We have measured the propagation distances of wedge plasmons and two-dimensionally localized gap plasmons (GPW)
at a vacuum wavelength of 632.8nm. The measured propagation distances of the wedge plasmons increased from
2.2μm to 3.1μm with increasing the wedge tip radius from 20nm to 125nm. The GPW has the measured propagation
distance of 8.2μm for a gap width of 100nm and 900nm height.
We have developed a finite-difference time-domain (FDTD) method represented by the spherical coordinates which is
applicable for numerical calculations of nonlinear optical responses. This FDTD technique gives information about
time-dependent spatial distributions of light intensity in nonlinear metallic particles and we can deeply understand
nonlinear optical phenomena related with localized surface plasmons in a spherical particle.
We have numerically investigated characteristics of plasmonic waveguides for coupled wedge plasmons (CWPs)
consisting two silver wedges separated by a nano gap all on a glass substrate. Three types of waveguides for CWPs on
a glass substrate are considered: (1) two metallic wedges on a planar substrate, (2) two metallic wedges built into the
substrate and (3) two-folded free-standing metallic wedges. For numerical calculation, we have employed the Drude
model for the dielectric constant of silver and the excitation light with the vacuum wavelength of 632.8 nm. The
refractive index of the glass n<sub>s</sub> is fixed at n<sub>s</sub> = 1.5. We have calculated field distributions in the waveguide as well as
dependence on changing the gap w between wedges and the wedge angle θ. CWPs eigenmodes of such structures are
shown to exist and propagate along waveguides structures employed here. The propagation constant k<sub>//</sub>, propagation
distance L and the beam area of a CWP depends on w and θ. L and the beam area size for waveguide employed here are
in the order of 10 μm and in the range from 10<sup>-4</sup> μm<sup>2</sup> to 10<sup>-1</sup> μm<sup>2</sup>, respectively. These values mean that waveguides for
CWPs have a potential to be utilized for the nano optical waveguides in future.