In this paper we present long-term stability results for a Fabry-Pérot optical fibre sensor in high temperatures environments. We introduce an intrinsic Fabry-Pérot type of sensor, which its sensing element is made with an undoped pure fused silica cavity. Furthermore, we will present results detailing dopant diffusion from core to cladding of standard optical fibres demonstrating their inherent unsuitability for high temperature environments. Finally, we display the manufacturing technique required to produce this sensor and we present results of 33 days long stability tests conducted at elevated temperatures of more than 900°C.
We present high temperature (~1100°C) stability tests of, Ge-doped and F-doped, optical fibre sensors. Our analysis includes the variation in their behaviours within high temperature environments and how the dopant diffusion affects their long term stability.
Applications of fibre optic sensors at high temperatures have gained a huge interest recently, as they appeared to be suitable for temperature recording in harsh environments. In this paper, we are demonstrating two intrinsic Fabry-Perot (F-P) fibre optic sensors for high temperature monitoring. The sensors are consisting of a 125μm diameter single mode fibre (SMF28) and a 125μm diameter PCF ESM-12B pure fused silica fibre spliced to a SMF28, respectively. The result was a low finesse optical SMF-Cr-SMF, and SMF-Cr-PCF, sensor with cavity lengths varying from 50μm to 100μm. Both types of Fabry-Perot sensors were tested in a tube furnace over a temperature range from room temperature up to 1100°C. Following a number of annealing cycles, between the above mentioned temperatures range, very good repeatability of the phase response was achieved. During the cycling process, thermal stress relief takes place which makes the sensors suitable for temperature testing at temperatures just in excess of 1000°C. After initial cycling the sensors are subjected to long term stability tests. The phase response is stable, less than 4°C, over a period of 5 days at a temperature of 1050°C for both sensors. The temperature resolution is around 3°C.
Smart metal having integrated high temperature sensing capability is reported. The SS316 structure is made by additive layer manufacturing via selective laser melting (SLM). Sensor component is embedded in to the structure during the SLM build process. The strain isolated in-fiber Fabry-Perot cavity sensor measures temperature up to 1100 °C inside the metal.
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