2 METHODS OF REDUCING THE DYNAMIC-RANGE OF A HOLOGRAPHIC FILTER

Two methods of reducing the dynamic range of the transmittance of comp uter-generated interconnection holograms are presented and compared. T he holograms are used in an optical implementation of an associative m emory to connect the input and the output planes but are representativ e of more general N-4 interconnection holograms. Because the holograms play a double correlation-reconstruction role, the standard spectrum- smoothing techniques (e.g., random phase) cannot be applied. We show, in computer simulations and optical experiments, that by using determi nistic phase functions that can be realized in the optical system (def ocusing the hologram or controlling the phases of the diffraction spot s of a Dammann grating used in the system input) the hologram dynamic range can be lowered, reducing the errors during the hologram binariza tion and increasing the hologram's diffraction efficiency. (C) 1996 Op tical Society of America