Prediction of radiation-induced light absorption in optical fibers with an undoped silica core for space applications

Radiation-induced absorption (RIA) of light in five isotropic optic fibers (OFs) with a core of undoped silica glass (SiO$_2$) and a fluorosilicate cladding and one birefringent OF of the “PANDA” type of the same chemical composition was measured at a wavelength $\lambda$ = 1.55 $\mu$m under $\gamma$-irradiation to a dose of 1 kGy ($\sim$1 Gy/s), 15–45 min after completion of irradiation, and in a few months at temperatures +25 and -60$^{\circ}$C. An extrapolation of the RIA after irradiation in the framework of the kinetic model of the $n$ th order, which gave a forecast of the RIA for isotropic OFs of $\sim$1.1 and $\sim$ 0.3 $\pm$ 0.1 dB/km at -60 and +25$^{\circ}$C, respectively, was made to assess the RIA at the end of a 15-year mission in space. It has been concluded that it is possible to use at least 4–5 km of OF in space under conditions of temperature variation within $\pm$ 60$^{\circ}$C at a maximum dose of 1 kGy and a mission duration of 15 years. It has also been established that the RIA will not have been higher in the birefringent OF than in the isotropic ones by the end of such a mission.