P. Waller, C. Plantard, ESA/ESTEC, European Space Research and Technology Centre, The Netherlands; E. Dierikx, M. van Veghel, VSL, Dutch Metrology Institute, The Netherlands; R. Smets, A. van den Hil, SURF, Dutch ICT cooperative for Education and Research, The Netherlands

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In 2018-2019, a 250 km White-Rabbit link was established between UTC(ESTC) and UTC(SMD) as a demonstrator for continuous metrological-quality time and frequency transfer between two UTC(k) realisations located in different countries. This demonstrator project was aimed at assessing the performance and operability of a long-distance optical fibre link as a potential technique to be used in the Galileo ground infrastructure. This project was closed in 2019 with successful operation over 10 months and performance significantly improved with respect to traditional techniques (GNSS or TWSTFT) in both stability and accuracy [1,2]. It was also concluded that for long-term operability and sustainability – an indispensable pre-requisite for metrological applications – suitable agreements have to be established with the operator of the optical fibre network. Based on these promising results, two UTC(k) labs (VSL and ESTEC) and the operator of Dutch research and education network (SURF) have joined forces to design, deploy and operate a new White-Rabbit link for a robust and sustainable time and frequency transfer link. A robust architecture based on existing SURF infrastructure has been defined, with solutions fully compatible with the SURF network operation, monitoring and maintenance standards. This solution is also an integral part of Time and Frequency Transfer service under development by SURF. A bi-directional link in an occupied DWDM fibre was established between VSL and ESTEC, allowing continuous time transfer between these two labs, together with the performance monitoring of the link. This paper will present the details of this new White Rabbit link design, its deployment, calibration, validation, operation and performances. Preliminary conclusions will be drawn, together with recommendations for possible improvement and extensions. [1]: E.Dierikx et al., “Transnational time and frequency links over optical fibre for GNSS timing infrastructure”, IFCS-EFTF 2019, Orlando [2]: E.Dierikx et al., “Comparing Optical Fibre versus GNSS Time and Frequency Transfer Supporting Galileo Infrastructure”, 7th International Colloquium on Scientific and Fundamental Aspects of GNSS, 2019, Zürich