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Optical Engineering

Symbolic substitution by means of one-of-many coding
Author(s): Ranjani Parthasarathi; Ashok Jhunjhunwala
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Paper Abstract

Symbolic substitution (SS) for digital optical computing initially used intensity coding with one pixel representing one bit. This required recognition of both the dark and the bright pixels in a pattern for complete recognition. To avoid this double recognition, dual-rail coding was introduced, where it is sufficient to recognize either the dark or the bright pixels alone for complete recognition. Subsequently, the modified signed-digit number system was proposed to fully exploit the parallelism of SS for arithmetic operations. This introduces a third symbol - 1 , and with dual-rail coding, this again necessitates recognition of both dark and bright pixels. We argue the usefulness of triple-rail coding to avoid this double recognition. We show that the nature of this one-of-three coding enables simplified recognition of a set of patterns. We present a new implementation of SS based on this coding. We also show that this one-of-many coding can be extended to high-radix arithmetic with equal efficiency. We present an evaluation scheme based on the number of optical hardware elements required by each implementation and use it to compare the different implementations of SS.

Paper Details

Date Published: 1 May 1995
PDF: 8 pages
Opt. Eng. 34(5) doi: 10.1117/12.199886
Published in: Optical Engineering Volume 34, Issue 5
Show Author Affiliations
Ranjani Parthasarathi, Indian Institute of Technology (India)
Ashok Jhunjhunwala, Indian Institute of Technology/Madras (India)

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