| 1. |
- Ebenhag, Sven-Christian, 1976, et al.
(författare)
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A fiber based frequency distribution system with enchanced output phase stability
- 2009
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Ingår i: Proceedings EFTF-IFCS2009 joint conference 20-24 April 2009, IEEE catalog number:CFP09FRE-CDR. - 1075-6787. - 9781424435104 ; , s. 1061-1064
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Konferensbidrag (refereegranskat)abstract
- Experimental results on the stability of the output phase of a frequency distribution system from several days of measurement is presented, in addition to a discussion regarding the influence of control loop parameters. The setup handles the issue that the output phase stability of a system depends on perturbations along the transmission length. This is especially critical if the signal is transmitted through optical fiber, at lengths of a few 100 m. An experimental evaluation using a laser based transmitter at a wavelength of 850 nm, and 625 m of multimode fiber where 575 m where placed outdoor, a temperature dependence of 100 ps/°C was detected. Tocompensate for these slow variations in real time, a setup using two-way transmission, in conjunction with an adjustable optical delay, was constructed. This device is adjusted to induce a delay variation of equal magnitude but opposite direction, in comparison to the delay change of the fiber. Calculating the modified Allan deviation of the transmitted signal, it is apparent that without active compensation, the deviation at τ below 1000 s is comparable to the values from the measurement system without transmission. At longer integration times, however, the slow variations in the fiber transmission will deteriorate the modified ADEV substantially. When activating the dynamic adjustment of pre-delay in the system, the deviation at shorter times will increase with a few dB, however, the modified ADEV decreases continuously with τ, eventually below the values for the uncompensated system. In conclusion, activating a dynamically controlled pre-delay in a fiber based frequency transmission system will induce a small penalty on fast variations of the output phase, however giving a remarkable improvement on slower variations. The usefulness of this added functionality must therefore be determined by the application of the signal.
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| 2. |
- Jaldehag, R. T. Kenneth, 1962, et al.
(författare)
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A GPS Carrier-Phase Aided Clock Transport for the Calibration of a Regional Distributed Time Scale
- 2009
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Ingår i: Proceedings EFTF-IFCS2009 joint conference 20-24 April 2009, IEEE catalog number:CFP09FRE-CDR. - 1075-6787. - 9781424435104 ; , s. 659-663
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Konferensbidrag (refereegranskat)abstract
- Clock transportation is a historically proven time transfer method for the calibration of time links and time scales. With the establishment of satellite-based time transfer methods, however, clock transportation has become less attractive especially on long baselines. In order to match for instance the GPS common view time transfer method with calibration uncertainties of a few nanoseconds, it is necessary to transport high quality, expensive clocks such as caesium beam frequency standards. The stability of the clock during transportation and the duration of the transport set the limit of the prediction uncertainty. Being able to measure the clock during transportation instead of predicting it would yield some major advantages: (a) the use of less expensive and small clocks such as rubidium or quartz oscillators for transportation, (b) no need for environmental conditioning of the transported clock, and (c) the duration of the transport is not critical as long as the clock can continuously be measured. One solution to the clock measurement problem during transport is the use of GPS carrier-phase observations as described and evaluated in this paper. It is shown that a calibration uncertainty of less than one nanosecond is potentially achievable.
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| 3. |
- 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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| 4. |
- 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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| 5. |
- Hedekvist, Per Olof E, 1967, et al.
(författare)
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Active optical pre-compensation in short range frequency transfer in optical single-mode fiber
- 2011
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Ingår i: 2011 Joint Conference of the IEEE International Frequency Control Symposium/European Frequency and Time Forum Proceedings. - 1075-6787. - 9781612841106 ; , s. 315-316
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Konferensbidrag (refereegranskat)abstract
- Short distance fiber based optic distribution of time and frequency is often considered sufficiently stable and therefore, uncompensated one way transfer is used. However, when fiber distances increase to a few km, and a substantial amount of the fiber is installed outdoors or in aisles and attics without temperature control, the delay through the fiber may vary substantially. Since the variations are slow, a microwave frequency modulated on an optical carrier may be assumed to remain sufficiently stable. The time delay through the fiber will nevertheless depend on the extremes of the temperature variation which must be taken into account or compensated for. This study presents the design issues of a real time compensation and some results of an optical compensation technique.
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