Research On Micro-displacement Sensor Based On Self-focusing Characteristics Of Graded Multimode Fiber

Micro-displacement sensing plays a vital role in many fields,such as structural health monitoring,landslide monitoring,and micro-manufacturing.Fiber Surface Plasmons Resonance(SPR)sensor,as a new type of high precision,high sensitivity,anti-interference fiber sensor,has been widely used in the fields of biomedicine,food safety and chemical reagent detection.However,its research and application in micro-displacement measurement are very scarce,and there are few applications in multi-dimensional microdisplacement detection.The fiber optic SPR micro-displacement sensors that have been proposed currently mainly have narrow micro-displacement range and probe manufacturing technology.Complexity and poor stability of the sensing structure.This article focuses on the research on the mechanism of optical fiber SPR micro-displacement sensing,focusing on solving the problem of the difficulty in establishing the relationship between microdisplacement and SPR generation conditions and how to make the evanescent wave contact the sensing film,and strive to design a probe with simple manufacturing process and sensing Optical fiber SPR micro-displacement sensor with stable structure and large detection range,and strive to explore the possibility of multi-dimensional micro-displacement detection on this basis.Therefore,the specific research work is as follows:First,conduct an in-depth study on the optical fiber SPR sensing mechanism.Analyze the sensing mechanism of optical fiber SPR and study the conditions of SPR generation.According to theoretical analysis,the relationship between the optical fiber SPR sensing conditions and the amount of micro-displacement is established.Second,carry out simulation research on optical fiber SPR micro-displacement sensor.First,conduct a theoretical analysis of the self-focusing propagation characteristics of the graded multimode fiber,explore the influence of changing the longitudinal offset,the axial offset angle and the lateral offset on the optical path propagation trajectory in GIMMF,and then use the RSoft simulation software to perform the optical field analysis.simulation Research.Finally,according to the simulation results,the Matlab simulation program is used to further simulate the SPR transmission spectrum.Third,a micro-displacement sensor based on the self-focusing characteristics of a graded multimode fiber is proposed.By controlling the injection of a single-mode fiber,the longitudinal offset and the axial offset angle of the injection are changed to realize optical fiber SPR micro-displacement and micro-angle sensing.Theoretical analysis and experiments have proved that as the axial deviation angle and longitudinal deviation of the incident light increase,the resonance wavelength of the transmission spectrum of the sensing probe all moves to the long wavelength direction,and the depth of the resonance valley increases accordingly.The wavelength sensitivity and light intensity sensitivity of the microdisplacement sensor are 0.7084nm/?m and 0.0236 a.u./?m,respectively,and the wavelength sensitivity and light intensity sensitivity of the micro-angle sensor are 2.417nm/° and0.0236 a.u./°,respectively.Fourth,a micro-displacement sensor based on a graded multimode fiber heterogeneous core structure is proposed.Through the research on the practical characteristics of the heterogeneous core structure fiber,and based on the self-focusing propagation characteristics of the graded multimode fiber,the micro-displacement sensing probe was designed and fabricated,and the wide beam and the tilted beam were studied separately for beam injection with longitudinal offset.The influence of micro-displacement sensing performance.The experimental results show that under the condition of oblique beam injection,as the longitudinal offset of the injection increases,the resonance wavelength of the transmission spectrum of the sensor probe moves to the long wavelength direction,and the depth of the resonance valley increases accordingly.The wavelength sensitivity and light intensity sensitivity are 0.5097nm/?m and 0.0097au/?m respectively,and the detection range of micro-displacement is expanded to 0-75?m.This is 3 times the range of the proposed optical fiber SPR micro-displacement sensor.Fifth,a two-dimensional micro-displacement sensor based on the self-focusing characteristics of a graded multimode fiber is proposed.By micro-machining the dual concentric-core fiber(Dual Concentric-Core Fiber,DCCF)into a tapered end surface structure,two different available output light fields are constructed on the same fiber,and then the two light fields are used to achieve different dimensions.Therefore,a twodimensional micro-displacement sensing probe based on the self-focusing characteristics of gradual multimode fiber is proposed.According to the experimental results,when the ring core of the DCCF passes through,the outgoing light field is in the shape of a ring horn.As the lateral offset increases,the SPR resonance wavelength is red-shifted and the resonance valley depth increases.The lateral displacement range is 10-Within 310?m,the wavelength sensitivity is 0.6594nm/?m,and the light intensity sensitivity is 0.00108au/?m.When the center core of the DCCF is lighted,the emitted beam is slightly larger than that of the singlemode fiber and is emitted horizontally.As the longitudinal offset increases,the SPR resonance wavelength is red-shifted and the resonance valley depth increases,and its longitudinal micro-displacement The wavelength sensitivity and light intensity sensitivity are 0.3935nm/?m and 0.00331au/?m,respectively,and the longitudinal displacement range is 0-60?m.In summary,this paper proposes a micro-displacement sensor based on the selffocusing characteristics of a graded multimode fiber,which realizes dual sensing of microdisplacement and micro-angle on a single tapered multi-mode fiber;and researches on the heterogeneous core structure fiber,and then proposes A micro-displacement sensing scheme based on a graded multimode fiber with a different core structure was developed and verified,which effectively reduced the complexity of probe production and improved the structural stability;finally,the tapered end face of the coaxial dual waveguide fiber The combination of the light-injecting structure and the micro-displacement sensing scheme based on the heterogeneous core structure of the graded multi-mode fiber effectively realizes the twodimensional micro-displacement sensing based on the self-focusing characteristics of the graded multi-mode fiber.