Bragg Grating Fabrication in Fibers by Near-UV Light

Abstract

The photosensitivity of germanosilicate fibers has been tied to the presence of germanium oxygen-deficient defects (GODC) [1,2]. These defects are identified by a strong absorption peak at 240 nm and a weaker absorption peak at 330 nm (Fig. 1) [3]. The microscopic model of these defects is still debated [4-7]; however, the three-level model of the defect shown in Fig. 2 nicely explains the defect’s main spectroscopic features [4]. It was thought that color center formation due to photoionization of defects by 240 nm light was the principal mechanism of index change (through the Kramers-Kronig relation) [8]. However recent tension measurements and observations of glass densification after UV exposure suggest that a structural transformation of the glass occurs [9,10].