Unidirectional reflectionlessness, asymmetric reflection, and asymmetric transmission with linear and circular polarizations in terahertz metamaterial

We propose a structure utilizing a double-layer aluminum ring resonator embedded in a dielectric layer of metamaterial to demonstrate the appearances of unidirectional reflectionlessness, asymmetric reflection, and asymmetric transmission for the incident linear and circular polarizations. A significant feature of this structure is that it allows multiple functions to be implemented in the same structure without changing any structure parameters. For the vertical incident x- and y-polarizations, not only significant unidirectional reflectionlessness and asymmetric reflection effects are verified but also the strong linear to circular polarization conversions are illustrated in both transmission and reflection modes. For the vertical incidences of right-handed and left-handed circular polarizations, unidirectional reflectionlessness and asymmetric reflection are also demonstrated in detail. In addition, when linearly or circularly polarized waves are incident obliquely, the structure exhibits a stable asymmetric transmission phenomenon within a wide incident angle range. Furthermore, it also supports the occurrences of unidirectional reflectionlessness and asymmetric reflection stably within wide ranges of incident angle, resonator spacing, and rotation angle of the upper aluminum ring.