Manipulation Over Surface Waves in Bilayer Hyperbolic Metasurfaces: Topological Transition and Multidirectional Canalization

Spoof surface plasmon-polariton is a type of surface wave (SW) propagating at the artificially engineered structures in microwave and terahertz ranges. These SWs are highly important in planar photonic and on-chip devices, integrated circuits, lenses, sensors, and antennas applications. However, it is still a challenge to control the propagation regime of such SWs including the wavefront shapes and propagation directions. In this letter, we study the SWs in bilayer hyperbolic metasurfaces and show that the interplay between two layers allows them to manage their regime of propagation. We demonstrate the switching between the angle and number of propagation directions of SWs at the same frequency. Finally, we demonstrate experimentally the tunable multidirectional in-plane canalization of SWs by adjusting the directions of their propagation within the angular range from 0° to 12.8°. The discovered rotation-mediated interlayer coupling of hyperbolic metasurfaces paves the way toward efficient in-plane transfer of localized electromagnetic signals.