| The distributed optical fiber sensing(DOFS) technology is a new kind of monitoring technology that uses the optical fiber as means of transmission and perception medium simultaneously. DOFS can realize distributed monitoring and has much more advantages than traditional electromechanical sensor system, such as small size, light weight, resistance to electromagnetic interference and high sensitivity,etc.The distributed optical fiber sensing based on the phase sensitive optical time-domain reflector(Φ-OTDR) can monitor vibration induced by the disturbance, such as the intrusion along a boundary. The distributed optical fiber sensing based on Brillouin Scattering can monitor temperature and strain of building. But these two technologies can only realize single function so far respectively. It costs a lot to realize multi-functional.Besides, the Stimulated Brillouin Threshold of single mode fiber in system that uses Spontaneous Brillouin Scattering is so small that it’s easy to be shifted to Stimulated Brillouin Scattering. In addition, the system for two-parameter(temperature and strain) monitoring simultaneously has complex structure and low accuracy of measurement. This paper makes researching on the problems above and presents solutions respectively, all of them have make contributions to engineering application of DOFS.The main researches presented in this paper are as follows:(1) The three kinds of scattering light in optical fiber is introduced. The principles of theΦ-OTDR and BOTDA system are analyzed respectively. Then the practicability of the combination of Φ-OTDR and BOTDA system has been demonstrated based on theoretical analysis.(2) Some kinds of DOFS, especially the system of Φ-OTDR and BOTDA have been introduced. The advantages and prospects of the combination of Φ-OTDR and BOTDA are analyzed.(3) This paper presents a multi-functional distributed optical fiber sensing system based on the similarities and the combination of the topological structure of Φ-OTDR and BOTDA.The choose of devices and their parameters in multi-functional system have been analyzed.The relationship of pulse width and the smallest detectable distance between two intrusions that can be detected simultaneously has been studied by Boltzmann linear fitting. Two peaks distinguishing accuracy of 1.23 m has been realized with 20 ns width light pulse. It’s also found that the strain-frequency sensitivity and temperature-frequency sensitivity in this system agree well with theoretical values. By optimizing device parameters of this system, strain measurement accuracy of 3.17 ?? and temperature measurement accuracy of 0.45℃ have been realized with 30 ns width light pulse successfully by Lorentz linear fitting.(4) The special optical fiber has been introduced,especially the principles and applications on DOFS of Polarization Maintaining Optical Fiber(PMF),Dispersion Compesation Fiber(DCF) and photonic crystal fiber(PCF) have been presented. A further study on the SBS characteristics of general single mode fiber and High Nonlinear Fiber(HNLF) have been made, including the comparison of Brillouin gain bandwidth, Brillouin gain center frequency and Stimulated Brillouin Scattering threshold. It’s found that HNLF has a wider Brillouin gain bandwidth,smaller Brillouin gain center frequency and higher SBS threshold of 78 mW. The SBS threshold of HNLF is bigger than that of single mode fiber. This characteristic can be used to reduce the influence of SBS in some situations that Spontaneous Brillouin Scattering must be applied. It’s also found that strain-frequency sensitivity and temperature-frequency sensitivity of the Brillouin frequency shift in HNLF are 0.0309MHz/ ?? and 0.413MHz/℃respectively.Finally, this paper presents a two-parameter of temperature and strain sensing system based on HNLF and the parameters of every devices have been analyzed. |
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