Multiple quasibound states in the continuum of permittivity-asymmetric all-dielectric metasurface: Group-theoretical description

Symmetry-protected bound states in the continuum (BICs) allow for high-efficiency light-matter interactions. Multi-channel BICs supported by a single nanophotonic-based device capable of further enriching the trapping and manipulation of light. It is well established that by breaking the in-plane geometrically symmetry, BICs can be transformed into quasi-BICs (qBICs). In this work, we propose and theoretically demonstrate that such optical states can also be accessed in metasurfaces with symmetric geometric parameters by breaking the in-plane symmetry in the permittivity of the comprising materials. We show that multiband qBICs with exquisitely high quality (Q) factors are excited under different polarization light incidence at near-infrared range, where a strong modulation of the optical response can be obtained by a small perturbation of the permittivity symmetry of the system. The group-theoretical methods and the representation theory are used to uncover the physical mechanism of qBICs and their polarization dependence. The full-wave and eigenfrequency simulations confirm the theoretical analysis.The results of near-field distributions and detailed multipole decompositions reveal that these qBICs present different optical characteristics. The polarization-multiplexed all-dielectric metasurfaces with high Q factors have great potential for applications in integrated multi-channel optical devices.