Optical Fiber Cable Structure for Small-Radius Bending
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Solution Overview
Problem
Optical fiber cables with existing tensile strength members tend to exhibit bending anisotropy and buckling when bent to small diameters, leading to reduced storability and increased space requirements, especially when the sheath thickness is reduced for higher density mounting.
Innovation Solution
The optical fiber cable design features a single tensile strength member located at one position on the sheath, using fiber reinforced plastic (FRP) with a Young's modulus between 400 MPa and 700 MPa, and a sheath made of ethylene-vinyl acetate copolymer resin (EVA) with a softening point between 40°C and 70°C, allowing for high fiber density and reduced buckling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If tensile strength members are arranged at equal intervals at four locations on the sheath to provide structural support, then the cable has high bending rigidity and resistance to buckling, but the cable requires large space for storage and cannot be bent to small diameters
Solution Approach 1:
The cable structure segments the tensile strength members from the optical fiber core by placing them at the periphery of the sheath rather than distributing them throughout the cable cross-section. This segmentation allows the strength members to provide buckling resistance while the central core area remains compact for storage.
Solution Approach 2:
The tensile strength members are positioned in a different spatial dimension (at the periphery of the sheath cross-section) rather than being distributed radially throughout the cable. This dimensional repositioning allows the cable to achieve high bending rigidity without increasing the central core diameter that would require more storage space.
2Quantity of substance
If the sheath thickness is reduced to increase fiber density, then the cable diameter is reduced for better storability, but the tensile strength member becomes more susceptible to buckling when bent
Solution Approach 1:
The sheath is constructed as a composite structure combining EVA resin base material with flame retardant additives and pigments. This composite approach allows the sheath to maintain adequate thickness for protecting the tensile strength member while achieving high fiber density through optimized material composition rather than increased physical dimensions.
Solution Approach 2:
The mechanical properties of the sheath are optimized by controlling the Young's modulus of the EVA resin between 400-700 MPa and the softening point between 40-70°C. These parameter changes allow the sheath to provide sufficient structural support for the tensile strength member while maintaining a compact cable diameter for high fiber density.
3Stability of the object's composition
If multiple tensile strength members are distributed around the cable core to provide uniform support, then the cable has isotropic mechanical properties, but the cable exhibits bending anisotropy and buckling when bent to small diameters
Solution Approach 1:
The cable structure intentionally employs asymmetry by positioning the tensile strength member (or members) at the periphery of the sheath rather than distributing them symmetrically around the cable core. This asymmetric configuration creates bending anisotropy that actually improves buckling resistance in the critical direction while maintaining adequate mechanical support.
Solution Approach 2:
The invention replicates the successful peripheral positioning concept from single strength member designs and applies it to multi-fiber cables with high core density (1.5 core/mm² or higher). This copying of the structural arrangement allows multiple optical fibers to be accommodated without compromising the buckling resistance provided by the peripheral tensile strength members.
4Productivity
If the cable is designed for high fiber density mounting, then more optical fibers can be mounted in less space, but the cable becomes more susceptible to buckling and requires thicker sheath that increases diameter
Solution Approach 1:
The sheath material parameters are precisely controlled with Young's modulus between 400-700 MPa and softening point between 40-70°C. These parameter specifications allow the sheath to achieve optimal balance between thickness (for protecting high-density fiber cores) and flexibility (for maintaining manageable cable diameter).
Solution Approach 2:
The sheath uses composite EVA resin materials incorporating flame retardant properties and specific pigments. This composite formulation enables the sheath to provide enhanced structural support and protection for high-density fiber configurations without proportionally increasing the cable outer diameter, thus maintaining productivity while controlling dimensions.
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 design enables high-density optical fiber mounting with reduced buckling of the tensile strength member, improving storability and facilitating easy bending to small diameters, while maintaining excellent flame retardance and transmission characteristics.
Implementation Method 1
at least one tensile strength member provided along the cable core; the tensile strength member is provided at one location on the sheath in a cross-sectional view
Implementation Method 2
a sheath made of ethylene-vinyl acetate copolymer resin (EVA) with a softening point between 40°C and 70°C
Data Source
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AI summary
An optical fiber cable includes a cable core including a plurality of optical fibers, at least one tensile strength member provided along the cable core, and a sheath configured to cover the cable core from an outside and enclose the tensile strength member. The tensile strength member is provided at one location on the sheath in a cross-sectional view. A core density obtained by dividing the number of the plurality of optical fibers by a cross-sectional area of the cable is 1.5 core/mm2 or more.