Nokia and Facebook have announced the successful completion of a series of field trials of new optical digital signal processing technologies over a 5,500-kilometre transatlantic subsea link between New York and Ireland. To increase the capacity capabilities of submarine fibre to cope with bandwidth-hungry applications, the companies 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 fibre-optic network, said the partners in a joint statement.
Nokia described PCS as a novel technique that uses 'shaped' quadrature amplitude modulation (QAM) formats to flexibly adjust transmission capacity to near the physical limits of a given fibre-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 bps/Hz, indicating the potential to upgrade this cable to 32 Tbps per fibre in the future.
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 Gbps and 16-QAM wavelengths running at 250 Gbps, a first for transatlantic transmission, added Nokia.
