Performances of an all-optical subtracted joint transform correlator that uses a photorefractive crystal

An all-optical subtracted joint transform correlator (JTC) was proposed and it was experimentally shown that the correlator successfully performs the pattern recognition with the number of reference patterns. In the correlato r, an optical interferometer was introduced to remove the additional correl ation signals between the reference patterns themselves-from the output pla ne and a photorefractive crystal was also introduced to record the joint po wer spectra as volume holograms. The processing for removing the additional correlation signals was performed by the parallel computations in the inte rferometer in real time. In this study it has been found that the correlato r yields significantly better correlation results than the classical joint transform correlator does and the recording of the volume hologram correspo nds to a nonlinear processing of the joint power spectrum in the fringe-adj usted joint transform correlator. However the volume hologram has angular s electivity for matching the Bragg condition. It would restrict the shift-in variant area of the input image plane. This restriction has been investigat ed experimentally.