Nokia and Facebook announced they have collaborated on field trials of new optical digital signal processing technologies over a 5,500 km trans-Atlantic link between New York and Ireland.
To help address increasing demand for capacity on subsea fibre networks, Nokia and Facebook tested Nokia Bell Labs' new probabilistic constellation shaping (PCS) technology. The companies stated that the trial achieved an increase of almost 2.5x in capacity compared with the stated transmission capacity of the system, demonstrating the feasibility of using the technology across a real-world optical network.
PCS, a field of research at Nokia Bell Labs, is an advanced technique that utilises 'shaped' QAM formats to flexibly adjust transmission capacity to close to the physical limits, the Shannon limit, of a given fibre-optic link. Believed to be a first-of-its-kind experiment conducted on an installed submarine link, the test was conceived and planned by Facebook,
Nokia noted that PCS is based on 64QAM and, combined with digital nonlinearity compensation and low-linewidth lasers, enabled a claimed record spectral efficiency of 7.46 b/s/Hz, indicating the potential to upgrade this cable to 32 Tbit/s per fibre in the future. The test also included round-trip submarine transmission over 11,000 km using 'shaped' 64QAM with spectral efficiency of 5.68 b/s/Hz.
During the trial transmission tests based on the commercially available Nokia Photonic Service Engine 2 (PSE-2) validated the transmission of 8QAM wavelengths running at 200 Gbit/s and 16QAM wavelengths running at 250 Gbit/s, which is believed to be a first for trans-Atlantic transmission. The 200 Gbit/s 8QAM wavelengths supported a spectral efficiency of 4 b/s/Hz while also exhibiting sufficient performance margin for commercial operation.
Nokia and Facebook stated that the results of the trial will be presented in a post-deadline paper at the OFC 2017.
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