Complex modes in open lossless dielectric waveguides

An approach to the analysis of complex modes in lossless isotropic dielectric waveguides is presented. The existing theory of complex modes is extended to the case of open structures by techniques of functional analysis. Mathematical and physical properties of complex modes, including some criteria of existence and mechanisms of occurrence, are formulated. The theory is demonstrated by the numerical example of a waveguide with a large core-cladding refractive-index difference. Computed complex-mode dispersion characteristics are analyzed, and the mode vector field, together with the power distribution in the waveguide cross section, is shown.