【作者】 许其推；

【导师】 赵建林；

【作者基本信息】 西北工业大学 ， 光学， 2002， 硕士

【摘要】 与匹配滤波相关器相比，联合变换相关器具有诸多优点，如空间带宽积高、无需滤波综合、易于实时操作等，所以近年来更加引起人们的研究兴趣。光折变晶体具有响应速度快、空间分辨率高、存储容量大等优点。将光折变晶体与联合变换相关器相结合构成光折变联合变换相关器，就可以充分发挥二者的优势。本文对非线性联合变换相关识别和光折变光学相关识别进行了较详细的研究。 首先比较研究了两种基本的光学相关识别理论：Vander Lugt匹配滤波相关识别和联合变换相关识别，并提出了一般化光学相关识别的概念。其次，通过理论分析、计算机模拟和实验研究的方法，对非线性联合变换相关识别和光折变光学相关识别进行了研究，并给出了研究结果：(1)对联合变换功率谱进行二值化处理可以使得功率谱高频成份得到较大提高，从而大大提高联合变换相关器的识别能力。同时在研究过程中发现，不同阈值对二值化联合变换相关结果有着较大的影响，在各种阈值中存在一最佳阈值。并通过计算机模拟，确定出该最佳阈值位于联合变换功率谱的平均灰度值附近。(2)利用SBN：61：Cr晶体(1000ppm)和KNSBN：Ce晶体(0.07wt％)的二波耦合能量非线性转移特性，对联合变换相关器的输入图像进行边缘增强预处理，提高了相关峰的归一化强度，减小了相关峰的半宽度，从而大大提高了相关器的识别能力。(3)对二值化与光折变边缘增强联合变换相关器各自的特点进行了比较。(4)利用光折变晶体的体全息存储特性来实时制作匹配滤波器，避免了利用全息干板制作滤波器时的显影、定影等化学操作和滤波器的严格复位问题。同时采用CRT-LCLV作为实时输入器件，避免了输入图像的准确复位问题。因此利用这种相关器结构进行实时操作具有较大的可行性。(5)利用KNSBN：Cu晶体作为平方律转换器件，实现实时的功率谱转换，从而实现联合变换相关识别。本文最后对光折变边缘增强和二波耦合联合变换相关识别进行了比较。并对光折变二波耦合实验中一些参数选择进行了分析。 研究结果表明，将光折变晶体与联合变换相关器相结合构成光折变联合变换相关器是可行的。更多还原

【Abstract】 The joint transform correlator (JTC) is paid more attention by researchers than the matched filtering correlator (MFC) with its advantages, such as high spatial bandwidth product, without integrated filtering and real-time operation etc. Photorefractive crystals have some advantages, such as fast response, high spatial resolution and large storage capacity etc. We can exert both advantages by combining the photorefractive crystal with the JTC. The theories and experiments of the nonlinear joint transform correlation recognition and the photorefractive correlation recognition are investigated detailedly in this thesis.Firstly, the analysis and comparison is made between two basic types of optical correlator: the Vander Lugt MFC and the JTC. And the concept of the general optical correlator is proposed. Secondly, the nonlinear joint transform correlation recognition and the photorefractive correlation recognition are investigated by computer simulation and experiment, and the research results are given as following: (1) The correlation discrimination of the JTC can be greatly improved by binarizing the joint transform power spectrum nonlinearly. It is found in our experiment that the threshold magnitude has great influence on the correlation output of a binary JTC. That is, there exists an optimal threshold, which lies in the average gray of the joint transform power spectrum by computer simulation. (2) Taking the nonlinear energy transfer property of the photorefractive two-beam coupling in the SBN:61 crystal doped with 1000ppm Cr and the KNSBN crystal doped with 0.07wt% Ce, edge-enhancement preprocessing can be achieved, which will results in the larger normalized intensity and narrower width of the correlation peaks. And the discrimination of the JTC is greatly improved. (3) We make a comparison between the binary and photorefractive edge-enhancement JTC. (4) Taking the volume hologram storage of the photorefractive crystals, we can carry out the matched filtering correlation recognition with real-time operation. (5) We present a photorefractive two-beam coupling JTC, in which a KNSBN:Cu crystal is used to a square-law converter by the nonlinear energy transfer property of the photorefractive two-beam coupling. Finally, the comparison is made between the photorefractive edge-enhancement and two-beam coupling JTC. And we also analysis the parameters in the photorefractive two-beam coupling experiment.In conclusion, the experiment results show that it is feasible to combine the photorefracitve crystal with the joint transform correlator.更多还原