640-Gbps/Carrier WDM Transmission over 6,400 km Based on PS-16QAM at 106 Gbaud Employing Advanced DSP
Miao Kong, Kaihui Wang, Junjie Ding, Jiao Zhang, Weiping Li, Junting Shi, Feng Wang, Li Zhao, Cuiwei Liu, Yanyi Wang, Wen Zhou, Jianjun Yu
Abstract
We experimentally demonstrated a 5-channel 125-GHz-grid wavelength division multiplexing (WDM) transmission over 6,400-km Raman amplified ultra large effective area fiber (ULAF) with 848-Gbps/carrier line-rate and 640-Gbps/carrier net-bit-rate. Our transmission is based on probabilistically shaped (PS) dual-polarization 16-ary quadrature-amplitude-modulation (16QAM) considering 25%-overhead low-density parity-check threshold of 4.6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> bit-error-rate. By utilizing a high-speed digital-analog-converter (DAC) with a 3-dB bandwidth of 35 GHz and innovative pre-equalization based on 4-level pulse-amplitude-modulation (PAM4), 106-Gbaud 16QAM signal is reliably generated and transmitted. Besides, the transmission distance is improved obviously by using ULAF and Raman amplifier. Our results show that the PS-16QAM outperforms the regular-16QAM by around 1.5-dB sensitivity gain and 33% transmission-distance improvement. Furthermore, we have successfully applied Volterra nonlinear equalization (VNLE) to ultra-long-haul coherent optical transmission and proposed a modified offline digital-signal-processing process. By utilizing VNLE, another 15% reach improvement is obtained for PS-16QAM signal. Our work can provide an effective solution for a 600G+ ultra-long-haul transmission. As we know, this is the first time to achieve 640-Gbps/carrier WDM transmission over 6,400 km based on 106-Gbaud PS-16QAM.