Valley photonic crystals

Topological photonics is an emerging field that attracts enormous interest for its novel ways to engineer the flow of light. With the help of topological protection, the surface modes of topological photonic systems have intriguing properties, such as the unidirectional propagation, robust transmission against defects and disorders, which meet the rapidly growing demands for information processing. Valley photonic crystals, as one kind of topological photonic systems, not only support protected surface modes, but also are friendly to micro-nano fabrication. These advantages show that it has broad prospects in constructing high-performance photonic devices or even photonic integrated circuits. Here, we review the properties and development of valley photonic crystals. Firstly, the theory and structure are briefly introduced and then the discussion of robust transmission will be followed. Furthermore, prototypes of on-chip devices based on valley photonic crystals are reviewed. As a perspective in photonics, valley photonic crystal is expected to become a good platform to study nanophotonics and realize advancing integrated photonics devices.