Experimental study of the influence of FBG length on optical shape sensor performance

Abstract This paper compares the performance of optical Multicore Fibres (MCFs) with inscribed Fibre Bragg Gratings (FBGs) used as curvature and shape sensors in relation to strain sensor length. Two fibre optic shape sensors, consisting of FBGs written in standard optical multicore fibre (diameter 124.5 μm), were assembled in the Institute for Telecommunications and Multimedia Applications (iTEAM) of the Universitat Politecnica de Valencia. The optical sensors were then positioned on an aluminium mould and quasi-distributed curvature and shape sensing were performed to compare the accuracy of the arrays. It was found that the MCF shape sensor performance strongly depended on FBG length and that sensors based on long FBGs were significantly more accurate, showing that long FBGs can considerably improve shape sensor accuracy at equal grating densities and achieve substantially better performance. This is a great advantage when wavelength division multiplexing is used, when only a limited number of usable FBGs can be applied. These new results, applicable to both multiple single-core optical fibres and multicore optical fibres with embedded quasi-distributed strain sensors, show the connection between strain sensor length and accuracy, hardly taken into account in previous studies, and lay the foundation for the design of new long-FBG-based shape sensors.