Watt-level single-frequency lasing enabled by an Er³⁺-doped fluoride fiber ring oscillator at 2.79 μm

In this Letter, we present watt-level single-frequency (SF) mid-infrared (MIR) laser generation directly from a fiber oscillator, for the first time, to the best of our knowledge. Based on the high-gain ~2.8 μm Er³⁺-doped fluoride fiber platform, a unidirectional ring cavity has been employed to eliminate the detrimental spatial hole burning effect, thereby suppressing, to some extent, mode hopping and multi-longitudinal-mode behaviors, while a germanium etalon and a diffraction grating are incorporated into the cavity to realize single longitudinal mode selection based on their combined filtering effects. Ultimately, stable SF lasing at 2.79 μm with a maximum power of 1.16 W has been achieved, exhibiting a linewidth narrower than 500 kHz. This work highlights the great potential of the fluoride fiber ring oscillator for generating high-power SF MIR laser.