ACOUSTOOPTIC IMPLEMENTATION OF REAL-TIME AND NEAR-REAL-TIME SIGNAL PROCESSING

Acoustooptic devices have been developed for implementing advanced signal processing functions required for real-time and near-real-time analysis of hf radar signals and lf sonar signals. These devices use the Bragg interaction between laser beams and surface acoustic waves (SAWs) to perform waveform convolution and correlation, achieving time-bandwidth products of 3000 to 10,000 with dynamic bandwidths of several hundred megahertz. Wideband (100 MHz) signals have been extracted from extremely noisy environments and a real-time Fourier transformation with a linear dynamic range exceeding 60 db has been performed. A programmable correlator and a programmable filter have been demonstrated that use the newly discovered acousto-photorefractive memory effect, based on a nonlinear interaction between intense, short-duration laser pulses permanent index-of-refraction pattern corresponding to the SAW signal. An implementation of the triple-product convolver architecture for performing either a long one- or a two-dimensional discrete Fourier transform can be obtained by combining an acoustooptic convolver with many CCD chirp-Z transform modules. This convolver would have rapid data handling capability and large dynamic range, and would be useful for ″omega -k″ beamforming for sonar signal processing. A programmable 1-, 2-, 3-dimensional beamformer with a one-second update capability may be feasible if the acousto-photorefractive memory effect is used to store SAW signals corresponding to the position of nonstationary sensors.