A transverse loading technique to enhance the pressure measurement capability of fibre Bragg gratings

Abstract

A fibre optic pressure sensor based on the application of a transverse load onto an epoxy-resin material embedded over a sub-section of a fibre Bragg grating (FBG) is presented. When a transverse load is applied to the epoxy material it deforms and transfers the load onto the optical fibre in the form of an axial strain that changes the period of the FBG over the embedded region. This introduces a phase shift between the two resulting identical gratings that lie either side of the loaded section, creating a spectral drop-out within the bandwidth of the FBG. A 2 mm section at the centre of FBGs of length 6 mm, recorded in both single mode and highly linearly birefringent optical fibres, was embedded in resin, and were subsequently subjected to a transverse load. The loading technique, while offering protection to the optical fibre from mechanical damage, enhances transverse load sensitivity, without introducing birefringence.