Abstract

New adaptive filtering structures have been developed which use AO delay lines in conjunction with photoretractive correlation techniques. Two different correlation techniques are described: one uses the charge transport effects due to the product of an applied piezoelectric field times photoconductivity, the second uses the product of source intensity modulation times the intensity modulation produced by an AO Bragg cell. In both cases the resultant trapped charge pattern is proportional to the correlation between the two input quantities. The correlation value is read optically by using the EO effect. The EO-induced index grating is superimposed on the original acoustic strain-induced grating to produce a tapped delay line with tap weights proportional to correlation values. The result is a simple implementation of all the functions required to execute the LMS adaptive algorithm.

© 1992 Optical Society of America