Narrow Linewidth 100w Single-Frequency 2048nm Improved Mopa System Based on Composite Cavities

Abstract

We propose and demonstrate a 2 μm single longitudinal mode (SLM) thulium-doped all-fiber master oscillator power amplifier (MOPA) system. The seed source, a thulium-doped fiber laser (TDFL), uses a uniform fiber Bragg grating (UFBG) and a passive composite cavity filter comprising four 2×2 fiber couplers to achieve SLM selection, resulting in stable SLM lasing. This paper introduces the simulation and design methods of a quad-coupler dual-ring composite cavity (QCD-CC) filter based on a genetic algorithm. For the first time, our custom-designed genetic algorithm, analyzing the SLM selection mechanism, was applied to develop a 2 μm seed source. The center wavelength of seed source is 2048.39 nm, with a linewidth of less than 4 kHz, as measured by phase noise demodulation method, and the optical signal-to-noise ratio (OSNR) greater than 70 dB. Using a MOPA system, the seed laser was amplified, achieving an average output power of 100 W with a slope efficiency of approximately 50%. At maximum output power, no significant amplified spontaneous emission or gain saturation was observed in the reverse monitoring end. Additionally, we discuss in detail the system architecture, nonlinear effects, and thermal management.

Keywords: 2μm, Single Frequency, Narrow, Linewidth, Composite Cavity, MOPA