Cherutoi, Henry C., et al. “Increasing the Capacity in NG-PON Using QPSK, 4-QAM, and 8-QAM Modulation Formats”. Journal of Optics and Photonics Research, vol. 3, no. 2, May 2026, pp. 166-73, https://doi.org/10.47852/bonviewJOPR52025167.