ULTRAVIOLET-ENHANCED PHOTOSENSITIVITY IN CERIUM-DOPED ALUMINOSILICATEFIBERS AND GLASSES THROUGH HIGH-PRESSURE HYDROGEN LOADING

We have studied the photosensitivity of both hydrogen-loaded and unloa ded Ce3(+)-doped aluminosilicate fibers. Refractive-index changes as g reat as 1.5 x 10(-3) have been achieved in the treated samples. The th ermal stability of gratings appears to depend not on whether the fiber is treated but rather on the UV cumulative fluence used for the inscr iption. The change in refractive index follows a power law dependence on exposure time and does not saturate for exposure times as long as s imilar to 2 h. In contrast, the changes in the absorption spectra satu rate after a few seconds of exposure time. This observation and others that we report show that the color-center model does not fully explai n the refractive-index change. As is observed in germanosilicate fiber s, exposure of the hydrogen-loaded fiber to UV light increases the hyd roxyl content according to a power law dependence as a function of tim e. This shows that enhancement of the fiber's photosensitivity is stro ngly related to hydrogen-assisted bond breaking within the glass netwo rk. Microscopic inspections of gratings written in the cores of hydrog en-loaded preforms have shown corrugations embedded in a valley. The d epth of the valley and the heights of the corrugations are more import ant in the hydrogen-loaded sample than in the case of an unloaded pref orm. This difference is closely correlated with the enhancement of the fiber's photosensitivity. (C) 1997 Optical Society of America.