  We experimentally demonstrate plasmonic nano-circuits operating as
sub-diffraction directional couplers optically excited with high efficiency
from free-space using optical Yagi-Uda style antennas at \lambda = 1550 nm. The
optical Yagi-Uda style antennas are designed to feed channel plasmon waveguides
with high efficiency (45 % in coupling, 60 % total emission), narrow angular
directivity (< 40{\deg}) and low insertion loss. SPP gap waveguides exhibit
propagation lengths as large as 34 {\mu}m with adiabatically tuned confinement,
and are integrated with ultra-compact (5 \mu m x 10 \mu m), highly dispersive
directional couplers, which enable 30 dB discrimination over {\Delta}{\lambda}
= 200 nm with only 0.3 dB device loss.
