Phase-Sensitive OTDR Monitoring for Fault Detection in High-Density Multi-Branch Passive Optical Networks

Passive optical networks (PONs) face significant challenges in fault detection and monitoring, particularly in high-density, multi-branch configurations. This study proposes a novel monitoring scheme for PONs based on phase-sensitive optical time-domain reflectometry (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\varphi$</tex-math></inline-formula>-OTDR). The system assigns a unique identification frequency (IF) generated by a single piezoelectric transducer (PZT) at each branch endpoint and leverages <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\varphi$</tex-math></inline-formula> -OTDR's distributed sensing capability to determine the physical status of individual branches. By quickly detecting these pre-configured IF labels, the method enables rapid and accurate identification of distribution drop fibers experiencing severe power anomalies, thus guiding physical link maintenance in PON systems. A new evaluation criterion, the detection margin (DM), is introduced to quantify the quality of the recovery of the IF signal. A higher DM value indicates superior performance in the monitoring of IF signals, reflecting improved system reliability, robustness, and improved fault detection capabilities. Experimental results demonstrate the system's ability to monitor up to 16 connected branches in a 1:16 split ratio, with a DM value consistently above 3.7dB, effectively mitigating inter-branch interference. This novel approach not only enhances the network's reliability and scalability but also provides valuable insights for advancing <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\varphi$</tex-math></inline-formula>-OTDR applications in multi-branch identification and next-generation optical networks