Infinera, Facebook, increase capacity, data rates in subsea cables

Created April 13, 2021
News and Business

A team of researchers from Infinera, and Steve Grubb of Facebook have demonstrated a record-breaking transatlantic transmission across the trans-Atlantic MAREA cable, which spans 6,605 km from Virginia Beach, Virginia, USA to Bilbao, Spain.

Originally intended to achieve a capacity of 20Tbps per fibre pair and a data rate of around 200Gbps per wavelength, the team’s improvements to MAREA enabled a capacity of 30Tbps and a data rate of 700Gbps, both of which are records for submarine cables of this length. The team says achieving the 30Tbps capacity required a combination of increasing the number of bits within each transmitted optical symbol, and tight, interference-free spacing between wavelengths on each fibre. Using a technique called super Gaussian probabilistic constellation shaping, the group was able to increase the overall spectral efficiency of each signal by selecting an appropriate distribution of individual symbols within to maximise the data carrier.

Infinera team member Marc Stephens will present the results generated from the group’s recent field trial during a session at this year’s OFC.

“There are over 400 subsea cables deployed around the world, and they include several different types of cable design, stretching back 20 years in some cases,” said Stephens. “We can use the tools in our optical engine to boost capacity on all of these cable types in a similar way to MAREA, although the absolute capacity may vary, because they are not optimised for coherent transmission as well as MAREA is.”

Stephens’ role in the work was to help understand the impacts of this constellation shaping approach with the hope of extending it to other submarine cable types beyond MAREA.

“I feel confident in saying that the MAREA cable will remain the benchmark for capacity per fibre pair across the Atlantic for the foreseeable future,” he said. “We feel there is still more to come but in a different way to how things have evolved in the past.”

A second record of 700Gbps per wavelength channel data rate required increasing the symbol rate of the signals carried across MAREA. Although this comes at the cost of increased impairments, both optical and electrical, the trade-off can be mitigated using Nyquist subcarriers, which divide the single optical signal into multiple, independent signals, allowing for the same advantages without the associated problems.Stephjens said, “The challenge soon becomes how do we make a petabit capacity at a cable level a practical reality for the operator? So, it is about shrinking the transponder and reducing its power consumption. Neither of those two are constrained by the Shannon limit, so the laws of physics are not stopping us getting there.”

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This article was written
by Peter Dykes

Peter Dykes is a independent telecoms and technology journalist who has over that last 30 years written for a wide range of B2B publications and companies. A former BT engineer, he specialises in networks and associated support systems. He is currently Editor of Optical Connections.