Optical frequency transfer with below 10(-21) uncertainty using a DFB-laser-based fiber Brillouin amplifier

verfasst von: Jaffar Emad Kadum, Jingxian Ji, Alexander Kuhl, Mattias Misera, Thomas Waterholter, Sebastian Koke
Abstract: Exploiting the outstanding performance of optical atomic clocks for improved timekeeping, relativistic geodesy, and fundamental physics beyond the standard model demands comparing distant state-of-the-art optical clocks. Interferometric optical fiber links have been demonstrated as an eminent method for such frequency comparisons over distances up to thousands of kilometers. However, for such distances, the optical fiber attenuation mandates signal amplification. Fiber Brillouin amplification (FBA) has been proven as an efficient amplification technique for coherent frequency transfer. Demonstrated FBA schemes have been designed based on costly narrow-linewidth pump lasers and analog pump-to-signal phase locking schemes. Furthermore, the high pump power requirement of these FBAs hinders the integration of FBA-based frequency dissemination on fiber connections for shared telecommunication signals in the C-band. In this paper, we propose and experimentally demonstrate a novel FBA module (FBAM) employing cost-effective distributed feedback (DFB) pump lasers assisted by a digital phase locking scheme based on a field programmable gated array. The new FBAM is compact, cost-effective, and directly applicable to different bands, which opens up new opportunities to establish a frequency metrology infrastructure within existing telecommunication fiber networks. Additionally, the small-footprint of the DFB-FBAM allows for frequent amplification stages with lower pump power to reach continental scale optical metrology links with an optimized signal-to-noise ratio. We characterized the DFB-FBAM's frequency transfer uncertainty using a two-way layout over an in-lab 100 km long optical fiber link and reach a fractional frequency instability of 9.3 × 10-22 at a 10 ks integration time. The DFB-FBAM characterizations show uncertainty contributions of (-2.1 ± 3.3) × 10-22 and below for averaging times >100 ks. For the first time, we assess the temporal Brillouin frequency shift variations in an underground fiber link and implement a scheme to track these changes in a remote FBAM.
Externe Organisation(en): DLR-Institut für Satellitengeodäsie und Inertialsensorik
Physikalisch-Technische Bundesanstalt (PTB)
Typ: Artikel
Journal: APL Photonics
Band: 8
ISSN: 2378-0967
Publikationsdatum: 03.2023
Publikationsstatus: Veröffentlicht
Peer-reviewed: Ja
Elektronische Version(en): https://doi.org/10.1063/5.0133919 (Zugang: Offen)

BibTeX

@article{9804a71fdeca465791cd7ddd3d41931b,
title = "Optical frequency transfer with below 10(-21) uncertainty using a DFB-laser-based fiber Brillouin amplifier",
abstract = "Exploiting the outstanding performance of optical atomic clocks for improved timekeeping, relativistic geodesy, and fundamental physics beyond the standard model demands comparing distant state-of-the-art optical clocks. Interferometric optical fiber links have been demonstrated as an eminent method for such frequency comparisons over distances up to thousands of kilometers. However, for such distances, the optical fiber attenuation mandates signal amplification. Fiber Brillouin amplification (FBA) has been proven as an efficient amplification technique for coherent frequency transfer. Demonstrated FBA schemes have been designed based on costly narrow-linewidth pump lasers and analog pump-to-signal phase locking schemes. Furthermore, the high pump power requirement of these FBAs hinders the integration of FBA-based frequency dissemination on fiber connections for shared telecommunication signals in the C-band. In this paper, we propose and experimentally demonstrate a novel FBA module (FBAM) employing cost-effective distributed feedback (DFB) pump lasers assisted by a digital phase locking scheme based on a field programmable gated array. The new FBAM is compact, cost-effective, and directly applicable to different bands, which opens up new opportunities to establish a frequency metrology infrastructure within existing telecommunication fiber networks. Additionally, the small-footprint of the DFB-FBAM allows for frequent amplification stages with lower pump power to reach continental scale optical metrology links with an optimized signal-to-noise ratio. We characterized the DFB-FBAM's frequency transfer uncertainty using a two-way layout over an in-lab 100 km long optical fiber link and reach a fractional frequency instability of 9.3 × 10-22 at a 10 ks integration time. The DFB-FBAM characterizations show uncertainty contributions of (-2.1 ± 3.3) × 10-22 and below for averaging times >100 ks. For the first time, we assess the temporal Brillouin frequency shift variations in an underground fiber link and implement a scheme to track these changes in a remote FBAM.",
author = "Kadum, {Jaffar Emad} and Jingxian Ji and Alexander Kuhl and Mattias Misera and Thomas Waterholter and Sebastian Koke",
note = "Funding Information: This project received funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany{\textquoteright}s Excellence Strategy—EXC-2123 QuantumFrontiers Grant No. 390837967.",
year = "2023",
month = mar,
doi = "10.1063/5.0133919",
language = "English",
volume = "8",
journal = "APL Photonics",
issn = "2378-0967",
publisher = "AIP Publishing LLC",
number = "3",
}