High-resolution microwave frequency transfer over an 86-km-long optical fiber network using a mode-locked laser

Area of Science:

• Physics
• Optical Engineering
• Metrology

Background:

• Accurate frequency transfer is crucial for modern scientific and technological applications, including global positioning systems and fundamental physics research.
• Traditional methods face limitations in stability and distance, necessitating advanced techniques for long-haul, high-precision frequency dissemination.

Purpose of the Study:

• To demonstrate the feasibility of transferring an ultrastable microwave frequency over a significant distance using an optical frequency comb.
• To achieve high fractional frequency stability at a remote location by compensating for environmental disturbances in installed optical fiber.

Main Methods:

• Transmission of a 30-nm-wide optical frequency comb generated by a mode-locked laser over 86 km of installed optical fiber.
• Utilized a round-trip configuration where the pulse train is returned via the same fiber to actively compensate for optical path length fluctuations caused by environmental factors.
• Measured the fractional transfer stability at the remote end of the fiber link.

Main Results:

• Achieved a fractional transfer stability of 4×10⁻¹⁷ at the remote end after 1600 seconds of measurement.
• The demonstrated stability corresponds to an impressive timing jitter of 64 femtoseconds (fs).
• Successfully transferred an ultrastable microwave frequency over a standard installed optical fiber infrastructure.

Conclusions:

• The study successfully demonstrates a robust method for long-distance, ultrastable microwave frequency transfer using optical frequency combs.
• The round-trip compensation technique effectively mitigates environmental impacts on the optical fiber, enabling high-precision frequency dissemination.
• This advancement has significant implications for next-generation timing systems, distributed quantum sensing, and fundamental metrology.