Abstract:  In order to solve the problem of low positioning accuracy in disturbance monitoring system, an
improved dual Mach-Zehnder distributed optical fiber sensing system is designed for real-time monitoring of
disturbances, which is based on the study of Mach-Zehnder fiber interferometer. The optical path difference in
the dual Mach-Zehnder optical fiber sensing system leads to the time difference, and then the system uses cross-
correlation algorithm to estimate the time difference, to ensure the perturbation point. The independently
designed the signal preprocessing circuit and filtering algorithm are realized through the Butterworth low-pass
filter filtering the high-frequency noise that above 3. 3 kHz. And via the embedded acquisition and processing
module the correlation is improved and positioning error is reduced. After repeated tests and data analysis, it is
shown that the system can be used for real-time disturbance monitoring and the positioning error is
about 5 meters.

Key words:  distributed fiber optic sensing, cross-correlation, low-pass butterworth filter, Mach-Zehnder interferometer(MZI), phase modulation