Properties of trapped electromagnetic modes in coupled waveguides

The existence of trapped modes in coupled electromagnetic waveguides is experimentally investigated for configurations with different degrees of symmetry supporting hybrid modes. The occurrence of confined solutions in such open geometries is proven to be much more general than demonstrated so far, as predicted by Goldstone and Jaffe (J. Goldstone and R. L. Jaffe, Phys. Rev. B 45, 14100 (1992). The identification of the observed modes is based on the numerical modeling of the relative vector fields. The experimental results make evident that an increasing aperture of the configuration can improve the confinement of the mode instead of generating additional leakage channels. In particular, long-lived trapped modes can be easily obtained in geometries with a large aperture. Their resonance parameters can compete with those of standard close cavities working at millimeter wavelengths. The role of the symmetry on the properties of these trapped modes is discussed in detail.