Multi-band near-perfect absorption via the resonance excitation of dark meta-molecules

We numerically study a multi-band absorption based on electromagnetic-induced-transparency effect of metamaterial. By exploiting the coupling between bright and dark plasmonic modes of cut-wire triplet, which consists of a vertical wire and two horizontal wires, a dual-band absorption is realized at 243 and 266 THz. Then, the absorber structure is improved by adding two new horizontal wires which play role as second dark meta-molecules. Due to the dark-dark coupling, another absorption band arises so that a triple-band absorption is created at 240, 250 and 264 THz. The role of interaction between dark meta-molecules in triple-band absorption is investigated, revealing a specific non-monotonic characteristic of the second absorption peak. Finally, the influence of incident angle of EM wave on multi-band absorbers shows that the absorption of lowest frequency peak is robust while those of higher frequency peaks are strongly weaken with increasing of the incident angle.