Infrared rainbow trapping via optical Tamm modes in an one-dimensional dielectric chirped photonic crystals.

Abstract

The phenomenon of trapping a broad spectrum of light is known as "rainbow trapping" and is achieved by using all-dielectric, hybrid metallo-dielectric, or all-metallic configurations. The latter architectures allow strong confinement but exhibit very high ohmic losses. This results in practical lifetimes of trapped modes to less than 1 ps. Therefore, novel strategies are required to be devised for trapping and, subsequently, releasing broadband electromagnetic field with lifetime >1ps. We present a rainbow trapping configuration using the excitation of multiple optical Tamm (OT) modes in an one-dimensional chirped photonic crystal (CPC) designed for adiabatically coupling counterpropagating modes. In the geometry, the backscattered phase undergoes multiple discontinuities (=π), which enables excitation of many OT modes in the presence of a thin plasmon-active metal, which is placed adjacent to the terminating layer of CPC. All the OT modes are spatially separated in the CPC, and the strong modal confinement manifests into group velocities as low as 0.17c. The time-domain simulations depict mode-localization in the dielectric sections of CPC, which manifest into lifetimes ∼3ps.