HIGH-SPEED HYBRID OPTICAL DIGITAL CORRELATOR SYSTEM

A hybrid optical/digital configuration to implement a high-speed corre lator is described. The input data is digitally Fourier transformed at video rates utilizing specialized digital signal processing chip sets and the computed spectral phase data passed to an electrically addres sed phase modulating spatial light modulator (SLM). Successive templat es, which are stored as angle multiplexed volume holograms in a photor efractive crystal, are reconstructed and optically correlated with the current input scene during an interval in which the SLM display is he ld stable. In this way, shift invariance, one of the major advantages of the correlation technique, is preserved. Of critical importance to the speed of operation are the energy losses of the coherent wavefront through the system and the rate at which correlation plane data can b e converted to an electronic signal; both of these issues are consider ed to estimate that at least a 3-kHz search rate is achievable from a 1000 template memory with system components currently available.