Fiber-Optic Time Transfer for UTC-Traceable Synchronization for Telecom Networks

Śliwczyński, Ł.; Krehlik, P.; Kołodziej, Jacek; Imlau, H.; Ender, H.; Schnatz, H.; Piester, D.; Bauch, A.

doi:10.1109/mcomstd.2017.1600766st

Cited by 22 publications

(11 citation statements)

References 8 publications

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“…In this scenario, a sub-nanosecond ground time scale could help reduce the trajectory uncertainty coming from the reference-time uncertainty (note, another way of reducing the trajectory uncertainty is to develop a stable space clock as suggested in [39]). Finally, it is interesting to note that in telecommunication, the performance requirement of primary reference clocks has dropped from the ~10 -11 level of frequency uncertainty in 1988 (ITU-T G.811), to 100 ns in 2012 (ITU-T G.8272), and then to 30 ns in 2016 (ITU-T G.8272.1) [40]. Following this trend, one can expect this requirement to drop to a few ns in coming years, which can be challenging for the existing microwave time scales to support.…”

Section: Iv(c) Future Time Keepingmentioning

confidence: 99%

Optical-Clock-Based Time Scale

et al. 2019

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A time scale is a procedure for accurately and continuously marking the passage of time. It is exemplified by Coordinated Universal Time (UTC), and provides the backbone for critical navigation tools such as the Global Positioning System (GPS). Present time scales employ microwave atomic clocks, whose attributes can be combined and averaged in a manner such that the composite is more stable, accurate, and reliable than the output of any individual clock. Over the past decade, clocks operating at optical frequencies have been introduced which are orders of magnitude more stable than any microwave clock. However, in spite of their great potential, these optical clocks cannot be operated continuously, which makes their use in a time scale problematic. In this paper, we report the development of a hybrid microwave-optical time scale, which only requires the optical clock to run intermittently while relying upon the ensemble of microwave clocks to serve as the flywheel oscillator. The benefit of using clock ensemble as the flywheel oscillator, instead of a single clock, can be understood by the Dick-effect limit. This time scale demonstrates for the first time sub-nanosecond accuracy for a few months, attaining a fractional frequency stability of 1.45×10 −16 at 30 days and reaching the 10 −17 decade at 50 days, with respect to UTC. This time scale significantly improves the accuracy in timekeeping and could change the existing time-scale architectures.

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Section: Iv(c) Future Time Keepingmentioning

confidence: 99%

Optical-Clock-Based Time Scale

et al. 2019

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“…The Physikalisch-Technische Bundesanstalt (PTB), Deutsche Telekom Technik GmbH, and AGH University of Science and Technology have collaborated in the field of synchronization of telecom networks by running jointly a series of proof of concept (PoC) experiments [26]. This paper is aimed to describe the most recent optical time transfer (OTT) installation (Section 2) and to report on its performance in the period between 2016 and 2018.…”

Section: Introductionmentioning

confidence: 99%

Calibrated optical time transfer of UTC(k) for supervision of telecom networks

et al. 2018

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We report on the evaluation of the performance of optical time transfer links connecting a facility of Deutsche Telekom in Bremen with the Physikalisch-Technische Bundesanstalt in Braunschweig. In the current configuration three links have been established, two via a hub in Hannover and one using an independent alternate route. They are equipped with electronically stabilized fiber optic time and frequency transfer systems and parallel operation is maintained since December 2016. A novel method of link calibration, composed of two steps (one performed in the laboratory and the second one in the field), to accurately determine the influence of fiber chromatic dispersion is discussed in detail, and a thorough analysis of the uncertainty budget is given. We show that the time transfer performance achieved is difficult to characterize based on measurements with time interval counters that are the standard equipment in timing laboratories and in the telecommunications sector. In our experiments, values of TDEV at the low ps-level at averaging times between 10 4 to 10 6 seconds have been achieved. The uncertainty of time transfer (including all kinds of delays) is of the order of 50 ps in a cascade of links. The results obtained show that such a kind of link is capable to deliver signals to a remote end with an instability being at least two orders of magnitude below the current requirements included in relevant Recommendations of the International Telecommunication Union-Telecommunication Sector (ITU-T). Moreover, the current implementation would allow primary Cs fountain clocks to be compared at the level of their performance, that is characterized by an uncertainty at the low 10-16 level and a frequency instability of the same order of magnitude at one day averaging.

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“…F REQUENCY-STABILIZED lasers are applied in not only precision metrology fields [1]- [3] but also in advanced spectroscopy laboratories [4], astronomy [5], [6] and very long baseline interferometry [7]- [9], telecommunications industries [10], measurement of basic physical parameters [11]- [14], gravitational wave detection [15], low-noise microwave signal generation [16]- [18] and optical clock comparison [19]- [21]. Optical atomic clocks can realize high-precision and accuracy timekeeping and provide an accurate quantum frequency standard.…”

Section: Introductionmentioning

confidence: 99%

A High-Precision Offset Frequency Locking Technique With Delay Line Reference and AOM-Based Compensation

et al. 2021

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We demonstrate a high-precision, high robustness frequency offset locking method,which made the frequency offset between mode-locked laser and continuous-wave laser below less than 3 Hz.The coarse frequency lock control is realized by the feedback control of PZT with electrical delay line as the reference. The fine frequency compensation is realized by feedforward control of an acousto-optic modulator. The fractional frequency instability was 7.4 × 10 −10 for an averaging time of 1 s, 3.3 × 10 −8 for an averaging time of 10,000 s when the narrow linewidth laser is free-running. In this experiment, the fractional frequency instability can be achieved at 1.1 × 10 −15 for an averaging time of 1 s, at 3.6 × 10 −18 for an averaging time of 10,000 s when the system is fine frequency locked. Compared with the unlocked laser, the fractional frequency instability can be improved about 5∼6 orders of magnitude. This work lays the foundation for simple structure, high robustness and high precision laser frequency control situation, such as quantum precision measurement and optical lattice clocks.

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Fiber-Optic Time Transfer for UTC-Traceable Synchronization for Telecom Networks

Cited by 22 publications

References 8 publications

Optical-Clock-Based Time Scale

Optical-Clock-Based Time Scale

Calibrated optical time transfer of UTC(k) for supervision of telecom networks

A High-Precision Offset Frequency Locking Technique With Delay Line Reference and AOM-Based Compensation

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