Plasmonic waveguides, which support surface plasmon polaritons (SPP)
propagating along metal-dielectric interfaces, offer strong field confinement and
are ideal for the design of integrated nano-scale photonic devices. However, due
to free-carrier absorption in the metal, the enhanced mode confinement inevitably
entails an increase in the waveguide loss. This lowers the device figure-of-merit
achievable with passive plasmonic components and in turn hinders the
performance of active plasmonic components such as optical modulators.