Optical frequency transfer via a 660 km underground fiber link using a remote Brillouin amplifier

Abstract

In long-haul optical continuous-wave frequency transfer via fiber, remote bidirectional Er${}^{+}$-doped fiber amplifiers are commonly used to mitigate signal attenuation. We demonstrate for the first time the ultrastable transfer of an optical frequency using a remote fiber Brillouin amplifier, placed in a server room along the link. Using it as the only means of remote amplification, on a 660 km loop of installed underground fiber we bridge distances of 250 km and 160 km between amplifications. Over several days of uninterrupted measurement we find an instability of the frequency transfer (Allan deviation of $\Lambda$-weighted data with 1 s gate time) of around $1\times 10^{-19}$ and less for averaging times longer than 3000 s. The modified Allan deviation reaches $3\times 10^{-19}$ at an averaging time of 100 s, corresponding to the current noise floor at this averaging time. For averaging times longer than 1000 s the modified Allan deviation is in the $10^{-20}$ range. A conservative value of the overall accuracy is $1\times 10^{-19}$.

arXiv commentpreliminary version; 4 figures

References in corpus (8)

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• A sub-40 mHz linewidth laser based on a silicon single-crystal optical cavity
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Cited by in corpus (6)

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• Studying fundamental limit of optical fiber links to $10^{-21}$ level
• Combining fiber Brillouin amplification with a repeater laser station for fiber-based optical frequency dissemination over 1400 km
• E-21 Level Instability Frequency Dissemination over 2067 km noisy Telecommunication Infrastructure