Optical Frequency Transfer – a European Network (OFTEN) The EMPIR-funded project OFTEN has close ties with OC18. It addresses the need to link clocks at different locations with optical fibres for high stability and accuracy frequency comparisons. By using such a fibre network, it will be possible to compare optical clocks across Europe at the 10-18 level. This is an important step in building confidence that the different clocks agree with each other, and is a necessary step before considering a redefinition of the SI second in terms of an optical frequency standard. Atomic Clock Ensemble in Space (ACES) In the ACES mission, a laser-cooled microwave atomic clock on board the international space station will be compared to an international network of ground-based clocks to perform tests of general relativity and alternative theories of gravitation. The clocks developed within the OC18 project will be used as part of the network of ground-based clocks within the ACES mission. Improving the clock accuracies and stabilities will ensure the best results in the shortest possible averaging times. EURAMET – The European Association of National Metrology Institutes EMPIR is the main programme for European research on metrology. It coordinates research projects to address grand challenges, while supporting and developing the SI system of measurement units. EMPIR – participant portal Reporting documents – guides and templates
