Single‐Channel Single‐Fiber 3D Shape Sensing Based on Cascaded Cladding Fiber Bragg Gratings Array

Abstract Optical fiber shape sensors offer reliable navigation and tracking capabilities for continuum robots used in endoscopy and minimally invasive surgery. Current advanced shape sensing solutions utilize highly integrated fiber Bragg gratings (FBGs) in single‐mode fibers, which are the smallest type of shape sensors. A significant challenge with these miniature sensors is the limited number of Bragg wavelengths, which restricts the resolution and length of the measurement. Here, a single‐channel single‐fiber shape sensing scheme is proposed based on cascaded cladding fiber Bragg gratings (cl‐FBGs) fabricated using femtosecond laser direct writing. Each sensing point consists of four mutually orthogonal cl‐FBGs with different wavelengths, which are then parallelly replicated along the fiber axis to form the cascaded structure. This design overcomes the limitation of wavelength channels, enabling the resolution of 104 cl‐FBGs using just four characteristic wavelengths. It is demonstrated that our sensing fiber, containing 26 sensing points, successfully reconstructs deformations of both 2D and 3D curves. Furthermore, it is showed that the intensity demodulation‐based shape sensing scheme exhibits minimal dependence on strain and temperature. This compact, interference‐resistant, and high‐precision shape reconstruction approach represents a significant advancement in micro‐scale spatial shape sensing, akin to applications in microvascular systems.