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Abstract

Determining the dependence of phase difference modulations between light pulses in a modified Mach-Zehnder interferometer was used to develop an optical system coding the information and working as an eavesdropping sensor for an optical fibre information exchange system. The basic challenge in the system development is to maintain stable operation in changing environmental conditions, as well as to ensure optimal parameters of the phase modulator. The system was tested for various many-kilometer long transmission lines of single-mode fibres. The research was focused on achieving the normative Bit Error Rate for the system in the 100 Mbit/s range (STM-1). Such a system can be used in commercial applications for the code key secure transmission in the physical layer of the link.
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Authors and Affiliations

M. Życzkowski
M. Karol
N. Pałka
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Abstract

A modified optical fibre based Mach-Zehnder interferometer was applied as a sensor to detect wiretapping in long transmission optical fibre lines. The signal consisting of short pulses (around 1 ns) was launched to the input of the interferometer based on the polarization maintaining fibres and polarization elements. When the sensing line was undisturbed, detectors registered only a single pulse. The additional two side pulses appear, if the wiretapping attempt took place. For robust detection of any alarm situation we proposed two-criteria algorithm to minimize false alarm rate. Moreover, slow environmental fluctuations were continuously monitored and compensated by polarization controllers. We measured frequency characteristics of the sensor and performed a hundred wiretapping attempts, which proved high performance of the sensor.

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Authors and Affiliations

M. Życzkowski
M. Karol

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