Vulnerability of rare-earth-doped fibers for space missions: origins of radiation-induced attenuation

We characterized the responses of different types of rare-earth doped fibers (Yb, Er and Er/ Yb) to various types of radiations like UV, gamma-rays, X-rays and protons. The understanding of the radiation-induced effects in this class of optical fibers is necessary as they are possible candidates for use as part of fiber-based systems like gyroscopes that will have to operate in space environment. For all types of irradiations, the main effect is an increase of the linear absorption of these waveguides due to the generation of point defects in the core and cladding. We characterize the growth and decay kinetics of the radiation-induced attenuation during and after irradiation for various compositions of optical fibers. In this paper, we particularly investigate the relative influence of the rare-earth ions (Er, Yb or Er/ Yb) and of the glass matrix dopants (Al, P,...) on the optical degradation induced by ultraviolet laser exposure at 5 eV. This has been done by using a set of five prototype optical fibers designed by iXFiber SAS to enlighten the role of these parameters. Additional spectroscopic tools like confocal microscopy of luminescence are also used to detect possible changes in the spectroscopy of the rare-earth ions and their consequence on the functionality of the active optical fibers.