A consortium of researchers demonstrated for the first time that a stable frequency reference — used to calibrate clocks and instruments — could be reliably transmitted more than 300 kilometres on AARNet optical fibre.

The new technology could be particularly useful for the Square Kilometre Array, a global effort to detect faint radio waves from deep space with a sensitivity about 50 times greater than that of the Hubble telescope.

Linking radio telescopes in an array requires that each telescope have access to an atomic clock to record the precise time at which a signal is detected from an object in space.

Stable transmitted references could be used to calibrate the relative time at each telescope, eliminating the need for multiple atomic clocks in a radio telescope array.

“This highly stable method for transmitting the frequency reference allows an atomic clock, which cost around two hundred thousand dollars, to be replaced with a system that only costs a few tens of thousand dollars,” said Kenneth Baldwin, a member of the research team from the Australian National University.

In the results published in Optica, the Optical Society journal, the researchers show that the technique is capable of compensating for signal fluctuations in the fiber optic network introduced by environmental factors such as temperature changes or vibrations.

The AARNet optical fibres were even carrying live traffic at the same time as the demonstration was performed.

“By running the experiment on optical fibers also carrying normal traffic, we showed that transmitting the stable frequency standard doesn’t affect the data or telephone calls on the other channels,” said Baldwin.

AARNet’s Tim Rayner, Optical Engineer, explains that AARNet’s dark fibre footprint already extended from the laboratories to the two telescope sites: the Australia Telescope Compact Array (ATCA) in north-west NSW and the Mopra radio telescope.

“We were keen to use our dark fibre infrastructure to support the research efforts of our community by running experimental services as well as contributing our expertise and operational capability.”

The AARNet team helped design the solution for the timing signals to use a particular optical wavelength, and installed optical amplifiers for the project in intermediate points co-located with other AARNet production equipment.

“Sending precise timing signals over optical fibre networks is essential to radio astronomy projects like the SKA,” said Tim.

“This work is an important example of AARNet’s support for research in the fibre optic and astronomy fields, which continues through our participation in the SKA project.”

The consortium of researchers are from AARNet, the Australian National University, CSIRO, the National Measurement Institute, Macquarie University and the University of Adelaide.

Paper: Y. He, K. G. H. Baldwin, B. J. Orr, R. B. Warrington, M. J. Wouters, A. N. Luiten, P. Mirtschin, T. Tzioumis, C. Phillips, J. Stevens, B. Lennon, S. Munting, G. Aben, T. Newlands, T. Rayner, “Long-distance telecom-fiber transfer of a radio-frequency reference for radio astronomy,” Optica, Volume 5, Issue 2, 138-146 (2018).
DOI: 10.1364/OPTICA.5.000138

Read the Optica media release – New use for telecommunications networks: helping scientists peer into deep space

Image credit: Radio telescopes, D Smyth CSIRO.