Inner-product implementations of optical associative memories

An inner-product expression of an associative memory is equivalent mathematically to the familiar outer-product formulation, but the former allows access to an interior plane where effective thresholding may be performed. An optical implementation in line with the inner-product approach is presented. It demonstrates high memory capacity and, in principle, the potential of being applied to many problems which are usually thought of as outer-product problems. Special optical problems arise when an inner-product associative memory is made all optical, but these can be resolved