Proton- and Gamma-Induced Effects on Erbium-Doped Optical Fibers

We characterized the responses of three erbium-doped fibers with slightly different concentrations of rare-earth ions (240-290 ppm) and Al₂O₃ (7-10 wt.%) during proton and gamma-ray exposures. We have simultaneously measured the radiation-induced attenuation (RIA) around the Er³⁺ ion pumping wavelength (980 nm) and the associated changes of the Er³⁺ emission around 1530 nm. The three erbium-doped fibers show similar radiation responses. All fibers exhibit RIA levels between 9 times 10^-3 and 1.7 times 10^-2 dB m^-1 Gy^-1 at 980 nm and between 4 times 10^-3 and 1.1 times 10^-2 dB m^-1 Gy^-1 at 1530 nm. Protons and gamma-rays lead to similar radiation damages, with small differences between the protons of different energies (50 MeV and 105 MeV). Furthermore, we have performed online measurements of the spectral dependence of RIA from 600 to 1600 nm and offline measurements from 1200 to 2400 nm. The three fibers exhibit the same spectral response. Losses decrease monotonically from the visible to the infrared part of the spectrum. We have performed spectral decomposition of these RIA curves with the help of absorption bands previously associated with radiation-induced point defects. Our analysis shows that the main part of the RIA (600-1700 nm) in erbium-doped glass can be explained by the generation of Al-related point defects. The other defects related to the germanium and phosphorus doping of the silica seem to have a lower contribution to the induced losses. The Er³⁺ ion properties seem to be mainly unaffected by proton exposure, suggesting a solvation shell around the Er³⁺ ion formed by Al₂O₃ species.