Fibre Bragg gratings (FBGs) written into polarisation maintaining (PM) fibreshave been employed for multi-axis strain and temperature sensing. In this paperwe report the development of a FBG interrogation system that is capable ofdetecting independently the two orthogonally polarised signals reflected from aPM FBG. The interrogation system imposes no limitation on the measurable strainrange. This relaxes the requirements on the bandwidth of the grating spectrum,allowing the use of a shorter PM FBG (larger bandwidth) for sensing applicationswhere a higher spatial resolution is required. In particular, this system isuseful in the cases where the spectra of the reflected polarised signals arebroadened or split, resulting from strain-induced structural changes of the PMfibre, or caused by the application of a non-uniform strain on the FBG.
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