Rainbows at the End of Subwavelength Discontinuities: Plasmonic Light Trapping for Sensing Applications

This article presents recent advances in plasmonic multiwavelength rainbow light trapping, a field that has evolved over the last decade and today is an active area of research interest encompassing a manifold of potential applications which include optical biosensing, photodetection, spectroscopy, and medicine. Conventional plasmonic devices are designed and optimized to enhance optical performance at single wavelengths, and as such are not suitable for applications that require electromagnetic field localization at multiple frequencies or broad frequency ranges of interest. To overcome these limitations, the ability to slow and trap light at multiple wavelengths and at different spatial locations has attracted significant scientific attention and opened up new research endeavors. Herein, fundamental principles of plasmonic light localization are presented, recent advances using breakthrough metamaterials are discussed—as well as major achievements and diverse device configurations used in the design and fabrication of plasmonic multiwavelength light trapping platforms with an emphasis on sensing applications. A presentation of salient works in this field is encapsulated, including the earliest invention of the concept of trapped rainbow, current trends, future directions, and emergent allied themes. This review also scrutinizes key developments and technical challenges vis-à-vis the physics of electromagnetic spectral localization and device fabrication which together provides insights and will inspire scientists and engineers to innovate and further develop the field.