Radio Astronomy Gets a Boost From Standard Telecom Network
Tony Pallone | February 05, 2018
A reference signal was successfully sent between two radio telescopes over a fiber-optic telecommunications link. Source: D. Smyth/CSIRO.
Stable frequency references, typically generated at facilities with expensive atomic clocks, are used to calibrate instruments that make ultraprecise measurements. Recently, researchers have demonstrated a new technique to reliably transmit a stable frequency reference more than 300 kilometers over a standard fiber optic telecommunications network — making it possible for scientists anywhere to access the frequency standard simply by tapping into the telecommunications network.
This could be particularly useful for projects such as the Square Kilometer Array (SKA), an international effort to build the world's largest radio telescope by using arrays of linked individual telescopes in Australia and South Africa. When complete, SKA will have a total collecting area of about 1 million square meters, and be able to detect faint radio waves from deep space with sensitivity about 50 times greater than that of the Hubble telescope.
The arrays that make up SKA are dependent on each radio telescope recording the precise time at which a signal is detected from an object in space. Calculating the slight differences in signal reception timing allows researchers to create a detailed observational picture and pinpoint an object’s location. The new method allows the use of stable transmitted references to calibrate relative time at each telescope, eliminating the need for multiple atomic clocks — which cost about $200,000 each.
Moreover, as reported in Optica, researchers from a consortium of Australian institutions that successfully transmitted a stable frequency reference between two radio telescopes via fiber link found performance to be superior to the use of an atomic clock at each scope.
The new technique does not require substantial changes to the rest of the fiber-optic network, and is easy to implement. It is possible to compensate for signal fluctuations introduced by environmental factors, and live telecommunications traffic simultaneously transmitted over the network was unaffected. "This is necessary to gain the cooperation of the telecommunications companies that own these fiber networks," notes Kenneth Baldwin, a member of the research team from the Australian National University (ANU).
To keep the frequency stable during transmission, the signal is sent through the network to a destination and then reflected back. The returning signal is used to determine if any changes occurred; after each round trip, any transmitted frequency shift is passively subtracted to compensate. A quartz oscillator at the remote location is also used to keep the time steady between round trips.
The researchers say that the new method is ready for implementation by radio astronomers who want to avoid using multiple atomic clocks across a telescope array. The method can also be used over longer distances by using amplifiers to boost the signal; this could also allow stable frequency references to be broadcast across a national fiber optic network, where any scientist with access to a telecommunications network could use them.
