“…Long-gauge distributed or quasi-distributed fiber optic sensing system can be used for intruder localization. First demonstration of the possibility of locating the disturbed phase using distributed sensors based on a combination of Sagnac and Mach-Zehnder interferometers was published by Dakin et al [1] in 1987. Spammer et al also described the inteferometric technique to detect and locate perturbations by merging a Sagnac interferometer with a Michelson interferometer [2].…”
A loop topology based white light interferometric sensor network for perimeter security has been designed and demonstrated. In the perimeter security sensing system, where fiber sensors are packaged in the suspended cable or buried cable, a bi-directional optical path interrogator is built by using Michelson or Mach-Zehnder interferometer. A practical implementation of this technique is presented by using an amplified spontaneous emission (ASE) light source and standard single mode fiber, which are common in communication industry. The sensor loop topology is completely passive and absolute length measurements can be obtained for each sensing fiber segment so that it can be used to measure quasi-distribution strain perturbation. For the long distance perimeter monitoring, this technique not only extends the multiplexing potential, but also provides a redundancy for the sensing system. One breakdown point is allowed in the sensor loop because the sensing system will still work even if the embedded sensor loop breaks somewhere.
“…Long-gauge distributed or quasi-distributed fiber optic sensing system can be used for intruder localization. First demonstration of the possibility of locating the disturbed phase using distributed sensors based on a combination of Sagnac and Mach-Zehnder interferometers was published by Dakin et al [1] in 1987. Spammer et al also described the inteferometric technique to detect and locate perturbations by merging a Sagnac interferometer with a Michelson interferometer [2].…”
A loop topology based white light interferometric sensor network for perimeter security has been designed and demonstrated. In the perimeter security sensing system, where fiber sensors are packaged in the suspended cable or buried cable, a bi-directional optical path interrogator is built by using Michelson or Mach-Zehnder interferometer. A practical implementation of this technique is presented by using an amplified spontaneous emission (ASE) light source and standard single mode fiber, which are common in communication industry. The sensor loop topology is completely passive and absolute length measurements can be obtained for each sensing fiber segment so that it can be used to measure quasi-distribution strain perturbation. For the long distance perimeter monitoring, this technique not only extends the multiplexing potential, but also provides a redundancy for the sensing system. One breakdown point is allowed in the sensor loop because the sensing system will still work even if the embedded sensor loop breaks somewhere.
“…One example would be the fluid pipelines leak detection, where leakage happens, it can be detected right away because it is being monitored in real time. Some types of interferometric distributed fiber sensors and optical time domain reflectometry have been proposed for detecting and locating perturbations along sensing fiber [2][3][4][5][6][7][8][9][10][11].…”
“…As a new quality, with reference to volume technique, it is possible to achieve detection and localization disturbance along the fibre. Dakin, Pearce, Strong, and Wade were the pioneers of this technique [1]. They showed that combination of two interferometers, Sagnac interferometer and Mach-Zehnder one, allowed for disturbance localization.…”
We present numerical and experimental results on a new generation fibre optic perimeter sensor based on a Sagnac and Michelson interferometers configuration. In particular, an original signal processing scheme is presented. The sensor can detect a potential intruder and determine its position along a protected zone. We propose a localization method that offers the inherent properties of both interferometers. After demodulation of the signals from both interferometers, the obtained amplitude characteristic of the Sagnac interferometer depends on a position of a disturbance along the interferometer, while amplitude characteristic of the Michelson interferometer does not depend on this position. So, quotient of both demodulated characteristics makes it possible to localize the disturbance. During investigations of a laboratory model of the sensor, it was possible to detect the position of the disturbance with a resolution of about 40 m along the 6-km-long sensor.
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