The ever-increasing demands for the use of fiber-optic sensors powered by long optical fibers is forcing developers to solve problems associated with powering these remote sensors. Due to their non-electric character, these sensors are suitable for many uses, including military applications. The Army of the Czech Republic is very interested in this type of optical fiber sensor as it fulfils the significant prerequisites for use in military areas. However, the army’s requirements are challenging because they require long supply cables in which there is significant attenuation of optical power. At the same time, there is a need for high sensitivity. The subject of our research team’s work was to use amplifiers to power these sensors. The army already uses this type of sensor for short distances as it cannot ignite a gas mixture with an explosive concentration and thus meet the strict requirements of the explosion-poof standard. The novelty of our research lies in the discovered measurement technique that allows the sensors to be powered remotely and in the saving of optical fibers by utilizing duplex communication with a circulator. Furthermore, the research presents an innovative approach to the optimization of the entire sensor by using a bidirectional, sensory, polarization-maintaining optical fiber. The proposed sensor was first verified in laboratory conditions at the Optoelectronics Laboratory of the University of Defense in Brno, and further tests were carried out in the military training areas of Boletice and Březina in the Czech Republic, which is a member of North Atlantic Treaty Organization.

The application in polarization sensor systems uses changes in the polarization of light in the optical fiber during temperature changes. The principle of operation consists in the specific propagation of polarized light by special optical fibers, which, thanks to their construction, keep the light in two axes, but change the speed of their propagation and thus the instantaneous state of light polarization. It has been shown that by suitable methods it is possible to transform changes in the polarization of light into changes in its intensity, which can be detected very efficiently and quickly by a photodiode. This method has been practically verified, implemented by fiber components and confirmed as suitable for the implementation of a fiber sensor of thermal field disturbance. However, it turns out that especially in military and biomedical applications it is impossible to place a source of optical radiation close to the measured subject and the sensor must be powered remotely using optical fibers of the order of kilometers. This paper shows the possibility of using long optical paths to power the polarization sensor.

In this paper, a novel current-mode shadow filter employing current-controlled current conveyors (CCCIIs) with controlled current gains is presented. The CCCII-based current-mode shadow filters are resistorless and can offer a number of advantages such as circuit simplicity and electronic tuning capability. The proposed shadow filters offer five filtering functions, i.e., low-pass, high-pass, band-pass, band-stop, and all-pass functions, in the same topology. Furthermore, no component matching condition is required to realize all the transfer functions. The natural frequency and quality factor adjustment is possible by using the CCCII current gains without the need to use external amplifiers, all capacitors are grounded, and the filter terminals offer low-input and high-output impedance. To verify the functionality and feasibility of the new topologies, the proposed circuits were simulated using SPICE and the transistor model process parameters NR100N (NPN) and PR100N (PNP) from AT&T’s bipolar arrays ALA400-CBIC-R. The simulation results are consistent with the theory. The CCCII experimental setup was designed using commercially available 2N3904 (NPN) and 2N3906 (PNP) transistors with a supply voltage of ±2.5 V. The measurement results confirm the performance of the designed filters.

The article deals with the possibilities of using polarization division multiplex technology from a practical point of view. By being able to deploy it into existing networks, it is possible to increase transmission capacity without significant financial investment. Current high-speed optical networks use it mainly in combination with suitable modulation technology and enable transmissions at speeds of the order of hundreds of Gbps and low latency. The work describes measurements on different lengths of optical paths and verifies the functionality of the polarization division multiplex for long paths. The article shows that polarization division multiplex is an ideal technology for use in metropolitan or university networks, or in networks for medical systems. It is also very suitable for routes over very long distances, for example on transcontinental routes laid on the ocean floor, where the laying of new fibers would be very costly. It can also be used in access networks for end users, to whom it will make available transmission speeds in the order of hundreds of Mbps to Gbps units.