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Record-breaking optical frequency dissemination over 2,067 km fiber network

Ziyang Chen, Xu KEmi, Hong Guo

Published Aug 14, 2026• 0 citations
Publisher

Abstract

Abstract A research team demonstrated a 2067-km field-deployed optical frequency dissemination link over standard telecommunications fiber. The system achieved a record fractional frequency instability of 2.9 × 10⁻ 21 at one day averaging time, and maintained continuous phase lock for more than four days, marking a major step toward large-scale optical clock networks and future precision timing infrastructure.

DOI
10.1186/s43593-026-00137-w

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Abstract A research team demonstrated a 2067-km field-deployed optical frequency dissemination link over standard telecommunications fiber. The system achieved a record fractional frequency instability of 2.9 × 10⁻ 21 at one day averaging time, and maintained continuous phase lock for more than four days, marking a major step toward large-scale optical clock networks and future precision timing infrastructure.
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Abstract Optical clock networks play important roles in various fields, such as precise navigation, redefinition of “second” unit, and gravitational tests. To establish a global-scale optical clock network, it is essential to disseminate time and frequency with a stability of 10^−19 over a long-distance free-space link. However, such attempts were limited to dozens of kilometers in mirror-folded configuration. Here, we take a crucial step toward future satellite-based time-frequency disseminations. By developing the key technologies, including high-power frequency combs, high-stability and high-efficiency optical transceiver systems, and efficient linear optical sampling, we demonstrate free-space time-frequency dissemination over two independent links with femtosecond time deviation, 3 × 10−19 at 10,000 s residual instability and 1.6 × 10^−20 ± 4.3 × 10^−19 offset. This level of the stability retains for an increased channel loss up to 89 dB. Our work can not only be directly used in ground-based application, but also firmly laid the groundwork for future satellite time-frequency dissemination.
With the progress in the development of optical frequency standards grows the demand for the dissemination of stable optical frequencies. To date, optical fiber links constitute the most promising medium to bridge large geographical distances while still maintaining a high degree of frequency stability and accuracy. We investigated the transfer of an optical frequency along different fiber links during the past years and achieved a fractional instability and uncertainty at a level lower than 10 − 19 using fiber links with lengths of up to almost 2000 km. We give an overview of different techniques and methods that can be used in combination with optical fiber links to achieve a stable frequency transfer. The results of different fiber links are summarized and an outlook of future links is given.
We demonstrate the ultra stable transfer an optical frequency over 300 km of installed optical fibers. This ultrastable optical link uses an optical telecommunication network simultaneously carrying Internet data and goes through two Data Center Facilities using multiplexers and bidirectional erbium-doped fiber amplifiers. We have obtained an instability of 3×10-15at 1 s which scales down to around 7×10-20after about 20 hours. These results are promising and represent an intermediate step for the future development of continental-scale frequency transfer.
Experiments of transmission of sub-Hz cavity-stabilized 1542 nm laser frequency using a pair of 43 km dark fibers in urban environment are reported on successively 86 km and 172 km, with fractional frequency instability in the 10-19 range. A new approach is then introduced consisting in using part of an optical telecommunications network carrying simultaneously data traffic using a DWDM scheme to multiplex the metrological signal. This method is experimentally implemented using 22 km of fiber linking Université Paris 13 to its internet access point without degradation of the link instability. We finally present a project of large scale link between Paris and the German border using RENATER network which could constitute the first step of the building of a European optical network for ultrastable frequency dissemination and comparison.