Research On Magnetic Field Sensor Based On Hollow Core Optical Fiber Devices

Based on the optical transmission characteristics of air-core optical fiber and the unique magnetic-field-dependent refractive index characteristics of magnetic fluid,this paper designs U-bent optical fiber magnetic field sensor.The proposed sensor probe consists mainly of a single-mode fiber(SMF)-U-shaped hollow-core fiber(UHCF)-singlemode fiber(SMF)(SMF-UHCF-SMF)structure,with a UHCF sandwiched between two SMFs.Firstly,this paper introduces the research status of optical fiber magnetic field sensor based on MF,analyzed the sensing principle of the optical fiber sensor and the preparation method of the optical fiber structure of the sensor probe SMF-UHCF-SMF.Then explore the sensor’s characteristics on the refractive index,magnetic field,and temperature,and finally analyzes the effects of sensor optical fiber structure parameters on the sensor transmission spectrum.The main research content and innovation of this paper are as follows:1.Taking advantage of the optical transmission characteristics of the hollow-core fiber and the adjustable refractive index characteristics of the magnetic fluid,the optical fiber sensor based on the magnetic fluid and the SMF-UHCF-SMF optical fiber structure was proposed,which realizes the dual parameter measurement of the magnetic field intensity and temperature.Unlike other sensors,our sensor is very simple to fabricate because only fusion splicing and encapsulation are involved.Our designed sensing structure has good sensitivity,good linearity of response,low cost,no other processing is required.In this paper,the preparation process of SMF-UHCF-SMF fiber structure is described,and the sensing principle of this sensor is analyzed theoretically.Combined with the multi-mode interference and macro bending loss of SMF-UHCF-SMF fiber structure,the U-shaped fiber sensor with different bend diameters was investigated.2.Through experimental investigation,the SMF-UHCF-SMF optical fiber structure sensor’s response to the magnetic field intensity and temperature,and obtained the corresponding transmission spectrum.After experimental and data analysis,it can be obtained that: The transmission spectrum of the sensor varies with the strength and temperature of the magnetic field around the sensor,the maximum magnetic field intensity sensitivity of 1.0898 nm/m T in the measurement range from 38 m T to 62 m T,and the maximum temperature sensitivity of 0.324 nm/°C under the range of 25°C ～65°C.3.The influence of the three parameters,the diameter of the core of the HCF,the length of the HCF,and the SMF-UHCF-SMF optical fiber structure bending diameter on the sensor output spectrum,and then obtain the best SMF-UHCF-SMF optical fiber structure parameters: The diameter of the core of the HCF is 10 μm,the length of the HCF is 5mm,and the diameter of the SMF-UHCF-SMF optical fiber is 54 mm.