Interferometric measurement of KrF-laser-induced refractive index changes in germanosilicate fibers

Abstract

Photosensitivity in germanosilicate optical fibers is studied with a fiber Michelson interferometer. Saturation characteristics for multiple KrF-laser exposure are measured, and the origin of the index change is 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 and the slow saturation components are found. An analysis using the Frantz-Nodvik equation shows that they are attributed to GeSi and Ge 2+ defects, resectively. The saturated index changes in highly reflective fiber gratings are due to Ge 2+ defects.