A polarization-maintaining fibre Bragg grating interrogation system for multi-axis strain sensing

We report the development of a fibre Bragg grating (FBG) interrogation system that is capable of detecting independently and simultaneously the two orthogonally polarized signals reflected from a polarization-maintaining (PM) FBG. This relaxes the constraints on the bandwidth of the FBG spectrum, allowing the use of a shorter PM FBG (larger bandwidth) for sensing applications where a higher spatial resolution is required. It imposes no limitation on the measurable strain range and strain profile. The interrogation system is capable of decoding the complex spectral responses of a PM FBG subjected to a transverse load.