Study On A Novel Optical Fiber Fabry-Perot Magnetic Field Sensor Based On Magnetic Fluids

In optical fiber sensors, optical fiber F-P sensor is one of the most developing rapidly optical fiber sensors in recent years. After 20 years of development, optical fiber F-P sensor is widely researched and applied in many fields. Compared with the electricity sensor, optical fiber F-P sensor has a series of unique advantages, such as high sensitivity, strong anti-electromagnetic interference, good electrical insulating property, anti-explosion, easy for optical fiber transmission system to consist of remote sensing network and so on.Magnetic fluids have been applied in many fields since the advent. It becomes a rookie in the functional materials, especially its refractive index control feature makes it become a kind of new optical material. In this thesis, used of the refractive index control feature of the magnetic fluids, combined with the advantages of optical fiber F-P interferometric sensor, the magnetic fluids as sensing medium, a new type of optical fiber F-P magnetic field sensor is proposed. The research of topic is bold innovation, make up and perfect to the blank in this study field. A laboratory method to make extrinsic optical fiber F-P sensor and to seal the sensor is developed.On the basis of a large number of domestic and foreign literatures, this topic has completed the following research work contents:(1) The basic principle and sensing properties of the optical fiber F-P sensor were studied. The numerical simulation analysis is done, and the simulation results showed that 80μm air cavity optical fiber F-P sensor had a good stability of temperature. Temperature measuring sensitivity of 80μm alcohol cavity optical fiber F-P sensor was -0.46nm/℃. The structure of the extrinsic optical fiber F-P sensor was designed. The performances of the materials were analyzed and chosen, and three different optical fiber F-P sensors were made.(2) On the basis of the principle of Fresnel reflex, a platform for measuring the refractive index was set up. The relationship between the magnetic fluids refractive index and magnetic field was measured, and the sensitivity was 0.00003RIU/Gs. The numerical simulation of magnetic fluids cavity optical fiber F-P sensor was analyzed. Optical fiber F-P sensor filled with magnetic fluids was produced. Magnetic field measurement experimental platform was set up, and the experimental results compared with the simulation results, the both magnetic field measurement sensitivity were the same about 0.03nm/Gs. It was proved that the method of making optical fiber F-P sensor was feasible. The measurement of magnetic field strength was realized.(3) In order to solve the problem of the temperature and magnetic field cross sensitive of the magnetic fluids, a sensor structure with temperature compensation was proposed, which was that on the basis of the magnetic fluids optical fiber F-P sensor a FBG temperature compensation unit was added. FBG reflectivity of 4% was put near the magnetic fluids, which effectively solved the problems of temperature and magnetic field cross sensitive. The measurement accuracy was improved. And double parameters measurement was implemented, the temperature sensitivity of 0.013nm/℃.In this thesis, the controllable feature of the magnetic fluids refractive index was experimentally studied. Filling the magnetic fluids into the optical fiber F-P sensor, a new type of magnetic field sensor was form. The magnetic field measurement was realized. Through further structural design, by using FBG the sensor temperature compensation was implemented. And the sensor with double parameters measurement of temperature and magnetic field was proved. However, the method of making the optical fiber F-P sensor and packaging method have yet to be perfect, which needs for a longer time to explore and research. The controllable characteristics of magnetic fluids refractive index still exists the magnetic field and temperature cross interference. Therefore, choosing a more effective method to remove the temperature cross interference, such as using a hollow photonic crystal fiber as the optical fiber F-P cavity etc., and improving the measuring accuracy are also the problems need to be further studied.