Trans-Atlantic Field Trial Using High Spectral Efficiency Probabilistically Shaped 64-QAM and Single-Carrier Real-Time 250-Gb/s 16-QAM

We report the transmission of probabilistically shaped (PS) 64-ary quadrature amplitude modulation (QAM) at 7.46 b/s/Hz over a 5,523-km in-service trans-Atlantic fiber-optic cable that consists of 65 89-km spans of EDFA-only amplified fiber. Using a looped-back system configuration, we achieve 5.68 b/s/Hz over a trans-Pacific-equivalent distance of 11,046 km. Net spectral efficiencies are increased by 18% and 80% by using PS, at 5,523 km and 11,046 km, respectively, compared to uniform square QAM. Throughout our experiments, we pay particular attention that our claims are backed by actually implementable forward error correction schemes. In addition, we demonstrate real-time coherent transmission of single-carrier 200-Gb/s and 250-Gb/s uniform 8-QAM and 16-QAM at 4 b/s/Hz over the 5,523-km cable.