Refractive Index Tomography for Non-Symmetric Glass Fiber Preforms
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Solution Overview
Problem
Existing methods for measuring the refractive index profile of non-symmetric transparent cylindrical objects, such as fiber preforms, suffer from measurement artifacts and systematic errors, leading to inaccurate and unreliable results due to refractive index discontinuities and non-symmetry, which are not adequately addressed by current state-of-the-art techniques.
Innovation Solution
A method involving computed tomography (CT) and a fitting procedure is employed, where the object is scanned at multiple projection angles, data is processed to form a sinogram, and a line section of interest is selected for applying a fitting procedure to determine refractive index steps and gradients, minimizing measurement artifacts and improving accuracy and reproducibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional deflection angle distribution measurement methods are used for non-symmetric objects, then measurement process is simple, but measurement precision deteriorates due to artifacts and systematic errors from refractive index discontinuities
Solution Approach 1:
The measurement process is segmented into multiple projection angle scans (e.g., 0°, 45°, 90°, 135°) rather than a single scan. Each projection angle provides partial information, and the combination of multiple segments enables accurate reconstruction of non-symmetric refractive index profiles while eliminating systematic errors that plague single-scan methods
Solution Approach 2:
The method transitions from measuring deflection angles in a single plane to acquiring deflection angle distributions across multiple projection angles (adding the angular dimension). This multi-dimensional data acquisition approach enables tomographic reconstruction algorithms to accurately determine refractive index profiles of non-symmetric objects by viewing the problem from multiple angular perspectives
2Measurement precision
If single projection angle scanning is used, then measurement time is short, but measurement precision deteriorates due to inability to capture non-symmetric features
Solution Approach 1:
The measurement employs periodic scanning at discrete projection angles (e.g., 0°, 45°, 90°, 135°) rather than continuous scanning. This periodic sampling approach efficiently captures the non-symmetric features of the object by strategically selecting measurement angles, achieving high precision without requiring excessive measurement time
Solution Approach 2:
The method uses a有限 number of projection angles (e.g., 4 angles) which is excessive compared to a single angle but far less than continuous 360° scanning. This partial action approach provides sufficient data for accurate reconstruction of non-symmetric profiles while maintaining practical measurement time constraints
3Measurement precision
If tomographic reconstruction with multiple projection angles is implemented, then measurement precision improves for non-symmetric objects, but device complexity increases
Solution Approach 1:
The method creates multiple copies of the deflection angle measurement at different projection angles. Instead of directly measuring the complex 3D refractive index distribution, it captures 2D deflection angle distributions at multiple angles, which serve as simplified copies that can be processed through tomographic reconstruction algorithms to recover the full 3D information
Solution Approach 2:
The patent replaces complex mechanical 3D scanning systems with a simpler approach using multiple 2D deflection angle measurements at different projection angles. The computational tomographic reconstruction algorithm substitutes for the need for complex mechanical positioning systems, achieving 3D refractive index mapping through mathematical processing rather than mechanical complexity
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 method provides a more accurate and reliable determination of the refractive index profile by reducing measurement artifacts and systematic errors, especially for complex, non-symmetric designs, enhancing the precision of preform assembly and meeting customer demands.
Implementation Method 1
The light beam is deflected by the glass of the preform and imaged with an optical device onto a positionable detector. The refractive index profile is calculated from the deflection angle distribution using numerical integration.
Data Source
AI summary
A method for determining the refractive index profile of a preform when the RIP is not substantially symmetrical. (i) The preform is scanned, starting with a first projection angle, and raw data are created representing the object through measured data. (ii) Optionally, the object is rotated and step (i) repeated iteratively until all projection angles have been scanned and all measured data have been created. (iii) The measured data are processed to form a sinogram and, if the optional step (ii) has been completed, the method proceeds to step (v). (iv) The object is rotated and steps (i) and (iii) are repeated iteratively until all projection angles have been scanned. (v) A 2D RIP is calculated. (vi) A line section of interest is selected within the 2D RIP. (vii) A fitting procedure is applied to the line section of interest. (viii) Finally, refractive index steps/gradients and dimensions are determined.