Relative Calibration of White Rabbit Switch Instrumental Delays for T-REFIMEVE

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Precise time and frequency signals are required for many applications such as navigation, cyber security, Internet of Things, and advanced scientific research in high-energy physics, astronomy, quantum telecommunications, etc. In France, the national time and frequency reference signals are generated at Observatoire de Paris/Laboratoire Temps Espace/LNE-OP. REFIMEVE is a French national infrastructure that disseminates these national standards to a wide community of laboratories and infrastructure via the fiber network of RENATER, the french national network for education and research [1]. REFIMEVE provides an ultra-stable optical frequency reference signal, and its extension T-REFIMEVE adds the dissemination of time and radio-frequency references via White Rabbit [2]. The WR network is currently being deployed over the telecommunication backbone of RENATER using unidirectional links, i.e. one wavelength and a pair of fibers, mainly at channel 21, λ = 1560 nm. We aim for time transfer accuracy at the 10 ns level, across more than 80 interconnected WR nodes over a 5000 km network. To achieve the targeted accuracy, a first step is to calibrate the instrumental delays of the WR devices. The propagation delay asymmetries through the fiber network will be later evaluated and mitigated. In this work we present the methodology and realization of a test bench that was developed to calibrate the instrumental delays of multiple White Rabbit Switches (WRS) in parallel before their deployment in the field. The calibration was performed by following the CERN calibration procedure [3] and the EMPIR/VSL best practices guide [4]. The major difference in our case is that we are using unidirectional long-range SFP transceivers at 1560.61 nm as our reference. We have established an independent calibration chain at Laboratoire Temps Espace based on a dedicated Golden Calibrator. We then calibrated all the ports of a "Golden calibrator switch", which we used to calibrate 68 standard…