We present a study of chalcogenide glass fiber lasers doped with Dy 3+ , Pr 3+ or Tb 3+ that would operate in the mid-infrared wavelength range. A set of chalcogenide glass samples doped with different concentrations of rare earth ions is fabricated. The modeling parameters are directly extracted from FTIR absorption measurements of the fabricated bulk glass samples using Judd-Ofelt, Füchtbauer-Ladenburg theory and McCumber theory. The modeling results show that, for all the dopants considered, an efficient mid-infrared laser action is possible if optical losses are kept at the level of 1dB/m or below.

A simple Dy 3+ -doped chalcogenide glass fibre laser design for mid-infrared light generation is studied using a one dimensional rate equation model. The fibre laser design employs the concept of cascade lasing. The results obtained demonstrate that efficient cascade lasing may be achieved in practice without the need for fibre grating fabrication, as a sufficient level of feedback for laser action is provided by Fresnel light reflection at chalcogenide glass fibre-air interfaces. Further enhancement of the laser efficiency can be achieved by terminating one of the fibre ends with a mirror. A numerical analysis of the effect of the Dy 3+ doping concentration and fibre loss on the laser operation shows that with 5 W of pump power, at 1.71 µm wavelength, output powers above 100 mW at ∼ 4.5 µm wavelength can be achieved with Dy 3+ ion concentrations as low as 3 × 10 19 cm −3 , when fibre loss is of the order 1dB/m.

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Gallium (Ga) helps solubilize rare-earth ions in chalcogenide glasses, but has been found to form the dominant crystallizing selenide phase in bulk glass in our previous work. Here, the crystallization behavior is compared of as-annealed 0-3000 ppmw Dy 3+ -doped Ge-As-Ga-Se glasses with different Ga levels: Ge 16.5 As (19 -x) Ga x Se 64.5 (at.%), for x = 3 and 10, named Ga 3 and Ga 10 glass series, respectively. X-ray diffraction and high-resolution transmission electron microscopy are employed to examine crystals in the bulk of the as-prepared glasses, and the crystalline phase is proved to be the same: Ge-modified, face centered cubic a-Ga 2 Se 3 . Light scattering of polished glass samples is monitored using Fourier transform spectroscopy. When Ga is decreased from 10 to 3 at.%, the bulk crystallization is dramatically reduced and the optical scattering loss decreases. Surface defects, with a rough topology observed for both series of as-prepared chalcogenide glasses, are demonstrated to comprise Dy, Si, and [O]. For the first time, evidence for the proposed nucleation agent Dy 2 O 3 is found inside the bulk of as-prepared glass. This is an important result because rare-earth ions bound in a high phonon-energy oxide local environment are, as a consequence, inactive mid-infrared fluorophores because they undergo preferential nonradiative decay of excited states.

The photoluminescent-(PL)-properties of Pr³⁺-ions in indium-containing selenide-chalcogenide bulk-glasses are found to be superior when compared with gallium-containing analogues. We observe circa doubling of mid-infrared (MIR) PL intensity from 3.5 to 6 μm for bulk glasses, pumped at 1.55 μm wavelength, and an increased excited state lifetime at 4.7 μm. PL is reported in optically-clad fiber. Ga addition is well known to enhance RE³⁺ solubility and PL behavior, and is believed to form ([RE³⁺]-Se-[Ga(III)]) in the glasses. Indium has the same outer electronic-structure as gallium for solvating the RE-ions. Moreover, indium is heavier and promotes lower phonon energy locally around the RE-ion, thereby enhancing the RE-ion PL behavior, as observed here.

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