Abstract
A plasmonic waveguide is a promising candidate for nano-optical waveguides. First we review the
principles and unique characteristics of plasmonic waveguides and compare them to conventional
dielectric waveguides. Then, we demonstrate the propagation of a surface plasmon polariton along a
metal slab waveguide. A symmetric metal slab waveguide simultaneously supports two opposite types
of a surface plasmon mode similar to a metal film: short-range and long-range type modes. The strong
field confinement of the short-range mode plays a crucial role in nano-optical waveguides. To avoid the
trade-off between field confinement and propagation length, we demonstrate selective mode excitation
and mutual mode conversion for superfocusing mediated by the long-range mode.
