Switchable multiple quasibound states in the continuum based on the phase transition of vanadium dioxide

Resonant dielectric nanostructures have achieved significant advancements in the manipulation of light at the nanoscale. Particularly, bound states in the continuum (BICs) based on dielectric metasurfaces have greatly enhanced the intensity of light–matter interaction. However, most BICs in dielectric metasurfaces are fixed in their functionality once they are made. In this study, we present the development of switchable multiple quasi-BICs by combining dielectric nanostructures with vanadium dioxide. The resulting hybrid dielectric metasurface can support three types of BICs with different multipole origins for vanadium dioxide in the insulating phase. By introducing structural asymmetry through width adjustment, one quasi-BIC with a longitudinal toroidal dipole characteristic is excited under x -polarized incidence. Further, tuning the width allows for the generation of two additional quasi-BICs with distinct electromagnetic sources under y -polarized incidence. Additionally, the hybrid dielectric metasurface also supports a high- Q transverse toroidal dipole mode. Moreover, all quasi-BICs and toroidal dipole modes can be turned off when vanadium dioxide transitions into the metallic phase. The switchable multiple quasi-BICs hold promise for applications in optical modulators, tunable harmonic generation, and biosensors.