Distributed Optical Fiber Vibration Sensor

Distributed optical fiber sensor technology is based on the lengthways characteristic of the fiber. It puts the measured parameters as a function of fiber length, and can maintain the external physical parameters throughout the fiber path continuously. It offers a way to measure the physical parameters of the spatial distribution and time-varying state at the same time for industry and research fields, and it has been widely used in intelligent vehicles, smart bridges, highways, major buildings, gas pipeline monitoring and fiber optic cable monitoring.The distributed optical fiber vibration sensors are studied in this dissertation. Two specific structures, which are based on Sagnac structure and Michelson structure OTDR respectively, are analyzed and studied in detail.The basic principle of a distributed optical fiber vibration sensor based on Sagnac structure is studied in this dissertation. Different from traditional Sagnac ring, this system uses a 3×3 fiber coupler to divide the laser and to bring a phase bias, a 1×2 fiber coupler to return the laser, a straight optical fiber as sensor component and a LD pulse light source. The laser's wavelength is 1316.7nm. It not only resolves a low-power incidence problem of the continuous light source, but also evades the stimulated Brillouin scattering threshold limit. By detecting the exchange component of the interference light intensity, finding out the zero frequency, the vibration spot can be located. The detection sensitivity and the maximum detection range of this system structure are also further analyzed. The experiment by using a PZT phase modulator to simulate the vibration demonstrates: the experimentation result accords with the theoretical analysis; when the vibration is 5.245km far away from the 1×2 fiber coupler, the relative error of location is 2.6% and the largest monitoring distance is more than 100km in theory.Since the Rayleigh backscattering in optical fiber contains some information, just as the location of dispersion and vibration, an OTDR with fiber Michelson structure is designed, in order that the tiny vibration along the sensor fiber could be monitored. A simple novel distributed vibration sensor system is proposed is this dissertation. In this system, the 1310nm laser source is divided by a 3dB coupler into two coherent light beams: the sensing light beam and the reference light beam. When the Rayleigh Backscattering in the two optical fibers transmits back to the coupler, it would interfere. The place where the interference light changes is the place where vibration occurs. Under the three conditions of no vibration, tiny vibration and a light-loss on fiber, we experiment respectively and observe the difference. Conclusion: Under the condition of tiny vibration, the light is changed faintly, but the light is changed obviously and the location is precise with a light loss.