The progress, and current challenges, in fabricating rare-earth-doped chalcogenide-glass fibers for developing mid-infrared (IR) fiber lasers are reviewed. For the first time a coherent explanation is forwarded for the failure to date to develop a gallium-lanthanum-sulfide glass mid-IR fiber laser. For the more covalent chalcogenide glasses, the importance of optimizing the glass host and glass processing routes in order to minimize non-radiative decay and to avoid rare earth ion clustering and glass devitrification is discussed. For the first time a new idea is explored to explain an additional method of non-radiative depopulation of the excited state in the mid-IR that has not been properly recognized before: that of impurity multiphonon relaxation. Practical characterization of candidate selenide glasses is presented. Potential applications of mid-infrared fiber lasers are suggested.

We present a study of chalcogenide glass fiber lasers doped with Dy³⁺, Pr³⁺ or Tb³⁺ 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.

We select a chalcogenide core glass, AsSe, and cladding glass, GeAsSe, for their disparate refractive indices yet sufficient thermal-compatibility for fabricating step index fiber (SIF) for mid-infrared supercontinuum generation (MIR-SCG). The refractive index dispersion of both bulk glasses is measured over the 0.4 µm–33 µm wavelength-range, probing the electronic and vibrational behavior of these glasses. We verify that a two-term Sellmeier model is unique and sufficient to describe the refractive index dispersion over the wavelength range for which the experimentally determined extinction coefficient is insignificant. A SIF composed of the glasses is fabricated and calculated to exhibit an ultra-high numerical aperture >0.97 over the entire wavelength range 0.4-33 µm suggesting that the SIF glass pair is a promising candidate for MIR-SCG. Material dispersion characteristics and the zero dispersion wavelength, both critical design parameters for SIF for MIR-SCG, are derived.

Chalcogenide glass fibers have attractive properties (e.g. wide transparent window, high optical non-linearity) and numerous potential applications in the mid-infrared (MIR) region. Low optical loss is desired and important in the development of these fibers. Ge-As-Se glass has a large glass-forming range to provide versatility of choice from continuously varying physical properties. Recently, broadband MIR supercontinuum generation has been achieved in chalcogenide fibers by using Ge-As-Se glass in the core/clad. structure. In the shaping of chalcogenide glass optical fiber preforms, extrusion is a useful technique. This work reports glass properties (viscosity-temperature curve and glass transition) and optical losses of Ge-As-Se fiber fabricated from an extruded preform. A robust cut-back method of fiber loss measurement is developed and the corresponding error calculation discussed. MIR light is propagated through 52 meters of a fiber, which has the lowest loss yet reported for Ge-As-Se fiber of 83 ± 2 dB/km at 6.60 μm wavelength. The fiber baseline loss is 83-90 dB/km across 5.6-6.8 μm, a Se-H impurity absorption band of 1.4 dB/m at 4.5 μm wavelength is superposed and other impurity bands (e.g. O-H, As-O, Ge-O) are ≤ 20 dB/km. Optical losses of fiber fabricated from different positions of the extruded preform are investigated.