Note: Optical fiber two-way time transfer based on single photon counting approach.

Area of Science:

• Quantum optics
• Metrology
• Optical communications

Background:

• Accurate time transfer is crucial for modern communication networks and scientific experiments.
• Traditional Two-Way Time Transfer (TWTT) methods face limitations in precision and range due to systematic errors and required optical power.
• Single Photon Avalanche Diode (SPAD) detectors offer high sensitivity and timing resolution, making them promising for advanced time transfer techniques.

Purpose of the Study:

• To present and evaluate a novel TWTT method employing single photon counting.
• To demonstrate the capability of the new method to achieve high precision time transfer over extended distances.
• To assess the elimination of systematic errors and the low optical power requirements of the proposed TWTT technique.

Main Methods:

• Utilizing two Single Photon Avalanche Diode (SPAD) detectors at opposite ends of an optical channel.
• Measuring a common signal at each detector location and mathematically decomposing it into separate signals.
• Calculating time shifts between the decomposed signals to determine absolute time differences between distant time scales.

Main Results:

• Achieved ultimate time transfer precision of less than 1 picosecond (ps) with averaging times of hours.
• Demonstrated the method's usability in optical fiber channels exceeding 500 km without amplification, requiring only -100 dBm optical power.
• Confirmed long-term timing stability of the SPAD detectors and timing system below 100 femtoseconds (fs).

Conclusions:

• The novel TWTT method based on single photon counting effectively eliminates systematic errors.
• The method provides highly precise and reliable time transfer, suitable for long-haul optical communication systems.
• This technique is versatile and can be implemented at various communication wavelengths with appropriate SPAD detectors.