Increasing the Capacity in NG-PON Using QPSK, 4-QAM, and 8-QAM Modulation Formats

Abstract

This work demonstrates the potential of a dual-polarized multilevel modulation format with coherent detection (CD) to maximize the spectral efficiency to meet the demand of the next-generation passive optical network (NG-PON). Maximizing capacity and spectral efficiency in NG-PON networks is particularly crucial for improving high-speed internet access, bridging the digital divide, and enabling new services and opportunities in rural and underserved areas, ultimately contributing to their socio-economic development. The proposed NG-PON system based on a higher modulation format can support 64 subscribers accessing the medium simultaneously at a 10 Gb/s data rate. The power splitting network was investigated using the Virtual Photonics Incorporation simulation tool. In this paper, we optimize the downstream transmission of the 1550.1 nm channel over 20 km standard single-mode fiber using Quadrature Phase Shift Keying and Quadrature Amplitude Modulation (4-QAM and 8-QAM) formats. A digital signal processing system was employed to mitigate fiber dispersion and losses. The modulation format of 8-QAM was discovered to maximize the spectral efficiency of the carrier. From the bit error rates analysis, an aggregate transmission capacity of 3.84 Tbps was achieved for 64 users using the 8-QAM format. The findings showed that CD with higher modulation formats improved receiver sensitivity by more than 7 dB to –22.69 dBm, compared to direct detection reported in the literature. This enhancement increases the capacity of optical networks. The study also provides an analytical perspective on high-capacity NG-PON systems utilizing advanced modulation techniques for diverse users.

Received: 6 January 2025 | Revised: 15 July 2025 | Accepted: 3 November 2025

Conflicts of Interest

The authors declare that they have no conflicts of interest to this work.

Data Availability Statement

Data sharing is not applicable to this article as no new data were created or analyzed in this study.

Author Contribution Statement

Henry C. Cherutoi: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Data curation, Writing – original draft, Writing – review & editing, Visualization, Project administration. Dismas K. Choge: Conceptualization, Validation, Investigation, Resources, Data curation, Writing – review & editing, Supervision, Project administration, Funding acquisition. David W. Waswa: Conceptualization, Validation, Investigation, Resources, Data curation, Writing – review & editing, Supervision, Project administration, Funding acquisition.