Long-Range Distributed Fiber Vibration Sensor Using an Asymmetric Dual Mach–Zehnder Interferometers

An asymmetric dual Mach-Zehnder interferometry (ADMZI) design is proposed to achieve distributed fiber vibration sensing at long range. In this structure, we utilized two distributed feedback laser beams and dense wavelength-division multiplexing to significantly reduce the influence of Rayleigh backscattering noise, which will seriously deteriorate the signal noise ratio (SNR) in traditional dual Mach=Zehnder interferometer (DMZI) sensor. At the sensing length of 61 km, the SNR achieved using the ADMZI design is 20 dB higher than that using the DMZI design. Using a positioning algorithm based on the time=frequency analysis, the positioning mean square error can reach 52.5 m at this distance.