APPLIED PHYSICS LETTERS, vol.97, no.2, 2010 (SCI-Expanded)
We study a plasmonic coupler involving backward (TM01) and forward (HE11) modes of dielectric waveguides embedded into an infinite metallic background. The simultaneously achievable contradirectional energy flows and codirectional phase velocities in different channels lead to a spectral gap, despite the absence of periodic structures along the waveguide. We demonstrate that a complete spectral gap can be achieved in a symmetric structure composed of four coupled waveguides. (C) 2010 American Institute of Physics. [doi:10.1063/1.3458694]