Photorefractive time-intergrating correlator

Abstract

The time-integrating property of photorefraction is a useful tool that has been used in conjunction with acousto-optic devices to produce correlation functions of rf signals.1That system consisted of two acousto-optic devices that were positioned so that the two diffracted beams (resulting from the two drive signals feeding the devices) wrote a grating within the photorefractive BiSiO12crystal. The two diffracted beams, with the spatiotemporal modulation impressed by the acousto-optic devices, intersect within the photorefractive BSO to create a holographic grating that forms with a time constant that is inversely proportional to the total intensity falling on the crystal. The time-integrated grating is then read out with a third beam, which then carries the correlation information. To obtain appreciably large amplitude gratings, the two beams must intersect with a large relative angle at the photorefractive crystal, resulting in a loss of resolution because of crosstalk within the thickness of the crystal; otherwise, a large eternal field must be applied, which also has some associated drawbacks.2We present a different architecture in which the acousto-optic devices are oriented orthogonally to the photorefractive grating direction, so that larger intersecting angles can be accommodated without a loss of resolution. Experimental results are given.