Research On The Key Technologies Of FBG Demodulation System And OTDR Networking

At present, fiber Bragg grating (FBG) temperature/strain sensors and optical time domain reflectometer have been commercialized, and have been widely used in the health diagnostics of large buildings, bridges, electrical equipment, and the fault localization of optical fiber cables. This thesis is mainly dedicated to the research on the key technologies of networking as using the above two types of sensor systems.Firstly, this thesis studies the principal of FBG temperature/strain sensor, and the issue of temperature-strain cross-sensitivity. Several important parameters of FBG are discribesd. The advantages and disadvantages of several wavelength multiplexing and demodulation technologies are compared. For the optical time domain reflectometer (OTDR), the factors that impact optical fiber transmission characteristics and the principles of Rayleigh scattering and Fresnel reflection are analyzed. The principle and configuation of OTDR are studied, and the main technical specifications of OTDR are discussed. Then, the thesis has introduced the features, applications, program architectures and development steps using LabWindows/CVI as a software development platform. The multithreading programming technology, dynamic link library technology and the transmission control protocol and other key technologies involved in the software development are analysed. On this basis, a fiber optic sensor network composed of two FBG interrogators and an OTDR is designed and built up. Lastly, according to ways of output data of the three different devices, the thesis has worked out different softwares, respectively. For the first FBG interrogator, based on the analysis of data format, the software for data communication between FBG interrogator and upper computer, and the software for peak wavelength detection and display have been developed by using multithreading technology. In order to ensure the secure data transmission between threads, the thesis also uses the thread-safe queue mechanism provided by LabWindows/CVI. For the second FBG interrogator, as the server sends wavelength data through broadcasting, the thesis has written a upper computer software to receive wavelength data directly, to judge whether the data packets are complete, and to process and display the complete data packets. Since the OTDR provides the dynamic link libraries conotdr.dll and analyse.dll, and the softwares for OTDR upper and lower computer are developed by using the LabWindows/CVI platform. The OTDR softwares can be used to access and analyze the sampled data, and to get event points and event contents. The OTDR softwares meet the requirements of fiber optic sensor network composed of two FBG interrogators and an OTDR.