  Propagating two-dimensional plasmon modes guided by elliptical cross section
silver nanoridges are investigated in this paper. Mode field profiles,
dispersion curves, propagation distances, and figure-of-merits of the plasmon
ridge modes are calculated for various elliptical cross sections. It is found
that an elliptical cross section metal nanoridge, if designed properly, can
support a well-confined plasmon mode with a longer propagation distance and a
higher figure-of-merit than the flat-top nanoridge plasmon waveguide of the
same width. The optimal ridge waveguide cross section is obtained when the
elliptical ridge top has a semicircular cross section. When the curvature of
the elliptical nanoridge is large, the mode approaches the tightly confined
wedge plasmon mode.
