Demonstration of 4 × 100 Gbit/s PAM-4 Transmission Over 40 km in an IM/DD System Based on Narrow Band DMLs

We demonstrate a four-lane wavelength division multiplexing (WDM) intensity modulation and direct detection (IM/DD) system at O-band. The 3-dB bandwidth of directly modulated lasers (DMLs) in this experiment is only 15 GHz. To support 100-Gbit/s/lane PAM-4 transmission in each lane, digital pre-equalization and advanced receiver-side DSPs are adopted to compensate for bandwidth limitation. Moreover, semiconductor optical amplifier (SOA) is utilized at the receiver to compensate for the optical power loss during fiber transmission so that 40-km transmission distance can be achieved. To the best of our knowledge, it is the first time to successfully transmit 400-Gbit/s PAM-4 signals over 40-km SSMF with 15-GHz DMLs.