| Magnetic fluid is a new type of functional material,and its unique magneto-optical properties make it attract much attention in the field of optical fiber magnetic field sensing.In recent years,experts and scholars have carried out a lot of research on the interference type optical fiber magnetic field sensor by combining magnetic fluid and optical fiber sensing structures.The interferometric fiber optic magnetic field sensor based on magnetic fluid has the characteristics of stable structure,low cost,high sensitivity and so on,and has great application prospects in the field of magnetic field sensing measurement.In this thesis,the composition and optical properties of the magnetic fluid are briefly introduced,and the response of the refractive index of the magnetic fluid to the external magnetic field and temperature is investigated experimentally,and three kinds of interference-type magnetic fluid optical magnetic field sensors with excellent performance are designed and fabricated from different combination angles of the magnetic fluid coating or filling the optical fiber sensor.The main work of this thesis is as follows:Firstly,we designed and fabricated a magnetic fluid refractive index measurement probe,built an end-reflection type magnetic fluid refractive index measurement system,and experimentally studied the variation trend of the refractive index of magnetic fluid with the change of magnetic field and temperature,which provides a theoretical and experimental basis for the design of magnetic field sensors using the tunable properties of refractive index of magnetic fluid.Secondly,we designed and fabricated a Mach-Zehnder interferometric magnetic field sensor with a magnetic fluid-clad spherical-thin-core-spherical structure using the tunable refractive index of the magnetic fluid.We can obtain the magnetic field sensitivity by monitoring the variation of the wavelength and amplitude parameters of the transmission spectrum with the magnetic field,and experiments show that the magnetic field sensitivity of this sensor is-98 pm/m T.Then,on the basis of spherical-thin-core-spherical sensing structure,we improved and designed a spherical-multimode-thin-core-spherical optical fiber magnetic field sensor based on magnetic fluid coating.The sensor excites more high-order modes,and couples more beams into the cladding of the sensing fiber for transmission,and improves the extinction ratio of the output transmission spectrum,so it has a strong anti-noise function,and the highest magnetic field sensitivity is128 pm/m T.In addition,since temperature is also a major factor affecting the refractive index of magnetic fluid,this thesis established a temperature response measurement system for a Mach-Zehnder interferometric optical fiber magnetic field sensor based on magnetic fluid,and explored the temperature response of the two sensors before and after improvement.By establishing a sensitive matrix,both sensors can measure the external temperature and magnetic field simultaneously.The optical fiber magnetic field sensor based on the magnetic fluid-coated spherical structure and the thin-core optical fiber has the advantages of stable structure and high sensitivity.Moreover,it can be successfully fabricated only with an optical fiber fusion splicer,which also has the advantages of simple operation and low cost,and has great application value in the field of simultaneous measurement of temperature and magnetic field.Finally,we designed and fabricated a magnetic fluid filled fiber-optic Fabry-Perot interferometric magnetic field sensor,and simulated and analyzed the effect of Fabry-Perot’s cavity length and refractive index on the reflection spectrum,and fabricated a magnetic fluid cavity Fabry-Perot interferometric magnetic field sensor with a cavity length of 35 μm,and conducted magnetic field sensing research on it.The results show that the sensor has a magnetic field sensitivity of 249.7pm/m T.The magnetic fluid filled Fabry-Perot interference magnetic field sensor has the advantages of high sensitivity and simple structure,and has a good application prospect in the field of magnetic field measurement. |
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