Digital optical processing with photorefractive materials: applications of a parallel half-adder circuit to algorithmic state machines

Theoretical and experimental results are presented for a real-time parallel half-adder circuit with the use of nonlinear interactions in photorefractive media. The two-valued intensity input bit planes contain 256 bits in a 16×16 format. They are processed in parallel by three photorefractive BaTiO3 crystals operating in a two-wave mixing configuration. Sequential algorithms for binary arithmetic can be implemented by providing the processor with a feedback loop. A prototype photorefractive algorithmic state machine that performs multibit operations between two arrays of numbers is proposed. The addition of two sequences of 5-bit numbers is experimentally demonstrated, and improved performances are expected with the use of phase conjugation techniques.