Optical processing using photorefractive GaAs and other compound semiconductor crystals (28) is achieved in a four-wave mixing configuration. Potential applications of optical processing include spatial light modulation, phase conjugation, correlation, convolution, edge enhancement, matrix multiplication, incoherent-to-coherent conversion, and many others. In particular embodiments, optical processing, matrix multiplication, and integrated semiconductor optical information processors are demonstrated. In the case of integration of semiconductors and optical information processors, a spatial light modulator (88) is fabricated on a surface of a compound semiconductor crystal to form an integrated device (86). The device uses the spatial light modulator to transfer electrical data into an optical form and then employs the photorefractive effect in the bulk for processing the data.