External Loose Tube
- Multimode, PE Sheath 4-36f
- Singlemode, PE Sheath, 4-36f
- Singlemode, PE/Nylon, 4-36f
- Composite SM/MM
- Monotube, PE/Nylon, 4-12f
- Multimode, PE/Nylon 4-36f
- Singlemode, PE/Nylon, 48-72f
- Singlemode, PE Sheath, 48-72f
- Corrugated Steel Tape Armoured SM/MM
- Multimode, Drycore 24f
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.