| 1. |
- Ebenhag, Sven-Christian, et al.
(författare)
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Redundant Distributed Timescale Traceable to UTC(SP)
- 2019
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Ingår i: 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.. - 9781538683057
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 2. |
- Ebenhag, Sven-Christian, et al.
(författare)
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Coherent optical two-way frequency transfer in a commercial DWDM network
- 2016
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Ingår i: Proceedings of the Annual Precise Time and Time Interval Systems and Applications Meeting. - : Institute of Navigation. ; , s. 116-120, s. 116-120
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 3. |
- Ebenhag, Sven-Christian, et al.
(författare)
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Evaluation of Fiber Optic Time and Frequency Distribution System in a Coherent Communication Network
- 2019
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Ingår i: 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.. - 9781538683057
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 4. |
- Ebenhag, Sven-Christian, et al.
(författare)
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Implementation of an optical fiber frequency distribution via commercial DWDM
- 2016
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Ingår i: 2016 IEEE International Frequency Control Symposium (IFCS). - 1075-6787. - 9781509020911
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 5. |
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| 6. |
- Ebenhag, Sven-Christian, et al.
(författare)
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Time and Frequency Dissemination in an All-optical Coherent Fiber Communication Network
- 2017
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 7. |
- Ebenhag, Sven-Christian, 1976, et al.
(författare)
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Two-way coherent frequency transfer in a commercial DWDM communication network in Sweden
- 2015
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Ingår i: 2015 Joint Conference of the IEEE International Frequency Control Symposium and the European Frequency and Time Forum, FCS 2015 - Proceedings. - 1075-6787. - 9781479988662 ; , s. 276-279
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 8. |
- Hedekvist, Per Olof, et al.
(författare)
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Analysis and compensation of polarization in an optical frequency transfer through a fiber communication network
- 2018
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 9. |
- Nilsson Tengelin, Maria, et al.
(författare)
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Measurement of the Effect of Dynamic Lighting on Alertness, Mood and Sleepiness
- 2017
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Ingår i: PROCEEDINGS OF THE LUX EUROPA 2017, Lighting for modern society.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The lighting in the workplace is known to have a significant effect on the workers’ well-being and alertness. It also affects sleep/wake-cycles and mood. The aim of this pilot study is to investigate a method to evaluate non-visual effects of variable lighting in workplaces using both self-assessed and physical data. The lighting in two offices was varied according to pre-programmed schedules, including daylight simulating scenario for two weeks and activity promoting scenario for two weeks. The method was successful and provided interesting results on the measured physical data. The resting pulse was lowered and the sleep quality improved for the test subjects during the weeks of dynamic office lighting.
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