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Optical fibers represent the key component of modern optical telecommunication networks. Such fibers are based on silica glass of high purity usually modified with several percent of glassforming oxides such as GeO₂ and P₂O₅. These materials with minimum optical losses around 1.5 μm are transparent up to ∼2 μm. In this paper, the attention is focused on silica glass materials doped with ions of rare-earth elemens for fiber lasers and fiber amplifiers. Since rare earths cause phase separation only in small amount incorporated into silica glass, ternary systems containing P₂O₅ or Al₂O₃ have been investigated. Latest results in GeO₂-based glasses transparent in mid infrared region are also presented.

International audience; Thulium-doped fibers are renowned for their applications in high power fiber lasers at around 2 µm. It is despite the low quantum conversion efficiency of 3F4 level in thulium doped silica fibers, which is about 10% compared to ~100% quantum conversion efficiency of the ytterbium- and erbium-doped fibers, at around 1 µm and 1.5 µm, respectively. The lower quantum conversion efficiency increases the 2 µm laser threshold but has almost no effect on the laser slope efficiency. Indeed, kW-class thulium-doped fiber lasers have been demonstrated recently. Quantum conversion efficiency of the 3H4 level in non-modified silica fibers is much lower than that of 3F4 level, only about 2% and therefore most of the applications of laser transitions originating from 3H4 level are hindered by the lack of reliable low-phonon fiber host. We review of our contributions towards the comprehension and improvement of the spectroscopic properties of thulium ions doped into silica. We show potential of the developed thuliumdoped fibers with enhanced 3H4 level lifetime for applications in fiber lasers around 810 nm and in fiber amplifiers for communication S-band (1460-1530 nm).