Research On The Refractive Index Modulation Change Of Regenerated Fiber Grating

As a passive optical fiber device,fiber grating is widely used in various sensing fields because of its excellent anti electromagnetic interference ability,small volume,high sensitivity and flexible operation.In fact,the common fiber grating will be attenuated and erased with the increasing temperature,so the high temperature environment has become a big obstacle for grating sensor measurement.Regenerated fiber grating is a kind of high temperature resistant grating based on the common type I grating.Because of its simple fabrication and low price,regenerated fiber grating has gradually become a research hotspot in the sensing field in recent years.One of the most important research contents of regenerated fiber grating is how to improve the regeneration rate of regenerated fiber grating to obtain higher reflectivity.For the same kind of fiber grating regeneration under the same conditions,it is now concluded that the higher the reflectivity of the seed grating,the higher the reflectivity of the regeneration grating.However,the conclusion is uncertain.The reflectivity of fiber grating can be adjusted by changing the refractive index modulation and length of fiber grating.The regeneration process is essentially the regeneration of refractive index modulation,and the influence of the intensity of refractive index modulation on the regeneration is not directly answered at present.In this thesis,a distributed measurement scheme of refractive index modulation of fiber grating is designed around this problem.The main work of this thesis is as follows:Firstly,the theory of fiber grating is introduced,and the regeneration of fiber grating is carried out by using suitable seed fiber grating.The temperature response and stability of the regenerated fiber grating are tested,and the reflectivity change of the regenerated fiber grating is recorded.Secondly,a new distributed measurement scheme of fiber grating refractive index modulation is proposed,and the working principle of optical low coherence reflectometer is introduced.The distributed interference peaks along the axis are formed by the back scattering of each position of the grating.The linear relationship between the interference intensity and the refractive index modulation is derived.The distributed measurement of refractive index modulation of grating is realized,and the reliability of measurement method is verified by simulation.Then,combined with the characteristic that the refractive index modulation of the apodized grating changes with a specific function along the axial direction,the distributed measurement of the refractive index modulation before and after the regeneration of the apodized grating is realized by using the low coherence white light interferometer.The relationship between the regeneration intensity and the change of the refractive index modulation of the grating is studied,and the conclusion that the refractive index modulation of the grating regenerates with the same ratio is obtained.Through simulation,the refractive index modulation regeneration ratio of grating is simulated and verified.Finally,the results of the regeneration speed in the whole regeneration process are studied,and the conclusion that the regeneration speed of the refractive index modulation is the same in different positions of the grating is obtained.