American Institute of Physics, Applied Physics Letters, 2(97), p. 021106
DOI: 10.1063/1.3458694
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We study a plasmonic coupler involving backward ( TM 01) and forward ( HE 11) 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.