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

Fiber optic weak magnetic sensor has high sensitivity, small volume, and can measure magnetic field along three orthogonal directions. It is widely used in national defence, medicine, geology and so on. In the thesis, a signal processing scheme of polarization-insensitive fiber optic Michelson interferometric magnetic sensor is described: making the interferometer work near the quadrature with closed loop controlling working point method, the fundamental frequency component of the magnetic field sensing signals can be detected to measure the input direct current (DC) magnetic field by phase sensitive demodulation. The algorithm principle, hardware design and software design of the scheme are proposed and experimentally demonstrated; the main contents of this thesis are as follows:Firstly, we study the principle of the fiber optic weak magnetic sensor based on magnetostrictive effect. After analyzing the characters of the magnetic field sensing signals, we know that the magnetic field sensing signals'fundamental component is proportional to input DC magnetic field. Then the signal fading problem of the sensor arising from environmental effects is presented and several solving methods are introduced. At last, we choose the closed loop controlling working point method to stabilize the sensor's working point because of its'high sensitivity and simple structure. Secondly, the noise of the system is analyzed. To improving the signal-to-noise of the system, design the phase sensitive demodulation system which contains three parts: Signal channel, reference channel and correlation demodulator. Signal channel is composed of photodetection preamplifier and filter circuit, reference channel and correlation demodulator are realized by Labview. Besides, we use software smooth filtering to minish the influence of white noise and high-frequency noise, ground connection and shield technology to eliminate electromagnetic interference, and rational circuit distribution to attain high signal-to-noise of the whole fiber optic weak magnetic sensor system.Finally, the fiber optic weak magnetic sensor system is verified by experiments using the signal processing scheme. We have tested the frequency response of the sensor...