Resonant field enhancement in all-dielectric metastructures supporting THz bound states in the continuum

Owing to their flexible and adaptable control in optics, active optical metastructures have attracted growing attention in nanophotonics. In this study, we investigate the manipulation of a resonant all-dielectric metastructure using the thermal-sensitive material SrTiO3, at different temperatures. A double-disk array has been designed to support responses that exhibit a strong toroidal dipole and a quasi-bound state in the continuum, which is magnetic dipole. The ultrahigh sensitivity level of 501 GHz/RIU is obtained by low-loss magnetic dipole resonances with extremely narrow linewidth that is very sensitive to alters in the dielectric constant of the sensing medium. These results are promising for the development of THz-range ultrasensitive optical sensors.