An asymmetric GaAs nanocylinder quasi-BIC metasurface for dual narrowband high- Q perfect absorption in the near-infrared region

This study presents a non-fully symmetric metasurface absorber based on GaAs nanocylinders, comprising a GaAs nanocylinder array, a SiO₂ spacer, and a gold back reflector. Finite-difference time-domain (FDTD) simulations under y-polarized illumination reveal two narrowband absorption peaks at 0.945 µm and 1.016 µm within the 0.92-1.04 µm range, with near-perfect absorption efficiencies of 99.4% and 99.5%, respectively. Impedance-matching theory and multipole decomposition indicate that these peaks are primarily governed by toroidal dipole and magnetic dipole resonances. The non-fully symmetric design introduces polarization-dependent responses across different polarization states, while maintaining robust performance within a certain range of incident angles. The simple structure ensures ease of fabrication, demonstrating potential for applications in optical switching, surface-enhanced spectroscopy, and biosensing.