Hollow Mie resonators based on toroidal magnetic dipole mode with enhanced sensitivity in refractometric sensing

We propose a refractometric sensor based on hollow silicon Mie resonators of a toroidal magnetic dipole mode. This mode has a pair of antiparallel electric dipoles perpendicular to the silica substrate; thus, the radiation of the mode is suppressed, resulting in an ultra-narrow reflection peak linewidth of 0.35 nm. In addition, the hollow structure enhances the interaction between the enhanced electric field and the surrounding medium, thus improving the sensitivity. The proposed Mie resonators achieve a sensitivity of 486 nm RIU ^−1 and a figure of merit up to 1389 RIU ^−1 , which are ideal for refractometric sensing.