X-rays, γ-rays, electrons and protons radiation-induced changes on the lifetimes of Er 3+ and Yb 3+ ions in silica-based optical fibers

Abstract : The evolution of Ytterbium 2F5/2 and Erbium 4I13/2 energy level lifetimes versus doses of various radiation types (40 keV X-rays, 480 MeV protons, 1.2 MeV γ-rays and 6 MeV electrons) were investigated on samples of silica-based Rare-Earth Doped optical Fibers (REDFs). For each studied sample (Er-doped and Er/Yb-doped), a strong dependence of the lifetime value on the irradiation dose (for equivalent doses ranging from 10 Gy(SiO2) to 10 MGy(SiO2)) is observed regardless of the radiation nature. For both fiber types and luminescent ions, complex dose dependences are observed: a limited decrease of the lifetime at the lower doses, whereas a large reduction is reported at doses exceeding 100 kGy(SiO2). The results highlighted the vulnerability of REDF based systems, such as optical amplifiers and sources, for space and nuclear applications. In such harsh environments, Radiation Induced Attenuation (RIA) is also a key issue. The positive effect of Ce co-doping on both the RIA and the lifetimes is reported even at the highest dose of 10 MGy(SiO2). The basic mechanisms involved during the interaction between radiation and fiber material were also investigated through low temperature spectroscopic measurements that revealed the fundamental role of radiation-induced point defects.