Optical fiber cable

Optical fiber cable

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An optical fiber cable is a cable
Cable
A cable is two or more wires running side by side and bonded, twisted or braided together to form a single assembly. In mechanics cables, otherwise known as wire ropes, are used for lifting, hauling and towing or conveying force through tension. In electrical engineering cables are used to carry...

 containing one or more optical fiber
Optical fiber
An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...

s. 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
Cladding (fiber optics)
Cladding is one or more layers of material of lower refractive index, in intimate contact with a core material of higher refractive index. The cladding causes light to be confined to the core of the fiber by total internal reflection at the boundary between the two. Light propagation in the...

 is usually coated with a layer of acrylate polymer or polyimide
Polyimide
Polyimide is a polymer of imide monomers. The structure of imide is as shown. Polyimides have been in mass production since 1955...

. This coating protects the fiber from damage but does not contribute to its optical waveguide properties. Individual coated fibers (or fibers formed into ribbons or bundles) then have a tough resin
Resin
Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...

 buffer
Buffer (optical fiber)
In a fiber optic cable, a buffer is one type of component used to encapsulate one or more optical fibers for the purpose of providing such functions as mechanical isolation, protection from physical damage and fiber identification....

 layer and/or core tube(s) extruded around them to form the cable core. Several layers of protective sheathing, depending on the application, are added to form the cable. 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
Lens flare
Lens flare is the light scattered in lens systems through generally unwanted image formation mechanisms, such as internal reflection and scattering from material inhomogeneities in the lens. These mechanisms differ from the intended image formation mechanism that depends on refraction of the image...

 in fiber bundle imaging applications.


For indoor applications, the jacketed fiber is generally enclosed, with a bundle of flexible fibrous polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

 strength members like Aramid
Aramid
Aramid fibers are a class of heat-resistant and strong synthetic fibers. They are used in aerospace and military applications, for ballistic rated body armor fabric and ballistic composites, in bicycle tires, and as an asbestos substitute. The name is a portmanteau of "aromatic polyamide"...

 (e.g. Twaron
Twaron
Twaron is the brandname of Teijin Aramid for a para-aramid. It is a heat-resistant and strong synthetic fibre developed in the early 1970s by the Dutch company AKZO, division Enka, later Akzo Industrial Fibers. The research name of the para-aramid fibre was originally Fiber X, but it was soon...

 or Kevlar
Kevlar
Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora. Developed at DuPont in 1965, this high strength material was first commercially used in the early 1970s as a replacement for steel in racing tires...

), in a lightweight plastic cover to form a simple cable. Each end of the cable may be terminated with a specialized optical fiber connector
Optical fiber connector
An optical fiber connector terminates the end of an optical fiber, and enables quicker connection and disconnection than splicing. The connectors mechanically couple and align the cores of fibers so that light can pass...

 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
Helix
A helix is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis. Examples of helixes are coil springs and the handrails of spiral staircases. A "filled-in" helix – for...

 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 ripcord, 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. The ripcord is a parallel cord of strong yarn that is situated under the jacket(s) of the cable for jacket removal. 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 outdoor cabling is to protect the fiber from contamination by water. This is accomplished by use of solid barriers such as copper tubes, and water-repellent jelly or 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 shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

s, 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
Dark fiber
A dark fiber or unlit fiber is an unused Optical fiber, available for use in fiber-optic communication.The term dark fiber was originally used when referring to the potential network capacity of telecommunication infrastructure, but now also refers to the increasingly common practice of leasing...

 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.

Reliability and quality


Optical fibers are inherently very strong, but the strength is drastically reduced by unavoidable microscopic surface flaws inherent in the manufacturing process. The initial fiber strength, as well as its change with time, must be considered relative to the stress imposed on the fiber during handling, cabling, and installation for a given set of environmental conditions. There are three basic scenarios that can lead to strength degradation and failure by inducing flaw growth: dynamic fatigue, static fatigues, and zero-stress aging.

Telcordia GR-20, Generic Requirements for Optical Fiber and Optical Fiber Cable, contains reliability and quality criteria to protect optical fiber in all operating conditions. The criteria concentrate on conditions in an outside plant (OSP) environment. For the indoor plant, similar criteria are in Telcordia GR-409, Generic Requirements for Indoor Fiber Optic Cable.

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
    Optical fiber composite overhead ground wire
    An optical ground wire is a type of cable that is used in the construction of electric power transmission and distribution lines. Such cable combines the functions of grounding and communications...

  • ADSS: All-Dielectric Self-Supporting

Jacket material


The jacket material is application specific. The material determines the mechanical robustness, aging due to UV radiation, oil resistance, etc.
Nowadays PVC is being replaced by halogen free alternatives, mainly driven by more stringent regulations.
MaterialHalogen-freeUV
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 Resistance
Remark
LSFH
Low Smoke Zero Halogen
Low smoke zero halogen or low smoke free of halogen is a material classification typically used for cable jacketing in the wire and cable industry. LSZH cable jacketing is composed of thermoplastic or thermoset compounds that emit limited smoke and no halogen when exposed to high sources of...

 Polymer
Good Good for indoor use
Polyvinyl chloride
Polyvinyl chloride
Polyvinyl chloride, commonly abbreviated PVC, is a thermoplastic polymer. It is a vinyl polymer constructed of repeating vinyl groups having one hydrogen replaced by chloride. Polyvinyl chloride is the third most widely produced plastic, after polyethylene and polypropylene. PVC is widely used in...

 (PVC)
Good Being replaced by LSFH Polymer
Polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...

 (PE)
Poor Good for outdoor applications
Polyurethane
Polyurethane
A polyurethane is any polymer composed of a chain of organic units joined by carbamate links. Polyurethane polymers are formed through step-growth polymerization, by reacting a monomer with another monomer in the presence of a catalyst.Polyurethanes are...

 (PUR)
Highly flexible cables
Polybutylene terephthalate
Polybutylene terephthalate
Polybutylene terephthalate is a thermoplastic engineering polymer, that is used as an insulator in the electrical and electronics industries. It is a thermoplastic crystalline polymer, and a type of polyester...

 (PBT)
Fair? Good for indoor use
Polyamide
Polyamide
A polyamide is a polymer containing monomers of amides joined by peptide bonds. They can occur both naturally and artificially, examples being proteins, such as wool and silk, and can be made artificially through step-growth polymerization or solid-phase synthesis, examples being nylons, aramids,...

 (PA)
Good-Poor Indoor and outdoor use

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:
Buffer/jacket color Meaning
Yellow single-mode optical fiber
Single-mode optical fiber
In fiber-optic communication, a single-mode optical fiber is an optical fiber designed to carry only a single ray of light . Modes are the possible solutions of the Helmholtz equation for waves, which is obtained by combining Maxwell's equations and the boundary conditions...

Orange multi-mode optical fiber
Multi-mode optical fiber
Multi-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus...

Aqua 10 gig laser-optimized 50/125 micrometer multi-mode optical fiber
Grey outdated color code for multi-mode optical fiber
Multi-mode optical fiber
Multi-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus...

Blue Sometimes used to designate polarization-maintaining optical fiber
Polarization-maintaining optical fiber
In fiber optics, polarization-maintaining optical fiber is optical fiber in which the polarization of linearly polarized light waves launched into the fiber is maintained during propagation, with little or no cross-coupling of optical power between the polarization modes...


Connector Boot Meaning Comment
Blue Physical Contact (PC), 0° mostly used for single mode fibers; some manufacturers use this for polarization-maintaining optical fiber
Polarization-maintaining optical fiber
In fiber optics, polarization-maintaining optical fiber is optical fiber in which the polarization of linearly polarized light waves launched into the fiber is maintained during propagation, with little or no cross-coupling of optical power between the polarization modes...

.
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.
EWLINE
EIA598-A Fiber Color Chart
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
EWLINE
Color coding of Premise Fiber Cable
Fiber Type / Class Diameter (µm) Jacket Color
Multimode 1a 50/125 Orange
Multimode 1a 62.5/125 Slate
Multimode 1a 85/125 Blue
Multimode 1a 100/140 Green
Singlemode IVa All Yellow
Singlemode IVb All Red

Propagation speed and delay


Optical cables transfer data at around 180,000 to 200,000 km/s, resulting in 5.0 to 5.5 microseconds of latency per km. Thus the round-trip delay time for 1000km is around 11 ms.

Losses


Typical modern Multimode Graded-Index fibers have 3 dB/km of attenuation loss at 850 nm and 1 dB/km at 1300 nm.
9/125 Singlemode loses 0.4/0.25 dB/km at 1310/1550 nm.
POF (plastic optical fiber) loses much more: 1 dB/m at 650 nm.
Plastic Optical Fiber is large core (about 1mm) fiber suitable only for short, low speed networks such as within cars.

Each connection made adds about 0.6 dB of average loss, and each joint (splice) adds about 0.1 dB.
Depending on the transmitter power and the sensitivity of the receiver, if the total loss is too large the link will not function reliably.

Invisible IR light is used in commercial glass fiber communications because it has lower attenuation in such materials than visible light. However, the glass fibers will transmit visible light somewhat, which is convenient for simple testing of the fibers without requiring expensive equipment. Splices can be inspected visually, and adjusted for minimal light leakage at the joint, which maximizes light transmission between the ends of the fibers being joined.

The charts at Understanding Wavelengths In Fiber Optics and Optical power loss (attenuation) in fiber illustrate the relationship of visible light to the IR frequencies used, and show the absorption water bands between 850, 1300 and 1550 nm.

Safety


Because the infrared light used in communications can not be seen, there is a potential laser safety
Laser safety
Laser safety is safe design, use and implementation of lasers to minimize the risk of laser accidents, especially those involving eye injuries. Since even relatively small amounts of laser light can lead to permanent eye injuries, the sale and usage of lasers is typically subject to government...

 hazard to technicians. In some cases the power levels are high enough to damage eyes, particularly when lenses or microscopes are used to inspect fibers which are inadvertently emitting invisible IR. Inspection microscopes with optical safety filters are available to guard against this.

Small glass fragments can also be a problem if they get under someone's skin, so care is needed to ensure that fragments produced when cleaving
Cleave (fiber)
A cleave in an optical fiber is a deliberate, controlled break, intended to create a perfectly flat endface, perpendicular to the longitudinal axis of the fiber...

 fiber are properly collected and disposed of appropriately.

See also


  • TIA/EIA-568-B Color coding for electrical cable
  • Optical fiber connector
    Optical fiber connector
    An optical fiber connector terminates the end of an optical fiber, and enables quicker connection and disconnection than splicing. The connectors mechanically couple and align the cores of fibers so that light can pass...

     Fiber Optic connector types
  • Optical attenuator
    Optical attenuator
    An optical attenuator is a device used to reduce the power level of an optical signal, either in free space or in an optical fiber. The basic types of optical attenuators are fixed, step-wise variable, and continuously variable....

     Fiber optic attenuator
  • Submarine communications cable
    Submarine communications cable
    A submarine communications cable is a cable laid on the sea bed between land-based stations to carry telecommunication signals across stretches of ocean....

  • Optical communication
    Optical communication
    Optical communication is any form of telecommunication that uses light as the transmission medium.An optical communication system consists of a transmitter, which encodes a message into an optical signal, a channel, which carries the signal to its destination, and a receiver, which reproduces the...

  • Optical interconnect
    Optical interconnect
    Optical interconnect is a way of communication by optical cables. Compared to traditional cables, optical wires are capable of a much higher bandwidth, from 10 Gb/s up to 100 Gb/s....

  • Optical power meter
    Optical power meter
    An optical power meter is a device used to measure the power in an optical signal. The term usually refers to a device for testing average power in fiber optic systems...

  • Optical time-domain reflectometer
  • Parallel optical interface
    Parallel optical interface
    A parallel optical interface is a form of fiber optic technology aimed primarily at communications and networking over relatively short distances , and at high bandwidths....

  • Interconnect bottleneck
    Interconnect bottleneck
    The interconnect bottleneck, the point at which integrated circuits reach their capacity, is expected sometime around 2010.Improved performance of computer systems has been achieved, in large part, by downscaling the IC minimum feature size. This allows the basic IC building block, the transistor,...


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