Optical frequency transfer - a European network
Short Name: OFTEN, Project Number: 15SIB05
First comparisons of networked optical clocks linked by fibre optics achieving high network frequency stability
Optical clocks outperform caesium-based atomic clocks in terms of accuracy and stability, with the potential to deliver time and frequency uncertainties 100x lower, so are expected to form the backbone of a future redefinition of the SI second. Such unprecedented measurement precision would unlock new timing applications, enhanced Earth- and space-based navigation, and new tests of physics beyond the Standard Model. However, satellite radio links, while sufficient for distributing timing frequencies to coordinate atomic clocks, were orders of magnitude less stable than necessary for optical clocks. New techniques were therefore required.
Frequency comparisons via optical fibre connections could offer the required stability, but only if the frequency instability contributed by the connection is negligible compared to that of the linked clocks.
Optical fibre carrier frequency transfer was demonstrated in the EMRP project NEAT-FT, but used equipment unsuited to continuous, autonomous operation, and was limited by lack of knowledge of noise processes, real-time evaluation tools, and protocols.
Building on NEAT-FT, and complementing EMPIR project OC18, OFTEN improved the reliability and scalability of optical fibre frequency transfer, demonstrating on-demand continuous clock comparisons and frequency dissemination over long-distance optical fibre links.
Four optical clock comparison campaigns were performed using a new link between NPL (UK), OBSPARIS (France) and PTB (Germany). These showed excellent frequency stability for frequency transfer, most measuring uncertainty in the low 10-17 levels for the optical clocks. Separate frequency comparisons with overall uncertainty at 10-19 levels were also achieved over upgraded fibre links.
A clock comparison campaign, involving a three-way maser comparison between NPL, OBSPARIS and PTB also showed this network was suited to atomic clock comparisons at target uncertainty levels.
Guidelines for frequency dissemination for non-NMI users were produced, including a common data format and methodology for assessing optical fibre link performance.
Project partners provided technical expertise to the CLOck NETwork Services (CLONET), a Horizon 2020 partnership building and innovation project, to prepare for a European high-performance optical fibre network.
The EMPIR TiFOON project builds on OFTEN, developing improved tools and refined techniques for transferring data over shared fibre optic networks.
The project supported confidence in optical clock comparisons via fibre networks and shows comparisons of primary caesium-based clocks can be delivered in days rather than weeks.
Optical clocks linked by optical fibres are likely to support cutting-edge fundamental science experimentation and earth observation methods, and likely stimulate innovation for European companies to profit from the fast-growing worldwide market for timing and positioning services.
New Journal of Physics
Metrologia
IEEE Transactions on Instrumentation and Measurement
2018 European Frequency and Time Forum (EFTF)
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
2017 Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFC)
Atomic Physics (physics.atom-ph)
2017 Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFC)
2017 Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)
2017 Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFC)
2017 Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFC)
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
Metrologia
2017 Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFC)
Physical Review Letters