Distributed Rayleigh Sensing
Rayleigh backscattering (RBS) in optical fiber is a fundamental phenomenon caused by random fluctuations in the index profile along the fiber length. Optical reflectometry is the best tool to obtain RBS signals with a distributed way along the fiber and is widely used as a nondestructive measurement at one end of the fiber. With the help of optical reflectometry, RBS signals are used for distributed fiber-optic sensing with temperature/strain/vibration information along the fiber. Understanding the mechanisms of RBS provides a powerful technique for static and vibration sensing used for applications such as structural health monitoring and damage assessment analysis. The technology based on RBS signals to extract the environmental perturbation is mature, but researches on obtaining a high spatial resolution together with a long measurement range are still very active, promoting the technology to be used in more industrial applications with strict requirements on these parameters such as monitoring the optical fiber inside the aircraft wings with a spatial resolution of better than 1 mm over several 100 m.
In this book chapter, after a first description of RBS mechanism in optical fibers, the working principle of static and vibration measurement based on RBS signals is provided. Then, different kinds of optical reflectometry based on time-domain, frequency-domain, and coherence-domain techniques are introduced in details. In the final section, advanced methods to improve both the spatial resolution and the measurement range are presented which pave the way for new horizons in high-end applications.
KeywordsRayleigh backscattering (RBS) Static measurement Vibration measurement Optical reflectometry Optical time-domain reflectometry (OTDR) Optical frequency-domain reflectometry (OFDR) Optical coherence-domain reflectometry (OCDR) Optical low coherence reflectometry (OLCR) Pulse compression Synthesis of optical coherence function (SOCF) Spatial resolution Measurement range Sensitivity
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