Topological Valley Transport of Terahertz Phonon–Polaritons in a LiNbO3 Chip

Topological photonics has thrived in various optical systems over the past decade for the fascinating properties of eliminating backscattering losses and enhancing the efficiency of communication systems. The demonstration of topology in strong light–matter coupling regimes may prove tunable optical devices that are immune to disorder and defects or achieve the extreme light confinement. Recently, the topological properties of exciton–polaritons were experimentally studied in deep cryogenic temperatures. As for another elementary quasiparticle in solids, phonon–polaritons, which can remain stable at a high temperature, the relative topological dispersion contours have been observed very recently at room temperatures. Here, we experimentally presented a topological valley transport of terahertz phonon–polaritons in LiNbO3 photonic crystal slab. Topological waveguides with two peculiar interfaces are designed and studied, where the phonon–polaritons are generated through femtosecond laser pulses. We show the intensity distribution and dispersion curves of phonon–polaritons propagating in the topological waveguides at different bended interfaces, in which the topological edge modes make smooth detours. Our work opened a new path toward topological polaritonics at a valley-edge-mode based phonon–polariton platform, which also provides insights to the low loss phonon–polariton chips, strong light–matter interactions, nonlinear topological photonics, and future THz communications.