用小型全息设备做傅里叶变换全息图存储资料实验

阐述了用小型全息设备做傅里叶变换全息图存储资料实验所采用的光路、详细的操作步骤和实验中的关键问题.     

Ruggedized digital holographic data storage with fast access

Recent investigations in holographic mass memory systems have produced proof-of-concept demonstrations that have highlighted their potential for providing unprecedented capacity, data transfer rates and fast random access performance (Heanue et al. 1994; Hong et al. 1995; Psaltis and Mok 1995; Bernal et al. 1996; McMichael et al. 1996). The exploratory nature of most such investigations has been largely confined to benchtop experiments which have ignored the practical constraints of packaging and environmental concerns. We have embarked on an effort to demonstrate the holographic mass memory concept by developing a compact prototype system geared for avionics and similar applications which demand the following features (mostly interdependent factors): (1) solid state design (no moving parts), (2) fast data seek time, (3) robust with respect to environmental factors (temperature, vibration, shock). In this paper, we report on the development and demonstration of two systems, one with 100 MB and the other with more than 1 GB of storage capacity. Both systems feature solid state design with the addressing mechanism realized with acoustooptic deflectors that are capable of better than 50 sec data seek time. Since the basic designs for the two systems are similar, we describe only the larger system in detail. The operation of the smaller system has been demonstrated in various environments including hand-held operation and thermal/mechanical shock; a photograph of the smaller system is provided, as well as actual digital data retrieved from the same system.     

二芳烯材料在重复擦写体全息存储中的应用研究

二芳烯材料是一种性能优异的光致色变材料,具有很好的抗疲劳性能,一般能重复擦写上万次,而不损失其性能。通过体全息光栅记录实验、角度复用体全息存储实验、重复擦写及强光记弱光读等实验,对二芳烯材料在重复擦写体全息存储中的应用进行了系统研究。由于二芳烯材料具有很高的折射率调制度(Δn=1.15×10-3)、可多次重复擦写、强光记弱光读的准非易失等性能,在可重复擦写的体全息存储中具有广阔的应用前景。     

像素1:1匹配的晶体全息存储系统中像素位置偏移的补偿算法

在体全息存储系统的数据读出过程中,为了提高读出速度,需要做到SLM与CCD像素的1∶1匹配。但在实现1∶1匹配的过程中,如何降低误码率是一个难点。利用傅里叶光学成像理论,推导出了在4f系统中单个SLM像素成像的光强分布,并由此定量地分析了像素位置偏移对读出误码率的影响。提出了针对像素偏移的数值补偿算法,并获得了较理想的实验结果。     

Holographic digital data storage using phase-modulated pixels

We propose and demonstrate the use of phase images for holographic data storage. Use of phase images as input leads to uniform diffraction efficiency of multiplexed data pages. Use of binary phase-based data pages with 0 and π phase changes produces uniform spectral distribution at the Fourier plane. This in turn facilitates better recording of higher spatial frequencies. We experimentally demonstrate a phase-based holographic data storage system using shift multiplexing in a Fe:LiNbO₃ crystal, and use it for associative retrieval. Preliminary studies indicate high discrimination capabilities of phase-based holographic data storage system over the amplitude-based system in a content-addressable memory.     

Research on true color computer generated hologram by lensless Fourier transform

Based on the theory of scalar diffraction, this paper makes research on the process of hologram reconstruction of true color calculation by lensless Fourier transform, and gives its algorithm on the basis of the angular spectrum theory as well as the instances of color image reconstruction under the red, green and blue colors wavelength. In order to eliminate the influence of color difference on the reconstructive image, this paper analyzes the causes of the color difference, and puts forward the method of interpolation reconstruction to the object information in the process of hologram reconstruction, so as to eliminate the color difference. With the advantages of computer generated holographic, the high-quality color hologram by lensless Fourier transform based on the angular spectrum theory has been realized, and the results of corresponding numerical simulation are given. The results show that the method in the paper can effectively eliminate the color difference caused by different wavelength, and the experimental results validate its feasibility.     

体全息存储系统读出图像的放大率的补偿算法研究

在1∶1体全息存储系统的读出过程中,保证图像的不失真和降低误码率是最关键的问题。提出了一种新颖的放大率补偿算法,定量分析了放大率偏移误差对图像的影响,并通过理论推导和实验模拟证明了这一算法的可行性。     

体全息存储中输入方参数对输出信号的影响

借助基于 4F成像系统的掩模版模拟SLM实验 ,在国内首次实现 10 0 0× 10 0 0高分辨率数据页输入 输出像素一对一匹配的基础上研究了体全息存储系统输入方重要参数 ,如 :输入器件 (空间光调制器 )像素填充因子和输入图案组合对输出器件 (电荷耦合器件 )读出图像的影响 ,为提高全息存储系统输出图像质量、降低误码率提供理论和实验基础。     

Diffraction patterns for a transmission volume hologram under Bragg mismatch

We have presented simulations and experiments for 2-dimensional diffraction distributions of a transmission volume hologram. We sample the input pattern with a few elementary points and calculate the diffraction of the corresponding elementary grating. The simulations can describe well the diffraction pattern obtained in the experiment and can be used to predict the tolerance for angular deviation of the reading beam. The tolerance for angular deviation depends on its direction. It is affected by the Bragg degeneracy. The simulation results provide a clear picture of the spatial tolerance for reading a transmission volume hologram.     

Multi-color encoded storage rainbow hologram

This paper proposes a simple method of making storage multi-color rainbow hologram. The principle of the optical design of this kind of hologram is described theoretically. Some technical problems in the recording processes are analyzed. The experimental arrangements and results are presented.     

体全息存储系统中的傅里叶变换透镜设计

提出和设计了一种应用于体全息存储系统的傅里叶变换透镜,是为了适应体全息存储系统对傅里叶变换透镜的特殊要求而设计的。设计中使用了光学自动设计软件ZEMAX。综合各方面考虑,采用双平凸结构,具有以下特点:焦距短,系统结构紧凑;焦距易于改变,以方便实现不同焦距比;工作视场大,能提高体全息存储系统的存储密度;结构简单,容易加工装调,造价低。透镜组用于像素数为1k×1k的空间光调制器(SLM)与CCD匹配对准。     

Phase modulated gray-scale data pages for digital holographic data storage

We propose a method for gray level holographic digital data storage by using three-gray levels in the phase mode. Gray level data pages are displayed on a SLM operating in the phase mode to obtain a homogenized Fourier spectrum by suppressing the extremely high intensity DC component in the Fourier spectrum of conventional amplitude based binary/gray level data pages. Holographic interferometry has been used to recover the gray level amplitude data page from phase data page. Numerical simulation results are presented for three-gray level data pages. Fourier plane homogeneity, bit-error-rate, storage density, phase modulation error of the SLM, and misalignment tolerances are investigated through computer modeling. A comparison of the present method with the amplitude-modulated gray level case with and without using a phase mask in conjunction with the data page is carried out. An experimental demonstration of the proposed three-gray level phase data page method is also presented.     

体全息存储技术

体全息存储技术以其存储密度和数据读出率高及相关内容寻址等特点而具有广阔的应用前景。但体全息存储技术要同其它已经成熟的技术竞争 ,以在存储市场上占有一席之地 ,就必须注重发挥自己的优势。另外体全息存储技术要实现商品化 ,还有两个重要的问题需要解决。一是以较低的价格实现激光、空间光调制器和探测器阵列的对准。其次是要寻找合适的存储材料。对体全息存储来说寻找合适的存储材料仍是一个尚待解决的问题 ,至今还没有一种材料具有性能、容量和价格的综合优势     

全息透镜用于彩色胶片全息高密度存储

本文提出一种利用全息透镜实现彩色胶片全息高密度存储的方法。用红、绿、蓝三基色激光分别记录三个焦距相同的全息透镜,用三个全息透镜依次用三基色波长记录胶片的傅氏全息图,用原参考光照明再现,可合成彩色像。     

利用傅里叶变换全息图实现彩色胶片存储

本文提出一种利用傅里叶变换全息图存储彩色胶片的方法.在参考光路和透明片后置入采栅,以红、绿、蓝三种波长记录+1级谱的点全息图.当三色光分别照明各自的全息图时,可再现两个真彩色图像.     

Digital hologram encryption using discrete wavelet packet transform

In this paper, key components of a digital hologram were tracked using discrete wavelet packet transform to propose an encryption. Information needed to handle digital holograms were obtained by analyzing the characteristic of digital holograms in the Fresnel and frequency domains. By integrating the information that was experimentally obtained, an encryption method that uses the wavelet transform and subband packetization was proposed. Thus it is possible to change the encryption strength by changing the level of wavelet transform and the energy value of the coefficients to be encrypted. Optimal parameters can be found by analyzing the encryption effect numerically and visually. Therefore, it is possible to execute the encryption efficiently using the parameters presented in this paper without a separate analysis process. The experimental results showed that encrypting only 0.032% of the entire data was enough to hide the contents of the hologram. Here, we regarded the key to encrypt the subband packetization information as the overall encryption key.     

无透镜傅里叶变换型全息瞄准具研究

基于无透镜傅里叶变换全息术制作了一种新型激光全息瞄准具。瞄准具的核心部件是由一块无透镜傅里叶变换位相全息图和一块全息光束变换器组成的全息光学元件。其突出优点是大视场,大出瞳距离,适合双眼瞄准。此外,瞄准线为明亮的虚像,不会暴露目标,结构简单,对射击近距离运动目标效果突出。介绍了全息瞄准具组件的原理和制作方法,并对其性能进行了分析。     

体全息存储系统图像质量因素MTF数值模拟分析

影响体全息存储系统中读出图像误码率的因素很多,其中输入与输出器件SLM、CCD的性能以及它们信号匹配关系起着关键的作用。针对这一实际问题,利用CCD成像系统的调制传递函数理论和数值模拟方法,通过对4f系统中周期性SLM像素分布的CCD输出响应分析,研究了SLM和CCD的填充因子、对比度、位相匹配关系对读出图像误码率的影响,并给出计算机仿真结果。     

体全息子波关联记忆器

基于子波匹配相关理论和光折变晶体的体全息关联存储特性,提出并实现了一个关联记忆的新构思。中根据缺损特征实现原始图像的记忆和恢复,其中光折变晶体兼作图像识别时的运算单元和图像恢复时的存储单元,文中以人脸为研究对象,给出了实验结果。     

Optical data storage in LC cells

Liquid crystal devices as a medium for holograms storage have been investigated. Long term memory effects in LC cells have been observed. Experiments proved that certain combination of insulating alignment layers has a major influence on the long term memory effect. Optimal liquid crystal cell construction allows us to achieve sufficient diffraction efficiency to record holographic patterns and to develop a re-writable holographic medium. The configuration of PVK and polyimide layers in LC cell construction with specific LC mixture was tested. The method of permanent and re-writable recording of optical data (holographic pattern) onto LC cells was achieved. However, the method of erasing recorded data was realized but mechanisms of this phenomenon are not clearly understood yet.