Multi-Core Fiber Shape Sensing via Rayleigh Backscatter
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Solution Overview
Problem
Existing shape measurement techniques for optical fibers are inadequate due to limitations in accuracy, speed, and ability to handle tight bends and torsional forces, which are essential for many applications.
Innovation Solution
The use of a multi-core optical fiber with a helical structure and the interpretation of back reflections of laser light scattered off glass molecules within the fiber to determine fiber position and shape with high accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional strain-based measurement techniques are used, then the measurement can be performed with existing equipment, but the measurement precision is insufficient to achieve tens of nanostrain accuracy
Solution Approach 1:
The patent replaces conventional mechanical/electrical strain gauges with an optical measurement system. Laser light is transmitted through the optical fiber and back-reflected Rayleigh scatter is detected. The phase difference of the optical signal provides strain measurement with precision reaching tens of nanostrain levels, eliminating the precision limitations of conventional resistive or optical strain gauges.
Solution Approach 2:
The patent changes the measurement parameter from direct electrical resistance change to optical phase difference. By measuring the phase difference of laser light that has traveled through the fiber and experienced Rayleigh backscatter, the system achieves extremely high strain measurement precision that cannot be obtained with conventional electrical strain measurement methods.
2Measurement precision
If multi-core fiber with Bragg gratings is used to achieve nanostrain resolution, then measurement precision improves, but manufacturing complexity and cost increase significantly
Solution Approach 1:
The patent extracts and eliminates the complex Bragg grating structure from the optical fiber. Instead of using multi-core fiber with inscribed Bragg gratings (which are difficult and expensive to manufacture), the invention uses standard optical fiber relying on intrinsic Rayleigh backscatter. This removes the manufacturing complexity while maintaining nanostrain measurement precision through optical phase detection.
Solution Approach 2:
The patent replaces expensive, difficult-to-manufacture Bragg grating structures with standard, readily available optical fiber. The use of intrinsic Rayleigh backscatter in conventional fiber eliminates the need for complex fabrication processes, making the system much more cost-effective and easier to manufacture while achieving the same measurement precision.
3Reliability
If conventional shape measurement techniques are used, then the system can handle simple geometries, but accuracy deteriorates when tight bends and torsional forces are present
Solution Approach 1:
The patent replaces mechanical strain gauge measurements with optical phase detection. The optical method is insensitive to the absolute position and orientation of the fiber, allowing accurate shape measurement even when the fiber undergoes tight bends or torsional forces. The phase difference measurement captures only the relative changes in optical path length, which remain accurate despite geometric distortions.
4Measurement precision
If high accuracy rotational sensing is implemented, then twist measurement precision improves, but the complexity of the sensor system increases
Solution Approach 1:
The patent creates a universal optical measurement system that simultaneously measures both linear strain and rotational twist using the same basic mechanism. The optical phase detection method works for both axial strain and torsional deformation, eliminating the need for separate sensor systems and reducing overall system complexity while maintaining high precision for both measurement types.
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 method enables accurate shape calculation with an accuracy better than 0.5% of the optical length of the multi-core fiber, effectively addressing the limitations of conventional techniques.
Implementation Method 1
the fiber position is determined by interpreting the back reflections of laser light scattered off the glass molecules within the fiber
Implementation Method 2
A change in optical length is detected in ones of the cores in the multi-core fiber... by calculating an optical phase change at each segment length along the multi-core fiber
Data Source
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AI summary
An accurate measurement method and apparatus are disclosed for shape sensing with a multi-core fiber. A change in optical length is detected in ones of the cores in the multi-core fiber up to a point on the multi-core fiber. A location and/or a pointing direction are/is determined at the point on the multi-core fiber based on the detected changes in optical length. The accuracy of the determination is better than 0.5% of the optical length of the multi-core fiber up to the point on the multi-core fiber. In a preferred example embodiment, the determining includes determining a shape of at least a portion of the multi-core fiber based on the detected changes in optical length.