Brillouin scattering by localized acoustic modes in silicon-oxynitride–fused-silica optical waveguides

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Abstract
Brillouin scattering connecting guided optical modes is used to study the acoustic waves in a silicon-oxynitride–fused-silica double layer deposited onto a Si substrate. The frequencies of the acoustic modes as derived from the acoustic wave equation are found to reproduce those of the experiment. The scattering intensities are in agreement with a calculation based on the coupled-waveguide-mode formalism with due account of the elasto-optic effect and the corrugation of the surface and silicon-oxynitride–silica interface. Finally, the sound velocities and Pockels coefficients of the silicon-oxynitride layer are determined.