Study On High-Temperature-Resistant Fiber Grating Sensor

Fiber Bragg grating (FBG) sensors have been widely used in sensing fields due to their distinguishing advantages, such as wavelength-encoded measurement, immunity to electromagnetic interference (EMI), light weight, simple for fabrication and so on. But FBG is not a permanent structure, it will be erased when operating for a long time under a sufficient high temperature. So they are only capable of operating in temperature range below 300℃. In order to extend FBG's sensing applications at higher temperature regions, the sensors with high temperature sustainability should be fabricated.In this thesis we fabricated high-temperature-resistant chemical-composition gratings (CCGs) by writing FBGs in Ge/F codoped fiber with 193 nm eximer laser followed by special annealing procedure. The refractive index modulation of the CCGs is caused by a change in the chemical composition, hence these gratings show extremely high thermal stability at temperature up to 1100℃. The temperature and strain response of CCGs were investigated. The experimental results indicate that the temperature response of the CCGs has a fairly good performance. Further, the CCGs show strain coefficient that is about the same with normal FBGs. It is expected that the CCGs are suitable for health monitoring of the high temperature structure.In order to increase the reflectivity of the CCGs, we also investigated effects of hydrogen concentration, initial grating strength and UV laser pulse energy on the reflectivity of the CCGs. It is found that improving the initial grating reflectivity, enhancing the hydrogen concentration or using lower pulse energy in the initial grating inscription help to increase the reflectivity of the CCGs.