Asymmetric-core long-period fiber grating for high-sensitivity vector bending sensing

We propose a vector bending sensor based on an asymmetric-core long-period fiber grating to address the directional ambiguity challenge in fiber sensing. The structure features a periodic and sinusoidal deformation engineered directly into the fiber core, which breaks the inherent cylindrical symmetry of the waveguide. This intrinsic geometric asymmetry endows the sensor with an exceptionally anisotropic response. Experimental results show a maximum sensitivity of -50.56 nm/m^-1 along the primary bending axis (0°), an opposing sensitivity of +99.55 nm/m^-1 at 180°, and a relatively small response of 0.9 nm/m^-1 on the orthogonal axis. This work presents a simple solution for vector sensing and a promising paradigm for functional photonic devices based on direct core geometry engineering.