A Watt-Level Single-Frequency Fiber Laser at 2 $\mu$ m Using a Silica Prolate Microresonator

We report on a single-frequency Tm-doped fiber laser based on a high-quality (Q) prolate microresonator. A maximum power of 0.9 W was extracted from the laser oscillator directly. To our best knowledge, it is the first report on a Wattlevel single-frequency laser at the 2-μm wavelength band with such a laser configuration. The laser linewidth is measured to be ~15.1 kHz by self-heterodyne method. Moreover, we explore the tuning ability of the laser through exciting different modes in the microresonator selectively. A wavelength-tuning range of 20 nm is obtained. The approach can be a competitive candidate for developing tunable, highly efficient, and high-power single-frequency lasers in the 2-μm band.