by TA Staff, March 21, 2017

Nokia and Facebook have collaborated to do spectral efficiency test of their undersea fiber network and the results were very encouraging. During the field trials the team witnessed 2.5 times more capacity than the traditional optical transmission technology.

Both the companies conducted this trial over a 5,500 km submarine cable between New York and Ireland using new optical digital processing technologies.

To increase the capacity capabilities of subsea fiber, Nokia and Facebook tested Nokia Bell Labs’ new probabilistic constellation shaping (PCS) technology. The test showed an increase of almost 2.5x more capacity than the stated optical transmission capacity of the system, demonstrating the feasibility of the technology across a challenging real-world fiber-optic network.

PCS, an area of active Nokia Bell Labs research, is a novel technique that uses ‘shaped’ quadrature amplitude modulation (QAM) formats to flexibly adjust transmission capacity to near the physical limits of a given fiber-optic link. In this first-of-its-kind experiment for an installed submarine link, conceived and planned by Facebook, PCS based on 64 QAM, combined with digital nonlinearity compensation and low-linewidth lasers, achieved a record spectral efficiency of 7.46 b/s/Hz, indicating the potential to upgrade this cable to 32 Tb/s per fiber in the future.

“Facebook wants to increase the pace of innovation and adoption of next-generation optical technologies. This field trial with Nokia demonstrates that the scalable optical technology of PCS together with narrow linewidth laser sources can achieve capacities extremely close to the Shannon limit. This ensures that we are both maximizing our investment in submarine cable systems, as well as continuing to drive the cost per bit of submarine transport lower,” said Dr. Stephen Grubb, global optical network architect at Facebook.

Transmission tests based on the commercially available Nokia Photonic Service Engine 2 (PSE-2) validated the successful transmission of 8-QAM wavelengths running at 200 Gb/s and 16-QAM wavelengths running at 250 Gb/s – a first for transatlantic transmission. 200G 8-QAM wavelengths supported a spectral efficiency of 4 b/s/Hz while exhibiting sufficient performance margin to support reliable, commercial operation.

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