Effect of the recurring random signal waveform on SBS and self-pulsing in a phase-modulated narrow-linewidth linearly polarized fiber amplifier

A high power, narrow linewidth, linearly polarized all-fiber amplifier with recurring random signal (RRS) or white noise signal (WNS) phase modulation is structured. The influence of the RRS waveforms on SBS and self-pulsing characteristics is experimentally studied. We find that choosing an appropriate RRS waveform can effectively improve the SBS and self-pulsing threshold. For that, the RRS phase modulation can provide larger than 1.6 times limited power compared to WNS phase modulation at the same linewidth. Meanwhile, we first demonstrate that the output power of a fiber amplifier based on RRS phase modulation is limited by the continuous wave (CW) SBS, while it is limited by the self-pulsing effect in the case of WNS phase modulation. The influence of random signal waveforms on SBS is analyzed theoretically. The results prove that the Stokes peak intensity is closely related to the fine structure of the modulated spectrum determined by the signal waveforms, and which cannot be characterized only from the spectral linewidth. The theoretical analysis is consistent with the experimental results. Finally, we obtain a 1.23 kW narrow linewidth linearly polarized laser output with a linewidth of ∼4 GHz based on RRS phase modulation.