【作者】 宋伟；

【导师】 王大勇；

【作者基本信息】 北京工业大学 ， 光学工程， 2013， 博士

【摘要】 信息存储技术发展是信息社会进步的基础，也是研究的热点。传统磁存储技术存储密度已经接近理论极限，光盘存储技术也因为衍射效应的限制，进一步提升存储密度空间逐渐缩小。而基于光致聚合物材料的体全息存储技术因为其更大的存储密度潜力以及相对较低的成本，成为一种具有竞争力的信息存储备选技术。光致聚合物是一种大幅面厚度相对较薄的材料，适用于全息图部分重叠的复用存储技术，国际上各个研机构和公司已经开展基于聚合物材料的全息存储系统研究。美国Inphase公司研制出采用polytopic复用方法的存储系统、斯坦福大学和日本Optware公司提出采用散斑调制光束位移复用的同轴系统。但是散斑调制光束存储全息图噪声很大，严重干扰存储信息。而使得重叠在一起记录的全息图，以均匀的衍射效率读出也是一个重要问题。为了实现有效信息记录的全息存储，有必要对参考光进行优化。我们先前的研究表明振幅分布符合平面波特点，而位相受到一定调制的参考光可以获得较好的存储质量；而且虽然位相调制参考光全息存储基本原理基于与材料厚度正相关的布拉格体光栅，但是复用特性不再受限于材料厚度，可以获得更高的复用密度。因此我们需要对这种位相调制参考光的全息存储性能进行研究，全息图部分重叠复用的等衍射效率问题也在位相调制参考光全息存储性能研究过程中得到解决。对于随机位相调制参考光，其复用特性已经得到充分的研究，我们进一步研究了随机位相调制光束全息记录图像质量的动态变化。在进行实验研究之前有必要对中科院理化所提供的自由基双单体光致聚合物材料全息性能进行测试。我们进行了全息记录和暗反应的实验，结合简化扩散理论模型进行了数据拟合，得到了反映材料全息性能的各个参量。接着，模拟随机位相调制参考光复用存储的情形，进行了光致聚合物中全息存储再现图像质量的动态特性研究。以信噪比损失作为图像质量变化的衡量指标，进行了暗增长和均匀后曝光过程监测图像实验，记录参考光和均匀照明光均采用随机位相调制参考光。实验结果表明，在暗增长和均匀后曝光过程中，再现图像强度和质量经历先增长后下降的动态过程。以噪声光栅的形成和发展对实验结果进行了初步的解释。用信噪比损失不大于3dB作为判据考察了全息图对暗反应和均匀后曝光过程的宽容度，对于不同的记录条件确定了暗反应和均匀后曝光过程的特征时间。在特征时间内，图像强度下降不到20%，图像质量也是可以接受的。可以根据特征时间控制全息存储过程时间，进行能够读出有效信息的全息存储。也可以根据对全息存储质量的不同要求，经材料测试实验得到相应的特征时间，提供了一种控制全息存储质量的途径。接着，以随机相调制参考光位移复用存储为例，我们建立了适用于全息图部分重叠复用存储的等衍射效率曝光时序模型。首先，利用简化扩散模型推导出描述全息图部分重叠复用存储过程折射率调制度随时间变化的解析式；接着，将等衍射效率问题转化为具有三个限制条件的优化问题，计算出了曝光时序等衍射效率曝光时序并且对读出图像衍射效率进行数值模拟，最后我们在双单体光致聚合物材料中进行了随机位相调制参考光位移复用存储实验，考察最终读出的全部图像的强度。数值模拟计算结果和实验结果都表明，在等衍射效率曝光时序的引导下，复用存储全息图衍射效率均匀一致，使得最终读出图像的强度达到均匀相等的效果，证明了曝光时序的有效性。对于确定性位相调制参考光，一般指正交位相编码参考光，传统复用方式实际上是在用正交位相编码参考光的傅里叶谱进行全息存储。数值模拟表明，在这种复用方式下，参考光波面振幅有剧烈起伏，位相在-到之间有连续分布，这会导致将额外噪声带入记录全息图中，影响存储质量，同时参考光正交性受到削弱。为此，我们提出正交位相编码参考光成像方式用于复用存储，即将受到位相码调制的光束通过4f系统成像到记录介质平面，保持振幅符合平面波特点，位相仅有0、位相分布。我们对这种成像方式应用的正交位相编码参考光全息性能进行了研究。在0位置处记录一幅全息图，参考光位移扫描读出。数值模拟和实验结果都表明，当正交位相编码参考光偏离记录位置时，读出图像强度急剧下降，随后趋于水平，得到了位移读出扫描峰。数值模拟和实验结果充分表明正交位相编码参考光具有位移复用特性。更多还原

【Abstract】 The improvement of data storage technology is the base of the progress ofinformation society, and also research focus today. The traditional magnetic recordingtechnology has come to its limit. Also the optical disc is going to its recording densitylimit gradually because of the effect of diffraction. By contrast, the holographicstorage technology with photopolymer has become the most competitive reserve datarecording method because of its great potential in storage density and relatively lowcosts.Photopolymer is a large area and relatively thin material, so it is suitable to apply inpartially-overlapping holograms storage with multiplexing method. And theholographic data storage systems based on the photopolymer have developed byinstitutes and companies all over the world. The Inphase Inc. has released its storagesystem by polytopic method. Stanford University and the Optware Inc. individuallyreleased their own coaxial system by speckle modulator. But there is much noise inthe system with the speckle modulated beams which influences the quality ofrecorded data. Additionally, it is also important to obtain the reconstructed images inuniform diffraction efficiency for all the overlapping recorded holograms.In order to implement high-density holographic storage with high reconstruct quality,the reference beam must be optimized. Our previous work has shown that thephase-modulated reference beams with amplitude distribution as plane wave recordedand reconstructed holograms in a high quality. And the multiplexing degree of phasemodulated reference beam is not confined by the thickness of the material, though itsbasic recording principle is based on the volume Bragg gratings which is positivelycorrelated to the thickness of the material. So it is meaningful to do research on theholographic storage properties of phase-modulated reference beams, and also theuniform diffraction holographic storage is going to be realized in the research on thephase modulated reference beam.For the random-phase modulated reference beam, the multiplexing properties havebeen discussed widely. We did further research to discuss about the recorded images’quality dynamic changes in the process of holographic storage. But before theexperimental research, it is necessary to test the holographic properties of the noveldual-monomer photopolymer based on the free-radical photopolymerization providedby the technical institute of physics and chemistry, Chinese Academy of Sciences (IPC_CAS). We did dark enhancement and holographic recording experiment. Andwith the simplified diffusion model, a data fitting has been done to obtain theparameters reflecting the holographic recording properties of the material with theexperimental data. Then we did research to the quality dynamic changes of hologramsrecorded in the material with random-phase modulated reference beam. The quality ofthe reconstructed images is evaluated by the loss of signal to noise (LSNR). Theexperimental results showed that the intensity and quality of the reconstructed imagesexperienced a dynamic change that the intensity and quality raised for a while andthen fell down until the images faded to disappear. It can be explained by the formingand developing of the scattering gratings. And it is defined that the time before thequality being less than3dB is character time of the material in dark enhancement anduniform post exposure. In the character time the quality and the intensity of thereconstructed images are acceptable and the intensity is descending less than20%. Soit is able to adjust and control the recording time to realize effective holographicstorage according to the character time. And it is also allowed to obtain the propercharacter time according to different demands of recording quality by material testexperiment, which also offers a method to adjust and control the quality ofholographic storage.After the research about the reconstructed images’ quality dynamic changes, takingshift-multiplexing by random-phase modulated reference beam for an example, webuilt up a uniform diffraction efficiency exposure schedule model for recordingpartially-overlapping holograms. Firstly we obtained the analytic expressionsdepicting the refractive index modulation and deduced the exposure schedule modelfor dual-monomer photopolymer. Then, the uniform diffraction efficiency model istransformed to an optimization problem with three constrictions. The exposureschedule was calculated by solving this problem through computer and we didnumerical simulation to calculate the diffraction efficiency of the recorded holograms.Then with the calculated schedule, multiplexing experiment was done to observe theintensity of the reconstructed images in the dual-monomer photopolymer. The resultsof numerical simulation and the experiments showed that following the exposureschedule, diffraction efficiency of all the recorded holograms were uniform, soreconstructed images also had a uniform intensity, which proved the exposureschedule model was effective. For the deterministic phase modulated reference beam, generally the orthogonalphase code modulated reference beam, the traditional multiplexing method actuallyapplied the Fourier transform of the reference beam to recording holograms. Thenumerical simulation results showed that there was a complex and serious fluctuationin both intensity and phase distribution. Moreover, the phase was no longer binary (0or) but varying continuously between–and, which would reduce the phaseorthogonality. Also the additional intensity distribution will influence the quality ofthe beam. A solution we suggested was an imaging setup applied for the orthogonalphase coded reference beam. And we have tested the holographic storage properties ofthe orthogonal phase code imaging reference beam. The numerical simulation andexperimental results showed that with orthogonal phase-coded reference beamposition shifting, the intensity of the reconstructed images is falling down very fastand becoming closely to a straight line, leading to a scanning peak. These come to aconclusion that the orthogonal phase code imaging reference beam has shiftselectivity.更多还原