Segmented Calibration for OFDR Shape Sensing Accuracy
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Solution Overview
Problem
The precision required to achieve accurate shape measurements with optical frequency domain reflectometry (OFDR) is compromised by the difficulty in maintaining a perfectly straight or known shape configuration, especially for longer lengths of optical fibers, leading to errors in strain and temperature measurements.
Innovation Solution
The method involves segmenting the optical fiber into shorter sections, collecting OFDR data sets for each segment in controlled configurations, and stitching these together to create a corrected reference data set that accounts for phase differences and changes in strain, temperature, and twist, thereby improving the accuracy and precision of shape sensing measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the optical fiber is measured as a single long segment, then the measurement covers the entire fiber length, but the precision of shape measurements deteriorates due to difficulty in maintaining a perfectly straight configuration
Solution Approach 1:
The optical fiber is divided into multiple shorter segments, each of which can be individually positioned and measured with higher precision. The segments are then stitched together to reconstruct the complete fiber shape, thereby maintaining both long measurement coverage and high precision.
2Measurement precision
If the optical fiber is segmented into shorter sections for measurement, then the measurement precision improves, but the device complexity increases due to the need to stitch multiple data sets
Solution Approach 1:
Overlapping regions between adjacent segments are used to provide feedback for alignment and stitching. By comparing measurements in the overlapping regions, the system can automatically align and merge segment data with high precision, reducing the complexity of manual stitching procedures.
3Ease of manufacture
If a single reference data set is used for the entire fiber, then the calibration process is simple, but errors accumulate along the fiber length reducing measurement accuracy
Solution Approach 1:
The reference data collection is segmented into multiple localized measurements, each valid for a specific fiber segment. This prevents error accumulation over long distances while maintaining calibration simplicity through automated stitching processes that merge segment-specific references.
4Measurement precision
If the optical fiber is positioned in a controlled configuration for each segment, then the reference data quality improves, but the time required for calibration increases
Solution Approach 1:
The fiber is pre-positioned into controlled configurations for each segment before measurement. This preliminary positioning ensures high reference data quality while reducing the time required during actual measurements, as the fiber doesn't need to be repositioned during data collection.
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 enhances the quality of reference OFDR data sets, reducing errors in shape measurements and improving the ability to detect 3D distributed shape and strain along optical fibers, even for longer lengths, by compensating for deviations from ideal configurations.
Implementation Method 1
small fractions of the incident light are reflected, either as a result of Rayleigh scatter or at FBGs or discrete reflectors
Implementation Method 2
The applied strain results in a spectral shift in the OFDR signal which varies as function of delay
Implementation Method 3
Fiber optic shape sensing technique may perform a phase-based measurement of distributed strain in each of the sensing fiber's four optical cores
Data Source
Figure 1~2(C)
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Figure 6~7
AI summary
Optical frequency domain reflectometry (OFDR) circuitry to perform tasks on an optical fiber to generate calibration or correction data for calibrating or correcting a reference OFDR data set. A segmented technique is used which permits precise and accurate determination of the correction data for even initial and long fiber lengths. Correction information for each segment is stitched together to generate the correction data for the fiber.