EDGE ENHANCEMENT BY USE OF MOVING GRATINGS IN A BISMUTH SILICON-OXIDECRYSTAL AND ITS APPLICATION TO OPTICAL CORRELATION

The technique of moving gratings in a photorefractive crystal is appli ed to the edge enhancement of objects and edge-enhanced optical correl ation. The nonlinear dependence of the optimum fringe velocity on the fringe modulation and the variation of the enhancement of the diffract ion efficiency with fringe modulation at a fixed fringe velocity appro priate to high fringe modulations are experimentally investigated. It is shown that the diffraction at high fringe modulations, which corres ponds to the high-spatial-frequency components of the Fourier spectrum , is enhanced by a factor of approximately 3.7, whereas the diffractio n at low fringe modulations is suppressed by a factor of 0.6. The prop osed technique has the advantages of real-time enhancement, arbitrary selection of the spatial frequency to be enhanced, and improved stabil ity of the output. Experimental results of the edge enhancement of obj ects and edge-enhanced correlation are presented. (C) 1998 Optical Soc iety of America.