High-Q Supercavity States in High-Index Subwavelength All-Dielectric Resonators

We study strong coupling between eigenmodes of a single subwavelength high-index dielectric resonator and analyse the mode transformation and Fano resonances by varying resonators aspect ratio. We demonstrate that the strong mode coupling is associated with formation of states with giant Q-factors similar to the physics of bound states in the continuum when the radiative losses are almost suppressed due to the Friedrich-Wintgen scenario of destructive interference. We confirm our theoretical findings with microwave experiments by using a high-index cylindrical resonator with tunable aspect ratio.