Ultra-stable oscillators comparison is important as they are at the heart of the generation of optical time scale. Just like microwave oscillators as Hydrogen masers are the necessary continuous flywheel to generate atomic time scales, ultra-stable lasers play here the same critical role for optical time scale. Ultra-stable lasers like the ones used in this study oscillates with residual fractional frequency deviations lesser than 6 parts in 100,000,000,000,000,000. Such a small relative deviations are equivalent to a wobble of the distance between the Earth and the Sun of less than the width of a hair. The frequency of the lasers can then be calibrated by any optical clock or atomic fountain part of this network. The extreme precision of optical atomic clocks network will enable new applications, such as chronometric geodesy where the change of rate of a clock related to a measure of gravity potential difference, and many other applications including ultra-precise spectroscopy, astronomy, high speed communication, synchronisation and localisation.

Being able to transfer such precision to distant locations enables more widespread, efficient utilisation of existing research infrastructures, otherwise only available at a few national laboratories. In this work we discuss how this measurement precision can be made available through optical fibre to a much larger community of users, ranging from other national laboratories, academia and industry.

Read the research article (open access):
M. Schioppo et al. "Comparing ultrastable lasers at 7 × 10-17 fractional frequency instability through a 2220 km optical fiber network", Nature Communications (2022).

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REFIMEVE
[EU projects ROCIT et TIFOON]
[team webpage Fréquence Optique du SYRTE]