Polarization-selective excitation of multiband quasibound states in the continuum supported by symmetry-perturbed silicon metasurface

Bound states in the continuum (BICs) possessing a typical characteristic of high quality (Q) factor allow for strong light–matter interactions and boost various research fields including optical detecting and nonlinear photonics. In this work, a spatial symmetry-perturbed metasurface composed of a period array of single-notched silicon nanodisk is proposed to support multiband quasi-BICs (QBICs). After group theory analysis of eigenmodes and group-theoretical symmetry arguments describing the symmetric matching relationship between BICs and external radiation, we numerically demonstrate that a magnetic quadrupole BIC and an electric dipole BIC are excited by x-polarized plane wave, and an electric quadrupole BIC and a magnetic quadrupole BIC are excited by y-polarized plane wave, achieving the polarization-selective excitation of multiband QBICs by adjusting the light polarization. The Q-factors of these four QBICs exhibit the inverse quadratic dependence on two different asymmetric parameters, which provides two independent channels for controlling the coupling to BICs. This new device featuring a simple bulk geometry will become an extremely important platform to obtain more flexible and stronger electromagnetic wave manipulation at the nanoscale, which facilitates large-scale and highly integrated electromagnetic applications in non-linear devices, high-throughput sensors, optical communications, and so on.