Efficient multi-watt 1720 nm ring-cavity Tm-doped fiber laser

Using commercial Tm-doped silica fiber and 1570-nm in-band pump source, we demonstrated an efficient 1720-nm all-fiber laser with ring-cavity configuration. The theoretical model based on rate equations was built up to analyze the laser performance of Tm-doped fiber, which exhibits strong absorption in the 1.7-μm region. The results show that efficient laser operation can be achieved through the optimization of output coupling and the length of Tm-doped fiber. An experimental investigation was performed and agreed with the calculation. By using homemade couplers, we experimentally achieved 2.36-W laser output at 1720 nm under a 6-W launched pump. The slope efficiency with respect to the absorbed pump power and optical efficiency were 50.2% and 39.3%, respectively. Due to the employment of a ring resonator, a narrow laser linewidth of ∼4 GHz at maximum output power was observed.