Determination of Propagation Constants of Guided Modes using the Beam Propagation Method

摘要

Propagation constants of guided modes of an optical directional coupler are calculated from two complex field quantities measured with the beam propagation method at two longitudinal positions and at a fixed transverse location. The method is based on the assumption that field profiles can be expressed as a linear combination of guided modes. The relationship between the two field quantities generate simultaneous equations for propagation constants which can be solved by iterations.The present analysis computes propagation constants faster than conventional Fourier transform method,while the numerical accuracy is comparable with that of the conventional one.