Abstract

Rare-earth (RE) doped fibre lasers and amplifiers based on silica offer the best performances in terms of combined efficiency, power and beam quality. Silica glass had indeed chemical, mechanical and economic advantages over alternative hosts such as fluoride glasses (ZBLAN). Nevertheless, some characteristics of silica limit the implementation of otherwise extremely interesting applications, such as short wavelength optical transitions, in selected RE ions, reachable by pump up-conversion. For instance, when thulium (Tm) is excited at 1.07 µm, up to eight laser emissions (spanning from 450 nm to 1.9 µm) are observed in ZBLAN [1], while only one (1.9 µm) is exploited in silica. In this glass, RE emissions from high energy levels undergo strong non-radiative decays (NRD) due to high phonon-energy (as compared with fluorides), whereas the up-conversion pumping schemes cause strong photo-induced absorption (photo-darkening, PD) accentuated by RE aggregation due to silica low solubility. The NRD may be mitigated by co-doping with aluminum ions [2,3]. However the mechanisms responsible for PD are still under debate [4]. It is therefore crucial to study alternative modifications of Tm-doped silica-based fibres.

© 2015 IEEE