Valley kink states and valley-polarized chiral edge states in substrate-integrated topological photonic crystals

Valley kink states and valley-polarized chiral edge states, whose topologically protected properties have great application potential in high-speed information processing and communication, have recently become important frontiers in topological photonics. However, valley photonic topological insulators mainly support single-type topological states through breaking lattice spatial symmetry. It remains difficult for different types of topological states to coexist in a specific photonic system. In this paper, we propose judiciously designed substrate-integrated topological photonic crystals (but without metal vias) with C₃ symmetry that can support valley kink states and valley-polarized chiral edge states in different waveguide channels. Via numerical simulations and measurements, we demonstrate the robust transmission of both valley kink states and valley-polarized chiral edge states through sharp corners and we show high-efficiency coupling between classical guided waves and topological waves. More importantly, we achieve smooth transitions between chiral and trivial edge states, trivial edge states and valley kink states, as well as valley kink states and valley-polarized chiral edge states by bridging different waveguide channels. Our proposed design is beneficial for interfacing with existing functional photonic waveguides or devices and opens up an alternative pathway for advanced planar integrated topological photonic systems with subwavelength thicknesses.