Optical fiber reflectometry detecting static and dynamic Rayleigh spectra

Abstract

Civil structures e.g. bridges, tunnels, and dams are essential to human societies. Currently, these complex engineered structures are challenged by aging issues. It is crucial to monitor the conditions of such structures in realtime to ensure their protection and conduct sufficient maintenance and rehabilitation when they begin to show omens of degradation or damage. Observation of Rayleigh scattering spectra from optical fibers using fiber Rayleigh reflectometry enables distributed sensing of static and dynamic strain in structural health monitoring for civil structures. Its key performance indices are the spatial resolution, the strain dynamic range, the measurement range, and the refresh rate. This article reviews tunable-wavelength optical time-domain reflectometry and coherent optical frequency-domain reflectometry and discusses the performance indices of each method in terms of the performance indices listed above. After analytical derivation, we have found that signal-to-noise ratios of both schemes are the same, which is a valuable discovery. In addition, we enumerate and review recent major industrial developments of both schemes.