  In this paper, we theoretically and numerically demonstrate a two-dimensional
Metal-Dielectric-Metal (MDM) waveguide based on finite-difference time-domain
simulation of the propagation characteristics of surface plasmon polaritons
(SPPs). For practical applications, we propose a plasmonic Y-branch waveguide
based on MDM structure for high integration. The simulation results show that
the Y-branch waveguide proposed here makes optical splitter with large
branching angle (~180 degree) come true. We also introduce a finite array of
periodic tooth structure on one surface of the MDM waveguide which is in a
similar way as FBGs or Bragg reflectors, potentially as filters for WDM
applications. Our results show that the novel structure not only can realize
filtering function of wavelength with a high transmittance over 92%, but also
with an ultra-compact size in the length of a few hundred nanometers, in
comparison with other grating-like SPPs filters. The MDM waveguide splitters
and filters could be utilized to achieve ultra-compact photonic filtering
devices for high integration in SPPs-based flat metallic surfaces.
