Fibre Bragg grating sensors

Volanthen, M., Geiger, H., Trundle, K.J. and Dakin, J.P. (1997) Fibre Bragg grating sensors. Optical Fibre Sensor Technologies and Applications, Munich, Germany.

Abstract

Three different fibre sensor systems using gratings are presented. Firstly, using an acousto-optic tunable filter and closed loop feedback, arrays of fibre Bragg gratings are being used to monitor small-scale perturbations in composite materials by mapping the strain field around a defect. Gratings are also used as distributed sensors by measuring the wavelength as a function of distance. Low-coherence interferometry selects the location under interrogation and a tunable filter measures the local wavelength. An open loop interrogation technique using a commercially available optical coherence domain reflectometer is demonstrated. The reflectivity of the sensor grating is measured as a function of both distance and wavelength. Gratings 40cm long are interrogated and several distributed grating sensors are multiplexed in an array. Thirdly, a new sensing concept using subcarrier fibre gratings (SFGs) has been proposed and modelled. The SFG is a periodic reflective array resonant at RF frequencies. The resonance may be measured using subcarrier interferometry. Modelling has demonstrated the SFG to have superior performance over other subcarrier sensors.

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