Applications in sensor systems utilize, for example, changes in the polarization of light in an optical fibre during temperature changes. The principle of operation is based on the specific propagation of polarized light by special optical fibres, which, due to their construction, keep the light in two axes, but the speed of their propagation and thus the instantaneous state of polarization of light change. It has been shown that by suitable methods it is possible to transform changes in light polarization into changes in light intensity, which can be detected very effectively by a photodiode. This method has been practically verified, implemented by fibre components and confirmed to be suitable for implementing a fibre sensor of thermal field disruption. The aim of this work is to point out the current possibilities of using polarized light in sensor technology. This polarization system can efficiently secure areas, the surrounding environment and monitor the changes that occur.
The accurate measurement of temperature changes is the key skill not only for predictions of various natural phenomena or to detect intrusion of the object. The temperature changes we nowadays measure in local climate zones or Urban Heat Islands. The environmental quality is an essential feature of life quality and to improve it serve many remote sensing-based urban planning indicators, which are the common part of present smart cities.<p> </p> Continuously developing fibre optic sensors allow their benefits to be exploited in more and more applications. Defensive Perimeter Detection by Polarization Change of the Fiber Optic Signal offers an effective possibility to detect quickly and in time disturbing a predefined space. This detection system uses the polarizing properties of light and, in particular, the birefringence of optical fibres. The disclosed detection system focuses on temperature changes that may be caused by external or internal disruption of the site. The main detection equipment is the polarization maintaining optical fibre with the same excitation in both polarization axes. The transmission rate in both axes is in the ideal case the same, but due to birefringence, inhomogeneity, and imperfection of production and next causes the mutual delay of both signals causes the signal polarization state change or even the series of polarization states changes, which can be observed in laboratory conditions and described by known mathematical methods. However, these changes can be transformed by linear polarizer to the intensity changes. This conversion allows the changes significantly easier to evaluate.
The paper deals with the analytical description of the sensitivity and dynamic characteristics of the birefringent fiber temperature response usable for realization of thermal field disturbance sensors. The response is given by changing the phase shift development between two polarization modes in birefringent fiber, caused by body heat transfer of different temperatures. The aim is to analyze sensitivity and dynamic behaviors, which are significant when optical fiber is used as a sensor of temperature field disturbance. The result shows a very good match with measured time responses, especially due to a specific arrangement for suppressing the influence of conduction and convection.
Due to increasing demands for bandwidth are nowadays very popular optical networks. Installation of new fiber-optic networks is expensive, so is necessary to use existing fiber optic network very effectively. The main parameters that limit the optical networks are dispersion and attenuation. Efficiency optical networks could improve the use of two polarization axes, similar to the technology used in radio technologies. Use of fiber preserves polarization allows the use of two polarization planes. This article deals with the optical wavelength division multiplex in the polarization maintaining fibers.