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  • 1.
    Bideberg, Glenn
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Ebenhag, Sven-Christian
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Construction of a secure clock location for alternative realization of UTC(SP)2014In: 2014 European Frequency and Time Forum (EFTF), 2014, p. 498-501, article id 7331545Conference 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.

  • 2.
    Ebenhag, Sven-Christian
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation. Chalmers University of Technology, Sweden.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation. Chalmers University of Technology, Sweden.
    Real-time phase stabilization utilizing two color one-way frequency transfer2012In: 2012 IEEE International Frequency Control Symposium, IFCS 2012, Proceedings, 2012, , p. 667-672p. 667-672, article id 6243710Conference paper (Refereed)
    Abstract [en]

    The two color one-way frequency transfer in optical fiber is an alternative method to two-way time and frequency transfer that is useful if there are unknown asymmetries in the connection. The method is possible to use in existing infrastructure and is able to coexist with data channels for example in WDM systems, which make it possible to broadcast to multiple users and enables the user to be anonymous to the time or frequency transfer. The goal is to develop a stable one-way transfer method comparable with well-established two-way methods, with a precision and accuracy comparable to readily used satellite-based methods. The recent progress in the determination of the error sources introduced by the equipment used for phase comparisons as well as results from increasing the modulation frequency is presented. It is shown how the increase in frequency also enhances the precision, and a result from real time phase stabilization is presented. Furthermore, results from the introduction of a third wavelength are presented, with experimental data over one week periods.

  • 3.
    Ebenhag, Sven-Christian
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Active detection of propagation delay variations in single way time transfer utilizing dual wavelengths in an optical fiber network2011In: Proceedings of 5th Joint Conference of the 65th IEEE International Frequency Control, 2011, , p. 5977328Conference paper (Refereed)
  • 4.
    Ebenhag, Sven-Christian
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    One way time transfer utilizing active detection of propagation delay variations of dual wavelenghts in an optical fiber network2011In: 43rd Annual Precise Time and Time Interval Systems and Applications Meeting 2011, 2011, , p. 9-16Conference paper (Refereed)
  • 5.
    Ebenhag, Sven-Christian
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Two-color One-Way Frequency Transfer in a Mtetropolitan Optical Fiber Data Network.2013In: NCSLI International Measure, Vol. 8, no 2, p. 10-Article in journal (Refereed)
  • 6.
    Ebenhag, Sven-Christian
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik. Chalmers University of Technology, Sweden.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik. Chalmers University of Technology, Sweden.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Two-Color One-Way FrequencyTransfer in a Metropolitan OpticalFiber Data Network2013In: NCSLI Measure, ISSN 1931-5775, Vol. 8, no 2Article in journal (Refereed)
    Abstract [en]

    Two-color one-way frequency transfer through one strand of optical fiber is an alternative method to two-way frequencytransfer, and is useful if unknown asymmetries exist in the link due to different paths for each direction. The term “twocolor”refers to the ability to send signals at two different wavelengths utilizing the same fiber in one direction. The methodis suitable for implementation in existing urban Single Mode Fiber networks, for instance in networks that are utilized for dataand television communication. It is therefore able to coexist with data channels in wavelength-division multiplexing (WDM)systems. It performs as a dynamical control of transit time and simultaneously enables a real-time phase stabilized output signal.This paper presents results from a comparison of two cesium beam frequency standards separated by about 3 km over an opticalfiber network located in a metropolitan area in Sweden. The cesium standards were simultaneously compared to each other witha Global Positioning System (GPS) satellite link and over optical fibers, so that the optical fiber technique could be evaluatedwith respect to the GPS technique. The difference in frequency stability between the two methods is shown to be about 3 × 10-15over an averaging interval of 10 000 s.1. IntroductionThe need for high accuracy time and frequencytransfer has significantly increased over thelast decade. Users with the most demandingrequirements for the characterization of remotelylocated time and frequency standardsare investigating the use of optical fibers, asthe accuracy and stability of methods based onGNSS (Global Navigation Satellite Systems)such as Global Positioning System (GPS) appearto be reaching their limits. Recent workin the field of optical frequency transfer showsresults with potential accuracies below 10-17obtained in less than a day, demonstrating thatthe technique is useful for the comparison ofoptical frequency standards [1, 2]. Most of theoptical frequency transfer methods or laserstabilizations [3] focus on two-way frequencytransfer [4], whether it uses the optical phase[5-10] or intensity modulation at microwavefrequencies [11], dark fiber, or data protocolsutilized for timing in wavelength division multiplexingchannels [12-14]. When two-wayfrequency transfer methods are used, there is apresumption that the signals delays are equivalent(symmetrical) in both directions, but inmost cases the two counter wise transmissionpaths are asymmetrical and this introduces a

  • 7.
    Ebenhag, Sven-Christian
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Rieck, Carsten
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jarlemark, Per
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Time transfer between UTC(SP) and UTC(MIKE) using frame detection in fiber-optical communication networks2011In: 43rd Annual Precise Time and Time Interval Systems and Applications Meeting 2011, 2011, , p. 431-441Conference paper (Refereed)
  • 8.
    Ebenhag, Sven-Christian
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jarlemark, Per
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Emardson, Ragne
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Rieck, Carsten
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Löthberg, Peter
    Measurements and Error Sources in Time Transfer Using Asynchronous Fiber Network2010In: IEEE Transactions on instrumentation and measurement, Vol. 59, no 7, p. 1918-1924Article in journal (Refereed)
  • 9.
    Ebenhag, Sven-Christian
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Hedekvist, Per Olof
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Jarlemark, Per
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Sundblad, Ragnar
    Netnod Internet Exchange, Sweden.
    Redundant Distributed Timescale Traceable to UTC(SP)2019In: 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 (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. 

  • 10.
    Ebenhag, Sven-Christian
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Hedekvist, Per Olof
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Liström, Stefan
    SUNET Swedish University Computer Network, Sweden.
    Bergroth, Magnus
    NORDUnet, Sweden.
    Time and Frequency Dissemination in an All-optical Coherent Fiber Communication Network2017Conference 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.

  • 11.
    Ebenhag, Sven-Christian
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Hedekvist, Per Olof
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Rieck, Carsten
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Bergroth, Magnus
    SUNET, Sweden.
    Krehlik, Przemyslaw
    AGH University of Science and Technology, Poland.
    Sliwczynski, Lukasz
    AGH University of Science and Technology, Poland.
    Evaluation of Fiber Optic Time and Frequency Distribution System in a Coherent Communication Network2019In: 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 (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.

  • 12.
    Ebenhag, Sven-Christian
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Hedekvist, Per Olof
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Weddig, Ludvig
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Measurement Science and Technology.
    Measurement and Analysis of Polarization Variations in an Optical Coherent Fiber Communication Network Utilized for Time and Frequency Distribution2018Conference 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.

  • 13.
    Ebenhag, Sven-Christian
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation. Chalmers University of Technology, Sweden.
    Wingqvist, Claes
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation. Chalmers University of Technology, Sweden.
    Real-time phase stable one-way frequency transfer over optical fiber2012In: EFTF 2012 - European Frequency and Time Forum, Proceedings, 2012, , p. 206-210p. 206-210, article id 6502368Conference paper (Refereed)
    Abstract [en]

    The fundamental and most straightforward method for high performance time and frequency transfer is the two-way technique, which is suitable 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 concerns limit the bidirectional connectivity.

  • 14.
    Ebenhag, Sven-Christian
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Zelan, Martin
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Karlsson, Magnus
    Chalmers University of Technology, Sweden.
    Implementation of an optical fiber frequency distribution via commercial DWDM2016In: 2016 IEEE International Frequency Control Symposium (IFCS), 2016, article id 7563586Conference 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.

  • 15.
    Ebenhag, Sven-Christian
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Zelan, Martin
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Karlsson, Magnus
    Chalmers University of Technology, Sweden.
    Josefsson, Börje
    SUNET Swedish University Computer Network, Sweden.
    Coherent optical two-way frequency transfer in a commercial DWDM network2016In: Proceedings of the Annual Precise Time and Time Interval Systems and Applications Meeting, 2016, p. 116-120Conference 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.

  • 16.
    Ebenhag, Sven-Christian
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Zelán, Martin
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Karlsson, Magnus
    Chalmers University of Technology, Sweden.
    Josefsson, Börje
    SUNET Swedish University Computer Network, Sweden.
    Two-way coherent frequency transfer in a commercial DWDM communication network in Sweden2015In: 2015 Joint Conference of the IEEE International Frequency Control Symposium & the European Frequency and Time Forum, 2015, p. 276-279, article id 7138840Conference 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.

  • 17.
    Emardson, Ragne
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Nilsson, Mattias
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Ebenhag, Sven-Christian
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jarlemark, Per
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Rieck, Carsten
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Johansson, Jan
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik. RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Pendrill, Leslie
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Löthberg, Peter
    Nilsson, Håkan
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Time Transfer by Passive Listening over 10 Gb/s Optical Fiber2008In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 57, no 11, p. 2495-2501Article in journal (Refereed)
  • 18.
    Hanssen, James L.
    et al.
    US Naval Observatory, USA.
    Ekström, Christopher R.
    US Naval Observatory, USA.
    Ebenhag, Sven-Christian
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Evaluation of time transfer units for time and frequency transfer in optical fibers utilizing a passive technique based on SONET/SDH2012In: 44th Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting 2012, 2012, , p. 371-376p. 371-376Conference paper (Refereed)
    Abstract [en]

    The time transfer method of using passive listening and detection of SDH frame headers in fiberoptical networks has been presented earlier. Previous results, using commercialized equipment and commercial fiber-links, have shown that time transfer with a precision of the order of a few nanoseconds is possible over links with network distances exceeding 1100 km. The motivation of the work has been to develop an alternative and complementary time transfer method using existing infrastructure and to make it accessible to regular users of time keeping equipment. All previous reported experimental results were performed by SP Technical Research Institute of Sweden in commercial data communication networks in Sweden and Finland. This paper will report on the recent results from an experimental fiber test network implemented at the U.S. Naval Observatory. The fiber network is in a loop-back configuration with the two node elements in the same rack. The fiber link that connects the nodes is in an environmental chamber that allows a means to apply controlled fiber length fluctuations to the link. The performance of the Time Transfer Unit (TTU) was evaluated in this setting. This will be the first independent evaluation of the TTU equipment.

  • 19.
    Hedekvist, Per Olof
    et al.
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Ebenhag, Sven-Christian
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Rieck, Carsten
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Wallberg, D.
    Sunet, Sweden.
    Bergroth, M.
    NORDUnet, Sweden.
    Fiber Optic Time Transfer from UTC(k) to a VLBI Antenna in a Coherent Communication Network2022In: 2022 Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium, EFTF/IFCS 2022 - Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2022Conference paper (Refereed)
    Abstract [en]

    The local time scale at Onsala Space Observatory is connected to UTC(SP) through a White Rabbit time transfer system operating on the Swedish University Computer Network SUNET. The time transfer enables a robust synchronization of the VLBI and the IGS stations operating at the observatory and can potentially improve the reliability and availability of traceable time at sufficient accuracy. Several months of data are gathered to evaluate long term events and stability metrics. 

  • 20.
    Hedekvist, Per Olof
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Ebenhag, Sven-Christian
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Rieck, Carsten
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Bideberg, Glenn
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Jaldehag, Kenneth
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik.
    Time and Frequency Activities at SP2013Conference 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.

  • 21.
    Jaldehag, Kenneth
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation. Chalmers University of Technology, Sweden.
    Ebenhag, Sven-Christian
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation. Chalmers University of Technology, Sweden.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Two color one-way frequency transfer in an urban optical fiber network2013In: 2013 Joint European Frequency and Time Forum and International Frequency Control Symposium, EFTF/IFC, 2013, , p. 1010-1013p. 1010-1013, article id 6702163Conference paper (Refereed)
    Abstract [en]

    SP Technical Research Institute of Sweden has previously presented results with a two color one-way method. This method is an alternative method to two-way time and frequency transfer that is useful if there are unknown asymmetries in the connection. The method is possible to use in existing infrastructure and is able to coexist with data channels for example in WDM systems, which make it possible to broadcast to multiple users and enables the user to be anonymous to the time or frequency transfer. This paper will present the results from the analysis when implementing the technique in an urban commercial optical fiber data communication WDM network between two clock labs in Sweden connecting two cesium clocks to each other for frequency comparison. The evaluation is performed with two wavelengths 8 nm apart on 6 km of installed fiber in an urban city network. The transmitter and the receiver are installed in an electromagnetically shielded room several meters below ground, and the fiber runs to a building at a distance of 3 km, and then back again. The comparison will be within the laboratory, eliminating any errors from a reference system. Results and conclusion from this evaluation reveals the propagation delay variations in the propagation distance and will display the need of compensation for these variations.

  • 22.
    Jaldehag, Kenneth
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Ebenhag, Sven-Christian
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Rieck, Carsten
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Time transfer using frame detection in fiber-optical communication networks: New hardware2011In: 5th Joint Conference of the 65th IEEE International Frequency Control Symposium, IFCS 2011, 2011, , p. 5977323Conference paper (Refereed)
  • 23.
    Jaldehag, Kenneth
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Hedekvist, Per Olof
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Ebenhag, Sven-Christian
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Mätteknik, Kommunikation.
    Active optical pre-compensation in short range frequency transfer in optical single-mode fiber2011In: Proceedings of the IEEE International Frequency Control Symposium and Exposition; 5th Joint Conf. of the 65th IEEE Int. Frequency Control Symposium,, 2011, , p. 5977329Conference paper (Refereed)
  • 24.
    Lindblom, Magnus
    et al.
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Patzauer, Maximilian
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Vogt, Ulrich
    KTH Royal Institute of Technology, Sweden.
    Wilbur, Scott
    University of Sheffield, UK.
    Safari Yazd, Nazila
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Hey Tow, Kenny
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Margulis, Walter
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Claesson, Åsa
    RISE Research Institutes of Sweden, Digital Systems, Smart Hardware.
    Ebenhag, Sven-Christian
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Flexible Liquid-Filled Scintillating Fibers for X-Ray Detection2023In: 2023 IEEE SENSORS, Institute of Electrical and Electronics Engineers (IEEE), 2023Conference paper (Refereed)
    Abstract [en]

    We present the design and fabrication of flexible, liquid-filled scintillating fibers for X-ray detection made from silica fibers and silica capillaries. The scintillating fibers were characterized using ultraviolet light exposure and we also performed an experiment demonstrating X-ray detection.

    Download full text (pdf)
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  • 25.
    Löthberg, Peter
    et al.
    STUPI, USA.
    Sundblad, Ragnar
    Netnod, Sweden.
    Andersson, Rolf
    Netnod, Sweden.
    Liström, Stefan
    Netnod, Sweden.
    Ebenhag, Sven-Christian
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Network time protocol from a distributed timescale traceable to UTC2016In: Proceedings of the 47th Annual Precise Time and Time Interval Systems and Applications Meeting, 2016, p. 187-192Conference paper (Refereed)
    Abstract [en]

    A nationwide robust distributed time scale and network time and frequency distribution infrastructure is implemented in Sweden. The system has been under evaluation since May 2015 and was started as an active service in December 2015. The six local time scales are traceable to UTC within ± 250 ns and NTP time is distributed using customized high performance servers. All output is externally monitored for independent quality and performance assessment.

  • 26.
    Rieck, Carsten
    et al.
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Jaldehag, Kenneth
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Ebenhag, Sven-Christian
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Jarlemark, Per
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Hedekvist, Per Olof
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Time and frequency laboratory activities at RISE2020In: Proceedings of the Annual Precise Time and Time Interval Systems and Applications Meeting, PTTI, Institute of Electrical and Electronics Engineers Inc. , 2020, p. 169-180Conference paper (Refereed)
    Abstract [en]

    RISE Research Institutes of Sweden is since 2018 the result of a rebranding of SP Technical Research Institute of Sweden and several other national research facilities and test beds in Sweden. This also comprises most national metrology institute (NMI) activities, including time and frequency that is still located at its Borås facilities in the southwest of Sweden since 1995. UTC(SP) remains the official designation of the Swedish UTC(k) realization. It is realized in a classical master clock and phase stepper setup and is locally distributed to different users and time transfer applications. The most recent local clock ensemble consists of four hydrogen masers and three high performance 5071A Cs standards. UTC(SP) is linked to TAI using TWSTFT and GNSS. The primary link is a combination TWGPPP with current calibration uncertainties of 1.1 ns. The time scale is regularly kept within ±5 ns of UTC. RISE has also established several distributed UTC(SP) copies, with both local backups in Borås and facilities at remote sites linked together by GNSS time transfer. Network time distribution at those sites make UTC(SP) publicly available. Additionally, RISE offers several calibration services for the distribution of UTC-traceable time and frequency signals. Time and frequency related metrological research at RISE is mostly concentrated on further refinement of GNSS and TWSTFT methods, their calibration and the dissemination using those methods. We are also active in research on fiber based optical time and frequency transfer. Outside the metrological responsibilities, many research projects focus on establishing metrological aspects of time and frequency within for instance the automotive and maritime domain.

1 - 26 of 26
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