ABSTRACT Slow light has attracted considerable attention for its potential in optical communication, information storage and signal processing. However, simultaneously achieving a large slow light factor and a wide operational bandwidth remains challenging. In this paper, we propose a magnetically tunable slow light waveguide based on a separated topological insulator. Both the simulated and experimental results reveal the coupling between the two counter‐propagating topological edge states gives rise to a coupling dispersion curve in the bandgap. By modulating the coupling strength, the dispersion of the coupled modes can be modified rather flat, corresponding to slow‐light modes with a stopped wave point. In view of the dependence of topological edge states on ferrites’ magnetic plasmon polaritons, the slow‐light operating frequency is adjusted by the biased magnetic field. This offers a viable strategy to solve the inherent compromise between the slow‐light factor and bandwidth. Further‐more, a slow‐light rainbow waveguide with gradient biased magnetic field is proposed which permits Electro‐magnetic waves at different frequencies to stop at distinct spatial locations. Our work paves a promising avenue for exploiting of topological states in future applications.
Xu et al. (2026) studied this question.