Optical fiber vibration sensing system using delay line method.

A delay line method for a distributed optical fiber vibration sensing system is reported. The sensing system is a combination of non‐balanced Sagnac/Mach‐Zehnder structure and an adjustable optical fiber delay line. The vibration location principle is the expansion of conventional null‐frequencies theory, which needs to adjust the length of delay line, in order to determine a zero point in the amplitude variation curve of detected light intensity for one characteristic frequency appearing in the vibration signal spectrum. Moreover, the location simulation using delay line method for narrowband vibration signals is affected. Finally, the experiment verifies that the location errors of vibration events are within ±70 m. The main advantage of proposed method is that it can locate not only the broadband vibration but also the narrowband vibration. [ABSTRACT FROM AUTHOR]