O2-Loading Treatment of Ge-Doped Silica Fibers: A Radiation Hardening Process

The effects of a high-pressure O2-loading treatment on the radiation response of Ge-doped optical fibers (OFs) were investigated. We found that the incorporation of high concentration of interstitial molecular oxygen remarkably enhances the resistance to ionizing radiation of Ge-doped OFs in the UV-Visible domain and, at the same time, improves the transmission of UV light in the unirradiated OF sample. By comparison with previously reported results, the O2-loading treatment turned out to increase the radiation resistance of Ge-doped OFs more efficiently than F or Ce codoping. The understanding of such amelioration relies in basic radiation-induced mechanisms that were characterized with three complementary experimental techniques: Confocal microluminescence (CML), online radiation-induced attenuation (RIA), and electron paramagnetic resonance (EPR). We have shown that the almost intrinsic oxygen-deficient character of germanosilicate fibers can be overturned by forcing O2 diffusion in the glass matrix. The Germanium lone pair centers, which are precursor defects invariantly present in the as-drawn Ge-doped OFs, are converted to some other yet-undetermined species. Consequently, the usual chain of radiation-activated processes leading to the creation of Ge(1) and Ge(2) is substantially suppressed. The experiments have also highlighted an increased production of oxygen-excess related defects under irradiation. Although in terms of RIA, the tradeoff between the oxygen-excess and oxygen-deficient defects is already a positive one, it is conceivable that the radiation resistance of Ge-doped OFs can be further improved by optimizing the O2-loading treatment.