Triple Fano resonances metasurface and its extension for multi-channel ultra-narrow band absorber

Metasurface excited multiple Fano resonances has become a hot spot and has been widely investigated and applied in the field of optics. A metasurface designed in this paper is composed of a silicon cuboid etched with an akin rhombus hole and deposited periodically on the silica substrate. By introducing symmetry breaking, the symmetry-protected BIC is transformed into the quasi-BIC, and triple sharp Fano resonances, corresponding to 1357 nm, 1421.7 nm, and 1588.8 nm respectively, with spectral contrasts of nearly 100 % are excited. Their maximum Q-factor can reach similar to 3 x 10(4). Results of multipole decomposition show that the triple Fano resonances are dominated by magnetic dipole (MD) or electric quadrupole (EQ). Additionally, by modifying the polarization angle of the incident light, the metasurface performs excellently as a bidirectional optical switch. By adding the aluminum layer under the original structure, an ultra-narrowband absorber is created with a maximum absorption rate of similar to 100 %. The sensing performance of the absorber is studied, yielding the maximum sensitivity of 255 nm/RIU and the maximum figure of merit (FOM) of 477 RIU-1. The proposed metasurface and its extension structure are potential to be applied in as high-performance biosensors, optical switch, and coherent thermal radiation.