Active optical modulation of quasi-BICs in Si-VO2 hybrid metasurfaces.

Active optical modulation breaks the limitation of a passive device, providing a new, to the best of our knowledge, alternative to achieve high-performance optical devices. The phase-change material vanadium dioxide (VO2) plays an important role in the active device due to its unique reversible phase transition. In this work, we numerically investigate the optical modulation in resonant Si-VO2 hybrid metasurfaces. The optical bound states in the continuum (BICs) in an Si dimer nanobar metasurface are studied. The quasi-BICs resonator with high quality factor (Q-factor) can be excited by rotating one of the dimer nanobars. The multipole response and near-field distribution confirm that magnetic dipoles dominate this resonance. Moreover, a dynamically tunable optical resonance is achieved by integrating a VO2 thin film to this quasi-BICs Si nanostructure. With the increase of temperature, VO2 gradually changes from the dielectric state to metal state, and the optical response exhibits a significant change. Then, the modulation of the transmission spectrum is calculated. Situations where VO2 is located in different positions are also discussed. A relative transmission modulation of 180% is achieved. These results fully confirm that the VO2 film shows an excellent ability to modulate the quasi-BICs resonator. Our work provides a route for the active modulation of resonant optical devices.