Ho³⁺-doped AlF₃–TeO₂-based glass fibers for 2.1 µ m laser applications

Ho³⁺-doped AlF₃–TeO₂-based glass fibers based on AlF₃–BaF₂–CaF₂–YF₃–SrF₂–MgF₂–TeO₂ glasses are fabricated by using a rod-in-tube method. The glass rod including a core and a thick cladding layer is prepared by using a suction method, where the thick cladding layer is used to protect the core from the effect of surface crystallization during the fiber drawing. By inserting the glass rod into a glass tube, the glass fibers with relatively low loss (∼2.3 dB m⁻¹ @ 1560 nm) are prepared. By using a 38 cm long Ho³⁺-doped AlF₃–TeO₂-based glass fiber as the gain medium and a 1965 nm fiber laser as the pump source, 2065 nm lasing is obtained for a threshold pump power of ∼220 mW. With further increasing the pump power to ∼325 mW, the unsaturated output power of the 2065 nm laser is about 82 mW and the corresponding slope efficiency is up to 68.8%. The effects of the gain fiber length on the lasing threshold, the slope efficiency, and the operating wavelength are also investigated. Our experimental results show that Ho³⁺-doped AlF₃–TeO₂-based glass fibers are promising gain media for 2.1 µ m laser applications. (letter)