Qiu Wenjun, Rakich Peter T, Shin Heedeuk, Dong Hui, Soljačić Marin, Wang Zheng
Opt Express. 2013 Dec 16;21(25):31402-19. doi: 10.1364/OE.21.031402.
We develop a general framework of evaluating the Stimulated Brillouin Scattering (SBS) gain coefficient in optical waveguides via the overlap integral between optical and elastic eigen-modes. This full-vectorial formulation of SBS coupling rigorously accounts for the effects of both radiation pressure and electrostriction within micro- and nano-scale waveguides. We show that both contributions play a critical role in SBS coupling as modal confinement approaches the sub-wavelength scale. Through analysis of each contribution to the optical force, 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 how the optical force distribution and elastic modal profiles jointly determine the magnitude and scaling of SBS gains in both forward and backward SBS processes. We further apply this method to the study of intra- and inter-modal SBS processes, and demonstrate that the coupling between distinct optical modes are necessary to excite elastic modes with all possible symmetries. For example, we show that strong inter-polarization coupling can be achieved between the fundamental TE- and TM-like modes of a suspended silicon waveguide.
我们通过光波与弹性本征模之间的重叠积分，建立了一个评估光波导中受激布里渊散射（SBS）增益系数的通用框架。这种SBS耦合的全矢量公式严格考虑了微纳尺度波导内辐射压力和电致伸缩的影响。我们表明，随着模式限制接近亚波长尺度，这两种贡献在SBS耦合中都起着关键作用。通过分析对光力的每种贡献，我们表明光力的空间对称性决定了可激发弹性模式的选择规则。通过将此方法应用于矩形硅波导，我们展示了光力分布和弹性模式轮廓如何共同决定前向和后向SBS过程中SBS增益的大小和比例。我们进一步将此方法应用于研究模内和模间SBS过程，并证明不同光学模式之间的耦合对于激发具有所有可能对称性的弹性模式是必要的。例如，我们表明在悬浮硅波导的基本类TE和类TM模式之间可以实现强偏振间耦合。
