Characterization of tilted fibre gratings under bending

The characteristics of low- and high-order cladding modes of tilted gratings (TFBG) under bending has little been investigated despite the popularity of TFBGs in different sensing applications. In this work a theoretical model to investigate the interaction between core and cladding modes in a bent fibre has been established. The influence of bending curvature on the low- and high- order cladding modes has been analyzed, based on the use of both simulation and theoretical calculation. The simulation and calculations carried out show that due to the different mode characteristics, the resonance wavelengths of the different cladding modes will shift in different way, as the bending curvature increases. A 3° tilted grating has been used as a bending sensor, whose operation was based on the mode characteristics of the low-order cladding modes. A linear response between the resonance wavelength of a low-order cladding mode and bending curvature has been obtained, creating a useful result for fibre optic bending mode sensors.