Manipulating Stimulated Brillouin Scattering Produced Gain Near Its Threshold via Slow Intensity Modulation

Increasing the threshold of stimulated Brillouin scattering (SBS) by frequency and phase modulation is a productive approach to suppress SBS in optical fiber communications. Generally, the modulation frequency is much higher than the Brillouin-gain bandwidth (about 10 MHz). However, the property of the SBS-produced gain is unclear when the frequency of intensity modulation is much lower than the Brillouin-gain bandwidth. Here, we find that the SBS-produced gain increases remarkably near its threshold under the above conditions. It is due to the nonlinearity feature of the SBS. A numerical simulation of the SBS coupled amplitude equations is studied to explain this phenomenon. We demonstrate that the modulation on/off gain produced by this slow intensity modulation is related to the modulation frequency, the waveguide length, and the modulation waveform. According to these new findings, we design a modulation waveform to boost the SBS-produced gain near its threshold by 35 dB in a 1 km length single-mode fiber. The method presented in this paper is expected to apply in SBS studies when the incident optical power is limited.