Stimulated Brillouin scattering in long fibers and light guides

Stimulated Brillouin Scattering (SBS) is a typical backward traveling wave parametric interaction(1) with inherent spatial feedback between the forward and backward scattered waves and may oscillate under high pump excitation. The pump excitation threshold is normally proportional to the nonlinearity of the medium and the interaction length. For long optical fibers and light guides, the high phonon loss and nonlinear interaction often changes the interacting field distribution into a special whispering mode(7) with the phonon loss effectively compensated by pump depletion such that the threshold for pump excitation is nearly independent of the interaction length. In this paper, we will discuss the characteristics of this model of SBS and propose methods to characterize it.