Pulsed X-ray and γ rays irradiation effects on polarization-maintaining optical fibers

We studied the sensitivities at 1.55 μm of three polarization-maintaining (PM) and three unstressed single-mode (SM) optical fibers under pulsed X-ray (∼1 MeV) and steady-state γ-ray (∼1 MeV) radiation. Our results showed no differential radiation-induced attenuation (RIA) between the two orthogonal polarization axes of PM fibers for times ranging from 10^-6 s to 100 s after ionization pulse (dose <1 kGy(SiO₂), dose rate >1MGy/s). The two inner cladding phosphorus-codoped PM fibers and their corresponding SM fibers exhibited the same RIA levels and kinetics after both irradiation types. Their radiation responses could be explained by their compositions and by the properties of the absorbing phosphorus-related defects generated in the light guiding region (core and inner cladding). The inner cladding fluorine-codoped PM fiber showed radiation-tolerant properties compared with its SM counterpart. We assumed, therefore, that the outer stress applying region dopants could have an impact on the fiber radiation sensitivity under both irradiation types. More particularly, we showed that the cladding phosphorus-codoping far from the light guiding region reduces the RIA related to the germanium defects in the fiber core. This effect could be due to the donor nature of the double phosphorus-oxygen bond and could be exploited to design radiation-hardened polarization-maintaining and single-mode optical fibers.