Investigation On The Key Technologies And Implementation Of Ultra-long Distance Distributed Fiber Intrusion Detecting System

With the development of perimeter security industry,various kinds of new technologies are employed to achieve intrusion detecting.In recent reports,distributed fiber perimeter security systems have attached intensive research due to their unique superiorities.The traditional perimeter security systems mainly focus on regional intrusion detection such as the communities,jails and banks.However,new perimeter security systems are imperative in some long-distance occasions such as border patrol and the security defense of communication fiber link and high-speed lines.In this thesis,several key technologies for ultra-long distance intrusion detecting system are thoroughly researched,experimentally tested and discussed in depth.Firstly,a brief introduction to the white light interferometric distributed optical fiber vibration sensing technology(WLI-DOFVS)based on linear Sagnac structure is made which is the premise of ultra-long distance distributed fiber intrusion detecting system.The deficiency analysis and related improvements in long-distance condition are also mentioned.Secondly,based on the theory of erbium doped fiber amplification(EDFA),optical amplifiers with the function of linear and bi-directional amplification which is the key point to multiply sensing distance are designed and tested.According to the signal features in ultra-long distance intrusion detecting,performance analysis of 2-FFT locating algorithm is shown and the modified 2-FFT locating algorithm is also introduced with implementation steps in the following,of which several key parameters are optimized with experimental verifications to realize accurate intrusion locating.The necessity of studying sensitivity-enhanced fiber package is analyzed,the new sensitivity-enhanced fiber package is developed with sensitivity enhancement simulation through ANSYS 14.0 and related experiments are implemented to testify how package diameters affect sensitivity enhancement effect.Finally,the system experiments are conducted to testify the main performance of ultra-long distance distributed fiber intrusion detecting system with single-point and multi-point locating tests,separately.It can be seen that this system can achieve intrusion detecting along 226 km sensing link,which is the reported longest distributed sensingsystem to the best of our knowledge.It can locate multiple vibration sources simultaneously with single-point locating error less than 400 m.Intrusion detecting system developed in this thesis not only realize ultra-long distance intrusion detecting with high locating accuracy,but also can be used in terrible conditions with low research costs.In addition,it is of broad application prospect which can be widely used in the long-distance perimeter security situations such as the border patrol and the security defense of submarine communication link,etc.