Build-up of stimulated Brillouin scattering excited by pulsed pump radiation in a long optical fibre

We study stimulated Brillouin scattering (SBS) in a long optical fibre with and without feedback under long pulse excitation, when the acoustic field is steady state. It is shown that, when the pump power is higher than the feedback free SBS threshold, the build-up time is inversely proportional to the pump power and independent of feedback. At lower pump power, for which feedback is required to produce SBS, the build-up time increases inversely with the difference between the pump power and the SBS threshold with feedback. The build-up time may be varied from submicroseconds to milliseconds dependent on the pump power and feedback strength in agreement with our theoretical description.