Measurement Of Dual Parameters Of Few Mode Fiber Bragg Grating

The number of modes transmitted by few mode fiber(FMF)is between single mode fiber(SMF)and multi-mode fiber,which can transmit fundamental mode and a few higher-order modes simultaneously.It has the advantages of large effective area,strong ability of limiting mode,easy control and analysis of transmission mode,etc.,so it has been paid more and more attention in the field of new sensing.Fiber Bragg grating(FBG)is an important reflective fiber passive device.In addition to the advantages of strong electromagnetic interference resistance and corrosion resistance of fiber devices,it also has the advantages of small structure size,high sensitivity,wavelength coding,wavelength division multiplexing and so on.Its wide reflection band and high reflectivity have been widely used in the field of communication and sensing.Compared with single-mode Fiber Bragg Grating,Few Mode Fiber Bragg Grating(FMF-FBG)has narrower line width and better polarization property,which can greatly improve sensor detection accuracy and stability.There is more than one mode in Grating.It can produce multiple reflection peaks of different intensity,so that the sensing becomes more convenient and flexible.In this paper,the theoretical analysis of FMF-FBG was performed,and then the temperature and strain sensing characteristics of FMF-FBG were analyzed through experiments.At last,Few Mode Tilted Fiber Bragg Grating(FMF-TFBG)was simulated.Specific work contents are as follows:1.Starting from the classification,application and development trend of fiber Bragg grating and the advantages of low-mode fiber,the introduction of low-mode fiber Bragg grating related aspects is carried out.2.The structure of FMF is introduced,and the coupling mode theory and dispersion characteristics of FMF are analyzed.3.The preparation of FMF-FBG is introduced.The photosensitivity of optical fiber is utilized,and the photosensitivity of optical fiber is increased by means of high voltage hydrogen loading.The theoretical analysis of FMF-FBG has laid the foundation for the following experiment and simulation.4.Aiming at the cross-sensitivity of temperature and strain in fiber Bragg grating sensing,the response characteristics of temperature and strain in each mode of low-mode fiber Bragg grating were studied,and a four-mode fiber Bragg grating temperature and strain dual-parameter sensor was proposed.By analyzing the different optical power sensitivity of LP01 mode in low-mode fiber Bragg grating at different temperatures,the wavelength,temperature and strain have good linearity under this mode.Thus,the temperature and strain dual parameter sensing of low-mode fiber Bragg grating is realized.This method uses a mathematical model to convert wavelength drift and reflected light intensity into numerical information of temperature and strain.The experimental results show that the method has high performance in measuring range and accuracy,and has the characteristics of high sensitivity and good real-time performance.The method can be widely used in many temperature and strain measuring situations and has great application prospect.5.The principle and method of FM-FBG for temperature and strain double parameter measurement are discussed.TFBG is a fiber Bragg grating with slanted grating lines.In FM-FBG,when the fiber is subjected to strain or temperature changes,two mode wavelengths of LP12 and LP01 in the transmission spectrum will produce different shifts,which can be used to measure temperature and strain simultaneously.