Asymmetric Cross Metasurfaces with Multiple Resonances Governed by Bound States in the Continuum

Abstract

The bound state in the continuum (BIC) has paved a new way to achieve excellent localization of the resonant mode coexisting with a continuous spectrum in the metasurface. Here, we propose an all-dielectric metasurface consisting of periodic pairs of asymmetric crosses that supports multiple Fano resonances. Due to the sufficient degrees of freedom in the unit cell, we displaced the vertical bars horizontally to introduce in-plane perturbation, doubling the unit cell structure. Dimerization directly resulted in the folding of the Brillouin zone in k space and transformed the BIC modes into quasi-BIC resonances. Then, simultaneous in-plane symmetry breaking was introduced in both the x and y directions to excite two more resonances. The physical mechanisms of these BIC modes were investigated by multipole decomposition of the scattering cross section and electromagnetic near-field analysis, confirming that they are governed by toroidal dipole (TD) modes and magnetic dipole (MD) modes. We also investigated the flexible tunability and evaluated the sensing performance of our proposed metasurface. Our work is promising for different applications requiring stable and tunable resonances, such as optical switching and biomolecule sensing.

Multi-function sensing applications based on high Q-factor multi-Fano resonances in an all-dielectric metastructure

“…An ideal BIC is a mathematical model existing in an ideal lossless structure, which cannot be used for practical applications due to the characteristics of an exceptionally thin linewidth and an infinitely high Q-factor [ 19 – 21 ]. However, by using the method of symmetry breaks in the metastructures, the radiation channel with the outside is established, which allows ideal BIC is disturbed and converted to the quasi-BIC, leading to limited linewidth and high Q-factor [ 22 – 24 ].…”