Optical Fiber Cable Foam Layer for Bend-Induced Attenuation
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Solution Overview
Problem
Optical fiber cables experience signal attenuation due to materials like polyolefins, metal armor, and glass-reinforced plastic strength members, which cause issues when bent, coiled, or twisted, and there is a need for improved cable designs that reduce attenuation and increase fiber density.
Innovation Solution
A thermoplastic foam layer is extruded around the cable core using a chemical foaming process, comprising a blend of thermoplastic elastomer, chemical foaming agent, and crosslinking agent, which provides cushioning and stress dispersion, reducing density and preventing attenuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If polyolefin materials are used for cable jacket and buffer tubes, then flexibility is improved, but signal attenuation increases when cable is bent, coiled, crushed, or twisted
Solution Approach 1:
The patent introduces a foam layer as an intermediary material between the buffer tube and the cable jacket/armor layer. This foam layer acts as a mediator that absorbs and disperses mechanical stresses (bending, crushing, twisting) before they reach the optical fibers, thereby preventing signal attenuation while allowing the outer polyolefin layers to maintain their flexibility.
Solution Approach 2:
The patent employs a foam material with porous structure as the protective layer. The foam's cellular structure provides cushioning and stress dispersion capabilities, allowing it to absorb mechanical deformations effectively. The porosity of the foam material enables it to compress and expand, providing protection during cable bending and crushing without transmitting harmful stresses to the fibers.
2Strength
If armor layer and strength members are added, then mechanical protection is improved, but signal attenuation increases during cable deformation
Solution Approach 1:
The patent applies beforehand cushioning by placing the foam layer between the rigid armor/strength members and the buffer tube containing the optical fibers. This foam cushioning layer is positioned in advance to absorb and distribute mechanical stresses from the armor and strength members during cable bending, coiling, crushing, or twisting, preventing these stresses from reaching the fibers and causing signal attenuation.
3Quantity of substance
If fiber density is increased, then cable capacity is improved, but stress concentration increases leading to attenuation
Solution Approach 1:
The foam layer's porous structure provides a compliant interface that distributes stresses evenly across multiple fibers in high-density ribbon stacks. The foam's ability to compress and expand allows it to accommodate fiber movements and stress distributions, preventing stress concentration on individual fibers even when fiber density is increased, thereby maintaining signal transmission quality.
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 foam layer significantly reduces signal attenuation and allows for increased fiber density by absorbing stress, improving cable flexibility and meeting industry standards for bend and twist performance while maintaining mechanical integrity.
Implementation Method 1
The foam is formed from the extruded product of a blend of thermoplastic elastomer (TPE), a chemical foaming agent, and a crosslinking agent
Implementation Method 2
The foam is formed from the extruded product of a blend of thermoplastic elastomer (TPE), a chemical foaming agent, and a crosslinking agent
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
Embodiments of the disclosure relate to an optical fiber cable having at least one optical fiber, a cable jacket and a foam layer. The cable jacket includes an inner surface and an outer surface in which the outer surface is an outermost surface of the optical fiber cable. The inner surface is disposed around the at least one optical fiber. The foam layer is disposed between the at least one optical fiber and the cable jacket. The foam layer is made of an extruded product of at least one thermoplastic elastomer (TPE), a chemical foaming agent, and a crosslinking agent. The foam layer has a closed-cell morphology having pores with an average effective circle diameter of less than 100 µm. Further, the foam layer has a compression modulus of less than 1 MPa when measured at 50% strain.