Ge- and Al-related point defects generated by gamma irradiation in nanostructured erbium-doped optical fiber preforms
Résumé
Erbium-doped amplifiers (EDFAs) are of special interest for space applications.
In this environment, the ionizing radiations decrease the gain of these optical
amplifiers, due to the ionization of defects precursors, mainly linked to dopants
as Germanium (Ge), Aluminum (Al), or Phosphorus (P). The aim of this work is
to study the influence of the Ge and Al relative concentration on the radiation
resistance of different nanostructured fiber preforms, manufactured by Modified
Chemical Vapor Deposition (MCVD), in which various types of nanoparticles
(Er@SiO2-NP, Al2O3-NP, and Er@Al2O3-NP) have been introduced in the
silica matrix. The radiation resistance of these fibers has been compared with
that of standard MCVD Er-doped preforms. All of them have been characterized
by optical absorption and Electronic Paramagnetic Resonance (EPR) spectroscopies
before and after irradiation with a total gamma dose of 5.9 kGy. EPR
results show that Al-related defects are not observed in fiber preforms with Ge
concentrations higher than 4.4 wt%. We also demonstrated that NP technology
can limit the formation of Aluminum-Oxygen Hole Centers (AlOHCs), reducing
the Radiation-Induced Attenuation at the energy of interest for EDFAs.