Efficient 2 µm polarization-maintaining Ho-doped fiber laser with intracavity core pumping

In this paper, a 2 µm intra-cavity core-pumped Ho-doped fiber laser with high efficiency by using a tandem in-band pump approach based on an all-polarization-maintaining structure is demonstrated. In the simulation, a rate equation model for the intracavity Tm and Ho laser is established to provide theoretical guidance for the experiment. In the experiment, a maximum output power of 12.1 W/11.8 W is realized with an optical-to-optical efficiency of 37.8%/36.9% and a slope efficiency of 39.2%/39.1% from 792 nm to 2050.7 nm/2088.7 nm. The power stability and beam quality M² at the maximum output power are ∼0.2% and 1.2, respectively. The polarization extinction ratio (PER) is optimized by precisely controlling the temperature of the fiber gratings, resulting in the PER of 17.2 dB at the maximum output power. These results show that all-fiber intra-cavity core pumping is an effective way for realizing high-compactness and high-efficiency 2 µm polarization-maintaining laser.