Study On Characteristics Of Fiber Bragg Gratings During The Process Of Regeneration

As a passive device,fiber Bragg gratings(FBGs)has become a kind of important component in the sensing field,because FBGs have lots of advantages such as electromagnetic immunity,low insertion loss,small dimension,easy to reuse and high sensitivity.However,ordinary FBGs can only be applied to medium and low temperature environment below 300 °C.When ordinary FBGs are applied in high temperature environment,the intensity of ordinary FBGs will decrease,even the phenomenon of spectral erasure,which will seriously affect the test result and limit the application of FBGs in high temperature environment.It is urgently to develop a high temperature resistant sensor.As a new type of optical fiber grating annealed by high temperature environment,the regenerated fiber Bragg gratings(RFBGs)can be applied in high temperature environment above 1100 °C.The fabrication process of the RFBGs is simple and the cost is low,which makes it attracts increasing attention in the field of high temperature sensing.This thesis mainly focuses on the characteristics of FBGs during the process of regeneration:Firstly,the research background,purpose and significance of RFBGs were analyzed.Then,we stated the temperature sensing characteristics and the strain sensing characteristics of the RFBGs.At the end of this chapter,we introduced the research divided into four categories on RFBGs at home and abroad.Secondly,the fabrication process of RFBGs was introduced and the characteristics of the regenerated fiber grating at different temperatures were compared.Several factors affecting FBGs’ regeneration were also discussed and each factor was analyzed separately.Then,two regeneration mechanisms for RFBGs are described.Then,the study of mechanical strength of the fiber during the process of the regeneration was introduced,and the experimental rules were summarized.Afterward,the reasons for the mechanical strength change of the fiber were analyzed.The mechanical strength of the RFBGs and the fiber was also compared,from which we obtained the quantitative relationship of mechanical strength between the two.Finally,the research on the refractive index modulation of fiber grating during the process of the regeneration was introduced.we simulated the condition of the optical low-coherence reflectometer(OLCR)scanning the apodized fiber grating and studied the refractive index modulation change rate before and after the regeneration of the apodized fiber grating by MATLAB.Then,the apodized FBGs was detected by OLCR for experimental research based on the principle of white light interference to obtain the experimental results of the refractive index modulation change rate before and after the regeneration of the apodized fiber grating.The experimental results were compared with the previous simulation results,and the simulation results are similar to the experimental results,which confirms the reliability of the results.