Preliminary results of an experimental verification of shear strain influence on fibre Bragg grating reflection spectra

Fibre Bragg gratings are used as temperature or longitudinal strain sensors in a number of applications. Only a few studies are concerned with transversal stress applied to these sensors. We recently derived an analytical solution for the reflection spectra of shear strain loaded fibre Bragg gratings. The experimental verification of this theory is presented in this work. A fibre-coupled spectra analyzer based on a Fabry-Perot tuneable filter was set up in order to measure the predicted effect. The setup is able to split and measure simultaneously the spectra of the two polarisation main axes of birefringent fibres. The experimental observations are in agreement with predictions derived by mode coupling theory.