| 1. |
- Ebenhag, Sven-Christian, 1976, et al.
(författare)
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One way time transfer utilizing active detection of propagation delay variations of dual wavelenghts in an optical fiber network
- 2011
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Ingår i: 43rd Annual Precise Time and Time Interval Systems and Applications Meeting 2011; Long Beach, CA; United States; 14 November 2011 through 17 November 2011. - 9781622767953 ; , s. 9-16
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Konferensbidrag (refereegranskat)abstract
- For time transfer on baselines exceeding 100km, GPS is the most common technical solution. The main benefit is that it is easy to install, but it is a single point of failure and it is sensitive to interruption by radio noise. For time transfer requiring high reliability a complementary backup method is therefore desirable, and time and frequency transfer utilizing optical fiber is a favorable alternative technique. The connectivity is simplified by the deployment of dense fiber optic communication networks in most countries and since it does not rely on transmission using radio waves in open air, it is robust against perturbations. The simplest and most straightforward method for high performance time transfer is the two-way technique, which is an excellent choice when the user has access to the whole system, and when both transmission paths are equal or with a known and predictable asymmetry. Furthermore it is most practical when the numbers of users are limited and when no security issues limit the bidirectional connectivity.A proof-of-concept for an alternative technique for fiber based time and frequency transfer, utilizing a one-way co-propagation of two light waves, has been presented previously. The technique utilizes dual wavelengths and measures the difference in group velocity to estimate the delay variation of the timing signal in one of the wavelength channels. This paper presents the recent improvements on this method, including new equipment, new algorithm and a demonstration of real-time compensation of delay time variations.
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| 2. |
- Ebenhag, Sven-Christian, 1976, et al.
(författare)
-
Time Transfer between UTC(SP) and UTC(MIKE) Using Frame Detection in Fiber-Optical Communication networks
- 2011
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Ingår i: 43rd Precise Time and Time Interval (PTTI) Systems and Applications Meeting. - 9781622767953 ; , s. 431-441
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Konferensbidrag (refereegranskat)abstract
- This paper presents recent results from a time transfer method using passive listening and detection of SDH frame headers in fiber-optical networks. The results are based on an experimental fiber-link that is implemented between the national time and frequency laboratories at SP in Borås, Sweden and at MIKES in Espoo, Finland with an intermediate connection at STUPI time and frequency facility in Stockholm, Sweden. The total fiber length exceeds 1129 km and is implemented in SUNET (Swedish University Network) and FUNET (Finnish University and Research Network). The two networks are connected via NORDUnet (Nordic Infrastructure for Research & Education) and the links are DWDM-based (Dense Wavelength Division Multiplexing).Both SP and MIKES maintains local representations of UTC and contributes with clock data to TAI, which gives the opportunity to compare the fiber-based method with those independent methods that are used regularly by the laboratories for the links to UTC. Preliminary results show that a time transfer stability of less than 10 picoseconds is obtained for averaging times of a few hundred seconds. The results also show that the method suffers from daily variations of a few nanoseconds, presumable due to temperature sensitive network equipment and asymmetric fiber paths. Nevertheless, a comparison to GPS carrier phase time transfer over three months shows an rms-agreement of less than 1 nanosecond.
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