Brillouin scattering: beyond threshold

Stimulated Brillouin scattering (SBS) can be the limiting nonlinearity in an optical fiber communications system, can provide optical amplification, or can act as an optical carrier filter. However, the analytical treatment of SBS has been limited to the undepleted pump regime and only numerical analysis is available for when the pump depletion is significant. In particular, the narrowing of the Stokes linewidth is well-known, yet the suppression of narrowing under high-gain, depleted-pump conditions has not been treated. We present a heuristic analysis to quantify pump depletion, which accurately predicts an experimentally observed linewidth minimum.