Nokia, Facebook Successfully Does Trials Of Undersea Spectral Efficiency

Nokia and Facebook have successfully set a new spectral efficiency record over a transatlantic subsea cable using Nokia Bell Labs’ new probabilistic constellation shaping (PCS) technology. The field trials saw 2.5 times more capacity than the traditional optical transmission technology.

The multiple field trials were conducted over a 5,500-kilometer (3,418-mile) submarine cable between New York and Ireland. The cable used new PCS from Nokia Bell Labs, which uses ‘shaped’ quadrature amplitude modulation (QAM) formats to flexibly adjust transmission capacity to near the physical limits of a given fiber-optic link. It shaped 64-QAM setting a spectral efficiency record of 7.46 b/s/Hz (bits per second per Hertz) 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,” Stephen Grubb, global optical network architect at Facebook, said.

“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,” he added.

Nokia achieved the highest ever spectral efficiencies for trans-oceanic distances, bringing the capacity of the cable from 13 Terabits per second (Tb/s) to 32 Tb/s. However, the tests increased capacity from 13 to over 17 Tb/s using commercially available hardware.

“We are thrilled to partner with Facebook to promote our common commitment to accelerating innovation in optical transmission. By demonstrating promising areas of Nokia Bell Labs research such as PCS, as well as coherent technologies available today, we hope to chart a path forward for the industry towards higher capacities, greater reach, and more network flexibility,” Sam Bucci, head of optical networking at Nokia, said.

Nokia also achieved the highest trans-oceanic single carrier (wavelength) data rate of 8-QAM wavelengths running at 200 Gb/s and 16-QAM wavelengths running at 250 Gb/s – a first for transatlantic transmission. While exhibiting sufficient performance margin to support reliable, commercial operation, 200G 8-QAM wavelengths supported a spectral efficiency of 4 b/s/Hz.

The results of the field trials will be presented in a post-deadline paper at the Optical Fibre Communication Conference and Exhibition (OFC) this week in Los Angeles, CA.

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