Multi-Core Optical Fiber for 3D Curvature Measurement
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Solution Overview
Problem
Existing optical fiber sensors for measuring three-dimensional curved shapes are limited in their ability to determine bending direction and have low distance resolution, requiring additional processing and temperature compensation due to their reliance on Fiber Bragg Gratings (FBG) and wavelength shifting, which complicates accurate curvature measurement.
Innovation Solution
A special optical fiber with a core, inner cladding, and outer cladding structure where the refractive indices are set in a specific relationship, and the inner cladding has a cut-open portion filled with a matching material, allowing for sensitive detection of bending direction and curvature without FBG, along with a system using LD, PD, TDC, and FPGA for precise measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If FBG-based optical fiber sensors are used to measure curved shapes, then bending location can be determined, but bending direction in three-dimensional space cannot be measured
Solution Approach 1:
The optical fiber is divided into multiple independent sensing units along its length, with each unit containing multiple core regions (first core, second core, third core) arranged at different spatial orientations. Each core independently detects bending in its specific direction, and the combination of signals from all cores enables full three-dimensional bending characterization.
Solution Approach 2:
The invention transitions from one-dimensional bending detection (along the fiber axis) to three-dimensional bending detection by arranging multiple core regions in different spatial dimensions. The first, second, and third core regions are oriented at different angles relative to the fiber axis, allowing detection of bending in multiple directions simultaneously.
2Measurement precision
If FBG is formed in optical fiber to enable curvature measurement, then optical loss can be generated for detection, but additional post-processing and secondary processing are required
Solution Approach 1:
The refractive index distribution is pre-configured during optical fiber manufacturing, with different core regions having distinct refractive index characteristics optimized for specific detection directions. This preliminary structuring eliminates the need for subsequent FBG formation and reduces post-processing requirements.
Solution Approach 2:
The invention extracts and removes the FBG component from the sensing mechanism, relying instead on the inherent optical properties of multi-core fiber structures with engineered refractive index distributions. This eliminates the complex FBG formation process and associated secondary processing steps.
3Measurement precision
If FBG-based optical fiber sensors are used for distance measurement, then bending can be detected, but distance resolution is low
Solution Approach 1:
Different core regions are assigned specific refractive index characteristics tailored to their detection functions. The first core, second core, and third core each have optimized local refractive index properties that enhance their sensitivity to bending in specific directions and improve distance resolution through localized optical field confinement.
4Measurement precision
If wavelength shifting is used for curvature measurement in FBG sensors, then curvature can be detected, but temperature compensation is required due to sensitivity to temperature changes
Solution Approach 1:
Multiple core regions are configured as redundant sensing channels with identical structural characteristics but different spatial orientations. By comparing signals from these copied sensing paths, the system can distinguish between curvature-induced wavelength shifts and temperature-induced shifts, enabling temperature compensation without additional sensors.
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
Enables accurate measurement of three-dimensional curved shapes with improved sensitivity and reduced temperature interference, allowing for precise detection of bending locations and curvatures without the need for FBG-based compensation, expanding the sensor's applicability and accuracy.
Implementation Method 1
an optical fiber core for transmitting an optical signal, an inner cladding covering the optical fiber core, and an outer cladding covering the inner cladding
Data Source
AI summary
Provided is a special optical fiber for measuring a 3D curved shape, and a system for measuring the 3D curved shape by using a special optical fiber. The special optical fiber comprises: an optical fiber core for transmitting an optical signal; an inner cladding covering the optical fiber core; and an outer cladding covering the inner cladding. In particular, the refractive index (n1) of the optical fiber core, the refractive index (n2) of the inner cladding, and the refractive index (n3) of the outer cladding are set in a relationship of n1≥n3>n2. The inner cladding covering the optical fiber core has a cut portion in the longitudinal direction. The optical fiber core is exposed through the cut portion. In addition, the cut portion is filled with a material having the same refractive index as the optical fiber core or the outer cladding.