Engineered cladding scatterers in optical fiber for 3D deformation encoding

Fiber-optic deformation sensors offer a promising solution for precise navigation in soft robotics. However, the inherent limitations of traditional sensing mechanisms present a persistent trade-off between sensor miniaturization and spatial resolution. Here, we introduce a novel fiber-based 3D deformation encoding technique enabled by an array of misplaced orthogonal eccentric scatterers (MOESs) inscribed in the cladding. The Rayleigh scattering intensity from each MOES depends on local fiber curvature, and the orthogonal configuration enables spatially resolved deformation data to be compactly encoded within a single-mode fiber. We have developed an advanced reel-to-reel femtosecond laser direct writing technique to fabricate the MOESs array fiber. Experimental results demonstrate accurate 2D bending and full 3D deformation reconstruction. Moreover, the proposed energy-based reconstruction algorithm exhibits strong immunity to environmental disturbances. These advancements mark a significant step toward miniaturized, low-cost, and high-precision fiber-optic solutions for tracking structural deformations in complex environments.