Study On The Distributed Fiber-optic Sensing And Information Processing Technology And Its Applications

Optical fiber sensing technology has been expanding rapidly along with the development of fiber communication technology from 1970's, which employs the light wave as carrier and the fiber as medium to sense and transmit the measured external signals. The distributed sensing technology is able to continuously detect the environment parameters along the whole fiber, and obtains their spatial distribution. Therefore, the distributed sensing technology has broad application prospect in the civil and military fields, and becomes the investigation hotspot both in domestic and foreign countries.In this dissertation, the full-distributed and quasi-distributed fiber-optic sensing and information processing technologies are comprehensively investigated both in theories and experiments, according to the research points of view such as long distance, high precision, multi-channel, and easy signal demodulation. Also, their application value is discussed. The main research achievements are as follows:Firstly, the novel full-distributed vibration sensing technique which adopts the long distance Mach-Zehnder interferometer (MZI), and the novel direct current light and fiber loop based real-time and dynamic locating technique are proposed. Moreover, two full distributed vibration sensing systems, which are respectively based on the linear MZI and the ring MZI structure, are discussed and demonstrated. The two sensors can be used to achieve the long distance pipe-line and perimeter monitoring, respectively, by exploiting only one MZI. It should be noted that the ring MZI based sensor is capable of precisely detecting and exactly locating the multiple vibrations.Secondly, the new interferometric sensor with ring feedback non-balanced MZI is proposed and analyzed. By introducing the passive or active ring feedback, the multi-light-wave interference is generated in MZI. Compared with the conventional MZI, such sensor is able to boost the phase sensitivity by two to three orders.Thirdly, the novel distributed fiber in which high density identical periodic structures with low Bragg reflective are written, and the detecting technique named"Optical Wavelength Time Domain Reflection (OWTDR)"which utilizes the two dimension data analysis method of time domain and frequency (wavelength) domain are presented. Combined with the detecting technique, the special fiber is able to precisely sense and exactly locate the external signals simultaneously. As a result, the new quasi-distributed fiber sensing system of large capacity, long distance, precise measurement and exact locating is constructed.Fourthly, the multi-channel temperature abnormal warning sensing technique is presented. Based on the multi-channel wavelength reflection characteristic of the multi-wavelength chirped sampled fiber Bragg grating (FBG), each reflective channel wavelength corresponds to one different monitoring positions. The sensor examines whether the temperature exceeds the tolerable value by comparing the nominal wavelength of the sensing FBG to the corresponding channel wavelength, and locates the abnormal temperature with the time-division-multiplexed (TDM) technique. Due to the reasons of no need of wavelength demodulation, flexible setting of the tolerable temperature at different positions, and quick response, such sensor is very suitable for fire detecting.Finally, the novel optic time-delay modulation based sensing technique is presented. The key sensing principle is the linear group delay of the chirped FBG (LCFBG). When a pulsed monochromatic light is injected to the LCFBG, the resultant time-delay of the reflected pulse light varies with the value of the measured parameter. The sensor has several advantages, such as simple structure and no need of wavelength demodulation, to be well applied in the quasi-distributed sensing network.