Abstract

Photorefractivity observed in an optical fibre germanium doped core at 240nm, allows the realization of fibre grating devices of great interest for optical telecommunications [1]. To master Bragg grating fabrication or predict the life time of those components, it is necessary to understand the involved physical phenomenons. Several mechanisms are proposed, essentially based on Kramers-Kronig conjugation [2,3]. However, by performing interferometric microscopy measurements at the surface of germanosilicate preforms after Bragg grating inscription, we have pointed out a corrugation. They are accounted for by a model of photoinduced densification grating [4,5]. If explains the major part of photorefractive index change In BPG285 preforms [6]. We generalize here the conclusions by presenting measurements done on a preform made in our laboratories and, for the first time, on the associated optical fibre.

© 1995 Optical Society of America