Multiwavelength Gas Sensing with Quasi-Bound States in the Continuum in an All-Dielectric Metamaterial of Permittivity-Asymmetric Nanoring Dimer

In this work, we theoretically demonstrate that multiwavelength gas sensing can be induced by quasi-bound states in the continuum in an all-dielectric metamaterial of permittivity-asymmetric nanoring dimer. By elaborately introducing the permittivity asymmetry, the nanoring dimer can not only enhance the magnetic dipole mode, but also simultaneously support dual symmetry-protected bound states in the continuum (BICs). Multipole expansion and near-field enhancement further indicate that such two quasi-BICs are distinguished as a magnetic dipole and electric quadrupole modes, where asymmetric magnetic dipole enhancement is mainly distributed in the hole and indirectly manipulates the localized magnetic field. The gas sensing shows that the sensitivities of modes can reach up to 210 nm/RIU, 292 nm/RIU, and 498 nm/RIU that corresponds to the figure of merit of 98, 621, and 16600, making the proposed metamaterial promising for multiwavelength gas sensing.