Collinear heterodyning in optical processors

The basic principles of several real-time optical processing schemes employing heterodyning are examined. In each case the method by which the correlation function is developed from the ultrasonic light modulator (ULM) is analyzed. It is shown that in some configurations it is possible to derive the heterodyne reference collinearly, thus increasing the mechanical stability and minimizing the effects of optical aberrations. Experimental results obtained with a correlator using a shear-wave ULM and collinear heterodyning confirm its stability and verify the fact that quality performance can be obtained with inexpensive optical components.