Heterodyne readout for read-write holographic memories.

A heterodyne readout technique for read-write holographic memory systems that reconstruct a virtual image wavefront is described and demonstrated. The conventionally recorded hologram is illuminated simultaneously with a suitable combination of temporally modulated reference and modified object waves for readout. The resulting enhancement of peak signal at the photodetector is 2 tau(0) (etaK)(-1/2), where tau(0) is the average amplitude transmittance of the hologram, K is the recording beam balance ratio, and eta is the efficiency for conventional readout. Best performance is obtained for temporal phase modulation. The coupling of the illuminating wavefronts by the hologram is analyzed.