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Publications (10 of 11) Show all publications
Ebenhag, S. C., Hedekvist, P. O., Rieck, C., Bergroth, M., Krehlik, P. & Sliwczynski, L. (2019). Evaluation of Fiber Optic Time and Frequency Distribution System in a Coherent Communication Network. In: IFCS/EFTF 2019 - Joint Conference of the IEEE International Frequency Control Symposium and European Frequency and Time Forum, Proceedings: . Paper presented at 2019 Joint Conference of the IEEE International Frequency Control Symposium and European Frequency and Time Forum, IFCS/EFTF 2019, 14 April 2019 through 18 April 2019. Institute of Electrical and Electronics Engineers Inc.
Open this publication in new window or tab >>Evaluation of Fiber Optic Time and Frequency Distribution System in a Coherent Communication Network
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2019 (English)In: IFCS/EFTF 2019 - Joint Conference of the IEEE International Frequency Control Symposium and European Frequency and Time Forum, Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2019Conference paper, Published paper (Refereed)
Abstract [en]

A fiber-based time transfer between UTC(SP) and the VLBI-station at Onsala Space Observatory has been evaluated. The transfer uses a single wavelength in an active coherent DWDM-network in unidirectional duplex fibers and is routed through Reconfigurable Optical Add-Drop Multiplexers.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers Inc., 2019
Keywords
fiber optics, time dissemination, traceable, Coherent communication, DWDM networks, Onsala Space Observatory, Reconfigurable optical add-drop multiplexer, Single wavelength, Time and frequencies, Fibers
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-40617 (URN)10.1109/FCS.2019.8856039 (DOI)2-s2.0-85073779075 (Scopus ID)9781538683057 (ISBN)
Conference
2019 Joint Conference of the IEEE International Frequency Control Symposium and European Frequency and Time Forum, IFCS/EFTF 2019, 14 April 2019 through 18 April 2019
Note

Funding text 1: This work was supported by 15SIB05-OFTEN, which has received funding from the EMPIR programme co-financed by the Participating States within Euramet and from the European Union's Horizon 2020 research and innovation programme.

Available from: 2019-11-25 Created: 2019-11-25 Last updated: 2019-11-25Bibliographically approved
Ebenhag, S. C., Hedekvist, P. O., Jarlemark, P. & Sundblad, R. (2019). Redundant Distributed Timescale Traceable to UTC(SP). In: IFCS/EFTF 2019 - Joint Conference of the IEEE International Frequency Control Symposium and European Frequency and Time Forum, Proceedings: . Paper presented at 2019 Joint Conference of the IEEE International Frequency Control Symposium and European Frequency and Time Forum, IFCS/EFTF 2019, 14 April 2019 through 18 April 2019. Institute of Electrical and Electronics Engineers Inc.
Open this publication in new window or tab >>Redundant Distributed Timescale Traceable to UTC(SP)
2019 (English)In: IFCS/EFTF 2019 - Joint Conference of the IEEE International Frequency Control Symposium and European Frequency and Time Forum, Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2019Conference paper, Published paper (Refereed)
Abstract [en]

A variety of commerce needs or requires accurate time, such as air traffic control, bank transactions and computer log file comparisons. Whenever the used time needs to be compared with a timestamp generated by another system, both systems must be traceable to a common reference, such as a local UTC(k) realization. Within this paper a distributed timescale using five nodes across Sweden is presented. The foundation for time keeping at each node is two cesium clocks, which are connected to time analysis equipment and equipment for producing redundant timescales. Both timescales are used and distributed throughout the time node and then prioritized by the local NTP servers, PTP grand masters, and other time distribution services. The timescales are monitored by RISE Research Institute of Sweden to ensure traceability to UTC(SP).To compare the timescales of each location with the other locations, GNSS common view is primarily used with an alternative fiber-based solution as back-up. All available time signals are measured relative to the master timescale, and that data is distributed to the other locations to be used as input in the steering of the local timescales. The NTP servers of the time nodes are directly connected to Internet Exchange points, for central, highly available and fair connectivity to the Internet. 

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers Inc., 2019
Keywords
holdover, redundant, robust, time dissemination, traceable, Location, Air traffic control
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-40616 (URN)10.1109/FCS.2019.8856058 (DOI)2-s2.0-85073793374 (Scopus ID)9781538683057 (ISBN)
Conference
2019 Joint Conference of the IEEE International Frequency Control Symposium and European Frequency and Time Forum, IFCS/EFTF 2019, 14 April 2019 through 18 April 2019
Note

Funding text 1: The project was funded by the Swedish Post and Telecom Authority (PTS).

Available from: 2019-11-25 Created: 2019-11-25 Last updated: 2019-11-25Bibliographically approved
Hedekvist, P. O., Weddig, L. & Ebenhag, S. C. (2018). Analysis and compensation of polarization in an optical frequency transfer through a fiber communication network. In: : . Paper presented at 2018 European Frequency and Time Forum (EFTF) (pp. 253-256).
Open this publication in new window or tab >>Analysis and compensation of polarization in an optical frequency transfer through a fiber communication network
2018 (English)Conference paper, Published paper (Refereed)
Abstract [en]

In the fiber optic link, connecting RISE research facilities in Borås with the Photonics Lab at Chalmers University of Technology in Gothenburg, the signal is substantially distorted by polarization variations. It has been verified that the variations are induced by the electrical power grid, however unknown at which segment of the link that it occurs. While this distortion is effectively handled by standard equipment for the data transmission, it deteriorates the detection of a transmitted ultra-stable frequency, using heterodyne mixing. Thus, the magnitude and severity of this distortion is quantified, and some compensation techniques are evaluated.

Keywords
Optical fiber networks, Optical fiber polarization, Optical fiber amplifiers, Optical variables measurement, fiber, frequency transfer, heterodyne detection, coherent, polarization
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-34324 (URN)10.1109/EFTF.2018.8409044 (DOI)2-s2.0-85050721935 (Scopus ID)
Conference
2018 European Frequency and Time Forum (EFTF)
Available from: 2018-08-07 Created: 2018-08-07 Last updated: 2019-01-07Bibliographically approved
Ebenhag, S.-C., Hedekvist, P. O. & Weddig, L. (2018). Measurement and Analysis of Polarization Variations in an Optical Coherent Fiber Communication Network Utilized for Time and Frequency Distribution. In: : . Paper presented at 49th Annual Precise Time and Time Interval Systems and Applications Meeting January 29 - 1, 2018 Hyatt Regency Reston Reston, Virginia, USA (pp. 233-236).
Open this publication in new window or tab >>Measurement and Analysis of Polarization Variations in an Optical Coherent Fiber Communication Network Utilized for Time and Frequency Distribution
2018 (English)Conference paper, Published paper (Refereed)
Abstract [en]

When fiber optic communication networks are used for ultra-stable timing or frequency transfer, there will always be an influence of polarization variation to some extent. The variations can be induced by e.g. mechanical vibration or electromagnetic effects from adjacent power lines. The output polarization from a 120 km fiber transmission of an ultra-stable optical frequency is analyzed and the requirements of a compensation device are quantified.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:ri:diva-37576 (URN)10.33012/2018.15620 (DOI)
Conference
49th Annual Precise Time and Time Interval Systems and Applications Meeting January 29 - 1, 2018 Hyatt Regency Reston Reston, Virginia, USA
Available from: 2019-01-24 Created: 2019-01-24 Last updated: 2019-02-01Bibliographically approved
Ebenhag, S.-C., Hedekvist, P. O., Liström, S. & Bergroth, M. (2017). Time and Frequency Dissemination in an All-optical Coherent Fiber Communication Network. In: : . Paper presented at 48th Annual Precise Time and Time Interval Systems and Applications Meeting January 30 - 2, 2017 Hyatt Regency Monterey Monterey, California, USA (pp. 306-311). Institute of Navigation
Open this publication in new window or tab >>Time and Frequency Dissemination in an All-optical Coherent Fiber Communication Network
2017 (English)Conference paper, Published paper (Refereed)
Abstract [en]

A nationwide fiber optic communication network utilizing state-of-the-art technologies with data modulation both in the polarization and in multi-level amplitude and phase is being deployed in Sweden. The network is operated by the Swedish University computer Network, and connects all universities and several research facilities in the country through redundant connections. Since there is a limited amount of clients connected to the network, each client will be assigned a personal wavelength. With a network that is all-optical through an advanced utilization of dynamically reconfigurable optical add and drop multiplexers, each wavelength can theoretically be connected to any other client within the network, enabling broadcasting on allocated wavelengths. The coherent modulation formats also enables signal recovery through electronic digital signal processing after detection, and no optical dispersion compensation is thereby installed. This new network scheme enables a brand new implementation of frequency and time dissemination in the network. The omission of dispersion compensation fibers enhances the symmetry in duplex fiber pair transmission. These optical add-drop installations allow for future efficient frequency and time signal broadcasting from reference nodes operated by distributors such as SP Technical Research Institute of Sweden to users connected to the network.

Place, publisher, year, edition, pages
Institute of Navigation, 2017
Keywords
Broadcasting, Digital signal processing, Dispersion compensation, Drops, Fibers, Light transmission, Modulation, Signal reconstruction, Dispersion-compensation fibers, Fiber communication networks, Fiber optic communications, Optical dispersion compensation, Redundant connections, Research facilities, State-of-the-art technology, Time and frequency disseminations
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:ri:diva-37577 (URN)10.33012/2017.14975 (DOI)2-s2.0-85047021729 (Scopus ID)
Conference
48th Annual Precise Time and Time Interval Systems and Applications Meeting January 30 - 2, 2017 Hyatt Regency Monterey Monterey, California, USA
Available from: 2019-01-24 Created: 2019-01-24 Last updated: 2019-03-07Bibliographically approved
Ebenhag, S.-C., Zelan, M., Hedekvist, P. O., Karlsson, M. & Josefsson, B. (2016). Coherent optical two-way frequency transfer in a commercial DWDM network. In: Proceedings of the Annual Precise Time and Time Interval Systems and Applications Meeting: . Paper presented at 47th Annual Precise Time and Time Interval Systems and Applications Meeting (PTTI 2016), 25-28 January, 2016, Monterey, US (pp. 116-120).
Open this publication in new window or tab >>Coherent optical two-way frequency transfer in a commercial DWDM network
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2016 (English)In: Proceedings of the Annual Precise Time and Time Interval Systems and Applications Meeting, 2016, p. 116-120Conference paper, Published paper (Refereed)
Abstract [en]

An experimental fiber connection for ultra-stable optical frequency transfer is established between SP Technical Research Institute of Sweden in Borås and Chalmers University of Technology in Gothenburg. The distance is approximately 60 km, and the connection is implemented in the Swedish University Computer Network. The sites are connected through an active flexible communication network where each optical channel can be configured with terminal equipment based on the user needs. The network is implemented with unidirectional optical amplifiers and duplex fibers. The signal quality and the stability when sending an optical coherent frequency utilizing a wavelength in a DWDM system fiber pair, is evaluated within this work. The aim of the system is to be ultra-stable which corresponds to a stability of 10-13 for t = 1 s (Overlapping Allan Variance), as well as providing the ability to distribute monitored ultra-stable frequency with a future traceability to UTC (SP) to multiple users within the future network. This paper describes the current status and results from the frequency transfer between SP and Chalmers.

Keywords
Dense wavelength division multiplexing, Fiber amplifiers, Optical communication, Platinum alloys, System stability, Telecommunication networks, Chalmers University of Technology, Coherent frequency, Fiber connections, Flexible communication, Frequency transfer, Stable frequencies, Technical research, Terminal equipment, Optical communication equipment
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-27665 (URN)10.33012/2016.13154 (DOI)2-s2.0-84964987466 (Scopus ID)
Conference
47th Annual Precise Time and Time Interval Systems and Applications Meeting (PTTI 2016), 25-28 January, 2016, Monterey, US
Available from: 2016-12-22 Created: 2016-12-21 Last updated: 2019-06-13Bibliographically approved
Ebenhag, S.-C., Zelan, M., Hedekvist, P. O. & Karlsson, M. (2016). Implementation of an optical fiber frequency distribution via commercial DWDM. In: 2016 IEEE International Frequency Control Symposium (IFCS): . Paper presented at 70th IEEE International Frequency Control Symposium (IFCS 2016), May 9-12, 2016, New Orleans, US. , Article ID 7563586.
Open this publication in new window or tab >>Implementation of an optical fiber frequency distribution via commercial DWDM
2016 (English)In: 2016 IEEE International Frequency Control Symposium (IFCS), 2016, article id 7563586Conference paper, Published paper (Refereed)
Abstract [en]

The rapid development in communication infrastructure over the past decades entails an increasing dependence on time and frequency, as well as its redundant distribution. This places demands not only on already existing distribution methods, but also on the development of new ones to meet future needs. To meet these demands several research groups are working on high performance fiber-based frequency transfer techniques. The best achieved performance so far is the techniques using a single bi-directional fiber connection, with customized bi-directional optical amplifiers [1]. The objective of this project is to develop a method that is compatible with data communication in DWDM-systems, i.e. using the existing infrastructure, as well as to be complementary technique for time and frequency distribution. Even though it is likely to have worse performance than the bi-directional system in terms of frequency stability, it will allow for the impassable obligation to follow the deployed structure of telecom networks. The establishment and early results of the non-stabilized link has been previously presented [2, 3]. The ongoing evaluation and improvement will be aimed at finding relevant performance specifications for a connection using this technique. The work presented here is the most recent results of the frequency transfer and discusses the future plans for the fiber connection, including the added time transfer method. If proven successful, the long-term objective is to establish a distribution network for optical frequency references in Sweden.

Keywords
DWDM, Frequency transfer, Optical fiber, Optical fiber network, Dense wavelength division multiplexing, Fibers, Optical fibers, Bi-directional optical amplifiers, Communication infrastructure, Complementary techniques, Evaluation and improvement, Optical fiber networks, Optical frequency references, Performance specifications, Fiber amplifiers
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-27623 (URN)10.1109/FCS.2016.7563586 (DOI)2-s2.0-84990998418 (Scopus ID)9781509020911 (ISBN)
Conference
70th IEEE International Frequency Control Symposium (IFCS 2016), May 9-12, 2016, New Orleans, US
Note

References: Droste, S., Ozimek, F., Udem, T., Predehl, K., Hansch, T.W., Schnatz, H., Grosche, G., Holzwarth, R., Optical-frequency transfer over a single-span 1840 km fiber link (2013) Physical Review Letters, 111 (11), p. 110801; Ebenhag, S.C., Zelan, M., Hedekvist, P.O., Karlsson, M., Josefsson, B., Two-way coherent frequency transfer in a commercial DWDM communication network in Sweden (2015) Frequency Control Symposium & the European Frequency and Time Forum (FCS), 2015 Joint Conference Ofthe IEEE International, pp. 276-279; Zelan, M., Ebenhag, S.C., Hedekvist, P.O., Karlsson, M., Josefsson, B., Two-way coherent optical frequency transfer using unidirectional amplifiers in parallel fibers (2015) 8th Symposium of Frequency Standards and Metrology, , Oct. 12-16, 2015, Potsdam, D. Also submitted to Journal ofPhysics: Conference Series (JPCS)

Available from: 2016-12-22 Created: 2016-12-21 Last updated: 2019-06-24Bibliographically approved
Ebenhag, S.-C., Zelán, M., Hedekvist, P. O., Karlsson, M. & Josefsson, B. (2015). Two-way coherent frequency transfer in a commercial DWDM communication network in Sweden. In: 2015 Joint Conference of the IEEE International Frequency Control Symposium & the European Frequency and Time Forum: . Paper presented at 2015 Joint Conference of the IEEE International Frequency Control Symposium and the European Frequency and Time Forum (FCS 2015), April 12-16, 2015, Denver, US (pp. 276-279). , Article ID 7138840.
Open this publication in new window or tab >>Two-way coherent frequency transfer in a commercial DWDM communication network in Sweden
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2015 (English)In: 2015 Joint Conference of the IEEE International Frequency Control Symposium & the European Frequency and Time Forum, 2015, p. 276-279, article id 7138840Conference paper, Published paper (Refereed)
Abstract [en]

An experimental fiber link is being established between SP Technical Research Institute of Sweden in Boras and Chalmers University of Gothenburg in Sweden. The one way fiber length is about 60 km and implemented in SUNET (Swedish University Network). The aim of the project is to evaluate the signal quality when sending a stable optical frequency utilizing a wavelength in a DWDM (Dense Wavelength Division Multiplexing) system fiber pair. The experiment uses a channel in the DWDM with the wavelength of 1542.14 nm. This wavelength is within the C band and is therefore compatible with common Erbium doped amplifiers in this network. Another aim of the system is to be ultra-stable which corresponds to a stability of 1×10-13 for τ = 1 s as well as providing the ability to distribute monitored ultra-stable frequency with a future traceability to UTC (SP) (National realization of Universal Time Coordinated within Sweden) to multiple users within the network. Measurements of an optical frequency transfer using a fiber-link based on unidirectional light signals in parallel fibers have shown promising results in a free-running setup and in a lab environment. The fractional frequency stability, analyzed as the Overlapping Allan deviation, is approximately 3×10-13 at τ = 10 s and almost 1×10-14 at 105 s.

Keywords
DWDM, Frequency transfer, Optical fiber, Optical fiber network
National Category
Engineering and Technology
Identifiers
urn:nbn:se:ri:diva-37677 (URN)10.1109/FCS.2015.7138840 (DOI)2-s2.0-84943339426 (Scopus ID)978-1-4799-8866-2 (ISBN)
Conference
2015 Joint Conference of the IEEE International Frequency Control Symposium and the European Frequency and Time Forum (FCS 2015), April 12-16, 2015, Denver, US
Available from: 2019-01-29 Created: 2019-01-29 Last updated: 2019-07-12Bibliographically approved
Bideberg, G., Ebenhag, S. C., Jaldehag, K. & Hedekvist, P. O. (2014). Construction of a secure clock location for alternative realization of UTC(SP). In: 2014 European Frequency and Time Forum (EFTF): . Paper presented at 28th European Frequency and Time Forum (EFTF 2014), June 23-26, 2014, Neuchatel, Switzerland (pp. 498-501). , Article ID 7331545.
Open this publication in new window or tab >>Construction of a secure clock location for alternative realization of UTC(SP)
2014 (English)In: 2014 European Frequency and Time Forum (EFTF), 2014, p. 498-501, article id 7331545Conference paper, Published paper (Refereed)
Abstract [en]

Swedish standard time is regulated by law to follow UTC as maintained by the BIPM. The atomic clocks that are used to implement UTC(SP), the realization of UTC in Sweden, are located at four different sites and are reported to TAI using data from TWSTFT and GNSS links. The activities in the Time and Frequency laboratory at SP are presently undergoing an expansion with the construction of a new additional secure site and the implementation of a distributed time scale.

Keywords
Distributed timescale, NMI, UTC, UTC(SP), Distributed time, Standard time, Swedishs, Time and frequencies, Time-scales
National Category
Engineering and Technology
Identifiers
urn:nbn:se:ri:diva-38525 (URN)10.1109/EFTF.2014.7331545 (DOI)2-s2.0-84971383871 (Scopus ID)978-1-4799-5252-6 (ISBN)
Conference
28th European Frequency and Time Forum (EFTF 2014), June 23-26, 2014, Neuchatel, Switzerland
Available from: 2019-05-06 Created: 2019-05-06 Last updated: 2019-07-10Bibliographically approved
Hedekvist, P. O., Jaldehag, K., Ebenhag, S.-C., Rieck, C., Bideberg, G. & Jaldehag, K. (2013). Time and Frequency Activities at SP. In: : . Paper presented at Proceedings of the 45th Annual Precise Time and Time Interval Systems and Applications Meeting, December 2 - 5, 2013, Hyatt Regency Bellevue, Bellevue, Washington (pp. 21-25).
Open this publication in new window or tab >>Time and Frequency Activities at SP
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2013 (English)Conference paper, Published paper (Other academic)
Abstract [en]

The national Time and Frequency laboratory of Sweden is a part of SP Technical Research Institute of Sweden since 1995. The laboratory is responsible for maintaining the official realization of Swedish standard time and the dissemination of it within Sweden. The objectives of the laboratory include supporting and making it accessible to Swedish industry and authorities with accurate measures of Time and Frequency by instrument calibration, knowledge-transfer, time dissemination, research and development. Swedish standard time is regulated by law to follow UTC as achieved and maintained by the BIPM. The atomic clocks that are used to implement UTC(SP), the realization of UTC in Sweden, are located at five different sites and are reported to TAI using data from TWSTFT and GNSS links. The activities in the Time and Frequency laboratory at SP is presently undergoing an expansion, with the construction of a new additional secure site, the implementation of a distributed time scale and the participation in the Galileo time scale.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:ri:diva-38800 (URN)
Conference
Proceedings of the 45th Annual Precise Time and Time Interval Systems and Applications Meeting, December 2 - 5, 2013, Hyatt Regency Bellevue, Bellevue, Washington
Available from: 2019-05-14 Created: 2019-05-14 Last updated: 2019-05-15Bibliographically approved
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-0801-3124

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