  On-chip optoelectronic and all-optical information processing paradigms
require compact implementation of signal transfer for which nanoscale surface
plasmons circuitry offers relevant solutions. This work demonstrates the
directional signal transmittance mediated by 2D plasmonic eigenmodes supported
by crystalline cavities. Channel devices comprising two mesoscopic triangular
input and output ports and sustaining delocalized, higher-order plasmon
resonances in the visible to infra-red range are shown to enable the
controllable transmittance between two confined entry and exit ports coupled
over a distance exceeding 2 $\mu$m. The transmittance is attenuated by > 20dB
upon rotating the incident linear polarization, thus offering a convenient
switching mechanism. The optimal transmittance for a given operating wavelength
depends on the geometrical design of the device that sets the spatial and
spectral characteristic of the supporting delocalized mode. Our approach is
highly versatile and opens the way to more complex information processing using
pure plasmonic or hybrid nanophotonic architectures.
