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Valley photonics, with its rapid advancements and immense potential, lays one pivotal cornerstone toward next-generation topological photonic devices. It enables valley-polarized topological states, whose valleys are intrinsically locked up with transmission directivity. However, these states are prone to defects in photonic structures, and backscattering may easily induce valley flipping. Hence, achieving a one-way valley-robust photonic crystal, immune to perturbations, remains elusive. Here, we demonstrate a one-way, valley-polarized state in an edge-tailored photonic crystal that is robust against defects. Such crystal possesses a Chern band gap and is achieved without using an interface between two crystals with opposite Berry curvatures. We show K-valley-robust transport in a defective crystal and demonstrate perfect conversion between the K and K^' valleys in a hybridized crystal while backscattering is greatly suppressed. Our results offer a promising approach for unidirectional control of the valley degrees of freedom in light.
Chen et al. (Thu,) studied this question.