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10-21-Level optical frequency dissemination over 2067 km of noise-loaded field-deployed fiber network
Fa-Xi Chen1,2, Li-Bo Li2, Jiu-Peng Chen1,2
1Hefei National Laboratory, University of Science and Technology of China, Hefei, China.
Light, Science & Applications
|June 22, 2026
Summary
We developed a new method for ultra-stable optical frequency dissemination over long fiber links. This bias-free digital phase recording technique significantly improves reliability and extends network reach for precise frequency transfer.
Area of Science:
- Physics
- Optical Engineering
- Telecommunications
Background:
- Ultra-stable optical frequency dissemination is critical for advanced applications.
- Existing optical phase-locked loop (OPLL) systems face limitations due to noise asymmetry and loss of lock in long-haul fiber networks.
- Continuous compensation bias hinders the performance of current frequency transfer systems.
Purpose of the Study:
- To propose and demonstrate a bias-free noise compensation method for optical frequency transfer.
- To enhance the reliability and dynamic range of optical frequency dissemination systems.
- To establish a robust, scalable, and field-deployable optical frequency network.
Main Methods:
- Implemented a bias-free noise compensation method using digital radio-frequency phase recording with a time-to-digital converter.
- Incorporated multifunctional relay stations and hertz-level optical bandpass filtering to enhance OPLL robustness.
- Utilized a 2067 km field fiber link under extreme noise conditions (5000 rad^2 Hz^-1 km^-1 at 1 Hz) for testing.
Main Results:
- Achieved a frequency instability of 2.9 × 10^-21 at 1 day, a threefold improvement over uncalibrated systems.
- Demonstrated continuous phase lock for over four days, overcoming the limitations of previous methods.
- The proposed method offers theoretically unlimited dynamic range and enables virtually unlimited link extension through noise purification.
Conclusions:
- The developed bias-free noise compensation method significantly enhances the stability and reliability of optical frequency dissemination.
- The scalable architecture is field-deployable and compatible with standard telecommunication infrastructure, paving the way for advanced optical networks.
- This breakthrough overcomes theoretical limits of uncalibrated systems and enables robust long-haul optical frequency transfer.
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