Performance analysis of various optical modulation formats for BPON systems under dispersion, fibre length and split ratio variations

Abstract

Selecting an appropriate modulation format is a crucial step in the design of optical communication systems, especially in passive optical networks (PONs). Various modulation formats such as NRZ, RZ, duobinary, CSRZ, CNRZ, NCNRZ, ACNRZ and VSBCSRZ are analyzed in this work using a BPON system operating at 622 Mbps. The transmitter is implemented in OptiSystem using a PRBS generator, a continuous-wave laser, Mach-Zehnder modulators, and pulse generators. Performance comparisons are carried out in terms of BER and Q -factor as fibre dispersion, fibre length, and split ratio are varied. The results show that no single format is optimal under all conditions, and that the best choice depends on the dominant impairment. Specifically, CNRZ and RZ achieve the lowest BER at short reach and low split ratios, while CSRZ and ACNRZ deliver the highest Q -factor overall. CSRZ emerges as the most robust format under the most demanding conditions, remaining the only format below the no-FEC reference threshold at a 50 km fibre length and, together with ACNRZ, the only format within the FEC-corrected limit at a 1:64 split ratio. Unlike existing studies, this work provides a unified comparative analysis of conventional, chirped, and advanced modulation formats under simultaneous variations in dispersion, fibre length, and split ratio in a BPON framework.