A novel three-dimensional holographic display system based on LC-R2500 spatial light modulator

A novel holographic display system is proposed in this paper. The system takes LC-R2500, a kind of reflective liquid crystal spatial light modulator, (LC-SLM) as the core display unit, which can meet the requirement of real-time reconstruction of three-dimensional (3D) objects from holograms in free space. The relationship between hologram recording and image reconstruction is discussed, and the parameters associated with the magnification of reconstructed image over original object are determined. Experimental results of holographic display using the system are also given in the end.     

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.     

Smart pixels in a focal-plane image compression system

Image compressors improve the handling of image data in image-processing systems. In our proposed image-compression system, we employ a smart complementary metal oxide semiconductor (CMOS) sensor and an integrated spatial light modulator (SLM) and then the optoelectronic architecture performs a large part of image-compression processes. Each pixel of the integrated SLM consists of multiple modulation pads; the integrated SLM then performs decoding and optical D/A conversion. A paired configuration of the smart CMOS sensor and the integrated SLM transforms optical analog signals into electronic digital signals. A theoretical analysis showed that the error ratio of the proposed systems was 3%.     

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.     

基于空间光调制器与CCD的衍射和干涉定量实验

利用空间光调制器与CCD摄像机,取代传统的光刻掩膜板及白屏,构建成新型光衍射与干涉定量实验系统,将PC机软件绘制的狭缝小孔等衍射图案传输至空间光调制器,用CCD接收其远场衍射和干涉图样,再用PC机处理图像,做定量分析.可验证狭缝和圆孔衍射公式;对形状和空间关系复杂的异形孔,也可方便地实现衍射干涉图样的观察存储与测算.     

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.     

一种三维全息图的数字化实现方法

提出一种实现三维显示的新方法,从两步法彩虹全息基本原理出发,通过分区域分幅的方式对多视角图形的波前进行数字化编码,获得夫琅和费光场分布,在位相型硅基液晶空间光调制器上按视角顺序输入该信息,利用透镜的傅里叶变换特性再现多视角子图像,干涉法逐区域拼接获得完整三维图像.最后通过实验获得了三维图像样品,验证了该方法.本方法可成为三维显示的重要技术手段.     

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.     

Pixel size and pitch measurements of liquid crystal spatial light modulator by optical diffraction

We present a simple technique for the determination of pixel size and pitch of liquid crystal (LC) based spatial light modulator (SLM). The proposed method is based on optical diffraction from pixelated LC panel that has been modeled as a two-dimensional array of rectangular apertures. A novel yet simple, two-plane measurement technique is implemented to circumvent the difficulty in absolute distance measurement. Experimental results are presented for electrically addressed twisted nematic LC-SLM removed from the display projector.     

Light efficiency of liquid crystal spatial light modulator using,for wavefront corrector in AO

Liquid crystal spatial light modulator (LC-SLM) has a series of attractive characteristics as a wavefront corrector in adaptive optics system such as compactness, high density integration, low cost and possibility of batch production. However it also suffers from several drawbacks such as low light efficiency. We present an analysis of the light efficiency of the phase by only using LC-SLM for wavefront corrector in AO system. The factors of polarization sensitive, pixel grid structure, phase quantization and limited phase stroke are discussed in theory. Simulation results are given based on a math model of a LC-SLM. The intensity variation results from pixel structure are measured. The light efficiency of the LC-SLM is tested for generating a series of Zernike aberrations. The effect of phase wrapping method is analyzed and tested. We demonstrate that the light efficiency reduces these factors. Experiment results from the use of the phase only liquid crystal spatial light modulator confirms these conclusions.     

Compatibility of temporal multiplexed spatial light modulator with optical image processing

The tendency today is to replace high-dynamic light modulators by high-speed binary ones (of which the micromirror is the best example). This kind of spatial light modulators (SLM) fulfils all the present needs in displays. They are used in optical communications as binary systems and also in display applications (video projectors) with temporal multiplexing, in order to generate greyscale or colour images. In optical processing, and in the majority of coherent applications, temporal dithering introduces some distortions. In this paper, this point is studied with simulations. We point out that temporal multiplexing cannot be used in the Fourier plane. In the imaging plane, the distortion is weak if the filter has a positive impulse response.     

基于细菌视紫红质薄膜的空间光调制器实验研究

阐述了利用细菌视紫红质薄膜（BR薄膜）优良的非线性光学特性作为光寻址的空间光调制器的实验研究.BR有两个重要的光敏中间态（B态和M态），其吸收带（B态吸收峰为570nm，M态吸收峰为412nm）重叠区域较少，利用其正向（B→M）和逆向（M→B）光反应之间转化关系和B态与M态的差异吸收实现了相干光学图像到非相干光学图像的转换实验.采用经基因改性的细菌视紫红质薄膜（BRD96N）材料，使用670nm相干光作为写入光，530nm非相干光作为读出光，得到了分辨率约为200 lines/mm，对比度约为2.1∶1的 关键词： 光寻址空间光调制器 细菌视紫红质薄膜（BR薄膜） 非线性光学特性 相干光与非相干光图像相互转换     

反射式电寻址红外切变聚合物网络液晶空间光调制器

为了给高帧频红外成像导引头半实物仿真提供高帧频、宽光谱、大动态范围的红外场景,利用切变聚合物网络液晶(SPNLC)电光调制机理制作了反射式电寻址SPNLC空间光调制器.通过LabView编写控制程序,利用计算机并口数据寄存器和控制寄存器为译码放大电路提供写入信号,驱动SPNLC盒各像素,实现红外图像的显示.实验得到厚度为13 μm的反射式电寻址红外SPNLC空间光调制器,当入射辐射的黑体温度为300℃,驱动电压为60 V时,测得样机所显示的几幅长波红外图像(8 μm～12 μm) 的帧频为100 Hz,输出最大温差大于15℃.     

Measurement of phase and intensity by Dual-imaging Interferometry for performance evaluation of liquid crystal spatial light modulator

In order to evaluate the performance of liquid crystal spatial light modulator Dual-imaging Interferometry is proposed by introducing a dual-imaging system into Michelson interferometer to obtain phase and intensity for the measurement of multiple parameters. The feasibility of the proposed method is verified through theory analysis and experiments. Experimental results indicate that the range of phase shift is from 0 to 2.07π, the nonlinearity of phase shift curve is 3.02% and the RMS of phase nonuniformity is 0.07π. The rising and fall time are 13 ms and 16 ms, respectively. Dual-imaging Interferometry can be used to measure multiple parameters on one experimental setup in place of conventional methods and avoid the complicated operation and extra errors resulting from arranging different experimental setups.     

利用空间光调制器实现计算全息三维显示

针对目前三维物体计算全息算法数据量大、计算速度慢及共轭像影响再现效果问题,提出一种全息体视图计算方法。根据人眼双目视差立体视觉原理,由摄像机获取三维物体不同角度的二维序列视差图像,通过计算全息算法得到多视角全息图,合成三维物体全息体视图。在迭代傅里叶变换算法的基础上,采用预设初始相位并增加反馈因子的方法,提高相息图的计算效率。基于液晶空间光调制器构建光学系统,对计算的全息体视图进行了光学再现。结果表明:该方法有效地排除了共轭像的干扰,相息图的迭代计算效率提高30%以上,再现图像与目标图像的结构相似度大于0.85。     

基于硅基液晶微显示立体投影光学引擎的设计

从平衡两路图像对比度的角度,采用双硅基液晶(LCoS)芯片设计了一种实用的微型立体投影光学引擎。光学引擎中双LCoS芯片分别用于调制左右眼的图像,一个白光LED作为投影光源,两个标准的MacNeille偏振分光棱镜(PBS)用于产生两路偏振方向相互垂直的高偏振度光束。整个引擎设计简单,结构紧凑,其尺寸约为105mm×28mm×25mm。测量了本设计中光学引擎的各部件的实际参数值,根据所测量的数据通过理论计算得到:左右两光路的对比度完全平衡且均为64…1,光效率均为3.61%,整机的光通量为20lm。     

基于液晶纯相位光调制器的4f系统去噪方法

分析了4f系统的噪声来源,提出使用液晶空间光调制器实时去除系统噪声.通过使用Zemike多项式拟合透镜等光学器件引入的像差,根据液晶纯相位光调制器利用位相共轭波进行静态波面校正的工作原理,提出了一种新的相位校正算法,模拟仿真美国BNS公司反射式256×256纯相位液晶空间光调制器,通过重构并逼近畸变波面,产生相位共轭波...     

Analysis of influence of black matrix effect in spatial light modulator on optical correlation detection

Motion detection with a joint transform optical correlator is based on the maximally correlated bright spots in a correlation image; therefore, the quality of a correlation image greatly influences optical correlation detection. As the core component of a joint transform optical correlator, a spatial light modulator has an opaque part (black matrix structure) that is an important factor that needs to be considered. In this paper, we first analyzed the effect of the fill factor on the light energy distribution in the image plane according to the mechanism of the spatial light modulator using a multiple-subpixel matrix to simulate a single pixel, while zeroing some subpixels to simulate the black matrix part in the single pixel and employing computer software to simulate the joint transform optical correlator to obtain the simulated correlation image result with a black matrix effect. In addition, we built an experimental setup to obtain an actually photographed correlation image, which was well consistent with the simulated result.     

基于互信息的高动态范围成像系统成像质量分析

为了优化高动态范围成像系统的设计,完善地评价系统性能,将信息论应用于高动态范围成像系统中,把高动态范围成像系统看作通信系统,采用端到端的互信息量来评价高动态范围成像系统的成像质量.在COMS采样成像模型的基础上引入空间光调制器反射式硅基液晶的影响,建立了基于互信息的高动态范围成像系统数学模型.利用该模型分析了反射式硅基液晶与CMOS阵列像素数比、像素开口率、相对平移、相对旋转对系统互信息量的影响及造成系统成像质量下降的原因.通过仿真计算,分别得到了像素数比例、像素开口率大小、相对平移量、相对旋转角度与互信息量的相互关系曲线,并定量分析了这些因素变化对系统互信息量的影响程度.仿真结果表明反射式硅基液晶和COMS阵列的最佳匹配条件是：反射式硅基液晶和CMOS像素的占空比尽可能大,CMOS像素尺寸尽可能小,避免相对平移和相对旋转,反射式硅基液晶像素数和CMOS像素数之比为1:1.     

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.