Improvement in holographic storage capacity by use of double-random phase encryption

We show that a double-random encryption technique can improve the storage c apacity of an angular-multiplexed holographic memory system. In the hologra phic memory system, input binary images are encrypted into white-noise-like images by use of two random phase masks located at the input and the Fouri er planes. These encrypted images are stored as holograms in a photorefract ive medium by use of angular multiplexing. All the images are encrypted by different sets of random phase masks. Even when the angle separation betwee n adjacent images is small enough to cause cross talk between adjacent imag es, original binary data can be recovered with the correct phase mask; the other reconstructed images remain white-noise-like images because incorrect masks are used. Therefore the capacity of the proposed system can be large r than that of a conventional holographic memory system without the random phase encryption technique. Numerical evaluation and experimental results a re presented to confirm that the capacity of the system with random phase m asks is larger than that of the conventional memory system. (C) 2001 Optica l Society of America.