Overlapping Chirped FBGs for Dynamic Range Extension
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional OFDR systems face limitations in sensing length, system update rate, and dynamic range due to interdependencies between strain or temperature dynamic range, system sample rate, and sensing length, requiring wide wavelength sweeps and increased complexity in grating fabrication and resolution.
Innovation Solution
The use of overlapping chirped fiber Bragg gratings (FBGs) forming a Fabry-Perot interferometer with varying free spectral range (FSR) allows for inference of strain or temperature over a large dynamic range using a narrow wavelength range, reducing the required wavelength range by an order of magnitude and increasing sensing length or sample rate without reducing dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If wide wavelength sweep range is employed to increase dynamic range, then strain or temperature dynamic range is improved, but OFDR bandwidth and system complexity increase
Solution Approach 1:
The patent segments the wavelength spectrum into multiple discrete spectral features (peaks) generated by overlapping chirped FBGs with different chirp slopes. Each spectral feature corresponds to a specific strain or temperature range, allowing the system to measure full dynamic range by identifying which spectral features are present rather than sweeping the entire wavelength range. This segmentation enables dynamic range extension without proportionally increasing OFDR bandwidth.
Solution Approach 2:
The patent changes the parameter of wavelength sweep range by using a fixed narrow sweep range and instead varying the spectral feature identification based on strain or temperature conditions. The overlapping chirped FBGs generate spectral features that shift or appear/disappear based on the physical quantity being measured, allowing dynamic range extension through parameter identification rather than sweep range expansion.
2Measurement precision
If wide wavelength sweep range is employed to increase dynamic range, then strain or temperature dynamic range is improved, but sensing length decreases
Solution Approach 1:
By segmenting the measurement into discrete spectral features that can be identified within a narrow wavelength range, the system maintains long sensing lengths without requiring wide wavelength sweeps. The spectral features act as markers that can be resolved along the entire fiber length, enabling both long sensing length and full dynamic range simultaneously.
3Measurement precision
If wide wavelength sweep range is employed to increase dynamic range, then strain or temperature dynamic range is improved, but system update rate decreases
Solution Approach 1:
The segmentation of spectral features allows the system to perform rapid identification of strain or temperature conditions by comparing which spectral features are present in consecutive measurements, rather than performing time-consuming wide wavelength sweeps. This enables high system update rates while maintaining full dynamic range capability.
Solution Approach 2:
The system uses periodic spectral feature identification within a narrow wavelength range, where the overlapping chirped FBGs generate recurring spectral patterns that can be rapidly identified and tracked, enabling high-frequency measurements without requiring proportionally wider wavelength sweeps.
4Device complexity
If narrow wavelength range is used to reduce OFDR bandwidth, then OFDR bandwidth is decreased, but strain or temperature dynamic range is limited
Solution Approach 1:
The patent segments the dynamic range measurement into multiple discrete spectral features that can be identified within a narrow wavelength range. By using overlapping chirped FBGs with different chirp slopes, the system creates distinct spectral markers for different strain or temperature conditions, enabling full dynamic range measurement without requiring wide wavelength sweeps.
Solution Approach 2:
The patent creates multiple spectral copies or representations of the same physical quantity (strain or temperature) through the overlapping chirped FBGs. Each grating contributes spectral features that replicate information about the physical quantity at different wavelength positions, allowing the system to infer full dynamic range from multiple copies within a narrow wavelength range.
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 an order of magnitude decrease in OFDR bandwidth for a given sensing length, an order of magnitude increase in sensing length for a given bandwidth, and improved accuracy and reliability, supporting full dynamic range at increased sample rates with reduced operational laser sweep range.
Implementation Method 1
overlapping chirped fiber Bragg gratings (FBGs) forming a Fabry-Perot interferometer with varying free spectral range (FSR)
Implementation Method 2
Fiber Bragg grating (FBG) optical fiber sensors exhibit a wavelength-selective reflection or transmission spectrum
Implementation Method 3
As tension or compression is longitudinally imparted on the fiber sensor, the spatial period of the refractive index profile is lengthened or shortened leading to an increase or decrease, respectively, of the center wavelength of the reflected spectrum
Implementation Method 4
as the FBG is heated or cooled, the effective index of refraction is altered resulting in a proportionally-shifted center wavelength
Data Source
AI summary
Various embodiments of sensors are described that exhibit several spectral features that together offer coverage of a wavelength range corresponding to the desired strain dynamic range (or temperature range) of a system. The spectral features arise from a Fabry-Perot interferometer formed by two overlapping chirped FBGs, the free-spectral range (FSR) of which varies with wavelength. The spectral features may be differentiated due to a combination of spacing and slope of the overlapped, chirped gratings.