Abstract

Earth-like planets, dark energy and variability of fundamental physical constants can be discovered by observing wavelength shifts in the optical spectra of astronomical objects1,2,3,4,5. These wavelength shifts are so tiny that exquisitely accurate and precise wavelength calibration of astronomical spectrometers is required. Laser frequency combs, broadband spectra of laser lines with absolutely known optical frequencies, are uniquely suited for this purpose6,7,8,9,10,11,12,13, provided their lines are resolved by the spectrometer. Generating such astronomical laser frequency combs (‘astrocombs’) remains challenging. Here, a microphotonic astrocomb is demonstrated via temporal dissipative Kerr solitons14,15,16 in photonic-chip-based silicon nitride microresonators17, directly providing a spurious-free spectrum of resolvable calibration lines. Sub-harmonically driven by temporally structured light18, the astrocomb is stabilized to a frequency standard, resulting in absolute calibration with a precision of 25 cm s–1 (radial velocity equivalent), relevant for Earth-like planet detection and cosmological research. The microphotonic technology can be extended in spectral span17,19,20,21,22,23,24, further boosting the calibration precision.

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The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

This work was supported by the Swiss National Science Foundation (grant nos. 166108, 16864, 165933), the NCCR-PlanetS and NCCR-PlanetS Technology Platform, the NCCR-QSIT (51NF40-160591), the Canton of Neuchatel and the INAF Progetto Premiale WOW. T.J.K. acknowledges additional support by the Air Force Office of Scientific Research, Air Force Material Command, USAF under award no. FA9550-15-1-0099, and the Defense Advanced Research Projects Agency (DARPA), Defense Sciences Office (DSO) under contract no. HR0011-15-C-0055. All samples were fabricated in the Center for Micro-Nanotechnology CMI at EPFL. D. F. Phillips and the Havard-Smithsonian Center for Astrophysics’ astrocomb team are acknowledged for providing the GPS-disciplined atomic clock.

Author information

Author notes

    • Monica Rainer

    Present address: National Institute of Astrophysics (INAF), Arcetri Astrophysical Observatory, Florence, Italy

Affiliations

  1. Swiss Centre for Electronics and Microtechnology (CSEM), Time and Frequency Sector, Neuchâtel, Switzerland

    • Ewelina Obrzud
    • , Stefan Kundermann
    • , Steve Lecomte
    •  & Tobias Herr
  2. University of Geneva, Department of Astronomy & Geneva Observatory/PlanetS, Versoix, Switzerland

    • Ewelina Obrzud
    • , Bruno Chazelas
    • , Francesco Pepe
    • , François Wildi
    •  & François Bouchy
  3. National Institute of Astrophysics (INAF), Astronomical Observatory of Brera, Milano, Italy

    • Monica Rainer
  4. National Institute of Astrophysics (INAF), Fundación Galileo Galilei, Breña Baja, Santa Cruz de Tenerife, Spain

    • Avet Harutyunyan
    • , Massimo Cecconi
    • , Adriano Ghedina
    •  & Emilio Molinari
  5. Swiss Federal Institute of Technology (EPFL), Photonics and Quantum Measurements, SB IPHYS LPQM, Lausanne, Switzerland

    • Miles H. Anderson
    • , Junqiu Liu
    • , Michael Geiselmann
    •  & Tobias J. Kippenberg
  6. Ligentec, EPFL Innovation Park, Bâtiment C, Lausanne, Switzerland

    • Michael Geiselmann
  7. National Institute of Astrophysics (INAF), Osservatorio Astronomico di Cagliari, Selargius, Italy

    • Emilio Molinari

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Contributions

E.O., S.K., S.L. and T.H. designed and implemented the microphotonic astrocomb. E.O., M.R., A.H. and T.H. performed the experiment and analysed the data. M.H.A., J.L., M.G. and T.J.K. designed, fabricated and provided the microresonator. B.C., F.W., F.P. and F.B. designed and implemented the light-coupling interface to the spectrometer. M.C., A.G. and E.M. provided critical support in connecting the astrocomb to the spectrometer as well as spectrometer operation. T.H. conceived and supervised the work. All authors participated in writing the manuscript.

Competing interests

E.O., S.L. and T.H. are inventors in a patent application concerning driving a microresonator with temporally structured light that has been filed by CSEM. T.H. and T.J.K. are co-inventors in a patent application in the technical field. T.J.K. is co-inventor of patents owned by the Max-Planck Society and EPFL in the technical field. M.G. and T.J.K. are co-founders of Ligentec, a start-up company that is engaged in making Si3N4 nonlinear photonic chips available via foundry service.

Corresponding author

Correspondence to Tobias Herr.

Supplementary information

  1. Supplementary Information

    This file contains more information on the stability of the microphotonic astrocomb, the GIANO-B spectrometer and the impact of photon noise on spectrometer calibration.

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