Triple-band perfect absorber based on the gold-Al2O3-grating structure in visible and near-infrared wavelength range

In this paper, a metal-dielectric-metal (MDM) structure consisting of the top gold-grating and Al2O3-grating compounded layer and the bottom gold substrate is proposed to realize the triple-band perfect absorption in visible and near-infrared wavelength range. The absorption characteristics of the proposed absorber are investigated theoretically by using of the finite-difference time-domain (FDTD) method. The numerical simulated results indicate that three perfect absorption modes are mainly attributed to the interaction among gap plasmon resonance, Fabry-Perot (F-P) cavity resonance, local surface plasmon resonance (LSPR) and surface plasma polarizations (SPPs) in the grating structure. Besides, the dependence of the absorption properties on the structural parameters is thoroughly investigated. An excellent linear relationship between the absorption peaks and the refractive index of the dielectric layer provides an effective way to realize an adjustable absorber for this structure. What’s more, the absorption strength to the polarization angle adjustable and incident angle insensitive properties of the plasmonic perfect absorber are obtained. Finally, the maximum refractive index sensing sensitivity to the surrounding medium reaches 362 nm/RIU and the maximum value of the reflection spectral difference ratio is up to 485. These properties will promote its enormous application in active optoelectronic devices.