基于LCD空间光调制器全息显示的若干问题研究

【作者】 张晓洁；

【导师】 刘旭；

【作者基本信息】 浙江大学 ， 光学工程， 2007， 博士

【摘要】 全息显示技术是迄今为止表现物体信息最完整的一种显示方法，由于这种技术保留了物光波的全部振幅和位相信息，人们在观察全息三维像时就会得到与观察原物时完全相同的视觉效果，获得所有的视觉深度暗示。随着实时显示要求的提出，结合空间光调制器和计算全息的数字全息技术开始发展，该技术无需传统的全息干板和严格的制作过程，具有数字化、可程控、实时方便的特点，是未来全息显示发展的主流方向。本论文对基于液晶空间光调制器的全息显示系统的相关问题进行了研究，内容涵盖理论研究、软件仿真、系统实现、实验论证和特性分析等各方面，取得了一些较有意义的成果。对扭曲向列型液晶器件用于纯位相调制进行了研究。结合前人的研究结果分析了扭曲向列型液晶器件制作纯位相调制器的可行性，并利用琼斯矩阵计算了不同的输入输出偏振态下液晶器件的电光特性；从液晶器件的本征矢量理论出发，通过计算模拟和实验验证获得了系统的纯位相调制状态。研究表明，引入四分之一波片可以得到液晶器件的平均本征矢量，从而获得系统在工作电压范围内的纯位相调制结构，并在LCD纯位相调制系统中再现了位相全息图，获得了较高的衍射效率。提出了主菲涅尔波带法计算三维物体的全息图，并完成了基于LCD的全息再现系统实现，获得了三维全息像的再现和无狭缝全息图的白光再现。介绍了主菲涅尔波带法的原理、流程和适用场合，该算法改变了依赖二维图计算三维全息的做法，直接对三维物点进行计算，减少了信息冗余；建立了以液晶屏为核心的全息再现系统，获得了三维全息像的再现并对其进行了特性分析；实现了无狭缝全息图的白光再现，获得了较好的显示效果，并和彩虹全息图的再现进行了比较。研究了液晶空间光调制器在全息显示系统中的相关特性，讨论了LCD的物理结构和空间分辨率对全息显示的影响。理论分析了由于液晶屏的“黑栅”结构和像素开口率而导致的再现像的阵列衍射现象；运用像素分割法模拟了全息图加载至LCD后的再现像场，从而用差分补偿方法来消除“黑栅效应”，达到了预期的效果；分析了液晶显示屏的有限分辨率对记录全息图的影响，提出了对参考光角度、物距和物体大小等参数的要求。更多还原

【Abstract】 Holography is a most attractive method of displaying 3D images because a single hologram includes all intensity and phase information of the object. When observing the volumetric images by the naked eyes, people can obtain all the accurate depth cues similar to the original object. With the demand of real-time display, digital holography combining the spatial light modulator (SLM) and computer-generated holography is developing, which is without of the strict recording system and the long film exposure and development process. This holographic technology has the advantages of digitization, programmable, real-time and convenience, and is the main developmental direction of the holographic display region in the future.In this paper, some relevant issues of the holographic display system based on the liquid crystal spatial light modulator is studied, concerning the theoretical study, software simulation, system realization, experimental discussion and characteristics analysis, et al. Considerable staggered progress has been made.The phase-only modulation characteristics of twisted-nematic liquid crystal device (TN-LCD) are studied in Chapter 2. Combining the research of predecessor, we analyzed the feasibility of the application of TN-LCD for phase-only modulator, and calculated the opto-electronic property of LCD with the different polarization state of incident and emergent light using Jones Matrix. Based on the theory of polarization eigenvectors, we obtained the phase-only modulation of the TN-LCD system. The study shows that the elliptically polarized eigenvectors can be generated by using a quarter wave plate at both sides of the LCD, then a configuration of phase-only modulation is achieved. The experimental results are also obtained, which proved the phase hologram has higher diffraction efficiency than amplitude hologram.In the Chapter 3, the master Fresnel zone algorithm to calculate the hologram of the three-dimensional objects is proposed which is different from the common ways depending on the 2D projections or sectional drawings. The principle, flow and applicability of the master Fresnel zone algorithm is introduced, which acts the 3Dpoints as the computational objects. The holographic reconstruction systems based on LCD are set up, and the no-slit hologram with the illumination of white light and the 3D holographic images are reconstructed, whose characteristics are analyzed.The limiting aperture opening ratio of the pixels and the matrix structure of the LC-SLM lead to the reduplicate images on the reconstruction plane. We simulated the reconstruction of the hologram displayed on the LCD by ’Splitting Pixel Method’, and put forward the ’Differential Compensation Method’ to eliminate the diffractive effect, obtaining the considerable result. The effect of the limited spatial resolution of the LCD on the recording process is studied, and the demands of the reference light’s angel, the dimension of the object and the distance between the hologram and object are proposed.更多还原