Fibre optic sensing for military bridge health and load monitoring

Design, preparation and characterisation are reported of intra-core fibre Bragg grating arrays, fabricated by holographic interferometry at 244 nm in hydrogen-sensitised fibre, followed by post-fabrication anneal. Array sizes range from three elements, manufactured in a single fibre length, to ten elements distributed over four discrete fibres with no loss of array homogeneity, with standard deviation between design target and manufactured wavelength of less than 0.1 nm. Over a ten-element array, designed for constant inter-grating wavelength interval of 3.5 nm, standard deviation from the target spacing was 0.07 nm. Arrays have been successfully incorporated into fibre-reinforced composite panels and surface-mounted on to a large mechanical structure using conventional strain-gauge mounting technology, with no significant modification of optical characteristics. (11 pages)