In Chapters 7–14 we concentrated on the use of one-dimensional acousto-optic cells used for processing wideband time signals, and we showed how multichannel versions of these devices are used to perform certain two-dimensional operations. The emphasis in this chapter is on the use of two or more acousto-optic cells, generally in orthogonal configurations, to more fully use the second dimension of the optical system. More powerful signal-processing operations are therefore possible. We describe both coherently and incoherently illuminated systems used in applications such as correlation, spectrum analysis, and range/Doppler processing (127–131).
In previous chapters we showed that the correlation between two signals is a powerful and useful operation. For example, we showed how a one-dimensional acousto-optic cell processor, as shown in Figure 14.8, is used to form the correlation function
where T is the time duration of the acousto-optic cell and kT is the integration interval. The correlation function reveals the degree of similarity between two signals and, in a general way, can be extended to include spectral analysis of signals. For example, if s(t) = exp[−j2πft], we find that
When we detect the squared magnitude of the correlation ...