LPL - Laboratoire de Physique des Lasers

Metrology, Molecules and Fundamental Tests (MMT)

The group Metrology, Molecules and Fundamental Tests is performing ultra-high resolution molecular spectroscopy in the near and middle infrared and optical frequency metrology. The main experimental projects are the following:


Frequency dissemination by optical fiber link

Anne Amy-Klein, Christian Chardonnet, Olivier Lopez, Etienne Cantin


The ultrastable dissemination of a frequency reference signal between distant labs is very challenging for time and frequency metrology, since frequency comparison using a satellite link (as for example GPS) are not sensitive enough to compare the last generation of atomic clocks. An optical link is designed to transfer from one to another lab an absolute and ultrastable frequency reference with a resolution of 10-15 on an averaging time of 1 s and better than 10-17 on a few hours. There is wide range of applications in the domain of time and frequency metrology and beyond, as for instance tests of fundamental physics using distant clocks comparison or new precision measurements in atomic and molecular physics.


Principle of an optical link

An optical link consists of an optical fiber where an ultrastable laser signal propagates and the fluctuations of the propagation delay are actively compensated. A radio frequency signal can also be transferred by modulating the laser amplitude.


Current developments

We first developed an optical link between SYRTE, the French Metrological Institute for time and frequency, and LPL, in order to benefit from the SYRTE excellent RF and optical references for our precision experiments with molecules. We then extended this technique at the national and European scale, in collaboration with SYRTE. For that purpose, we had the opportunities to access the fibers from the French academic network RENATER and we share this network with the usual data traffic by wavelength multiplexing, using a dedicated frequency channel. In order to extend the ultrastable dissemination on longer distances we have developed some repeater laser stations, which are designed to repeat the optical phase from one link span to the next link span with optimal power. We finally demonstrated an optical link of 1500 km, from Paris to Strasbourg and back, where the residual frequency fluctuations due to the propagation are as low as 10-16 for an averaging time of 1 s and around 10-19 for 103 s. This allows us to transfer the best optical clocks without any degradation of their stability and accuracy.
We also studied various architectures of signal distribution, for instance the extraction of the signal along the link, and we explored the technological and fundamental limits of the rejection of the propagation noise.
We have now set-up two international optical links towards the German and English metrological institute for time and frequency. The French and German Sr lattice clocks were compared with an unrivalled resolution of 4x10-17. This opened the way to ultra-high precision experiments, as for example the differential measurement of earth potential.

Last, we were supported by the French program “Investissement d’avenir” (Equipex Refimeve+) to build a national fiber network in order to distribute the ultrastable signal from SYRTE to tens of labs and institutes. Our know-how was transferred to three companies which are now building such an operational network.



Anne Amy-KleinOlivier Lopez



  1. J. Guéna, S. Weyers, M. Abgrall, C. Grebing, V. Gerginov, P. Rosenbusch, S. Bize, B. Lipphardt, H. Denker, N. Quintin, S. M. F. Raupach, D. Nicolodi, F. Stefani, N. Chiodo, S. Koke, A. Kuhl, F. Wiotte, F. Meynadier, E. Camisard, C. Chardonnet, Y. Le Coq, M. Lours, G. Santarelli, A. Amy-Klein, R. Le Targat, O. Lopez, P. E. Pottie, G. Grosche,
    First international comparison of fountain primary frequency standards via a long distance optical fiber link,
    Metrologia 54, 348–354, (2017).
  2. Won-Kyu Lee, Fabio Stefani, Anthony Bercy, Olivier Lopez, Anne Amy-Klein, and Paul-Eric Pottie,
    Hybrid fiber links for accurate optical frequency comparisons,
    Appl. Phys. B 123, 161, (2017).
  3. P. Delva, J. Lodewyck, S. Bilicki, E. Bookjans, G. Vallet, R. Le Targat, P.-E. Pottie, C. Guerlin, F. Meynadier, C. Le Poncin-Laffitte, O. Lopez, A. Amy-Klein, W. Kyu Lee, N. Quintin, C. Lisdat, A. Al-Masoudi, S. Dorscher, C. Grebing, G. Grosche, U. Sterr, I. R. Hill, R. Hobson, W. Bowden, J. Kronjager, G. Marra, A. Rolland, F. N. Baynes, H. S. Margolis, and P. Gill,
    Test of special relativity using a fiber network of optical clocks,
    Phys. Rev. Lett. 118, 221102, (2017).
  4. Lisdat C., Grosche G., Quintin N., Shi C., Raupach S.M.F., Grebing C., Nicolodi D., Stefani F., Al-Masoudi A., Dörscher S., Häfner S., Robyr J.-.-L, Chiodo N., Bilicki S., Bookjans E., Koczwara A., Koke S., Kuhl A., Wiotte F., Meynadier F., Camisard E., Abgrall M., Lours M., Legero T., Schnatz H., Sterr U., Denker H., Chardonnet C., Le Coq Y., Santarelli G., Amy-Klein A., Le Targat R., Lodewyck J., Lopez O., Pottie P.-É.,
    A clock network for geodesy and fundamental science,
    Nature Communications, 7, 12443, (2016).
  5. Bercy A., Lopez O., Pottie P.-É., Amy-Klein A.,
    Ultra-stable optical frequency dissemination on a multi-access fibre network,
    Applied Physics B: Lasers and Optics, 122, 7, 189, (2016).
  6. Chiodo N., Quintin N., Stefani F., Wiotte F., Camisard E., Chardonnet C., Santarelli G., Amy-Klein A., Pottie P.-É., Lopez O.,
    Cascaded optical fiber link using the internet network for remote clocks comparison,
    Optics Express, 23, 26, 33927-33937, (2015).
  7. Fabio Stefani, Olivier Lopez, Anthony Bercy, Won-Kyu Lee, Christian Chardonnet, Giorgio Santarelli, Paul-Eric Pottie, and Anne Amy-Klein,
    Tackling the Limits of Optical Fiber Links,
    JOSAB 32, 787-797 (2015).
  8. A. Bercy, F. Stefani, Olivier Lopez, Christian Chardonnet, Paul-Eric Pottie, and Anne Amy-Klein,
    Two-Way Optical Frequency Comparisons Over 100 km Telecommunication Network Fibers,
    Physical Review A Rapid Comm, 90, 001802(R) (2014).
  9. Lopez O., Kanj A., Pottie P.E., Rovera D., Achkar J., Chardonnet C., Amy-Klein A., Santarelli G.,
    Simultaneous remote transfer of accurate timing and optical frequency over a public fiber network,
    Applied Physics B 110 (1), 3-6 (2013).
  10. Lopez O., Haboucha A., Chanteau B., Chardonnet C., Amy-Klein A., Santarelli G.,
    Ultra-stable long distance optical frequency distribution using the Internet fiber network,
    Optics Express 20, 23518-23526 (2012).
  11. O. Lopez, A. Haboucha, F. Kéfélian, H. Jiang, B. Chanteau, V. Roncin, C. Chardonnet, A. Amy-Klein and G. Santarelli,
    Cascaded multiplexed optical link on a telecommunication network for frequency dissemination,
    Optics Express 18, 16849-16857, (2010).
  12. O. Lopez, A. Amy-Klein, M. Lours, Ch. Chardonnet, G. Santarelli,
    High-resolution microwave frequency dissemination on an 86-km urban optical link,
    Applied Physics B 98, 723-727, (2010).
  13. F. Kéfélian, O. Lopez, H. Jiang, C. Chardonnet, A. Amy-Klein and G. Santarelli,
    High-resolution optical frequency dissemination on a telecommunication network with data traffic,
    Optics Letters 34, 1573, (2009).
  14. O. Lopez, A. Amy-Klein, C. Daussy, Ch. Chardonnet, F. Narbonneau, M. Lours, and G. Santarelli,
    86-km optical link with a resolution of 2x10 -18 for RF frequency transfer,
    EPJD 48, 35, (2008).
  15. H. Jiang, F. Kéfélian, S. Crane, O. Lopez, M. Lours, J. Millo, D. Holleville, P. Lemonde, Ch. Chardonnet, A. Amy-Klein, G. Santarelli,
    Long-distance frequency transfer over an urban fiber link using optical phase stabilization,
    JOSA B 25, 20292035, (2008).

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