Four Fiber Unit Cable Design for Flexibility and Strength
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Solution Overview
Problem
High fiber count fiber optic cables are stiff and difficult to bend, making them unsuitable for confined spaces, and existing solutions that attempt to reduce stress on fibers often result in fiber breaks over time due to the use of highly bend-resistant fibers and strength members.
Innovation Solution
A compact high fiber count fiber optic cable design with loose tube construction using four fibers per buffer tube, arranged in larger sub-units and coated with a polymer jacket, which allows for flexibility and reduced stress on fibers without the need for additional strength members, utilizing novel polymer blends for fire resistance and a release agent for improved stripability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high fiber count cables are constructed with tight bundles of twelve fiber units or ribbon cables, then fiber count is increased, but cable flexibility deteriorates and stiffness increases
Solution Approach 1:
The cable is divided into multiple independent buffer tubes, each containing a small number of fibers (e.g., 6 fibers per tube). These buffer tubes are individually loose and flexible, allowing the overall cable to maintain flexibility while achieving high fiber count through the combination of multiple segmented units.
Solution Approach 2:
Multiple buffer tubes are nested within a common outer jacket or sheath. This nested structure allows each inner buffer tube to move independently, maintaining cable flexibility while accommodating a high total fiber count through the nested arrangement of multiple sub-units.
2Strength
If strength members are added to reduce stress on fibers, then fiber strength is improved, but cable flexibility deteriorates further
Solution Approach 1:
The invention extracts or removes traditional strength members (such as steel wires or aramid yarns) from the cable structure. Instead, the strength function is achieved through the collective strength of numerous individual fibers distributed across multiple loose buffer tubes, eliminating the stiffness introduced by conventional strength members.
Solution Approach 2:
The fibers themselves serve their dual function: they provide both the optical transmission function and the strength function. The collective tensile strength of all fibers in the cable replaces the need for separate strength members, allowing the cable to remain flexible while maintaining adequate strength through the self-service capability of the fiber bundle.
3Reliability
If highly bend resistant fibers are used in tight bundles, then immediate fiber protection is improved, but long-term reliability deteriorates due to fiber breaks
Solution Approach 1:
Each fiber is surrounded by its own buffer tube that provides cushioning and stress distribution. This beforehand cushioning protects individual fibers from stress concentration and bending-induced microbends, preventing the development of stress points that would lead to long-term fiber breaks while maintaining overall cable flexibility.
Data Source
AI summary
A fiber optic cable includes a plurality of optical fiber subunits, each of the subunits including four fiber optic elements and an enclosing jacket. A plurality of optical fiber subunit assemblies are also included, each of which includes a plurality of the optical fiber subunits and an enclosing micro-sheath. The subunits are stranded around one another. A sheath encloses the plurality of optical fiber subunit assemblies.