Narrow-linewidth all-fiber amplifier with up to 3.01  kW output power based on commercial 20/400  μm active fiber and counterpumped configuration

A multikilowatt all-fiber amplifier with narrow spectral linewidth is investigated by using commercial 20/400 μm active fiber due to its more extensive application prospects. Stimulated Brillouin scattering (SBS) is suppressed effectively by combining multiple approaches including optimizing linewidth-broadened seed, shortening fiber length, and a counterpumped configuration. Consequently, the output power is pushed up to 3.01 kW with M =1.17, and the linewidth is maintained at 48 GHz. The detailed characteristics of SBS are presented and analyzed in the frequency and time domains as output power is gradually raised. A high optical-to-optical efficiency is obtained with 85.6% and amplified spontaneous emission is reduced to 40 dB with respect to a laser signal. The proposed architecture reaches a relatively high output power with excellent beam quality under the condition of the equivalent linewidth for the commercial 20/400 μm active fibers in robustly all-fiberized structures.