Real-Time Optical Correlation With Solid-State Sources

A coherent optical correlator using a diode injection laser source spatially modulated with a liquid crystal light valve was demonstrated for cross correlation and tracking of vehicles in scenes and of areas in aerial scenes. The light valve was optically addressed with a TV monitor allowing imagery from a TV camera or video tapes to be used for input to the correlator. The long wavelength and low coherence make filter recording with laser diodes difficult if not impossible. Filters were therefore recorded with a helium-neon laser for use with the correlator. Correlations obtained with these filters had similar line widths and signal-to-noise ratios when used with helium-neon or diode laser sources. The small size and low power consumption of laser diodes permit the miniaturization of a coherent optical correlator. Two 3 compact correlators using available components were designed. One, a cylindrical package, required 300 cm volume and another more novel arrangement resulted in a 60 cm3 package.