Capped Core Canes for Optical Fiber Preforms
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Solution Overview
Problem
The cane-in-soot process for producing optical fiber preforms with large core-clad ratios often results in defects due to stresses from differential thermal expansion between the core cane and soot cladding monolith, leading to potential failures during fiber draw.
Innovation Solution
Incorporating a capped core cane with a capping material having a thermal expansion coefficient that matches or closely aligns with the soot cladding monolith, reducing radial tensile stresses and minimizing defect formation during the consolidation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capped core cane is used to reduce thermal expansion stress, then the reliability of the preform is improved, but the device complexity increases
Solution Approach 1:
A cap is placed on the core cane before insertion into the soot cladding monolith. This preliminary action prevents radial tensile stress from developing during consolidation by restraining the core cane's thermal expansion, thereby preventing defect formation and improving preform reliability.
Solution Approach 2:
The cap acts as an intermediary element between the core cane and the soot cladding monolith. It mediates the thermal expansion interaction by providing a restraining force that counteracts the radial tensile stress, preventing direct stress transmission that would cause defects.
2Productivity
If the core-clad ratio is increased to improve fiber performance, then the productivity and quality of optical fiber are improved, but the manufacturing precision becomes more difficult to control due to stress-induced defects
Solution Approach 1:
The cap is installed on the core cane before assembly into the preform structure. This preliminary restraint prevents thermal expansion-induced defects during consolidation, enabling manufacturers to produce preforms with large core-clad ratios without suffering from stress-related manufacturing defects.
3Strength
If the core cane is fully consolidated to improve structural integrity, then the strength of the preform is improved, but the differential thermal expansion with soot cladding causes stress and potential cracking
Solution Approach 1:
The cap provides a counteracting force against the radial tensile stress generated by differential thermal expansion between the fully consolidated core cane and the soot cladding monolith. This counterforce prevents stress accumulation and potential cracking, maintaining preform structural integrity.
Solution Approach 2:
The cap changes the stress state parameters within the core cane by providing mechanical restraint. This alters the thermal expansion behavior during consolidation, preventing the development of harmful radial tensile stresses while maintaining the structural benefits of full consolidation.
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
The use of capped core canes significantly reduces radial tensile stresses and defect formation, enabling the production of crack-free optical fiber preforms with large core-clad ratios that can withstand fiber draw temperatures without failure.
Implementation Method 1
Incorporating a capped core cane with a capping material having a thermal expansion coefficient that matches or closely aligns with the soot cladding monolith, reducing radial tensile stresses
Implementation Method 2
The core-cladding assembly is consolidated to form an optical fiber preform
Data Source
Figure 1A~2A
Figure 2B~3
Figure 4~5
AI summary
The present disclosure provides optical fiber preforms formed from core canes having large core-clad ratio, intermediate core-cladding assemblies, and methods for making the preforms and core cladding assemblies. The preforms are made with capped core canes. The capping material has a coefficient of thermal expansion less than the coefficient of thermal expansion of the core cane and more closely matched to or lower than the coefficient of thermal expansion of the surrounding cladding monolith in a cane-in-soot process. Presence of the cap reduces stresses that arise from differential thermal expansion of the core cane and cladding materials and leads to preforms having low defect concentration and low probability of failure during subsequent thermal processing steps.