Single-fiber three-dimensional shape sensing via femtosecond laser inscribed orthogonal eccentric scatterers.

Optical fiber sensors have emerged as a powerful platform for high-precision shape detection in soft robotics and minimally invasive medical devices. However, existing fiber-sensing architectures face a long-standing trade-off between device size and spatial resolution. This work reports a miniaturized three-dimensional shape-sensing system based on misplaced orthogonal eccentric scatterers (MOESs) densely inscribed into the cladding of a standard single-mode fiber. The MOESs array is fabricated through a scalable reel-to-reel femtosecond laser writing process. Each MOES element functions as a curvature-dependent Rayleigh scatterer, and their misplaced orthogonal arrangement spatially encodes full 3D deformation information within a single fiber core. Experimental results demonstrate high-fidelity 2D bending and full 3D deformation reconstruction. The intensity-domain reconstruction algorithm further exhibits strong immunity to environmental perturbations. This approach defines a new paradigm for compact, cost-effective, and high-fidelity fiber sensors, paving the way for applications in unstructured and dynamic environments.