Electrically tunable toroidal Fano resonances of symmetry-breaking dielectric metasurfaces using graphene in the infrared region

The magnitudes of coupling strength play an important role in various resonant phenomena such as Fano resonances (FRs). However, the coupling strength within the FRs using dielectric metasurfaces cannot be easily manipulated once they have been made. In this paper, toroidal FR is excited using the silicon metasurface with symmetry-breaking nanocylinders. Inserting a graphene layer with an ion-gel top gate onto the silicon metasurface, actively tunable response of a toroidal FR resulting from the manipulated coupling strength and the phase shift between two states. The hybrid graphene-silicon metasurface realize tunable Fano parameter (q) from -1.38 to -1.85 with applied voltage ranging from 0 to 2 v. Theoretical results predicted that higher q values are reachable relying on the hybrid graphene-silicon metasurface. The high-quality(Q)-factor (similar to 444) tunable FR of metasurface in the near-infrared region is observed. By applying a bias voltage to graphene obtain a blueshift of resonant wavelength (similar to 4 nm) with a maximum change of transmission spectrum peak up to 30%. These results have potential in high-efficient tunable electro-optic modulators, near-infrared optical switches, etc.