High visibility phase-sensitive optical time domain reflectometer for distributed sensing of ultrasonic waves

Abstract

In structural health monitoring, the propagation of ultrasonic waves along a structure can reveal interesting data relevant to the integrity of the whole structure. The availability of a system for distributed sensing of ultrasonic waves could, in some cases (e.g. pipelines) provide extremely valuable information to civil engineers. Phase-sensitive optical time domain reflectometry (ΦOTDR) is a simple and effective tool allowing the distributed monitoring of vibrations along single-mode fibers. Up to now, ΦOTDRs have been used mostly for the measurement of sub-kHz vibrations. In this work, the authors present an experimental characterization of a high-visibility ΦOTDR and its performance when used for ultrasonic vibration measurements. The sensor was able to measure vibrations of up to 39.5 kHz with a resolution of 5 m over a range which could go up to 1.25 km. This is the first time to our knowledge that a ΦOTDR is demonstrated for distributed measurement of ultrasonic waves.