Elliptical-core, two-mode optical fibre sensors as vibration-mode filters

Ruggedised two-mode, elliptical-core fibre sensors are shown to be selective in sensing the different modal frequencies of vibration from a clamped-clamped beam. Sensor placement on a flexible structre is shown to be critical in the design of fibre sensors that measure an integral of strain over their entire sensing lengths. Experimental results confirm theoretical predictions and efficient vibration-mode selectivity is demonstrated.