Research Of Deep-Grooved Fiber Grating Inscribed By CO₂ Laser And Its Strain Sensing Characteristics

The fiber grating is formed by the periodic change of the refractive index in the fiber core.The fiber grating can be used to measure the physical quantity for the refractive index,bending rate,twist,strain or temperature,which has wide application prospect in the field of communication and sensing.The use of high-frequency CO₂laser writing method,which is easy to writing cycle control,good stability,etc.,can make the grating writing efficiency improved,and increase the sensitivity of the strain testing.The use of high-frequency CO₂ laser writing method and its parameters optimized the treatment to produce groove-type fiber grating,can make the production stability and efficiency improved.By use of high-frequency CO₂ laser writing method for processing and optimizing its parameters,the groove-type fiber grating can be produced,which can make the production stability and efficiency improved.Based on the principle of high frequency CO₂ laser writing method in this thesis,the fiber grating with different depth of groove is designed and fabricated by high frequency CO₂ laser,and it is applied to axial strain experiment and lateral load experiment based on cantilever beam.In this thesis,the strain sensitivity of different grooved depth gratings is compared and analyzed.On this basis of this,it proposed the strain sensor of the groove-type fiber.The main contents of this thesis are described in the following aspects:Firstly,according to the theory of fiber grating coupled mode and the principle of high frequency CO₂ laser writing,combining with the strain sensing theory of grooved fiber grating,the thesis built the experimental model of slotted fiber grating strain sensor.The fiber grating grid with different groove depth is modeled by ANSYS software,and the strain characteristics of the three-dimensional simulation model are analyzed.The displacement degree and strain distribution of the groove structure can be obtained.The results show that the deep-grooved type grating has better strain effect than the shallow-grooved type grating.Secondly,the three kinds of fiber grating samples with different groove depths were fabricated by using high frequency CO₂ laser parameters which have been optimized,and we can build writing experimental platform based on the high frequency CO₂ laser.The experimental data were used to verify the characteristic of the grating with different grooves,and analyze the effect of different factors on grating formation during the fabrication.The experimental results show that the excellent grooved fiber grating can be produced during high frequency CO₂ laser writing with the optimization of laser parameters.Finally,the transverse load experiment and the axial strain experiment of the grooved fiber grating are designed,and the strain testing experiment platform is designed.Under the same external conditions,the micro-bending phenomenon of the deep-grooved fiber grating is better than that of the shallow-grooved grating,with more resonant wavelength drifting.The experimental results show that the average sensitivity of the deep-grooved grating strain is-6.82pm??,which is 4.73 times higher than that of the shallow-grooved grating,which indicates that the deep-groove grating has better strain performance.