Development of optical fibre curvateure sensors for subsea instrumentation
MetadataShow full item record
The experimental results presented in this thesis were part of a bigger research project (LAkHsMI) funded by the European Union (Horizon 2020). The overall project’s aim is to monitor sea flow speeds for different applications with electrical and optical fibre sensors. Here, the fabrication of the sensors which exploit Fibre Bragg Grating (FBG) using conventional, as well as novel optical fibres is presented. Two different curvature sensors were produced for the purposes of the project. The first one was fabricated using four single mode fibres (SMFs) bundled together, while the second used one Multicore fibre (MCF) with four optical cores. The structure of both permitted their curvature to be determined in two dimensions. The first type of optical fibre curvature sensor was also used for the fabrication of a FBG Attitude sensor, where the orientation of a platform in two planes could be determined with accuracy of ±2°. The main priority of the studies presented here was the fabrication and performance of the MCF curvature sensors. The transmittance and reflectance (using inscribed FBGs) of the light into the MCF is explored, where an interface device between the MCF to SMF is required. Two different cases are reported, the first uses a silica inscribed waveguide fan-out device, while the second uses a tapered MCF fan-out device. In the first case the temperature sensitivity of the silica waveguide fan-out device is detected. This sensitivity can be diminished with the use of the tapered MCF fan-out device and discussed. Moreover, in the second case coupling of light from one core of the MCF to all four cores is required. Hence, inscription of different FBGs into the cores of the MCF was achieved so that the overlap of the FBGs spectra would be avoided. The challenges that arose during the fabrication and performance of these sensors are reported. Moreover, their temperature sensitivity as well as the strengths and weaknesses over several aspects are reported. Finally, a comparison between the curvature sensors is included and states which sensor can be used for subsea flow measurements and which has the potentials for further development.