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The constructive interference of surface plasmon polaritons (SPP) launched by nanometric holes allows us to focus SPP into a spot of high near-field intensity having subwavelength width. Near-field scanning optical microscopy is used to map the local SPP intensity. The resulting SPP patterns and their polarization dependence are accurately described in model calculations based on a dipolar model for the SPP emission at each hole. Furthermore, we show that the high SPP intensity in the focal spot can be launched and propagated on a Ag strip guide with a 250 x 50 nm2 cross section, thus overcoming the diffraction limit of conventional optics. The combination of focusing arrays and nano-waveguides may serve as a basic element in planar nano-photonic circuits.

The generation of surface plasmon polaritons (SPP's) at isolated nanoholes in 100 nm thick Au films is studied using near-field scanning optical microscopy (NSOM). Finitedifference time-domain calculations, some explicitly including a model of the NSOM tip, are used to interpret the results. We find the holes act as point-like sources of SPP's and demonstrate that the interference between the SPP and a directly transmitted wave allows for the determination of the wavelength, phase, and decay length of the SPP. The nearfield intensity patterns can be manipulated by varying the angle and polarization of the incident beam.