image: The research scope covers the typical platforms, key modules and typical applications of optical two-way time-frequency transfer (O-TWTFT). Three mainstream transfer methods include optical frequency transfer, modulated laser transfer, and comb transfer. Key modules of fiber-based O-TWTFT comprise the carrier, load, channel, download, discrimination, processor, and compensation. Fiber-based O-TWTFT finds applications in areas such as global positioning, navigation and timing (PNT), sensitive probes of environmental fluctuations, and fundamental physics testing.
Credit: ©Science China Press
This study is led by Prof. Hong Guo and Dr. Ziyang Chen (State Key Laboratory of Photonics and Communications, School of Electronics, and Center for Quantum Information Technology, Peking University). The researchers claimed that high-precision time-frequency transfer forms the backbone of crucial advancements in global positioning, navigation and timing (PNT), sensitive probes of environmental fluctuations, and fundamental physics testing, where high-precision synchronization is increasingly demanded. However, disseminating these ultra-stable signals over long distances faces significant challenges, including environmental disturbances, signal degradation, and infrastructure limitations. While methods using free-space or satellite techniques offer flexibility for mobile and remote applications, their vulnerability to atmospheric disturbances and line-of-sight constraints compromise their stability.
In contrast, optical fiber networks, widely deployed for telecommunications, present a resilient option by combining inherent immunity to environmental disturbances with the capability for active noise elimination. Leveraging existing fiber infrastructure, fiber-based optical two-way time-frequency transfer (O-TWTFT) achieves unparalleled stability across vast distances, enabling applications such as the redefinition of the second, continent-spanning clock networks, resilient PNT and precision geodesy. Therefore, fiber optics opens up a new avenue for high-precision time services.
Guo et al. focus exclusively on fiber-based approaches due to their mature infrastructure and high stability, and this review focuses on the advancement of fiber-based O-TWTFT, which has progressed from laboratory demonstrations to field applications that rival the performance of free-space systems.
The researchers summarized the widely used characterization methods for frequency stability, and gave the general configuration of an O-TWTFT system and key modules, evaluated mainstream transfer methods, including optical frequency, modulated laser, and comb-based schemes, highlighting their respective milestones and limitations. Finally, the researchers discussed emerging challenges and opportunities, including the development of novel transfer methods, and integration with free-space networks, toward realizing a globally synchronized metrological infrastructure.
See the article:
Time-Frequency Transfer over Optical Fiber
https://doi.org/10.1093/nsr/nwaf236
Journal
National Science Review