Analysis of ridge-type LiNbO₃ optical waveguide modulators with the extended point-matching method

The point-matching method is extended to analyze a travelling-wave electrode structure for ridge-type LiNbO₃ optical modulators. The potential function is expended in terms of a Fourier sine series, and the coefficients of the series are obtained by satisfying the boundary conditions in the contact plane at a finite, discrete set of points. The calculated fields are used to estimate the characteristic impedance and microwave effective index. This method provides a simple and fast approach to the quasi-static analysis of the multi-layered structures with finite electrode thickness. The results agree well with those obtained using the finite-element method. Some significant conclusions are obtained for design and optimization of modulators.