A narrowband perfect absorber with high Q-factor and its application in sensing in the visible region

Metamaterial absorbers have attracted more and more attention because they can achieve perfect absorption in some specific structures. At present, although most absorbers can achieve perfect absorption in one or more frequencies of the visible or near infrared regions, its cannot achieve ultra-narrow band absorption. Ultra-narrow band absorption means that devices have the opportunity to improve the effectiveness and accuracy of detection in many applications. Here, a novel design of narrowband perfect absorber based on a dielectric-dielectric-metal structure is studied, which comprises of an Al2O3 nanodisk arrays, a SiO2 dielectric layer, an Au film, and a substrate layer. The simulated results reveal that the optimized nanoabsorber can excite resonances with a narrow absorption bandwidth (FWHM) of 0.45 nm and a high-quality (Q) factor up to 1499 in the visible regime. Moreover, when it as a refractive index (RI) sensor, the maximum sensitivity(S) of 108.32 nm/RIU and figure of merit (FOM) reaching 240.7 are obtained. The device exhibits angle and polarization independence, which will eliminate the polarization and angle requirement of the equipment. As a consequence, we believe our narrowband absorber could be used in many potential applications such as the detection of photodetectors, biological, chemical and so on.