High order stimulated Brillouin scattering in single-mode fibers with   strong feedback
  We present an experimental and theoretical study of cascaded high order Stimulated Brillouin Scatterings (SBS) in single mode fibers. It is shown that because of the back-scattering nature of the process, feedback in the input port is needed for obtaining a significant cascaded effect in nonresonant systems. We also discuss similarities to nonlinear photorefractive processes. 
Assaf Ben-Bassat, Ariel Gordon, Baruch Fischer