Fiber Optic Interference Sensor

Fiber Optic Interference Sensor Securelight-1LP is a system which allows detection and location of mechanical disorders influencing on the sensor part of the system. Sensor system is built on the basis of two Mach РZehnder interferometers using the same optical fibers but with the opposite direction of light propagation. Interference sensor is  based on 3 fibers of single mode optical fiber.

There are two sections of optical fibers in the system. Section sensitive to external disturbances consist of optical fibers which are arms of the interferometer and transceiver fibers transmitting output signals from the interferometers and ensuring transmission of power to optical interferometers.

External disturbances are located and alarm is generated based on analysis of interference contrast and by appropriate signal processing. In addition, the system through the use of appropriate modulation of the power emission, automatically adapts to environmental changes affecting its sensitive part providing automatic compensation for low-frequency background signals.

Interference sensor system is able to monitor zones up to 49 kilometers long and to locate a place of disturbances with accuracy to several meters by dividing the protected zone into smaller safety zones. There is also a possibility to configure location of detection zones.


  • Monitoring of integrity several kilometers long fiber optic transmission line.
  • Generating alarm signals and locating an area where external disturbances occurred.
  • High security of transmitted data in the supervised transmission channel.
  • Ease of installation and troubleshooting.
  • Perimeter security of extensive facilities.
  • Protection of pipelines.
  • Border Protection.

Proper analysis of data consists of several phases:

  • determination of disruption location from correlation
  • verification if the location is within a specified range
  • verification if level of correlation exceeds defined value
  • verification of correlation shape in interference location

Calculated location of disruption is subject to statistical analysis after fulfilling all conditions.


Interferometric sensor features simplicity of installation and maintenance of communication track damage due to possibility to use standard fiber optic cables. Therefore, it is possible to restore the system to function quickly in case of a failure on the line.

The interference sensor may be used as a module for monitoring the integrity of a telecommunication lines. It ensures high security of transferred data in the supervised transmission channel due to the usage of sensitive fibers for the transmission.

The security system based on the interference sensor can be integrated with maps visualizing location of an alarm.

Software of the system offers features, such as: visualization of system operation and configuration of its parameters.

This system was developed by the Consortium of Military University of Technology and KenBIT Sp. J. under contract no. PBS1/B3/3/2012 funded by The National Centre for Research and Development.