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Nanofocusing in laterally tapered plasmonic waveguides
Ewold Verhagen1, Albert Polman, L Kobus Kuipers
1Center for Nanophotonics, FOM-Institute for Atomic and Molecular Physics (AMOLF), Kruislaan 407, 1098 SJ Amsterdam, The Netherlands. verhagen@amolf.nl
Optics Express
|June 4, 2008
Summary
We demonstrate practical plasmonic nanofocusing using tapered gold waveguides. Exciting an asymmetric bound mode enables surface plasmon polaritons (SPPs) to concentrate without a cutoff width.
Area of Science:
- Plasmonics
- Nanophotonics
- Optics
Background:
- Surface plasmon polaritons (SPPs) are light-driven electron oscillations at metal-dielectric interfaces.
- Efficiently focusing SPPs is crucial for nanoscale optical applications.
Purpose of the Study:
- To investigate the nanofocusing of SPPs in a tapered gold waveguide on a planar substrate.
- To demonstrate a practical method for achieving plasmonic nanofocusing.
Main Methods:
- Experimental excitation of SPPs using 1.5 micrometer light.
- Numerical simulations of SPP propagation and concentration in tapered waveguides.
- Analysis of different excitation modes on the metal film.
Main Results:
- Nanofocusing of SPPs was achieved by exciting an asymmetric bound mode at the substrate side.
- SPPs propagated and concentrated to the waveguide tip without a cutoff width.
- Focusing was not observed when exciting the mode at the low-index side of the film.
Conclusions:
- The asymmetric bound mode is key for achieving plasmonic nanofocusing in this planar geometry.
- This approach offers a practical implementation of nanofocusing on a planar substrate.
- The observed mode resembles that used in conical waveguides for focusing.
