Article

Nanofocusing in laterally tapered plasmonic waveguides.

Center for Nanophotonics, FOM-Institute for Atomic and Molecular Physics (AMOLF), Kruislaan 407, 1098 SJ Amsterdam, The Netherlands.
Optics Express (Impact Factor: 3.53). 01/2008; 16(1):45-57. DOI: 10.1364/OE.16.000045
Source: PubMed

ABSTRACT We investigate the focusing of surface plasmon polaritons (SPPs) excited with 1.5 microm light in a tapered Au waveguide on a planar dielectric substrate by experiments and simulations. We find that nanofocusing can be obtained when the asymmetric bound mode at the substrate side of the metal film is excited. The propagation and concentration of this mode to the tip is demonstrated. No sign of a cutoff waveguide width is observed as the SPPs propagate along the tapered waveguide. Simulations show that such concentrating behavior is not possible for excitation of the mode at the low-index side of the film. The mode that enables the focusing exhibits a strong resemblance to the asymmetric mode responsible for focusing in conical waveguides. This work demonstrates a practical implementation of plasmonic nanofocusing on a planar substrate.

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