Sharp optical magnetic resonances in dielectric waveguide grating structures

We report that a sharp resonance is observed in an asymmetric dielectric waveguide grating structure. This resonance can be characterized by a circulating displacement current in the sub-wavelength unit cell that is associated with a magnetic-dipole mode. It is shown that such a sharp resonance comes from the interaction between two non-degenerate waveguide modes, and can be explained by use of a radiant two-resonator model based on coupled-mode theory. Our analytical model agrees well with the numerical results, and can be used to exploit additional intriguing physical characteristics in the system. (C) 2017 Optical Society of America