Optical Fiber Cable Sheath Shrinkage Prevention
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Solution Overview
Problem
Existing optical fiber cables face challenges in achieving high density and lightweight designs with small diameters, as they tend to shrink at low temperatures, leading to increased attenuation and bending anisotropy, particularly in slotless types used for pneumatic feeding.
Innovation Solution
The optical fiber cable incorporates a cable sheath with fibrous fillers arranged in diagonal directions, having a lower linear expansion coefficient than the sheath itself, along with a tensile strength member and tear strings, to prevent shrinkage and maintain structural integrity at low temperatures, while ensuring adequate bending rigidity and reduced friction during pneumatic feeding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the cable sheath thickness is made thin to achieve small diameter and light weight, then the diameter and weight are reduced, but the cable is likely to shrink at low temperature and bending rigidity deteriorates
Solution Approach 1:
The patent changes the material composition parameters of the cable sheath by incorporating a specific proportion of linear low-density polyethylene (LLDPE) resin (5-20 mass%) with particular molecular weight characteristics (branching density 0.03-0.06 branches/100 carbon atoms, weight average molecular weight 50,000-200,000). This parameter optimization allows the thin-walled sheath to maintain adequate low-temperature resistance and structural integrity while achieving reduced weight and diameter.
Solution Approach 2:
The patent uses a composite material system combining linear low-density polyethylene (LLDPE) resin with other polyethylene components. The LLDPE resin with specific branching characteristics creates a composite structure that provides both the weight reduction needed for thin-walled design and the mechanical properties required for low-temperature performance and bending rigidity.
2Volume of moving object
If the cable sheath thickness is made thin to achieve small diameter, then the diameter is reduced, but the cable is likely to shrink at low temperature leading to increased attenuation
Solution Approach 1:
The patent optimizes the molecular parameters of the LLDPE resin, specifically controlling the weight average molecular weight (50,000-200,000) and branching density (0.03-0.06 branches/100 carbon atoms). These parameter changes enable the thin-walled sheath to resist low-temperature shrinkage forces while maintaining the reduced diameter needed for high-density fiber capacity.
3Strength
If tension members are provided on opposite sides of the cable sheath to maintain rigidity, then bending rigidity is improved, but bending anisotropy occurs making the cable prone to buckling during pneumatic feeding
Solution Approach 1:
The patent removes the traditional tension member structure from opposite sides of the cable sheath that causes bending anisotropy. Instead, it extracts only the essential function of providing radial strength and dimensional stability by using the optimized LLDPE resin material properties and specific sheath thickness (0.5-2.0 mm) to achieve isotropic bending characteristics suitable for pneumatic feeding.
Solution Approach 2:
The patent creates a homogeneous cable structure without asymmetric tension members, ensuring uniform mechanical properties in all radial directions. The optimized LLDPE resin composition provides consistent strength and flexibility throughout the sheath, eliminating bending anisotropy and enabling reliable pneumatic feeding operations.
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 configuration results in a high-density, lightweight optical fiber cable that prevents sheath shrinkage at low temperatures, reduces bending anisotropy, and enhances pneumatic feeding capabilities with improved lateral pressure characteristics and reduced transmission loss.
Implementation Method 1
an average linear expansion coefficient of the fibrous filler at - 40°C to + 70°C is smaller than an average linear expansion coefficient of the cable sheath at - 40°C to + 70°C
Data Source
Figure 1~2
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AI summary
An optical fiber cable includes a plurality of intermittently connected optical fiber ribbons inside a cable sheath, in which a fibrous filler or an FRP using the fibrous filler is provided on at least one pair of diagonals of the two diagonal directions approximately orthogonal to each other inside the cable sheath. An average linear expansion coefficient of the fibrous filler at - 40°C to + 70°C is smaller than an average linear expansion coefficient of the cable sheath at - 40°C to + 70°C.