Continuous 5.22–5.31 μm wavelength lasing in optical fiber based on Tb3+-doped gallium-free selenide glass

A gallium-free terbium-doped Ge–Sb–Se chalcogenide glass, suitable for preparation and purification by effective and relatively low-labor methods of reactive and simple distillation of germanium and antimony selenides, is proposed as a middle IR laser material. The effect of impurities in terbium on the glass purity is reduced by decreasing rare earth metal concentration. A 15/230 μm diameter core-clad Tb³⁺-doped Ge–Sb–Se/As–Ge–S glass fiber is fabricated by a double crucible technique. It is shown that a 7 m long piece of produced active fiber provides continuous wave lasing in the spectral range of 5.22–5.31 μm with an output power of up to 60 mW and a slope efficiency of 3.7 %. Transition metal impurities with a total content of 0.7 ppm(wt), impurities of H₂O, SeH-, GeH-, Ge–O groups and bonds with absorption coefficients of 0.002–0.007 cm⁻¹, and total optical losses of 2.5 dB/m at 1.46 μm do not limit the possibility of achieving mid-IR laser emission in this active fiber.