Fiber-optic Perimeter Security System Based On Dual Mach-Zehnder Interferometer Structure

Since optical fiber sensor has its unique advantages in sensor applications, it isnow focusing much more on higher sensitivity, integration and networking, whichalso symbolizes that optical fiber sensor and its counter-part systems have functionedvery well. In recent years, much attention has been paid to the security of life andproperty,so that the perimeter prevention system based on distributed optical fibersensor has become hot spot of the research. This paper mainly explores the distributedfiber-optic perimeter security system based on dual Mach-Zehnder interferometerstructure with the following content included:The detection principles of distributed fiber-optic perimeter security system andits classification are studied. The optical fiber interferometer phase-demodulationmethod is introduced in detail, including the methods of phase generated carrier(PGC) and two-beam polarization interference, etc.A positioning system based on dual Mach-Zehnder interferometer is designed.The cross-correlation algorithm has been adopted to calculate the time difference ofsignals on two channels of the Mach-Zehnder optical fiber interferometer for locatinginvasion points, and we put forward polarization control feedback and3×3coupler-used symmetric demodulation methods to restrain polarization decline. Thetheoretical principle and concrete implementation steps of this demodulation methodare described, then the hardware demodulation circuit is successfully designed whichrealizes the interference signal’s effectively demodulation.The positioning programs of optical fiber perimeter security system is fulfilledwith LabVIEW, including the signal collecting module, trigger judgment module andcross-correlation algorithm based positioning module. The positioning experimentscarried out on system platform in our laboratory demonstrate the effectiveness of themethods presented in this paper, which can prove the feasibility of this system usedfor perimeter intrusion detection. Based on the data of test results，the positioningprecision of the system and some other performance indicators are calculated,meanwhile, the reasons which affect the positioning accuracy is analyzed. Last of all, the total research content is summarized and some parts to be furtherperfected is pointed out as well.The experiment results show that the perimeter security system based on dualMach-Zehnder interferometer designed in this paper can realize real-time location ofthe intrusion points. By means of processing data in segments, the stability andaccuracy of system has been improved effectively. An experiment with2-kilometer-long sensing fiber has been carried out, whose results show that the dualMach-Zehnder perimeter protection system can identify the position of vibrationinstantaneously and has a location accuracy of200meters within the total sensingdistance, ensures stable long-time work as well. We are able to average a responsetime of less than1s and a false alarm rate of5%.Experiment results meet therequirements of the system and have high reference value for engineering applications...