Perfect absorption and refractive index sensing of an E-shaped hole array metasurface through BICs

In this Letter, we propose an E-shaped hole metasurface leveraging bound states in the continuum (BICs) for perfect absorption and ultrasensitive refractive index sensing.We can achieve 98.9% optical absorption at 909 nm in the symmetric metasurface through a symmetry-protected BIC mode.It is found that there is a squared relationship between the Q-factor and the asymmetry factor.More importantly, we successfully activate the quasi-BIC (Q-BIC) mode in a symmetry-broken structure at an 8light incidence angle.Both the symmetry-protected BIC and Q-BIC modes show 1000 nm/RIU (refractive index unit) sensitivity in air, while the latter outperforms in organic solutions with a figure of merit (FOM) of 463.9.This platform offers a versatile solution for ultra-narrowband photonics and high-precision biosensing applications.