Fibre Bragg grating location by a side scatter technique based on cladding mode coupling

Fibre Bragg grating (FBG) sensor techniques require, in many cases, the exact knowledge of the location of the Bragg grating structure within a single mode fibre in order to maximise a sensor response or to carry out a measurement at a specific location. In this paper we describe the development of a technique for the accurate location of FBG's based on detection of core guided light which is "backward coupled" by the grating into the cladding and thence scattered into radiation modes. We demonstrate that it is therefore straight forward to measure the position of the FBG to within 0.5 mm.