【作者】 郑华东；

【导师】 于瀛洁；

【作者基本信息】 上海大学 ， 机械电子工程， 2009， 博士

【摘要】 真实地再现三维(3D)物场是成像技术的重要发展趋势,而全息显示的特点正是能够在空间再现具有真实立体感的3D影像。近年来,基于空间光调制器的数字全息3D立体显示技术的研究逐渐受到重视。本文在对该技术目前的研究现状和存在的问题进行分析的基础上,开展了相关的研究工作,主要内容涵盖计算全息理论与算法研究、真彩色3D物体的全息计算方法、器件的特性分析、系统构建及实验研究。在对典型的编码方式的再现效果进行综合分析的基础上,突出了相息图编码方式因其具有高衍射效率且再现时无共轭像的特点,而在数字全息显示中的重要地位。将“混合遗传-模拟退火”算法(GA-SA)的思想引入到位相全息图的优化设计中,并对典型的全息图优化算法(包括GA-SA算法)的优缺点进行了分析和归纳。对优化算法的进一步研究具有指导意义。为了获得良好的3D再现效果,本研究在对典型的3D物体全息图计算方法的原理和和特点进行分析的基础上,提出了一种新的3D物体全息图计算方法——“动态随机位相层析法”。利用该方法计算3D物体的相息图,能够有效地抑制3D再现像的噪声,且具有衍射效率高、无零级斑和共轭像的特点。并采用峰值信噪比(PSNR)和互相关系数(CC)对算法的噪声抑制效果进行评价,验证了该方法的有效性。为了实现真彩色3D物体的全息显示,本研究提出了两种计算RGB真彩色相息图的方案——“等距方案”和“等像素总量方案”。在此基础上,结合动态随机位相层析法,实现了真彩色3D物体多视角相息图的计算和数值再现,并对两种计算方案的各自特点进行了对比分析。在利用空间光调制器(SLM)对位相型全息图进行再现时,为了使位相型全息图获得良好的再现效果,要求SLM具备纯位相(或接近纯位相)的调制能力。本研究对数字微反射器件(DMD)以及LC-R2500 (LCoS-SLM)的振幅和位相调制特性进行了测试和比较分析,表明LCoS-SLM在适当的器件配置和参数设置时能够实现纯位相调制,有利于位相型全息图的正确再现。在此基础上,分析了RGB各分量的调制特性曲线对多阶位相型傅立叶变换相息图再现效果的影响,并提出了“灰度映射法”对位相型全息图进行矫正,以改善相息图的再现效果,并通过数值再现验证了该方法的有效性,为进一步改善相息图光电再现效果提供了新思路。从理论上分析了LCoS-SLM的像素开口率和像素间距对衍射场分布的影响,并探讨了改善再现像强度的均匀性、增大再现像的尺度以及提高光能利用效率的途径。针对利用LCoS-SLM对位相型全息图进行光电再现时,栅格效应导致单一再现像的能量利用效率较低的问题,本研究提出了在位相型全息图中加载特定周期和特定槽向的“数字闪耀光栅”的方法,提高了再现像的强度和光能利用效率。从理论上分析了光电再现时,实际再现距离和再现像的尺寸与全息图记录(或计算)时的真实值存在偏差的影响因素,为数字全息光电再现系统的设计提供了理论依据。对采用本研究提出的动态随机位相法计算的相息图进行光电再现,结果表明:该方法能够对光电再现像的噪声进行有效地抑制。分析了在对RGB真彩色3D物体进行全息光电再现时,各分量相息图再现像存在空间位置偏差(即色差)的影响因素,提出了在相息图中加载特定周期和槽向的数字闪耀光栅以及特定焦距的数字菲涅耳透镜的方法,对RGB各分量再现像的空间位置偏差进行矫正,并进行了实验验证。更多还原

【Abstract】 The important trend of display technologies is to display real-existing three-dimensional (3D) images. More and more attentions are now paid on 3D electro-holographic display (3D-EHD) because of its capability of reconstructing real-existing 3D images. Some researching works associated with 3D-EHD are described in this paper, including theories and methods of computer holography, algorithms for calculating computer-generated hologram (CGH) of true-color 3D object, characteristics analysis of the spatial light modulator (SLM), establishment of 3D-EHD system and experiment for displaying true-color 3D images. They are described in detail as follows:Basic theories and typical methods of computer holography are described, and comprehensive analysis is carried out for some typical coding methods in computer holography. Analytical result shows that, kinoform is an important coding method in electro-holographic display for its advantages such as high diffraction efficiency, without twin image in image-plane. Genetic simulated annealing algorithm (GA-SA) is introduced to CGH calculation. Typical optimization algorithms for CGH calculation are compared by considering convergence, efficiency and adaptability.Typical algorithms for calculating the CGH of 3D object are introduced. A novel algorithm is proposed and named as dynamic-pseudorandom-phase tomographic computer holography (DPP-TCH), in order to reduce speckle noise, improve diffraction efficiency and eliminate twin image. The qualities of digital reconstructed images are evaluated with peak signal-noise ratio (PSNR) and correlation coefficient (CC). Two strategies, named as“Equidistant Strategy”and“Pixel Number Equalized Strategy”, are proposed for calculating CGHs of true-color object, and their characteristics are also analyzed. Multi-angle kinoforms of the true-color 3D objects are calculated and digital reconstructed RGB true-color 3D images are obtained by use of DPP-TCH and the calculation strategies.Phase-only or approximately phase-only modulation is needed to realize correct reconstruction of phase hologram. The amplitude and phase modulation properties of digital micro-mirror device (DMD) and LC-R2500 (LCoS-SLM) are measured. Analytical results show that, LC-R2500 can realize phase-only modulation under special system configurations and settings, and it can be used for phase hologram reconstruction. The modulation curves of LCoS-SLM are measured under different situations, such as different wavelengths used for RGB true-color holographic display, different incident angles and polarizing angles of laser beams. Phase-only modulation (POM) mode is then realized in order to meet the requirement of phase hologram reconstruction. The effects of phase modulation curves on the reconstructed images are also analyzed under POM mode. Gray level mapping (GLP) is proposed to adjust the gray level of each pixel in phase holograms, and the factors influencing the error between theoretical calculation and experiment result are analyzed, which can guide further optimization of optoelectronic reconstruction for phase holograms. The effects of aperture ratio and pixel pitch on the diffraction pattern are analyzed theoretically, and approaches are discussed for improving the intensity uniformity of image, enlarging the size of image and improving the utilization ratio of light power.A novel method is proposed to improve the intensity of reconstructed image by superposing digital blazed grating (DBG) with phase hologram in optoelectronic reconstruction system based on LCoS-SLM. The effects of superposing DBG with different grating periods and orientations on the position and intensity of reconstructed image are also analyzed. Experimental results also verify that, by the proposed method, the intensity of reconstructed image is increased and the utilization efficiency of light power is improved. Theoretical analysis is carried out for the differences of position and size between optoelectronic reconstruction and digital reconstruction, which can guide the design of optoelectronic display system. Experiments are carried out for true-color 3D holographic display with the system and kinoforms calculated by DPP-TCH. The results also show that the speckle noise of reconstructed images can be reduced significantly by use of DPP-TCH. Factors influencing the position deviations of the reconstructed RGB section images are analyzed. A novel method is proposed to correct the deviations by superposing DBG with proper grating period and orientation, and digital Fresnel lens (DFL) with proper focal length in the kinoforms. Theoretical calculation method is described, and experimental results verify that the proposed method is feasible.更多还原