Optical Waveguide Curvature Detection via Intensity Shifts
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Solution Overview
Problem
Existing methods for determining the curvature and/or torsion of a fiber optic sensor face challenges due to the small wavelength changes caused by curvature, which result in a barely detectable signal, making it difficult to achieve reliable and sensitive measurements.
Innovation Solution
The proposed procedure involves measuring the light intensities at multiple Bragg grids located in fixed positions along the fiber optic sensor, allowing for a more sensitive and reliable determination of curvature and torsion by analyzing the shifts in the light intensity distribution caused by curvature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If wavelength changes of individual Bragg gratings are measured to determine curvature and/or torsion, then the measurement principle can detect rotations and temperature changes, but the signal change is extremely small (more than an order of magnitude smaller than Bragg gratings in multi-core fibers or waveguides in the cladding), making wavelength analysis almost impossible even with large curvatures
Solution Approach 1:
The patent transitions from measuring wavelength changes (spectral domain) to measuring intensity changes of reflected light (intensity domain). By detecting the intensity of light reflected from multiple Bragg gratings at different radial positions and analyzing the intensity distribution pattern, the system can determine curvature and torsion with much higher sensitivity. This dimensional change from wavelength to intensity measurement enables detection of the extremely small curvature-induced signal changes that were previously undetectable.
Solution Approach 2:
The patent places Bragg gratings at specific radial positions within the optical waveguide (in the core and/or in the cladding within the evanescence region) to create localized intensity variations. When curvature occurs, the intensity distribution among gratings at different radial positions changes in a characteristic pattern. By analyzing these localized intensity changes rather than relying on small absolute wavelength shifts, the system achieves high measurement sensitivity for curvature and torsion.
2Measurement precision
If Bragg gratings are placed in the core and/or cladding to enable curvature measurement, then sensitivity can be improved, but the manufacturing complexity increases due to the need for precise positioning of multiple gratings
Solution Approach 1:
The patent incorporates multiple Bragg gratings at predetermined radial positions during the manufacturing process. These gratings are pre-positioned in the core and/or cladding at specific locations that will optimally detect curvature-induced intensity changes. By establishing this grating configuration in advance during manufacturing, the sensor is ready for high-precision curvature measurement without requiring complex post-manufacturing adjustments or alignments.
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 enhances the sensitivity of curvature and torsion measurements, enabling accurate determination of deformations in fiber optic sensors, even in the presence of intensity losses, and allows for independent measurement of temperature and stretching effects.
Implementation Method 1
A Bragg grating is a region of periodic refractive index modulation in the material of the optical waveguide. The period of the refractive index modulation is also referred to as the grating constant and is in the range of the wavelength of the light being guided in the optical waveguide. This light is at least partially reflected by the Bragg grating, with the intensity of the reflected light depending in particular on its wavelength, the angle of incidence on the Bragg grating, and the grating constant of the Bragg grating.
Implementation Method 2
When the optical fiber is bent, the position of the maximum light intensity within the optical fiber shifts in the opposite direction to the curvature.
Data Source
Figure 1~2f
Figure 3a~3b
AI summary
A method for determining a curvature and/or torsion of an optical waveguide (3) of a fibre-optic sensor (1), comprising at least two Bragg gratings (8, 9, 20) introduced into the optical waveguide (3) and extending through a common cross-sectional plane (11), situated in a radial direction, through the optical waveguide, wherein the Bragg gratings (8, 9, 20) are introduced in the core (5) and/or on the boundary between the core (5) and the cladding (6) and/or in an inner edge region of the cladding (6) within an evanescence region of the light, comprising the following method steps: a) providing reference data of intensities of reflected light portions of light coupled into the optical waveguide, in particular depending on known reference deformations of the optical waveguide, b) measuring at least one light intensity (35) of reflected light portions of light coupled into the optical waveguide, wherein the optical waveguide has a deformation to be determined, and c) determining the deformation by comparing the light intensity (35) with the reference data.