ANALYSIS OF SPATIAL LIGHT-MODULATOR CONTRAST RATIOS AND OPTICAL CORRELATION

We have performed a general analysis of optical correlators with spata l light modulators (SLM's) whose primary defect is a finite contrast r atio (CR). Our mathematical analysis identifies three noise terms that appear in addition to the correlation term. The filter SLM contains e ither a phase-only filter (POF) or a binary-phase-only filter (BPOF). Insertion of a de block at the center of the filter SLM decreases the noise background in the correlator plane; this de block is larger than that required for the same level of performance in a correlator whose SLM's have transmissive (or reflective) dead zones. With a noise-free input and the de block, our computer simulations that show the peak i ntensity falling off as the CR decreases are in quantitative agreement with the correlation term of the mathematical model. For a cluttered, disjoint noise input this agreement is only qualitative, and at low C R's the de block is definitely required for the BPOF correlator if the secondary peaks in the output are to be brought below the correlation peak.