Thresholdless nanoscale coaxial lasers

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The effects of cavity quantum electrodynamics (QED), caused by the interaction of matter and the electromagnetic field in subwavelength resonant structures, have been the subject of intense research in recent years1. The generation of coherent radiation by subwavelength resonant structures has attracted considerable interest, not only as a means of exploring the QED effects that emerge at small volume, but also for its potential in applications ranging from on-chip optical communication to ultrahigh-resolution and high-throughput imaging, sensing and spectroscopy. One such strand of research is aimed at developing the ‘ultimate’ nanolaser: a scalable, low-threshold, efficient source of radiation that operates at room temperature and occupies a small volume on a chip2. Different resonators have been proposed for the realization of such a nanolaser—microdisk3 and photonic bandgap4 resonators, and, more recently, metallic5, 6, metallo-dielectric7, 8, 9, 10 and plasmonic11, 12 resonators. But progress towards realizing the ultimate nanolaser has been hindered by the lack of a systematic approach to scaling down the size of the laser cavity without significantly increasing the threshold power required for lasing. Here we describe a family of coaxial nanostructured cavities that potentially solve the resonator scalability challenge by means of their geometry and metal composition. Using these coaxial nanocavities, we demonstrate the smallest room-temperature, continuous-wave telecommunications-frequency laser to date. In addition, by further modifying the design of these coaxial nanocavities, we achieve thresholdless lasing with a broadband gain medium. In addition to enabling laser applications, these nanoscale resonators should provide a powerful platform for the development of other QED devices and metamaterials in which atom–field interactions generate new functionalities13, 14.

At a glance


  1. Nanoscale coaxial laser cavity.
    Figure 1: Nanoscale coaxial laser cavity.

    a, Diagram of a coaxial laser cavity; the gain medium is shown in red. See main text for description of nomenclature. b, c, Scanning electron microscope images of the constituent rings in structure A and structure B, respectively. A side view of the rings comprising the coaxial structures is seen; the rings consist of SiO2 on top, and a quantum-well gain region underneath. See main text for details.

  2. Simulation of the electromagnetic properties of nanoscale coaxial cavities.
    Figure 2: Simulation of the electromagnetic properties of nanoscale coaxial cavities.

    a, The modal spectrum of the cavity of structure A at a temperature of 4.5K. b, As a but for structure B. Q, quality factor; Γ, factor giving extent of energy confinement to the semiconductor region30; Vmode, the effective modal volume30. The colour bar shows normalized |E|2, where E is the electric field intensity. Nominal permittivity values are used in this simulation. (See Supplementary Information parts 2 and 3 for nominal permittivities and the deviation of the permittivities from the nominal values, respectively.)

  3. Optical characterization of nanoscale coaxial cavities of structure A at 4.5[thinsp]K and room temperature, showing lasing.
    Figure 3: Optical characterization of nanoscale coaxial cavities of structure A at 4.5K and room temperature, showing lasing.

    ac, At 4.5K; df, at room temperature. Shown are light–light curves (a, d), spectral evolution diagrams for lasers with threshold (b, e), and linewidth versus pump power (c, f). The pump power is calculated as the fraction of the power incident on the laser aperture. The solid curves in a and d are the best fit of the rate-equation model. The solid lines in c and f show the inverse power narrowing rate of the linewidth. The resolution of the monochromator was set to 3.3nm.

  4. Optical characterization of nanoscale coaxial cavities of structure B at 4.5[thinsp]K, showing thresholdless lasing.
    Figure 4: Optical characterization of nanoscale coaxial cavities of structure B at 4.5K, showing thresholdless lasing.

    a, Light–light curve; b, spectral evolution; and c, linewidth evolution. The pump power is calculated as in Fig. 3; the solid curve in a is the best fit of the rate-equation model. The resolution of the monochromator was set to 1.6 nm.


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Author information

  1. These authors contributed equally to this work.

    • A. Simic &
    • M. Katz


  1. Department of Electrical and Computer Engineering, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093-0407, USA

    • M. Khajavikhan,
    • A. Simic,
    • M. Katz,
    • J. H. Lee,
    • B. Slutsky,
    • A. Mizrahi,
    • V. Lomakin &
    • Y. Fainman
  2. Present address: Oracle Labs, 9515 Town Centre Drive, San Diego, California 92121, USA.

    • J. H. Lee


M. Khajavikhan conceived the idea of thresholdless laser using nanoscale coaxial structures. The electromagnetic design, simulation, and analysis of the structures were carried out by M. Khajavikhan, A.M. and V.L. Fabrication of the devices was carried out by M. Khajavikhan and J.H.L. The optical measurements were performed by A.S. and M. Khajavikhan. The rate equation model was developed by M. Katz. The optical characterization and analysis of laser behaviour was carried out by M. Khajavikhan, M. Katz, A.M., B.S. and Y.F. The manuscript was written by M. Khajavikhan, with contributions from A.M., M. Katz, Y.F., A.S., B.S. and V.L.

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  1. Supplementary Information (1.5M)

    This file contains Supplementary Text and Data, Supplementary Figures 1-14 with legends and additional references.

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