Photonic Topological Valley-Locked Waveguides

Photonic topological valley kink states have become a significant research frontier with a plethora of applications. Unlike the guided modes with adjustable widths in conventional waveguides, the valley kink states are usually highly confined around the domain walls. They thus lack the mode width degree of freedom (DOF), posing a serious limitation to potential device applications. Here, by adding a photonic crystal (PhC) featuring Dirac points between two valley PhCs with opposite valley-Chern numbers, we design and experimentally demonstrate topological valley-locked waveguides (TVLWs) with tunable mode widths. The valley-locked waveguide modes are directly visualized via a near-field scan. Moreover, the photonic TVLWs have some unique applications, such as high-energy-capacity topological channel intersections, valley-locked energy concentrators, and topological cavities with designable confinement, as verified numerically and experimentally. The TVLWs with width DOF could be beneficial for interfacing with the existing photonic waveguides and devices, and may serve as a novel platform for practical use of topological lasing, field enhancement, and high-capacity energy transport.