Influence of Self-Trapped Holes on the Responses of Fluorine-Doped Multimode Optical Fibers Exposed to Low Fluences of Protons

The radiation vulnerability of various classes of multimode silica-based optical fibers is investigated for space applications operating from the ultraviolet up to near-infrared spectral domains. For this, radiation-induced attenuation (RIA) levels and kinetics in the 300 ÷ 1100 nm wavelength range are monitored during and after steady state 105 MeV proton exposure at room temperature (RT, equivalent dose of ∼250 Gy(SiO₂)). The responses of three types of “radiation hardened” optical fibers with either a pure-silica core (PSC) or fluorine-doped cores are compared to the one of a Telecom-grade germanosilicate optical fiber. RIA growth during irradiation and decay after irradiation (recovery phase) reveal that the highly fluorine (2 wt.%)-doped optical fiber, manufactured by axial vapor deposition process, presents higher RIA levels above 600 nm than other tested optical fibers. Indeed, if the high F-doping level reduces the UV-RIA related to SiE’, NBOHC or chlorine-related centers this composition appears as associated with a strong RIA increase in the visible-near-IR through the more efficient generation of RT unstable strain-assisted or inherent self-trapped holes.