IMPLEMENTATION CONSIDERATIONS OF SYMBOLIC SUBSTITUTION IN DIGITAL OPTICAL COMPUTING

An important area of current focus in optical computing research is th e technique of Symbolic Substitution (SS), proposed by Huang in 1983. The technique is successful by virtue of its parallel signal processin g ability. Coupled with modified signed digit (MSD) arithmetic and/or high-radix arithmetic, serval researchers have been able to achieve hi gh speed of parallel operations in digital computing. Although dual-ra il logic for SS avoided the troublesome need for recognition of both b right and dark pixels, with the introduction of MSD, the dual recognit ion problem reappeared. A triple-rail logic which is compatible with b oth MSD and optical computing requirements of SS has been suggested. B esides explaining the scheme of triple-rail coding for MSD, techniques for its implementation in digital optical computing are presented and discussed. Possible extension of the scheme to high-radix arithmetic is indicated.