Sensors based on fiber optics are irreplaceable wherever immunity to strong electro-magnetic fields or safe operation in explosive atmospheres is needed. Furthermore, it is often essential to be able to monitor high temperatures of over 500°C in such environments (e.g. in cooling systems or equipment monitoring in power plants). In order to meet this demand, we have designed and manufactured a fiber optic sensor with which temperatures up to 900°C can be measured. The sensor utilizes multi-core fibers which are recognized as the dedicated medium for telecommunication or shape sensing, but as we show may be also deployed advantageously in new types of fiber optic temperature sensors. The sensor presented in this paper is based on a dual-core microstructured fiber Michelson interferometer. The fiber is characterized by strongly coupled cores, hence it acts as an all-fiber coupler, but with an outer diameter significantly wider than a standard fused biconical taper coupler, which significantly increases the coupling region’s mechanical reliability. Owing to the proposed interferometer imbalance, effective operation and high-sensitivity can be achieved. The presented sensor is designed to be used at high temperatures as a result of the developed low temperature chemical process of metal (copper or gold) coating. The hermetic metal coating can be applied directly to the silica cladding of the fiber or the fiber component. This operation significantly reduces the degradation of sensors due to hydrolysis in uncontrolled atmospheres and high temperatures.
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.
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.
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.
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.
In this work we present a nanocrystalline monoclinic ZrO<sub>2</sub> with large free volumen open towards the nanocrystals surface dedicated for optical oxygen sensors. Nanoporous zirconia nanopowder was fabricated in hydrothermal microwave-driven process followed by annealing at 800°C. Metal-coated optical fibers are proposed as a light carrier when the working temperature exceeds 500°C. The obtained results may also find application in luminescent fiber optic oxygen sensors.