Ultra-high quality perfect absorber based on quasi bound states in the continuum

Ultra-high-quality perfect optical absorption structures based on quasi-bound states in the continuum (quasi-BICs) are investigated and numerically demonstrated. When the radiation rate of the magnetic dipole quasi-BICs resonance is equal to the dissipate loss rate of the system, the critical coupling condition is satisfied and the perfect absorption (nearly 100%) is obtained. The ultra-high-quality factor (1.7 × 105) perfect absorption in the proposed design is mainly attributed to the extremely low external leakage loss rate of quasi-BIC and relatively small intrinsic absorption loss rate in the constituent materials. The structure exhibits excellent sensing properties with a sensitivity of 108 nm/RIU and ultra-high FOM of ∼12013. The proposed scheme is of importance in potential biosensing applications.