Optical digital comparison unit for equal-to, less-than, and greater-than determination

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Abstract
A number of nonnumerical processing applications, including database management, full text search, and pattern recognition rely heavily on digital comparisons. The development of massive-capacity optical memories coupled with the high speed and parallelism of optics have led to the investigation of optical techniques for nonnumerical processing. This 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-dimensional arrays of optical elements based on a new optical logic device called the light-amplifying optical switch. The first two stages contain 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 × 104 pixels could theoretically attain a processing rate of approximately 4 × 1010 16-bit word comparisons/s.