【作者】 董磊；

【导师】 明海； 王安廷；

【作者基本信息】 中国科学技术大学 ， 光学， 2013， 博士

【摘要】 伴随着激光技术、液晶技术等的迅速发展,显示技术的发展也是日新月异。激光显示、三维显示已经成为现在显示中重要的研究方向。然而这些显示技术本身依旧存在着诸多问题,诸如激光散斑严重限制成像质量、三维显示裸眼显示串扰严重、片源偏少等严重制约着这些技术在市场上的推广。本文以激光显示为主线,建立了激光显示系统中的散斑模型,研究了光源的统计特性对散斑性质的影响,分析了直接投影式激光显示系统中散斑的特点,并针对这些特点研究了振动式和非振动式散斑抑制方案。散斑测量是研究散斑抑制、散斑追踪重要的实现手段,但并没有被系统的研究分析过,本文实验分析了测量仪器参数对散斑测量的影响,并对拍摄到的散斑图样进行处理,降低噪声。三维显示中裸眼显示是立体显示的发展趋势,多视角立体显示在降低图样串扰、提升图像立体感方面有着独到的优势,但是片源稀少成为发展的瓶颈,基于此本文研制了一种双视角图样转换成多视角图样算法。为了满足家庭应用立体显示的需求,我们开发了一套激光单投影偏振旋转立体显示系统。本论文的主要研究工作概述如下：1.详细阐述了激光散斑理论,介绍并归纳了激光散斑的统计特性,分析了光源时间相干性和空间相干性对散斑性质的影响。通过理论模拟验证了空间相干对散斑抑制的效果：当两束非相干光源之间的夹角正弦值大于成像系统的数值孔径时,两光源之间的相干性最低。分析了散斑与投影面的依赖关系,通过理论和实验证明,散斑对比度大小与散射体的厚度成反比,当投影屏幕厚度到0.5cm时,对比度由0.25下降到0.15。2.分析了直接投影式激光投影系统中散斑的特性,归纳总结了目前常见的散斑抑制方案。推导出使用漫射体抑制散斑时,散斑对比度的大小与照射在漫射体上的光斑大小的平方根成反比。在此基础上,针对于大型投影系统提出利用压电陶瓷和介电弹性调节器振动位相片来进行散斑抑制,可以将散斑对比度分别抑制到0.06和0.1,完全满足观众观看时对图像质量的要求；针对于小型投影系统,提出采用电控聚合物分散液晶和液晶改变空间光偏振态的方案进行散斑抑制,进行理论计算和实验验证,可以将对比度抑制为原先的60%,能够作为现有散斑抑制方案的一种有力补充。综合上述几种散斑抑制方案,可以将对比度最终抑制到0.04以下,实现人眼观察激光光源图样时观看不到散斑图样。3.为了解决散斑测量没有一个通用标准的问题,对测量仪器的参数(如f数、距离、角度、积分时间、离焦程度)与对比度之间的关系通过实验进行量化。分析人眼的独特结构以及会对散斑观察造成的影响,并通过Zemax进行模拟验证。然后搭建了一套模拟人眼结构的散斑测量系统以期对散斑进行标准化测量。对拍摄到的散斑图样进行算法处理：包括利用傅里叶变换去除拍摄过程中由于空间光调制器产生的周期性结构噪声,拍摄用彩色CCD引入的插值噪声的处理。并提出一种新型的散斑对比度计算方案：利用彩色CCD所拍摄到的滤色片后真实的色彩值来计算散斑对比度,并通过实验验证。而且提出一个新的物理量：对比度噪声比来表征散斑图样中图像的清晰度。4.详细介绍了裸眼立体显示和佩戴眼镜式立体显示的工作原理,分析了多视角裸眼立体显示系统相对于两视角立体显示系统在降低串扰、增强深度感等方面的优势。对于目前多视角立体显示片源匮乏的现状,详细研究了SIFT算法的工作机理,在此基础上提出了利用SIFT算法和深度计算算法来插值重建出多视角的视差图样,实现了两视角立体图样转换为多视角立体图样的算法。针对于家庭用立体显示系统,搭建了一套激光光源的、液晶偏振单投立体显示系统,对于系统中的关键器件如液晶偏振器、背投屏幕进行分析,并对存在的问题提出了理论解决方案,以期在下一阶段的工作中加以改进完善。本文的创新点主要包括：1.提出了利用压电陶瓷、介电弹性调节器、电控聚合物分散液晶和控制液晶相位变化等进行散斑抑制的方案并进行实验验证,实验得出了散斑抑制的效果、所采用液晶性质的要求、设计的改进之处等,为下一步的实验改进提供了依据。2.模拟了人眼系统对散斑观察的影响,实验研究了测量仪器参数对散斑对比度的影响,搭建了一套模拟人眼的散斑测量系统用于测量。对拍摄到的散斑图样进行去噪声处理,去除了存在的空间噪声和颜色噪声,对彩色散斑测量中滤色片对散斑的影响进行分析,并提出了一种新型彩色散斑对比度计算方法。3.提出了双视角立体图样转化为多视角立体图样的算法,部分解决目前多视角立体图样匮乏的问题；搭建了一套激光光源的、液晶偏振单投立体显示系统。分析了激光直接投影式显示系统散斑的形成机理,对于光源的位置、光斑照射在漫射体上的大小以及投影屏幕的性质对散斑的影响进行了理论推导并进行了实验验证,结论对于投影系统设计有着很好的指导作用。更多还原

【Abstract】 With the rapid development of laser and liquid crystal technology, display technology has also been developed very fast. Laser display and three-dimensional (3D) display have become an important part of modern display technology. But there are lots of problems which prevent these technologies becoming popular in the market, for example, the image quality is very poor in laser display because of speckle, the cross talk and lack of film sources make the auto-stereoscopic can’t go into families. Speckle is a phenomena which is result from laser’s high coherence, it reduce the resolution of images. To reduce speckle, the model of speckle in laser display system has been established, the influence of laser source’s statistical properties on speckle have been studied, the feature of speckle in laser projection system has also been studied, and two kinds of speckle suppression methods have been proposed based on the features. Speckle contrast is the basement of speckle reduction and speckle sensing technology, but the contrast measurement hasn’t been standardized. The influence of parameter of CCD has been investigated and the images of speckle photo by CCD are also been analyzed and the noise caused by spatial light modulator (SLM) and color filter array (CFA) are suppressed by algorithms. Auto-stereoscopic is the development trend of3D display, the multi-view point has lots of advantages such as low cross-talk, high sense of depth, but lack of film sources makes it not be popular. To fix this problem we developed a single projection3D display system using laser resource.The main research works are as follows:1. Laser speckle theory is introduced in detail, the statistical properties are analyzed and the influence of laser coherence properties on speckle has been studied. It has been proved that when the sinusoidal of the angle between two incoherence light sources is less than the number aperture of imaging system, the coherence between the two light sources is the least. And the dependencies between speckle and projection screen is analyzed, after theoretical simulation and experimental verification, it has been proved that the speckle contrast is inversely proportional to the thickness of rear projection screen, 2. The characteristic of speckle in laser projection system has been analyzed, the most common methods of speckle suppression have been summarized. And it is proved that when speckle is reduced with diffuser, the speckle contrast is inversely proportional to the square root of the spot illuminated on the diffuser. On this basis, the set up using piezoelectric ceramics (PZT) and dielectric elastomer actuators (DEAs) vibrating the diffuser in the larger projection display system have been designed, and the speckle contrast is reduced to0.06and0.1, which satisfied people’s watching needs. And in the smaller projection display system, electronic controls Polymer Dispersed Liquid Crystal (PDLC) and liquid crystal modulates spatial polarization state have been proposed, the theoretical simulation and experimental have been verified, these methods can be supplement of the current speckle reduction methods.3. To resolve the problem of speckle measurement standardization, we test the relationship between parameter of charge-coupled device (CCD) such as f-number, distance, angle, integration time, defocus and speckle contrast in experiment. To simulate human eyes’characteristic an eye model is designed with Zemax and the influence of eyes on speckle is also analyzed. Thus a standardized speckle measurement system is set up with human eyes’ property. The noise in the image shoot by this system has also been suppressed, including removing the array noise which is result from the SLM by Fourier translation, the suppression of the noise introduced by the CFA and experiment is also verified. And a new evaluation criteria is introduced to judge the image clarity.4. The principle of auto-stereoscopic display and glasses-stereoscopic display are introduced clearly, the advantage of auto-stereoscopic in reducing cross-talk, enhancing depth sensing are analyzed. A new algorithm is developed to solve the question that lack of multi-view point movie. This algorithm is based on SIFT algorithm and depth calculation algorithm, and it achieve to change two-view point figure into multi-view point figure. To meet the needs of family life, a single projection3D display system using laser resource is developed; the performance of key element such as SLM, LC polarizer, rear screen is analyzed. The shortage of this system is also analyzed and the theoretical solutions is put forward which can guide the next stage’s experiment work.Highlights of the dissertation are as follows:1. A new algorithm is developed to change two-view point figure into multi-view point figure. A single chip rear projection display system with the laser resource is built, the shortage of this system is also analyzed and the theoretical solutions is put forward which can guide the next stage’s experiment work. The principle of speckle in laser projection display system has been analyzed, the influence of the location of laser and the laser spot’s size illuminated on the diffuser on speckle are derived in theoretical and verified in experiment, the result can guide the design of projection system.2. It’s first time to propose electronic controls PDLC and change polarization of LC to reduce speckle, experiment has been verified. The suppression effect, the requirement of LC’s parameter and the improvement of the system can be achieved from experiment.3. Simulating the human eyes and the influence of characteristic on speckle is analyzed. The influence of CCD’s parameter on speckle measurement has been qualified from experiment. A standardized speckle measurement system is set up with human eyes’ property. The noise in the image shoot by this system has also been suppressed and a new evaluation criteria is introduced to judge the image clarity.更多还原