The Research Of FBG Vibrating Sensor Network Demodulation System Based On WDM

In recent twenty years, fiber sensors have broadly been applied in the field of optical sensor and measurement due to its light weight, small size and high sensitivity. As one kind of fiber sensors, fiber Bragg grating sensors have those unique advantages as its insensitivity to the power fluctuation of light source, high sensitivity, good repeatability and easily distributed sensing by the means of wavelength division multiplexing, time division multiplexing and space division multiplexing, etc. Therefore it has been widely employed and becomes one of the hot topics in the field of optical fiber sensor technology. Today the technique is more mature in static parameter measurements and sensor networks, but in some applications, where FBG sensors are urgent need to measure parameters as transient and varying fast in time. For example, the strain measurement of pulsed strong magnets coil when the power moments, because the pulsed strong magnet works in the liquid nitrogen, strong electromagnetic field environment, the interior space is narrow, conventional electric sensors can’t be embedded inside the magnet coil. And the wire connection of electric sensors is complex and they are sensitive to electromagnetic interference; online health monitoring of rotating blades in aircraft run-time; the transient strain or vibration induced by petrochemical facilities faults where has a rigorous demanding for explosion-proof devices, the leakage of oil tank or oil pipeline; accelerometers based on FBG, etc. It is more desirable to know the transient strain and spectral information involved in the perturbation on an FBG, a direct knowledge of their spectrum content is highly advantageous for studying the structure stability and integrity at extreme conditions. The tunable F-P filter is used as a wavelength selection device in the traditional wavelength demodulation equipment, and tunable F-P filter is commonly used mechanical structure of the piezoelectric ceramics, so scan frequency is only a few thousand Hz. In order to service the actual projects, a demodulation system for optical fiber grating high speed vibration sensor network based on edge filter technology is studied and designed in this paper. Without the use of tunable F-P filter for circulation scanning, the speed of demodulation based on edge filter principle can reach up to dozens of thousands Hz; Adopt close-loop feedback system and algorithm processing can monitor the linear edge area of fiber Bragg grating automatically and avoid the inconvenience of manual tuning; Take the output of erbium-doped fiber ring laser based on a tunable F-P filter as a wavelength reference. And, by tuning the output wavelength, distributed measuring can be realized.The main content of the paper are arranged as following:Introduce the basic background of optical fiber Bragg grating, such as the basic principle of optical fiber Bragg grating sensor, the present development situation at home and abroad. Especially focus on the development status of demodulation technology of optical fiber grating both domestic and overseas. Give a detailed description to several common demodulation technologies of optical fiber Bragg grating sensor from the perspective of principle and mathematics. Then, compare the advantages and disadvantages of each various solutions and their scope of application. Design a kind of new high-speed demodulation system of optical fiber grating which can realize automatic tracking and distributed measuring. And achieve the overall design of the system; make a tunable narrowband light source which can be used to the vibration demodulation system of fiber Bragg grating. In the experiment, two light source solutions are tested. One is the scheme of ASE add FP filter and the other is the scheme of tunable laser light source based on erbium-doped fiber ring cavity. And the performance of the two schemes is compared. Finish the hardware circuit design of each part in the system, such as the drive circuit for980nm pump sources, drive circuit for F-P scanning and photoelectric translating circuit. Complete design of the light path in the system. Use NI acquisition card to accomplish data acquisition and processing. And design data acquisition and processing software of the system with LabVIEW. Three different solutions to the influence of the light intensity disturbance are given, and the advantages and disadvantages of each method are analyzed deeply. The performance of the system is evaluated by combining the high frequency vibration sensors of optical fiber grating. Test the dynamic measurement range, sensitivity and the measurement capability of sensor network of this demodulating system by corresponding testing experiments, which prove the whole system has the characteristics such as a big dynamic range, high sensitivity, a function of distributed measuring, low cost and so on.