Abstract
We demonstrate long-distance (≥100-km) synchronization of the phase of a radio-frequency reference over an optical-fiber network without needing to actively stabilize the optical path length. Frequency mixing is used to achieve passive phase-conjugate cancellation of fiber-length fluctuations, ensuring that the phase difference between the reference and synchronized oscillators is independent of the link length. The fractional radio-frequency-transfer stability through a 100-km "real-world" urban optical-fiber network is 6 × 10(-17) with an averaging time of 10(4) s. Our compensation technique is robust, providing long-term stability superior to that of a hydrogen maser. By combining our technique with the short-term stability provided by a remote, high-quality quartz oscillator, this system is potentially applicable to transcontinental optical-fiber time and frequency dissemination where the optical round-trip propagation time is significant.
Highlights
It has been shown that optical-fiber networks have the potential to disseminate highly stable time and frequency standards over very long distances [1,2]
We demonstrate long-distance ( 100-km) synchronization of the phase of a radio-frequency reference over an optical-fiber network without needing to actively stabilize the optical path length
Frequency mixing is used to achieve passive phase-conjugate cancellation of fiber-length fluctuations, ensuring that the phase difference between the reference and synchronized oscillators is independent of the link length
Summary
It has been shown that optical-fiber networks have the potential to disseminate highly stable time and frequency standards over very long distances [1,2]. The most commonly used remedy is to measure the round-trip phase and to suppress the effect of phase fluctuations by either actively altering the fiber length [1,8,9,10,13,14,15] or indirectly by electronically pre-compensating the outgoing signal phase/frequency [1,8,9,11,12,16,17,19,20]. A key outcome of our work is to demonstrate phase synchronization (or RF-frequency syntonization) with better stability than that of a hydrogen maser
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