消除零级衍射和循环移位改善计算机合成全息图的再现质量

分析了影响计算机合成全息再现像质量的主要因素,提出了一种改善计算机合成全息再现像质量的方法。零级衍射严重降低了再现像的对比度,连续两次离散傅里叶变换的循环移位作用使得再现虚像最后一行和最后一列被分别循环移位到第一行和第一列。采用Burch型合成全息图再现算法消除了零级衍射,调整像素的位置消除了虚像的循环移位,使得全息图能够精确恢复原始图像,实验证明这种方法能改善再现像质量。     

数字全息信息记录最大化及简化相移技术

本丈从信息论的角度研究了数字全息信息量与记录光路的关系,证明了同轴傅里叶变换全息是实现全息信息量最大记录的光路.同时提出了一种新的简化相移数字全息显微技术,本技术采用四分之一波片作为相移器,结合计算机模拟原参考光,只需进行一次相移,拍摄两次全息图和一次物光强度分布图就可以有效的消除数字全息再现像中的零级像和共轭像.将新的相移技术与同轴无透镜傅里叶变换全息相结合,简化了相移步骤,实现了数字全息再现实像最高像素输出,从而提高了数字全息再现像分辨力.     

单次相移数字全息中相移值的提取

为了消除相移误差对数字全息中再现像的像质的影响,本文时单次相移数字全息进行了研究.基于相位统计特性,提出了一种有效消除相移误差的新方法,该方法能够对任意未知相移量进行提取,并利用数字全息图所有抽样点的强度偏差之和作为评价标准,通过逐步改变计算得到的初始相移值来寻找正确的实际相移角.计算机模拟得到了很好的再现结果,证明了该方法的可行性和有效性.     

全息空间三维显示研究

本文基于计算全息、光电衍射再现及散射成像等技术,研究全息空间三维显示,利用随机相位抑制全息空间三维再现像的散斑噪声,实现高分辨率全息空间三维显示。同时,测试不同厚度的散射介质屏对三维成像的影响,探究全息空间三维显示的亮度变化规律。     

同轴数字全息用于粒径测量的影响因素分析

采用同轴数字全息技术测量研究粒子场,其高分辨力的再现像和粒径高精度测量受到诸多因素的影响.本文简要介绍了同轴数字全息的基本概念、原理、方法及其在粒子直径测量中的应用,主要通过计算机仿真研究了记录距离和粒子浓度这两个因素对粒径测量精度的影响,给出了记录距离的范围,同时提出了基于灰度梯度提取粒子边缘进行粒径测量的方法,并通过实验进行了验证.     

全息体视图打印技术三维成像研究

本文研制了全息体视图打印系统,并用其制作三维显示效果;介绍了获取视差图像、全息单元图像生成以及记录再现的原理和方法;通过搭建全息打印光路,进行实验论证;测量实验再现像的观察视场角,并将再现三维效果与原三维场景的结构相似度进行比对。     

一种去除离焦粒子像的简便方法

记录着不同深度位置的粒子全息图在数值重构过程中由于直透光、孪生像的影响以及离焦粒子像的存在,导致了聚焦粒子再现像质量的下降.针对这一问题,本文提出一种数值处理方法来减小上述三因素对聚焦粒子再现像的影响.该方法通过对数值重构出的两个聚焦与非聚焦面上粒子复振幅相减,将直透光、孪生像和离焦粒子像对聚焦粒子的影响同时减小,因此提高和改善了聚焦粒子再现像的对比度.在同轴数字全息层析再现粒子场过程中,该方法适用于在某一聚焦面仅显示聚焦粒子.此外,该过程仅需要一张全息图,而且不需要对全息图做预前和后期处理.给出了简要理论以及仿真、实验结果.     

医学层析图像的计算全息三维可视化

提出了一种医学层析图像的计算全息三维可视化技术。首先研究了层析图像序列的三维信息融合,将层析图像序列的二维信息融合成三维信息,用计算全息图的方法进行三维信息记录。然后结合空间光调制器的结构特性,对全息系统的空间频率、参物光夹角、取样间隔以及全息再现像的再现区域和视角等进行了讨论和分析,并设置了相关参数,使计算全息系统与电子显示系统相匹配。最后用液晶空间光调制器作为全息图显示载体,用计算机控制全息图的实时输出,用雾屏承载三维空间再现像,建立三维图像光电再现与实时显示系统,实现层析图像序列的三维可视化,给出了理论分析与实验结果。     

同轴数字全息视频动态跟踪处理实验

用数字全息进行动态观测时,由于不同物体记录距离不同,且不断地变化,再现像不能始终处于清晰状态。本文提出了利用同轴数字全息视频技术实现在三维空间内对运动物体进行连续动态观测的方法,研究了其中的动态跟踪聚焦算法和视频处理算法。利用上一帧再现像中观测物体的中心位置作为下一帧全息再现中聚焦窗口的中心位置,使聚焦窗口始终跟随观测目标移动,从而保证处理全息视频时每一帧再现像都能准确自动聚焦,使再现视频中要观测的目标始终处于清晰状态。采用上一帧的聚焦距离为下一帧再现距离的搜索中心、避免处理不同全息图时的重复运算等方式来提高数字全息视频的处理速度。实验结果表明,本文提出的数字全息视频成像技术能实现在三维空间内对某一特定运动物体进行连续动态观测。     

光全息中傅里叶变换透镜设计

针对光学全息再现像质较差,本文提出四片式近似全对称傅里叶变换透镜的设计.该设计根据电寻址液晶和CCD对傅里叶变换透镜的匹配要求确定设计参数.为了缩短总长,系统采用双远距结构,并利用ZEMAX自动设计软件进行优化设计.将设计结果应用于实验,获得了清晰的光学全息再现像.实验结果表明,该设计的各项指标与实验系统相匹配,具有结...     

Suppression of the zero-order diffracted beam from a pixelated spatial light modulator by phase compression

Phase compression is used to suppress the on-axis zero-order diffracted (ZOD) beam from a pixelated phase-only spatial light modulator (SLM) by a simple modification to the computer generated hologram (CGH) loaded onto the SLM. After CGH design, the phase of each SLM element is identically compressed by multiplying by a constant scale factor and rotated on the complex unit-circle to produce a cancellation beam that destructively interferes with the ZOD beam. Experiments achieved a factor of 3 reduction of the ZOD beam using two different liquid-crystal SLMs. Numerical simulation analyzed the reconstructed image quality and diffraction efficiency versus degree of phase compression and showed that phase compression resulted in little image degradation or power loss.     

Properties of DMDs for holographic displays

Digital micromirror device’s (DMD) properties as being a display device for holographic displays are investigated. High speed, a large separation between reconstructed image and reconstruction beam, two symmetric diffraction patterns, and low intensity (0,0)th-order beam at a blazed grating condition are the desired properties for the displays. The blazed grating condition of a DMD can reconstruct images with higher diffraction efficiency than the line grating condition. DMD’s high speed enables to present colors and gray levels to the reconstructed image. However, reconstructed images from a gray-level computer-generated hologram (CGH) and its binary form hologram reveal no noticeable difference between them, except the background noise in the image from the CGH.     

Fast computation for generating CGH of a 3D object by employing connections between layers

An approximate method for generating computer-generated holograms (CGH) of a 3D object with six times faster speed than the conventional algorithm is presented. In the conventional algorithm, a 3D object is sliced into many layers and treated as a collection of self-illuminated point light source. The propagation process of a light ray from every point of an object to all the points on the hologram plane is simulated and interfered with by the reference beam to form a CGH. In our proposed method, under the assumption that the depth of a 3D object is much smaller than the recording distance, we just need to calculate the oblique distance between the first layer and the hologram plane, and then the oblique distances from the other layers to the hologram plane can be obtained from a simple relation, thus the computational time is much reduced. The CGH is optically reconstructed and the quality of the reconstructed image agrees well with that from the conventional algorithm.     

太赫兹光场数据采集与数字重聚焦实验研究

本文对太赫兹光场数据采集与数字重聚焦成像进行实验研究。太赫兹成像因其穿透性、无损性等优点,近年来备受国内外研究者关注。太赫兹波段的光场成像技术有望增强图像质量、改善应用效果。本文在分析光场成像基本原理、系统结构、重建方法的基础上,应用太赫兹焦平面阵列相机进行太赫兹光场数据采集和数字重聚焦实验。首先采集太赫兹光场原始数据,然后通过数字重聚焦进行计算成像,最后对重构图像做增强处理,得到了深度、角度及目标物轮廓分辨力强的太赫兹图像。实验证明了太赫兹光场成像技术的可行性及其改善图像质量、丰富复现效果的能力。     

Demonstration of a computed-tomography imaging spectrometer using a computer-generated hologram disperser

We have constructed a computed-tomography imaging spectrometer that uses a phase-only computer-generated hologram (CGH) array illuminator as the disperser. This imaging spectrometer collects multiplexed spatial and spectral data simultaneously and can be used for flash spectral imaging. The CGH disperser has been designed to maintain nearly equal spectral diffraction efficiency among a 5 x 5 array of diffraction orders and to minimize diffraction efficiency into higher orders. Reconstruction of the (x, y, lambda) image cube from the raw, two-dimensional data is achieved by computed-tomography techniques. The reconstructed image and spectral-signature data compare favorably with measurements by other spectrometric methods.     

Optode positional calibration in diffuse optical tomography

Although diffuse optical tomography is a highly promising technique used to noninvasively image blood volume and oxygenation, the reconstructed data are sensitive to systemic difference between the forward model and the actual experimental conditions. In particular, small changes in optode location or in the optode-tissue coupling coefficient significantly degrade the quality of the reconstruction images. Accurate system calibration therefore is an essential part of any experimental protocol. We present a technique for simultaneously calibrating optode positions and reconstructing images that significantly improves image quality, as we demonstrate with simulations and phantom experiments.     

数字加网图像的质量评价研究

介绍了两类典型的数字半色调算法以及主观评价和客观评价两种传统的半色调图像质量评价方法.基于VisualC#编程语言建立了加网算法实验平台,并根据所得图像质量参数对各算法在再现图像的质量、运行时间等方面进行了比较和分析.     

Holography with surface-plasmon-coupled waveguide modes

We report on an attempt to use the enhancement effect of surface-plasmon resonance to improve the image quality of a waveguide hologram. With a structure consisting of a waveguide medium sandwiched between a metal film and a hologram, we obtained holographic images reconstructed by surface-plasmon-coupled waveguide modes. Comparison of the holographic images reconstructed by TM and TE modes indicates that the surface-plasmon effect is responsible for better image quality in diffraction efficiency and image contrast.     

SRR在多线阵错位排列扫描系统中的实现

为了获得尽可能高的空间分辨率的图像,超分辨率重构技术(SRR)成为了红外扫描成像的研究热点.本文以红外多线阵错位排列扫描成像系统为研究平台,通过分析SRR实现过程及待重构图像获取的方式,分析了红外多线阵错位排列扫描成像系统中SRR有效的关键.实验表明:对于固定错位量的多排传感器扫描成像系统,影响重构图像质量的主要因素是各通道所获得的待重构图像同位像素灰度不一致引入的噪声.本文提出的基于序列逐像素比较滤波法,可以大大提高重构图像质量.