Figure 1
From: Phase-locking and Pulse Generation in Multi-Frequency Brillouin Oscillator via Four Wave Mixing

Concept of pulse train generation via SBS and FWM.
CW light is coupled into a short, nonlinear fibre resonator. New frequencies are generated via SBS and FWM. At the output a train of phase-locked pulses can be observed with repetition rate equal to the SBS frequency shift.