Investigation Of Photorefractive Joint Transform Correlator

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.