The role of fluorine-doped cladding in radiation-induced absorption of silica optical fibers

Radiation-induced absorption spectra and radial distribution of non-bridging oxygen over the fiber core are compared in fibers and preform slices fabricated under different technological regimes with KU-1 and KS-4V silicas in the core. The radiation-induced non-bridging oxygen concentration is found to peak at the core-cladding interface. Fiber perform fabrication and fiber drawing processes are found to have different influence on its value in fibers with low-OH (KS-4V) and high-OH (KU-1) silicas in the core. The precursors of non-bridging oxygen near the core-cladding interface are argued to arise at the stage of preform fabrication at least in the case of KU-1 fibers. Their concentration decreases with increasing the fluorine concentration in the cladding. In the case of KS-4V fibers the increase of the radiation-induced non-bridging oxygen concentration at the core periphery is argued to have a different nature as compared to KU-1 fibers.