| With the rapid development of the national economy,the demand for security is increasing in all walks of life,and various perimeter security systems are emerging.As a perimeter security system,distributed optical fiber sensing system based on the ?-OTDR has many advantages compared with the traditional sensing system.Its concealment is strong,the laying and maintenance of detecting optical cable is convenient,and can deal with all kinds of complex detection environment.Based on the traditional OTDR technology,this thesis analyzes and discusses three kinds of signal demodulation schemes based on the ?-OTDR Technology.The author has done a great deal of pioneering research on three aspects: extending sensing distance,practicability and sensitivity.At the same time,two optical path systems are designed and built to verify the feasibility of the design idea.The main content of the thesis includes:(1)This thesis summarizes the background and application of the distributed optical fiber sensing technology,and sums up some key factors of the ?-OTDR technology.(2)The existing technology of phase generated carrier technology is analyzed theoretically,and the advantages and disadvantages of the technology are analyzed according to the actual simulation results.(3)An ?-OTDR distributed optic fiber sensing system based on symmetrical 2×2 fiber coupler is designed,and the advantages and disadvantages of the technique are analyzed according to the actual measurement results.The sensing distance of the system is 32 km and the SNR is 9.6dB.(4)An ?-OTDR distributed optic fiber sensing system based on symmetrical 3×3 fiber coupler and bidirectional raman amplifier is designed.Through the subsequent improvement,the sensing distance of the system reaches 104 km and the SNR is 11.4dB.At the same time,the edge detection technology is used to optimize the demodulation structure,and the signal-to-noise ratio is increased to 14 dB under the same data. |
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