Automatic Optimization Program Of Long-period Grating Based On Mode Transition And Dual-peak Resonance

Long-period fiber grating(LPG)is a hotspot in the field of sensing due to its low insertion loss,no backward reflection,anti-electromagnetic interference,corrosion resistance and high sensitivity.LPG with mode transition and dual-peak resonance can achieve extremely high sensitivity,which has good application prospects in environmental refractive index sensing and chemical sensing.Focusing on the research of the optimization design of coated LPG,this paper compiles a numerical simulation program which is suitable for the research of coated LPG.Besides,this paper studies the mode transition phenomenon and the dual-peak resonance phenomenon,then puts forward the optimization design method of LPG based on these two phenomena.The method is realized by the automatic computer program.The main contents are as follows:(1)LP mode(Linearly Polarized mode)theory,transfer matrix method,coupled mode theory and their applications in LPG are introduced.The calculation process and data characteristics of numerical simulation of LPG are analyzed with a calculation example.Based on these analysis theories and the numerical simulation process,a numerical simulation program is compiled.The program is suitable for the study of mode transition and dual-peak resonance.(2)In the research of mode transition phenomenon,the causes and characteristics,the influence on sensitivity,and the interaction between parameters are studied.In the research of dual-peak resonance,the causes and characteristics,and the influence on sensitivity are studied.These researches provide methods for the optimization design of LPG based on these two phenomena.(3)the parameters needed to be optimized and the optimization sequence are analyzed.The optimization design methods under different sensing principles are given.According to the optimization design methods and the numerical simulation program,the automatic optimization design program is compiled.The program is used in two optimization design examples with different sensing principles.The transmission spectra and sensitivity are calculated based on the results given by the program.In the optimization design example of environmental refractive index sensing,the average sensitivity is 7475nm/RIU in the environmental refractive index range of 1.33-1.37.In the example of coating parameter sensing optimization design,the average sensitivity is21333nm/RIU in the coating refractive index range of 1.525-1.540.