Optical Fiber Cable Sheath Structure for Air-Blown Micro-Ducts
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Solution Overview
Problem
Existing optical fiber cables face issues with rigidity, air-blowing characteristics, and transmission loss, particularly due to stress concentration and increased diameter when using UV curable resin coatings, and lack of rigidity when optical fibers are simply twisted.
Innovation Solution
An optical fiber cable design featuring a sheath with intermittently adhered optical fiber ribbons, alternating recesses and protrusions, and embedded tensile strength members, which enhances strength, reduces diameter, and improves air-blowing characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a plurality of optical fibers are collectively coated with UV curable resin to form a tape core wire, then the rigidity of the optical fiber cable is improved, but the core diameter increases and transmission loss increases due to large strain on the optical fiber
Solution Approach 1:
The optical fiber ribbon is divided into multiple individual optical fibers that are intermittently adhered together through adhesive portions, rather than being collectively coated with resin. This segmentation maintains rigidity through the ribbon structure while reducing core diameter and strain on individual fibers.
Solution Approach 2:
The patent uses a thin adhesive layer instead of thick UV curable resin coating. The adhesive portions are minimal in quantity and thickness, providing just enough bonding to maintain ribbon structure without adding excessive diameter or strain to the optical fibers.
2Device complexity
If the recess is formed as a V-shaped groove on the sheath surface, then the sheath structure is simple, but stress concentrates on the inner end portion of the groove causing the sheath to crack
Solution Approach 1:
The recess is designed with a curved bottom surface instead of a sharp V-shaped groove. This curvature distributes stress more evenly across the recess area, preventing stress concentration at the inner end portion and eliminating the risk of sheath cracking while maintaining structural simplicity.
3Ease of manufacture
If a plurality of optical fibers are simply twisted and housed in a tube, then the manufacturing process is simple, but the optical fiber cable lacks rigidity and has poor air-blowing characteristics
Solution Approach 1:
Multiple optical fibers are merged into a ribbon structure with intermittent adhesive bonding, combining the simplicity of twisting with the rigidity of a unified structure. The adhesive portions bond adjacent optical fibers together to form a rigid ribbon that maintains air-blowing characteristics.
4Strength
If the core is made larger to improve rigidity, then the rigidity of the optical fiber cable is improved, but the diameter of the cable increases which is disadvantageous for reducing cable size
Solution Approach 1:
The patent uses a thin adhesive film structure to bond optical fibers into a ribbon. This thin bonding layer provides structural rigidity without adding significant diameter, allowing the cable to maintain small size while achieving the required rigidity for air-blowing installation.
Data Source
AI summary
An optical fiber cable includes: a sheath; a core that is housed in the sheath and comprises optical fibers; tensile strength members embedded in the sheath; and ripcords embedded in the sheath. Recesses and protrusions are disposed alternately in a circumferential direction on an outer circumferential surface of the sheath. The recesses each include: two connecting portions respectively connected to radial inner ends of two adjacent protrusions; and a bottom surface positioned between the two connecting portions. In a transverse cross-sectional view, the ripcords are positioned inside some of the protrusions, and the tensile strength members are positioned inside the remaining protrusions.