Fabrication of double‐cladding Ho 3+ /Tm 3+ co‐doped Bi 2 O 3 –GeO 2 –Ga 2 O 3 –BaF 2 glass fiber and its performance in a 2.0‐μm laser

A novel double‐cladding Ho 3+ /Tm 3+ co‐doped Bi 2 O 3 –GeO 2 –Ga 2 O 3 –BaF 2 glass fiber, which can be applied to a 2.0‐μm infrared laser, was fabricated by a rod‐tube drawing method. The thermal properties of the glass were studied by differential scanning calorimetry. It showed good thermal stability and matching thermal expansion coefficient for fiber drawing when T x − T g  > 193°C and the maximum difference of the thermal expansion coefficient is 3.55 × 10 −6 /°C or less. The 2.0‐μm luminescence characteristics were studied using the central wavelength of 808 nm pump light excitation. The results show that when the concentration ratio of Ho 3+ /Tm 3+ reaches 0.5 mol%:1.0 mol%, the maximum fluorescence intensity was obtained in the core glass, the emission cross section reached 10.09 × 10 −21  cm 2 , and the maximum phonon energy was 751 cm −1 . In this paper, a continuous laser output with a maximum power of 0.986 W and a wavelength of 2030 nm was obtained using an erbium‐doped fiber laser as a pump source in a 0.5 m long Ho 3+ /Tm 3+ co‐doped glass fiber. In short, the results show that Ho 3+ /Tm 3+ co‐doped 36Bi 2 O 3 –30GeO 2 –15Ga 2 O 3 –10BaF 2 –9Na 2 O glass fiber has excellent laser properties, and it is an ideal mid‐infrared fiber material for a 2.0‐μm fiber laser with excellent characteristics