Compact self-Q-switched, tunable mid-infrared all-fiber pulsed laser

A compact self-Q-switched wavelength-tunable Ho³⁺:ZBLAN fiber laser around 3 μm is experimentally demonstrated for the first time. The mid-IR all-fiber cavity is formed by a pair of fiber end-facet mirrors. A 2 m-long heavily-doped Ho³⁺:ZBLAN fiber pumped by a homemade 1.15 μm fiber laser not only provides mid-IR optical gain, but also functions as an equivalent saturable absorber. Stable self-Q-switched pulses around 2.9 μm are generated at a low threshold of 36.6 mW, and the maximum average power obtained is 3.17 mW, corresponding to a pulse width of 1.54 μs and repetition rate of 67.8 kHz, respectively. By simply increasing the incident pump power, the mid-IR laser wavelength can be continuously tunable from 2927 nm to 2960 nm. Furthermore, when the pump power is fixed at 207.7 mW, a 42 nm wavelength tuning (2923 ∼ 2965 nm) from the self-Q-switched all-fiber laser is also achieved by applying the novel loss-adjusting technique.