Optimal suppression of SBS in narrow-linewidth, high-power fiber lasers

We investigate the use of pseudo-random bit sequence (PRBS) phase modulation to tailor the spectral properties of narrow-linewidth fiber lasers, enabling power scaling through suppression of stimulated Brillouin scattering (SBS). We systematically investigate the impact of PRBS order (from #5 to #14), modulation frequency (0.2–10 GHz), and Brillouin linewidth (20–50 MHz) on the SBS threshold and the statistical properties of the backward-propagating Stokes signal. Our simulations reveal a non-monotonic relationship between the PRBS order and the SBS threshold. Lower-order PRBS sequences are optimal at lower modulation frequencies due to shorter dwell times, while higher-order sequences (particularly PRBS #10) provide superior SBS suppression above 7.5 GHz. However, we also find that higher-order PRBS modulation leads to increased fluctuations and large power spikes in the Stokes signal. This work highlights the trade-off between maximizing SBS suppression and minimizing detrimental pulsing effects, providing practical guidance for optimizing PRBS parameters in high-power fiber laser systems.