Key enabling techniques and deployment of 120Gb/s long-haul optical transmission in backbone networks

The explosive increase in data traffic requires networks to provide higher capacity and long-haul transmission capabilities. This paper introduces new results on high-order modulation and efficient Digital Signal Processing algorithms to reduce various transmission limitations in coherent receiving systems. Polarization Division Multiplexed Quadrature Phase Shift Keying (PDM-QPSK) is deployed to reach high bit rates, provides modified digital clock recovery, and allows BER-Aided Constant Modulus Algorithm (BA-CMA) equalising. A Soft Decision-Forward Error Correction (SD-FEC) algorithm and a joint scheme with timing recovery and adaptive equaliser are used to achieve better performance. A compact coherent transceiver is also developed. These techniques have been applied in the largest 100 G Optical Transport Network (OTN) deployment in the world, the backbone expansion project for Phase 3 of the China Education and Research Network (CERNET), with a total transmission length of 10 000 km.