Optical Preform Circularity via Internal Pressure and Heating
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Solution Overview
Problem
The existing methods for manufacturing optical preforms using internal vapour deposition result in substrate tubes with non-circular cross sections, leading to non-circularity in the core of drawn optical fibers, which causes increased attenuation, high polarisation mode dispersion, and differential mode delay due to asymmetry.
Innovation Solution
The method involves increasing the outer diameter of the substrate tube with deposited glass layers by heating it above its softening temperature and applying an internal pressure higher than ambient pressure, followed by collapsing the tube to produce a more circular optical preform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If internal vapour deposition is used to deposit glass layers on the substrate tube, then glass layers are successfully deposited on the inside surface, but the substrate tube develops non-circular cross section leading to non-circularity in the optical preform
Solution Approach 1:
The patent applies preliminary anti-action by introducing internal pressure into the substrate tube before and during the collapsing process. This pre-applied counter-force prevents the tube from deforming into a non-circular shape during heating, thereby counteracting the harmful effect of ovalization before it can occur. The pressure is maintained throughout the collapsing process to ensure the tube maintains its circular cross-section.
Solution Approach 2:
The patent changes the pressure parameter from atmospheric (zero gauge pressure) to positive internal pressure during the collapsing process. This parameter change fundamentally alters the behavior of the glass tube under thermal stress, preventing non-circular deformation. The pressure is carefully controlled to be sufficient to maintain circularity but not so high as to cause other defects.
2Productivity
If the substrate tube is collapsed by heating above softening temperature, then the tube is contracted into an optical preform, but non-circularity increases due to asymmetry in the collapsed structure
Solution Approach 1:
The patent applies preliminary anti-action by establishing internal pressure in the substrate tube before heating begins. This pre-applied counter-force prevents the tube from deforming into a non-circular shape during the collapsing process, thereby counteracting the harmful effect of asymmetry before it can develop. The pressure is maintained throughout the entire heating and collapsing sequence.
Solution Approach 2:
The patent performs preliminary action by pressurizing the substrate tube with gas or vapor before the collapsing process starts. This preliminary pressurization ensures that the tube is in a stress-balanced state ready to resist deformation during heating, rather than allowing asymmetry to develop during the process itself.
3Manufacturing precision
If vacuum pressure is applied during deposition, then glass layers are deposited evenly on the substrate tube, but the remaining internal diameter decreases with each pass
Solution Approach 1:
The patent applies partial or excessive action by using a pressure that is higher than atmospheric pressure (positive gauge pressure) during the collapsing process, which is more than the minimum pressure needed to maintain circularity. This excessive pressure ensures that even as the wall thickness increases with each deposition pass, there is sufficient counter-force to prevent any non-circular deformation during collapsing.
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 reduces non-circularity in the optical preform, resulting in improved circularity of the fiber core, minimizing attenuation and polarisation mode dispersion, and enhancing the symmetry of the core.
Implementation Method 1
applying a traversing heat source to heat the substrate tube to above its softening temperature
Implementation Method 2
providing an internal pressure in the substrate tube higher than an ambient pressure
Data Source
AI summary
A method for manufacturing an optical preform including the steps of providing a substrate tube having deposited layers of glass on an inside surface thereof, increasing an outer diameter of the substrate tube by means of applying a traversing heat source to heat the substrate tube to above a softening temperature thereof and by providing an internal pressure in the substrate tube higher than an ambient pressure, and collapsing the substrate tube of increased outer diameter by means of applying the traversing heat source to heat the substrate tube to above the softening temperature thereof such that an optical preform is manufactured.