Light in the mid-infrared spectral region holds many promises: molecular fingerprinting, remote sensing, eye-safe lidars or deep-tissue medical imaging are just some of the keywords that are often cited. Yet developing user-friendly, compact, and powerful mid-IR laser sources has remained challenging. Lasers and amplifiers based on active, rare-earth doped optical fibers have obvious advantages over corresponding bulk solutions. But to date, such mid-IR fibers are mostly based on fluoride glasses, which are notoriously difficult to work with due to their brittleness and low softening temperature. In this context, Muraviev and coworkers have fabricated high purity Erbium-doped tungsten tellurite glass fibers with superior physical and mechanical properties, and demonstrated a gain bandwidth of more than 250 nm at 2.7 µm central wavelength when pumped with a 976 nm laser diode. This broadband gain is enabled by the low phonon energy of the host glass material, and is particularly suitable for the amplification of mid-IR supercontinuum generated in highly nonlinear fibers, as the authors demonstrate. The work establishes active multicomponent oxide glass fibers as a viable alternative for mid-IR photonics.

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