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.     

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.     

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.     

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.     

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.     

Phase measurements of a twisted nematic liquid crystal spatial light modulator with a common-path interferometer

We present a novel and high accuracy (±1°) technique for measuring the difference in phase delay between the positive and negative eigenvectors of a twisted nematic liquid crystal spatial light modulator (LCSLM) as a function of applied voltage. We show a new architecture for a common-path interferometer where we simultaneously generate both the positive and negative eigenvectors of the LCSLM. We use an electro-optic light modulator to provide a time varying phase shift between the two eigenvectors and measure the phase delay difference between the two eigenvectors. We compare the phase delay values with those obtained using a Mach–Zehnder interferometer and find good agreement.     

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。     

液晶空间光调制器在光信息综合实验中的应用

提出了一种把液晶空间光调制器应用于光电信息综合实验的光学实验系统。系统中的空间光调制器采用光寻址液晶光阀和电寻址液晶光阀。给出了利用这一系统开设的四个光学信息处理实验。实践表明,该系统具有较好的教学效果。     

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.     

利用纯相位型液晶空间光调制器实现空心光束

为了提高激光系统的整体效率,需要将出射光强整形为空心分布。采用纯相位型液晶空间光调制器整形近高斯分布光强到空心分布。基于能量守恒定律和等光程原理,分析了纯相位型液晶空间光调制器光束整形系统,得出了整形系统所需的相位分布。采用衍射光学方法,数值模拟了整形效果,讨论了入射光束束腰半径和强度分布等因素对整形效果的影响。利用纯相位型液晶空间光调制器实验实现了空心光束,实验测得的转换效率大于99%。     

利用纯相位型液晶空间光调制器实现空心光束

为了提高激光系统的整体效率,需要将出射光强整形为空心分布。采用纯相位型液晶空间光调制器整形近高斯分布光强到空心分布。基于能量守恒定律和等光程原理,分析了纯相位型液晶空间光调制器光束整形系统,得出了整形系统所需的相位分布。采用衍射光学方法,数值模拟了整形效果,讨论了入射光束束腰半径和强度分布等因素对整形效果的影响。利用纯相位型液晶空间光调制器实验实现了空心光束,实验测得的转换效率大于99%。     

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.     

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℃.     

纯相位液晶空间光调制器拟合泽尼克像差性能分析

纯相位液晶空间光调制器作为波前校正器构成的高分辨率、低能耗、价格低廉、易于控制的自适应光学系统受到越来越多的关注.作为一种新型波前校正器件,它对波前像差的校正能力是反映其在自适应光学系统中应用的一个重要的指标,因此有必要仔细地研究它对各种像差的校正能力,以确定其可能的应用范围.波前校正器对各阶泽尼克像差的拟合效果有效地反映了该器件对不同像差的校正能力.利用256×256像素的纯相位液晶空间光调制器(LC-SLM)产生不同系数的前36项泽尼克像差分析LC-SLM对不同像差的校正能力.讨论了填充因子、离散像素 关键词： 液晶空间光调制器 相位调制 自适应光学 泽尼克多项式     

Application of a liquid crystal spatial light modulator on optical roughness measurements by a speckle correlation method using two refractive indices

A system of roughness measurements using a CCD camera and a liquid crystal spatial light modulator (LCSLM) has been developed. The scattered light patterns from the surface, which is covered by liquids with several different refractive indices, are acquired by the CCD camera and stored in a frame grabber in a computer. The superposition of two arbitrary patterns is calculated by the computer and displayed on the LCSLM. It is then illuminated by coherent light to produce interference fringes of equal inclination at infinity. The surface roughness can be determined through the relationship between the fringe visibility and the difference of refractive indices. The performance of this system is estimated by experiments.     

液晶空间光调制器在阿达玛变换光谱仪中的应用研究—编码模板缺陷的补偿措施

论述了液晶空间光调制器作为固定不动的编码模板在阿达玛变换光谱仪中的应用,对编码模板的缺陷进行了研究,提出了编码模板缺陷的补偿措施.模拟实验证明了我们给出的补偿措施是正确的.     

铁电液晶光寻址空间光调制器响应速度的宏模型研究

将铁电液晶(FLC)的本征电路模型扩展到以FLC为调制层,a Si∶H为光敏层的光寻址空间光调制器(OASLM),建立了FLC OASLM的宏模型。用电路方法模拟了控制光强度以及外部激励信号的特征参数对FLC OASLM响应速度的影响。模拟结果表明,FLC OASLM的响应速度随写入光强度和激励信号幅度的增大而加快,随擦除光强度和激励信号频率的提高而减慢。同时,激励信号存在一个上界频率,当频率参数取值超过界值时,响应峰值迅速下降。     

用液晶空间光调制器产生光阱阵列

液晶空间光调制器能够方便地用于制作各种衍射型光学元件, 但液晶空间光调制器存在分辨率有限的缺点, 本文提出了用液晶空间光调制器制作相位型光栅, 产生一维和二维光阱阵列的新方案, 用迭代傅里叶级数算法优化设计光栅的相位分布, 在不改变空间光调制器硬件参数设置的情况下, 充分利用和发掘了空间光调制器的优点, 同时又能较好地回避其所存在的缺陷. 根据现有的空间光调制器的技术参数, 模拟仿真设计光栅, 计算光强分布, 结果表明: 用大失谐、小功率激光照明, 能够产生具有很高峰值光强和光强梯度的光阱阵列, 囚禁冷原子的光学偶极势达到mK量级, 对原子的作用力远大于原子的重力.     

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.