Phase-Engineering Strategy for Multidimensional Light Steering in a Photonic Higher-Order Topological Insulator

Higher-order topological (HOT) insulators have been extensively studied for their unique multidimensional boundary states such as hinge states and corner states. However, most of the recent studies are limited to static excitation of topological boundary states, restricting the development of their practical devices that possess the capability of diverse and programmable dynamic control of states. Here, a facile approach to achieve flexible control of light-steering based on the symmetrized wave profiles of topological corner states is introduced. Specifically, multiple coherent sources are imported at symmetrical positions in higher-order topological photonic crystals. By engineering phase differences among the sources, a controllable spatial-resolved excitation of topological corner states is realized and a coding technique via controllable excitation of topological corner states is raised conceptually. Furthermore, an effective way to achieve direction-selective excitation of topological edge states without the requirement of circularly polarized sources is proposed. The result provides a reliable active technique to modulate HOT boundary states while keeping the photonic structure invariable, which might be a practical alternative to manipulate light flexibly in integrated topological photonic devices with fixed configuration.