Research On Multi-physical Monitoring Technology Based On No-core Fiber Sensing

In recent years,a novel structure of optical fiber—No-core fiber(NCF)has attracted the attention of many researchers both at home and abroad.The mode-based interferometric sensor based on NCF has many advantages such as compact structure,high sensitivity and easy to realize multi-parameter measurement,and has been widely used in the field of environmental monitoring,biological and medical treatment,power system etc.This paper mainly focuses on the no core fiber-based all-fiber interference sensor combined with different sensing structures to study the response sensitivity to different environmental parameters and the response to vibration and impact loads in the field of structural health monitoring.The main work includes the following aspects:Firstly,according to the interference type sensing structure of single-no-core-single-mode(SNS)fiber,the theoretical basis of multimode interference is analyzed and with the help of Rsoft,an optical simulation software,the influence of the no-core fiber's size parameters and the environment refractive index on the optical field energy distribution and mode coupling efficiency is numerically simulated,which provided a theoretical basis for the subsequent design of the sensing structure and various sensing experiments.Secondly,based on the simulation study of the transmission spectrum characteristics of the no-core fiber(NCF)under different environmental refractive index,two refractive index fiber sensing structures are proposed,and the experimental system is established to study the response characteristics of liquid refractive index based on spectral identification.Thirdly,according to the requirement of simultaneous monitoring of environmental multi-paraeters,and the simultaneous measurement of temperature and refractive index is realized by cascading SNS structure and FBG.On the basis of this,the strain and bending response characteristics of SNS-FBG sensing structure are studied,the experimental results show that the structure can be used for temperature and strain,strain and bending and other dual-parameter s measurement field.Finally,the experimental system of vibration and impact load monitoring based on SNS structure was established with four solid aluminum alloy plate,and a graphical data acquisition and analysis software based on LabVIEW was compiled to study the response characteristics of SNS sensing structure to continuous vibration signals and transient excitation signals respectively.