Eigenmode analysis of symmetric parallel waveguide couplers

Abstract

An analysis of a laterally symmetric parallel waveguide structure has been carried out by using symmetric and antisymmetric eigenmodes in the coupled made equations. As opposed to modes of each individual guide, eigenmodes are orthogonal and therefore comply with coupled mode formalism. Of particular interest has been the popular configuration Z-cut LiNbO3 with wave propagation along the crystal Y-axis. The theory shows that output versus voltage characteristics are nonperiodic in voltage, and furthermore, they are asymmetric if the eigenmodes are not equally excited. The uniform electrode coupler can easily be explained in terms of eigenmode coupling and interference. Copyright © 1987 by The Institute of Electrical and Electronics Engineers, Inc.