Design And Implementation Of Distributed Long Period Fiber Grating Pair Demodulation Multiplexing System

Fiber optic sensors have received extensive attention and research since their inception.Long period fiber grating and long period fiber grating pair sensors are important branches of fiber optic sensor research in recent years.They have the advantages of small size,light weight,corrosion resistance,electromagnetic interference resistance,easy access to fiber optic networks and sensitivity to multiple parameters.However,due to the special coupling mode and spectral characteristics of long period fiber grating and long period fiber grating pair,few distributed multiplexing and demodulation systems have been proposed,which seriously hindered the process of distributed sensing by long period fiber grating and long period fiber grating pair.Firstly,based on the basic theory of fiber grating,the coupling equation and transmission matrix of LPFG were derived,and the spectral characteristics of LPFG under different grating parameters were analyzed,which provides a basis for improving the spectral characteristics of LPFG.Secondly,based on the long period fiber grating theory,the transmission matrix of long period fiber grating pair was derived,and the spectral characteristics of long period fiber grating pair under different structural parameters were analyzed.Based on the sensing principle of long period fiber grating pair,the refractive index,temperature and strain sensing characteristics of long period fiber grating pair were analyzed.Aiming at the nonlinear sensing characteristic of long period fiber grating pair,it is difficult to predict the refractive index accurately,a model of refractive index prediction based on adaptive neuro-fuzzy system was proposed,which can predict the refractive index.All research provide a basis for the design and application of long period fiber grating pair.Finally,according to the working mode of the cascade long period fiber grating,the method of the traditional spectrometer demodulation combined with virtual instrument technology,through the optical switch light path switching was adopted,a multiplexing demodulation system for distributed long period fiber grating pair was designed,the program of each module of the system was designed on the Lab VIEW platform of the computer,the long period fiber grating pair's demodulation spectrum reduction,the resonant wavelength and temperature was implemented,the design of the system has high precision,good compatibility,friendly interface,etc.