Polygonal Core Glass-Fibre Preform via Sectored Cladding
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Solution Overview
Problem
The existing methods for producing glass-fibre preforms with polygonal core cross-sections, such as the rod-in-tube process and direct deposition process, face challenges in achieving a homogeneous interface between the core and cladding, leading to bubble formation, deformation of the core corners, and undesirable rounding, especially for rectangular cores.
Innovation Solution
A method involving a sectored sandwich tube is used, where the starting tube is slit into circular sectors, and the core rod is threaded and aligned within this tube, allowing individual sectors to fuse onto the core rod, preventing corner deformation and ensuring a bubble-free interface, with an optional outer casing tube for even melting and precise alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a complete circular cladding tube is used in the rod-in-tube process, then the tube can be pushed over the polygonal core rod, but the tube folds on the core surface during cladding and cannot form a clean interface
Solution Approach 1:
The cladding tube is divided into multiple separate arc-shaped tube sections instead of a complete circular tube. Each tube section corresponds to a specific angular range and is positioned adjacent to the core rod during cladding. This segmentation allows each section to make controlled contact with the core surface, preventing folding while enabling complete coverage.
2Ease of operation
If the tube is dimensioned to fit the polygonal core, then the inner circular arc length must be significantly greater than the core circumference, but this causes the tube to fold during cladding
Solution Approach 1:
The tube is segmented into multiple arc-shaped sections, each with a specific inner arc length matched to the core perimeter. This allows precise dimensional matching without requiring the entire tube to accommodate the polygonal shape, eliminating folding deformation.
Solution Approach 2:
Each tube section is designed with specific local dimensions and angular positioning tailored to its designated region on the core rod. This local optimization ensures proper fit and contact without causing deformation, as each section independently adapts to the core geometry in its specific location.
3Ease of manufacture
If the cladding tube touches the rectangular core corners first, then pressure is exerted on the corners causing rounding, but this distorts the core cross-section
Solution Approach 1:
The segmented tube sections are positioned and supported such that they contact the core rod along its flat surfaces rather than at the corners. The segmentation allows controlled positioning that distributes contact pressure evenly across the core surfaces, preventing corner rounding while maintaining complete coverage.
4Device complexity
If a complete circular tube is used, then the tube structure is simple, but the cladding layer thickness changes due to wrinkle formation
Solution Approach 1:
The tube is divided into multiple independent arc-shaped sections that can be positioned and clamped separately. This segmentation prevents wrinkle formation by allowing each section to be independently controlled and evenly distributed around the core, ensuring uniform cladding layer thickness while maintaining a relatively simple overall structure.
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 ensures high homogeneity and quality of the interface between the core and cladding, preventing corner rounding and deformation, while allowing for precise control of refractive index and layer thickness, resulting in high-quality glass-fibre preforms with improved waveguiding properties.
Implementation Method 1
the individual outer segments are fused onto the side faces of the core rod
Implementation Method 2
The outer casing tube is fused onto the sectored sandwich tube in a graphite furnace or in a flame device
Data Source
AI summary
The invention relates to a method for producing a glass-fibre preform with a core of a polygonal cross section by using a rod-in-tube method and comprising the method steps of: providing a core rod (1) of a polygonal core rod cross section (2), producing a sectored sandwich tube (3) from a starting tube (4), wherein the lateral surface of the starting tube (4) is slit in the longitudinal direction into a series of outer segments (8), and so the tube cross section of the starting tube (4) is subdivided into a series of sectors of a circle (7), inserting the core rod (1) into the sectored sandwich tube (3) and aligning it and, in the case of one embodiment, inserting the core rod (1) and the sectored sandwich tube (3) into an outer casing tube (10) with a complete annular cross section and melting the sectored sandwich tube (3) and possibly the outer casing tube (10) onto the sectored sandwich tube (3), wherein the outer segments (8) of the sectored sandwich tube (3) are fused to the respective side surfaces (9) of the core rod (1).