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A quasi-distributed FBG-based fiber-optic fence is investigated in this paper. A novel intrusion detection method is proposed based on the autocorrelation characteristics of the signal with and without disturbances, which is very effective to detect extremely weak signals even from nonequivalent sensor nodes in a large sensor network. When analyzing the intrusion signal's characteristics and excluding the false alarm sources, such as environmental interferences and others, Nuisance Alarm Rate (NAR) is well controlled while extremely high Probability of Detection (PD) is assured. The experimental results show that the PD of the fiber fence using these methods for detecting the single and multiple events can be both higher than 99.5%, while the NAR can be controlled well below 0.5%.

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The fiber Bragg grating (FBG) strain sensor is used in the oil and gas derricks for the health monitoring. The system consisted of the FBG strain sensors, optical interrogator and monitoring software. 64 sensors were installed on a derrick for loading and unloading tests. The results showed that the monitoring system had the advantages of the high accuracy, good repeatability, large capacity and real-time monitoring ability.