Discrimination of strain and temperature using Bragg gratings in microstructured and standard optical fibres

In this work two sensing heads based on fibre Bragg grating structures are demonstrated, one for temperature independent measurement of strain and the other for simultaneous measurement of these two parameters. The first one relies on a single Bragg grating inscription in a microstructured optical fibre, resulting for two input orthogonal polarizations in two distinct resonance peaks with similar temperature sensitivities and different strain sensitivities. In the second structure two gratings were considered, one written in the same microstructured fibre and the other on a standard SMF fibre. Considerably different strain and temperature sensitivities were obtained for these two gratings, enabling simultaneous temperature and strain measurement with resolutions of +/- 1.5 degrees C and +/- 10.7 mu epsilon over a measurement range of 100 degrees C and 2000 mu epsilon, respectively.