Abstract

A time-domain beam former spatially filters signals by weighting, delaying, and coherently summing the outputs of an array of sensors. Since a wavefront propagating across the array arrives at different sensors at different times, this operation can steer a maximum-response axis (or beam) of the array toward the propagation direction of the wavefront and discriminate against uncorrelated background noise. Since the transmission medium is often nondispersive (e.g., in sonar), the delays are independent of frequency; thus, this technique works well for broadband signals. We have built an eight-element eight-beam delay-sum beam former using a total internal reflection spatial light modulator as an electrical-to-optical transducer for the sensor signals, a commercial liquid-crystal television (LCTV) and the necessary optical elements as a crossbar switch, and a time-integrating photodetector array. A microcomputer was used for storage and control. The experimental beam-response pattern for hard-clipped (i.e., binary) input signals was obtained and compared with the calculated beam pattern. The throughput of this system was limited by the time response and instabilities of the LCTV. For improved response we are building a partial-sum beam former using optical fiber connections and a charge-transfer-device detector.

© 1986 Optical Society of America