Research On Fabrication And Sensing Characteristics Of Sensitivity Enhancement Fiber Optic Sensor Based On Fused Tapering Method

Compared with other optical fiber sensors,tapered fiber sensor has the advantages of strong stability,simple control method and low cost,so it occupies a place in the field of optical fiber sensing.Fiber temperature sensor and fiber refractive index sensor based on fused tapering equipment show wonderful sensing characteristics in terms of temperature and refractive index sensing.First of all,the technology of fused tapering method,theoretical analysis and sensing mechanism of tapered fiber structure are introduced.The tapered fiber structure includes fused tapered Mach-Zehnder Interferometer;fused tapered two mode fiber;Mach-Zehnder Interferometer fused tapered long-period fiber grating;periodic tapered single-mode fiber and multi-mode fiber splicing structure.The temperature sensitivity of fused tapered Mach-Zehnder Interferometer structure is 47.82 pm/℃,and the refractive index sensitivity is too low,so the optical spectrum analyzer resolution has a certain influence on it.The temperature sensitivity of fused tapered two-mode fiber Mach-Zehnder Interferometer is 56.92 pm/℃,and the sensitivity of refractive index is too low,which is less than the resolution of the optical spectrum analyzer.The temperature sensitivity and refractive index sensitivity of the fused tapered longperiod fiber grating are 36.73 pm/℃ and-15.59 nm/RIU.The periodic tapered single-mode fiber and multi-mode fiber splice structure has low temperature sensitivity,which is affected by optical spectrum analyzer resolution and the refractive index sensitivity is 273.20 nm/RIU.Experimental results show that the sensitivity is low.In order to improve the sensitivity,a double tapered Mach-Zehnder Interferometer structure based on vernier effect and a flat tapered two-mode fiber long-period fiber grating are proposed.Secondly,in order to improve the temperature sensitivity,two double-taper Mach-Zehnder interference structures are cascaded using the vernier effect principle.The distances between the taper of the two structures are 4.6 cm and 3.5 cm respectively,and the FSR of their spectra are 7.50 nm and 10.91 nm,respectively.Experimental results show that the temperature sensitivity of the cascaded vernier envelope reaches 197.90 pm/℃,and the temperature sensitivity is 3.58 times higher than that of a single double-taper structure.Finally,in order to improve the sensitivity of refractive index,a flat taper type two-mode fiber long-period fiber grating refractometer is proposed,which successfully solves the problem of low sensitivity of refractive index.The sensor is composed of two mode fiber and single mode fiber spliced with fixed length period,and then fused tapered.The spectra of embedded different special fibers,the spectra of different lengths,the spectra of different number of periods,and the experimental of refractive index of different tapered diameters are compared.It is concluded that the smaller the diameter of the taper is,the higher the sensitivity is.The structure with the smallest taper waist diameter is 36 μm,and its refractive index sensitivity reaches 1360.64 nm/RIU.The temperature sensitivity of the structure was 11.19 pm/℃,and temperature had little effect on the refractive index experiment.In this paper,optical fiber sensors based on the fused tapering method are proposed.They not only show good sensing characteristics,but also carry out experimental research to increase their sensitivity,which can more accurately measure the experimental physical quantity,improve the measurement accuracy.