Topological valley-locked waveguides with C₄ impurity

Heterostructures play a pivotal role in the design of valley-locked waveguides, facilitating the manipulation of width as an additional degree of freedom. Through this design, we demonstrate the extension of the topological guided modes from the domain wall of topologically nontrivial valley photonic crystals (VPCs) into the trivial VPCs. We propose a C₄ impurity to control the states of the light wave transmission in topological valley-locked waveguides through the intervalley scattering of defects in Quantum Valley Spin Hall topological insulators. By rotating the C₄ structure, the ON/OFF (0°/45°) state of the valley-locked waveguides can be controlled, effectively serving as a switch component. Furthermore, many unique applications could be devised based on the introduced impurity. Examples include the development of coding channels with arbitrary output ports and energy concentrators with enhanced secondary concentration. The proposed topological valley-locked waveguides with C₄ impurity will be beneficial for on-chip integrated photonic networks.