High-Precision Fiber Noise Detection and Comparison over a 260 km Field Fiber Link

Area of Science:

• Metrology
• Optical Physics
• Fiber Optics

Background:

• Accurate optical frequency comparisons are crucial for advancing optical clocks and fundamental physics.
• Existing methods often require complex data transfer or active noise cancellation over long distances.

Purpose of the Study:

• To develop a high-precision optical frequency noise detection and comparison technique.
• To enable remote optical frequency comparison without data transfer over communication links.
• To demonstrate the effectiveness of a two-way transfer method over a long-field fiber link.

Main Methods:

• Utilizing a two-way transfer method with two optical carrier signals injected into a bidirectional fiber link.
• Implementing a single-site data acquisition and phase comparison scheme by reflecting one carrier signal.
• Detecting and suppressing common-mode frequency noise inherent to the fiber link.

Main Results:

• Achieved a fractional instability of 2.5×10^-17 at 1 s and 3.5×10^-21 at 8000 s over a 260 km fiber link.
• Successfully demonstrated common-mode frequency noise suppression without active fiber control.
• Validated the feasibility of comparing remote optical frequencies at a single site.

Conclusions:

• The proposed two-way transfer method offers a reliable and simplified approach for high-precision remote optical frequency comparisons.
• This technique eliminates the need for remote data transmission, enhancing system robustness.
• It is expected to significantly improve the performance and reliability of advanced optical and atomic clocks.