Dynamic tunable multi-channel ultra-narrowband absorber based on hollowed-out trapezoidal Si-graphene-Au metasurface

Abstract Dynamic tunable metasurfaces are of great interest for their optical modulation properties. This study proposes a metasurface with a rectangular hole etched from a silicon square. By converting this rectangular hole into a trapezoid, we disrupt the symmetry, transforming the symmetry-protected bound states in the continuum (BIC) into a quasi-BIC (Q-BIC) state, achieving triple Fano resonances with a maximum Q factor of 1074. The results of the multipole analysis suggest resonance modes are magnetic dipole and electric quadrupole. A typical dielectric/dielectric/metal structure is then formed by adding an Au layer below the original structure. The polarized-light absorption of the metasurface is found to be unaffected by the angle of incident light. An analysis of the thickness of the Si is studied on the effect of absorption. Eventually, a single layer of graphene is incorporated at the bottom of the Si. The dynamic modulation of the three absorption peaks of the composite metasurface is achieved by controlling the bias voltage to alter the Fermi level Ef of graphene. The Si-graphene-Au structure has a sensitivity of 252.5 nm/RIU and the maximum performance value of 126.25 RIU-1 at Ef = 1 eV. These results indicate that this composite metasurface has potential applications in the research of sensor direction.