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

We applied theoretical and experimental spectroscopytools to ad hoc silica-based “canonical” samples tocharacterize the influence of several dopants and of some drawingprocess parameters on their radiation sensitivities. We presentin this paper, the recent advances and results occurring fromour coupled approach. On the experimental side, we studied thedoping influence on the response of optical fibers and showed thatchanging the drawing parameters has a negligible influence on thefiber response in the case of specialty fibers. We focus mainly onthe SiE' defect that is observed through Electron ParamagneticResonance (EPR) measurements in all canonical samples. Onthe theoretical side, we exhibit the improvements obtained inthe calculations of electronic and optical properties of defects byusingMany Body Perturbation Theory through the use of the GWapproximation and the resolution of the Bethe-Salpeter equationinstead of the Density Functional Theory (Local Density Approximation).To continue to strengthen the link between experimentand simulation, we have performed first-principles calculationsof EPR parameters of some silica-based defects. The first resultsallowing for an attribution of EPR E'signals to structural modelsare presented. In particular, we confirm that the E'_gamma center isoriginated by an unpaired electron in a sp^3 state at a three-foldcoordinated silicon atom.