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 grating, which is limited by the response time of the photorefractive material (˜100 ms for the polymer used) and the time to diffract light from the grating, which is essentially instantaneous. For the matched-filter optical correlator we have obtained correlations comparing two 5000-pixel images, using 220-fs pulses with 5-mW average power, demonstrating that the time to compare the test image and the reference image is not limited by the relatively slow response time of the photorefractive polymer. Since the photorefractive grating is erasable the device can be reprogrammed for a different reference image in less than 1 s. The results show that photorefractive polymers can be used efficiently in optical image processing applications.