Fibre bragg gratings and their sensing applications

Lu, Ping (2007) Fibre bragg gratings and their sensing applications. Masters thesis, Memorial University of Newfoundland.

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Abstract

Fibre Bragg gratings have been investigated for their sensing of environmental parameters, including temperature, humidity, axial strain, bending and flow rate. The changes in different environmental parameters result in monotonous spectrum shift of the fibre Bragg gratings. The sensitivities of acrylate-coating fibre Bragg grating on temperature, axial strain and flow rate are 0.0102 nm/⁰C, 0.732 pm/με and 0.0092 nm/cm³s⁻¹, respectively. The sensitivities of polyimide-coating fibre Bragg grating on temperature, humidity and axial strain are 0.0094 nm/°C, 2.60 pm/%RH and 0.99 pm/με, respectively. The experimental results on the polarization characterization indicate that the maximum polarization dependent loss of a single mode polyimide-coated fibre Bragg grating and the Bragg wavelengths corresponding to the fast-axis mode and slow-axis mode of a polarization maintaining fibre Bragg grating will increase with the rising temperature. We propose and demonstrate for the first time that a new multiplexed fibre Bragg grating sensor system is capable of achieving simultaneous measurement of different measurands. The multiplexed sensor system, which consists of two fibre Bragg gratings with different coating materials of acrylate and polyimide, exhibits distinguishable characteristics to different measurands owing to the unique hygroscopic and swelling properties of the polyimide coating. Experimental results on the simultaneous measurement of temperature and saccharinity/salinity indicated corresponding sensitivities of 0.0102 nm/°C and 0.0012 nm/°Bx I 0.0038 nm/%. Simultaneous measurement of temperature and axial strain has also been achieved. The results achieved in this thesis are promising for applications on multimeasurand, quasi-distributed and in-situ sensing measurement using multiplexed FBG sensors.

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