Topological Line Defect Waveguide

Photonic crystal line-defect waveguides featuring bandgap confined low loss waveguiding are hindered by high bending losses. Although vortex-mediated topological modes can facilitate seamless propagation through sharp bends, studies of topological transport have primarily focused on interfacial waveguides. In this work, we unveil the prevalence of topological modes across diverse photonic crystal platforms by experimentally demonstrating topological transport in line-defect waveguides. Furthermore, this is achieved by employing interfacial waveguides as mode convertors to selectively excite latent topological states. Topological mode signatures, such as counterpropagating waves, are utilized to establish the existence of topological transport in line-defect waveguides designed using translational unit cells whose electromagnetic eigenstates exhibit phase vortices and non-zero Berry curvatures. It is envisioned that extending topological photonics beyond interfacial systems unlocks new avenues in applications ranging from non-Hermitian topological photonics to topological light-matter interactions.