  Experimental evidence of mode-selective evanescent power coupling at
telecommunication frequencies with efficiencies up to 75 % from a tapered
optical fiber to a carefully designed metal nanoparticle plasmon waveguide is
presented. The waveguide consists of a two-dimensional square lattice of
lithographically defined Au nanoparticles on an optically thin silicon
membrane. The dispersion and attenuation properties of the waveguide are
analyzed using the fiber taper. The high efficiency of power transfer into
these waveguides solves the coupling problem between conventional optics and
plasmonic devices and could lead to the development of highly efficient
plasmonic sensors and optical switches.
