Superstructure Fiber Grating Sensor System And Its Application On The Measurement Of Oil/gas Down-hole

This paper focused on the basic theoretical and technical researches of the optical fiber grating sensors,proposed the scheme of temperature and strain measurement under oil/gas down-hole based on superstructure fiber grating sensor. Different types of parameter that affects the characteristic of superstructure fiber grating's spectra are systematically analyzed and do a lot of experiments and emulations, high sensitivity and good linearity superstructure fiber grating sensor is achieved.The main content of this paper includes:the basic theory and property of fiber grating and its sensor application,the sensing mechanism and demodulating schemes of fiber grating sensor,the study of superstructure fiber grating's reflection spectra,superstructure fiber grating sensor's measurement of temperature and strain under oil/gas down-hole and its experimental researches.Firstly,the general situation of fiber grating's development are reviewed and analyzed,the main type of fiber grating and its tailor technique are studied.Then,the recent developments in the technologies of fiber grating sensing are reviewed and several different fiber-optic sensing technologies,particularly for the oil/gas down-hole are analyzed in a comparing way,and it indicates that the fiber-optic grating sensing method is the best one in all our discussion and has a brilliant application foreground.The theory of superstructure fiber grating is systematically analyzed.From Maxwell equation we get the couple modeling equation in optical waveguide,then use it into fiber grating waveguide and derived the couple modeling equation in fiber grating.Through the equation we get the expression of fiber grating's reflection spectrum.On this basis,we use the way of transmission matrix to analysis the superstructure fiber grating carefully and get the expression of superstructure fiber grating's reflection spectrum which are very useful in sensor applications.The temperature,pressure,and strain sensing mechanism of fiber grating are studied,the relationship of outside parameters and fiber grating spectrum are gained which are very useful for new measurement and demodulating schemes' development. The advantage and defects of many demodulating schemes are analyzed and provide wisdom choice for practical use.Temperature and strain measurement under oil/gas down-hole base on superstructure fiber grating sensor are studied.The relationship of fiber grating's parameter and its reflection spectrum,outside parameter and fiber grating's parameter are systematically analyzed,and get useful results.High sensitivity (M₁₁=44nm/Mpa,M₁₂=0.025nm/℃,M₂₁=28.13dBm/Mpa,M₂₂=0.17dBm/℃)and good linearity superstructure fiber grating sensor is achieved through a lot of experiments and the feasibility and advantage of using superstructure fiber grating to measure temperature and strain in oil/gas down-hole which have a bright future is also proved.