Fabry–Pérot cavities critically coupled to metal nanodisk arrays for multi-narrowband perfect absorption

In this work, a simple absorber composed of a Fabry–Pérot (FP) cavity and an array of an Au nanodisk is investigated via the temporal coupled-mode theory and numerical simulations, which enable perfect narrow-band absorption in the visible and near-infrared regions. The absorption of the optimized structure exceeds 99.9% at specific wavelengths, which is primarily attributed to the critical coupling between the FP cavity and the Au nanodisk array. Moreover, by modulating the length of the FP cavity, perfect absorption of multiple narrowbands is achieved. Compared with other results, the hybrid structure has the advantages of high efficiency and tunable multiple narrowband absorption in both visible and near-infrared wavebands, as well as excellent angular tolerance. We argue that this hybrid structure provides a promising route to utilize the FP cavity for designing multiple narrow-band absorbers, which can be used as optical filters, thermophotovoltaics, and biosensors.