Independently tunable triple-band infrared perfect absorber based on the square loops-shaped nano-silver structure

Recently, the keen demand for multi-band perfect absorbers in spectroscopy, infrared detection, and other fields has intensified. To meet the energy demand, here we propose an Ag-Dielectric-Ag multilayer triple-band perfect absorber exhibiting perfectly resonance absorption in the near-infrared region. And the numerical calculations indicate that we obtain three resonance absorption peaks (908 nm, 1085 nm, and 1216 nm) with the maximal absorption of 99.09%, 99.84%, and 99.21%, respectively. Based on this, we propose that the physical formation mechanism of three resonance peaks are the Fabry-Pérot resonance effect and Localized surface plasmon polaritons resonance. Theoretically combined with the electromagnetic coupling theory to explain how the resonance-enhanced absorption. At the same time, by the comparison with the complementary structure, it is theoretically proposed that the MIM structure has a Fabry-Pérot resonance effect in the near-infrared region and then computationally verified the Fabry-Pérot formula. Furthermore, we can adjust the amplitude and wavelength of resonance peaks by modifying the geometry unit cell. And our proposed triple-band perfect absorber has some excellent properties, such as high absorptivity, multi-band, tunable, suitability for wide incidence angles, excellent angle tolerance, polarization tolerance, etc. In addition, our TBPA has a simple structure, which simplifies the processing technology and economically saves processing costs. Furthermore, the following simulations investigate the absorption spectrum of our TBPA exhibit property changes significantly as the environment changes. So we can calculate the sensitivity of three modes (sorted by resonance wavelength from short to long) is S1 = 70.09 nm/RIU, S2 = 208.26 nm/RIU, and S3 = 50.06 nm/RIU, respectively. Therefore, we believe that this triple-band perfect absorber can capture maximize optical energy and apply it in devices and materials for light conversions, like plasmon-enhanced photovoltaics, optical absorption switching, and modulator-optical communications.