Robust broadband large-area photonic waveguides based on topological states

Recent advancements in topological insulators have opened new possibilities for efficient and robust waveguides. The physical width and operating bandwidth are crucial factors for the performance of topological waveguides. While most topological waveguides are confined to narrow regions around the interface, existing large-area waveguides, although offering adjustable physical widths, typically face the challenge of decreasing operating bandwidths as the mode width increases. In this study, we propose a photonic topological heterostructure that creates multiple domain walls supporting topological edge states by alternately arranging unit cells with different topological properties. This design enables broadband, large-area topological waveguides based on the pseudospin Hall effect, overcoming the limitations of narrow operating bandwidths typically observed in large-area topological waveguides. We investigate the influence of waveguide coupling on the photonic band structure and reveal the relationship between the waveguide's physical width and its operating bandwidth. Electromagnetic simulations show that the large-area waveguides in the proposed heterostructure exhibit broad operating bandwidths and excellent robustness, effectively resisting various structural defects. Sensitivity analysis further demonstrates that the heterostructure is not dependent on specific parameter optimizations, indicating its inherent versatility. This work expands design concepts for large-area topological waveguides and provides avenues for developing multifunctional, stable, and flexible topological devices.