Research On Optical Fiber Refractive Index Sensor Based On S-cone Structur

With the rapid development of optical fiber sensing technology,researchers have developed many new micro sensors by simplifying preparation methods,combining new materials,improving device sensitivity,optimizing sensing parameters and other aspects.These sensors have broad application prospects in environmental sensitivity,chemical detection,biological monitoring and other aspects.In this paper,based on the MachZunder(MZI)principle,on the basis of simple preparation,stable structure and low cost,using arc discharge technology,S-cone structure fiber sensor and S-taper structure fiber sensor coated with dimethylsiloxane were designed and prepared,and the refractive index sensing characteristics and temperature sensing characteristics of the structure experiments,the main contents are as follows:(1)The interference principle of MZI and S-taper structure of single-mode fiber is studied.On this basis,the theoretical model of S-taper is established by using the beam propagation method,and the relationship between the geometric parameters such as the axial dislocation,the diameter and the length of the waist cone and the interference spectrum is analyzed,which lays a foundation for the fabrication of S-taper fiber.(2)The S-taper structure optical fiber sensor was prepared by arc discharge technology.By changing the parameter setting of the optical fiber welding machine and manually controlling the amount of axial dislocation,the S-taper structure with different diameter of the waist cone and axial dislocation was obtained.The spectral characteristics of a variety of S-taper with different waist diameter and axial dislocation were compared and analyzed.Finally,the S-taper structure with waist diameter of 40μm and axial dislocation of 80μm was selected.Therefore,the experiments of refractive index and temperature sensing characteristics were carried out.The experimental results show that the structure has high sensitivity,the refractive index wavelength sensitivity is 524.41nm/RIU,and the S-taper is insensitive to temperature under indoor temperature.In order to ensure the reliability and stability of S-taper,repeatability experiments of refractive index sensing characteristics of the structure were carried out,and the experimental results show that the structure has good repeatability.(3)In order to enhance the stability of the S-taper structure and the sensitivity of the sensor’s refractive index intensity,the single-mode S-taper was coated with polydimethylsiloxane(PDMS)to improve its refractive index intensity sensitivity.The experimental results showed that the sensitivity of the structure was significantly improved compared with that of the single-mode S-taper without PDMS coating.The intensity sensitivity of refractive index was-50.7 d B/RIU,wavelength sensitivity was209.54 nm/RIU,and temperature sensitivity was 0.182 d B/℃.The problem of temperature cross-sensitivity is solved by using two-parameter measurement method.The repeatability experiments of refractive index sensing and temperature sensing characteristics of the structure were carried out.The simple preparation of the structure,high sensitivity,good repeatability has a certain practical value.