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.
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[edit] 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.[1]
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. Alternatively the fiber may be embedded in a heavy polymer jacket, commonly called "tight buffer" construction. 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'.
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 [1], 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.
[edit] 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
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[edit] Color coding
Individual optical fibers in a 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[2].
| Position | Jacket color |
|---|---|
| 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 |
[edit] See also
- TIA/EIA-568-B Color coding for electrical cable
[edit] Notes and references
- ^ Light collection and propagation. National Instruments' Developer Zone. Retrieved on 2007-03-19.
Hecht, Jeff (2002). Understanding Fiber Optics, 4th ed., Prentice Hall. ISBN 0-13-027828-9. - ^ Leroy Davis (2007-02-21). Fiber wire color coding. Retrieved on 2007-12-01.
