Letter | Published:

High-Q surface-plasmon-polariton whispering-gallery microcavity

Nature volume 457, pages 455458 (22 January 2009) | Download Citation

Abstract

Surface plasmon polaritons (SPPs) are electron density waves excited at the interfaces between metals and dielectric materials1. Owing to their highly localized electromagnetic fields, they may be used for the transport and manipulation of photons on subwavelength scales2,3,4,5,6,7,8,9. In particular, plasmonic resonant cavities represent an application that could exploit this field compression to create ultrasmall-mode-volume devices. A key figure of merit in this regard is the ratio of cavity quality factor, Q (related to the dissipation rate of photons confined to the cavity), to cavity mode volume, V (refs 10, 11). However, plasmonic cavity Q factors have so far been limited to values less than 100 both for visible and near-infrared wavelengths12,13,14,15,16. Significantly, such values are far below the theoretically achievable Q factors for plasmonic resonant structures. Here we demonstrate a high-Q SPP whispering-gallery microcavity that is made by coating the surface of a high-Q silica microresonator with a thin layer of a noble metal. Using this structure, Q factors of 1,376 ± 65 can be achieved in the near infrared for surface-plasmonic whispering-gallery modes at room temperature. This nearly ideal value, which is close to the theoretical metal-loss-limited Q factor, is attributed to the suppression and minimization of radiation and scattering losses that are made possible by the geometrical structure and the fabrication method. The SPP eigenmodes, as well as the dielectric eigenmodes, are confined within the whispering-gallery microcavity and accessed evanescently using a single strand of low-loss, tapered optical waveguide17,18. This coupling scheme provides a convenient way of selectively exciting and probing confined SPP eigenmodes. Up to 49.7 per cent of input power is coupled by phase-matching control between the microcavity SPP and the tapered fibre eigenmodes.

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Acknowledgements

We thank R. F. Oulton and G. Bartal for discussions and S. Zhang for a critical reading of the manuscript. This work was supported by the US Air Force Office of Scientific Research MURI program (grant no. FA9550-04-1-0434) and by the NSF Nanoscale Science and Engineering Center under award no. DMI-0327077.

Author information

Author notes

    • Bumki Min
    •  & Lan Yang

    Present addresses: Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-751, Republic of Korea (B.M.); Department of Electrical and Systems Engineering, Washington University in St Louis, St Louis, Missouri 63130, USA (L.Y.).

Affiliations

  1. Thomas J. Watson Laboratory of Applied Physics, California Institute of Technology, Pasadena, California 91125, USA

    • Bumki Min
    • , Eric Ostby
    • , Lan Yang
    •  & Kerry Vahala
  2. Nanoscale Science and Engineering Center, 5130 Etcheverry Hall, University of California, Berkeley, California 94720, USA

    • Bumki Min
    • , Volker Sorger
    • , Erick Ulin-Avila
    •  & Xiang Zhang
  3. Material Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    • Xiang Zhang

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Corresponding authors

Correspondence to Xiang Zhang or Kerry Vahala.

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    Supplementary Information

    This file contains a Supplementary Discussion and Notes, Supplementary Figures S1-S5 with Legends and Supplementary References

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https://doi.org/10.1038/nature07627

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