3 kW high OSNR 1030 nm single-mode monolithic fiber amplifier with a 180 pm linewidth.

In this Letter, the amplified spontaneous emission (ASE) effect of a 1030 nm fiber laser is studied theoretically and, based on the theoretical results, a 3 kW high optical signal-to-noise ratio (OSNR) 1030 nm fiber amplifier with a 180 pm linewidth and near-diffraction-limited beam quality is achieved. A theoretical model, which takes simulate ASE light falling in the range of Raman light as the Raman seed, has been used to optimize the power scaling capability of 1030 nm fiber amplifiers. It shows that the SRS effect seeded by the ASE is the main limiting factor for the fiber amplifiers operating at 1030 nm, and >3 output power with a high OSNR can be achieved by proper parameter designing of the fiber laser system. A 1030 nm monolithic narrow linewidth fiber amplifier, which delivers 3 kW output power with the OSNR being 37 dB and a 0.18 nm spectrum linewidth, has been demonstrated. At the maximum 3 kW output power, the SRS light peak is obviously higher than ASE light, which agrees with the theoretical predictions. Neither a stimulated Brillouin scattering effect nor a thermal-induced mode instability effect has been observed at ultimate power level, and the beam quality factor is measured to be less than 1.2. To the best of our knowledge, this is the highest average power for a narrow linewidth single-channel fiber laser system reported so far operating at 1030 nm.