Optical Fiber Drawing Apparatus Stacked Preform Joints
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Solution Overview
Problem
Conventional optical fiber drawing processes face challenges with abrupt increases in bare fiber diameter near preform joints due to hydroxyl ion diffusion, leading to breakage and increased preform changeover time, and are limited by impurity diffusion and cost in forming large-sized preforms.
Innovation Solution
Stacking glass sub-preforms inside a hollow cylindrical glass tube with a specific D/d ratio, minimizing OH diffusion and allowing continuous drawing at high temperatures, and using low-quality silica materials for the tube to reduce costs and improve control over core and clad dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If multiple glass preforms are joined together to form a large size preform, then the continuous drawing length is improved, but the bare fiber diameter increases abruptly near preform joints due to hydroxyl ion diffusion
Solution Approach 1:
The large preform is segmented into multiple smaller glass preforms (first glass preform, second glass preform, etc.) that are joined together. Each preform segment has controlled dimensions and can be manufactured with high precision, reducing the overall impact of joint regions on the total drawing length while maintaining diameter uniformity.
Solution Approach 2:
The joining process uses localized heating with a oxy hydrogen or propane burner to melt and fuse preform ends together. This localized treatment minimizes the affected zone around joints, confining hydroxyl ion diffusion to a small region and preventing widespread diameter variations along the drawn fiber.
2Duration of action of moving object
If multiple glass preforms are joined together using oxy hydrogen or propane burner, then the continuous drawing length is improved, but the glass properties such as viscosity, stress, and attenuation are altered due to hydroxyl ion diffusion
Solution Approach 1:
Dividing the preform into multiple segments allows the use of controlled joining processes that minimize compositional changes. Each segment can be treated independently during joining, reducing cumulative effects on glass properties throughout the entire preform structure.
Solution Approach 2:
The joining process parameters (temperature, atmosphere, heating rate) are optimized to minimize hydroxyl ion generation and diffusion. By controlling these parameters, the alteration of glass properties such as viscosity, stress, and attenuation is reduced to acceptable levels while still achieving adequate bonding between preforms.
3Productivity
If the preform size is increased to reduce changeover time, then the productivity is improved, but the risk of die sticking and fiber breakage increases due to diameter variation near joints
Solution Approach 1:
The preform is divided into manageable segments that can be joined to achieve the desired total length without creating excessive diameter variations. This segmentation allows for controlled joint regions that minimize die sticking risk while maintaining high drawing speeds and fiber continuity.
Solution Approach 2:
The preforms are pre-heated and joined together before the actual fiber drawing process begins. This preliminary joining is performed under controlled conditions that minimize diameter variations, ensuring that when drawing starts, the preform is ready for continuous high-speed production without interruptions due to die sticking or breakage.
4Ease of manufacture
If core rods with lower D/d ratio are stacked in tubes, then the manufacturing flexibility is improved, but the impurity diffusion in core regions increases and OH ion concentration rises
Solution Approach 1:
The core rods are designed with specific D/d ratios optimized for their local function. By allowing different D/d ratios in different preform segments or core regions, the manufacturing process gains flexibility while maintaining control over impurity diffusion. Critical core regions can use higher D/d ratios to minimize impurity effects, while less critical areas can use lower ratios for manufacturing ease.
Solution Approach 2:
The D/d ratio parameter is optimized based on the specific requirements of each preform segment and its position in the stack. By varying this parameter locally rather than uniformly, the invention achieves both manufacturing flexibility and control over impurity diffusion, preventing excessive OH ion concentration in sensitive core regions.
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 method enables continuous and efficient optical fiber drawing with reduced preform changeover time, improved control over impurity diffusion, and cost-effectiveness, facilitating high-throughput manufacturing of large-sized preforms without breaks.
Implementation Method 1
melting the bottom end of the master glass preform in a furnace to draw an optical fiber continuously at the temperature of at least 1650° C.
Implementation Method 2
This sudden change in bare fiber diameter near the preform joint is due to the presence of high concentration of hydroxyl ion (OH) diffused during glass joining process
Data Source
AI summary
The present invention relates to a method (300) for drawing an optical fiber (101) having step of stacking (302) at least two glass sub-preforms of a plurality of glass sub-preforms (114a-114n) inside a hollow cylindrical glass tube (108) to form a master glass preform (130) and melting (304) the bottom end (134) of the master glass preform (130) in a furnace (110) to continuously draw an optical fiber (101). In particular, the at least two glass sub-preforms are stacked in such that the master glass preform has a top end (132) and a bottom end (134) and each of the glass sub-preforms is defined by a first end (126) and a second end (128). Further, the first end (126) of a successive glass sub-preform is stacked on the second end (128) of a previous glass sub-perform such that the successive glass sub-preform rests on the previous glass sub-preform.