400 Gb/s CWDM-4 PAM-4 data transmission over 20 km optical fiber using direct modulated laser and KP-4 FEC limit

Directly modulated lasers (DMLs) are a highly desirable optical communication technology to achieve 100 Gb/s-class 4-level pulse amplitude modulation (PAM-4) per channel pluggable transceivers because this type of light source can reduce power consumption, footprint and production cost. However, extending the reach of 100 Gb/s PAM-4 directly modulated transmission system is challenging since DMLs exhibit a mixture of transient and adiabatic chirp. In this paper, we present a simple and effective dispersion pre-compensation technique combined with a third order diagonally-pruned Volterra nonlinear equalization for extending the reach of 100 Gb/s PAM-4 DML transmission systems. Using the proposed scheme, we demonstrate the first 400 Gb/s 4-coarse wavelength division multiplexed (CWDM-4) PAM-4 transmission over 20 km with BER below KP-4 forward error correction (FEC) limit using commercially available 25-GHz class directly modulated lasers.