Effect of low dose rate irradiation on doped silica core optical fibers.

The optical attenuation induced in multimode doped silica core optical fiber waveguides by a year's exposure to low dose rate (1 rad/day) ionizing radiation was studied, allowing a characterization of fibers deployed in these environments and a determination of the permanent induced loss in the waveguides. Variations in the induced attenuation at 0.85 microm have been observed with changes in the dose rate between 1 rad/day and 9000 rads/min. These dose rate dependences have been found to derive directly from the recovery that occurs during the exposure; the recovery data predict little or no dose rate dependence of the damage at 1.3 microm. The low dose rate exposure has been found to induce significant permanent attenuation in the 0.7-1.7-microm spectral region in all fibers containing P in the core, whether doped uniformly across the diameter or constrained to a narrow spike on the centerline. Whereas permanent loss was induced at 0.85 microm in a P-free binary Ge-doped silica core fiber by the year's exposure, virtually no damage was observed at 1.3 microm.