Bipolar Joint Transform Image Correlator

Recently, we have introduced a bipolar joint transform image correlator+ with substantially superior performance compared to the classical optical correlator. The bipolar image correlator uses nonlinearity at the Fourier plane to binarize the Fourier transforms’ interference intensity to only two values, 1 and -1. The performance of the bipolar optical correlator has been compared to the classical optical correlator in the areas of light efficiency, correlation peak to sidelobe ratio, autocorrelation bandwidth, and cross-correlation sensitivity. The correlation signals obtained by the conventional technique suffer from low light efficiency, large correlation sidelobes, large autocorrelation bandwidth, and low discrimination ability. It was shown that compared to the classical correlator, the bipolar joint transform correlator provides significantly higher peak intensity, larger peak to sidelobe ratio, narrower autocorrelation bandwidth, and better cross-correlation sensitivity. The bipolar joint transform correlator produces delta function-like autocorrelation signals, and much narrower and smaller zero order term on the optical axis. Since the autocorrelation functions have delta function features, larger reference images can be used and the restrictions on the locations of the images and their autocorrelation bandwidth, which exists for the classical joint Fourier transform correlator, is eliminated.