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Multimode,
PE Sheath 4-36f
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Multimode,
PE/Nylon 4-36f
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Singlemode,
PE Sheath, 4-36f
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Singlemode,
PE Sheath, 48-72f
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Singlemode,
PE/Nylon, 4-36f
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Singlemode,
PE/Nylon, 48-72f
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Composite SM/MM
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Corrugated Steel Tape Armoured SM/MM
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Monotube, PE/Nylon, 4-12f |
Multimode, Drycore 24f |
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Optical fibre is a versatile yet fragile material. It must be packaged – cabled
- in a manner suitable to its deployment. Tensile strength, crush resistance, UV
resistance and thermal stability are all considered when selecting an optical
fibre cable.
The two fundamental optical fibre cable types are loose tube and tight buffered.
Loose tube construction
In this construction, the optical fibres are protected by incorporating them
within jelly-filled loose tubes. The tubes are manufactured from a relatively
hard and stiff plastic material called polybutylene terepthalate (PBT). Loose
tubes are usually designed to each contain either six or twelve optical fibres.
The jelly filling protects the fibres from moisture, whilst the spaces between
the fibres and tube inner wall accommodate fibre movement when cables are
subject to tension or compression – either mechanically or thermally induced.
Loose tubes are traditionally cabled by wrapping (or stranding) them around the
central strength element (typically a fiberglass rod) and covering this core by
extrusion of polyethylene and nylon. Several variations are possible including
the inclusion of steel tape armouring for increased crush, moisture and rodent
protection.
Fibres within stranded loose tube cables are held within a protected,
strain-free environment. This means the cable can be subjected to defined
worst-case events involving tension (usually during installation), temperature
variation, and crush, without damaging tensile or bending loads being imposed
upon the fibres. Such damage can lead to degraded optical power transmission (ie
increased optical attenuation) and reduced product life through breakage.
Loose tube cable constructions are not only possible in stranded form, but also
in “monotube”. In monotube form, the tube is located as a central, unstranded
element surrounded by strength member components such as fiberglass yarn, prior
to oversheathing.
Loose tube cables are typically deployed in diverse external environments where
robustness is paramount.
Tight Buffer Construction
In this construction, the optical fibres are protected by directly extruding a
polymer coating on to each individual fibre. The polymer is typically a grade of
plasticised PVC, with thickness tuned to set the diameter of each tight buffered
fibre to 900 microns (0.9mm). Tight buffering permits the fibres to be directly
handled with reduced risk of damage, for example when terminating to connectors.
As tight buffering does not impart the same protection as the “loose buffering”
afforded by loose tubes, tight buffered fibres are most commonly deployed for
indoor cable runs, in conjunction with cable constructions/materials suitable
for indoor use. Such cables do not have the same mechanical robustness as loose
tube cables, but do have the advantage of reduced weight and the use of flame
retardant materials, making them safer and more convenient to deploy indoors.
The most common construction method for tight buffered optical fibre cables is
by producing a core of tight buffered fibres mixed with strength member yarns
(usually aramid yarns), then oversheathing with flame retardant PVC.
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Copyright 2004 General Cable Australia Pty Limited
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Telephone Cables
