Fiber-optic Magnetic Field Sensor Signal Processing Research

The optical fiber magnetic field sensor has high magnetic-sensing sensitivity, and can be used in national defence, industry, agriculture, and medicine fields. The development and current research status of optical fiber magnetic field sensor are outlined in this thesis. The main contents of this thesis are as follows: Firstly, the principle of eliminating polarization-induced fading in fiber interferometer with Faraday Rotator Mirrors (FRM) is analyzed by Jones matrix method. The optical fiber magnetic field sensor system based on polarization-insensitive Michelson interferometer is presented. In this thesis we analyze the sensing signal and sensor system noise, and bring forward methods of decreasing noises. Secondly, because of slow speed in sensor signal processing by Simple Genetic Algorithm, the methods of elitist model and quality judgment of population are used to improve Simple Genetic Algorithm and accelerate signal processing speed. The emulational results indicate: picking up sensor information and interferometer working point can be finished at the same time, and sensing signal is independent with working point. The sensing signal can be exactly obtained by the improved Genetic Algorithm, it adapts especially to the nonlinear and large signals when SNR≥10. Thirdly, aiming at the signal fading by random phase shift caused by the environment factor , we bring forward the f-2f method. The principle of using f-2f method for active phase compensation is analyzed, controlling working point flow by closed loop is designed and has been verified by experiment, the experimental results indicated that working point is well stabilized, the signal of magnetic field sensor has high stability, good linearity and high response speed. Furthermore, the principle of externally modulated PGC is introduced, and the signal characteristics are analyzed. The externally modulated PGC is verified by experiment, and several methods of decreasing noise are brought forward. At last, the thesis summarized the works which have been done, and gave some advice for the improvement of optic fiber magnetic field sensor.