Unique Properties of SBN and Their Use in a Layered Optical Memory

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Abstract
Holographic storage experiments using crystal Sr0.75Ba0.25Nb2O6 (SBN 75/25) as a volume-phase holographic medium show that this material is the most sensitive crystalline storage medium yet discovered. An exposure level of 0.003 J/cm2 at 0.488 μm produces a 1% diffraction efficiency in a 5-mm length of crystal. In addition to high recording sensitivity, SBN 75/25 exhibits interesting electric-field induced effects that include electric-field enhanced recording sensitivity and voltage-switchable latent-to-active holographic reconstruction efficiency. These effects are explained in terms of drift and diffusion of photoionized carriers coupled with the nonlinear electrooptic behavior characteristic of this low Curie temperature ferroelectric crystal. Detailed measurements of the holographic recording and reconstruction properties of thick phase-volume holograms stored in SBN 75/25 are reported. A mechanism is proposed that correlates the observed electrically controlled holographic response with the dielectric behavior of the crystal. These interesting effects are used to implement a novel, layered optical memory having no moving parts and having electrical access for writing or reading selected layers. An experimental model of the layered memory was constructed to demonstrate the interrelation of the several phenomena involved in the layered concept.