Shift-invariant photorefractive joint-transform correlator using Fe:LiNbO_3 crystal plates

Abstract

We report the results of our experimental investigation on a shift-invariant photorefractive image correlator that uses a thin crystal plate of Fe:LiNbO(3), which operates in the Raman-Nath regime of diffraction.

Translation-invariant object recognition system using an optical correlator and a super-parallel holographic random access memory

“…A translation-invariant JTC utilizing a 48-m thin Fe: LiNbO 3 photorefractive crystal, operating at a 2.5-Hz rate with a 3% diffraction efficiency, was demonstrated in the past. 13 Recently, a high-speed but not quite translation-invariant JTC with an effective thickness of the crystal of 560 m was demonstrated to operate at a 10-kHz rate with 0.01% diffraction efficiency using a photorefractive Sn 2 P 2 S 6 crystal. 5 In principle, a translationinvariant correlator in a thick medium can be realized by making use of the high angular bandwidth in the plane that contains the object beam, but is perpendicular to the plane formed by the object and the reference beam.…”

Shift-invariant limited photorefractive-based correlators

“…In recent years, the use of photorefractive (PR) crystals to synthesize largecapacity spatial filters have played a crucial role in the development of real-time correlators [3][4][5][6][7][8][9][10][11][12][13]. The salient features of using thick PR materials for the matched-filter implementation are large capacity, real-time addressing ability, high diffraction efficiency, and higher angular and wavelength selectivities.…”

“…Since the optical correlators that we will discuss are photorefractive (PR) based correlators, the apparent focal depth within the crystal is subjected by the Snell's law of refraction, which can be shown as(4) where r is the refractive index of the thick crystal filter, and f' is the apparent or actual focal length, which is approximately by f' = u+' f+2X(-l). (5)Thus, the allowable thickness of the PR crystal filter is given by t = 2'(6) in which we assume that the thick-crystal filter is centered at the apparent focal length f'.Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/24/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx3.…”