OPTICAL COMPUTING BY USE OF PHOTOREFRACTIVE POLYMERS

A matched-filter four-wave-mixing optical correlator was built with a photorefractive polymer as the nonlinear material. Two different time scales are important for this type of device: the time to write a grat ing, which is limited by the response time of the photorefractive mate rial (approximately 100 ms for the polymer used) and the time to diffr act light from the grating, which is essentially instantaneous. For th e matched-filter optical correlator we have obtained correlations comp aring two 5000-pixel images, using 220-fs pulses with 5-mW average pow er, demonstrating that the time to compare the test image and the refe rence image is not limited by the relatively slow response time of the photorefractive polymer. Since the photorefractive grating is erasabl e the device can be reprogrammed for a different reference image in le ss than 1 s. The results show that photorefractive polymers can be use d efficiently in optical image processing applications.