Abstract

We report the implementation and demonstration of a real-time, acousto-optic, photorefractive optical correlator. A dynamic range of up to 50 dB and phase stability of less than 1° is achieved by a heterodyne detection scheme. The basic operation of the system is as follows. A laser beam is modulated with the first signal. It then diffracted by an acoustooptic Bragg cell that is driven by the second signal. The diffracted beams are imaged on a photorefractive crystal. If the two signals have identical frequencies, a stationary, spatially periodic intensity distribution that is proportional to the product of the first signal and the time-delayed second signal is produced. Time integration of the product is accomplished by means of the buildup in the photorefractive space-charge field. A detector tuned to the frequency of the signal monitors the correlation between the two signals, which is weighted by the second signal. The acousto-optic Bragg cell operates at 75 MHz. A frequency mismatch of a few hertz results in a moving grating in the photorefractive material so that no field will build up, which leads to zero correlation. The operation and the limitations of the system, as well as potential applications in adaptive filtering, will be discussed.

© 1990 Optical Society of America