Comparison of 51.84-Gb/s VSB PAM4 and OOK Signal In An EML-Based Intensity-Modulation and Direct-Detection 80-km Transmission System

A comparison between 51.84-Gb/s vestigial sideband (VSB) 4-level pulse amplitude modulation (PAM4) and on-off keying (OOK) signals at a transmission distance of 80 km is experimentally demonstrated. An electro-absorption modulated laser (EML) based intensity-modulation and direct-detection (IM/DD) 80-km transmission is achieved by both modulation formats without using dispersion compensating fiber (DCF). The relative frequency between SSB filter and signal is adjusted to find an optimized condition for both carrier to signal power ratio (CSPR) and sideband suppression ratio (SSR). The experimental results show that the OOK signal has a 4 dB better sensitivity compared to the PAM4 signal with 80-km standard single-mode fiber transmission.