Hollow Core Fibre Drawing with Intermediate Cane Pressurization
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Solution Overview
Problem
The production of hollow core optical fibers is inefficient due to the difficulty in achieving high drawdown ratios, leading to limited fiber length and increased complexity, particularly for fibers designed to propagate shorter wavelengths, which require thinner glass membranes and smaller structures.
Innovation Solution
A modified fiber drawing process with phased drawdown stages, involving an intermediate cane that remains unitary with the initial preform, allowing for controlled pressurization and higher drawdown ratios, thereby facilitating the production of longer fibers with thinner membranes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a wide preform is used to increase drawdown ratio, then fiber yield is improved, but pressurisation control becomes difficult and structure collapse occurs
Solution Approach 1:
The preform is divided into multiple separate preform sections (first preform section, second preform section, etc.) that are drawn independently. This segmentation allows each section to be pressurised and drawn separately, improving control over the drawdown process while maintaining high overall fiber yield. The modular approach enables precise management of pressurisation for each segment rather than attempting to control a single large preform.
2Manufacturing precision
If pressurisation is applied to maintain void structure, then structural quality is improved, but mid-draw contact occurs limiting drawdown ratio
Solution Approach 1:
Dividing the preform into multiple sections allows each section to be drawn with appropriate pressurisation to maintain void structure quality, while the segmented nature prevents mid-draw contact that would limit the overall drawdown ratio. Each segment can be optimised independently for both structural quality and drawdown efficiency.
Solution Approach 2:
The invention introduces an intermediate cane as a mediator between the preform and final fiber. The preform is first drawn into an intermediate cane with preserved void structure through controlled pressurisation, then the intermediate cane is further drawn into the final fiber. This intermediate stage acts as a buffer that maintains structural quality while enabling higher overall drawdown ratios by breaking the process into manageable stages.
3Productivity
If preform width is increased for high drawdown ratio, then fiber yield is improved, but surface tension causes void collapse
Solution Approach 1:
By segmenting the preform into multiple smaller sections, each section maintains sufficient void structure integrity against surface tension forces while collectively providing high fiber yield. Each segmented preform section is drawn independently with controlled pressurisation to prevent void collapse, avoiding the surface tension problems that would occur with a single wide preform.
Solution Approach 2:
The intermediate cane serves as an intermediary structure that is formed first with preserved void integrity through controlled drawdown from the preform. This intermediate structure then serves as the basis for drawing the final fiber, allowing the system to achieve high drawdown ratios without compromising void structure integrity at any stage.
4Ease of manufacture
If narrower preform is used for pressurisation control, then pressurisation is easier to implement, but fiber yield decreases
Solution Approach 1:
The preform is divided into multiple narrower segments that are easier to pressurise and control, while the cumulative fiber yield from all segments achieves the desired high productivity. Each segment can be independently pressurised with ease, and the total fiber output from multiple segments matches or exceeds what a single wide preform would produce.
Solution Approach 2:
Multiple narrower preform sections are combined in series to achieve the total fiber yield equivalent to or greater than a single wide preform. Each narrow section is easy to pressurise and control, and when their outputs are combined, the overall productivity meets high-volume production requirements while maintaining manufacturing ease.
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 the production of hollow core fibers with improved yield and longer lengths, particularly for fibers designed for visible and ultraviolet wavelengths, by overcoming the limitations of mid-draw contact and surface tension issues, enhancing production efficiency and fiber quality.
Implementation Method 1
heating an end portion of the initial preform in order to soften the glass of the end portion
Implementation Method 2
heats and softens the glass
Implementation Method 3
pressure is typically applied to the voids during drawing of the fibre from the preform or the cane
Implementation Method 4
The pressurisation counteracts surface tension in the softened glass which otherwise tends to cause collapse of the voids
Data Source
AI summary
A method of fabricating a hollow core optical fibre comprises: providing an initial preform formed from glass and having a transverse cross-sectional structure configured to form, in an optical fibre drawn from the preform, a transverse cross-sectional structure comprising a hollow core surrounded by a plurality of voids defining a microstructured cladding; heating an end portion of the preform; drawing a length of intermediate cane from the softened glass of the preform, via a first neckdown, the cane having a glass cross-sectional area less than the glass cross-sectional area of the preform; heating a portion of the cane spaced from the first neckdown, the cane remaining unitary with the preform; and drawing a length of hollow core optical fibre from the softened glass of the cane, via a second neckdown, the hollow core optical fibre having a glass cross-sectional area less than the glass cross-sectional area of the cane.