  Metamaterials, which are materials engineered to possess novel optical
properties, have been increasingly studied. The ability to fabricate
metamaterials has sparked an interest in determining possible applications. We
investigate using a metamaterial for boundary engineering in waveguides.
  A metamaterial-clad cylindrical waveguide is used to provide confinement for
an optical signal, thereby increasing the local electromagnetic energy density.
We show that metamaterial-clad waveguides have unique optical properties,
including new modes, which we call hybrid modes. These modes have properties of
both ordinary guided modes and surface plasmon-polariton modes.
  We show that for certain metamaterial parameters, the surface
plasmon-polariton modes of a metamaterial-clad waveguide have less propagation
loss than those of a metal-clad guide with the same permittivity. This low-loss
mode is exploited for all-optical control of weak fields. Embedding three-level
{\Lambda} atoms in the dielectric core of a metamaterial-clad waveguide allows
the use of electromagnetically induced transparency to control an optical
signal. Adjusting the pump field alters the group velocity of the signal,
thereby controllably delaying pulses.
  Using the low-loss surface mode of a metamaterial-clad guide reduces losses
by 20% over a metal cladding without sacrificing the group velocity reduction
or confinement. In addition, we show that losses can be reduced by as much as
40% with sufficient reduction of the magnetic damping constant of the
metamaterial.
  As this work aims for applications, practical considerations for fabricating
and testing metamaterial-clad waveguides are discussed. An overview of the
benefits and drawbacks for two different dielectric core materials is given.
Also, a short discussion of other modes that could be used is given.
