Photorefractive half-adder: beam-fanning for optical generation of ‘SUM’ and ‘CARRY’

Abstract

Optical implementation of an adder of arithmetic units that processes binary numbers is outlined. Dynamic range compression using biasing illumination in beam-fanning geometry as observed in a photorefractive BaTiO 3:Fe crystal forms the underlying principle of operation. By proper choice of polarization for two input signals, XOR and AND operations are realized. These two operations are essentially analogous to SUM and CARRY generation for binary addition. By providing shift (only in case of CARRY) and feedback, experimental results for half-adder are obtained. In addition, the technique forms a very simple way of implementing ‘original carries’ as required for full-adder. The geometry proposed is simple, energy-efficient and can be easily extended to multi-wavelength operations thus achieving spectral parallelism in optical domain.