Enhanced Acousto-Optic Diffraction Efficiency in a Symmetric SrTiO(3)/BaTiO(3)/SrTiO(3) Thin-Film Heterostructure

Guided-wave acousto-optic Bragg diffraction and surface acoustic-wave propagation in epitaxially matched SrTiO(3)/BaTiO(3)(001)/SrTiO(3) thin-film heterostructures have been theoretically studied. The optimum electromechanical coupling and Bragg diffraction efficiency have been determined at several acoustic frequencies by means of varying the thickness of the SrTiO(3) overlayer and the BaTiO(3) waveguiding layer. A strain-controlling nonpiezoelectric SrTiO(3) overlayer upon the BaTiO(3)/SrTiO(3) structure is found to enhance the coupling coefficient (k(2)) and the diffraction efficiency significantly. A comparison of asymmetric and symmetric structures shows an increase in the diffraction efficiency from 10.5% to 43.0% and a decrease in the untuned-transducer conversion efficiency from 36 to 23 dB at an operating frequency of 1 GHz with an interaction length of 1 mm and an acoustic power of 1 mW.