Multimode Bragg Grating Sensing for Separate Temperature and Strain
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Solution Overview
Problem
Existing methods for measuring temperature and mechanical strain using Bragg gratings in optical fibers are complex due to the need for specific structures in the gratings or fibers, and the simultaneous excitation of multiple modes complicates implementation.
Innovation Solution
A method using a single Bragg grating in a multimode optical fiber with distinct mode groups, where each group has a unique wavelength, allowing separate measurement of temperature and mechanical strain by analyzing spectral responses in each group.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a Bragg grating with a specific structure (e.g., Superstructure Fiber Grating, tilted Fiber Bragg Grating) is used to simultaneously measure temperature and mechanical strain, then measurement capability is improved, but device complexity increases
Solution Approach 1:
The patent applies multi-functionality by enabling a single Bragg grating in a multimode optical fiber to perform multiple measurement functions (temperature and strain) simultaneously. This is achieved by exploiting the different sensitivities of various mode groups to different physical quantities, allowing one transducer to replace what would traditionally require multiple specialized sensors or complex grating structures.
Solution Approach 2:
The patent changes the operational parameters by utilizing different mode groups (each with distinct propagation constants) of the multimode optical fiber. By measuring spectral responses across multiple mode groups and analyzing their differential responses to temperature and strain, the system achieves simultaneous measurement without requiring complex grating structures, thus resolving the contradiction between measurement capability and device complexity.
2Measurement precision
If several groups of modes are simultaneously excited in the optical fiber to measure spectral responses, then measurement accuracy is improved, but ease of operation deteriorates
Solution Approach 1:
The patent applies segmentation by dividing the measurement process into distinct mode group measurements. Instead of simultaneously exciting and measuring all modes (which would be complex), the method sequentially measures spectral responses of different mode groups, each with known sensitivity characteristics. This segmented approach maintains measurement accuracy while significantly simplifying the operational complexity.
Solution Approach 2:
The patent uses feedback through a processing unit that receives spectral response data from multiple mode groups and applies algorithms to separate temperature and strain effects. The system uses the known sensitivity coefficients of different mode groups to mathematically resolve the coupled measurements, providing accurate results while keeping the actual measurement process simple and sequential rather than simultaneously complex.
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
Simplifies the implementation of simultaneous temperature and mechanical strain measurements by isolating the effects of each physical quantity through distinct spectral responses in different mode groups, providing accurate and efficient measurements.
Implementation Method 1
The power spectrum of the Bragg grating varies with both temperature and mechanical strain
Data Source
Figure 1~2
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Figure 5~6
AI summary
This process includes: - the measurement (122) of a spectral response of a Bragg grating in, respectively, a first and a second group of spatial modes, then - the determination (130) of a first displacement amplitude of a first power peak in the spectral response of the Bragg grating in the first group of spatial modes and the determination (130) of a second displacement amplitude of a second power peak in the spectral response of the Bragg grating in the second group of spatial modes, then - the establishment (132) of the variations of the first and second physical quantities from the first and second displacement amplitudes determined.