Large area/low loss fibre is prime candidate for undersea cabling

This trial shows the dramatic improvement in optical reach and capacity that can be expected as these fibres are deployed in next-gen terrestrial and submarine fibre links. LA/LL fibres are being deployed in a handful of submarine cables now and will likely be the technology of choice for future submarine cable builds. The deployment of LA/LL fibre in terrestrial applications could be delayed because of the large base of existing fibre, but there are early examples of such deployments. Existing fibre types typically have a much lower optical performance compared to LA/LL fibre.

High order modulations, such as 16QAM, promise to deliver double the capacity of QPSK - the de facto 100Gb/s modulation - at the expense of 80% reduction in reach, using existing fibre types. This makes 8QAM a promising option over existing fibres for both submarine and terrestrial applications. In a recent submarine trial performed on existing fibre, 8QAM delivered a reach of over 2,200km while increasing capacity by 50%. When the same test was performed on the LA/LL fibre, 8QAM demonstrated an optical reach up to 7,400km with a 50% increase in fibre capacity.

“With the optical reach we achieved using this type of LA/LL fibre we could envisage a future in which PM-QPSK could be used to close trans-Pacific links, PM-8QAM could cross the Atlantic, and PM-16QAM could span a European backbone,” summarised Steve Grubb, Fellow, Infinera, and the architect behind the trial. “This would enable between 50% and 100% increase in submarine or terrestrial cable capacity.”

“This trial was extremely useful for our future network planning process,” added Eric Loos, Senior Product Manager Capacity & IP at BICS. “It’s clear to us that many of the trials of 16QAM in the market today are performed on these fibre types – because they dramatically improve the optical reach. When it comes to existing fibre types in the terrestrial applications, like SMF or LEAF, it’s clear that 16QAM can be useful at the shorter reach end of the scale, especially where no optical protection will be used. In contrast PM-8QAM seems to offer a sweet spot for longer metro, regional and even long haul distances, and could give us enough reach to include optical protection. 8QAM delivers a 50% capacity boost compared to QPSK, and that’s going to be extremely useful for service providers facing the unprecedented demand increase from Cloud-based services.”