A 1908 nm Internal-Cavity Tm-Doped Fiber Laser Pumped by a 1570 nm Er/Yb Fiber Laser

An internal-cavity Tm-doped all-fiber laser at 1908 nm in-band-pumped by a 1570 nm Er/Yb co-doped fiber laser is proposed. An external-cavity fiber oscillator composed of a pair of high-reflectivity (HR) fiber Bragg gratings (FBGs) at 1570 nm pumped by 915 nm laser diodes (LDs) serves as the bidirectional pumping source for the 1908 nm internal-cavity fiber oscillator to achieve high-efficiency laser output. Firstly, a maximum output power of 10 W is realized at a 915 nm pump power of 36.8 W in the single 1570 nm Er/Yb fiber oscillator, with a corresponding slope efficiency and a signal-to-noise ratio (SNR) of 28.1% and 62 dB, respectively. The beam quality factor M2 of the single 1570 nm Er/Yb fiber oscillator is about 1.2. In the 1908 nm internal-cavity Tm-doped all-fiber laser, the maximum output power is 482 mW when the pump power at 915 nm reaches 12.6 W, with a corresponding slope efficiency of 8.1%. Under the same 915 nm pump power, the slope efficiency of the 1908 nm Tm-doped fiber laser with an external-cavity pump is 5.3%.