The development of semiconductor technology has led to an increase of the usable bandwidth of light-emitting diodes (LED), which are suitable for indoor high-speed communications or free-space optical (FSO) communications over a relatively short distance. The high-speed long-distance FSO links, where turbulence effects are considerably high, are a domain of laser sources. Hence, the paper covers the study of an exact analytical model of FSO link attenuation and the benefits of using an elliptically symmetrical Gaussian beam rather than a circularly symmetrical one.The paper further generalises the study to the FSO link misalignment and the pointing error analysis. The main contribution is in the derivation of an exact laser beam attenuation model, which is further used to analyse the geometrical losses in FSO systems as well as a general misalignment of an elliptically symmetrical beam in any direction from a circular receiver aperture. The challenging mathematical part includes two and six expressions of the general laser beam attenuation model for FSO communications taking into consideration circular and elliptical beams, respectively. The paper concludes with an analysis of advantages of using elliptical beams in FSO systems and a discussion on optimal orientation of the major beam axis with respect to the maximisation of the link availability.The paper summarises some previous results of the team of authors to further extend the model's applicability into more general terms towards a unified model.

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Polarization changes inside a single-mode fiber due to birefringence are studied in this paper. We demonstrate a measurement system for the detection of fast and slow polarization transients in a single-mode optical fiber route. The output signals from a polarimeter based on tilted fiber gratings and a polarimeter based on a polarizing beam splitter and a balanced detector (PBS polarimeter) are processed. The processed data reveal that the detected signal depends on the vibration along the fiber route caused by trains and the temperature instability around the fiber. The proposed system is sufficient for detecting polarization transients and can be used for the detection of suspicious events that would lead to a disruption of the optical path.

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The paper deals with terrestrial optical wireless links operating with coherent laser beams. The contribution discusses the full photonic transceiver concept (transmitter and receiver). Two main types of optical wireless links are mentioned: test link and data link. The purely photonic concept of the links with its advantages over the conventional concept is presented and discussed. The modeling of the full photonic receiver using matrix optics is shown.