Coherent optical correlator based on combined halftone and position modulation of light phase

Abstract

Usually only a halftone (grayscale) modulation of light is used to present the processed and reference signals in the input plane of analog coherent optical (ACO) correlators, based on spatially integrating the product of two (processed and reference) signals. The halftone modulation requires two transparencies to record two signals separately, as the desired product of two spatial signals is obtained by sequential location of two spatial halftone records along the light path. Such an optical layout leads to the need for precision mutual alignment of two separate signal recordings. This paper presents a one-stage ACO correlation method based on combined halftone and position modulation of the light phase, which is produced by joint phase recording two signals on a single transparency. The joint phase recording provides the high optical efficiency of informational light modulation, automatically supports the spatial coincidence of corresponding elements of both recorded signals, and provides the same spatial scale for both recordings. The suggested method can also be used for introducing phase weight functions in the schemes of space-time ACO processing of wave signals. Advantages of ACO signal processing methods in comparison with corresponding electronic approaches are briefly noted.