Bending sensors based on fiber Bragg gratings: The key role of the mean effective index R. Guyard, D. Leduc, Y. Lecieux, C. Lupi, J. Potet, J. Beaucé, M. Douay and L. Lablonde EPL, 119 2 (2017) 24004 Published online: 05 October 2017 DOI: 10.1209/0295-5075/119/24004