Surface electromagnetic modes contribution to the anomalous terahertz transmission through double-layered metal hole array

Terahertz transmission spectra through both single-layered and double-layered sub-wavelength metal hole arrays were calculated using rigorous mode-matching method. The dispersion relations of the single-layered and double-layered metal hole arrays were obtained by FDTD method. There are three anomalous peaks in the spectrum of the double-layered metal hole array, which arise from the three surface electromagnetic modes appearing in the dispersion relation. By comparing the transmission spectra and the dispersion relations of the single-layered and double-layered metal hole arrays, it was found that the two surface electromagnetic modes at higher frequencies are introduced by the single-layered metal hole array, while the one at lower frequencies is introduced by the double-layered metal hole array. The validity of the analysis was qualitatively verified by the experimental results. This structure can be finely designed for potential applications, such as wideband filtering.