Study On The Temperature Characteristics Of Fiber Grating

In recent years, fiber grating temperature sensor has been fully investigated and used in development and measurement of engineering projects. However, nowadays the researches about the characteristic of fiber grating temperature sensing mostly concentrate in the entire section of fiber grating as a sensing element. In some fields, the information about the local temperature of fiber grating is needed in time. For instances, in the research about the transient temperature measurement and dynamic response of fiber grating, when the temperature rapidly increases or decreases, the information about temperature variation can not be obtained in time because of the thermal inertia of fiber grating materials. Therefore, it is important to study the characteristics of fiber grating at local temperature. In this paper, the characteristics of fiber grating at local transient temperature and linear temperature are studied. The primary content includes:Firstly, the basic concepts on fiber grating, including the mode coupling theory and transfer matrix method, are introduced. The characteristics of reflective spectrum are deduced based on the two methods. Then the elementary sensing models of fiber grating in stress and temperature are deduced.Secondly, the characteristics of fiber grating at local transient temperature are investigated in detail. The reflective spectrum model of fiber grating is established based on the transfer matrix method. By theories and simulations, the results show that when a small section of the fiber grating is affected by the transient temperature variation, the reflective spectrum splits into two main peaks, the wavelength of the splitting point shifts linearly and periodically with the local transient temperature on the fiber grating, and the relationship between the reflectivity of the splitting point and the position of local transient temperature on fiber grating is hyperbolic tangent. Based on these, the relationships between parameters of fiber grating and the bandwidth, symmetrical wavelength of spectrum are deduced.Thereafter, the characteristics of fiber grating at linear temperature are investigated. Based on the transfer matrix method, the reflective spectrum model of fiber grating is analyzed by theories and simulations. The results show that for the linear temperature on the fiber grating, the slope is proportional to bandwidth. And the initial temperature and slope are also proportional to the symmetric wavelength shift of the reflective spectrum.At last, an experiment about the characteristics of fiber grating at local transient temperature is presented. Its results are agreement with the simulations, which provide theoretical basis for the practical application of fiber grating in sensing fields.