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.

To adapt to current changes, such as globalization, climate change, and demographic growth, modern cities must embrace the digitalization of city management. In this paper, we examine a concept for digitalizing a city based on Rotterdam’s digital twin showcase. Data-processing frameworks for different sources of data are presented. Security risks and the potential of smart cities for military usage are discussed. Lastly, using an example of available datasets for air quality and public lighting consumption, functions of the Rotterdam digital twin are compared with the Brno city digital platform. It was found that every city has its approach to digitalization, and it is probably impossible to unify every city’s digitalization process. This means that the digitalization of the city is very individual. Both systems in their current form make it possible to visualize the collected data about the city. So far, however, these systems do not use advanced functions such as AI-assisted decision-making and prediction of various events in the city. Even so, they are a source of very interesting data that can be used by third parties.

This study is focused on analysing the optimal distribution of optical intensity within a radiated laser beam at a transmitter plane which is propagated through free space as well as through a turbulent atmosphere. To analyse the propagation of an optical wave through atmospheric turbulence, the simulation, based on the split‐step beam propagation method, was utilised. The aim of this study is to determine the optimal parameters for a flattened Gaussian beam at the transmitter plane. As a result, the scintillation index should be reduced. There are a number of theoretical studies aimed at propagating the flattened beam despite the lack of experimental work in this area. Therefore the techniques for generating the flattened Gaussian beam will also be mentioned.

Since free-space optical links (especially fully photonic ones) are very challenging to accurately align; scanning algorithms are used for the initial search and alignment of the transceivers. The initial alignment aims to intercept the optical beam so that it hits a position-sensitive detector. However, this operation can be very time-consuming (depending on the system parameters, such as transceiver parameters, distance between transceivers, divergence of the transmitter, angle of view of the receiver, etc.). A spiral scan is used as the most widespread pattern for scanning. This article examines the effects of system parameters (e.g., global navigation satellite systems and compass accuracy) on the angular area of uncertainty that must be scanned to find the optical beam. Furthermore, several types of spiral pattern are compared depending on the time of the scan execution and the required number of points for scanning the given uncertainty area. The cut hexagonal spiral scan achieved the best results as it required 18.1% less time than the common spiral scan for the presented transceiver.