Phase Modulation Characteristics Analysis of Optically-Addressed Parallel-Aligned Nematic Liquid Crystal Phase-Only Spatial Light Modulator Combined with a Liquid Crystal Display

An optically addressed parallel-aligned nematic-liquid-crystal spatial light modulator (PAL-SLM) has been studied as a dynamic phase-only light modulation device. The phase modulation characteristics of the PAL-SLM using a liquid crystal display (LCD) as an addressing mask were investigated by analyzing diffraction efficiencies resulting from binary gratings projected from the LCD. A more than 2π phase-only modulation depth was achieved. The highest first-order diffraction efficiency of approximately 38% was also obtained; this is close to the theoretical limit. The experimental results of diffraction efficiencies depending on the phase modulation depth are in good agreement with the simulation for the system operation.     

Spatial Temporal Analysis of Electrically-Addressable Phase-Only Spatial Light Modulator

An optically addressed parallel-aligned nematic-liquid-crystal spatial light modulator (PAL-SLM) has been studied as a dynamic phase-only modulation device. A computer control feature of the spatial light modulator is strongly desired for practical applications. For those demands, an electrically-addressable phase-only spatial light modulator has been developed to combine a liquid crystal display (LCD) with a PAL-SLM (LCD-coupled PAL-SLM) and its performance has been reported. However, a temporal characteristic especially two-dimensional (2D) response has not been discussed before. In this paper, 2D response analysis system has been constructed by using a high-speed complementary Metal-Oxide-Semiconductor (CMOS) camera (1000 frames/sec) and the 2D-modulation characteristic of the LCD-coupled PAL-SLM has been observed. As a result, the LCD has a spatially non-uniform modulation characteristic due to a scanning addressing. It has the potential to cause problems in high speed switching for a computer generated hologram. On the other hand, the spatial non-uniformity has not been observed with the LCD-coupled PAL-SLM.     

Oblique-Incidence Characteristics of a Parallel-Aligned Nematic-Liquid-Crystal Spatial Light Modulator

We have developed optically-addressed and electrically-addressed liquid crystal spatial phase-only light modulators having no pixelized structures. We obtained a large depth of phase-only modulation and high diffraction efficiency based on the electro-optical characteristics of a parallel-aligned nematic liquid crystal. These spatial light modulators (SLM) are of the reflection type, so there would be a loss of power in the readout light from the half mirror, which was set up so as to separate the incident and reflected lights. To optimize the characteristics of a reflection type spatial phase-only light modulator, we have proposed an oblique incident optical readout setup. We have examined the effect of conditions such as the polarization direction and the incidence angle of the readout light, and the orientation of liquid crystal molecules in the SLM. High diffraction efficiency close to the theoretical maximum value was obtained by adjusting the above conditions. The simulation analysis can well explain the experimental results of phase modulation.     

液晶相息图用于光学检测

根据液晶的动态响应和位相调制特性,研究了一种利用液晶显示器进行光学检测的检测方法.实验中,把液晶显示器改造为纯位相的空间光调制器,并测定了它的位相调制特性.实验测得：改造后的液晶显示器可实现1 λ(λ=632.8 nm)的调制量.通过引入相息图的方法,实现了液晶空间光调制器的大位相调制量.并产生了调制量为3.4 λ的球面波.最后,利用液晶显示器检测了凸透镜的前表面.检测结果发现,干涉条纹为平行直条纹且PV值为0.32λ.     

基于数字闪耀光栅的位相全息图光电再现优化

针对利用液晶空间光调制器（LC-SLM）进行全息图光电再现过程中,再现像面存在多级衍射像造成单一像能量利用率低的问题,提出了一种在位相全息图中加载数字闪耀光栅的方法,以提高全息图光电再现中单一衍射像的衍射效率.分析了闪耀光栅作为衍射光学元件的特性及其对光波进行位相调制的原理,并阐述了在LC-SLM中加载数字闪耀光栅对位相全息图光电再现时像面能量分布的影响.搭建了基于LC-SLM的位相全息图光电再现实验系统.理论分析表明：在其他条件不变的情况下,加载竖直（或水平）槽向周期为2 pixels的数字闪耀光栅可使 关键词： 全息光电再现 位相全息图 数字闪耀光栅 液晶空间光调制器     

Fast generation of controllable equal-intensity four beams based on isosceles triangle multilevel phase grating realized by liquid crystal spatial light modulator

Liquid crystal spatial light modulator (LCSLM) realizing equal-intensity multiple beams often has some features, i.e., phase valley between two adjacent pixels, flyback region when phase decreases immediately from 2π to 0, and inevitable backplane curvature, which are different from those of most conventional diffractive optical elements (DOEs), such as static DOEs. For optimal intensity uniformity, equal-intensity multi-beam generation must be considered for these artifacts. We present a tunable-grating method in which the intensity uniformity can be improved by considering the LCSLM artifacts. For instance, tuning phase modulation depth of the grating, called isosceles triangle multilevel phase grating (ITMPG), can be used not only to improve the intensity uniformity, but also to fast steer four beams with narrow beamwidths, determined by the same effective aperture of ITMPG. Improved intensity uniformity and high relative diffraction efficiency are demonstrated through experiments with phase-only LCSLM.     

二元光学液晶闪耀光栅的特性分析

在二元光学理论的基础上,结合波动光学理论和液晶指向矢的计算提出一种新的二元光学液晶闪耀光栅设计.对液晶光栅电极施加阶梯分布的电压使之形成相位阶梯形分布,推导出液晶闪耀光栅的衍射效率.结果表明,通过改变周期单元光栅电极数日而改变光栅常数,可以改变光衍射角度,一级衍射角度调节范围0°～10°;调节电极电压可以使特定级次衍射光效率达到90%以上,使该级次得到闪耀.     

用于彩色液晶显示器的色分离光栅的优化设计

利用光栅实现液晶显示器中的色分离可以提高液晶显示器对光能的利用率。为了提高光能利用率,对光栅台阶数进行了优化设计,经矢量衍射理论计算,优化后的多台阶色分离光栅的能量利用率达到了65.3%,与采用滤色片的方法相比,光能利用率提高了近一倍;与三台阶相比,光能利用率提高了9.3%。     

基于液晶空间光调制器的光栅衍射效率

基于Jones矩阵理论和液晶弹性自由能理论，分析计算了扭曲向列型液晶空间光调制器（TN-LCSLM）的复振幅调制特性.以显示一维矩形光栅为例，详细计算了不同输入输出偏振器配置下的一级衍射效率.数值计算结果和分析表明，在加输出偏振器和不加输出偏振器两种情况下都存在一个具有最大一级衍射效率的取向配置.     

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。     

高精度纯相位液晶空间光调制器的研究

研制了平行排列液晶空间光调制器（LC SLM）。论述了平行排列液晶相位调制的理论,进行了计算模拟。对液晶空间光调制器相位调制特性和振幅调制特性进行了测量,实验结果表明,在整个灰度级范围内是纯相位调制的空间光调制器,并且调制的范围可达到0．6λ。在ZYGO菲佐干涉仪上进行了精度特性的研究,得到了非常好的结果,在1cm^2的面积上,进行了畸变波前的调制,其精度峰谷值可达0．098λ,均方根值可达0．017λ。在此精度的基础上产生了π相位差的栅结构,证明了这种液晶空间光调制器可以很好的进行相位调制。     

反射型LCOS器件纯相位调制特性的研究

研究了反射型的LCOS显示器件的相位调制特性.采用2×2的Jones矩阵计算仿真，从理论上分析了它的相位调制特性，建立了一套测量振幅和相位特性的测试系统.它采用He-Ne激光为光源，用干涉仪观察波前相位，将LCOS显示器件作为液晶空间光调制器，用计算机和相关的电路系统驱动控制，并用CCD采样数据，测试了1024×768 LCOS显示器件的相位调制特性.理论和实验的一致性说明了在特定的入射、出射偏振光配制下，LCOS显示器件可以做纯相位调制器. 关键词： 空间光调制器 液晶显示器 反射型LCOS     

可操控二种冷原子或冷分子样品的光学双阱新方案及其实验研究

提出了一种构建可囚禁与操控二种冷原子或冷分子样品的光学双阱的新方案,该方案采用常用的液晶空间光调制器作为分光器件,分光调制函数类似二元相位光栅;对提出的方案进行了模拟实验研究,并研究了从光学双阱到单阱的双向演化过程,该光学双阱的模拟实验结果表明与理论方案相符,双阱的操控性好,有利于二种不同的冷原子或冷分子样品的装载与操控等相关实验研究. 关键词： 原子光学 原子分子囚禁 液晶空间光相位调制器 光学双阱     

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.     

表面摩擦处理对全息聚合物分散液晶光栅电光特性的影响

为了提高全息聚合物分散液晶光栅的衍射效率并降低其驱动电压,改善光栅的电光特性,研究了表面平行摩擦取向对全息聚合物分散液晶光栅电光特性的影响.理论分析认为,改善相分离结构和降低液晶微滴之间的有序度差异是优化光栅电光特性的根本所在.由于进行表面取向处理后的液晶和单体之间达到扩散匹配,使得相分离的程度大幅提高,在衍射能力增强的同时驱动电压也实现了大幅下降,而且,表面取向作用也使光栅内的液晶分子均匀排列,降低了液晶微滴之间的有序度差异,从而减少了光栅的散射损失.实验结果表明:进行取向处理后的光栅其衍射效率由传统光 关键词： 全息聚合物分散液晶 衍射效率 驱动电压     

二维光栅光调制器阵列的光学分析与实验

基于标量衍射理论分析了二维光栅光调制器的衍射特性,提出了投影系统的光学处理方法,利用Matlab软件进行了仿真分析.分析结果表明,二维光栅光调制器的衍射光强分布是单个像素衍射光强的干涉叠加,其分布趋势与单个光调制器的衍射光强分布类似;通过反傅里叶变换可将各个调制器的衍射光重新分开而成像.如果用±1级衍射光的成像,相位为2kπ的调制器在投影面得到一个明亮的像,而相位为(2k-1)π的调制器在投影像面上得到一个黑暗的像.通过一个基于静态微光电系统光栅光调制器的投影光学系统得到了一幅明暗调制的像,证明了光栅光调制器用于投影显示的可行性.     

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.     

基于液晶/聚合物光栅的高转化效率有机半导体激光器

采用有机半导体发光材料聚[2-甲氧基-5-(2-乙基己氧基)-1,4-苯乙炔]作为增益介质,低官能度光敏单体制备的液晶/聚合物光栅作为外部反馈谐振腔,制备出参数可独立控制的分离式结构的有机半导体激光器.液晶/聚合物光栅中液晶分子的取向影响光栅折射率调制量,从而影响光栅的反馈能力,最终影响激光器出射激光的性能.通过研究发现决定液晶分子取向的主要有两种与光栅周期有关的作用力,利用这一原理制备不同周期的光栅,光栅周期小于450 nm时,相分离出的液晶分子取向由光栅矢量方向变为光栅沟槽方向,此时光栅的折射率调制量增加,光反馈能力增强.采用周期为395 nm的液晶/聚合物光栅制备二级布拉格散射的有机半导体激光器,相较于大周期光栅(593 nm)制备的激光器,激光阈值由0.70μJ/pulse降低至0.18μJ/pulse,转化效率由2.5%提高到6.4%,且出射激光垂直于基板表面发射,有利于后续的处理及应用.     

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.     

反射式液晶空间光调制器电控光束偏转

为获得较大的光束电控偏转范围,使用空间分辨力高达8 m的反射式液晶空间光调制器实现了对入射632 nm激光的电控偏转。利用双光束共焦干涉方法测量了液晶空间光调制器的电控相位延迟特性,最大相移量可达3。根据二元光学理论和器件的电控相位延迟特性,设计了周期台阶相位模式和相应的加载灰度图,以最大衍射效率实现对入射光束的闪耀电控偏转。结果表明:相位模式台阶数为8时,可以实现10 mrad的光束偏转,闪耀级次衍射效率可达46%。利用二元光学的衍射模型对影响衍射效率的关键因素进行了分析,认为器件较低的填充因子和周期台阶模式相位重置点诱导的指向矢回程区是限制光束衍射效率的主要因素。