Dual polarization-independent quasi-bound states in the continuum in a hetero-out-of-plane dielectric metasurface

Symmetry-protected quasi-bound states in the continuum (qBICs) in metasurfaces with broken in-plane symmetry are extensively investigated to achieve high quality-factor (Q-factor) resonances. Herein, we propose the hetero-out-of-plane (H-OP) dielectric metasurface, which is composed of Si cuboids tetramer broken out-of-plane symmetry by adding a layer of silica. Dual polarization-independent qBICs are realized. The multipolar decomposition of scattering powers and near-field distributions reveal the physical mechanism of dual qBICs modes, which are dominated by the magnetic quadrupole and the toroidal dipole. The two symmetry-protected qBICs in the H-OP metasurface have robust Q-factors and stable resonance wavelengths compared with these in the out-of-plane metasurface. Our results provide a route to achieve the high Q-factor resonator with better performance applied in many optical and optoelectronic devices.