“Advanced time/frequency comparison and dissemination through optical telecommunication networks” Short Name: TiFOON TiFOON stands for “Time and Frequency over Optical Networks”. EMPIR Project Number: 18SIB06 The EMPIR initiative is co-funded by the European Union’s Horizon 2020 research and innovation programme and the EMPIR participating states. Aim To advance fibre-based frequency transfer capabilities in Europe towards a universal tool for time and frequency metrology and beyond. Motivation Redefinition of the SI second: Fibre links enable the remote clock comparisons required for the redefinition of the SI second, but their current reliability and availability are insufficient. International time scales: Fibre-based time transfer offers performance and resilience beyond satellite techniques. Only combined optical frequency and time services in shared fibre will be economically sustainable. Applications beyond metrology: Many applications in research and industry require synchronisation. Fibre links provide access to ultra-stable and accurate optical time and frequency references. Scientific objectives Optical time transfer: Develop technologies for combined time and frequency transfer within one ITU channel, with a target accuracy of 100 ps and 10-18 respectively. Explore novel approaches with potential for sub-picosecond accuracy. Reliable optical frequency transfer: Enhance the phase coherence of existing technologies with a target instability below 10-18 within one hour. Develop advanced link management tools for human-intervention free operation over weeks. Telecom infrastructure sharing: Evaluate the compatibility of time and frequency transfer techniques with data traffic. Engage with network operators and equipment manufacturers to promote shared use of fibres. Applications beyond metrology: Investigate the specific benefits of time transfer as opposed to frequency. Focus on geodesy and earth observation (VLBI, SLR, GNSS). Establish the regional dissemination of optical frequency standards with sub-Hz linewidth. Explore data mining of link diagnostic data, e.g. for seismology. Early impact On industry: Commercial systems, sub-systems and components. Accepted standards for sharing fibre infrastructure. On metrology: Capability for rapid, high accuracy international time scale comparisons. Improved ability to remotely compare optical frequency standards. A leading role for Europe in the redefinition of the SI second. On science: World-class clocks for the wider scientific community. Fibre links as a tool in geophysics. Enhanced accuracy of geodetic techniques. Tests of fundamental physics. Wider impact Enhanced international time scales will benefit satellite navigation (e.g. Galileo) and future telecommunication networks. All-optical time keeping based on optical frequency standards, oscillators and signalling may lead to femtosecond timing. A pan-European fibre network for time and frequency will enable dissemination of state-of-the-art frequency standards and secure traceable timing. Advanced time and frequency technologies may play a role in tackling the global challenges of climate change, water and energy supply.