Discrete Multitone Format for Repeater-Less Direct-Modulation Direct-Detection Over 150 km

High-capacity and low-cost repeater-less transmission beyond 50 km is of interest for the next-generation inter-data center communications. Transmission over such relatively long distance generally requires transmission in the 1550-nm low-loss telecom band that is, however, impaired by chromatic dispersion. Here, we study the performance of the direct modulation direct detection system using the discrete multi-tone format for repeater-less transmission through up to 150 km of a standard single mode fiber (SMF-28) using the 1550-nm band. The achievable capacity for two different types of directly modulated lasers is studied experimentally and compared with that achievable using chirp-free modulation using a push-pull LiNbO
₃
Mach-Zehnder external modulator. The benefit of using a larger bandwidth signal is found to diminish as the transmission distance increases. 28 and 25 Gbit/s signal transmission (Bit Error Ratio, BER <; 3.8 × 10
^-3
) over 50 km and 75 km are achieved using just 8-GHz modulation-bandwidth.