Coupled Theoretical and Experimental Studies for the Radiation Hardening of Silica-Based Optical Fibers

Abstract : We applied theoretical and experimental spectroscopy tools to ad hoc silica-based "canonical" samples to characterize the influence of several dopants and of some drawing process parameters on their radiation sensitivities. We present in this paper, the recent advances and results occurring from our coupled approach. On the experimental side, we studied the doping influence on the response of optical fibers and showed that changing the drawing parameters has a negligible influence on the fiber response in the case of specialty fibers. We focus mainly on the ${rm SiE}^prime$ defect that is observed through Electron Paramagnetic Resonance (EPR) measurements in all canonical samples. On the theoretical side, we exhibit the improvements obtained in the calculations of electronic and optical properties of defects by using Many Body Perturbation Theory through the use of the GW approximation and the resolution of the Bethe-Salpeter equation instead of the Density Functional Theory (Local Density Approximation). To continue to strengthen the link between experiment and simulation, we have performed first-principles calculations of EPR parameters of some silica-based defects. The first results allowing for an attribution of EPR E' signals to structural models are presented. In particular, we confirm that the E'g center is originated by an unpaired electron in a sp3 state at a three-fold coordinated silicon atom.