X-ray irradiation effects on a multistep Ge-doped silica fiber produced using different drawing conditions

We report an experimental study based on confocal microscopy luminescence (CML) and electron paramagnetic resonance (EPR) measurements to investigate the effects of the X-ray (from 50 krad to 200 Mrad) on three specific multistep Ge doped fibers obtained from the same preform by changing some of the drawing conditions (tension and speed). CML data show that, both before and after the irradiation, Germanium Lone Pair Center (GLPC) concentrations are similarly distributed along the diameters of the three fibers and they are partially reduced by irradiation. The irradiation induces also the Non Bridging Oxygen Hole Center (NBOHC) investigated by CML and other paramagnetic defects as the Ge(1), Ge(2), E'Ge and E'Si investigated by EPR. We do not observe significant differences in the induced concentrations of these types of defects in the three fibers. All the results suggest that within the range of investigated drawing parameters (usual range for specialty optical fibers), the fiber radiation sensitivity is unaffected by these variations. Consequently, these results show that the drawing parameters (drawing tension and speed) cannot easily be adjusted to improve the radiation hardness of germanosilicate optical fibers.