Fiber optic sensors (FOS) are insensitive to external EM fields and are intrinsically safe (as no electrical power is needed at the sensing point), so the measurement can be performed in areas where standard electronic devices cannot easily be applied. What is more, due to the very low silica fiber attenuation the measurement point can be located kilometers away from a light source and detector, which makes the sensors independent of a local power source. Furthermore the FOS are small so they can be used for sensing in mechanical mechanisms where there is not much free space. They can also be easily integrated with the structure of different materials for military applications (e.g. in tanks and airplanes).<p> </p> In this work we propose an intrinsically safe temperature sensor based on fiber optic technology. The presented sensor is entirely passive and benefits from all of the advantages mentioned above, which allows it to be applied in the most demanding environments. The construction of the presented sensor is based on a dedicated microstructured optical fiber which allows both the range and sensitivity of the sensor to be adjusted to a specific application.
A matrix of optical fiber sensors eligible for remote measurements is reported in this paper. The aim of work was to monitor the air quality with a device, which does not need any electricity on site of the measurement. The matrix consists of several sensors detecting carbon dioxide concentration, relative humidity and temperature. Sensors utilize active optical materials, which change their color when exposed to varied conditions. All the sensors are powered with standard light emitting diodes. Light is transmitted by an optical fiber from the light source and then it reaches the active layer which changes its color, when the conditions change. This results in a change of attenuation of light passing through the active layer. Modified light is then transmitted by another optical fiber to the detector, where simple photoresistor is used. It is powered by a stabilized DC power supply and the current is measured. Since no expensive elements are needed to manufacture such a matrix of sensors, its price may be competitive to the price of the devices already available on the market, while the matrix also exhibits other valuable properties.
An novel low-temperature method was used to enhance the corrosion resistance of copper or gold-coated optical fibers. A characterization of the elaborated materials and reports on selected studies such as cyclic temperature tests together with tensile tests is presented. Gold-coated optical fibers are proposed as a component of optical fiber sensors working in oxidizing atmospheres under temperatures exceeding ~900 °C.
CO<sub>2</sub> optical fiber sensors based on polymer active materials are presented in this paper. Ethyl cellulose was proven to be a good candidate for a matrix material of the sensor, since it gives porous, thick and very sensitive layers. Low-cost sensors based on polymer optical fibers have been elaborated. Sensors have been examined for their sensitivity to CO<sub>2</sub>, temperature and humidity. Response time during cyclic exposures to CO<sub>2</sub> have been also determined. Special layers exhibiting irreversible change of color during exposure to carbon dioxide have been developed. They have been verified for a possible use in smart food packaging.
This paper focuses on the utilization of crosstalk phenomenon to construct an innovative strain sensor. In our experiments, we take advantage of special fiber design and technology of fiber post-processing in order to receive strain sensing areas. We present results, which indicate possibility of achieving strain sensitivity at level of several mε/nm with negligible temperature cross-sensitivity at the same time. Furthermore after coating the sensor with the developed copper and gold coatings, it can be easily applied in extremely high temperature (e.g. 500 – 800 ⁰C) and/or aggressive media applications.
In this work we present an innovative method of enhancing optical fibers’ resistance to extremely high temperatures by deposition of a multilayer metal coating on the fibers’ surface. Such multilayer coating is necessary because of the silica degradation at elevated temperatures. Despite the fact that copper coated fibers work well at temperatures up to 400°C, at higher temperatures copper oxidizes and can no longer protect the fiber. To hold back the copper oxidation and silica degradation processes we developed a dedicated multilayer coating which allows fibers to operate at temperatures up to 700°C. The optimal protective layer has been chosen after numerous high-temperature tests, where copper plates coated with different kinds of coatings were evaluated. What is more, we present results of the high-temperature reliability tests of copper coated fibers protected with our multilayer coating. Performed tests proved that our solution significantly improved optical fibers’ reliability to both: elevated temperatures and rapid changes of temperature. Furthermore the developed metal coatings allow fibers’ to be electrolytically bonded to other metal elements (e.g. sensor transducers) what makes them great candidates for harsh environment fiber optic sensor applications.
Optical fiber carbon dioxide gas sensors are reported. The sensors utilize pH sensitive indicator dyes, which change color, when exposed to varied concentrations of CO<sub>2</sub>. Sensors were made by deposition of silica sol solution on the Plastic Clad Silica fiber side surface. The possibility of preparing the sensors by deposition of active layer on the surface of etched fibers has also been demonstrated. Dependence between the fiber diameter and the sensitivity of the sensor has been presented. Morphology of the active layer has been investigated by the analysis of SEM images.
The paper reports on the metal (Cu, Ni, Au)-coated fibers annealed under concentrated solar radiation in ammonia and N<sub>2</sub>/H<sub>2</sub> atmospheres at temperatures up to 580 °C. Tensile strength of the annealed fiber components was studied from the point of view of their possible application as a fiber optic sensors in urea chemical synthesis process control.
An optical fiber CO<sub>2</sub> gas sensor is reported in this work. Sensor is based on the change of absorption of a selected dye dissolved in an organically modified silica coating of an optical fiber. CO<sub>2</sub> in the atmosphere decreases the pH of the deposited active layer, which eventually leads to the change of the fiber transmittance. Elaborated sensor exhibits high sensitivity, short response time and good stability, which makes it suitable for potential industrial, agricultural and household use. Described method can also be used for sensing other gases in sensor matrices.
In this work we present an innovative method of connecting metal coated optical fibers with metal surfaces. The process is based on electrolytic reaction between copper and allows to obtain a robustand inflexible connection. Furthermore reliability tests of such fiber to metal joints have been performed, with the results of mechanical strength and temperature resistance tests presented. Additionally, as accelerated oxidation of copper at elevated temperatures is a major concern in long term temperature stability of the connection, we propose a method of slowing down the oxidation process with chemical nickel coating. Analysis of the obtained results allows us to predict that the investigated connection may find applications in various industrial optical sensors with special focus on harsh environments.