The distributed optical fiber magnetic field sensors have a capability of spatially resolving the magnetic field along the
entire sensing fiber that is distinguishes from other sensing methods. We present a distributed optical fiber magnetic field
sensor based on magnetostriction using Rayleigh backscattering spectra shift in OFDR (optical frequency-domain
reflectometry). As the spectral shift of Rayleigh backscattering can be used to achieve a distributed strain measurements
with high sensitivity and high spatial resolution using OFDR. In the proposed sensor, the magnetostrictive Fe-Co-V alloy
thin films as sensing materials are attached to a 51 m standard single mode fiber (SMF). We detect the strain coupled to
SMF caused by variation of magnetic field by measuring Rayleigh Backscattering spectra shift in OFDR. In our
experiment, we measure the range of the magnetic field is from 12.9 mT~143.3 mT using proposed method. The
minimal measurable magnetic field variation is 12.9 mT when the spatial resolution is 4 cm. The minimal measurable
magnetic field variation can be improved to 5.3 mT by increasing the spatial resolution to 14 cm. Moreover, we present
the simulation result of two dimension (2D) distribution for the static magnetic field using the Maxwell software
program.
We present a long-range high spatial resolution optical frequency-domain reflectometry (OFDR) based on optimized deskew filter method. In proposed method, the frequency tuning nonlinear phase obtained from an auxiliary interferometer is used to compensate the nonlinear phase of the beating signals generated from a main OFDR interferometer using a deskew filter. The method can be applied for the entire spatial domain of the OFDR signals at once with a high computational efficiency. In addition, we apply the methods of higher orders of Taylor expansion and cepstrum analysis to improve the estimation accuracy of nonlinear phase. We experimentally achieve a measurement range of 80 km and a spatial resolution of 20 cm and 80 cm at distances of 10 km and 80 km that is about 187 times enhancement when compared with that of the same OFDR trace without nonlinearity compensation. The improved performance of the OFDR with the high spatial resolution, long measurement range and short process time will lead to practical applications in real-time monitoring and measurement of the optical fiber communication and sensing systems.
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