Researchers build ultra-long distance fibre links

Estonian and Swedish researchers have shown its possible to extend the reach of fibre-optic data transmission links by almost six times using new phase-sensitive amplifiers (PSAs).

Researchers from Tallinn University of Technology and Chalmers University of Technology found they could overcome current distance limits by reducing noise accumulated on fibre links.

The results were published in the scientific journal Nature Communications.

The researchers built an 80km long test link, using standard single-mode optical fibre to simulate long-haul data transmission of a 10Gbps capacity signal.

Results from the testing showed that, compared to conventional in-line erbium-doped fiber amplifiers (EDFAs), the ultra-low noise PSAs extended the reach of the link by 5.6 times to 4000km.

Reach-limiting signal distortion on the link was also substantially reduced through the use of PSAs.

Ultra-low noise and distortion amplifiers on fibre optic links could help meet insatiable demand for video streaming, cloud storage, online services and might also find application in quantum informatics and spectroscopy, the researchers said.

However, several engineering challenges remain before such PSAs can be implemented commercially.

For the test link, the researchers used two weak lightwaves, called signal and idler, that are amplified by one or two high-power waves, called pumps.

This setup is sensitive to frequency differencies between the waves.

"In a real transmission link, a feedback system would be required to tune the frequency of the slave lasers to match the frequency of the incoming pump wave," the researchers said.

In addition, the researchers tuned the polarisation alignment between the waves manually on the test link, whereas in a real-world scenario, polarisation tracking would be required to align the waves, something that the researchers said would be challenging to implement.