Research Of Fiber Sensor By The Finite Element Method

With the advancement of technology and the development of society, there are many large andcomplicated structures, and the safety factor becomes the focus. Therefore, structural healthmonitoring system began to be used on the structures. The signals transmitted by the sensor are usedto monitor the safety. Sensors are widely applied in monitoring, and the fiber grating sensor becomesthe first consideration for its own advantages.Currently, we use the axial stress-strain behavior of fiber grating, the transverse straincharacteristics are also very important in monitoring.Six fiber types typically used in fiber Bragg grating sensors (circle core fiber, elliptical core fiber,D-fiber, elliptical SAP fiber (62.5un and40um), Bow-Tie SAP fiber) are compared. Base onmechanical and optical characters, we calculate the effective refractive index in the cross-section bythe scalar finite element method. The middle wavelength corresponds to the transverse load by onerelationship. In addition, we study the temperature influence on the SAP fiber.Once the effective refractive indexes are known along the fiber, we can calculate the spectralresponse. Coupled mode theory is applied to analyze the mode-coupled phenomena in fiber gratings.We do the simulation analysis by the transfer matrix method and the Runge-kutta method, and the twomethods can obtain the same result.The relationships obtained by the scalar finite element method are consistence the result by thecenter stress approximation it shows the scalar finite element method can be used to predict thesensitivity. And the scalar finite element method verifies the experimental result. The scalar finiteelement method is feasible.Fiber Gratings analysis provides a reference for the practical application..