Plasmon Waveguides

Abstract

Having described the basics of surface plasmon polaritons in chapter 2, we continue the discussion by providing a number of examples of control over their propagation in the context of waveguiding. Here, the trade-off between confinement and loss demands a judicious choice of geometry, depending on the length scale over which energy is to be transferred. For example, thin metallic slabs embedded in a homogeneous dielectric medium can guide SPPs over distances of many centimeters at near-infrared frequencies, but the associ- ated fields are only weakly confined in the perpendicular direction. In the other extreme, metal nanowire or nanoparticle waveguides exhibit a transverse mode confinement below the diffraction limit in the surrounding host, but with large attenuation losses, leading to propagation lengths on the order of micrometers or below. Routing of SPPs on planar interfaces can be achieved by locally modifying their dispersion via surface modulations, which will be described in the first two sections of this chapter. We then focus on studies of lateral confinement in metal stripe and wire waveguides, including focusing of SPPs in conical structures. The inverse structure to metal stripes, namely metal/insulator/metal heterostructures, also show high promise for waveguiding with good confine- ment and acceptable propagation length, especially in V-groove geometries. Towards the end of this chapter, we show that localized plasmon excitations in metal nanoparticles can also be used as waveguiding modalities, since en- ergy is transferred via near-field coupling between adjacent particles in linear chains. The chapter closes with a description of emerging efforts to combat attenuation via optical gain media as waveguide hosts.