Radiation-induced absorption and photobleaching in erbium Al–Ge-codoped optical fiber

In this work, we analyze the absorption spectra of silica fibers doped with erbium (Er) and usual codoping atoms such as aluminum (Al) and germanium (Ge). This study is performed in the 400 nm to 1000 nm wavelength range. We describe and identify relations between the optical fiber composition and the changes in their absorption spectra after two consecutive processes: a 300-Gy gamma irradiation and then after photobleaching obtained with a 980 nm laser light. Among the results we obtained, we want to emphasize that the creation of Al-related defects, known to be the main origin of radio-darkening in aluminosilicate fibers, depends also on the Al/Er ratio. We also identify a new Al originated trap, different from Al-OHC and not referenced in the existing scientific literature to our knowledge. Its contribution to the RIA seems to be really significant. Moreover, photobleaching appears to be a possible recovery mechanism as the Al-colored centers vanish under 980 nm laser light.