Plasmonics: Metal nanostructures for subwavelength photonic devices

This paper reviews recent progress toward the creation of a nanophotonic framework for confining and guiding electromagnetic energy at visible and near-infrared frequencies using surface plasmon excitations sustained by metallic nanostructures. Prominent geometries such as metal/insulator/metal-gap waveguides are assessed in terms of light confinement and the energy attenuation of the guided modes, as well as metal-nanoparticle waveguides that guide light via near-field coupling of localized particle or gap plasmon modes for deep subwavelength confinement. The effective mode volume concept of dielectric optics is then applied to plasmonic nanoresonators, which allows a comparison with established dielectric microcavities and demonstrates the deep subwavelength confinement achievable in metallic nanocavities. Lastly, a solution to the coupling problem of surface plasmon-polariton modes to the outside world is presented in the form of a fiber-accessible metal-nanoparticle plasmon waveguide with experimentally demonstrated power transfer up to 75% at λ = 1.5 μm.