Topological surface states at the free space termination of uncorrugated finite square photonic crystals

We present a square-lattice photonic crystal that supports chiral topological photonic surface states at the interface to free space. Such unidirectional, back-scattering-immune surface states, as opposed to topological states at the interface between band-gap materials, allow to simplify the design of out-coupling from surface modes to functionalized radiated fields, removing the usual impedance ...