Nokia, Facebook set transatlantic efficiency record

Nokia and Facebook have announced they have set a new spectral efficiency record over a transatlantic subsea cable using Nokia Bell Labs’ new probabilistic constellation shaping technology (PCS).

During the trial involving a 5,500km subsea cable between New York and Ireland, shaped 64 quadrature amplitude modulation (64-QAM) was used to achieve record spectral efficiency of 7.46 b/s/Hz.

PCS uses shaped QAM formats to flexibly adjust transmission capacity to near the physical limits of a fiber link.

The results showed an increase of nearly 2.5 times more capacity than the stated limit of the system, indicating the potential to upgrade the cable to 32 Tbps per fiber.

Transmission tests validated the successful transmission of 8-QAM wavelengths running at 200 Gbps and 16-QAM wavelengths running at 250 Gbps, a first for a transatlantic transmission.

“Facebook wants to increase the pace of innovation and adoption of next-generation optical technologies,” Facebook global optical network architect Dr Stephen Grubb 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.”