Symmetry-protected bound state in the continuum in the metasurface of dielectric nanodisk with the inclined surface

Abstract

We design and numerically investigate an all-dielectric metasurface with a single nanodisk in a unit cell supporting quasi-bound state in the continuum (BIC) arising from the distortion of symmetry-protected BIC. We demonstrate that by breaking out-of-plane symmetry, in the direction perpendicular to a nanodisk with an inclined surface, the transformation of BIC into quasi-BIC, having Fano line-shape, can be observed with an increasing inclination angle. Such transformation is analysed in detail by calculating charge density distributions, far-field radiations and near-field distributions, demonstrating the dominant electric quadrupole component in the quasi-BIC. In addition, the quasi-BIC can be easily tailored by the intrinsic material loss and the Fermi energy of graphene. By introducing this unique degree of freedom beyond the in-plane symmetry, one can realize access to the multipolar BIC-associated leaky state in simpler metasurface, indicating potential applications in the quasi-BIC-based switching and optical modulators.