Coupling between metallic structure and phonon polaritons for sensing applications

Abstract

The field of nanophotonics consists of interesting phenomena such as polaritons; quasi-particles that arise from lightmatter coupling. Some of the well-studied kinds of polaritons include surface plasmon polaritons (SPPs) and surface phonon polaritons (SPhPs). Surface enhanced infrared absorption (SEIRA) technique is a popular application of SPPs where the limitation of low molecular absorption cross section in IR-spectroscopy can be overcome by the introduction of SPPs in this technique. Especially in sensing applications, resonant SEIRA uses resonant metal nanoantennas in order to increase the EM near-fields on the nanometer scale, increasing light-matter interaction and thus amplifying the measured signature of very small particles. Mode coupling between metallic resonant structures and phonon polaritons supported by polar dielectric materials (e.g., h-BN, AlN, and SiC) in the IR regime with resulting field enhancement and transparency windows exhibiting Fano-like line shape will be presented. Finite element analysis is implemented to characterize the individual modes, validated against theory, in order to identify and fully characterize the resulting coupled modes in the integrated structure. Coupled-mode theory analysis reveals the anti-crossing modal coupling behavior via extinction cross-section.