Optical Preform Substrate Tube Assembly for Stress-Free Internal Vapour Deposition
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Solution Overview
Problem
Internal stress build-up and mechanical tension in optical preform manufacturing due to glass deposition outside the deposition area and connection issues between substrate and elongation tubes lead to cracking and substrate breakage, with soot pollution complicating the process.
Innovation Solution
A device and method where the hollow substrate tube extends into an elongation tube with a larger internal diameter, reducing mechanical stress and avoiding direct glass deposition contact between the tubes, and using an insertion tube within the elongation tube to catch soot and reduce turbulence, ensuring a more rigid connection and preventing unwanted glass deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If glass deposition is performed outside the deposition area on the substrate tube, then the deposition process can continue, but internal stress build-up occurs leading to cracking and substrate breakage
Solution Approach 1:
The tube system is divided into three distinct segments: substrate tube, elongation tube, and insertion tube. This segmentation isolates the deposition area from the elongation region, preventing stress transmission while maintaining continuous deposition capability. The insertion tube specifically captures unwanted glass deposits outside the deposition zone, preventing them from causing internal stress build-up in the substrate tube.
Solution Approach 2:
The insertion tube acts as an intermediary element between the substrate tube and the external environment. It captures soot and unwanted glass deposits that would otherwise accumulate outside the deposition area, preventing these harmful substances from entering the substrate tube and causing cracking during the collapsing process.
2Device complexity
If the substrate tube is connected directly to the elongation tube, then the structure is simplified, but mechanical tension at the connection point causes cracking
Solution Approach 1:
The insertion tube is nested within the elongation tube, creating a concentric structure. This nesting arrangement distributes mechanical stresses more evenly across the connection interface compared to direct end-to-end connections. The insertion tube acts as a stress-distributing element that prevents concentration of mechanical tension at the substrate tube-elongation tube junction.
3Stress or pressure
If the internal diameter of the elongation tube is made larger, then mechanical stress is reduced, but the device complexity increases
Solution Approach 1:
The elongation tube is designed with a specifically larger internal diameter only in the region where it surrounds the substrate tube and insertion tube. This localized dimensional change provides the necessary stress relief without requiring the entire tube system to have increased dimensions. The larger internal diameter is concentrated precisely where mechanical stress occurs, minimizing overall device 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
This configuration reduces mechanical stress and cracking risks, maintains the quality of the substrate tube, and simplifies the process by preventing soot pollution and turbulence, leading to a more reliable and efficient optical preform production.
Implementation Method 1
Plasma-enhanced chemical vapour deposition (PECVD or PCVD) is a process used to deposit thin films from a gas state (vapour) to a solid state on a substrate. Chemical reactions are involved in the process, which occur after creation of a plasma of the reacting gasses.
Implementation Method 2
Generally, the plasma is induced by the use of electromagnetic radiation, preferably microwaves. Usually, electromagnetic radiation from a generator are directed towards an applicator via a waveguide
Implementation Method 3
The vacuum pump has the effect of generating a reduced pressure in the interior of the substrate tube, which reduced pressure generally comprises a pressure value ranging between 5 and 50 mbar
Implementation Method 4
Several types of internal chemical vapour depositions (CVD) are known, vapour axial deposition (VAD), modified chemical vapour deposition (MDVD) and plasma-enhanced chemical vapour deposition (PECVD or PCVD).
Data Source
AI summary
A device for manufacturing an optical preform by means of an internal vapour deposition process including an energy source, a hollow substrate tube having a supply side and a discharge side and the energy source being moveable along a length of the hollow substrate tube, and an elongation tube connected to the hollow substrate tube at the discharge side thereof, wherein the hollow substrate tube extends into an interior of the elongation tube and an internal diameter of the elongation tube is at least 0.5 millimeters larger than an external diameter of the hollow substrate tube.