纯相位菲涅尔全息图的反馈迭代算法及其硅基液晶显示

研究了纯相位菲涅尔计算全息图的制作方法,给出了一种生成纯相位菲涅尔计算全息图的算法.首先研究了菲涅尔衍射的数值模拟算法,分析了两种数值模拟算法的计算速度.将计算速度较快的菲涅尔衍射数值模拟算法和迭代算法相结合,并引入比例反馈,得到纯相位菲涅尔计算全息图的反馈迭代算法.其次,对比例反馈系数的选取进行了实验研究,得到其最优经验值范围,然后进行了仿真实验.仿真结果表明,该算法降低了重构误差,提高了全息图重构质量.最后基于新型空间光调制器反射型硅基液晶,建立了全息显示光电实验系统,对该算法进行了验证.     

层析法计算三维物体全息图的并行加速研究

随着计算空间光调制器的分辨率的尺寸逐渐变大，全息图三维动态显示的计算量也越来越大，使得对全息计算速度提出了新的要求。利用GPU并行计算处理的方式实现全息图的快速层析法计算，该方法利用GPU并行多线程和层析法中的图像二维傅里叶变换的优势对菲涅尔衍射变换算法加速计算；同时通过对GPU底层资源的调用和对CUDA中程序的流处理过程，有效减少中间的延时等待。通过对计算速度对比分析表明:与在CPU上运算相比，计算速度大幅提升，基于GPU并行计算的方法比基于CPU计算的方法速度快10倍左右。     

采用层析法对实际三维数据深度图的全息计算

提出利用层析法计算实际三维数据的强度图和深度图生成全息图的方法。根据层析法的原理,把复杂三维数据按照深度图的灰度值分成多层物面信息,并根据深度图把每层物面的深度转换成菲涅尔衍射距离。采用角谱算法分别对每层物面进行菲涅尔衍射计算,得到三维物体的全息图。研究结果显示该方法可以快速、准确地对实际复杂的三维物体进行全息图的记录和再现。     

利用反射全息实现计算全息三维显示

计算全息和光学全息都可应用于三维显示,但各有自己的优势和缺陷.将计算全息和光学反射全息相结合,可以突破光学全息对记录物体的限制,进行虚拟物体或自然场景的全息图的制作,同时可以实现白光再现.本文首先用三维扫描仪获得实际物体的三维数据,用"点云算法"模拟得到其菲涅耳全息图透射率数据,采用计算全息打印机将其输出于全息记录介质,得到可光学再现的菲涅耳计算全息图H1.然后将H1作为光学全息的记录物体进行反射全息记录,将平面全息转化为体全息,实现了计算全息白光再现.     

利用反射全息实现计算全息三维显示

计算全息和光学全息都可应用于三维显示,但各有自己的优势和缺陷.将计算全息和光学反射全息相结合,可以突破光学全息对记录物体的限制,进行虚拟物体或自然场景的全息图的制作,同时可以实现白光再现.本文首先用三维扫描仪获得实际物体的三维数据,用"点云算法"模拟得到其菲涅耳全息图透射率数据,采用计算全息打印机将其输出于全息记录介质,得到可光学再现的菲涅耳计算全息图H₁.然后将H₁作为光学全息的记录物体进行反射全息记录,将平面全息转化为体全息,实现了计算全息白光再现.     

结合计算全息与混沌的彩色图像加密方法

针对现有彩色图像光学加密方法存在解密结果失真的问题,提出一种结合混沌运算与菲涅耳衍射全息的彩色图像单通道加密新方法.首次加密操作利用菲涅耳衍射将彩色图像RGB通道分量转换成一幅实值计算全息图;第二次加密操作是利用改造的Logistic混沌系统对计算全息图像素进行置换与扩散.结果 表明,本文方法除传统混沌系统密钥以外,菲涅耳衍射距离、参考光波长和入射角方向余弦作为关键密钥均可以增大密钥空间(约为10249),而且具有较小的密钥体积;解密图像的保真度高且相邻像素相关性、信息熵、像素数改变率和归一化改变强度等评价指标均接近理想值;密文图像的直方图平坦,灰度分布均匀,完全隐藏了原始彩色图像的灰度和色彩信息.     

菲涅尔数字全息的脉冲响应

数字全息是用CCD记录全息图并用计算机数值重建全息像的一种全息新方法.在数字全息中,通过对不同记录参数下记录的全息图的数值处理,可以消除零级光和共轭光,从而将数字全息系统看作是一个线性系统.本文依据全息理论和付里叶频谱分析,对菲涅尔数字全息系统的脉冲响应和分辨本领进行了理论分析.结果表明,在矩形等间隔抽样的情形下,菲涅尔数字全息的脉冲响应是由CCD有限大小的孔径衍射斑调制的矩形函数;菲涅尔数字全息的分辨率由CCD的孔径尺寸决定;由于CCD像素具有一定的大小,使得点光源的像发生弥散.     

信息光学 全息术与器件

O438．1 2005021186 利用菲涅尔波带法计算三维全息=Study of CGH for 3D image using Fresnel zone[刊,中]／张晓洁(浙江大学现代 光学仪器国家重点实验室．浙江,杭州(310027)),刘旭… //光电工程．-2004,31(12)．-58-60,67 根据全息理论,从点光源菲涅尔全息图的计算出发, 提出一种利用主菲涅尔波带计算三维物体菲涅尔全息图 的方法。通过读取3DS文件直接获得三维物体表面各点     

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.     

基于深度学习的离轴菲涅耳数字全息非线性重构

针对离轴菲涅耳数字全息图,提出基于深度学习的单幅数字全息非线性重构方法 .采用经典的菲涅耳衍射积分模拟数字全息成像以供给网络训练所需样本,利用深度卷积残差神经网络通过学习数字全息图与相关物像之间的非线性数学映射关系实现全息图的物像重构.数值模拟表明,与传统的频率滤波和四步相移技术实现菲涅耳数字全息重构相比,本文提出的方法可直接消除零级像及孪生像,无需条纹物项抽取预处理步骤,且重构的物像具有较高的质量,针对相同记录参考光下不同衍射距离所生成的测试集亦具有较强的稳健性.     

Fast Calculation of Computer-Generated Fresnel Hologram Utilizing Distributed Parallel Processing and Array Operation

Fresnel CGH for a three-dimensional (3-D) object is generated by calculating the Fresnel diffraction, but it requires a huge amount of calculation. This is one reason for the difficulty in realizing real-time holography. We propose fast calculation method of computer-generated Fresnel hologram (Fresnel CGH) utilizing distributed parallel processing and array operation. In our method, a projected image with depth information of the 3-D object is prepared to calculate the Fresnel diffraction. The Fresnel diffraction of the projected image is then calculated with depth information by array operation and distributed parallel processing. Parallel processing is realized using JavaSpaces and many standard computers. In our array operation, calculation error in phase distribution on a hologram occurs more than the strict Fresnel diffraction. However, it was confirmed by experiments that the influence of an error can be controlled and ignored. In this paper, our proposed method and some experimental results are shown.     

Data-embedded-error-diffusion hologram (Invited Paper)

This paper describes a method for converting a complex Fresnel hologram into a phase-only hologram that can be embedded with large amount of data. Briefly, each row of pixels in the hologram is scanned sequentially in a left-to-right direction. The magnitude of each visited pixel is set to a constant, and its phase is embedded with the data. Subsequently, the error is diffused to the neighborhood pixels. The phase hologram realized with such means, which is referred to as the data-embedded-error-diffusion （DEED） hologram, is capable of preserving high fidelity on the content of the hologram and the embedded data.     

Off-axis phase-only holograms of 3D objects using accelerated point-based Fresnel diffraction algorithm

A method for calculating off-axis phase-only holograms of three-dimensional (3D) object using accelerated point-based Fresnel diffraction algorithm (PB-FDA) is proposed. The complex amplitude of the object points on the z-axis in hologram plane is calculated using Fresnel diffraction formula, called principal complex amplitudes (PCAs). The complex amplitudes of those off-axis object points of the same depth can be obtained by 2D shifting of PCAs. In order to improve the calculating speed of the PB-FDA, the convolution operation based on fast Fourier transform (FFT) is used to calculate the holograms rather than using the point-by-point spatial 2D shifting of the PCAs. The shortest recording distance of the PB-FDA is analyzed in order to remove the influence of multiple-order images in reconstructed images. The optimal recording distance of the PB-FDA is also analyzed to improve the quality of reconstructed images. Numerical reconstructions and optical reconstructions with a phase-only spatial light modulator (SLM) show that holographic 3D display is feasible with the proposed algorithm. The proposed PB-FDA can also avoid the influence of the zero-order image introduced by SLM in optical reconstructed images.     

Phase-only hologram generation based on integral imaging and its enhancement in depth resolution

We introduce a phase-only hologram generation method based on an integral imaging,and propose an enhancement method in representable depth interval.The computational integral imaging reconstruction method is modified based on optical flow to obtain depth-slice images for the focused objects only.A phaseonly hologram for multiple plane images is generated using the iterative Fresnel transform algorithm.In addition,a division method in hologram plane is proposed for enhancement in the representable minimum depth interval.     

Computer Generated Rainbow Hologram

The rainbow hologram is very practical to display 3-D images because it can be reconstructed with white light. We propose a simplified model to calculate the computer generated rainbow hologram quickly. In the proposed method, we can simply generate the final hologram from intermediate data, whose total number of samples can be less than one tenth of the final hologram. This intermediate format makes fast computation and effective storage/transmission possible. Only multiple and additional operation need be used to convert the intermediate data to final data. Therefore, it is possible that hardware can be added to an electro-holographic display or printer. In this paper, we discuss both theory of the simplified model and experimental results of white light reconstructed images. Full color holograms are also discussed.     

Fast Computation of Fresnel Holograms Employing Difference

We propose an approximation method that can calculate the Fresnel hologram 16 times faster than the conventional method. To compute the hologram, an object is assumed to be a collection of self-illuminated points and the fringes from each object point are superposed. The distance between object point and sampling point on the hologram is used to obtain the phase of the light. Since a sampled hologram usually has small pixel intervals, the difference of the distance values between adjacent pixels is also small and its n-th order difference can be assumed to be constant. Therefore, the distance value at a certain pixel can be obtained from its neighbor with simple additions. The distance error can be reduced less that one wavelength with practical parameters. A hologram, which has a horizontal parallax only, 1.3 Mega-pixels and 1,000 object points, can be calculated in less than one second with a personal computer.