The present invention relates to an optical based bending sensor. In particular, the present invention relates to a fibre-based bending sensor for the determination of the direction and the amplitude of a bend. The present invention further relates to fibre-based bending sensors using long-period fibre gratings (LPG), in which the intrinsic properties of the fibre and the bend sensitivity of LPG is utilised. In a preferred embodiment, the connection between the Core Concentricity Error (CCE) of the fibre and the LPG in the asymmetric bend behaviour results in coupling resonance between the core and the cladding modes. Thereby a relative splitting of transmission peaks in the spectrum of the LPG is induced, which is used to determine the bending amplitude and direction.