Evaluation of 4-PAM, NRZ and Duobinary Modulation Formats Performance for Use in 20 Gbit/s DWDM-PON Optical Access Systems

In this paper we compared performance of different modulation formats in 8-channel dense wavelength division multiplexed passive optical network (DWDM-PON). Higher spectral efficiency four-level pulse amplitude modulation (PAM-4) format operating at 10 Gbaud/s (20 Gbit/s) transmission speed per channel is compared to same bitrate non-return-to-zero (NRZ) and duobinary (DB) modulation formats in order analyze their performance in terms of maximal transmission distance and minimal channel spacing with pre-FEC BER ≤ 10
^-3
. Through mathematical modelling it was found that the maximal achievable transmission distance of DB and spectrally efficient PAM-4 modulation formats in DWDM-PON system are 62 km and 50 km, respectively. It is numerically shown that DB modulation format has 19% better transmission reach than PAM-4 for 20 Gbit/s transmission systems.