A photorefractive organically modified silica glass with high optical gain

Photorefractive materials(1) exhibit a spatial modulation of the refractive index due to redistribution of photogenerated charges in an optically nonl inear medium. As such, they have the ability to manipulate light and are po tentially important for optical applications(1) including image processing, optical storage, programmable optical interconnects and simulation of neur al networks. Photorefractive materials are generally crystals, polymers and glasses with electro-optic or birefringent properties and noncentrosymmetr ic structure(2). Here we report the photorefractive effect in both non-cent rosymmetric and centrosymmetric azo-dye-doped silica glasses, in which refr active index gratings that are spatially phase-shifted with respect to the incident light intensity pattern are observed. The effect results from a no nlocal response of the material to optical illumination, and enables the tr ansfer of energy between two interfering light beams (asymmetric two-beam c oupling). Although the writing time for the present grating is relatively s low, 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-centrosymmetr ic structures. The latter are fabricated using a corona discharge process 3 to induce a permanent arrangement of azo-dye chromophores.