Terahertz dual phase gradient metasurfaces: high-efficiency binary-channel spoof surface plasmon excitation

Spoof surface plasmon meta-couplers are compact antennas that link propagating waves and surface waves. However, most of them are designed with a fixed phase gradient and channel for the incident waves with specific polarization, which limits their further applications in multichannel scenarios. In this Letter, a new, to the best of our knowledge, method that combines the Brillouin zone folding theory with the generalized Snell's law is proposed. We demonstrate that when the phase gradient of the metasurface is large enough, Brillouin zone folding effect will occur, which will create dual phase gradient space in a single metasurface. With this method, we design two novel terahertz meta-couplers with functionalities of symmetrical and asymmetrical binary-channel spoof surface plasmon (SSP) excitation. Furthermore, finite element method simulations are performed to demonstrate their functionalities. Considering the orthogonality of the incident waves, there can be a total of four independent space channels to excite SSPs on one metasurface. This work may open up new routes in multichannel SSP meta-couplers and multibeam surface wave antennas. (C) 2020 Optical Society of America