Directly modulated lasers (DMLs) have been implemented in short-reach optical networks as an intensity modulation and direct detection (IM-DD) scheme due to their high output power, small footprint, and low-cost fabrication. However, the attainable data rate of C-band DML-based IM-DD systems faces limitations imposed by the DML bandwidth, power fading due to chromatic dispersion, and nonlinear impairments resulting from the interplay between frequency chirp and chromatic dispersion. In this paper, we propose a joint sparse Volterra nonlinear equalization (SVNE) and gradient-descent noise whitening (GD-NW) digital signal processing technique to effectively mitigate the overall impairments. Through experimental verification, we achieve, to the best of our knowledge, the highest net data rates of 142.3/143/134.6/102.8/73.7/61.4 Gb/s over 0/5/10/20/40/60 km standard single-mode fiber for C-band DML-based IM-DD links, with the help of the proposed technique. Compared with previous works, our approach leads to an increase in transmission capacity by at least 10%. Furthermore, we conduct a comprehensive investigation into the achieved net data rate considering various factors, including modulation format, peak-to-peak voltage of the electrical output, utilization of the electrical amplifier, transmission reaches and different application scenarios, DML's chirp and extinction ratio, and the roll-off factor of the pulse shaping filter. Detailed guidelines are provided for performance-oriented efficient operations and measurements of DML-based IM-DD links.
