Study On The Detection And Location Of Disturbance In Optical Fiber Sensor Based On Sagnac Interferometer

Optical fiber Sagnac sensors are optical phase-modulated fiber sensors and have been used to measure the physical parameters such as angular velocity and time-varying signals. Fiber-Optic Gyroscope based on Sagnac Interferometers has been applied in military affairs and business. Optical fiber Sagnac sensors have a lot of advantages, such as easy installation, simple maintenance and lower costs, and have been applied in perimeter security system, pipeline leakage detection and location system.In this dissertation, firstly the theory and technology of optical fiber sensing system as well as the technologies of data acquisition system have been introduced. Then the principle of Sagnac Interferometer and the position determination experiment of disturbance in Sagnac Interferometer are studied. Some useful conclusions have been achieved. The primary achievements are as follows:(1) The principle of Sagnac Interferometer is studied. The relationship between the phase and angular velocity of rotation is obtained as a result of Sagnac Effect, when the light propagates in the optical path where the optical refractive index is n.(2) The data acquisition system which is based on Virtual Instrument and PCI bus technology is studied. Advantech PCI-1714 is used as the hardware platform of the system. The data acquisition program is developed with LabVIEW in order to drive the PCI-1714 and acquire sensing signal.(3) The position determining experiment of disturbance at a particular place along a Sagnac Interferometer is made. After the experiment, the acquired data is analyzed in order to monitor and locate the position of disturbance. The error between the theoretical result and numerical analysis result is analyzed. In the meantime, the problems which would be encountered in practical applications are discussed.(4) The method of spectrum processing of the acquired data is studied. The approximate part of the spectrum can be achieved by the method of discrete wavelet transform so that better resolution of the spectrum can be got.(5) The method to achieve the null frequency of the acquired data spectrum during the process of signal processing is studied. A new way to get the null frequency has been proposed and implemented by programming, which is the key step in the whole process of signal processing. And this method can also be used to a wider range of applications.