Research On The Characteristics Of The All-Fiber Interferometric Micro-Cavity Sensing Structure

All-fiber interferometric sensor is generally based on the core mismatched structure,which uses mismatch coupling between modes,carries the sensing information through cladding mode,and couples back to fiber core to interfere,so as to achieve the purpose of sensing.This snsor has the advantages of simple fabrication,high measurement accuracy,low cost and flexible structure.Therefore,it has become a research hotspot of optical fiber sensing structure.In recent years,on the basis of existing sensor structures,exploring new sensing structures has become the primary goal of this structure research,the purpose is to improve sensing performance.Based on the all-fiber interferometric structure,a new interferometric micro-cavity structure is proposed.The sensing characteristics of this structure are studied through the combination of theoretical and experimental research.The main work includes:1.The development status of all-fiber interferometric sensing structure is reviewed.The sensitization methods(structure sensitization and material sensitization)of all-fiber interferometric sensor are reviewed.Structural sensitization includes optical fiber splicing,dislocation fusion,fused taper,femtosecond laser cavity opening,chemical etching,and material sensitization includes filling and coating.2.Based on the theory of multi-beam interference and analysis of refractive index power control of graphene,the optical power control characteristics of all-fiber interferometric micro-cavity structure are experimentally studied.Firstly,the optical field transmission of micro-air cavity structure and graphene-filled micro-cavity structure are simulated,the energy distribution of two structures are also studied.Secondly,the optical power control characteristics of the two structures are experimentally studied.The experimental results show that micro-air cavity is insensitive to the optical power control,and graphene-filled micro-cavity reflects a good optical power control characteristic.The interference wavelength drifts to the long wave with the increase of optical power,and the maximum wavelength drift can reach 0.883nm.At the same time,the optical power control characteristics of different wavelengths are also studied.The results show that the shorter the wavelength,the higher the corresponding sensitivity.Finally,the relationship between cavity length and sensitivity is studied.The results show that the longer the cavity length,the higher the sensitivity.When the cavity length is 56.0?m,the sensitivity is 66.4pm/mw.3.The liquid refractive index sensing characteristics of micro-air cavity and graphene-filled micro-cavity all-fiber interferometric sensing structure are studied.Firstly,the liquid refractive index of micro-air cavity sensing structure is experimentally studied.The experimental results show that the interference wavelength drifts to short wave with the increase of the liquid refractive index,the sensing sensitivity increases with the increase of micro-cavity length.The sensing characteristics of the sensing structure with the cavity length of 25.1?m,38.4?m,47.2?m and 56.0?m are studied respectively,and the maximum sensitivity is-85.488nm/RIU;Secondly,the liquid refractive index of graphene-filled micro-cavity structure is experimentally studied.The results show that the interference wavelength drifts to short wave with the increase of liquid refractive index,and the sensing sensitivity increases with the increase of micro-cavity length.The maximum sensitivity can reach-121.19nm/RIU.4.Double micro-cavity all-fiber interferometric sensing structure is constructed and its liquid refractive index sensing characteristics are experimentally studied.The experimental results show that with the increase of external liquid refractive index,the interference wavelength drifts to long wave,and the sensing sensitivity is 391.08nm/RIU in the refractive index range of 1.3415?1.3737.