INTERFEROMETRIC MEASUREMENT OF KRF-LASER-INDUCED REFRACTIVE-INDEX CHANGES IN GERMANOSILICATE FIBERS

Photosensitivity in germanosilicate optical fibers is studied with a f iber Michelson interferometer. Saturation characteristics for multiple KrF-laser exposure are measured, and the origin of the index change i s discussed. The total index change of a high-Ge (35 mol%) fiber is 6 times that of a low-Ge (3 mol%) fiber. In both fibers, the fast end th e slow saturation components are found. An analysis using the Frantz-N odvik equation shows that they are attributed to Ge-Si and Ge2+ defect s, respectively. The saturated index changes in highly reflective fibe r gratings are due to Ge2+ defects.