Ultra-high- Q mid-infrared metasurface sensor via asymmetric ‘internally cut four-hole’ meta-atoms

Abstract Optical metasurface sensors play a significant role in fields such as biochemical sensing and environmental monitoring. Bound states in the continuum is a commonly used method to achieve high quality ( Q ) factors in recent years. However, how to maximize the Q value in the actual structure remains a key challenge. Here, we propose a mid-infrared (MIR) all-dielectric metasurface sensor based on asymmetric ‘internally cut four-hole’ cylindrical meta-atoms. This structure creates a composite optical resonator with ultra-high quality factor and optical localization capability by fusing photonic crystal plates with cylindrical resonators. We successfully excite dual-band narrowband resonance, and systematically compare different symmetry-breaking strategies. Research has demonstrated that by exciting the magnetic dipole (MD) mode and adopting a superior symmetry-breaking scheme, higher Q value and high sensitivity can be achieved. The simulation and multipole analysis results confirmed the existence of MD and electric quadrupole modes, demonstrating a peak (maximum) Q factor of ∼1.8 × 10⁵ under minimal asymmetry (Δ r = 10 nm). At a larger asymmetry optimized for sensing (Δ r = 50 nm), the device operates with a high Q factor of ∼4.8 × 10⁴ while achieving sensitivities ( S ) of 1110 nm RIU −1 and 1478 nm RIU −1 , leading to outstanding figures of merit of 3500 RIU −1 and 6000 RIU −1 , respectively. This research provides an effective solution for the development of high-performance MIR sensing chips.