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Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)

Optical frequency transfer over a single-span 1840-km fiber link

Stefan Droste, Thomas Udem, Theodor W. Hänsch, Ronald Holzwarth, Filip Ozimek, S. M. F. Raupach, H. Schnatz, Gesine Grosche

Published Jul 1, 2013• 18 citations
Publisher

Abstract

We demonstrate optical frequency transfer over an 1840 km underground optical fiber link using a single-span stabilization. To compensate for more than 420 dB of optical attenuation of the light we use twenty Erbium doped fiber amplifiers along the entire link and two additional fiber Brillouin amplifiers. The good passive stability of our fiber link allows us to reach short term instabilities expressed as the modified Allan deviation of 3 × 10-15for a gate time τ of 1 s reaching 4 × 10-19in just 100 s. By comparing the sent and transferred frequencies we find no systematic offset within the statistical uncertainty of about 3 × 10-19. The spectral noise distribution of our fiber link at low Fourier frequencies leads to a τ-2slope in the modified Allan deviation.

DOI
10.1109/eftf-ifc.2013.6702150

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Optical frequency transfer via a 1840 km fiber link has been investigated. Twenty fiber amplifiers and two fiber Brillouin amplifiers are needed to compensate for 420 dB of loss. Active noise compensation reduces the instability to 2.7 × 10−15 at 1 s with 4 × 10−19 after 100 s and an accuracy of a few parts in 1019.

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We investigated the transfer of a 194 THz optical frequency along a 1840 km fiber link. The fractional frequency instability expressed as the modified Allan deviation is 2.7 × 10−15 at 1 s with 4 × 10−19 after 100 s. The transferred frequency shows no systematic offset within an uncertainty of 3 × 10−19. Analyzing the underlying noise structure reveals a τ−2 response in the modified Allan deviation, which is confirmed by calculations of the frequency instability from frequency counter data as well as from phase noise data.

•Jan 1, 2014•0 citations

Optical frequency transfer via 1840 km fiber link with superior stability

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Optical frequency transfer over a 1840 km fiber link is presented. The link is actively stabilized to deliver a frequency with superior stability and accuracy. The spectral noise distribution of the stabilized link leads to an unprece-dented fast averaging in the modified Allan deviation.

Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)•May 1, 2014•1 citation

Coherent transfer of an optical carrier over 251 km

Nathan R. Newbury, Paul A. Williams, William C. Swann

We transfer an optical frequency over 251 km of optical fiber with a residual instability of 6x10(-19) at 100 s. This instability and the associated timing jitter are limited fundamentally by the noise on the optical fiber and the link length. We give a simple expression for calculating the achievable instability and jitter over a fiber link. Transfer of optical stability over this long distance requires a highly coherent optical source, provided here by a cw fiber laser locked to a high finesse optical cavity. A sufficient optical carrier signal is delivered to the remote fiber end by incorporating two-way, in-line erbium-doped fiber amplifiers to balance the 62 dB link loss.

Optics Letters•Oct 15, 2007•228 citations
We demonstrate optical frequency transfer over an 1840 km underground optical fiber link using a single-span stabilization. To compensate for more than 420 dB of optical attenuation of the light we use twenty Erbium doped fiber amplifiers along the entire link and two additional fiber Brillouin amplifiers. The good passive stability of our fiber link allows us to reach short term instabilities expressed as the modified Allan deviation of 3 × 10-15for a gate time τ of 1 s reaching 4 × 10-19in just 100 s. By comparing the sent and transferred frequencies we find no systematic offset within the statistical uncertainty of about 3 × 10-19. The spectral noise distribution of our fiber link at low Fourier frequencies leads to a τ-2slope in the modified Allan deviation.
To compare the increasing number of optical frequency standards, highly stable optical signals have to be transferred over continental distances. We demonstrate optical-frequency transfer over a 1840-km underground optical fiber link using a single-span stabilization. The low inherent noise introduced by the fiber allows us to reach short term instabilities expressed as the modified Allan deviation of $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ for a gate time $\ensuremath{\tau}$ of 1 s reaching $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}$ in just 100 s. We find no systematic offset between the sent and transferred frequencies within the statistical uncertainty of about $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}$. The spectral noise distribution of our fiber link at low Fourier frequencies leads to a ${\ensuremath{\tau}}^{\ensuremath{-}2}$ slope in the modified Allan deviation, which is also derived theoretically.
In long-distance, optical continuous-wave frequency transfer via fiber, remote bidirectional Er³ ⁺ -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 Λ-weighted data with 1 s gate time) of around 1 × 10(-19) and less for averaging times longer than 3000 s. The modified Allan deviation reaches 3 × 10(-19) at an averaging time of 100 s. Beyond 100 s it follows the interferometer noise floor, and 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 × 10(-19)
We investigated the transfer of a 194 THz optical frequency along a 1840 km fiber link. The fractional frequency instability expressed as the modified Allan deviation is 2.7 × 10−15 at 1 s with 4 × 10−19 after 100 s. The transferred frequency shows no systematic offset within an uncertainty of 3 × 10−19. Analyzing the underlying noise structure reveals a τ−2 response in the modified Allan deviation, which is confirmed by calculations of the frequency instability from frequency counter data as well as from phase noise data.
We transfer an optical frequency over 251 km of optical fiber with a residual instability of 6x10(-19) at 100 s. This instability and the associated timing jitter are limited fundamentally by the noise on the optical fiber and the link length. We give a simple expression for calculating the achievable instability and jitter over a fiber link. Transfer of optical stability over this long distance requires a highly coherent optical source, provided here by a cw fiber laser locked to a high finesse optical cavity. A sufficient optical carrier signal is delivered to the remote fiber end by incorporating two-way, in-line erbium-doped fiber amplifiers to balance the 62 dB link loss.