Conventional optical time-domain reflectometry (OTDR) schemes for passive optical network (PON) link monitoring are limited by insufficient dynamic range and spatial resolution. The expansion of PONs, with increasing optical network units (ONUs) and cascaded splitters, imposes even more stringent demands on the dynamic range of monitoring systems. To address these challenges, we propose a time-gated digital optical frequency-domain reflectometry (TGD-OFDR) system for PON monitoring that effectively decouples the inherent coupling between spatial resolution and pulse width. The proposed system achieves both high spatial resolution (~0.3 m) and high dynamic range (~30 dB) simultaneously, marking a significant advancement in optical link monitoring.

At present, the demand for perimeter security system is increasing greatly, especially for such system based on distributed optical fiber sensing. This paper proposes a perimeter security monitoring system based on phase-sensitive coherent optical time domain reflectometry(Ф-COTDR) with the practical pattern recognition function. We use fast Fourier transform (FFT) to exact features from intrusion events and a multi-class classification algorithm derived from support vector machine (SVM) to work as a pattern recognition technique. Five different types of events are classified by using a classification algorithm based on SVM through a three-dimensional feature vector. Moreover, the identification results of the pattern recognition system show that an identification accurate rate of 92.62% on average can be achieved.