Multi-Spectral-Feature Sensor for OFDR Strain Measurement
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Solution Overview
Problem
Conventional optical frequency domain reflectometry (OFDR) systems face limitations in interdependencies between strain dynamic range, system update rate, and sensing length, leading to reduced wavelength range and increased complexity in fiber Bragg grating (FBG) systems, which complicates the differentiation of spectral features and reduces measurement accuracy.
Innovation Solution
The implementation of multi-spectral-feature sensors with grating segments exhibiting distinct spectral features across a wide wavelength range, allowing for unambiguous identification of spectral features using a narrow wavelength sweep, thereby relaxing the interdependencies between strain dynamic range and wavelength range, and enabling enhanced system sample rates and reduced digital signal processing requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the wavelength sweep range is increased to accommodate a wider strain dynamic range, then the strain measurement range is improved, but the system update rate decreases due to longer sweep time required
Solution Approach 1:
The sensing fiber is divided into multiple discrete sensor locations along its length, with each location having an independent FBG. This segmentation allows the system to use a narrow wavelength sweep range while still achieving wide strain dynamic range measurement by combining data from multiple sensors with different wavelength responses.
Solution Approach 2:
The patent transitions from using a single wavelength dimension to using multiple wavelength dimensions by implementing multiple FBGs at different locations with different center wavelengths. This multi-dimensional approach allows the system to achieve wide measurement range without increasing the sweep range of any single wavelength, thereby maintaining high update rates.
2Length of stationary object
If the sensing length is increased to monitor longer fiber spans, then the coverage area is improved, but the spatial resolution decreases due to the inverse relationship between sensing length and resolution
Solution Approach 1:
The long sensing fiber is segmented into multiple discrete sensor locations spaced at specific intervals. Each sensor provides localized high-resolution measurement, while the collection of all sensors together provides coverage over the entire long fiber span. This segmentation resolves the contradiction by maintaining high spatial resolution at each point while achieving long overall sensing length.
Solution Approach 2:
The patent changes the parameter of sensor distribution by placing multiple FBGs at specific spaced intervals along the fiber rather than using a continuous sensing approach. This parameter change allows the system to maintain high spatial resolution through the discrete nature of individual sensors while achieving long sensing length through the distributed arrangement.
3Productivity
If entirely-overlapped single-frequency fiber Bragg gratings are used to narrow the wavelength sweep range, then the system update rate is improved, but the complexity of identifying spectral features increases due to overlapping reflection peaks
Solution Approach 1:
Each FBG sensor location is designed with a specific center wavelength and reflection characteristics tailored to its position in the array. This local quality differentiation ensures that while wavelengths overlap, each sensor has a unique spectral signature that can be identified through its spatial position and relative wavelength offset, reducing the complexity of spectral feature identification.
Solution Approach 2:
The patent uses the spatial position of FBGs along the fiber as an intermediary to resolve spectral ambiguities. By combining wavelength information with spatial location information, the system can uniquely identify each sensor's response even when wavelength ranges overlap, thereby simplifying spectral feature identification while maintaining narrow sweep ranges.
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 a wide dynamic range measurement with a narrow wavelength range, increasing system sample rates, reducing digital signal processing complexity, and improving measurement accuracy by unambiguously differentiating spectral features and reducing interference between neighboring features.
Implementation Method 1
optical frequency domain reflectometry (OFDR) system and methods to perform distributed or quasi-distributed sensing of strain, temperature
Implementation Method 2
The individual single-frequency FBGs yielding the multi-wavelength spectral response
Data Source
AI summary
The various embodiments described here comprise an OFDR system and technique that may be used for inference of strain or temperature over a large dynamic range using a narrow wavelength range. Embodiments of the sensor fiber may be composed of one or more multi-spectral-feature sensors, each sensor exhibiting several spectral features that together offer coverage over a wavelength range corresponding to the desired system strain and or temperature dynamic range.