Photosensitivity in Ce³⁺-doped optical fibres

Abstract

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 2h. 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 1.33µm is still more than 50% of that at 0.5µm, demonstrating the potential of the technique for producing gratings with optical communication applications.

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