Multimode Fiber Bragg Gratings for Simpler Curvature Measurement
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Solution Overview
Problem
Existing devices for measuring radius of curvature using optical fiber Bragg gratings are complex due to the need for specific multimode fibers and tilted gratings, requiring complex setups and difficulty in separating absorption bands, especially for fibers with multiple mode groups.
Innovation Solution
A device using a multimode optical fiber with a set of Bragg gratings, including a central and eccentric gratings, allows for simpler measurement by isolating spectral responses of different mode groups, utilizing a modal demultiplexer and spectral analyzer to determine radius and orientation of curvature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tilted fiber Bragg grating (TFBG) is used to measure radius of curvature, then the measurement is relatively insensitive to temperature variations, but the device complexity increases due to requirements for specific multimode optical fiber and complex excitation setups
Solution Approach 1:
The patent segments the measurement function by using multiple straight Bragg gratings instead of a single tilted grating. Each grating is positioned at a different location along the optical fiber, allowing the system to measure curvature through distributed measurements rather than requiring a complex tilted grating configuration. This segmentation simplifies the overall device architecture while maintaining temperature insensitivity.
Solution Approach 2:
The patent transitions from measuring only radius of curvature to simultaneously measuring both radius of curvature and orientation of the plane of curvature. By adding the orientation measurement dimension, the system achieves more comprehensive curvature characterization while using simpler straight grating configurations rather than complex tilted grating arrangements.
2Measurement precision
If multiple mode groups are used in the optical fiber, then more absorption bands are observed providing more measurement data, but it becomes more difficult to separate the peaks making measurement more complex
Solution Approach 1:
The patent applies local quality by positioning Bragg gratings at specific locations along the optical fiber where they interact with particular mode groups. Each grating is strategically placed to capture measurements from specific spatial modes, allowing the system to selectively measure from different mode groups without the overlapping complexity that would arise from uniform distribution. This localized approach enables clear peak separation while maintaining measurement precision.
Solution Approach 2:
The patent performs preliminary action by pre-positioning multiple Bragg gratings at optimized locations before measurement. The gratings are placed in advance at specific positions along the fiber where they will interact with different mode groups, allowing the system to capture distinct absorption bands from multiple modes simultaneously. This pre-positioning eliminates the need for complex real-time peak separation algorithms.
3Measurement precision
If a modal demultiplexer is used to inject only the LP01 mode, then the measurement setup becomes more complex, but the absorption bands corresponding to couplings from other modes are avoided
Solution Approach 1:
The patent extracts the measurement function from a single complex tilted grating configuration and distributes it across multiple straight grating positions. By removing the requirement for modal demultiplexing and LP01-only injection, the system allows multiple modes to propagate naturally through the fiber. The multiple gratings are positioned to capture measurements from these different modes, extracting clear absorption band information without the need for complex mode selection hardware.
Solution Approach 2:
The patent creates multiple copies of the Bragg grating structure at different positions along the fiber rather than using a single complex tilted grating. Each grating copy interacts with different mode groups, providing redundant measurement pathways. This copying approach eliminates the need for modal demultiplexing while maintaining measurement precision through distributed sampling of the optical field.
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
The solution provides a simpler and more effective method for measuring radius of curvature by isolating spectral responses, reducing complexity and improving accuracy in curvature measurement.
Implementation Method 1
a transducer comprising an optical fiber and a Bragg grating within that optical fiber
Implementation Method 2
an optical fiber and a Bragg grating within that optical fiber
Data Source
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AI summary
This device comprises: - an array (16) of Bragg gratings, each Bragg grating being made in the core of a multimode optical fiber (14) and comprising at least three identical patterns aligned one behind the other, - a spectral analyzer (42) configured to: - emit, in the multimode optical fiber, an optical excitation signal the majority of whose power is within a wavelength range [λmin; λmax], then - establish a value of the radius of curvature from the measured amplitude of a power peak of the measured spectral response of a Bragg grating of the array (16), in which, for each Bragg grating of the array (16), the largest transverse dimension of the patterns of that Bragg grating is less than the wavelength λmin.