Research On Optical Fiber Magnetic Field Sensor Based On Mach-Zehnder Interferometer

The application of magnetic fluid and Mach–Zehnder interferometer is studied in this paper.As we know,magnetic particles whose magnetization direction is the same as external magnetic field direction will be arranged along the direction of magnetic field because of the chain aggregation.The radius of the chain structure will increase when the magnetic field strength increases.Besides,the refractive index and dielectric constant of magnetic fluid will change when the external magnetic field changes.Not only the wavelength and intensity but also the phase and polarization state will change when optical fiber sensor head is covered or filled with magnetic fluid.So sensors based on magnetic fluid and optical fiber can be applied to detect magnetic field.The main work of this thesis as follows:1.The research status of magnetic fluid and optical fiber sensor is introduced.The principle of optical fiber magnetic field sensor is discussed and explain advantages and disadvantages of several kinds of sensors.2.The constituent elements of magnetic fluid is introduced in detail.The characteristics of magnetic fluid,such as stability,birefrigent effect,magnetron refractive effect and super-paramagnetic effect are explained.Also,we present the preparation processes,such as pyrolytic process and mechanical mill method.3.An optical fiber magnetic sensor based on waist-enlarged tapers is proposed.In the magnetic field experiment,the intensity of light wave shifts monotonically from-50.28 dBm to-61.601 dBm when the magnetic induction intensity changes from 0 mT and 120 mT.The sensitivity of this sensor is 0.0943dBm/mT.4.An optical fiber magnetic sensor based on peanut shape and core-offset structure is proposed and demonstrated.Measurements of refractive index and temperature base on peanut shape and core-offset structure(no magnetic fluid film)are carried out.The sensitivity of refractive and temperature is 29.68934nm/RIU and 57.86pm/? respectively.In the magnetic field experiment,the sensor head is covered with magnetic fluid film and its sensitivity is 12.227pm/mT.