Tunnel monitoring using multicore fiber displacement sensor

We describe the first application of multiplexed fibre Bragg grating strain sensors in a multicore fibre. Sets of gratings, acting as strain gauges, are co-located in the multicore fibre such that they enable the curvature to be measured. Multiple sets of these gratings allow the curvature to be measured at several points along the fibre. This sensor is configured to monitor displacement of concrete tunnel sections, and was demonstrated capable of displacement measurement with a resolution of ±0.1 mm over a range of several millimeters.