Fabrication And Sensing Characteristics Research By Heterogeneous Fiber Splicing Of Fiber Optic Sensor

With the advantages of high sensitivity,high accuracy,anti-electromagnetic interference,safety and reliability,and long-distance transmission,fiber-optic sensors are widely used in industrial production,food safety,biomedicine,environmental monitoring and other fields.Fiber optic sensors based on continuous splicing of heterogeneous optical fibers have the advantages of simple structure,high integration and easy preparation,and have the potential of multi-point series and parallel connection to form a sensing network.In this paper,we designed and built a spliced fiber optic sensor with a simple structure,low cost and temperature compensation,and used the fiber optic precision cutting and splicing device to prepare a variety of new spliced fiber optic sensors and study their sensing characteristics.In this paper,the theoretical study of the heterogeneous fiber splicing fiber sensor was presented,and the simulation model of the heterogeneous fiber splicing fiber sensing structure was established by using the three-dimensional finite difference beam propagation method,and the influence of the length and number of periods of the fiber on the transmission spectrum was determined by analyzing the energy exchange and transmission spectrum between the heterogeneous fibers in the simulation model.Secondly,a preparation device for heterogeneous fiber splicing fiber sensor was developed.The device is simple and inexpensive,and can be used to prepare a variety of different types of spliced optical fiber sensors,which can excite higher order cladding modes in a shorter length and achieve the measurement of a variety of physical parameters.Finally,two different types of heterogeneous fiber optic spliced fiber optic sensors were prepared,and the sensing characteristics of both were investigated.1)A simultaneous axial strain and temperature measurement sensor based on misaligned splicing cascade of multimode and single-mode fibers（MS-GISMS）.The structure splices a gradual refractive index multimode fiber（GIF）with a single-mode fiber（SMF）in a periodic continuous splice（4 cycles）and staggers the input fiber with the periodic continuous splice structure at the input end to achieve simultaneous measurement of axial strain and temperature.Through both theoretical modeling and simulation analysis,the effects of fiber length selection,period number selection and misalignment fusion offset on transmission spectrum were carried out,and finally the design of the sensor structure and peak formation mechanism were realized,and on this basis,a sensor with a length of 4.8 mm was developed and the sensing characteristics experiments of simultaneous measurement of axial strain and temperature were completed.The experimental results show that the temperature sensitivity of the sensor is_TK₁=55.4p m℃ andK_T2=48p m℃,The axial strain sensitivity is respectivelyK_ε1=-8.7pm/με and K_ε2=7.6pm/με.2)A temperature-insensitive refractive index sensor based on a D-type fiber embedded in a coreless fiber.The structure is based on a directly drawn D-type optical fiber and a coreless fiber（NCF）with a periodic continuous splicing（5 cycles）,and a sensor with a length of 5.2mm is developed to achieve refractive index measurement,and the structure is insensitive to temperature.In addition,this structure can further improve the integration and mechanical properties of the sensor because it uses a directly drawn D-type fiber instead of a D-type fiber prepared by polishing the side edges of a single-mode fiber or a multimode fiber.The experimental results show that the sensor has a refractive index measurement sensitivity of244.11 nm/RIU in the refractive index range of 1.3443RIU-1.4230RIU.In summary,in this paper,two different structures of heterogeneous optical fiber splicing fiber sensors with good sensing characteristics are prepared with heterogeneous optical fiber as the substrate and fiber coupling mode theory as the theoretical basis,using self-developed fiber precision cutting and splicing device.The developed heterogeneous optical fiber splicing fiber sensor has the advantages of high mechanical performance,high integration,high sensitivity and low cost.This project can provide an effective preparation technology for the development of miniature optical fiber sensors.