Rainbow Trapping on Plasmonic Surface Gratings and Beyond

On-chip rainbow trapping enables precise light manipulation for slow light, photonics trapping, absorption, and sensing in advanced photonic devices. Although metallic graded grating nanostructures facilitate efficient rainbow trapping, broadband plasmonic trapping remains challenging. Over the past decades, metamaterials, microstructures, and nanostructures have been extensively studied and surface-trapped rainbows have been incorporated in novel applications. This review examines the key achievements, challenges, and practical applications of rainbow trapping, focusing on broadband light control through plasmonic surface gratings. We discuss the fundamental mechanisms of rainbow trapping through simulations and experimental demonstrations across various geometries, especially those of graded gratings. In addition, we explore advanced fabrication techniques and emerging applications of rainbow trapping in optical sensing, communication, and light absorption, highlighting new possibilities for multi-spectrum and broadband light manipulation. Finally, we highlight the challenges and future perspectives of this emerging technology.