Photosensitivity in germano-silicate sol-gel thin films

Binary germano-silicate thin-film waveguides were produced by the sol-gel method with 10, 25 and 45 mol% GeO₂. Post-depositin, reducing-atmosphere heat treatments were used to induce a variety of photosensitive defects in the films. The waveguides were subsequently exposed to guided counter-propagating beams at 488 nm to seed and grow permanent optical gratings. The mechanisms of defect formation and bleaching following exposure at 488 and at 248 nm are analyzed, and the role of these mechanisms in developing photosensitivity is elucidated. New photo-induced absorptive processes are observed and related to the optical behavior. Models for photosensitivity are reviewed in light of these observations.