100-km DWDM Transmission of 56-Gb/s PAM4 per $\lambda $ via Tunable Laser and 10-Gb/s InP MZM

We experimentally demonstrated the feasibility of using a co-packaged tunable laser and 10-Gb/s InP Mach–Zehnder modulator to carry a 56-Gb/s four-level pulse-amplitude-modulation signal in a dispersion-compensated 100-km standard single-mode-fiber dense wavelength division multiplexing system. Various system impairments, e.g., bandwidth limitation, residual dispersion, fiber nonlinearity, and laser frequency drift, have been considered and discussed. This technology may enable a cost-effective ≥4-Tb/s system capacity for inter-data center connection optical networks.