Research On Michelson Sensor Based On Side-polished Two-core Fiber

With the rapidly developing communication networks,optical fiber devices with various functions have been widely used in the fields of environmental monitoring,aerospace,national defense,military and machinery industry.However,with the expansion of application fields and higher performance requirements,the traditional optical fiber sensor based on single mode fiber(SMF)has limited its application in some new fields because of its low sensitivity,single structure and other disadvantages.Special fiber has unique structure and optical properties.Optical fiber devices designed on the basis of them can improve the performance of optical fiber devices and make them have a wider application prospect.Fiber processing technology will make special fiber produce strong evanescent field,enhance the interaction ability of light signal and external environment.Therefore,in order to further improve the sensitivity performance of fiber optic sensor and expand its measurement range,special fiber with strong evanescent field can also be combined with two-dimensional materials to realize the high sensitivity measurement of fiber optic sensor to different physical quantities.Based on the combination of polished two-core fiber(TCF)with magnetic fluid(MF),polydimethylsiloxane(PDMS)and other two-dimensional materials,vector magnetic field sensor,refractive index sensor and humidity insensitive temperature sensor are proposed in this thesis.The main work of this thesis includes:(1)A temperature sensor based on PDMS coated polished TCF is proposed.Firstly,a core of the TCF was exposed to air by wheel mechanical polishing method to generate a strong evanescent field.The PDMS with high thermal sensitivity is coated on the polishing surface,and the change of external temperature changes the refractive index(RI)of the PDMS,resulting in the change of the effective RI of the polished fiber core,so as to change the resonant peak of the spectrum and realize the measurement of temperature.The temperature sensitivity is as high as 694.3 pm/°C when the polished length is 8 mm and the polished depth is 29.5 μm.The longer the polished length,the deeper the polished,the greater the transmission loss and sensor sensitivity.the stronger the evanescent field of fiber generation and the greater the temperature sensitivity.The temperature sensor is insensitive to the change of ambient humidity due to the protective effect of hydrophobic PDMS on the polished area.(2)A refractive index and vector magnetic field sensor based on side-polished TCF Michelson interferometer is proposed.In order to evaluate and measure the refractive index sensing characteristics,a microchannel was constructed in the polishing area of the TCF using a capillary tube.The sensor sensitivity was as high as 703.5 nm/RIU.The polished TCF is sealed in a capillary filled with magnetic fluid.Through the evanescent field generated by polished core,the sensor senses the refractive index change of the magnetic fluid to realize the magnetic field intensity measurement.The magnetic field sensor designed in this paper can measure the direction of the magnetic field because the symmetrical structure of the TCF is broken by side throwing.The maximum sensitivity of the sensor in the direction of the magnetic field is 55.2 pm/°.When the magnetic field is parallel to the polished plane,the device is least affected by temperature changes in the field intensity range of 0 ～ 5 m T and the temperature range of 20 ～ 85℃,and the sensitivity can reach 1.262nm/m T.The sensor has the characteristics of low cost,strong anti-interference ability,simple structure,high stability,suitable for a variety of applications.