56 Gb/s PAM-4 directly modulated laser for 200G/400G data-center optical links. - Prashant P. Baveja; Mingshan Li 002; Ding Wang; Chiuhui Hsieh; Huanlin Zhang; Ning Ma; Yi Wang; Justin Lii; Yongxuan Liang; Chong Wang; I-Lung Ho; Jun Zheng 013 (OFC, 2017)