基于矩阵理论的螺旋液晶透射光偏振态研究

将螺旋型液品看作是N层双折射材料晶片叠合而成,而每层光轴相对于相邻的晶片有一个小的旋转.本文基于矩阵理论,研究了光在螺旋液晶中传输时偏振态的变化.经过详细的数学推导,理论研究表明.线性偏振光经过螺旋液晶后偏振态会发生改变.当满足一定的条件时,线偏振光的偏振方向旋转90°,左旋圆偏振光经过左旋螺旋液晶后转变为右旋圆偏振光.     

胆甾相液晶电控螺旋畸变导致的布拉格反射特性

研究了平面织构胆甾相液晶在垂直于螺旋轴方向施加电场后,引起螺旋畸变导致布拉格反射光强度变化特性,利用液晶矩阵光学,琼斯矩阵法与Matlab矩阵计算软件对有螺旋畸变情况下的布拉格反射光谱特性进行了分析和数值计算.从数值计算和实验结果可知,胆甾相液晶在其垂直螺旋轴方向施加不同电压电场时,布拉格反射光中心波长不随电压改变,而布拉格反射光强会随电压的增大而减弱.提出一种电致螺旋畸变模型,对实验结果和数值计算结果给出了合理的解释,认为利用电场改变胆甾相液晶螺距进而设计电控颜色变化液晶器件的原理是不可靠的.     

相位延迟法平行排列丝状液晶在静磁场中扭曲效应研究

对平行排列5CB（4′-n-penty1-4-cyanobinpheny1)丝状液晶在静磁场中扭曲变形做了严格的数值解,给出了严格分布情况;利用光学“4*4”矩阵算法,计算了线偏振光在严格分布下的传输情况;在实验方面,应用光学相位延迟法对平行排列5CB丝状液晶在静磁场中（温度27℃）线偏振光的通过情况进行了测量.理论计算和实验结果说明在非长螺距近似条件下可用线偏振光对平行排列丝状液晶的物理性质进行实验研究.     

液晶磁致旋光的研究

利用矩阵方法分析了液晶的旋光效应，导出了液晶旋光的矩阵表示. 利用JG-3型连续可调谐磁场仪搭建实验装置，红外1350 nm激光器做光源，测量了偏振光通过磁场作用下BL-009型向列相液晶的旋光角，详细分析了磁场对液晶旋光性能的影响. 通过实验测试，对液晶的阈值磁场强度进行了讨论，同时对实验结果进行了理论上的分析，得出了液晶旋光角随磁场与液晶盒表面夹角而变化的结论，验证了液晶分子轴的旋转方向与磁场的方向无关，这为更好的研究液晶的特性以及液晶器件的设计具有重要的参考价值. 关键词： 液晶 矩阵 磁致旋光     

弱磁场中向列相液晶的磁光效应

当外磁场强度比较小时,液晶不会发生Freedericksz转变.利用介电张量分析了扭曲型向列液晶在弱磁场中的旋光效应.通过理论分析表明,线性偏振光经过磁场中的扭曲型向列液晶,会产生左右两束椭圆偏振光.这两束椭圆偏振光在该液晶中的传播速度不同,导致光经过液晶盒后光电场振动面发生偏转.进一步分析表明,对于同一种波长的光,磁场强度越大,其电场振动面旋转角度越大.在相同的磁场强度下,光波长越短,其电场振动面旋转角度越大.如果加上高的偏置电压,使向列型液晶分子长轴方向与外磁场方向平行,线性偏振光经过磁场中的该扭曲型向列液晶,其振动面会也发生偏转.     

垂直向列型彩色滤光膜硅覆液晶微显示器的三维光学建模

针对垂直向列型彩色滤光膜硅覆液晶微显示器件中的微型彩色像素建立了三维光学模型. 首先, 对彩色液晶器件的机电特性进行了分析; 其次, 利用扩展琼斯矩阵计算出器件的光反射率; 最后, 采用标准RGB协议将所研究的垂直向列型彩色滤光膜硅覆液晶微显示器件中各像素点的光反射特性还原成彩色图像. 用上述过程所建立的三维光学模型进行了垂直向列型彩色滤光膜硅覆液晶微显示器件的光学特性研究, 并与实验数据进行了比较. 比较结果显示, 模拟得到的垂直向列型彩色滤光膜硅覆液晶微显示器件的光学特性与实验结果非常符合.     

电控液晶光阀中的指向矢分布特性

液晶分子具有介电和光学各向异性,在外电场作用下,液晶指向矢将会重新分布,具有高效的光学相位调制能力.本文从实验和理论角度对电控液晶光阀的光学调制特性进行了研究,结果表明:光阀阈值电压约为4V,且当外加电压高于阈值电压时,液晶光阀的透射强度随外加电压表现出非周期性特性.根据液晶连续体弹性理论,对电场作用下液晶光阀的指向矢分布特性进行数值分析,分析结果表明液晶光阀对透射光强的非周期调制特性取决于液晶体系的偏转状态,为研究液晶的偏振光调制特性提供理论依据及实验基础.     

手性介质中后向散射米勒矩阵特性及其在血糖无创检测中的应用初探

利用斯托克斯-米勒矩阵表述分析偏振光在手性介质中的传输规律,利用瑞利近似下的单次散射模型和基于米氏散射理论的多次散射的蒙特卡罗方法,探讨葡萄糖对后向散射偏振光传输特性的影响,计算了不同葡萄糖浓度下的后向散射米勒矩阵. 结果表明在含有葡萄糖的手性介质中后向散射米勒矩阵的若干矩阵元表现出微弱的旋光效应,旋光度随葡萄糖浓度增大而增大. 为了检测低浓度下微小的旋光变化,定义了函数对含-不含葡萄糖的米勒矩阵元图像进行处理,提取由葡萄糖引入的图像差异. 结合无创血糖检测应用要求,分析了葡萄糖生理浓度下的矩阵元图像,获 关键词： 医用光学与生物技术 偏振光 斯托克斯-米勒表述 蒙特卡罗模拟     

液晶光阀的偏光显示特性分析

讨论了液晶光阀的偏光扭曲向列性效应, 分析了液晶光阀中液晶分子在交流电场作用下重新取向后的扭曲, 测量了TB3639型液晶光阀在特定的频率连续改变外加交流电压条件下,液晶分子重新取向后的扭曲角度以及液晶光阀的电光特性。测量结果表明,在外加电压连续改变时,入射线偏振光的透射率呈现连续非线性变化,这种非线性变化可以由液晶分子的扭曲量来改变。同时液晶分子180°的扭曲使得液晶光阀具有较陡的电光特性曲线,这对于多通道矩阵寻址方式的液晶光阀而言在矩阵显示中可有更多的通道寻址线和更高的对比度。     

液晶旋光偏振仪

在光学实验中,偏振光总和晶体(片)构成一定的光路。如在两正交的偏振片之间插入晶片产生旋光现象等。本文提出了一种实验设计,采用液晶显示器作为基本元件,取材方便,费用低廉,富有新意,易于推广。     

NLC-CLC-NLC cell as an electrically tunable polarization plane rotator

A liquid crystal optical device made of an optically anisotropic heterostructure is considered. The device consists of a cholesteric liquid crystal (CLC) layer sandwiched by two phase-shifting anisotropic layers of a nematic liquid crystal (NLC). In this structure each of the NLC layers is a quarterwave plate. The problem is solved both by Ambartsumian’s method of layer addition and Muller’s matrix method. The peculiarities of reflection spectra, eigen polarizations, rotation of polarization plane and polarization ellipticity are studied. It is shown that this device can work as a light modulator or a system for obtaining linearly polarized light with electrically tunable rotation of the polarization plane (which is especially important for optical communication), as well as a device for obtaining the linearly polarized light from a non-polarized one.     

The new matrix and the polarization state of the transmitted light through the cholesteric liquid crystal

The cholesteric liquid crystal can be regarded as a multilayer that consists of many layer uniaxial thin films that exhibit optical rotation. For the convenient discussion of the polarization states of the transmitted wave through a cholesteric liquid crystal, a new 2×2 matrix is given, in which the matrix element is changed into the complex exponential. Here we discuss the treatment process of this method in detail and its role in the investigation of the polarization states. Using this method we easily study the polarization states of the transmitted wave. The calculated results show that the polarization states of wave will be changed when it propagates along the cholesteric liquid crystal.     

Laser-induced helical structure in the isotropic phase of nematic liquid crystal

We report on the first observation of laser-induced helical structure in the isotropic phase of a nematic liquid crystal. The helical structure was induced by two nearly counter-propagating waves circularly polarized in the same sense. Bragg reflection in the optical tunneling region was studied. We made an extensive investigation on the analogy between Bragg reflection from a cholesteric liquid crystal slab and four-wave mixing. It provides a deeper insight into the physics of the optical properties of cholesteric liquid crystal.     

Experimental investigation of one-sided optical transparency in cholesteric liquid crystal thin film

Influence of boundary conditions on optical properties of a layer of cholesteric liquid crystal (CLC) has been investigated. In particular, a sample was obtained which is transparent for circularly polarized light incident from one side and gives losses in the transmission spectrum (within nearly 100 nm wide wavelength range) if light is incident from the opposite side, i.e. exhibits optical diode behavior. Two selective reflection bands were detected in the reflection spectrum of the sample. Spectral position of both selective reflection bands and transmission spectrum are shown to be CLC temperature-controllable.     

Photonic density and nonreciprocal optical properties in chiral liquid crystals

Nonreciprocal optical properties of anisotropic (nano-film) heterostructures made of a cholesteric and nematic liquid crystal (CLC-NLC) layers are studied. Namely, a NLC-CLC (and CLC-NLC) structures are considered in which the NLC layer is a quarter-wave plate. The problem is exactly solvable by Ambartsumians’ modified layer addition and Mullers’ transfer-matrix methods. The peculiarities of the polarization dependent properties, such as the photonic density of states, reflection spectra, the polarization plane rotation and ellipticity spectra are investigated. It is shown that such a system canwork as a light modulator, an element for obtaining linearly polarized light with an electrically tunable polarization plane rotation, or a transformer of non-polarized source into linearly polarized light. The analysis of the optical properties in investigated structures can be used for design of perspective optical diodes, microlasers and multifunctional elements on chiral liquid crystals with electrically tunable polarization plane rotation and field controlled light polarization.     

Optical vortices generated by dislocations in a cholesteric liquid crystal

We report the observation of optical vortices in a laser beam propagating through the stripe pattern of a cholesteric liquid crystal. The liquid crystal is confined in a cell with homogeneous boundary conditions and forms a diffraction phase grating. Optical vortices are produced by edge dislocations of the cholesteric grating. The vortices show up as spots of zero light intensity in the diffraction maxima. There is one spot in each +1 and -1 diffraction maximum and two spots in diffraction maxima +2 and -2.     

Light-induced instabilities driven by competing helical patterns in long-pitch cholesterics

We study theoretically the dynamical reorientation phenomena when a long-pitch cholesteric liquid-crystal film with homeotropic alignment is illuminated by a circularly polarized lightwave. In the present case, the natural cholesteric pitch is of the order of (or larger than) the film thickness. The helical cholesteric structure is thus frustrated by the boundary conditions without illumination. However, above a light intensity threshold reorientation occurs and the bifurcation scenario depends strongly on the natural cholesteric pitch. Recalling that a long-pitch cholesteric is achieved in practice by adding a small amount of chiral agents in a nematic liquid crystal, the observed dynamics can be viewed as the result of the competition between intrinsic and extrinsic unidimensional helical patterns. The intrinsic part consists of the helical deformations induced by the chirality of the dopant, whereas the extrinsic part is related to the chirality induced by the optical field through the non-uniform angular momentum transfer of light to a nematic. The all-optical analog in the case of a pure nematic (without chiral dopant), is also discussed.     

Accumulation and transmission of the light energy in nonreciprocal multilayer systems

The specific features of light energy distribution within a multiplayer optical system are calculated by using the effective layer addition method. Various mechanisms of nonreciprocity are discussed, and Jones matrices of systems with different mechanisms of nonreciprocity are considered and compared. Accumulation of polarized light energy and resonance light diode transmission (due to the asymmetric character of interaction between the light and nonreciprocal anisotropic system) in multilayer systems with cholesteric liquid crystal layer(s) in presence of small absorption are predicted in certain range of the light spectrum and polarization. The accumulation of light in the multilayer optical systems with the defects, based on realistic solid materials with periodical structure, are also discussed, aiming at their applications in the liquid or gas-heaters and solar energy and fiber optics converters.     

胆甾相和蓝相液晶的透射和反射特性

针对蓝相液晶显示器中的暗态漏光特性, 采用时域有限差分方法模拟计算了胆甾相液晶的平面态和焦锥态以及蓝相II态液晶的透射和反射特性, 得到了它们在正交和平行偏振片之间的漏光, 并提出了计算等效旋光能力的公式以比较它们的旋光能力. 通过对比焦锥态和蓝相液晶的旋光能力和漏光特性发现, 采用焦锥态替代蓝相液晶而得到良好的暗态特性是一种可行的方法. 通过研究它们的布拉格反射特性, 得知蓝相液晶的布拉格反射与平面态相似, 但反射强度小, 焦锥态无明显的布拉格反射特性.