Abstract: High power fibre amplifier systems avoid inadvertent generation of Stimulated Brillion Scattering (SBS) that causes optical losses and, if large enough, may damage the system. The standard active technique used to suppress SBS is to modulate the seed beam with a radio frequency line width broadening signal, e.g. white noise, to increase the spectral linewidth of the seed beam. This significantly increases the threshold power at which SBS becomes a problem by significantly reducing the coherence length. The problem accompanying a reduced coherence length is that the tolerance in variations in optical path length reduces markedly. The solution provided to this problem is to delay the line width broadening signal by predetermined amount to compensate for the difference in optical path lengths.