High-power single longitudinal-mode thulium-doped fiber laser based on a composite cavity seed source

Abstract

We propose and have demonstrated a single longitudinal mode (SLM) thulium-doped fiber laser (TDFL) in the 2-μm wavelength range and have amplified its output power to achieve high power output. The seed source employs a uniform fiber Bragg grating (UFBG) and a passive sub-ring cavity filter composed of two 3 × 3 couplers to achieve single longitudinal mode selection, resulting in stable single longitudinal mode lasing. This paper explains the design and fabrication of a dual-coupler composite cavity filter (DC-DRC) sub-ring cavity, analyzes the SLM selection mechanism, and reports a seed-source output of 10 mW of SLM laser power at a center wavelength of 1940.79 nm, with a 3 dB spectral bandwidth of 0.05 nm and an optical signal-to-noise ratio (OSNR) greater than 70 dB, the line width of the seed source is approximately 2.91 kHz. The seed laser is amplified using a master oscillator power amplifier (MOPA) system, achieving an average output power of 15.36 W and a slope efficiency of approximately 31 %. At maximum output power, no stimulated Brillouin scattering (SBS) or gain saturation was observed at the reverse monitoring end. We discuss in detail the system architecture and key considerations for power amplification.