Polarization-independent multiband absorbers based on two types of bound states in the continuum for sensing application

In this work, we present a tri-band polarization-insensitive silicon-based near-infrared absorber driven by two types of BIC resonances. Three polarization-insensitive near-perfect absorption peaks are obtained, which are based on the superposition of three different quasi-BIC (Q-BIC), and their mechanisms are further elucidated through impedance matching theory, far-field multipole decomposition, and near-field distributions. We also investigate the sensing application of the tri-band polarization-insensitive silicon-based absorber, demonstrating its excellent sensing capability of up to 427.6 nm/RIU. Our study paves a feasible path for the design of multiband polarization-independent, narrowband, and high-sensing performance absorbers, which hold potential in sensors and photodetectors.