Optical Fiber Preform Collapse with Negative Pressure
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The manufacturing of optical fiber preforms with fluorine-doped intermediate cladding regions faces challenges such as contamination and defects due to uneven heating and premature collapse of glass tubes during the collapsing process, leading to non-uniformity and instability in the refractive index profile.
Innovation Solution
A method involving a fluorine-doped intermediate cladding tube is collapsed around a core rod with a predetermined annular gap and negative pressure applied, using a heater moving axially at controlled speed to ensure uniform heating and prevent defects, with specific gap and radial thickness ranges to optimize the process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fluorine-doped glass tube is collapsed around a core rod to produce a fluorine-doped intermediate cladding region, then the refractive index profile is shaped to achieve low bending loss, but contamination and defects occur due to uneven heating and premature collapse
Solution Approach 1:
The glass tube is pre-heated to a temperature between 400°C and 800°C before the collapsing operation begins. This preliminary heating ensures the tube reaches uniform temperature gradually, preventing thermal shock and premature collapse, thereby eliminating contamination and defects at the interface between the cladding and core rod
Solution Approach 2:
The heating temperature is controlled within a specific range (400°C to 800°C) during the collapsing process. This parameter control ensures uniform heating without causing the glass tube to collapse prematurely, resolving the contradiction between achieving proper refractive index profiling and maintaining interface uniformity
2Productivity
If the glass tube is heated to collapse around the core rod, then the intermediate cladding region is formed, but uneven heating causes premature collapse and defects
Solution Approach 1:
The glass tube is pre-heated to a controlled temperature range (400°C to 800°C) before collapsing. This preliminary action ensures uniform temperature distribution throughout the tube, preventing premature collapse and defects while maintaining efficient production
Solution Approach 2:
The heating temperature is maintained within the specific range of 400°C to 800°C during the collapsing process. This parameter control achieves uniform heating without causing defects, resolving the contradiction between manufacturing efficiency and heating uniformity
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 produces defect-free optical fiber preforms with a smooth interface, enabling the fabrication of bend-insensitive single-mode transmission fibers that meet ITU-T standards like G.652 and G.657, with improved production efficiency and reduced seed formation.
Implementation Method 1
heating for the collapsing step is provided by a heater moving axially along the tube/rod assembly
Implementation Method 2
when heating a glass tube of relatively small thickness - such as the fluorinated glass tube to form an intermediate cladding - to soften and collapse around the core rod
Implementation Method 3
collapsing a fluorine-doped intermediate cladding tube around a core rod, the tube and the rod being spaced by a predetermined annular gap in which a negative pressure is applied
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The present invention relates to a method of manufacturing an optical fibre preform comprising: producing a core rod having a core rod diameter; inserting the core rod into a glass fluorine-doped intermediate cladding tube so as to form a core assembly, the intermediate cladding tube having an inner diameter and an outer diameter, wherein the inner diameter is larger than the core rod diameter, the radial difference between the inner diameter and the core rod diameter defining an annular gap; applying a negative pressure inside the annular gap; forming a core preform by heating the core assembly to collapse the intermediate cladding tube around the core rod while maintaining the negative pressure, wherein heating comprises moving a heater outside the intermediate cladding tube and along an axial direction of the same, and forming an overcladding region surrounding the core preform so as to form an optical fibre preform.