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Optical fiber cable
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An optical fiber cable is a cable containing one or more optical fibers. The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed.
ractical fibers, the cladding is usually coated with a tough resin buffer layer, which may be further surrounded by a jacket layer, usually plastic.
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Encyclopedia
An optical fiber cable is a cable containing one or more optical fibers. The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed.
Design
In practical fibers, the cladding is usually coated with a tough resin buffer layer, which may be further surrounded by a jacket layer, usually plastic. These layers add strength to the fiber but do not contribute to its optical wave guide properties. Rigid fiber assemblies sometimes put light-absorbing ("dark") glass between the fibers, to prevent light that leaks out of one fiber from entering another. This reduces cross-talk between the fibers, or reduces flare in fiber bundle imaging applications.
For indoor applications, the jacketed fiber is generally enclosed, with a bundle of flexible fibrous polymer strength members like Aramid (e.g. Twaron or Kevlar), in a lightweight plastic cover to form a simple cable. Each end of the cable may be terminated with a specialized optical fiber connector to allow it to be easily connected and disconnected from transmitting and receiving equipment.
For use in more strenuous environments, a much more robust cable construction is required. In loose-tube construction the fiber is laid helically into semi-rigid tubes, allowing the cable to stretch without stretching the fiber itself. This protects the fiber from tension during laying and due to temperature changes. Loose-tube fiber may be "dry block" or gel-filled. Dry block offers less protection to the fibers than gel-filled, but costs considerably less. Instead of a loose tube, the fiber may be embedded in a heavy polymer jacket, commonly called "tight buffer" construction. Tight buffer cables are offered for a variety of applications, but the two most common are "Breakout" and "Distribution". Breakout cables normally contain a rip cord, two non-conductive dielectric strengthening members (normally a glass rod epoxy), an aramid yarn, and 3 mm buffer tubing with an additional layer of Kevlar surrounding each fiber. Distribution cables have an overall Kevlar wrapping, a ripcord, and a 900 micrometer buffer coating surrounding each fiber. These fiber units are commonly bundled with additional steel strength members, again with a helical twist to allow for stretching.
A critical concern in cabling is to protect the fiber from contamination by water, because its component hydrogen (hydronium) and hydroxyl ions can diffuse into the fiber, reducing the fiber's strength and increasing the optical attenuation. Water is kept out of the cable by use of solid barriers such as copper tubes, water-repellant jelly, or more recently water absorbing powder, surrounding the fiber.
Finally, the cable may be armored to protect it from environmental hazards, such as construction work or gnawing animals. Undersea cables are more heavily armored in their near-shore portions to protect them from boat anchors, fishing gear, and even sharks, which may be attracted to the electrical power signals that are carried to power amplifiers or repeaters in the cable.
Modern fiber cables can contain up to a thousand fibers in a single cable, so the performance of optical networks easily accommodates even today's demands for bandwidth on a point-to-point basis. However, unused point-to-point potential bandwidth does not translate to operating profits, and it is estimated that no more than 1% of the optical fiber buried in recent years is actually 'lit'. While unused fiber may not be carrying traffic, it still has value as dark backbone fiber. Companies can lease or sell the unused fiber to other providers who are looking for service in or through an area. Many companies are "overbuilding" their networks for the specific purpose of having a large network of dark fiber for sale. This is a great idea as many cities are difficult to deal with when applying for permits and trenching in new ducts is very costly.
Modern cables come in a wide variety of sheathings and armor, designed for applications such as direct burial in trenches, dual use as power lines, installation in conduit, lashing to aerial telephone poles, submarine installation, or insertion in paved streets. In recent years the cost of small fiber-count pole-mounted cables has greatly decreased due to the high Japanese and South Korean demand for fiber to the home (FTTH) installations.
Cable types
- OFC: Optical fiber, conductive
- OFN: Optical fiber, nonconductive
- OFCG: Optical fiber, conductive, general use
- OFNG: Optical fiber, nonconductive, general use
- OFCP: Optical fiber, conductive, plenum
- OFNP: Optical fiber, nonconductive, plenum
- OFCR: Optical fiber, conductive, riser
- OFNR: Optical fiber, nonconductive, riser
- OPGW: Optical fiber composite overhead ground wire
Jacket material
The jacket material is application specific. The material determines the mechanical robustness, ageing due to UV radiation, oil resistance, etc.
Nowadays PVC is being replaced by halogen free alternatives, mainly driven by more stringent regulations.
| Material | Halogen free | Remark |
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| LSFH Polymer | yes | Good for indoor use | | Polyvinyl chloride (PVC) | no | Being replaced by LSFH Polymer | | Polyethylene (PE) | yes | Good for outdoor applications | | Polyurethane (PUR) | yes | Highly flexible cables | | Polybutylene terephthalate (PBT) | yes | Good for indoor use | | Polyamide (PA) | yes | Indoor and outdoor use |
Color coding
Patch cords
The buffer or jacket on patchcords is often color-coded to indicate the type of fiber used. The strain relief "boot" that protects the fiber from bending at a connector is color-coded to indicate the type of connection. Connectors with a plastic shell (such as SC connectors) typically use a color-coded shell. Standard color codings for jackets and boots (or connector shells) are shown below:
| Connector Boot | Meaning | Comment |
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| Blue | Physical Contact (PC), 0° | mostly used for single mode fibers; some manufacturers use this for polarization-maintaining fiber. | | Green | Angle Polished (APC), 8° | not available for multimode fibers | | Black | Physical Contact (PC), 0° | | | Grey, Beige | Physical Contact (PC), 0° | multimode fiber connectors | | White | Physical Contact (PC), 0° | | | Red | | High optical power. Sometimes used to connect external pump lasers or Raman pumps. |
Remark: It is also possible that a small part of a connector is additionally colour-coded, e.g. the leaver of an E-2000 connector or a frame of an adapter. This additional colour coding indicates the correct port for a patchcord, if many patchcords are installed at one point.
Multi-fiber cables
Individual fibers in a multi-fiber cable are often distinguished from one another by color-coded jackets or buffers on each fiber. The identification scheme used by Corning Cable Systems is based on EIA/TIA-598, "Optical Fiber Cable Color Coding." EIA/TIA-598 defines identification schemes for fibers, buffered fibers, fiber units, and groups of fiber units within outside plant and premises optical fiber cables. This standard allows for fiber units to be identified by means of a printed legend. This method can be used for identification of fiber ribbons and fiber subunits. The legend will contain a corresponding printed numerical position number and/or color for use in identification.
| Position | Jacket color |
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| 1 | Blue | | 2 | Orange | | 3 | Green | | 4 | Brown | | 5 | Slate | | 6 | White | | 7 | Red | | 8 | Black | | 9 | Yellow | | 10 | Violet | | 11 | Rose | | 12 | Aqua | | 13 | Blue with black tracer | | 14 | Orange with black tracer | | 15 | Green with black tracer | | 16 | Brown with black tracer | | 17 | Slate with black tracer | | 18 | White with black tracer | | 19 | Red with black tracer | | 20 | Black with yellow tracer | | 21 | Yellow with black tracer | | 22 | Violet with black tracer | | 23 | Rose with black tracer | | 24 | Aqua with black tracer |
See also
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