Dispersion properties of uniform trapezoidal optical waveguides

A method for calculation of the propagation constant of guided modes in the optical waveguides with trapezoidal cross-sections is proposed. The method enables to calculate a propagation constant correction factor that arises due to perturbations of the cross-section of a reference rectangular waveguide. The correction factor is analytically calculated within the framework of the coupled-mode theory. A refined form of the coupling coefficient is obtained owing to the application of a concept of effective excitation sources and accurate account of boundary conditions. An impact of the waveguide cross-section shape on its dispersion properties is analysed. The necessity to take into account the proposed form of the coupling coefficient is demonstrated by comparison of the simulation results with other methods of dispersion calculation.