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the reduction of the effectiveness by the coincidence between a pattern of the information and a phase shifter can be withdrawn under the probability of 10−10.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 105 bits/mm2 and 2.0 × 103 characters/mm2 are demonstrated.
© 1972 Optical Society of America
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