A description of test-assessment of TELECOM 1550 nm optical fiber used for a quantum channel in entangled Quantum Key Distribution (QKD) setup, EPR S405 Quelle (Aus-trian Institute of Technology) is presented. The system at work was observed and parameters related to dark quantum channel were collected by an appropriately designed test card. Series of measurements were carried out for various configurations of 1550 nm (optimal transmission wavelength) optical fiber patch-cord the same as used

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... standard metropolitan TELECOM networks including distances up to 6.5 km long. The particular attention has been paid to model the real lines with welding points and connectors in view of rigorous requirements regarded conservation of photon polarization in EPR S405 system. Tests allowed for assessment of Qantum Bit Error (QBER) level in standard telecommunication fiber infrastructure when trying to implement entangled QKD system vulnerable in particular to polarization perturbations. Another drawback, incommensurability of the central transmission wavelength in fiber with the wavelength of photons in EPR S405 system, was also assessed and the possibility of implementation of QKD EPR S405 system with 1550 nm optical fibers has been verified.