Abstract

The photorefractive crystals LiNbO₃, SBN, and BaTiO₃ are leading candidates for holographic data storage because they provide high values of diffraction efficiency for thick gratings and are self-processing. The storage capacity in photore materials is determined by the hologram selectivity (angular and/or wavelength), the maximum index modulation (dynamic range), and the noise arising from incoherent scattering or stimulated photorefractive scattering (SPS). In the writing process, a 90° beam-crossing angle provides optimum angular selectivity but requires the use of s-polarized beams, typically corresponding to ordinary polarization in the crystal. Even with the grating k-vector parallel to the c-axis, the dynamic range with ordinary-polarized readout is far from optimum. When the 90° requirement on crossing angle is relaxed and extraordinary-polarized readout beams are used, a much larger dynamic range can be obtained, but Bragg-mismatch issues must then be carefully considered. In this study, we focus on the angular-multiplexing approach to data storage and address the tradeoffs between the dynamic range and the angular selectivity in determining the storage capacity for ferroelectric oxide photorefractive crystals.

© 1995 Optical Society of America