High-efficiency sub-watt in-band-pumped single-frequency DBR Tm3+-doped germanate fiber laser at 1950 nm

-doped germanate fiber and being in-band-pumped by a 1610 nm single-mode laser, a high-efficiency and high-power single-frequency distribute Bragg reflector (DBR) fiber laser emitting at 1950 nm is demonstrated. The DBR fiber laser has a maximum output power of ~617 mW and a slope efficiency for the absorbed pump power reaches to more than 42.2%. A stable single-longitudinal-mode laser output with a signal-to-noise ratio of greater than 63 dB is realized. The measured relative intensity-noise of the fiber laser reaches to around -150 dB/Hz at frequencies of over 8.4 MHz. It is beneficial to exploit the sub-watt and high-efficiency single-frequency laser from fiber oscillators directly, especially in the application of multiple paths coherent beam combination and optical medical technology.