Silicon-based metal-loaded plasmonic waveguides for low-loss nanofocusing

We introduce plasmonic waveguides based on metal loading of silicon-on-insulator (SOI) substrates. Here slab waveguide modes hybridize with the plasmonic modes of either a metal nanowire or a slot in a metal film. By tapering a single dimension of either structure, the resulting hybrid mode can be converted from photon-like to plasmon-like, allowing up to millimeter-range transport and rapid nanoscale focusing down to mode areas ∼λ²/400. Metal loading is achievable with a single lithography step directly on SOI without the need for etching and, thus, opens practical possibilities for silicon nanoplasmonics.