Does Probabilistic Constellation Shaping Benefit IM-DD Systems Without Optical Amplifiers?

Probabilistic constellation shaping (PCS) has been widely applied to amplified coherent optical transmissions owing its gain over the uniform signaling and fine-granularity rate adaptation underlying fiber channel condition. These merits stimulate study of PCS for short-reach applications dominated by intensity modulation (IM) - direct detection (DD) systems. As commercial IM-DD systems typically do not employ amplification save cost power consumption, they are no longer subject an average constraint (APC) but a peak (PPC), which poses unique challenges take full advantages PCS. This paper provides comprehensive investigation in without amplifiers. In particular, we reveal when transmitter enhances peak-to-average ratio signal, PPC system can be partially or even fully converted APC classical offers merits. The findings verified through experiment using 4- 8-ary pulse amplitude modulations.