Anomalous dispersion of electromagnetic eigenwaves in a sandwich structure with a gap

A system of two different isotropic dielectric plates aligned parallel to each other and separated by a gap is considered. For a sufficiently large gap, electromagnetic eigenwaves in the plates are virtually independent and dispersion curves for the studied system are characterized by an infinite set of intersections. A decrease in the gap thickness leads to coupling between the wave fields and the disappearance of the intersection points due to divergence of the dispersion curves. Each of the dispersion curves of the spectrum transformed under the action of coupling is formed by a set of adjacent portions of initially independent branches corresponding to different plates. A gradual change in the frequency along one of the new dispersion curves results in a periodic displacement of the localization zone of the wave field from one plate to the other.