10 W-Level High-Efficiency Continuous-Wave and Gain-Switched All-Fiber Laser at 1.7 μm

We report $1.7~\boldsymbol {\mu }$ m high-efficiency, high-power continuous-wave (CW) and gain-switched thulium-doped all-fiber lasers with master oscillator power amplifier (MOPA) configuration. The $1.7~\boldsymbol {\mu }$ m seed source comprises a homemade 1566 nm fiber laser as pump source, a femtosecond direct-written fiber Bragg grating pair, and a low-dopant Tm3+ gain fiber. By changing the operating mode (CW/pulsed) of the 1566 nm pump source, CW/gain-switched output of the $1.7~\boldsymbol {\mu }$ m seed source can be achieved, respectively. The CW MOPA achieves a maximum output power of 10 W with a slope efficiency of 68%, representing the highest power level from a $1.7~\boldsymbol {\mu }$ m Tm-doped CW laser in all-fiber format. Moreover, the amplified average output power of the demonstrated gain-switched operation is 2.28 W with the amplification slope efficiency, pulse energy, and peak power of 76.8%, $152~\boldsymbol {\mu }$ J, and 2.054 kW, respectively. This is, to the best of our knowledge, the highest single pulse energy and amplification efficiency of a Tm-doped gain-switched all-fiber laser. This work provides a new path to achieve high power and large energy of $1.7~\boldsymbol {\mu }$ m all-fiber laser for applications in bio-imaging and long-distance sensing technology.