Random phase shifters for fourier transformed holograms.

The random phase shifter method for Fourier transformed holograms is discussed. It is shown that by adopting the random phase shifters of the phase quantization levels beyond 2 (4, for example), the effectiveness becomes about twice that of 2, and that the reduction of the effectiveness by the coincidence between a pattern of the information and a phase shifter can be withdrawn under the probability of 10(-10). Hologram memories of information storage density of 10(5) bits/mm(2) and 2.0 x 10(3) characters/ mm(2) are demonstrated.