3.3 kW narrow linewidth FBG-based MOPA configuration fiber laser with near-diffraction-limited beam quality.

• Having established a simulation model, the spectrum broadening characteristics of the narrow-linewidth FBG-based amplifier were analyzed based on multiple factors. • A plum-shaped coiling design for the gain fiber was used to filter out high-order modes thus obtaining a beam quality m2 of 1.32 at the maximum output power of 3.3 kW. • A Raman suppression ratio of 26.3 dB was obtained at the maximum output power of 3.3 kW. • To the best of our knowledge, this is the highest record of narrow-linewidth fiber laser based on one stage MOPA configuration with normal commercial narrow-bandwidth fiber gratings and non-wavelength-locked laser diodes. This paper demonstrates a narrow-linewidth fiber laser with near-diffraction-limited beam quality and high Raman suppression ratio by utilizing Master Oscillator Power-Amplifier structure based on narrow-bandwidth fiber Bragg gratings. The output power reaches 3.31 kW with a slope efficiency of 85.0 %. At the maximum output power, the 3 dB, 10 dB, and 20 dB linewidths are 0.40 nm, 1.20 nm, and 3.09 nm, respectively. The beam quality M2 factor is 1.32 and the Raman suppression ratio reaches 26.3 dB. A pair of narrow-bandwidth fiber gratings were used in the oscillator to compress the linewidth of the seed laser. We used backward-pumping configuration and plum-coiled gain fiber in the amplification stage to suppress the Raman effect and select transverse mode by fiber-bending. Finally, a compact all-fiber laser was obtained with narrow-linewidth, high beam quality, and effective suppression of the Raman effect. To the best of our knowledge, this is the highest output power for a sub-nanometer-linewidth laser using narrow-bandwidth fiber gratings and none-wavelength-locked laser diodes, which achieves near-diffraction-limit beam quality. This provides a solution for high-power narrow-linewidth laser sources with high beam quality. [ABSTRACT FROM AUTHOR]