OPTICAL DIGITAL COMPARISON UNIT FOR EQUAL-TO, LESS-THAN, AND GREATER-THAN DETERMINATION

A number of nonnumerical processing applications, including database m anagement, full text search, and pattern recognition rely heavily on d igital comparisons. The development of massive-capacity optical memori es coupled with the high speed and parallelism of optics have led to t he investigation of optical techniques for nonnumerical processing. Th is paper proposes a system design for an optical comparator capable of performing multiple equal-to, less-than, and greater-than comparisons between pairs of binary words. The comparator consists of three two-d imensional arrays of optical elements based on a new optical logic dev ice called the light-amplifying optical switch. The first two stages c ontain inverters, NOR gates, and flip-flops, while the third stage is a custom-designed winner-takes-all network. With a compact design and with small high-speed devices a comparator with 2.5 x 10(4) pixels cou ld theoretically attain a processing rate of approximately 4 x 10(10) 16-bit word comparisons/s.