Abstract

We review recent advances in the mitigation of inter-channel four-wave-mixing (FWM) based on “XYYX” input polarization alignment, statistical fiber zero-dispersion wavelength (ZDW) distribution, real-world fiber cable installation with randomized fiber ZDW for every fiber segment of typically 2∼3 km during fiber cabling to enable high-performance O-band WDM transmission for 800G-LR4 with four 800 GHz-spaced 200 Gb/s PAM-4 channels reaching up to 10 km, 1.6T-LR8 with eight 800 GHz-spaced 200 Gb/s PAM-4 channels reaching up to 10 km, and 400G-ER4-30 km with four 400 GHz-spaced 100 Gb/s PAM-4 channels reaching up to 30 km. In addition, a novel unequal channel spacing scheme for co-propagating wavelength channels is shown to effectively mitigate the FWM impairment in a bidirectional 5G fronthaul transmission system with twelve 800 GHz-spaced 25 Gb/s NRZ channels reaching up to 20 km. These inter-channel FWM mitigation techniques are expected to aid the standardization of intensity-modulation and direct-detection (IM/DD) based high-speed O-band WDM systems in both IEEE and ITU-T, aiming to cost-effectively and energy-efficiently support future data center, 5G, and metro-access networks.