Tunable Slow Light in Valley-Locked Topological Photonic Crystal Waveguide

This study introduces a topological photonic slow-light waveguide based on a honeycomb unit cell, which allows for the convenient tuning of the group index and bandwidth through the valley-locked effect. The topological properties of the unit cell are initially assessed. By adjusting the air gap in the topologically protected photonic crystal (PhC) waveguide, it is possible to continuously vary the group index from 47 to 6 and the normalized group index–bandwidth product (NGBP) from 0.495 to 0.573. Furthermore, the chiral propagation characteristics and propagation loss of the topologically protected PhC waveguide are evaluated. The findings indicate that the structure supports chiral propagation and maintains a high transmission rate even after passing through sharp corners. The results contribute to a deeper understanding of topological photonics and suggest potential for applications in future photonic technologies, such as dynamic topological photonic retarders and nonlinear localization enhancers.