Fiber-Optic Sensor with Elliptical Bragg Grating for Torsion Measurement
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Solution Overview
Problem
Existing fiber optic sensors cannot accurately distinguish between torsion and curvature as both result in similar changes in lattice constants of the Bragg grating, leading to corrupted measurement values.
Innovation Solution
The use of Bragg gratings with an elongated cross section, where the short semi-axis is smaller than the core diameter, allows for the differentiation of torsion through the intensity of reflected light, while the wavelength of reflected light is used to measure mechanical stress and temperature, enabling more accurate determination of curvature and shape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Bragg gratings with circular cross section are used, then the sensor can measure mechanical stresses and temperatures, but it cannot distinguish between torsion and curvature, leading to corrupted measurement values
Solution Approach 1:
The patent applies asymmetry by changing the Bragg grating cross-section from circular to elongated (elliptical). This asymmetric geometry creates different optical responses to torsion versus curvature: torsion rotates the elongation direction relative to the polarization plane, while curvature does not. This allows the sensor to distinguish between these two previously indistinguishable mechanical states, resolving the measurement corruption issue.
2Measurement precision
If multiple Bragg gratings are disposed at different distances to the axis of symmetry, then curvature can be determined, but the sensor remains sensitive to torsion interference
Solution Approach 1:
The elongated cross-section of the Bragg grating introduces asymmetry that enables torsion detection. When torsion occurs, the major axis of the elliptical grating rotates relative to the incident light polarization plane, modulating the reflected light intensity. This asymmetric response allows the system to separate torsion effects from curvature effects, improving measurement reliability.
Solution Approach 2:
The patent adds a new measurement dimension by utilizing the polarization state of light in conjunction with the elongated grating geometry. The interaction between the grating's asymmetric structure and polarized light creates an additional degree of freedom in the measurement space, enabling independent determination of both curvature and torsion parameters.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for precise measurement of torsion and mechanical stress, correcting for unrecognized torsional loads and improving the accuracy of determining the shape and position of mechanical components.
Implementation Method 1
at least one Bragg grating is introduced into the first core
Implementation Method 2
the core and the cladding respectively have different refractive indices, resulting in total reflection of the light propagating in the core at the boundary between the core and the cladding
Data Source
AI summary
A fiber optic sensor may be provided comprising an optical waveguide having at least one first core and a cladding surrounding the first core, wherein the first core extends substantially over the entire length of the optical waveguide and at least one Bragg grating is introduced into the first core, wherein the Bragg grating has an elongated cross section, wherein the short semi-axis is smaller than the diameter of the first core and the center of gravity of the cross section of the at least one Bragg grating lies on the axis of symmetry of the optical waveguide. A method may be provided for determining torsion with such a sensor. A method for the production of such a sensor may be provided.