Real-time convolution using acousto-optic diffraction from surface waves

Convolution of two signals has been obtained in real time using the efficient diffraction of laser light from acoustic surface waves. Two pulse-modulated 45-MHz surface waves are launched from the two ends of a surface wave delay line. Laser light enters the delay line from one side, interacts with two oppositely directed parallel acoustic beams along their widths, and exits from the other side. The diffracted light, after an optical Fourier transformation, is incident on a photodiode which produces an electrical output containing the desired convolution signal. With the present 5-μsec interaction length and 9-MHz transducer bandwidth, the time-bandwidth product is 45.