Localized Chemical Detection in Quasi-Distributed Multi-Node Fiber-Ring Network

Laser-based molecular spectroscopy plays an important role in chemical analysis and gas detection. Here we present how optical spectroscopy can be combined with quasi-distributed fiber-based passive sensing networks. Simultaneous gas detection and localization is demonstrated using photothermal interferometry at 1.55 mu m. With heterodyne-based signal retrieval sensor node position can be determined through measurement of phase/time delay of photothermal signal. This is performed using simple and passive network configuration. Proof-of-concept experiments are presented in which distance resolving power of approximately 5 meters was achieved with 1 second integration time. System performance, limitations, and capabilities are analyzed and discussed.