Stimulated brillouin scattering in nanoscale silicon step-index   waveguides: A general framework of selection rules and calculating SBS gain
  We develop a general framework of evaluating the gain coefficient of Stimulated Brillouin Scattering (SBS) in optical waveguides via the overlap integral between optical and elastic eigen-modes. We show that spatial symmetry of the optical force dictates the selection rules of the excitable elastic modes. By applying this method to a rectangular silicon waveguide, we demonstrate the spatial distributions of optical force and elastic eigen-modes jointly determine the magnitude and scaling of SBS gain coefficient in both forward and backward SBS processes. We further apply this method to inter-modal SBS process, and demonstrate that the coupling between distinct optical modes are necessary to excite elastic modes with all possible symmetries. 
Wenjun Qiu, Peter T. Rakich, Marin Soljacic, Zheng Wang
cond-mat.mes-hall physics.optics