光栅分振幅光偏振测量系统的研制

使用一个既能产生反射光衍射又能产生透射光衍射的特殊金属光栅作为分光器,研制一种新颖的高速光波偏振态测量系统。它没有使用转动光学部件或调制器,而是将金属光栅产生的四条1级衍射光的光强线性地转换为电信号,通过定标方法得到系统的非奇异的仪器矩阵,然后通过线性运算得到入射光的待测Stokes矢量。该系统结构紧凑、安装方便,可用作实时偏振测量术和椭偏测量术中的偏振态探测器。     

分振幅光偏振测量仪

分振幅光偏振测量仪（DOAP）是高速测量光偏振的传感器，它利用振幅分割原理，能够同时近似实时地测量出描述光偏振态的所有4个Stokes参数。从装置结构、定标方法、工作波长和应用领域等方面，对最近20年多年来国内外在该领域的研究状况进行了较为详细的分析和总结，并指出了该技术的发展方向。     

琼斯矩阵在分布式光纤传感器偏振态分析中的应用

针对基于Sagnac原理的分布式光纤传感器中光波偏振态在双折射影响下所带来的干涉信号"偏振诱导衰落"问题,运用琼斯矩阵分析法,建立了传输光偏振态影响系统功率传输系数的数学模型;根据仿真分析的结果,发现使用反射镜作为反射元件,只能消除光纤圆双折射的影响,而不能消除线性双折射的影响.因此,提出了使用法拉第旋转镜提高系统抗偏振衰落能力的改进方法,仿真结果表明可以很好地消除传感光纤的线性双折射和圆双折射的影响.     

一种新型偏振分光棱镜的设计和应用

一种新型的偏振分光棱镜结构,实现了将偏振态相互垂直的光以不同的角度输入后合为一 束的功能,尤其能与双光纤准直器配合使用。通过计算说明二者角度可相互匹配,并分析了在准直器的角度加工出现小的偏差时,通过微量调节输入光束的方向能予以补偿。实验将该棱镜用于偏振光合束器和光学环行器等无源器件中取得了良好效果。     

基于Stokes矢量分析的偏光片光学参数测量

目前偏光片透过率的传统测量方法依赖偏光片的相对转动,受光源偏振度以及探测器偏振响应的影响大,测量精度低。为解决上述问题,本文提出了基于Stokes矢量分析的方法,通过分析入射到偏光片以及从偏光片出射的偏振光的Stokes矢量的改变,结合最优化算法来解析样品的偏振特性,从而快速、精确地测量偏光片的透过率。该方法测量速度快、可扩展性强,对平板显示产业中光学薄膜的偏振特性的测量具有普适性。     

光纤传感器中偏振开关法消偏振衰落技术

针对低双折射光纤双光束干涉型传感器两臂偏振态随机变化引起的信号衰落,提出的一种新型消偏振方式可以在可见度略有下降的情况下,较好地消除偏振态变化引起的干涉信号可见度的随机变化。该方案是通过相互正交的两个偏振态,补偿由于其中一个偏振态变化导致的干涉信号衰落。通过自动增益控制电路（AGC）可以使传感信号稳定,能够在信噪比有所下降的情况下消除偏振衰落的影响,实现干涉型光纤传感器的消偏振衰落。     

利用挤压光纤双折射效应的自适应偏振控制器

报导了利用光纤应力双折射效应研制的1．55μm波长的自适应偏振控制 器,该控制器具有自动搜索、跟踪和精确控制光纤输出偏振态的功能。经初步检测,当偏振态变化3π/s时,输出偏振光强度为给定偏振方向分量总光强的92％,平均偏差小于2％。     

偏振无关的可变纯相位延迟器研究

提出了一种由快轴保持正交方位放置的两片相同的液晶可变相位延迟器构成的可变纯相位延迟器结构设计.利用琼斯矩阵,从理论上推导了该结构在任意偏振光入射条件下,出射光偏振态与入射光偏振态保持一致.实验上,在两片液晶可变相位延迟器所加电压分别为1.55V和1.49V时,分别测量了入射光和出射光的偏振态,表征偏振态的入射光和出射光的Stokes参教基本一致.上述两者结果都表明,该结构具有较好的纯相位调制特性,并给出了控制电压在1～2.7V范围时的相位变化.     

单模光纤偏振态测试研究

本工作在光栅偏振态数学描述的基础上，建立了单模光纤偏振特性的测试系统，并对测试装置及其原理作了详细分析和讨论。     

偏振激光照明对多层薄膜结构成像对比度影响

光学多层干涉断层扫描技术(Optical multilayer interference tomography,OMLIT)应用于光电关联显微镜中以实现清晰的光学大视场成像，为高分辨率电镜图像提供目标区域标定。为了进一步提升成像对比度和定位精度，将偏振照明和OMLIT成像技术相结合，提出一种多层薄膜偏振照明的理论模型，使用矩阵传输方法对不同入射角的偏振光在不同材质、厚度的多层薄膜介质间的传播及干涉成像进行了仿真。结果表明，当照明光的电场振荡方向平行于入射面时，能够获得比非偏振光更高的图像对比度。当照明光以62°入射角照射金属银镀层样品表面，成像对比度提升高达138倍。这项工作为偏振照明OMLIT提供了理论基础，为光电融合显微成像技术的发展提供了全新的技术方案。     

Development of a bioengineered tissue model and its application in the investigation of the depth selectivity of polarization gating

Understanding the propagation of polarized light in tissue is crucial for a number of biomedical optics applications. Here we report the development of a bioengineered connective tissue model fabricated by the combination of scaffolding and cross-linking techniques to study light transport in biological tissue. It demonstrates great similarity to real connective tissue in its optical properties as well as microarchitecture. Moreover, the optical properties of the model can be reproducibly controlled. As an example, we report the utilization of this model to study the effect of epithelium and the underlying connective tissue on the depth selectivity of polarization gating.     

Polarization discrimination of coherently propagating light in turbid media

We describe the use of degree of polarization to discriminate unscattered and weakly scattered light from multiply scattered light in an optically turbid material. We use spatially resolved measurements of the degree of polarization to compare how well linearly and circularly polarized light survives in a sample. Experiments were performed on common tissue phantoms consisting of polystyrene and Intralipid microsphere suspensions and on adipose and arterial tissue. The results indicate that polarization is maintained even after unpolarized irradiance through each sample has been extinguished by several orders of magnitude. The results also show that polarized light propagation in common tissue phantoms is distinctly different from polarized light propagation in the two tissues investigated. Further, these experiments illustrate when polarization is an effective discrimination criterion and when it is not. The potential of a polarization-based discrimination scheme to image through the biological and nonbiological samples investigated here is also discussed.     

Nonreciprocal waves in absorbing multilayer systems

The propagation of naturally polarized light through a Fabry-Perot resonator with a layer of cholesteric liquid crystal is considered. In the presence of absorption, this system exhibits nonreciprocity even for naturally polarized light, which implies the existence of a new type of nonreciprocal reflection. An analysis of the peculiarities of this nonreciprocity shows that strongly nonreciprocal multilayer systems can be used as optical diodes or optical insulators (transmitting signals via an optical communication channel in one direction and blocking signals propagating in the opposite direction) or as systems for the accumulation of light energy.     

Imaging objects hidden in scattering media with fluorescence polarization preservation of contrast agents

A method for fluorescence polarization difference imaging is demonstrated for enhancing the image quality of a luminous object embedded in a random medium. The polarization preservation of light propagating in the scattering medium leads to partially polarized light emission by a contrast-agent dye located inside the object. Subtraction of the images of the luminous object detected at two orthogonal polarization directions improves the image resolution compared with a conventional optical imaging approach.     

Monte carlo simulation of converging laser beams propagating in biological materials

A new method of Monte Carlo simulation has been developed to simulate the spatial distribution of photon density of converging laser beams propagating in a turbid medium such as the phantom of biological tissue. This method can be used to obtain steady-state light distribution in the tissue phantom for a continuous-wave laser beam. We have calculated the steady-state distribution of the photon density and found important features that are uniquely related to the propagation of the converging beams in the tissue phantom.     

轴向磁场对铌酸锂半波电压的影响

提出了平行与铌酸锂波导方向的轴向磁场对其半波电压产生影响的机理:加在电极上的电场对其中传播的偏振光产生线双折射,而磁场产生圆双折射,两者作用的结果是使得半波电压随磁场而变化。由此导出了半波电压随外界磁场变化的数学模型。仿真和实验结果表明,对于平均波长为1.30μm,20T的磁场,铌酸锂的半波电压可以减小了2.13%。     

Coherence and polarization of light propagating through scattering media and biological tissues

The degree of polarization of light propagating through scattering media was measured as a function of the sample thickness in a Mach-Zehnder interferometer at a wavelength of lambda = 633 nm. For polystyrene microspheres of diameters 200, 430, and 940 nm, depolarization began to appear for thicknesses larger than 23, 19, and 15 scattering mean free paths (SMFP's), respectively, where the coherently detected scattered component dominates the ballistic component. For large particles (940 nm) the initial polarization survived partially in the scattering regime and progressively vanished up to the detection limit of our setup. This phenomenon was similarly observed in diluted blood from 12.5 to 280 SMFP's. Beyond this thickness the fluctuating parallel and crossed components of polarization became random. A dual-channel interferometer allowed us to detect simultaneously the low-frequency fluctuations of both polarized components through a few millimeters in liver tissue.     

Nanoparticle-mediated coupling of light into a nanowire

We show that a nanoparticle can serve as an efficient antenna for coupling of visible light into propagating plasmons of an Ag nanowire. For long wires, the coupling is maximal for incident light polarized perpendicular to the nanowire. For sub-10-mum nanowires, the polarization corresponding to maximum emission from the ends of the nanowire was found to be strongly dependent on the nanowire geometry and position of the vicinal nanoparticle. This nanoparticle antenna-based approach offers a potential strategy for optimizing plasmon coupling into nanoscale metallic waveguides.     

Modelling planar polarity of epithelia: the role of signal relay in collective cell polarization

Collective cell polarization is an important characteristic of tissues. Epithelia commonly display cellular structures that are polarized within the plane of the tissue. Establishment of this planar cell polarity requires mechanisms that locally align polarized structures between neighbouring cells, as well as cues that provide global information about alignment relative to an axis of a tissue. In the Drosophila ovary, the cadherin Fat2 is required to orient actin filaments located at the basal side of follicle cells perpendicular to the long axis of the egg chamber. The mechanisms directing this orientation of actin filaments, however, remain unknown. Here we show, using genetic mosaic analysis, that fat2 is not essential for the local alignment of actin filaments between neighbouring cells. Moreover, we provide evidence that Fat2 is involved in the propagation of a cue specifying the orientation of actin filaments relative to the tissue axis. Monte Carlo simulations of actin filament orientation resemble the results of the genetic mosaic analysis, if it is assumed that a polarity signal can propagate from a signal source only through a connected chain of wild-type cells. Our results suggest that Fat2 is required for propagating global polarity information within the follicle epithelium through direct cell–cell contact. Our computational model might be more generally applicable to study collective cell polarization in tissues.     

Near-infrared laser tomographic imaging with right-angled scattered coherent light using an optical heterodyne-detection-based confocal scanning system

We demonstrate, what is to the best of our knowledge, a novel optical tomographic method for the visualization of the inner structure of scattering media such as biological tissue in the near-infrared region. We constructed a scanning confocal imaging system with a cross-axes arrangement using optical fibers. This system is based on the optical heterodyne technique and enables the detection of very weak coherence photons that are generated in the spatially restricted confocal region and scattered laterally (90 degrees ) against an incident beam. To evaluate the fundamental imaging capabilities of the system, we assessed measurements from scattering phantoms composed of an Intralipid suspension with varying volume concentrations. The results of this study demonstrate that the right-angled scattered light adheres to the Lambert-Beer law and that the present system can detect light propagating through a distance of approximately 31l of the mean free path. An inclusion as small as 100 microm can be discriminated in a scattering media with an optical thickness of 4. We investigated the potential of the proposed system for imaging biological tissues in preliminary experiments using samples of chicken breast tissue.