Theoretical Research On Micro-Strain Sensing Characteristics Of Tapered Optical Fiber

Strain is an important parameter to evaluate the health of building structure in engineering field,so it is very important to detect it timely and effectively.Compared with the traditional electrical sensors,optical fiber sensors have the advantages of corrosion resistance,small size,anti electromagnetic interference and so on,which are widely used in strainmeasurement.However,strain measurement in micro strain and complex environment has always been the research hotspot and difficulty of optical fiber strain sensor.In this paper,the micro strain sensing characteristics of tapered fiber are studied theoretically.Firstly,the principle of all fiber on-line Mach Zehnder interferometer sensor is analyzed,and the energy changes of core and cladding in straight tapered fiber and S-tapered fiber are compared and analyzed by using beam propagation method.The results show that S-tapered fiber is easier to excite cladding mode than straight tapered fiber.Secondly,based on Mach Zehnder interferometer theory,the sensing relationship between wavelength and strain is established to improve the sensitivity The strain sensing characteristics of straight tapered single-mode fiber,straight tapered photonic crystal fiber,S-tapered single-mode fiber and S-tapered photonic crystal fiber are analyzed by finite element method.The results show that the S-tapered photonic crystal fiber has the best sensitivity than the other three kinds of fibers in measuring the same fiber elongation.Then,according to the analysis results,a S-tapered photonic crystal fiber micro strain sensor based on inter mode interference is designed.The influence of the tapered length,tapered diameter,axial offset,air hole and its duty cycle on the strain sensing characteristics of S-tapered photonic crystal fiber is investigated by using the finite element analysis method from two aspects of wavelength change and light intensity change.Finally,taking the inverse piezoelectric fiber voltage sensor as the application object,aiming at its disadvantages such as complex structure,difficult manufacturing process and easy to produce bending loss,a new scheme of inverse piezoelectric fiber voltage sensor based on S-tapered photonic crystal fiber is proposed,and its theoretical feasibility is briefly analyzed.In addition,in order to promote the practicality of tapered fiber strain sensor,the laboratory fabrication of tapered fiber is also explored.The research of this paper provides a new idea and theoretical basis for the design of micro strain sensor.At the same time,due to the flexible structure design of s-tapered photonic crystal fiber,it provides more analysis angles for the optimization of micro strain sensor.In addition,the new optical fiber structure is applied to the inverse piezoelectric optical fiber voltage sensor,which greatly simplifies the system structure,solves the problems of manufacturing process and loss,and provides a theoretical reference for the research of the new inverse piezoelectric optical fiber voltage sensor.