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Optical correlator using a LCTV CGH filter and a thresholding photodetector array chip

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Abstract

An optical correlator using a CGH filter encoded in a liquid crystal television spatial light modulator (LCTV SLM) and a custom designed VLSI photodetector array chip is reported. A Burckhardt-type CGH filter was written in a commercially available thin film transistor-type LCTV SLM that contains 320 × 220 pixels and has a contrast ratio of ~100:1. Both gray scale and binary holographic images are reconstructed from the LCTV CGH. This CGH filter is successfully used in an optical correlator for pattern recognition experiments. To further enhance the system speed and discrimination capability, a novel CMOS 32 × 32 postprocessing photodetector array chip is designed and fabricated for the correlator peak detection. The two main novel features of this detector array are its thresholding capability and high speed. The thresholding capacity is achieved by building a comparator and logic circuits around each pixel of the detector array. Parallel detection across the entire output plane is done in each clock cycle. Digitized addresses of locations of all the correlation peaks that exceed the thresholding level are present in the output port. The speed of the detector is ~1-10 msec, depending upon the level of the thresholding current.

© 1991 Optical Society of America

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