The objective of this thesis is to analyze the possibilities of using telecom fiber infrastructure for absolutely (fundamentally) secure communication provided by the quantum key distribution (QKD) methods, together with demonstration of a model secure communications link based on quantum cryptography. A study on the feasibility of QKD-based unconditionally secure communication channels is presented, and possibilities for their practical implementations in real applications are analyzed. The first part of this thesis presents a summary of the current knowledge on classical methods for secure information transmission and the novel concepts of quantum cryptography, as well as an overview of existing research applications, both academic and commercial, with an analysis of commercially available solutions. In the second part, an experimental QKD-based network link for unconditionally secure network services at the Wroclaw University of Technology is proposed, based on the cryptographic equipment of the WUT’s Institute of Physics within the National Laboratory of Quantum Technologies.