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

In this paper we report the development of a FBG (fibre Bragg grating) interrogation system, that is capable of detecting independently the two orthogonally polarised signals reflected from a FBG fabricated in a PM (polarisation maintaining) fibre. The interrogation system imposes no limitation on the measurable strain. It is possible to detect a strain gradient by measuring independently the spectral broadening of the two polarised signals. The system has been used to fabricate and characterise FBGs in different PM fibres. As a demonstration of the feasibility of the interrogation system for multi-axis strain sensing, the transverse strain sensing characteristics of PM FBGs are presented.