Acousto-optic Bragg diffraction in SiGe/Si planar waveguides

The interaction of guided optical waves and surface acoustic waves (SAWs) in SiGe/Si planar waveguide structures is studied by first determining the electric field profile of the optical modes and the strain profiles induced by the propagating SAW. Coupled-mode theory provides the basis for the study of the acousto-optic interaction and results in the determination of diffraction efficiency as a function of acoustic frequency, for different material structures and acoustic powers. It is found that for most SiGe/Si structures significantly more acoustic power is needed to produce diffraction efficiencies comparable to those of material systems such as AlGaAs/GaAs. Also it is shown that a high germanium concentration could be desirable for increasing the diffraction efficiency to useful levels