The use of fiber optic sensors in composite structures for applications in the field of security systems

The use of fiber optic sensors in composite structures for applications in the field of security systems.
M. Szustakowski, M. Zyczkowski, P. Markowski*, K. Brewczynski
Institute of Optoelectronics, Military University of Technology, Poland
*piotr.markowski@wat.edu.pl

Composite structures are increasingly used by replacing the classic elements made mainly of metal. An example of such innovative solutions can be fences used to protect the critical infrastructure facilities. Currently, the most commonly used fences are made of metal net or wire blade. This type of mechanical barriers made of metal, disturb the work of electronic security systems such as linear electromagnetic sensors, radars and microwave barriers. Thus these systems become ineffective. In addition, currently use fencing systems in practice exclude the possibility of using fiber optic sensors as an integral part of the fence. This forces surface mount of the sensing elements, through which they become visible for a potential intruder. The use of the composite material allows in the production process to put the optical fiber inside the structure of the fence. Thereby the fence with integrated fiber optic which can be used as a sensor for security systems.
This paper presents the design and operation of two fiber optic sensors that can be used as sensors in perimeter protection systems. Both described sensors are characterized by sensitivity to signals generated by direct mechanical stimulation remained insensitive to the effects of environmental conditions.
The first described sensor is double Mach-Zehnder interferometer with stabilization to environmental changes. In this system the state of polarization of the input light is optimized to achieve maximum contrast. By continuously measuring the interference contrast it can be determined whether there is external stimulation. Due to propagating optical signal in both directions by the arms of the interferometer it is possible to determine the location of the mechanical stimulation.
The second described sensor is modalmetric sensor. Operation of this system is based on measuring changes in the transverse modal field. Each mechanical stimulation of multimode fiber causes a change in the distribution of transverse modal field at the output of multimode fiber. By analyzing the changes in its distribution, it is possible to determine whether there is an external mechanical stimulation.
The described sensors allow the use of composite fencing in protection systems without putting in the fence structure any metal object. Thus the fence is monitored for forcing attempts and remaining full dielectric properties.