Applications of an acousto-optical bispectrum processor

The ''bispectrum'' of a signal measures the degree of correlation between three interacting frequency components due to a quadratic nonlinearity. Attention is here given to an acoustooptic implementation of the bispectrum which can operate on relatively wide-bandwidth signals. The overall architecture employed is that of a modified Mach-Zehnder interferometer which contains three acoustooptic modulators in conjunction with appropriate transforming lenses. The cross-bispectrum of the input and output signals are computed for a quadratically nonlinear system; an accurate estimate of the time delay between the signals is derived from the cross-bispectrum information.