Raman-based distributed optical fiber temperature sensors: industrial applications and future developments

This book chapter describes Raman Based Distributed Optical Fiber Sensors and their main industrial applications. In particular, after a brief introduction on the basic physical mechanisms, and a theoretical description of distributed optical fiber sensors based on spontaneous Raman scattering, we have focused our attention on the most attractive applications in terms of market opportunity: fire detection in tunnels and industrial plants and leakage detection in pipelines. We show that in order to achieve long sensing distances with high temperature resolution and good reliability, most standard Raman based distributed temperature sensors make use of graded-index multi-mode fibers, in double-ended or looped configuration. Advanced pulse coding techniques can however be effectively applied to make Raman sensors based on standard single mode fibers competitive with respect to other distributed optical fiber sensing technologies, such as Brillouin-based optical fiber sensors. Future developments of Raman based distributed temperature sensors will likely exploit standard single mode fibers, achieving meter-scale spatial resolutions over ultra-long distances, with high temperature resolution, fast response time, high robustness and reliability.