FIELD: physics, optics.
SUBSTANCE: invention relates to fibre optics and can be used in systems for protecting the perimeter of sites and premises from unauthorised access. The distributed coherent reflectometric system with phase demodulation comprises a laser pulse source, an optical receiver, a circulator, an unbalanced Mach-Zehnder interferometer, a fibre-optic cable and a control and processing unit. The output of the laser pulse source is connected to the first output of the circulator, the second output of which is connected to the fibre-optic cable, and the third output is connected to the input of the unbalanced Mach-Zehnder interferometer, the output of which is connected to the optical receiver, which is electrically connected to the input of the control and processing unit. One of the arms of the Mach-Zehnder interferometer contains a Mach-Zehnder electrooptical modulator which can independently control the arms, and the second input of the control and processing unit is connected to the Mach-Zehnder electrooptical modulator. In another version, one of the arms of the Mach-Zehnder interferometer contains a Mach-Zehnder electrooptical modulator which can independently control the arms, and the second input of the control and processing unit is connected to the Mach-Zehnder electrooptical modulator.
EFFECT: obtaining phase distribution of an optical signal along a fibre, which makes it possible to carry out reliable measurement of an action on a cable.
2 cl, 2 dwg
