Wave propagation in integrated acoustooptical anisotropic waveguides

A system of coupled scalar wave equations is derived for anisotropic inhomogeneous media. Conditions of small index gradients, paraxial propagation and moderate anisotropy are used. The equations obtained serve as a basis for a beam propagation method (BPM) algorithm in anisotropic media. The anisotropy slightly modifies the dispersion characteristics of diffused channel waveguides. The BPM algorithm is tested by application to Ti indiffused waveguides in LiNbO₃, the principal axes declined against the laboratory coordinate system about an arbitrary angle. Very good agreement with results obtained from a plane wave analysis is confirmed. The method is applied to combined collinear acoustooptical waveguide with transverse and longitudinal variation of one off-diagonal element of the permittivity tensor. Coupling to radiation modes occurs for sufficiently high off diagonal elements