Polarization-independent Fiber-optic Michelson Interferometer Weak Magnetic Field Sensor

In this thesis, a scheme of polarization-insensitive fiber optic Michelson interferometric magnetic sensor is proposed on the base of analyzing several kinds of fiber optic magnetic sensors. The principle of the scheme has been expounded in detail. After designing the sensor head, we set up the experiment system, and then completed the experiment.Firstly, the principle of the fiber optic interferometer is analyzed. The main factors that influence the visibility of the interferometer have been discussed, and the corresponding improving methods have been given. In this thesis we analyze in detail the influence, created by random change of the optical wave polarization, on the output of the interferometer. Then several principles of eliminating polarization-induced fading are introduced, and the principle that inserting two Faraday Rotator Mirrors into the end of Michelson fiber interferometer to eliminate the fading is analyzed in detail. This method can eliminate polarization-induced fading without additional signal processing, and make the output of the sensor stable.Secondly, we introduce the sensor system, analyze the optic noise and the output signal in detail and get the scheme of measuring the DC and AC magnetic field. We improve the sensor head structure on the basis of analyzing the factors influencing the sensor head sensitivity. Using thin fiber withФ80μm and special framework, we get magnetic sensor head with small volume, high sensitivity and wide frequency response spectrum.Then, we set up the experiment system. After stabling the working point, we measured the frequency response of the system, then measured the output of the DC magnetic field under different AC modulating magnetic fields.The experimental results show that the output of the system is linear with the detected signal when the measured magnetic field is small. With an AC modulating magnetic field of amplitude of 4000nT, the magnetic sensor phase sensitivity to detecting DC magnetic field can reach 1.4×10-3 rad/nT, and the minimum detectable DC magnetic field is 0.57nT. Then the scheme of...