Remote atomic clock synchronization via satellites and optical fibers

[摘要] In the global network of institutions engaged with the realization ofInternational Atomic Time (TAI), atomic clocks and time scales are comparedby means of the Global Positioning System (GPS) and by employingtelecommunication satellites for two-way satellite time and frequencytransfer (TWSTFT). The frequencies of the state-of-the-art primary caesiumfountain clocks can be compared at the level of 10⁻¹⁵ (relative, 1 dayaveraging) and time scales can be synchronized with an uncertainty of onenanosecond. Future improvements of worldwide clock comparisons will requirealso an improvement of the local signal distribution systems. For example,the future ACES (atomic clock ensemble in space) mission shall demonstrateremote time scale comparisons at the uncertainty level of 100 ps.

To ensure that the ACES ground instrument will be synchronized to the localtime scale at the Physikalisch-Technische Bundesanstalt (PTB) without asignificant uncertainty contribution, we have developed a means forcalibrated clock comparisons through optical fibers. An uncertainty below40 ps over a distance of 2 km has been demonstrated on the campus of PTB. Thistechnology is thus in general a promising candidate for synchronization ofenhanced time transfer equipment with the local realizations of Coordinated Universal Time UTC.

Based on these experiments we estimate the uncertainty level for calibratedtime transfer through optical fibers over longer distances. These findingsare compared with the current status and developments of satellite basedtime transfer systems, with a focus on the calibration techniques foroperational systems.

[学科分类] 电子、光学、磁材料