Bragg grating fabrication in germanosilicate fibers by use of near-UV light: a new pathway for refractive-index changes

Using 334-nm light, we demonstrate side writing of Bragg gratings with an index change of $\sim {10}^{-4}$ in germanium-doped fibers. No hydrogen loading of the fibers was required. These gratings have the same temperature stability as gratings fabricated with 240-nm light. Our results suggest that photoionization is not needed for formation of gratings in Ge-doped glass. We observe an enhancement of the 334-nm photosensitivity in boron-codoped fibers and suggest that B facilitates a structural transformation of the glass.