Cover story: A robust fiber-based frequency synchronization system immune to strong temperature fluctuation
At: 2017/12/26 17:09:43 by admin

Square KilometreArray (SKA) is an international large-scale scientific engineering project thatinvolves multiple countries, aiming at building the largest and most sensitive radiotelescope in theworld. SKA will be constructed in the areas inAustralia and South Africa. The total collecting area of all the SKA antennascombined will be over one square kilometre, about the size of 140 football fields. A keyprerequisite for the telescope array to work is to keep thousands of telescopesin the array highly synchronized in time and frequency.


The fiber networkstructure for SKA frequency synchronization is complicated and the environmentcondition is tough. The fiber network is thousands of kilometers long. The SKAsites are mostly located deep in the deserts, where there is always strongtemperature fluctuation, together with occasionally bad weather conditions suchas heavy rain and hail. In some parts, overhead fiber links are used instead ofburied ones, which makes them confronted with severer temperature fluctuation,vibration and mechanical stress, and raises great difficulties in frequencytransfer. So far there has not been any previous fiber-based frequencysynchronization network at such a large scale, high precision and reliabilityin the world.


With the rapiddevelopment of the technology on fiber-based frequency synchronization anddissemination in recent years, various related designs and applications keepshowing up. The Joint Institute for Measurement Science (JMI) led by Prof.Lijun Wang in Tsinghua University have participated in the Signal and DataTransport consortium of SKA since 2013, providing fiber-based solutions forreference frequency dissemination among each telescope.


Regarding thespecific requirements of SKA, the JMI team proposed an innovative design whichuses an asymmetrical phase noise compensation method. By introducing a smallfrequency offset intentionally, the non-linear effect and signal leakage in thesystem can be suppressed efficiently, so that the system can be immune tostrong ambient environment disturbances. This work has been published in ChineseOptics Letters, Volume 16, No. 1, 2018 (Xi Zhu, et al., Robustfiber-based frequency synchronization system immune to strong temperaturefluctuation).


“Currently thisfrequency dissemination system can fully meet SKA requirements in all aspectssuch as synchronization stability and environmental adaptability,” says thecorresponding author Dr. Bo Wang. “And this system has the advantages of simplestructure, easy operation and expansion, which make it very suitable forlarge-scale utilization in SKA. It also gives a good reference to otherapplications with similar demands.”


The design wasselected as the frequency dissemination scheme for SKA-Australia and will gointo the phase of procurement and construction in 2018.

Graphic description:

Fig.1 (a)    Artist’s impression of the fullSquare Kilometre Array (SKA) at night (image provided by SKA Organization). (b)Scheme diagram of the robust fiber-based frequency synchronization systemimmune to strong temperature fluctuation for SKA designed by JMI in Tsinghua University.(c) Production of the frequency synchronization system.

Fig.2 Group photo of JMI crew

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