Topological insulators constitute a new phase of matters insulating in bulk but conducting at edge or interface . Withtopological protection, the edge states are robust against disorders and defects. This concept was first proposed for electronicsystems and has recently been applied to photonic systems, including photonic quantum anomalous Hall effect and quantumspin Hall effect . The photonic topological insulators provide ideal platforms for photonic applications, which alwaysrequire defect-tolerant properties to reduce losses. However, most photonic topological states work in the microwave frequencyband, and require external magnetic field, which hinder their usages in applications.
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