A hybrid plasmonic waveguide for subwavelength confinement and long-range propagation

Abstract

The emerging field of nanophotonics1 addresses the critical challenge of manipulating light on scales much smaller than the wavelength. However, very few feasible practical approaches exist at present. Surface plasmon polaritons2,3 are among the most promising candidates for subwavelength optical confinement3,4,5,6,7,8,9,10. However, studies of long-range surface plasmon polaritons have only demonstrated optical confinement comparable to that of conventional dielectric waveguides, because of practical issues including optical losses and stringent fabrication demands3,11,12,13. Here, we propose a new approach that integrates dielectric waveguiding with plasmonics. The hybrid optical waveguide consists of a dielectric nanowire separated from a metal surface by a nanoscale dielectric gap. The coupling between the plasmonic and waveguide modes across the gap enables ‘capacitor-like’ energy storage that allows effective subwavelength transmission in non-metallic regions. In this way, surface plasmon polaritons can travel over large distances (40–150 µm) with strong mode confinement (ranging from λ2/400 to λ2/40). This approach is fully compatible with semiconductor fabrication techniques and could lead to truly nanoscale semiconductor-based plasmonics and photonics.

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Figure 1: The hybrid optical waveguide.
Figure 2: Propagation distance, mode area and field distributions of the hybrid mode.
Figure 3: Confinement in the dielectric gap region in the x and y directions.
Figure 4: The hybridization of the dielectric cylinder and SPP modes as modelled by coupled mode theory.
Figure 5: A plot of normalized mode area versus normalized propagation distance enables a comparison of various plasmonic waveguides.

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Acknowledgements

The authors thank G. Bartal for valuable discussions. This work was supported by the Air Force Office of Scientific Research (AFOSR), the Multidisciplinary University Research Initiative (MURI) (FA9550-04-1-0434) and the National Science Foundation (NSF) Nanoscale Science and Engineering Center (DMI-0327077).

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R.F.O. conceived of the original concept and carried out the calculations. All authors contributed equally in developing the concept and writing the manuscript.

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Correspondence to X. Zhang.

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Oulton, R., Sorger, V., Genov, D. et al. A hybrid plasmonic waveguide for subwavelength confinement and long-range propagation. Nature Photon 2, 496–500 (2008). https://doi.org/10.1038/nphoton.2008.131

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