Current solutions used for protection of information transmitted in fibre optic networks are based on direct detection of fibre optic cable eavesdropping and encryption of transmitted information. Protection of fibre optic cables from physical intrusion in to the transmission channel is realized on dark optical fibres, not used in the transmission of information. Security of encrypted information is based on the assumption of limited computing power used for cryptanalysis, what with the introduction of operating quantum computers will cease to apply. So ideal solution for information protection is physical it coding that makes eavesdropping near to impossible, in the same time allows of constant monitoring of fibre physical integrity. The article describes the construction and principle of operation used in fibre optic pulse interferometer, that allows to detect mechanical disorders of fibre optic transmission line with simultaneous transmission of information. Operation of the system relies on encoding information in phase of optical radiation pulses and for monitoring the status of the transmission line by analysis polarization of radiation in interferometer. System configuration provides stabilized work of pulse interferometer over several kilometres, under varying environmental conditions. Unique capabilities of detection system enable the use of two independent criteria for alarm signal excitation. The aim of the study was to determine the security degree provided by system to protection of transmitted information in proposed arrangement.
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