Acousto-optic interaction in optical waveguides

In optical waveguides, which are a thin layer of transparent material on the substrate surface (so-called planar waveguides), the interaction of optical waveguide modes with surface acoustic waves (SAW), usually Rayleigh, occurs. As a result, light appears that propagates along the plane of the waveguide, but deviates from its original direction. For effective diffraction, it is necessary that the light beams in the plane of the waveguide fall on the surfactant beam at an appropriate Bragg angle. Since even in an isotropic waveguide system, the propagation speeds of different optical modes are different from each other, then at different angles of incidence of the light beam both diffraction of the light is possible without changing the mode number, similar to conventional Bragg diffraction, and diffraction at which the incident and diffracted light belongs to different waveguide modes. In the latter case, the laws of diffraction are similar to the laws of anisotropic diffraction arising from the interaction of bulk waves in a birefringent medium. In waveguide systems, the distribution of both electromagnetic fields for the optical mode and the strain field in surfactants is non-uniform in the cross section of the waveguide. The efficiency of acousto-optic diffraction in an optical waveguide strongly depends on the degree of overlap of these fields.