Precise and continuous time and frequency synchronisation at the 5×10⁻¹⁹ accuracy level

Area of Science:

• Metrology
• Optical Communications
• Geophysics

Background:

• Precise time and frequency synchronization between remote locations is essential for numerous scientific and technological applications.
• Traditional methods often rely on satellite links, which can be susceptible to environmental factors and signal degradation.
• Communication fiber networks present a promising alternative for robust, long-distance time and frequency dissemination.

Purpose of the Study:

• To demonstrate accurate frequency transfer and time synchronization using a standard urban fiber optic link.
• To evaluate the stability and precision of time and frequency dissemination over an 80 km fiber path.
• To explore the potential for scaling this technology to longer distances (1000 km) and its application in fields like radio astronomy.

Main Methods:

• Utilized a 9.1 GHz microwave modulation and a timing signal.
• Employed two continuous-wave lasers for signal transfer across an 80 km urban fiber link between Tsinghua University (THU) and the National Institute of Metrology of China (NIM).
• Monitored system performance over several months for reliability assessment.

Main Results:

• Achieved frequency transfer stability at the 5×10⁻¹⁹/day level.
• Demonstrated time synchronization with a precision of 50 picoseconds (ps).
• The system operated reliably and continuously for an extended period.

Conclusions:

• The study successfully demonstrated high-precision time and frequency transfer over an 80 km fiber link.
• This fiber-based approach offers a reliable and accurate alternative to satellite-based dissemination.
• The technology shows potential for long-distance applications, including enhancing long-baseline radio astronomy.