Effect Of Hydrogen Treatment On Radiation Hardness Of Optical Fibers

We have treated optical fibers in different hydrogen environments to examine the effect of hydrogen treatment on radiation hardness of optical fibers. Both radiation-induced loss and hydrogen-induced loss are related to defect center formation in optical fibers. We have investigated the effects of treatment conditions on defects produced by drawing and 7-irradiation using the techniques of spectral attenuation, Raman scattering, and photoluminescence. Using Ge/P-codoped multimode optical fibers, we observed considerable reduction in the radiation-induced absorption at long wavelengths (X > 1µm) for hydrogen-treated fibers. Post-treatment of irradiated fibers by hydrogen can also reduce existing radiation-induced absorption significantly and increase the hardness of the fibers under sub-sequent irradiation. For Ge /F-codoped multimode fibers, hydrogen treatment has also shown its effectiveness in enhancing radiation hardness. The pretreated fibers show s5.15 % improvement at 850 nm in radiation resistance over untreated fibers. Varying the hydrogen treatment and irradiation history of the fiber had little effect upon the Raman spectrum. However, significant trends were found in the behavior of the photoluminescence. Emission bands in the 600-900 nm spectral region have been found to have intensities which depend upon fiber history. We attribute the improvement in radiation resistance to the passivation of precursors or defects in the optical fiber. Treatment with hydrogen converts certain types of defects into types which do not form deleterious color centers after irradiation. This defect-conversion interpretation is supported by the photoluminescence measurements which reveal variations in color center concentrations with hydrogen treatment, y-irradiation, and optical excitation.