Offset Core Optical Fiber for Sub-Millimeter Contortion Detection
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Solution Overview
Problem
Current optical fiber sensors are unable to effectively measure sub-millimeter contortions and applied forces due to limitations in recognizing and measuring small-scale changes in bending and strain.
Innovation Solution
An offset core optical fiber with a spiral configuration and inscribed continuous Bragg grating, combined with optical frequency domain reflectometry (OFDR) and spatial Fourier analysis, allows for sub-millimeter resolution measurements of contortions and forces by shifting the Bragg wavelength in response to applied forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical fiber sensors are used, then the sensor can detect general bending and strain, but it cannot measure sub-millimeter contortions and applied forces
Solution Approach 1:
The patent employs an offset core configuration where the light-guiding core is deliberately positioned asymmetrically from the central axis of the optical fiber. This asymmetric positioning enables the core to experience differential strain when the fiber bends, allowing detection of sub-millimeter contortions. The offset core experiences greater strain than a central core would, thereby enhancing sensitivity to small-scale deformations and applied forces.
Solution Approach 2:
The patent inscribes Bragg gratings at specific locations within the offset core region rather than uniformly throughout the fiber. This localized grating placement concentrates the sensing function at the region experiencing maximum strain during bending, thereby optimizing the measurement of sub-millimeter contortions and applied forces at the most sensitive location along the fiber.
2Measurement precision
If Bragg gratings are inscribed within a central axis core region, then the sensor can measure strain along the fiber, but it cannot detect off-axis strain and bends
Solution Approach 1:
The patent deliberately positions the light-guiding core asymmetrically from the central axis of the optical fiber. This asymmetric configuration enables the core to experience differential strain when the fiber bends in any direction. The offset core experiences greater strain than a central core would, thereby enabling detection of off-axis strain and bends in multiple directions along the fiber.
3Length of stationary object
If extended length of optical fiber is used as distributed sensor, then the sensor can detect measurands along entire length, but the resolution for sub-millimeter contortions is insufficient
Solution Approach 1:
The patent employs an offset core configuration throughout the extended length of the optical fiber. This consistent asymmetric positioning along the entire fiber length enables the distributed sensor to maintain high sensitivity to sub-millimeter contortions at any location along its extended length, resolving the contradiction between long sensing range and fine resolution capability.
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 enables high-resolution detection of micron-scale deformations and applied forces, providing accurate distributed contortion measurements over extended distances with sub-micron resolution, enhancing sensitivity and spatial resolution in sensing applications.
Implementation Method 1
a fiber with a light-guiding core that is offset from the central axis can be used to detect bends and contortions (i.e., twists) along the fiber by performing localized strain measurements of the shift in Bragg grating wavelength in the offset core
Implementation Method 2
performing localized strain measurements of the shift in Bragg grating wavelength in the offset core
Implementation Method 3
use an offset core optical fiber with inscribed gratings to perform optical frequency domain reflectometry (OFDR) measurements of small-scale (sub-millimeter) contortions and applied forces
Data Source
AI summary
An extended length of optical fiber having an offset core with an inscribed Bragg grating is used a distributed sensor in combination with an optical frequency domain reflectometer (OFDR) to enable measurement small-scale (e.g., sub-millimeter) contortions and forces as applied to the fiber. The offset core may be disposed in a spiral configuration around the central axis of the optical fiber to improve the spatial resolution of the measurement. A reference surface exhibit a predetermined texture (in the form of a series of corrugations, for example, that may be periodic or aperiodic, as long as known a priori) is disposed adjacent to a longitudinal portion of the sensor fiber. The application of a force to the combination of the plate and the fiber creates a local strain in the grating formed along the offset core of the fiber that results in a shift in the Bragg wavelength of the grating. Using ODFR measurement techniques, an analysis of the Bragg wavelength shift allows for a high resolution force measurement to be obtained.