  Propagating two-dimensional plasmon modes guided along silver nanoridge
waveguides with triangular and inverted triangular cross sections are
investigated in this paper. Mode field profiles, dispersion curves, propagation
distances, and figure-of-merits of the plasmon ridge modes are calculated for
silver nanoridge waveguides with various triangular and inverted triangular
waveguide cross sections. It is found that the triangular cross section
nanoridge waveguide, if designed properly, can have longer propagation distance
and higher figure-of-merit than the flat-top nanoridge waveguide of the same
width. When the triangle height of the nanoridge is high, the mode approaches
to the small angle wedge mode. An inverted triangular cross section nanoridge
mode can be considered as a hybrid mode of two metal wedge plasmon modes. When
inverted triangle depth increases, the propagation distance and the
figure-of-merit decrease dramatically, suggesting the poorer performance when
compared to the flat-top nanoridge plasmon waveguide.
