Topological photonics: Fundamental concepts, recent developments, and future directions

Observation of topological frequency combs

“…Concurrently, topological photonics has emerged as a powerful paradigm for the design of photonic devices with novel functionalities ( 17 – 22 ). More specifically, topological systems exhibit chiral or helical edge states that are confined to the boundary of the system and are exceptionally robust against imperfections common to integrated photonic devices ( 23 – 25 ).…”