Two-step recording in photorefractive crystals

Abstract

Many photorefractive crystals that are insensitive in the IR spectral region may be sensitized for IR recording by two-step processes. Nondestructive readout of the holograms recorded by two-step processes is possible. In contrast to other methods for hologram stabilization, e.g., thermal fixing, the versatility of desired optical erasure is maintained. Utilization of the pyroelectric effect even promises to shift the recording wavelength to the region of the telecommunication wavelengths around 1.5 μm. The lifetime of the holograms can approach years in materials like LiNbO3 if the doping level is optimized and if the crystals are dehydrated. Direct IR recording with light of the operational wavelength has two practical advantages: (1) Not only gratings, but also more sophisticated components can be fabricated. A wavelength filter that focuses the diffracted light into a fiber is one example. (2) The holograms can be recorded in the final device. This simplifies assembling and adjustment of the components. © 2006 Springer Science+Business Media, Inc.