Terahertz dual-band asymmetric transmission for a single cross-polarized linear wave

The reported dual-band asymmetric transmission is usually an effect of mutual polarization conversion, where one polarized wave is converted to its cross-polarization in the first band while the other polarized wave is converted to its cross-polarization in the second band. In this work, we experimentally demonstrate a dual-band asymmetric transmission effect only for one-polarized linear wave in the terahertz band. It is measured that the cross-polarization transmission coefficient T_yx reaches two peaks of 0.715 and 0.548 at the frequency of 0.74 THz and 1.22 THz, respectively. While the transmission coefficient T_xy is lower than 0.2 in the wide-band from 0.5 THz to 1.5 THz. Firstly, the multiple interference model is used to discuss the physical mechanism of the dual-band asymmetric transmission. However, the second band of the calculated spectrum is offset due to the strong near field coupling between the two metal layers. The coupled-mode theory is then introduced and the fitting result of the coupled-mode theory is in good agreement with that of the experiment in the two bands. This research would provide new theoretical instructions in designing and analyzing multiband asymmetric transmission in the terahertz, microwave or the optical bands.