Numerical realization of tunable triple-band slow wave and bidirectional rainbow trapping in magneto-optical heterostructures

Flexible energy storage and retrieval have long garnered significant attention as key research directions in modern science and technology. In recent decades, the realization of slow light/wave propagation and rainbow trapping/releasing using novel materials or mechanisms-such as metamaterials and metasurfaces-has emerged as a major research focus. However, existing slow-wave and rainbow-trapping structures-including those based on photonic crystals-suffer from key limitations: (1) structural complexity, (2) limited tunability, and (3) confinement to a single slow-wave band. Here, we propose, for what we believe is the first time, a bidirectional rainbow trapping and releasing (RTR) mechanism supported by three distinct and tunable slow-wave bands in magneto-optical heterostructures. By precisely tuning external magnetic fields or material parameters, we achieve dynamic control over slow-wave peaks, enabling tunable RTR band engineering. Furthermore, under a constant external magnetic field, we design a tapered magneto-optical heterostructure that serves as a high-sensitivity sensor for detecting the relative permittivity of dielectric media. The proposed tunable structure, featuring three slow-wave peak dispersions for bidirectional rainbow manipulation, along with the dielectric sensing platform, demonstrates strong potential for applications in physical/biological detection, high-efficiency optical communication, and advanced energy storage.