Optimization of Inversion Probability Tunable Sequence Phase Modulation for SBS Suppression in Fiber System

Phase modulation optical spectral broadening has been widely used as an effective stimulated Brillouin scattering suppressing scheme in narrow linewidth fiber amplifiers. In particular, tunable inversion probability sequence (p-tunable sequence) phase modulation effectively optimizes the spectral envelope, improving the SBS threshold in a monolithic narrow linewidth fiber amplifier. This paper theoretically and experimentally investigates the SBS suppression capability of p-tunable phase modulation. Firstly, we introduce a theoretical model to illustrate, for the first time, the temporal and spectral properties of light waves that have been phase-modulated by a p-tunable sequence. An optimization scheme for parameter selection of p-tunable sequence phase modulation is established by calculating the SBS threshold. Meanwhile, we establish a three-stage fiber amplifier system with p-tunable phase modulation to verify our theory. The output power is 2390 W with an FWHM optical linewidth of 10 GHz. Compared to the pseudo-random binary sequence (PRBS) case, this scheme increases the output power by 700 W at 10 GHz FWHM optical linewidth.