Description:
The Naval Research Laboratory (NRL) has developed a method for concurrently measuring bending and twisting along an optical fiber, using only the properties of light guided within the fiber. The NRL method exploits polarization dependent reflectivity from fiber Bragg gratings (FBGs) in a centrally located core. This polarization-based approach fundamentally separates the detection of fiber bending and fiber twist, and no twist bias must be applied during fiber draw. Conventional strain sensing in cores near the fiber's periphery is used to measure bending, and this information is combined with measurements of the state of polarization of light launched into the central core to deduce twist. Because bending only moderately affects birefringence in the central core, measurable polarization effects due to twisting are practicably separable. By accurately measuring both bending and twisting deflections along its length, the overall shape of a fiber can be estimated. Many areas of interest involve obscuring environments where conventional telemetry is impractical. Search and rescue in mines and collapsed structures, submarine deployments, and medical procedures via laparoscopy and catheterization would all benefit from location and attitude information best provided by shape-sensing fibers.

Advantages/Features Include:

  • Requires no change to existing FBG fiber manufacturing process.
  • Offers unambiguous resolution of fiber deflection into bend and twist components.
  • Allows for single fiber end connection to instrumentation.

Applications Include

  • Minimally invasive surgery
  • Structural health monitoring (i.e. strain, displacement, temperature) for search and rescue
  • Sensor array baseline determination

References:

  • "Bend and Twist Sensing in a Multiple-Core Optical Fiber" Proceedings of Optical Fiber Communications 2008, OMT3.
  • "Bend and Twist Sensing in a Multi-Core Optical Fiber" Proceedings of IEEE LEOS Annual Meeting 2008, MM2.

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