White-Light Correlator Character Recognition
Charles L. Woods, Peter D. Gianino · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1987
Optical correlators operating with spatially coherent white light are simulated on a computer. There are two sources of error in the correlators studied: 1) diffraction spot size changes and 2) transverse dispersion for diffraction grating encoded images and filters. The quality of the output correlation signal is analyzed in terms of peak intensity maximum, peak full-width-half-maximum (FWHM) size and peak-related energy efficiencies. Classical Matched Filter (CMF) operation of the white-light correlator is compared with that of a monochromatic correlator. A 4-filter dispersed white-light processor is required to produce "correlation" peaks with width approaching those of the monochromatic CMF correlator. Possible compensation of the diffractive Vander Lugt white-light dispersion blur in output plane is required for narrow peak operation of single-filter correlators. The corrected on-axis white-light CMF correlator had operating parameters very similar to those of the monochromatic correlator for discrimination between the 25 x 35 pixel letters 0 and G. The 0 and G differ by shifting of one 5 x 5 block of pixels. A phase-only filter dispersed processor simulation shows a dramatic improvement in operating parameters.