Frequency transfer via a two-way optical phase comparison on a multiplexed fiber network

We performed a two-way remote optical phase comparison on optical fiber. Two optical frequency signals were launched in opposite directions in an optical fiber and their phases were simultaneously measured at the other end. In this technique, the fiber noise was passively cancelled, and we compared two optical frequencies at the ultimate 1E-21 stability level. The experiment was performed on a 47 km fiber that is part of the metropolitan network for Internet traffic. The technique relies on the synchronous measurement of the optical phases at the two ends of the link, that is made possible by the use of digital electronics. This scheme offers several advantages with respect to active noise cancellation, and can be upgraded to perform more complex tasks

Atomic clock dataset for 'Coherent Optical-Fiber Link Across Italy and France'

Dataset of the comparison of the atomic clocks at LNE-SYRTE and INRIM via optical fibre link between October 2021 and February 2022. Results discussed in Clivati et al., Coherent Optical-Fiber Link Across Italy and France, Phys. Rev. Applied, American Physical Society, 18, 054009, 2022. The involved atomic clocks are the Cs fountains SYRTE-F02Cs, IT-CsF2, the Rb fountain SYRTE-F02Rb and the Yb optical lattice clock IT-Yb1. Data is organized in folders, one for each comparison. In the folders data is separated is one file per day. Data is reported as fractional frequency ratios in bins of 864 s. Timetags are reported in modified Julian date (MJD). A validity flag is given where 0 = invalid, valid otherwise. Each folder includes a yaml file with metadata required for generalized data processing as in [Lodewyck et al., 2020]. The Python package used for data processing can be found on github.This work was supported by: the European Metrology Program for Innovation and Research (EMPIR) Projects 18SIB05 ROCIT, 18SIB06 TIFOON, 20FUN08 NextLasers, which received funding from the EMPIR programme co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme; the European Union's Horizon 2020 research and innovation programme under Grant Agreement No. 951886 (CLONETS-DS); Program "Investissements d'Avenir" launched by the French Government and implemented by Agence Nationale de la Recherche with references ANR-10-LABX-48-01 (Labex First-TF), ANR-21-ESRE-0029 (ESR/Equipex T-REFIMEVE), ANR-11-EQPX-0039 (Equipex REFIMEVE+), ANR-10-IDEX-0001-002 (Idex PSL); Conseil Régional Bourgogne-Franche-Comté; Domaine d'Intérêt Majeur Science et Ingénierie en Région Île-de-France pour les Technologies Quantiques (DIM SIRTEQ)