Blown Microcable Dual-Layer Sheath Design
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Solution Overview
Problem
Existing optical fiber cables are inefficient in utilizing space within small microducts and lack the mechanical robustness needed for outside plant installations, particularly in terms of resistance to mechanical damage and temperature variations.
Innovation Solution
A microcable with a protective sheath composed of two layers of synthetic materials, where the inner layer has an elasticity modulus of 1500-10,000 MPa and the outer layer has a modulus of 600-1200 MPa, providing high tensile strength, crush resistance, and flexibility, along with a low thermal expansion coefficient, allowing for high fiber count and easy installation in small microducts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional single-layer protective sheath is used, then manufacturing is simple, but mechanical robustness and resistance to temperature variations are insufficient
Solution Approach 1:
The protective sheath is constructed as a composite structure with an inner layer of PTFE (polytetrafluoroethylene) and an outer layer of polyethylene. The PTFE inner layer provides smooth surface for fiber sliding and chemical inertness, while the polyethylene outer layer provides mechanical strength and environmental resistance. This composite material approach resolves the contradiction by combining materials with complementary properties to achieve both simplicity and robustness.
2Quantity of substance
If high fiber count is achieved in small diameter, then space utilization improves, but mechanical damage risk increases
Solution Approach 1:
The PTFE inner layer acts as a flexible protective shell that surrounds each optical fiber individually. This flexible membrane provides mechanical protection while allowing the fiber to move slightly without damage. The thin film structure enables high fiber density while maintaining the ability to absorb mechanical stresses, thus protecting the fibers even when packed tightly in small microducts.
Solution Approach 2:
The protective sheath structure with its two-layer construction provides beforehand cushioning against mechanical damage. The softer PTFE inner layer absorbs and distributes mechanical stresses before they can reach the fragile optical fibers, while the outer polyethylene layer provides additional structural protection. This pre-established protective system prevents mechanical damage before it can occur during installation or service.
3Length of moving object
If microcable stiffness is increased for pushing installation, then installation distance improves, but flexibility for blowing installation decreases
Solution Approach 1:
The protective sheath structure provides dynamic mechanical properties that adapt to different installation methods. The two-layer construction with PTFE inner layer and polyethylene outer layer creates a structure that can exhibit different degrees of flexibility and stiffness depending on the installation forces applied. During blowing installation, the cable can flex and conform to duct bends; during pushing installation, the structure maintains sufficient rigidity to transmit pushing forces over long distances.
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 microcable achieves high fiber density, mechanical robustness, and temperature resilience, enabling safe and efficient installation in outdoor environments with reduced mechanical damage and operational flexibility, while maintaining low manufacturing costs and ease of handling.
Implementation Method 1
the inner layer consists of a material having an elasticity modulus in the range of 1500-10,000 MPa at room temperature
Implementation Method 2
a low thermal expansion coefficient, allowing for high fiber count and easy installation in small microducts
Data Source
Figure 1~2
AI summary
The invention relates to the field of optical fiber cables and more specifically to an optical fiber cable especially suited for blown installation or pushing installation in microducts of small diameter. The microcable comprises a protective sheath holding a plurality of optical fibers, wherein said protective sheath is composed of two layers of different synthetic materials, in which the inner layer of said protective sheath consists of a material having an elasticity modulus in a range of 1500-3000 MPa at room temperature, and that the outer layer of said protective sheath consists of a material having an elasticity modulus in the range of 600-1200 MPa at room temperature.