Research On The Distributed Fbg Demodulation System Based Oncascaded Long-Period Fiber Gratings

People pay close attention to optical fiber Bragg grating(FBG) sensor.Because it is the characteristics of the sensitivity of the strain, temperature and other physical quantities,it is widely used in many fields.Because it is the essential characteristic of wavelength coding, usually using wavelength demodulation technology to test the data analysis.Cascaded long-period fiber grating(CLPG) with its rich spectral type and easy to adjust the characteristics of other range is widely used for a variety of filters and so on.Subject based on cascade spectral characteristics of long period fiber grating as the edge filter, realized the distributed optical fiber Bragg grating sensor signal demodulation.In this paper, the research work mainly includes the following:Firstly,development and classification of fiber Bragg grating sensing technology is introduced and the fiber Bragg grating demodulation technology, reuse technology has made the narration.Research in detail cascade long period fiber grating in recent years in various aspects of the research status in application. The coupled-mode theory of optical fiber grating is analyzed, explained the behavior of light waves in the waveguide. The coupled-mode equations are derived by maxwell’s equations, it is concluded that optical fiber Bragg grating condition and reflectivity formula.Secondly,detailed interpretation of the theory of fiber Bragg grating, focusing on coupled mode theory, transfer matrix method and Fourier transform method. With OptiGrating simulation software on the transmission spectrum of long period fiber grating are simulated, and by changing the grating,grating length and refractive index modulation depth and cladding refractive index parameter analysis of its impact on long period fiber grating transmission spectrum.Thirdly, The cascade of long period fiber grating pattern theory and cascade long period fiber grating method of calculating the transmission spectrum formula are introduced in detail. Using Matlab to cascade the transmission spectrum of long period fiber grating are simulatedFourthly, based on the edge of the cascaded long-period fiber grating filter demodulation technology made a detailed research, proposing based on the of the cascaded long-period fiber grating edge filter demodulation technology. The demodulation technology is to use cascading transmission spectrum of long period fiber grating linear area as edge filter, realized with axial strain sensor.It improves the sampling rate and wavelength accuracy of the system.