After considering the time lag caused by RC delay,reasonable calibration of current response over the voltage pulse stimulus was employed in the integral of polarization current over time.In such a method,rational P-V loops measured at high frequencies(>1 MHz)was successfully achieved.This work provides a comprehensive understanding on the effect of parasitic factors on the polarization switching behavior of FE films.     

基于偏振光的精密角度测量及传递技术

调制偏振光可作为方位信息的载体,实现方位角度信息沿角度矢量方向传递和精密测量,在精密计量、航空航天、军事、生物医药等领域具有广泛的应用前景.基于调制偏振光用于方位信息传递技术的实现原理,深入分析了磁旋光玻璃对传递和测量精度影响的作用机理,实现了优于1"的传递精度.介绍了利用调制偏振光进行三维方位信息传递以及精密角度测量系统的实现方案,并对主要的技术问题给出理论分析结果.     

Analysis and measurement of polarization conversion in a periodically loaded dielectric waveguide

The full-vectorial beam-propagation method with the improved finite-difference formula is applied to the analysis of a TE/TM mode converter based on an asymmetric periodic loaded waveguide. The polarization conversion behavior is measured at a microwave frequency. It is demonstrated that the calculated complete conversion length is in agreement with the experimental result.     

红外与可见光图像配准方法分类及现状

红外与可见光图像配准作为一类重要的多传感器图像配准方法,在自动控制、机器人、遥感及军事应用等领域发挥着重要作用.介绍了红外与可见光图像配准问题的本质及难点,从原理上总结了大部分配准算法的基本步骤,并将现有的配准方法分为两类:基于区域的配准方法和基于特征的配准方法.从算法的可行性角度出发,分析了几种具有代表性的配准方法及其优缺点,最后对其未来的发展进行了展望.     

系统误差对分布目标极化散射测量的影响

首先统一推广了现有极化定标模型.系统地评估了极化通道幅相不平衡、天线串扰、法拉第旋转、地形坡度导致的极化角度偏转、干扰和系统环境噪声等因素对分布目标全极化散射测量的影响.在此基础上,结合应用需求对上述因素的约束条件,通过仿真得到了一些对极化合成孔径雷达系统设计和极化定标有参考价值的结论.     

基于强度调制的编码孔径光谱偏振测量方法

为实现在单次成像条件下获取图像的光谱偏振信息,提出了一种基于强度调制的编码孔径测量方法。该方法采用消色差1/4波片、多级相位延迟器和检偏器组成的光谱偏振强度调制模块,将入射光的Stokes参量各元素谱调制到不同的频率上,利用编码孔径和色散棱镜组成的光谱成像系统对该调制光谱进行压缩编码,并通过CCD进行探测。利用TwIST算法重构出经调制的光谱信息,对各个频谱通道进行分离重构出Stokes元素谱。以单一像素点为例,对入射光强度调制、光谱重构及Stokes参量的解调进行了数值模拟。结果表明:该方法可实现对稀疏图像的光谱偏振信息的获取,该过程仅需对图像进行一次测量,因此具备高速获取能力。     

载波调制法提高保偏光纤偏振耦合检测的信噪比

保偏光纤偏振耦合系统能有效检测保偏光纤中偏振耦合点的空间位置及耦合强度,因而可被广泛地应用于应力、应变、温度和位置的分布式传感中。由于噪声影响,测试系统中的信噪比和耦合强度检测灵敏度会下降。为了改善系统信噪比,提高保偏光纤中弱耦合点的检测能力,将铌酸锂外调制技术应用于白光干涉保偏光纤耦合测试系统。调制后的信号经光电探测器接收,用数字解调算法进行数据处理。实验结果表明:在电机扫描速度为0.75 mm/s,调制频率为9.1 kHz,采样率为140 kHz时,载波调制时信噪比提高了8 dB,解调耗时仅1.12 s。     

Method of polarization reflection matrix measurement in the submillimeter wave range

Homodyne method of measurement of polarization reflection matrix, providing the possibility of simultaneous measurement of all four complex coefficients of polarization reflection matrix in submillimeter quasi-optical (QO) circuits is presented. Technical realizability of the method for QO waveguides of the class of "hollow dielectric wavequide" is shown.     

Accurate measurement of antenna gain and polarization at reduced distances by an extrapolation technique

A new technique is described for determining power gain and polarization of antennas at reduced range distances. It is based on a generalized three-antenna approach which, for the first time, permits absolute gain and polarization measurements to be performed without quantitative a priori knowledge of the antennas. The required data are obtained by an extrapolation technique which includes provisions for rigorously evaluating and correcting for errors due to proximity and multipath interference effects. The theoretical basis provides a convenient and powerful approach for describing and solving antenna measurement problems, and the experimental method employed illustrates the utility of this approach. Examples of measurements are included which exhibit errors in gain as small aspm0.11dB (3sigma).     

Study on monopulse angle measurement method based on virtual polarization matching

A monopulse angle measurement method for polarization array radar is studied in this paper. The receiving signal model is established and then a monopulse angle measurement method based on virtual polarization matching is proposed. To analyze the estimation performance, the Cramer-Rao Lower Bound （CRLB） of angle estimation is derived. Both theoretical analysis and simulation show that： firstly, the proposed method is superior to the traditional angle measurement methods based on the single polarization. Secondly, the performance of the new method is unrelated to the echo polarization. Thirdly, angle estimation of this method is asymptotically optimal. The results show that this method has great potential to be used in polarization array radar.