Novel cell parameter determination of a twisted-nematic liquid crystal display

In this paper a novel method is proposed to determine the cell parameters including the twist angle, optic retardation and rubbing direction of twisted-nematic liquid crystal displays （TNLCD） by rotating the TNLCD. It is a single-wavelength method. Because using subtraction equation of transmittance as curve fitting equation, the influence of the light from environment and the absorption by polarizer, the sample of TNLCD and analyser on the transmittance is eliminated. Accurate results can also be obtained in imperfect darkness. By large numbers of experiments, we found that not only the experimental setup is quite simple and can be easily adopted to be carried out, but also the results are accurate.     

基于液晶空间光调制器的全息显示

在传统的纯相位全息显示系统中, 一般基于快速傅里叶变换(FFT)算法来计算相位全息图, 在FFT的计算中需要遵循Nyquist采样定理, 因此, 重建图像的尺寸往往受限于空间光调制器的固定采样率. 这个限制可以通过卷积算法或者两步菲涅耳衍射算法来解决, 但是需要使用多个FFT的计算, 导致计算量增大. 鉴于此, 提出了一种基于透镜的纯相位全息图计算方法. 在全息图的计算中, 通过透镜的成像原理建立一个采样率可变的虚拟全息面, 通过调节相应的距离参数使得在全息图的计算中可以任意调节原始图像的采样率, 摆脱了传统方法中液晶空间光调制器带宽积对重建图像尺寸的限制, 并且这种算法只需使用一次FFT就能达到变采样率的衍射计算, 大幅提高了全息图的计算速度. 数值模拟及光学实验结果证明了此方法可以在全息显示光学系统中清晰地重建不同尺寸的图像. 同时该系统可以有效地消除由空间光调制器的像素化结构带来的零级衍射.     

Genetic optimization of modulation characteristics for two twisted nematic liquid crystal spatial light modulators

A single twisted nematic liquid crystal spatial light modulator may suffer from coupled amplitude modulation and a phase modulation capability of less than 2, although almost all panels can achieve . Two twisted nematic liquid crystal panels can be combined in an optical system to produce a total phase modulation of at least 2, and a minimal coupled amplitude modulation. A genetic algorithm is used to optimize the combined modulation characteristics of two liquid crystal panels in a multiplicative architecture. Simulation results and experimental verification are presented which show a substantial reduction in the combined amplitude modulation, and a total phase modulation of 2.     

液晶空间光调制器的调制特性测量

分析了液晶空间光调制器LC2002的工作原理,测量了振幅调制特性和最佳相位调制特性曲线.对经扭曲向列液晶空间光调制后的待测波面进行横向剪切干涉,用CCD记录其干涉图样,采用一维图像分析法得到最大相位调制为0.837π.实验证明液晶空间光调制器可以很好地进行相位调制.     

Complex modulation with a twisted-nematic liquid-crystal spatial light modulator: double-pixel approach

I modify the double-phase holographic code to implement complex modulation with a transmission twisted-nematic liquid-crystal display. This device is employed in the mostly phase configuration, for which the phase modulation is coupled with a nonconstant amplitude modulation. The modified double-phase code implements arbitrary complex modulation employing the constrained complex modulation of the display.     

彩色全息显示中液晶空间光调制器位相调制偏差的矫正方法

采用三基色激光照明并结合时分复用或空间复用技术,可实现基于液晶空间光调制器(LC-SLM)的彩色全息显示.但由于在不同激光波长入射条件下LC-SLM的位相调制特性曲线不同,难以同时满足多波长入射条件下2π线性位相调制的要求,致使彩色全息再现结果受到共轭像和零级斑的干扰.针对该问题,本文通过实验测试获得LC-SLM在不同波长入射时的位相调制特性曲线,并分析了RGB激光器各分量的位相调制特性曲线非线性偏差和调制幅度偏差对多阶位相型傅里叶变换相息图再现效果的影响.根据"查表法"建立了各波长入射条件下满足2π线性位相调制的灰度映射关系,并对RGB分量相息图进行修正.通过对修正前后RGB分量相息图的数值模拟再现和光电再现实验与分析,结果表明:该方法有效地克服了LC-SLM位相调制特性曲线偏差的不利影响,从而改善了彩色全息显示中各分量相息图的再现质量.     

液晶空间光调制器相位调制测量及波前校正

提供了一种简单且精度较好的测量液晶空间光调制器相位调制特性的方法,即相位与电压(灰度)之间的关系。采用数字波面移相干涉仪,由干涉仪直接给出不同灰度对应的相位差,从而得到液晶空间光调制器的相位调制曲线。利用液晶空间光调制器实现了波前校正。由干涉仪作波前测试,对待校正的畸变波前进行泽尼克多项式描述,根据液晶空间光调制器的相位与灰度的关系,产生相应的灰度图,获得畸变波前的共轭波前,从而完成静态波前的校正,使相关参数如PV值、RMS值和Strehl比值得到了改善。     

Non-linear response of liquid crystal spatial light modulators

This technical note outlines the results of a series of experiments performed on two spatial light modulators. The two modulators were a Hughes Corporation LCLV and an optically-addressed ferroelectric liquid crystal SLM fabricated by the University of Colorado at Boulder and Displaytech. These experiments were performed to determine the modulated response of the read beam as a function of the write light intensity.     

Resolution improvement of surface plasmon-enhanced, liquid crystal spatial light modulator: Simulation studies

Spatial resolution is an important performance characteristic of spatial light modulators (SLM). One of the key factors affecting the spatial resolution of liquid crystal (LC)-based SLM is the fringing field effect. This effect can be reduced in thin LC cells with corresponding reduction in the electro-optical response. A strong electro-optic response in thin LC layer can be attained using the surface plasmon resonance (SPR) phenomenon. While SPR-based LC SLMs were already demonstrated about 15 years ago, their development has been hampered in part by low resolution, due to the finite propagation length of the surface plasmons (SPs). A fine patterning of the metal layer supporting the propagation of SPs is studied as a possible solution for reducing the spatial blurring associated with the long propagation length of SPs. The results of detailed computer simulations showing improved resolution SPR-LC-SLM are presented.     

Bistability and spatial hysteresis in an Nd:GdVO4 laser with an intracavity twisted-nematic liquid crystal

In this study, optical bistability accompanied by spatial hysteresis was demonstrated in an Nd:GdVO₄ laser with an intracavity twisted-nematic liquid crystal. The low branch of power hysteresis mainly has the spatial distribution of the fundamental mode as the pump power increases, whereas a four-mode and varying transverse pattern exist in the high branch of power hysteresis as the pump power decreases. The result revealed that the power and spatial hysteresis is controlled by the director axis reorientation and the order parameter modification in twisted-nematic liquid crystals, which is determined by the non-uniform transverse distribution of the intracavity laser intensity.     

Diffractive characteristics of the liquid crystal spatial light modulator

The liquid crystal spatial light modulator (LC SLM) is very suitable for wavefront correction and optical testing and can produce a wavefront with large phase change and high accuracy. The LC SLM is composed of thousands of pixels and the pixel size and shape have effects on the diffractive characteristics of the LC SLM. This paper investigates the pixel effect on the phase of the wavefront with the scalar diffractive theory. The results show that the maximum optical path difference modulation is 41\,$\mu$m to produce the paraboloid wavefront with the peak to valley accuracy better than $\la$/10. Effects of the mismatch between the pixel and the period, and black matrix on the diffraction efficiency of the LC SLM are also analysed with the Fresnel phase lens model. The ability of the LC SLM is discussed for optical testing and wavefront correction based on the calculated results. It shows that the LC SLM can be used as a wavefront corrector and a compensator.     

Computer-generated holograms from 3D-objects written on twisted-nematic liquid crystal displays

In order to optimize computer-generated holograms (CGHs) for three-dimensional objects, an extension of the well known Gerchberg-Saxton algorithm is used. Optical reconstructions using an electrically addressed twisted-nematic liquid crystal display are presented. For arbitrary CGHs, reconstructing 3D-objects, we will discuss the problems and solutions associated with periodic replication of holograms.     

Nonlinear image self-filtering with liquid crystal spatial light modulator

Nonlinear spatial filtering is realized due to the electro-optical effect in spatial light modulators (SLMs). Optical methods with nonlinear filtering are suggested for various optical applications such as optical inspection of photolithography masks, wavefront sensor, etc. A fast optical response of the SLM allows optical inspection with a video (or faster) rate. The optical system proposed is tolerant to the vibrations and temperature variations because of the dynamic properties of the SLM.     

Modulation transfer function of a liquid crystal spatial light modulator

The modulation transfer function (MTF) of a pixelated liquid crystal spatial light modulator (LC-SLM) has been derived as a function of the fill factor. Based on the formula, we have investigated the dependence of the MTF on the orientations and spatial frequency of the input patterns. Furthermore, we have proposed and demonstrated a method for improving the MTF of a LC-SLM.     

Mueller-Stokes polarimetric characterization of transmissive liquid crystal spatial light modulator

In the twisted nematic liquid crystal spatial light modulators (TN-LCSLM), distortion of uniform twist and decrease in tilt angle of liquid crystal molecules on application of an electric field lead to amplitude and phase modulations of the transmitted or reflected wavefront, respectively. The amplitude and phase modulation characterization of TN-LCSLM using Jones calculi is simple and extensively used but does not give any information about important polarimetric parameters such as diattenuation and depolarizance. On the other hand, the characterization using Mueller calculi provides all information in terms of polarimetric properties such as diattenuation, retardance (birefringence) and depolarization. In this paper, polarimetric properties of the transmissive TN-LCSLM (HOLOEYE LC2002) are characterized measuring 17 different Mueller matrices at different addressed gray scale through Mueller Matrix Imaging Polarimeter (MMIP) at 530 nm wavelength. Lu-Chipman polar decomposition for Mueller matrix is utilized to separate out three independent Mueller matrices for diattenuation, depolarization and retardance as a function of addressed gray scale. Further, Mueller-Stokes combined formulation is used to examine the effect of depolarization present in the TN-LCSLM on six different states of polarization and evaluation of eigenpolarization states for the TN-LCSLM has been presented.     

铁电液晶光寻址空间光调制器性能分析

针对氢化非晶硅/铝/铁电液晶结构的光寻址空间光调制器（OASLM）,依据其等效电路模型,利用Pspice和Matlab软件对其分辨率、响应速度、对比度及灰度响应等性能进行了分析。结果表明:在铁电液晶（FLC）层厚度一定的情况下,减小光敏感层（a-Si:H层）的厚度可以提高FLC-OASLM的调制传递函数,从而提高分辨率;在其他参量一定的情况下,FLC-OASLM的响应速度随写入光光强增大而增大（写入光从0.08 mW/cm2增大到10 mW/cm2,延迟时间减小110 s,上升时间减小154 s）,随擦除光光强增大而减小（擦除光从0增大到1 mW/cm2,延迟时间增大41 s,上升时间仅增加3 s）;FLC-OASLM的对比度随控制光光强增大而增大,最终趋于一个稳定值21∶1;在其他参量不变时,随着擦除光光强的增大,输出光响应呈现等级下降,且发现当擦除光光强达到一定值（3 mW/cm2）后,擦除光的改变主要影响下降时间而对上升时间几乎无影响;合理设计激励源信号波形,可以得到超过十级灰度输出,表明擦除光具有实现FLC OASLM的灰度响应的功能。     

Modeling and computer design of liquid crystal display backlight with light polarization film

The article is devoted to elaboration of the model of scattering polarization film like dual brightness enhancement film (DBEF). This model is used for computer design of backlighting system of liquid crystal display (LCD) where light polarization is important. The model elaboration required development of measurement methods and reconstruction of the parameters for the film polarization, development of the accurate computer model of the polarized light scattering on thin surface. The results of design of LCD backlight with polarization film are presented in the article as well. So it was demonstrated that design of backlight devices with DBEF is possible with help of elaborated software.     

基于液晶空间光调制器的光束变换研究

搭建了基于液晶空间光调制器的光束变换光路系统,介绍了一种通过编写程序来实现特定的光束强度分布的方法。利用MATLAB编写了闪耀光栅、菲涅尔透镜、环聚焦透镜、柱面菲涅尔透镜、小孔以及衍射调制板的灰度光栅图,并将其加载于液晶空间光调制器上,成功实现了光束变换。     

反射式液晶空间光调制器用于光束会聚控制

根据偏心透镜组的结构原理,利用液晶空间光调制器(LC-SLM)对其结构进行了优化。对LC-SLM等效透镜功能的原理进行了分析,模拟仿真了利用LC-SLM对光束进行调制的结果。实验验证了LC-SLM通过加载菲涅尔透镜相位图,实现了对光束会聚功能,并且通过耦合位移相位因子可以实现会聚光斑平移的功能,能够代替在偏心透镜组中实现同一功能的透镜。配合后续的透镜组,理论上可以控制光束实现大角度的扫描。     

液晶空间光调制器光谱整形的理论研究

 将液晶空间光调制器用于超高斯种子脉冲光谱整形,重点分析了调制器参数对压缩脉冲信噪比的影响,以此为依据对其结构参数进行优化设计,以降低其影响。对整形、放大及压缩过程的理论模拟表明:应用液晶空间光调制器进行光谱整形时,能够有效克服钕玻璃啁啾脉冲放大系统的非线性效应,在放大器输出端保持原始光谱宽度,但液晶空间光调制器对光谱的调制作用使压缩脉冲信噪比降低。