Valley photonic crystals and topological propagation of light

Within the framework of classical optics, high-efficiency light propagation is limited in integrated optoelectronics. An important objective is to realize high fidelity light propagation based on either a new optical principle or design. Topological photonics could fulfill this goal, and thus has attracted much attention in recent years and has been demonstrated in many different electromagnetic systems such as photonic crystals and metamaterials. In this paper we present a brief introduction to the recent development of topological photonics, and an overview of theoretical and experimental research on valley photonic crystals, including the proposal for electromagnetic-dual valley photonic crystals, the classification of valley photonic crystals, experimental observations at microwave wavelengths, and the realization of visible light propagation in silicon-on-insulator photonic crystal slabs. Finally, we take a look at topological photonics, especially the realm of topological nanophotonics.