Abstract
<jats:p>The rapid deployment of Gigabit Passive Optical Networks (GPON) as a core technol-ogy for broadband access has significantly increased the requirements for transmission reli-ability and physical layer stability. In shared optical access networks, such as GPON, the quality of the fiber-optic link plays a crucial role in ensuring stable data transmission, espe-cially under high split ratios and limited optical power budgets. One of the critical physical factors affecting network performance is optical return loss (ORL), which is caused by Fres-nel reflections and Rayleigh backscattering in optical fibers, connectors, splices, and other network components.This paper investigates the impact of optical return loss on data transmission reliability in GPON networks. The study focuses on the influence of back-reflected optical signals on signal quality, synchronization stability, and error performance, particularly in the upstream direction, where burst-mode receivers are used. The aim of the research is to assess the rela-tionship between ORL levels, optical budget margins, and key quality indicators of GPON systems.The research methodology combines theoretical analysis of physical processes in fiber-optic links, experimental measurements of real GPON lines using optical time-domain reflec-tometry, and mathematical as well as simulation modeling. The obtained results demonstrate that increased optical return loss leads to degradation of the signal-to-noise ratio, higher bit error rates, and reduced operational stability, especially when the network operates close to its maximum allowable optical budget.Based on the analysis, practical recommendations are proposed to minimize optical re-turn loss and improve GPON network reliability, including the use of angled physical contact connectors, optimization of connection topology, reduction of reflective events, and continu-ous monitoring of ORL parameters. The results confirm that effective control of optical return loss is a necessary condition for ensuring reliable and stable operation of GPON access net-works.</jats:p>