Research team extends fibre reach to 4,000km without repeaters

Research team extends fibre reach to 4,000km without repeaters

A team from two European universities have found a way of extending the reach of repeaterless fibre by six times – potentially reducing the cost of subsea and terrestrial cables.

The researchers, from Chalmers University of Technology in Sweden and Tallinn University of Technology, Estonia, say they have developed new optical amplifiers that extend the range to 4,000km.

Professor Peter Andrekson, who leads the research on optical communication at Chalmers University, said that the team used ultra low-noise, phase-sensitive optical amplifiers.

“While there remain several engineering challenges before these results can be implemented commercially, the results show, for the first time, in a very clear way, the great benefits of using these amplifiers in optical communication,” said Andrekson.

The team of five researchers published their research in Nature Communications, a peer-reviewed scientific journal.

They report that not only did they demonstrate “a reach improvement of 5.6 times” using the new amplifiers, but there was a significant increase in bandwidth. “The phase-sensitively amplified link transmits two data-carrying waves, thus occupying twice the bandwidth and propagating twice the total power compared to the phase-insensitively amplified link.”

There is a lot of research going on at the moment into ways of improving the performance of fibre. Challenges include amplifier noise and nonlinearities in the fibre, both of which degrade the signal. These researchers have used phase-sensitive amplifiers (PSAs) to counter some of the challenges.

The researchers used a recirculating loop, but they recognise that “in order to realise a real transmission link with in-line PSAs a few challenges remain to be solved”.

They say the PSAs can provide a very significant reach improvement over conventional approaches, and could potentially improve the performance of future fibre communication systems.

“Such amplifiers may also find applications in quantum informatics and related fields, where generation and processing of quantum states are of interest, as well as in spectroscopy or any other application which could benefit from ultra-low-noise amplification,” said Andrekson.

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