What is the principle of fiber optic shape sensing

Fiber optic shape sensing determines the 3D shape of an optical fiber by measuring strain-induced wavelength shifts in embedded Fiber Bragg Gratings (FBGs) or via distributed scattering, converting these signals into curvature and spatial coordinates.

Core Principle

Fiber optic shape sensing relies on the detection of strain along an optical fiber, which occurs when the fiber bends or deforms. The most common approach uses Fiber Bragg Gratings (FBGs) inscribed in multi-core optical fibers.

Each FB

G reflects a specific wavelength of light, and when the fiber bends, the strain changes the reflected wavelength. By measuring these wavelength shifts, the local strain at multiple points along the fiber can be determined, which is then used to reconstruct the fiber's curvature and 3D shape in real time.

Multi-

Core Fiber Approach

In multi-core fibers, several cores run parallel within a single fiber. When the fiber bends, the outer cores experience tension or compression relative to the central core, producing differential strain readings. These relative strains are processed to calculate local curvature and bending orientation, which are then integrated along the fiber length to reconstruct the overall shape.

Advanced methods use polynomial approximations or deep learning models to convert strain data into precise 3D tip positions, achieving sub-millimeter accuracy. Distributed vs.

Quasi-

Distributed Sensing

Distributed sensing uses scattering phenomena such as Rayleigh, Brillouin, or Raman scattering to measure strain continuously along the fiber. Techniques like Optical Time Domain Reflectometry (OTDR) or Optical Frequency Domain Reflectometry (OFDR) provide high spatial resolution but require complex readout systems. Quasi-distributed sensing relies on discrete FBGs at specific points along the fiber, offering a simpler and commercially widespread solution, especially in medical robotics and minimally invasive surgery.

Applications

Fiber optic shape sensing is widely used in: Medical devices: Catheter navigation, instrument tracking, and minimally invasive surgery. Robotics: Real-time position tracking and deformation monitoring. Structural monitoring: Aerospace, energy, and civil engineering applications where precise shape and strain measurements are critical.

Summary

The principle of fiber optic shape sensing is based on converting strain measurements from optical fibers into curvature and spatial coordinates. Multi-core fibers with FBGs provide high-resolution, real-time shape reconstruction, while distributed scattering methods allow continuous sensing over long distances. This technology enables precise navigation, deformation monitoring, and control in complex or constrained environments.