Research On Optical Fiber Magnetic Field Sensor Based On Surface Plasmon Resonance

As an important device to realize high sensitivity and high stability magnetic field sensing,optical fiber magnetic field sensor has been widely used in industrial production,residents’life,military navigation,medical inspection and other fields,and is developing towards miniaturization and high integration.As an effective means to realize optical modulation in nano size,SPR（surface plasmon resonance）effect can combine conventional optical fiber devices with magnetic fluid with unique optical properties（such as magneto-optical effect,magneto-induced anisotropy and tunable transmittance）,which provides a new way to prepare optical fiber magnetic field sensors with high sensitivity,miniaturization and stable performance.This thesis mainly analyzes and studies the operation principle and sensing characteristics of optical fiber SPR magnetic field sensor.The main work and innovative achievements are as follows:（1）The current research progress of optical fiber SPR sensor and magnetic field sensor are sorted out and summarized,on this basis,a new exploration on the development direction of optical fiber SPR magnetic field sensor is carried out.The excitation principle of metal surface plasma is deduced theoretically,and the photoelectric characteristics of graphene and its enhancement mechanism to metal SPR effect are analyzed theoretically.In addition,the physical characteristics and application scenarios of magnetic fluid materials are introduced.（2）An elliptical dielectric layer optical fiber magnetic field sensor based on surface plasmon resonance is proposed.The elliptical cavity of the optical fiber cladding is filled with magnetic fluid.By exciting the wave vector matching effect of the core mode and the metal surface plasma mode,the external magnetic field intensity in the range of50-115 Oe can be measured.The results show that the average sensitivity is 2.02 nm/Oe.In the range of magnetic induction intensity of 50-115 Oe,the highest sensitivity is S=2.28 nm/Oe,the calculated Figure of Merit is FOM=0.024 Oe^-1,and the resolution of output spectrum is R=4.9×10^-3Oe。（3）A new dual-channel optical fiber SPR magnetic field sensor is proposed,which measures the external magnetic field environment based on two dimensions,and has better sensitivity and anti-interference.Based on the common single-mode optical fiber,two fan-shaped air holes filled with magnetic fluid are ground on both sides of the cladding,and the inner surface of the cavity is filled with 40 nm gold film.The sensor can be used to measure the magnetic field strength in the range of 50-120 Oe.The results show that there are two loss peaks in the output spectrum.The sensitivity of the sensor is S=1.45 nm/Oe and the resolution is R=2.5×10^-5Oe,Figure of Merit FOM=0.018 Oe^-1.