Signal processing with surface waves via the double acousto-optic interaction

Optical diffraction by two successive surface acoustic waves was used to achieve various signal-processing operations. Expressions were derived for the frequency spectrum and bilinearity factor associated with this double interaction and these formulas were verified experimentally using Fabry-Perot interferometry. An aperture function formalism was used to demonstrate that the doubly diffracted field corresponds in form to that required for real-time convolution. The addition of a simple lens system extended the capability of this technique to a full range of processing functions. The following operations were demonstrated for pulses of the order of 1 μs: squaring convolution, squaring correlation, variable time expansion, variable time compression, time inversion, and image scanning. This processor is characterized by large bandwidth since the diffraction takes place in the Raman-Nath limit up to GHz frequencies.