Investigation by Thermoluminescence of the Ionization and Annealing Processes in Irradiated Ge-Doped Silica Fiber Preform

Germano-silicate fibers, mostly employed for telecom applications, are also implemented in radiation environments for data links or sensing. In this field, the understanding of radiation-induced mechanisms leading to the degradation of the performances of silica optical fibers has an essential role. Particularly, the estimation of the activation energies of the density of trapped states (DOTSs) governing the radiation-induced attenuation (RIA) is of primary importance. To investigate these mechanisms, the thermoluminescence (TL) is a powerful technique, by which the extrapolation of DOTSs has been previously largely achieved for pure and Al-, P-, Er-, and Yb-doped silica. Despite the key applications related to Ge-doped silica, one cannot do the same for this kind of fiber, due to an “anomalous” increase of their TL response along with the heating rate. The objective of this work is primarily to elucidate the specific radiation-induced mechanisms associated with the presence of Ge in silica that notably induce the anomalous TL response. We show from the experimental study of the RIA thermal annealing during the TL readout, and its correlation with the TL glow curve, that oxygen-deficient centers (ODCs) centers, trapping electrons during irradiation, form deep states which act as recombination center (RC) in the TL process. Finally, and most important, we propose a model that explains the TL anomalous features and how they are arisen from two specific properties of the annealing processes of Ge-related radiation-induced centers.