Study On Fabrication And Applications Of Key Devices Of Smart Optical-Fiber Sensor Network

Intelligentizing and Networking are developing trend of modern optical-fiber sensing technology. The fiber Bragg grating (FBG) and Fabry-Perot Interferometer (FPI) are key devices of the smart optical-fiber sensor network at present and in the future. In this dissertation, the characteristics of FBG, FPI and coherent FBG group are investigated in detail. Both the theoretical and experimental investigations are performed. The fiber sensor for the vibration measurement based on the coherent FBG group is studied and fabricated. The smart optical-fiber sensor network based on the coherent FBG group is set up and applied to the high speed train locating. The main contributions of the dissertation are listed as follows:1. The effect of optical coherence of the light source on the FPI was investigated. The relationship between the transmissivity of the FPI and auto-correlative function of power spectral density of source is built up. The effect of the optical coherence of the light source on the sensitivity of FPI sensor is analyzed. A new method for measuring the line width of single frequency laser with FPI is proposed, which extend the application of FPI.2. The effect of the distributed nature of FBGs on the mode-selecting characteristic of coherent FBG group is investigated. The analytical expression of the effective length of the uniform FBG is obtained. It is shown that the mode-spacing of the coherent FBG group should be calculated by using the averaged effective length of the FBG. The conclusion is applied to the analysis and design of the Distributed Bragg Reflection (DBR) fiber laser. Quasi-single-frequency output is obtained by using the self-made Photosensitive Er-doped fiber.3. The effect of the background loss on the FBG spectra is investigated. The concepts of "DC" and "AC" loss penetration depths of the uniform FBG are proposed and the exact analytical expressions of them are derived by using the Coupled-mode theory. The two penetration depths only depend on parameters of the lossless FBG and can be used to simply the correlative analysis.4. The relationship between the UV-induced background loss and the UV-induced index change of the hydrogen-loaded fiber is measured for the first time, which is helpful to the fabrication, analysis and application of the coherent FBG group with high finess. Also it can be reference for the multiplexing of FBG based sensors. 5. Smart optical-fiber sensor network based on the coherent FBG group is applied to the high speed train locating for the first time. The correlative devices are studied and fabricated, and experiment on the railway is performed. A China invention patented "The method for the train locating and real-time tracking by using coherent FBG group" for the locating method has been issued.6. Take part in the development of optical fiber cable early warning system. The system has been used in the drill camps for the security precaution during the Military Review for 60th anniversary of National Day.