Stretchable Fiber Optic Cable Strain Management
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Solution Overview
Problem
Fiber optic cables face signal attenuation due to stretching or straining of optical fibers, which is exacerbated by variations in excess optical fiber length caused by manufacturing processes and environmental factors, leading to unnecessary strength component sizing that is not optimal for all fibers.
Innovation Solution
A fiber optic cable design featuring strength members, buffer tubes with cavities allowing optical fibers to be highly contorted, providing a large strain window with minimal attenuation, and a binder sleeve for even distribution, allowing for reduced strength component usage and increased flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If strength components are sized to accommodate the lower end of excess optical fiber length range, then fibers with least excess length are protected from straining, but fibers with greater excess length experience unnecessary constraint and the cable structure becomes overly robust
Solution Approach 1:
The patent applies local quality by allowing different optical fibers within the same cable to have different amounts of excess length, with each fiber experiencing appropriate strain levels based on its individual characteristics. The buffer tube design enables local variation in fiber protection levels rather than uniform constraint across all fibers.
Solution Approach 2:
The patent changes the parameter of excess optical fiber length from a fixed design value to a variable parameter that can range across different fibers. This allows the cable to accommodate a distribution of excess lengths, with strength components sized for the lower end but allowing higher excess length fibers to experience reduced constraint.
2Reliability
If optical fibers are loosely arranged in buffer tubes with excess length, then strain window is provided, but manufacturing variations cause inconsistent excess length distribution leading to unpredictable attenuation behavior
Solution Approach 1:
The patent applies beforehand cushioning by intentionally providing excess optical fiber length in the buffer tubes before the cable is subjected to strain. This excess length acts as a cushion that absorbs strain effects, protecting the fibers from direct mechanical stress during cable installation and operation.
Solution Approach 2:
The patent applies dynamics by allowing the excess optical fiber length to dynamically adjust during cable strain events. As the cable is pulled or bent, the fibers can straighten from their contorted state within the buffer tubes, absorbing the strain dynamically rather than transmitting it directly to the fiber cores.
3Reliability
If optical fibers are highly contorted in buffer tubes, then excess length is maximized for strain protection, but uniformity of contortion is difficult to achieve due to manufacturing variations
Solution Approach 1:
The patent applies partial or excessive action by providing more excess optical fiber length than the minimum required for strain protection. This excessive contortion ensures that even with manufacturing variations, all fibers have sufficient excess length to protect them from straining, and the system can accommodate the natural distribution of contortion uniformity.
Data Source
AI summary
A fiber optic cable includes a strength member, tubes coupled to the strength member, and optical fibers. The strength member provides tensile and anti-buckling strength. The tubes have a cavity into which the optical fibers are packed. The cable is stretchable in that the optical fibers experience less than 0.5 dB/km of increased average attenuation at 1310 nanometers wavelength when the cable experiences strain of up to 2×10−3.