<title>Laboratory Comparison Of Continuous VS. Binary Phase-Mostly Filters</title>

Abstract

Recent developments in spatial light modulators have led to devices which are capable of continuous phase modulation, even if only over a limited range. We used one of these devices, the Texas Instruments deformable mirror device, to compare the relative merits of binary and partially-continuous phase filters in a specific problem of pattern recognition by optical correlation. Each filter was physically limited to only about a radian of modulation. Researchers have predicted that for low input noise levels, continuous phase-only filters should have a higher absolute correlator peak output than the corresponding binary filters, as well as having a larger signal-to-noise ratio. When continuous and binary filters were implemented on the DMD and they exhibited the same performance, an ad hoc filter optimization procedure was developed for use in the laboratory. The optimized continuous filter gave higher correlation peaks than did an independently optimized binary filter. Background behavior in the correlation plane was similar for the two filters, and thus the signal-to-noise ratio showed the same improvement for the continuous filter. A phasor diagram analysis and computer simulation have explained part of the optimization procedure's success.