Numerical calculation of waveguide modulator with Mach-Zehnder structure

A three-dimensional beam propagation method (BPM) based on the series expansion method (3D-SEM-BPM) transforms the BPM into first-order normal differential equations. Reducing the basic BPM equation to first-order normal differential equations makes the computational program simple, and the method is efficient due to its small matrix. Based on this method, we examine and simulate the optical distribution of the lithium niobate electro-optic waveguide modulator with Mach-Zehnder structure. The device structure is optimized for high extinction ratio and low propagation loss. The tangent function is applied to map the infinite space into a finite space to avoid boundary truncation.