A reverse process of acoustooptic diffraction in thin films is studied. The high optical field concentration in thin films is utilized by mixing two optical guided modes electrostrictively to generate an acoustic surface wave. A theoretical analysis analogous to acoustooptic diffraction is presented by taking the power balance approach. The nonuniform electric and acoustic field distributions are fully taken into account. A relation between electrostriction and diffraction is established, and the published results on Bragg diffraction are applied directly to Bragg electrostriction. Bragg electrostriction is film thickness dependent, and cw operation of acoustic wave generation is possible.
M. S. Chang, "Bragg electrostriction in optical waveguides," Appl. Opt. 16, 1960-1965 (1977)