Fiber-optic All-polarization Sagnac Magnetic Field Sensor

Magnetic field is one of the most basic physical quantities,and the precise measurement of magnetic field represents to a large extent the level of national high-tech development.At present,magnetic field sensors have been widely used in scientific research,production and life areas such as military,geospatial physics,industrial manufacturing,and biomedicine.According to different measurement principles,magnetic field sensors can be divided into two types:optical and non-optical.Most non-optical magnetic field sensors have shortcomings such as susceptibility to electromagnetic interference,temperature sensitivity,and the contradiction between high precision and small size.In contrast,optical magnetic field sensors naturally have the advantages of anti-electromagnetic interference and integration,among which the development of optical fiber magnetic field sensors is particularly rapidThe purpose of this thesis is to develop a novel vector type optical fiber magnetic field sensor with high precision,large dynamic range and high stability,providing methods and solutions for solving the current problems of low sensitivity,poor stability,and inability to distinguish the directionThis thesis proposes a fiber optic all-polarization Sagnac magnetic field sensor,which combines the sensor unit with high magnetic field sensitivity and a high-stability Sagnac system,and innovatively proposes the use of polarization interference detection to precisely measure weak magnetic signals.Based on the theory of polarization interference and the Jones matrix,the thesis establishes a theoretical model,derives a quantitative mathematical model,and carries out simulation analysis and experiments on the model to verify the theory.The correctness and feasibility of the theoretical model and detection method are verified,and preliminary experimental results show that the system has a magnetic field resolution of the magnitude of nT.The overall design of the fiber optic all-polarization Sagnac magnetic field sensor is completed.The key technologies involved in the system are studied and verified,including magnetic flux amplifier,Faraday modulation and lock-phase detection,polarization control,special fiber loop,etc.,laying the foundation for the construction of the prototype.The analysis of the main errors in the system is completed,including photoelectric detection error,optical path system error and environmental error.Detailed theoretical analysis and simulation of each error is carried out,and the corresponding error suppression methods are proposed,which effectively improved the weak magnetic field measuremen performance of the system.The experimental research of the fiber optic all-polarization Sagnac magnetic field sensor is completed.The prototype built achieves a DC magnetic field resolution of 5.6nT under an AC modulation with the frequency of 100Hz and the amplitude of 0.75G.Since the magnetic saturation intensity of the used magnetic optical crystal is greater than 500G,the dynamic range of the system is thought to be larger than 70dB.Besides,the linearity of the system is greater than 99.8%and the instability of the system is less than 0.5%.