All-dielectric double near-perfect absorptions and optical switchings in a permittivity-asymmetric multiple-qBIC-driven metasurface

We propose a tunable all-dielectric permittivity-asymmetric metasurface capable of supporting dual high-quality (<i>Q</i>) qBIC modes, leading to double near-perfect absorptions (PAs). By breaking the permittivity tensor symmetry through the magneto-optical (MO) effect, electric quadrupole modes-dominated double qBICs are excited. The high-reflection background toroidal dipole mode suppresses radiative loss in transmission, enabling the metasurface to surpass the 50% absorption limit and achieve double high-<i>Q</i> near-PAs of 88.08% and 96.12% at 1448.3 nm and 1457.9 nm under critical coupling condition, with high<i>Q</i>-factors up to 8.7 × 10³ and 1.2 × 10⁴, respectively. The proposed all-dielectric MO metasurface exhibits robust near-PAs against variations in geometrical parameters. Moreover, by dual MO and polarization angle of incident light control, the double qBICs exhibit high-performance optical switchings with a maximum modulation depth of 100% and the corresponding ON/OFF ratio exceeding 39 dB, demonstrating their potential for ultra-efficient light manipulation.