Fabrication of intrinsic fibre Fabry–Perot sensors in silica fibres using hydrofluoric acid etching

When a cleaved optical fibre is immersed in hydrofluoric acid, the compositional variation within the core and the cladding results in the core-region being etched at a faster rate. This paper presents details of the experimental procedures that were used to etch SM 800 optical fibres and the characterization of the micro-cavities using a 3D surface profiler, optical and scanning electron microscopy. Two such acid-etched fibres were fusion spliced to create an intrinsic Fabry–Perot cavity. These strain sensors were surface-mounted on to fibre reinforced composite test specimens and subjected to quasi-static and cyclic loading. The intrinsic fibre Fabry–Perot sensors were interrogated using low-coherence interferometry. The output from the intrinsic Fabry–Perot sensors showed excellent correlation with surface-mounted electrical resistance strain gauges during quasi-static and cyclic loading.