  This doctoral dissertation deals with the subject of single-photon technology
applications. Particular emphasis was placed on the use of single-photon
sources in quantum communication, metrology, and further development of quantum
computers.
  At the beginning of this thesis, the development history of cryptography is
described, starting from steganography and ending with quantum key distribution
protocols. Later, the key elements of the quantum network, such as end nodes
and transmission channels, are presented. Various types of sources and
single-photon detectors are discussed. Methods for amplifying the signal and
correcting errors that occur during transmission are also mentioned.
  In the further part of this thesis, two examples of single-photon sources are
described, along with their experimental implementation. These sources are
based on the nonlinear spontaneous parametric down-conversion (SPDC) process,
which has also been described in detail. Parameters that specify the quality of
a single-photon source (such as conversion efficiency, phase-matching
conditions, singleness and photonic density matrix) are also characterized,
both mathematically and experimentally.
  Furthermore, this doctoral dissertation consists of definitions and
elaborated descriptions of quantum optical phenomena, which should be useful
for those who are not yet familiar with the subject of single-photon sources
and their applications or just start their work in this field.
