We report the experimental realization of a robust silicon-based plasmonic waveguide structure which can theoretically provide sub-wavelength confinement for E-x- and E-y-polarized surface plasmon polariton modes. Our waveguides exhibit propagation loss as low as 0.2 dB/mu m with similar to 50% coupling efficiency. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4739523]