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

Performance of the 1880 km Long, Brillouin Amplification Based Fibre Link PTB-MPQ–PTB

Alexander Kühl, Thomas Waterholter, Sebastian Koke, Gesine Grosche, Gulnara A. Vishnyakova, Ronald Holzwarth

Published Apr 1, 2019• 2 citations
Publisher

Abstract

We have extended the existing interferometric fibre link PTB-Strasbourg with a branch connecting the node at Karlsruhe Institute of Technology (KIT) to the Max Planck Institute of Quantum Optics (MPQ) in Garching/Munich. This fibre connection enables chronometric levelling experiments between PTB and MPQ, separated by a line-of-sight distance of about 460 km. Here, we study the performance of the PTB-MPQ fibre link which mainly employs stimulated Brillouin scattering as means of amplification. We consider two configurations: a single-span loop configuration and an antiparallel configuration with frequency transfer over the two concatenated, individually stabilized forward and backward links.

DOI
10.1109/fcs.2019.8855994

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Chronometrie levelling [1-3] is a technique of deriving gravitational potential differences from clock frequency comparisons allowing the determination of height differences. Interferometric optical fibre links (IFL) [4] enable chronometric levelling between distant labs housing optical clocks [5]. An IFL is a phase stabilized telecom fibre link connection establishing a fixed optical phase relationship between two locations up to ~1000 km apart [6]. To perform a chronometric levelling campaign between the stationary optical clocks of the Physikalisch-Technische Bundesanstalt (PTB) and PTB's transportable Strontium clock [7] placed at the Max Planck Institute of Quantum Optics (MPQ) we have established a new 940 km long IFL between the two locations. At both link ends the frequencies of the clock lasers are compared to the 1,5 pm link transfer laser via fs-combs. To enable chronometric levelling experiments at the level of 10 cm height resolution, we aim a fractional frequency uncertainty of the frequency transfer of-18for averaging times of ~40 ks. To monitor the frequency transfer over the complete 940 km long fibre link the signal is sent back from the receiving end to the sender on a second fibre, which allows an out-of-loop characterization using data of the 1880 km loop. We study two different link setups, cf. Fig. 1a: i) a single-span loop configuration with the option to tap off the signal at MPQ with a passive frequency extraction unit [8]. This setup requires monitoring at the sending end only and allows us to investigate an ultralong IFL, even longer than the previous record [9]. And ii) an antiparallel configuration of two concatenated, individually stabilized interferometric fibre links. This setup offers lower instabilities due to a decreased delay-limit [10] but requires setting up and maintaining a stabilization system at both link ends. To compensate the attenuation of the fibres we used fibre Brillouin amplifier modules (FBAM) developed inhouse providing a typical gain of > 40 dB.

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Ultra Precise Frequency Dissemination across Germany – Towards a 900 km Optical Fiber Link from PTB to MPQ

Katharina Predehl, Ronald Holzwarth, Thomas Udem +5 more

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text K. Predehl, R. Holzwarth, T. Udem, T. Hänsch, O. Terra, G. Grosche, B. Lipphardt, and H. Schnatz, "Ultra Precise Frequency Dissemination across Germany – Towards a 900 km Optical Fiber Link from PTB to MPQ," in Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, OSA Technical Digest (CD) (Optica Publishing Group, 2009), paper CTuS2. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Conference on Lasers and Electro-Optics•Jan 1, 2009•1 citation
We have extended the existing interferometric fibre link PTB-Strasbourg with a branch connecting the node at Karlsruhe Institute of Technology (KIT) to the Max Planck Institute of Quantum Optics (MPQ) in Garching/Munich. This fibre connection enables chronometric levelling experiments between PTB and MPQ, separated by a line-of-sight distance of about 460 km. Here, we study the performance of the PTB-MPQ fibre link which mainly employs stimulated Brillouin scattering as means of amplification. We consider two configurations: a single-span loop configuration and an antiparallel configuration with frequency transfer over the two concatenated, individually stabilized forward and backward links.
Chronometrie levelling [1-3] is a technique of deriving gravitational potential differences from clock frequency comparisons allowing the determination of height differences. Interferometric optical fibre links (IFL) [4] enable chronometric levelling between distant labs housing optical clocks [5]. An IFL is a phase stabilized telecom fibre link connection establishing a fixed optical phase relationship between two locations up to ~1000 km apart [6]. To perform a chronometric levelling campaign between the stationary optical clocks of the Physikalisch-Technische Bundesanstalt (PTB) and PTB's transportable Strontium clock [7] placed at the Max Planck Institute of Quantum Optics (MPQ) we have established a new 940 km long IFL between the two locations. At both link ends the frequencies of the clock lasers are compared to the 1,5 pm link transfer laser via fs-combs. To enable chronometric levelling experiments at the level of 10 cm height resolution, we aim a fractional frequency uncertainty of the frequency transfer of-18for averaging times of ~40 ks. To monitor the frequency transfer over the complete 940 km long fibre link the signal is sent back from the receiving end to the sender on a second fibre, which allows an out-of-loop characterization using data of the 1880 km loop. We study two different link setups, cf. Fig. 1a: i) a single-span loop configuration with the option to tap off the signal at MPQ with a passive frequency extraction unit [8]. This setup requires monitoring at the sending end only and allows us to investigate an ultralong IFL, even longer than the previous record [9]. And ii) an antiparallel configuration of two concatenated, individually stabilized interferometric fibre links. This setup offers lower instabilities due to a decreased delay-limit [10] but requires setting up and maintaining a stabilization system at both link ends. To compensate the attenuation of the fibres we used fibre Brillouin amplifier modules (FBAM) developed inhouse providing a typical gain of > 40 dB.
We have explored the performance of two ldquodark fibersrdquo of a commercial telecommunication fiber link for a remote comparison of optical clocks. These fibers establish a network in Germany that will eventually link optical frequency standards at PTB with those at the Institute of Quantum Optics (IQ) at the Leibniz University of Hanover, and the Max Planck Institutes in Erlangen (MPL) and Garching (MPQ). We demonstrate for the first time that within several minutes a phase coherent comparison of clock lasers at the few 10-15level can also be accomplished when the lasers are more than 100 km apart. Based on the performance of the fiber link to the IQ we estimate the expected stability for the link from PTB to MPQ via MPL that bridges a distance of approximately 900 km.
We have explored the performance of 2 "dark fibers" of a commercial telecommunication fiber link for a remote comparison of optical clocks. These fibers establish a network in Germany that will eventually link optical frequency standards at PTB with those at the Institute of Quantum Optics (IQ) at the Leibniz University of Hanover, and the Max Planck Institutes in Erlangen (MPL) and Garching (MPQ). We demonstrate for the first time that within several minutes a phase coherent comparison of clock lasers at the few 10(-15) level can also be accomplished when the lasers are more than 100 km apart. Based on the performance of the fiber link to the IQ, we estimate the expected stability for the link from PTB to MPQ via MPL that bridges a distance of approximately 900 km.
Abstract We investigate optical frequency dissemination over a 1400 km long fiber link in looped configuration over a pair of underground fibers between Braunschweig and Strasbourg. This fiber link is the first to combine fiber Brillouin amplifiers with a repeater laser station. Phase-coherent operation over more than five days is demonstrated. We analyze the repeatability of the performance over four campaigns and present results of 65 d in total. The weighted mean of the fractional frequency offset of the transferred optical frequency over the complete data set is (−1.1 ± 0.4)×10–20. By analyzing the stabilization signals of the two individual fibers, the correlation of the phase noise on the two fibers is shown to be >98%.
Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text K. Predehl, R. Holzwarth, T. Udem, T. Hänsch, O. Terra, G. Grosche, B. Lipphardt, and H. Schnatz, "Ultra Precise Frequency Dissemination across Germany – Towards a 900 km Optical Fiber Link from PTB to MPQ," in Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, OSA Technical Digest (CD) (Optica Publishing Group, 2009), paper CTuS2. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article