Tunable Electromagnetic Flow Control in Valley Photonic Crystal Waveguides

In photonic systems, exploring the valley degree of freedom (due to the presence of a local extremum in band structure in momentum space) is interesting for application of the photonic Hall effect, robust delay lines, and perfect outcoupling refraction. This work demonstrates that electromagnetic flow in a photonic-crystal waveguide can be tuned using this topological degree of freedom. Both tunable excitation of valley bulk states and tunable valley-dependent edge-state dispersion are shown. These results may impact the dynamic modulation of light in devices.