A photorefractive organically modified silica glass with high optical gain

Photorefractive materials1 exhibit a spatial modulation of the refractive index due to redistribution of photogenerated charges in an optically nonlinear medium. As such, they have the ability to manipulate light and are potentially important for optical applications1 including image processing, optical storage, programmable optical interconnects and simulation of neural networks. Photorefractive materials are generally crystals, polymers and glasses with electro-optic or birefringent properties and non-centrosymmetric structure2. Here we report the photorefractive effect in both non-centrosymmetric and centrosymmetric azo-dye-doped silica glasses, in which refractive index gratings that are spatially phase-shifted with respect to the incident light intensity pattern are observed. The effect results from a non-local response of the material to optical illumination, and enables the transfer of energy between two interfering light beams (asymmetric two-beam coupling). Although the writing time for the present grating is relatively slow, we have achieved a two-beam coupling optical gain of 188 cm-1 in the centrosymmetric glasses, and a gain of 444 cm-1 in the non-centrosymmetric structures. The latter are fabricated using a corona discharge process3 to induce a permanent arrangement of azo-dye chromophores.