The properties of silica waveguide Bragg devices are analyzed. The field distribution of the transverse electric (TE) mode is given for the silica asymmetric slab waveguide. The characteristic equations for SiO2/ZnO/Air multilayered structures are obtained after writing the equations of state, equations of motion and Maxwell′s equations, then the displacement and the electromagnetic field in each region are found with the appropriate boundary conditions. The change of the relative dielectric permeability tensor by the acoustic surface wave is calculated. The relationships among acousto-optic diffraction efficiency, overlap integral between the optical and acoustic fields, acoustic power, acoustic frequency, acoustic aperture and waveguide parameters are discussed. The results show that there is a good overlap of the optical and surface acoustic wave fields in the low surface acoustic wave frequency range; the overlap integral of the lower-order mode is always larger than that of the higher-order; the lowest-order waveguide mode exhibits the strongest acousto-optic interaction and requires the lowest acoustic power; at the same acoustic power, increasing acoustic aperture results in an increase in the diffraction efficiency.