Multicore Optical Fiber Preform Drawing With Low-Contamination Gaps
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Solution Overview
Problem
The existing methods for manufacturing multicore optical fibers (MCFs) face challenges with increased core density leading to higher frequency of quality abnormalities due to foreign substances mixing with the preform during the drawing process, which also reduces the obtainable fiber length.
Innovation Solution
The method involves inserting glass rods into a glass tube, sealing one end, and drawing while integrating them under controlled pressure, ensuring the sum of gaps between the glass tube and rods is minimized, and maintaining a high cleanliness level, thereby reducing the frequency of quality abnormalities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If core density is improved by arranging multiple cores in one fiber, then the number of cores increases while outer diameter is kept constant, but the frequency of quality abnormalities increases due to foreign substances mixing during drawing
Solution Approach 1:
The patent applies the inert atmosphere principle by introducing a protective gas (nitrogen or carbon dioxide) into the glass tube before and during the drawing process. This creates an inert environment that prevents foreign substances from entering the preform through the gaps between glass rods and the tube wall, thereby maintaining high reliability and reducing quality abnormalities while enabling increased core density.
2Quantity of substance
If the number of cores is increased while keeping outer diameter constant, then core density improves, but the gap area between glass tube and glass rods increases leading to more foreign substance contamination
Solution Approach 1:
By filling the glass tube with protective gas, the patent creates an inert atmosphere that eliminates the harmful effect of foreign substance contamination. This allows the design to accommodate higher core density with larger gap areas without suffering from increased contamination, as the protective gas prevents foreign substances from entering through the gaps.
Solution Approach 2:
The protective gas acts as an intermediary substance between the foreign environment and the preform interior. It mediates the interaction by forming a barrier that prevents foreign substances from contaminating the preform through the gaps, enabling higher core density without proportionally increasing contamination risk.
3Reliability
If foreign substances mix with the preform during drawing, then quality abnormalities increase, but the obtainable fiber length from one preform decreases
Solution Approach 1:
The protective gas atmosphere prevents foreign substance contamination throughout the entire drawing process, ensuring high reliability and reducing quality abnormalities. This enables longer fiber lengths to be obtained from single preforms, as the contamination that would normally limit production length is eliminated.
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 effectively reduces the frequency of quality abnormalities to 0.02 /km or less, maintaining high cleanliness levels and ensuring consistent fiber production.
Implementation Method 1
an end of the preform is heated to draw the outer overclad tube and the core rod while consolidating them
Implementation Method 2
the lower end of the preform is heated to draw the first overclad tube and the second overclad tube while reducing the diameters thereof
Data Source
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AI summary
This method of manufacturing a multicore optical fiber includes: a step for inserting multiple glass rods into multiple holes provided in a glass tube; a step for sealing a first end of the glass tube; and a step for decompressing the inside of the multiple holes from a second end of the glass tube and drawing the glass tube and the multiple glass rods while integrating same. When the cross-sectional area of the glass tube before the drawing step is defined as S1 [m2], the sum of the cross-sectional areas of the multiple glass rods before the drawing step is defined as S2 [m2], and the cross-sectional area of the multicore optical fiber after the drawing step is defined as S3 [m2], the inserting step is carried out so that the sum of the areas of gaps between the glass tube and the multiple glass rods before the drawing step in a cross-section orthogonal to the axial direction of the glass tube is equal to or less than (S1 + S2)/S3 × 5.66 × 10-4 [mm2], and the inserting step is carried out in an environment having cleanliness higher than class 1,000.