A distributed curvature sensor based on Brillouin optical time-domain reflectometry interrogation technique in a D-shaped 7-core fibre is presented. By comparing the relative Brillouin frequency shift between the central core and three of the outer cores of the 7-core fibre, the curvature of various spools with different diameters is measured with a deviation from the actual value ranging between 9% and 15%. The analysis and results presented in this study show the first demonstration of distributed bend sensing using a specially designed multicore D-shaped fibre, paving the way for fully distributed 3D shape sensing.

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A D-shaped 7-core fibre is used for curvature sensing with a BOTDR technique. Due to the asymmetry in its geometry, the D-shaped fibre bends along a preferred plane, self-correcting for any twist. This renders it a good candidate for field applications.