Co-located angularly offset fiber Bragg grating pair for temperature-compensated unambiguous 3D shape sensing.

Area of Science:

• Fiber optics
• Optical sensing
• Materials science

Background:

• Fiber Bragg gratings (FBGs) are widely used for sensing applications.
• Existing FBG sensors often lack the ability to measure 3D shape or are sensitive to external factors like temperature.
• A need exists for robust, multi-dimensional fiber optic shape sensing.

Purpose of the Study:

• To develop and experimentally demonstrate a 10 mm-long, single-mode fiber optic sensor capable of 3D shape measurement.
• To investigate the sensor's sensitivity to bending in all azimuthal directions.
• To evaluate the sensor's immunity to axial deformation and temperature variations.

Main Methods:

• Inscribing a pair of offset fiber Bragg gratings at the same location but different radial directions within a single-mode fiber.
• Utilizing the differential amplitude response of cladding mode resonances from the two gratings to detect directional bending.
• Analyzing the spectral shifts and amplitude changes in response to bending, axial strain, and temperature.

Main Results:

• The sensor demonstrated unambiguous 3D shape orientation determination across a full 360° range.
• High sensitivity to bending (order of 1 dB/m⁻¹) was achieved for small curvatures (0-1 m⁻¹).
• Axial deformation and temperature changes resulted only in global wavelength shifts, not affecting shape measurement accuracy.

Conclusions:

• The developed fiber optic sensor provides a robust and accurate method for 3D shape sensing.
• The sensor's design offers immunity to axial strain and temperature, enhancing its practical applicability.
• This technology has potential applications in robotics, medical devices, and structural health monitoring.