Volume holographic storage system

A phase encoded volume holographic storage system uses a phase encoding multiplexer 40 that generates truly binary phases of light in the reference beam. The phase encoding multiplexer comprises a liquid crystal device having an array of liquid crystal cells 71, 73 that convert the reference beam into an array of parallel beamlets 65, 67 of light. Each cell in the array has electrodes patterned as two sets of parallel fingers, with each set forming a diffraction grating 83, 85. The sets of fingers are interdigitally spaced so that fingers on the two sets are spaced apart a distance equal to one-half the grating period. Means are provided for activating only one of the diffraction gratings in each cell at any one time. Thus each beamlet of light exiting each cell when one of the diffraction grating patterns is activated is precisely 180 degrees out of phase with the light exiting the cell when the other complementary diffraction grating pattern is activated. The phase modulator is connected to a data controller that activates each electrode in each cell of the array according to predetermined orthogonal codes, thereby permitting multiple pages of data to be recorded in the holographic medium with each page being recorded according to a different one of the phase codes from the reference beam.