Information capacity of holograms in photorefractive crystals

Three-dimensional color holographic display

Three-dimensional (3D) color holograms are recorded in a cerium-doped, strontium barium niobate (SBN:60) photorefractive crystal. These holograms are shown to reconstruct true color reproductions of the original object with an observable field of view of 37 degrees. Angle multiplexing of two or more 3D color holograms is also demonstrated with angle tuning of the reference beam corresponding to a separation angle between stored images of 0.082 degrees. Each of these results is compared with corresponding theoretical predictions.

Interleaving and error correction in volume holographic memory systems

We study the use of error-correction coding (ECC) and two-dimensional interleaving for volume holographic memory (VHM) systems suffering from both random and systematic errors. The bit-error rate (BER) is used as the data-fidelity measure and as a design metric for optical 4f systems. The correlated error patterns arising from both lens aberrations and misalignment errors are analyzed, and we discuss the information theoretic storage capacity of VHM in the presence of such correlated error patterns. The performance of interleaving and ECC is analyzed from both BER and storage-capacity perspectives. Magnification, rotation, tilt, and defocus errors are also studied, and an experimental demonstration that combines ECC with two-dimensional interleaving is included.

High-speed, acousto-optically addressed optical memory

A page-oriented, angle-multiplexed volume holographic optical-memory recording system has been constructed. This memory is addressed by the use of an acousto-optic deflector with a random-access time of 16 µs per page. This enables data transfer rates of 5.28 Gbits/s when pages of binary data are being stored. The reconstruction quality of images stored as memory pages is assessed with the quality achieved with the acousto-optic device compared with that achieved with the original recording optics.

Error correction for increasing the usable capacity of photorefractive memories

Conventional error-correction coding techniques can be used to reduce the minimum signal-to-noise ratio required for achievement an acceptable bit-error rate and can therefore be used to increase the maximum number of pages that can be stored in a photorefractive memory. Because error-correction bits will exact some cost per page in terms of memory capacity, we address the question of when the gain in capacity surpasses this cost. It is found that a factor-of-2 improvement in capacity can be readily achieved.