Experimental Realization of Self-Guiding Unidirectional Electromagnetic Edge States

We present an experimental demonstration of self-guiding electromagnetic edge states existing along the zigzag edge of a honeycomb magnetic photonic crystal. These edge states are shown to possess unidirectional propagation characteristics that are robust against various types of defects and obstacles. In particular, they allow for the unidirectional transport of electromagnetic energy without requiring an ancillary cladding layer.

Figure 1

(a) A schematic picture of the ferrite array sample inside the parallel plate waveguide. The waveguide is sandwiched between two metallic plates and surrounded by the absorber. To test the robustness of the wave propagation, defects in the form of a metal slab or a rod are added to the zigzag edge. (b) A closer look at the fabricated sample with the top plate removed.

Figure 2

The band structure of (a) the bulk MPC and (b) the MPC ribbon projected along the zigzag axis ($\Gamma -\mathrm{K}$). The light cone is shaded and the edge states are shown in red (dark gray) and green (light gray). (c) The unprocessed transmission data for the bulk MPC (data presented as is, without renormalization); (d) the unprocessed transmission data measured at the zigzag edge exposed to air. The transmissions denoted by the solid and dashed lines in panel (d) are obtained with opposite direction of the BMF.

Figure 3

The unprocessed transmission data measured when (a) an absorber, (b) a metal block is placed near the edge of the MPC, as illustrated in the inset.

Figure 4

The unprocessed transmission data measured with different types of disruptions on the zigzag edge. (a) Measured transmission and (b) simulated power flow when a ferrite rod on the edge is replaced by a metallic rod of the same size; (c) Measured transmission and (d) simulated power flow when a ferrite rod on the zigzag edge is removed; (e) Measured transmission and (f) simulated power flow when the first zigzag chain is blocked by a metallic slab; Panels (g) and (h) illustrate, respectively, measured transmission when two and three zigzag chains are blocked.