Photonic Weyl waveguide and saddle-chips-like modes

Topological Weyl semimetals are characterized by open Fermi arcs on their terminal surfaces, which not only renewed our well-accepted concepts of the Fermi loop but also enabled many exotic phenomena, such as one-way propagation. The key prerequisite is that the two terminal surfaces have to be well-separated far away, i.e. the Fermi arcs are not allowed to couple with each other. Thus, their interaction was overlooked before. Here, we consider the coupled Fermi arcs and propose a Weyl planar waveguide, where we found a saddle-chips-like guiding mode. Compared with the conventional waveguiding mode, the new guiding mode propagates along different directions depending on the vertical excitation position. Experimentally, we drill periodic holes in metal plates to sandwich an ideal Weyl meta-crystal and characterize the topological guiding mode. Our study shows the intriguing behaviors of topological photonic waveguides, which could lead to beam manipulation, position sensing, and even 3D information processing on photonic chips.