Non?diffraction-limited light transport by gold nanowires

We show that metal nanowires sustaining collective electron oscillations (surface plasmon polaritons) can be used as optical waveguides. Thereby, the use of a metal allows to overcome the limitations of miniaturization imposed on conventional dielectric waveguides due to diffraction. To demonstrate this effect we investigate a 200 nm wide and 50 nm high gold nanowire locally excited at a light wavelength of 800 nm. By direct imaging the optical near-field with subwavelength-resolution photon scanning tunneling microscopy we observe light transport along the nanowire over a distance of a few μm. Besides the realization of unprecedented integration densities of photonic devices, metal nanowires could be effectively used to optically address individual nanostructures or molecules.