BICs supported by different polarized light in notched silicon nanorods metasurface

Symmetry-protected bound states in the continuum (BICs) are the eigenstates with forbidden radiation lying in the radiation continuum due to the symmetry incompatibility. When the symmetry is broken, BICs are transformed into quasi-BICs (Q-BICs) with an ultra-high quality factor. Typically, notches are created by adding or removing portions of dielectric nanostructures in a certain direction. This results in structures that only support Q-BICs excited by specific polarized light. In this work, we introduce a metasurface composed of bevelled double silicon nanorods, which supports the Q-BICs excited by not only y-polarized but also x-polarized incident light. Analysis from multipole decompositions and electromagnetic fields distributions confirm that the dominant contributions to the quasi-BICs under y-polarization are the toroidal dipole moment and magnetic quadrupole. The quasi-BICs under x-polarization are dominated by magnetic dipole and electric quadrupole. Our results may provide a route for enhance light–matter interaction, such as lasing, switching, nonlinear optics, and so on.