Advantages of EADFB laser for 25 Gbaud/s 4‐PAM (50 Gbit/s) modulation and 10 km single‐mode fibre transmission

Abstract
The 25 Gbaud/s 4-level pulse amplitude modulation (4-PAM) of a 1.3 μm electroabsorption modulator integrated with a distributed feedback (DFB) laser is demonstrated for the first time. The linearities of the electroabsorption DFB (EADFB) laser and the directly modulated laser are evaluated to investigate the applicability of the PAM format to these devices.