  A novel nanometeric plasmonic filter in a tooth-shaped Metal-Insulator-Metal
waveguide is proposed and demonstrated numerically. An analytic model based on
the scattering matrix method is given. The result reveals that the single
tooth-shaped filter has a wavelength filtering characteristic and an
ultra-compact size in the length of a few hundred nanometers, compared to
grating-like SPPs filters. Both analytic and simulation results show that the
wavelength of the trough of the transmission has linear and nonlinear
relationships with the tooth depth and the tooth width, respectively. The
waveguide filter could be utilized to develop ultra-compact photonic filters
for high integration.
