Active polarization imaging system to discriminate adaptively with diagonal Mueller matrix

A promising method to optimize the polarization state of two-channel active polarization imaging system is presented. In this method, it is seminal that the detecting function of the imaging system is regarded as a discriminant projection of the observed objects’ polarization features (elements of the Mueller matrix). The polarization state can be seen as a physical classifier which can be obtained by training samples. The image acquired with the system that has the designed optimal polarization state become discriminative results directly. The effectiveness of the proposed method and the discriminative ability of the optimal polarization state are demonstrated by the experimental results.     

Optical path difference evaluation of the polarization interference imaging spectrometer

The optical path difference (OPD) of the static polarization interference imaging spectrometer and wide-field-of-view polarization interference imaging spectrometer are calculated and analyzed, simultaneously. The analysis results show that the actual total OPD contains two parts, the Savart polariscope introduces the first part, and the second part is introduced when imaging lens reunites two beams in its focal plane. Since the first part OPD accounts for about half of the actual total OPD, it has influences on the resulting spectrum and thus cannot be neglected. The influences of the uniaxial crystal dispersion on the OPD and resulting spectrum are analyzed, and the results show that the OPD decreased with the wavelength, the spectral resolution increased with the wavelength. There are no fixed spectral resolution over the entire detection spectral region, and the spectral resolution would become worse with the increase of the wavelength.     

Analysis of the lateral displacement and optical path difference in wide-field-of-view polarization interference imaging spectrometer

The mechanism of beam splitting and principle of wide-field-of-view compensation of modified Savart polariscope in the wide-field-of-view polarization interference imaging spectrometer (WPIIS) are analyzed and discussed. Formulas for the lateral displacement and optical path difference (OPD) produced by the modified Savart polariscope are derived by ray-tracing method. The theoretical and practical guidance is thereby provided for the study, design, modulation, experiment and engineering of the polarization interference imaging spectrometers and other birefringent Fourier-transform spectrometers based on Savart polariscopes.     

偏振对光学系统成像质量的影响

通常情况下,评价光学成像系统像质的几个重要参数,如能量集中度(Strehl比)、分辨率、焦深等,都是以标量衍射理论为基础进行计算和分析的.考虑光波的矢量偏振特性,尤其是在高数值孔径系统中,标量衍射的精度已不能满足精度要求.本文讨论了在采用矢量衍射计算方法基础上,上述成像参数的变化,所讨论系统入瞳面各点为偏振方向一致的线偏光或部分偏光,以便于考察偏振对所述成像参数的影响,通过公式推导和数值计算,得出了由于偏振的影响.系统衍射斑能量极大值变小,像面和偏振平行方向分辨率降低,分辨率出现各向异性,只有系统焦深受偏振影响较小.而这些矢量效应会随着系统数值孔径的提高而愈加明显,因此在分析处理数值孔径较高的光学系统时必须使用矢量衍射方法.最后讨论了轴外点衍射斑的计算.     

Polarization detection with polarization interference imaging spectrometer

A new method of measuring the intensity and state of polarization of optical radiation by means of the high resolution polarization interference imaging spectrometer (PIIS) is introduced and theoretically investigated in this paper. The error accuracy analysis is proposed, and it is proved that the system is very stable and precise in theory. In this new way, the polarized characteristics of light could be taken good use to analyze and distinguish objects in passive remote sensing with the PIIS, which means that the polarization interference imaging spectrometer now can be used not only as cameras and interferometers but also as polaristrobometers.     

A LabVIEW-based real-time measurement system for polarization detection and calibration

A rapid real-time polarization measurement system was designed and implemented in this paper. The system is centered round a computer running application developed for the purpose. The paper illustrates how to build such an excellent application with National Instruments’ graphical programming language LabVIEW, a synchronized high speed multi-channels data acquisition card and some photoelectric conversion module in detail. With simple and friendly user interface, the experimental result shows that the measurement system has high computational efficiency, high precision calibration matrix, which can be efficiently utilized in experiments relating to the measurement of polarization.     

Approximate polarization calculations with scalar radiative transfer theory

The Pomraning phase function can be used to perform approximate polarized Rayleigh transfer calculations with a scalar radiative transfer equation. The approximation is numerically tested for the albedo problem consisting of azimuthally independent radiation incident on a homogeneous semi-infinite atmosphere. The numerical tests were carried out with the same approach used by Viik (JQSRT 68 (2000) 319-326) to numerically test the approximate phase function for solving the Milne problem. Away from the surface the Pomraning phase function gives marginally better results for the diffuse radiation than the usual scalar Rayleigh phase function because it was derived from an asymptotic limit more appropriate for deeper locations in an atmosphere. For optical depths less than unity, though, the scalar Rayleigh approximation is better than the Pomraning approximation.     

利用表面散射光偏振差异的目标识别技术

 分析了不同物体散射场偏振特性的差异,依据消光定理的矢量微扰解方法将物体散射场分为零阶和高阶解,零阶反射光可完全保持入射光的偏振度,高阶散射则会导致偏振度的降低,因而总散射光的偏振度依赖于散射表面的粗糙程度。提出了利用斯托克斯-穆勒体系测量物体消偏特性的方法并通过实验对一些物体作了测量,实验结果表明：光滑表面可以较好地保留入射光偏振度,而粗糙表面则有很强的消偏作用,因此偏振成像方法可有效地提高目标探测和识别效率。     

A polarization interference imaging spectrometer and its calibration

A polarization interference imaging spectrometer for remote sensing is developed. Its operation principle and typical configuration are introduced. A polarization beam-splitter is its key component of the spectrometer. The advantages and disadvantages of the instrument are discussed compared with those of other instruments, which are based on the principle of active exploration for remote targets. The principles, strategies, methods, contents, aspects, and steps of calibration for the instrument are introduced. The experimental result of relative calibration for the CCD detector of a PIIS is given. Some applications and expectations of polarization interference imaging spectroscopy are put forward.     

Impact of polarization mode dispersion on the performance of optical CDMA transmission system

The impact of fiber polarization mode dispersion (PMD) on the bit error rate (BER) performance of a direct sequence optical code-division multiple-access system is analyzed by the split-step Fourier method based on the coupled nonlinear Schrödinger equation, the three-dimensional Poincare sphere theory and the Jones matrix method. When the incident pulse's width is bigness than the chip duration, which causes spreading and overlapping of chips and degrades system performance due to increased interchip interference and reduced received optical power conduce cannot decoding or error decoding. When the incident pulse's width is less than the chip duration, good encoding/decoding performance can be achieved.     

Time-resolved fluorescence polarization anisotropy and optical imaging of Cybesin in cancerous and normal prostate tissues

Time-resolved polarization-dependent fluorescence of Cybesin in solution and in cancerous and normal prostate tissues were measured. The polarization preservation property of Cybesin in tissue was observed. The fluorescence intensity emitted from a Cybesin-stained cancerous tissue area was found to be much stronger than that from a Cybesin-stained normal tissue area indicating that cancerous prostate tissue takes-up more Cybesin than normal tissue. The polarization anisotropy of Cybesin contained in cancerous prostate tissue was found to be larger than that of Cybesin in normal prostate tissue indicating that a larger degree of polarization was preserved in the Cybesin-stained cancerous tissue due to structures. A static anisotropy component from the emission of cell-bonded Cybesin molecules in tissue and a time-dependent anisotropy component from the emission of un-bonded Cybesin molecules were determined and discussed. The static anisotropy value of Cybesin in stained cancerous tissue was found to be much larger than that in stained normal tissue. The fluorescence polarization difference imaging technique based on the polarization preservation of Cybesin was used to enhance the image contrast between cancerous and normal prostate tissue areas.     

一种分焦平面偏振成像系统光源标定方法北大核心CSCD

水下偏振成像技术是目前水下成像研究的热点,由于自然光在水中衰减大,水下成像系统多采用主动照明方式。针对分焦平面偏振成像系统中偏振照明光源与偏振探测像元偏振方向不匹配引起采集图像偏振信息存在的偏差,进而影响目标图像增强质量的问题,提出了一种分焦平面偏振成像系统光源标定方法。阐述了偏振光源的标定原理,然后给出偏振光源标定的实施步骤,最后采用偏振去雾算法和图像质量评价方法对标定前后的水下目标图像进行了图像增强和图像质量评价。评价结果表明,标定后的增强图像质量优于未标定的增强图像质量,平均梯度最大提升了2.48倍。该标定方法简单有效,实用性强,适用于分焦平面偏振成像系统偏振光源标定。     

极化合成孔径雷达海面成像模拟及分析

海浪极化SAR成像模拟对海面散射的研究有重要的意义.基于海浪谱理论,在考虑大、小尺度海浪影响的基础上,构建了双尺度的随机粗糙海面.根据该海面模型,利用Bragg散射模型,小扰动模型与速度聚束理论,模拟了不同状况下海浪的极化SAR图像.并针对海浪参数对极化图像的影响进行了分析,结果符合成像统计特性,得出了一些有益于海浪信...     

太阳极紫外成像光谱仪光学系统设计

在极紫外波段对太阳进行超光谱成像观测是研究太阳上层大气,日冕中等离子物理特性的重要手段。依据太阳极紫外成像光谱仪的应用,结合国内外极紫外成像光谱仪发展现状,制定了太阳极紫外成像光谱仪的性能指标。通过比较各种光学结构的优缺点,选择望远镜与光谱仪组合的结构。讨论并选择了可用的基本元器件,望远系统采用离轴抛物面反射镜,分光器件为高密度超环面等间距光栅。设计出符合指标的光学系统。最后给出了太阳极紫外成像光谱仪的设计过程、详细参数与结果。光学系统的工作波段为17.0～21.0nm,视场是1 228″×1 024″,空间分辨率达到0.8arcsec.pixel-1,光谱分辨率约为0.001 98nm.pixel-1,系统总长度约为2.8m。     

基于加权能量集中度的光条成像质量评价方法研究

线结构光视觉传感器的光条成像质量是判断摄像机曝光时间设置是否合适,系统能否达到最佳测试精度的重要因素。从横截面近似高斯分布的光条出发,综合考虑影响能量集中度的峰值灰度和光条宽度,提出了一种基于加权能量集中度的光条像质量评价方法。光条图像和背景图像作差获取差分图像,提取光条直线方程并根据法线方向旋转差分图像使得光条完全垂直于图像水平轴,获取光条的截面灰度分布情况,并计算加权能量集中度,根据经验阈值判断光条成像的质量。实验表明,随着曝光时间加大,加权能量集中度在数值上先增大后减小,因此通过阈值可以很好地评价光条成像质量。     

干涉成像系统传递函数的数值分析

干涉仪系统传递函数能有效地表征系统相位成像的性能。通过假设干涉成像系统是复振幅的线性平移不变系统,模拟计算正弦相位光栅和相位台阶这两类标准相位物体的成像,确定干涉仪系统传递函数。数值分析结果表明:系统传递函数随着波像差的增加而减小;干涉成像系统对小幅度相位（远小于1 rad）成像是近似线性的,而对大幅度相位(大于0.5 rad）成像则是明显非线性的。当正弦相位的幅度为1时,系统传递函数在1/2和1/3截止频率处出现明显的急剧下降。高度为/2的相位台阶成像时,系统传递函数随着空间频率的增加而缓慢地降低。 The performance of phase imaging in interferometric imaging system is well characterized by the system transfer function (STF). The STF of the interferometric imaging system is analyzed numerically by assuming that the system is linear and shift-invariant for the complex field. Two standard phase objects, sinusoidal phase grating and phase step, are employed and simulated to determine the STF. Numerical simulation results show that the STF decreases as the wavefront aberration of interferometric imaging system increases. It also shows that the interferometric imaging system is approximately linear for small phase (far less than 1 rad) but explicitly nonlinear for large phase (larger than 0.5 rad). The STF has a visible drop at one half or one third of the cut-off frequency of the imaging system when the amplitude of sinusoidal phase is 1 rad. For a phase step with a height of /2 rad, the STF has no visible drop but decreases slowly with the increasing of spatial frequency. The results provide a useful guidance to the design of interferometer and the measurement of STF and power spectrum density in experiment.     

轴对称综合孔径光学系统的调制传递函数和成像性质

综合分析目前各种综合孔径光学系统的结构和成像特征,并对它们作了比较。使用数值模拟方法,对单环轴对称综合孔径光学系统和双环结构的轴对称系统进行分析,研究了轴对称综合孔径光学系统的结构形式及其调制传递函数(MTF),并对其成像性质作了评估与比较。讨论了一种4+2双环结构的轴对称综合孔径系统的结构形式,对其成像特点作了详细描述,最后运用图像复原维纳滤波器对系统成像图做了处理,以使这种轴对称综合孔径系统具有更理想的成像效果。     

Real-time optical imaging and tracking of micron-sized particles

We report real-time imaging and dynamics monitoring of micrometer predefined and random sized particles by time-space-wavelength mapping technology using a single-detector. Experimentally, we demonstrate real-time line imaging of a 5 μm polystyrene microsphere, glass powder particles and patterns such as fingerprints with up to 5 μm resolution at 1 line/50 ns capture rate. By using the same setup, real-time displacement tracking of micrometer-size glass particles with 50 ns temporal resolution and up to 5 μm spatial resolution is achieved. We also show that existing correlation spectroscopy algorithms can be adopted to extract dynamic information in a complex environment.     

A deeper analysis of the second order polarization mode dispersion in optical communications systems

This article presents a new approach to the combined analysis of the first and second-order polarization mode dispersion (SOPMD) and shows their importance in optical communication systems performance. How it affects the relation between second-order polarization mode dispersion (PMD) and the differential group delay (DGD) in a single mode fiber is discussed. The analysis is based on time or wavelength and temperature variations changing/impacting PMD and DGD measured values. We present long term statistical characteristics of second-order PMD over a PMD emulator, and investigate the correlation between SOPMD, depolarization (DEP) and polarization dependent chromatic dispersion (PCD). Some authors calculate these modes from measurements obtained from the first order polarization mode dispersion, assuming a positive correlation between these effects, but this not the real relationship between them. A new interpretation of SOPMD was used to analyze the problem of the spectral stability in terms of the temperature. Actual techniques for determination SOPMD, consequently DEP and PCD, use the variation in time and/or wavelength. In some studies the results obtained for SOPMD are correlated to first-order PMD (FOPMD). This paper shows, based on measurements, that the correlation between first and second order Polarization Mode Dispersion (PMD) in the case where the last one is a function of the temperature can assume positive or negative values.     

通道调制型偏振成像系统的波段宽度限制判据

通道调制型偏振成像技术是一种体积紧凑、空间分辨率高且能够实时获取全偏振信息的新型偏振成像探测技术. 但该技术目前只能实现准单色光的全偏振探测, 严重制约了其实用化. 本文首先对宽带光通道调制型偏振成像出现混叠现象的原因进行了分析, 得出载波频率是限制波段宽度的主要因素. 据此在空间频谱域上分析并推导了通道调制型偏振成像系统的光谱宽度限制判据公式, 同时通过模型仿真得到了系统的极限有效光谱范围, 与理论推导公式结果进行了对比分析, 验证了判据的准确性. 基于该判据可预测给定通道调制型偏振成像系统的有效工作波段, 同时还可为扩展系统波段宽度提供理论支撑.