PHOTOSENSITIVITY IN CE-3+-DOPED OPTICAL FIBERS

A UV-induced absorption change has been studied in Ce3+-doped preforms and fibers made by a solution-doping modified-chemical-vapor-deposition technique. A reduction in the Ce3+ concentration and the creation of a broad absorption band extending from the UV to the IR were seen on UV exposure. In addition, a peak in the absorption band is created at 245 nm, attributed to Ce4+. The reduction in Ce3+ concentration was observed to remain for at least 3 months, whereas the created broad absorption bands at 632.8 nm recovered by 90% in 2 h. Large UV-induced refractive-index changes (10(-4)) in Ce3+-doped fibers are also demonstrated. A linear dependence on the average UV intensity is found below 4 kW/m2, above which saturation occurs. The index change also increases with increasing Ce3+ concentration, again saturating at high levels. A decrease in magnitude with increasing wavelength is observed, but the index change at 1.55 mum is still more than 50% of that at 0.5 mum, demonstrating the potential of the technique for producing gratings with optical communication applications.