Suppression of stimulated Raman scattering in a high-power fiber amplifier by inserting long transmission fibers in a seed laser

We demonstrate the suppression of stimulated Raman scattering (SRS) in a kilowatt fiber amplifier by reducing the temporal fluctuations of the seed oscillator, which is achieved by simply inserting a long piece of transmission fiber between the seed source and amplifier. We experimentally investigate the dependence of the amount of Raman light in the amplifier on the seed oscillator's transmission fiber length. We also numerically analyze the temporal features of the corresponding seed sources and amplifiers. Experiments and simulations indicate that long transmission fibers will flatten temporal fluctuations of the seed laser, and thereby the SRS effect in the amplifier can be mitigated. The difference of the SRS suppression mechanisms between the method proposed here and the conventional method employing spectrally wider fiber Bragg grating is also presented.