Simultaneously Temperature And Strain Sensing Based On Fbg Using Fluorescence Intensity Ratio Technique

Optical fiber for temperature sensing has many advantages over electrical sensors, including high sensitivity, wide sensing range, immunity to electromagnetic interference, etc. Fluorescence intensity-based rare earth-doped fiber temperature sensor are sensitive to external perturbations, any changes in the excitation intensity or in transmission losses in guiding fibers in such a system, however, would be interpreted incorrectly as changes in temperature. The ratio of the fluorescence intensity (FIR) from two thermally coupled energy levels of rare earth ions is relatively immune to bend losses and fluctuation in the pump power. Fiber Bragg grating is widely used in fiber sensor flied, but the temperature and strain cross-sensitivity in Bragg grating senor is a major issue. However, the FIR is insensitive to strain, so it can provide temperature compensation for FBG in a simultaneous strain and temperature monitoring system. The main results of this paper are:1. The energy levels of rare earth ions in rare earth-doped fibers and the absorption and emission property are analyzed theoretically; the paper mainly introduces the energy levels of erbium ions in erbium-doped fibers, and the influence of Stark effect on fluorescence spectrum. The paper also introduces the theory of using the ratio of fluorescence intensity from Stark levels of 4I13/2, and the advantages over using the ratio of fluorescence intensity from 2H11/2 and 4S3/2.2. The development of the FIR-based temperature sensor at home and abroad is summarized, and the performance of the Erbium-doped, Neodymium-doped and Ytterbium-doped silica fiber temperature sensor using FIR technique is introduced.3. The scheme of using the property of temperature dependence of the FIR from the two sublevels of split 4I13/2energy level of erbium ions for temperature sensing is put forward, the low cost laser diodes or light-emitting diodes can be used in the scheme, owing to the fluorescence locates the 1550nm low-loss window of optical communication, the commonly available detectors such as silica photodiodes can be used, so the cost of sensor system is very low. The temperature sensing experimental system based on FIR technique is established, by change the temperature of erbium-doped fiber which is monitored by oven, the ratio of fluorescence intensity from two sublevels of split 4I13/2energy level is measured. The linear relationship between FIR and temperature has been obtained. 4. A FBG is written in a photosensitive fiber, and the fiber is subject to both strain and temperature. The effects of the applied strain and temperature on the Bragg wavelength and fluorescence intensity ratio were measured by oven and a pulley system, the temperature and strain is changed every minute, then measuring the change of fluorescence intensity ratio AR and the shift of Bragg wavelength△λB·According to△R and△AλB, the change of temperature△T and strain△s can be calculated respectively. The experiment is carried out 10 times, then analyzing the accuracy of the system for temperature and strain sensing.