In this article, a coupled wave equation of a two-dimensional acousto-elect
ro-optic (AEO) effect is given. A formula of diffraction efficiency of the
two-dimensional AEO effect is derived. A two-dimensional AEO device with KD
P crystal is made. Curves of relative diffraction efficiency versus direct
current voltage are shown. The measured results agree with theoretical calc
ulation. (C) 2000 American Institute of Physics. [S0021-8979(00)07311-4].