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Fibre Optic Cabling Definitions

Multi-mode (OM1, OM2, OM3, OM4)
Multi-mode optical fibre is a type of optical fibre mostly used for communication over short distances, such as within a building or on a campus.  In optical fibre technology, multi-mode fibre is optical fibre that is designed to carry multiple light rays or modes at the same time, each at a slightly different reflection angle within the optical fibre core.
Multi-mode fibre transmission is used for relatively short distances because the modes tend to disperse over longer lengths. Typical multimode fibre core diameters are 50, 62.5, and 100 micrometres.

This chart compares distances achieved with each fibre type;


* overfill launch bandwidth.

Single-mode (OS1, OS2)
Single-mode fibre gives you a higher transmission rate than Multi-mode fibre and up to 50 times more distance. Single Mode has a much smaller core size of 9 microns and has a single light path and can travel much longer distances to up to 100km.
The small core and single light-wave virtually eliminate any distortion that could result from overlapping light pulses, providing the least signal attenuation and the highest transmission speeds of any fibre cable type.  Single-mode optical fibre is an optical fibre in which only the lowest order bound mode can propagate at the wavelength of interest typically 1300 to 1320nm.

Tight Buffered, Loose Tube
Loose tube cables are designed for harsh environment conditions in the outdoors. They protect the Fibre core, cladding, and Coating by enclosing everything within fairly rigid protective sleeves or tubes. Many loose tube cables contain a water resistant Gel surrounding the fibres. The gel helps protect the fibers from moisture, making the cables ideal for high humidity environments, where water or condensation may otherwise be problematic. Despite the benefits, gel filled loose tube cables are not the right choice if the Cable needs to be submerged in water, or routed around multiple bends. Excess Strain may cause the fibers to emerge from the gel.
Tight buffered cables are optimal for indoor applications. Being more robust than loose-tube cables, they are best suited for moderate length LAN or WAN connections, long indoor runs, direct burial, and for underwater use. Rather than using the gel Layer loose tube has, tight buffered cables have a two-layer coating. The first is plastic, and the other, waterproof acrylate. The Acrylate keeps moisture away from the cable. The Core is never exposed when bend or compressed underwater. Tight buffered cables may be easier to install, because there is no gel to clean up and it does not require a fan out kit for Splicing or termination.

Rodent Resistant (CST), Steel Wire Armoured (SWA)
Optical fibre cables can be damaged seriously by gnawing rodents. Such damage can impact the long-term reliability of both outdoor and indoor installed cables. Rodent protection for optical fibre cables is generally based on making it difficult for the animal to gnaw into the cable core. Corrosion Steel Tape (CST ) gives a very effective protection and the cable is relatively lightweight, and has a good flexibility.
Steel Wire Armour (SWA) makes it suitable for all external applications even in the harshest of environments. As well as being tough enough to pull through ducts, directly bury in the ground or install in any environment susceptible to vandalism, the cable also protects against moisture and is extremely rodent resistant. The outer sheath is also low smoke zero halogen making it safe to install internally.

Fibre To The Desk (FTTD)
FTTD represents a new type of optical cables especially designed for last mile network cabling. Considering the increasing development of broadband services, this type of cable will be one of the most rapidly developing sectors in the next few years.
These cables run vertically from the bottom to the top of the building, and one or more of the cables in the bundle can be branched off at any point and connected to the end user. Either through an optical connector installed in a wall socket where computers/printers/IP phones are connected with an optical cable to the wall socket, this assumes that optical Ethernet ports become standard in office equipment. Alternatively an individual fibre is terminated in an opto-electronic converter installed in a wall socket. The converter has a RJ-45 socket for UTP cabling so legacy equipment based on UTP can be used.

An optical fibre connector terminates the end of an optical fibre, and enables quicker connection and disconnection than splicing. The connectors mechanically couple and align the cores of fibres so light can pass. Better connectors lose very little light due to reflection or misalignment of the fibres.

LC: A push/pull type fibre optic connector similar to SC but half the size. Often found on SFP/mini GIBC's and current generation switches.
Ferule - 1.25mm
ST: A metal cylindrical keyed bayonet type fibre connector that is spring loaded and attached using a push and twist motion. It is most widely used as a connector for multimode networks.
Ferule - 2.5mm
SC: A plastic push/pull type connector that is used for multimode and singlemode due to its excellent performance. Often used on GBIC's and legacy switches.
Ferule - 2.5mm
MT-RJ: A duplex only push/pull small form factor fibre connector (about half the size of an SC) which houses two fibres and mates with locating pins on the plug. Easy to install but not widely used.
Ferule - 2.45x4.4mm

A variety of optical fibre connectors are available, but SC and LC connectors are the most common types of connectors on the market.  In many data centre applications, small (e.g. LC) and multi-fibre (e.g., MT-RJ) connectors are replacing larger, older styles (e.g., SC), allowing more fibre ports per unit of rack space. The MT-RJ Connector for example is significantly lower in cost and smaller in size than the SC Duplex interface.

Campus Backbone Links
A backbone is the part of the computer network infrastructure that interconnects different networks and provides a path for exchange of data between these different networks. A backbone may interconnect different local area networks in offices, campuses or buildings. When several local area networks (LAN) are being interconnected over a considerable area, the result is a wide area network (WAN), or metropolitan area network (MAN) if it happens to serve the whole city. The most common deployment for single mode fibre is in the campus backbone for inter-building networks, such as on a university campus, military installation, multi-building factory complex, or a large industrial or business park.

Building Backbone links
These are multicore fibre links between a central comms room to distributed cabinets.  The backbone fibre cable provides the physical link between the floor distributor and the building distributor. Backbone fibre cable is available in counts of 6-, 12-, 24-, 48-, 72- and 96- fibres. Each pair of 250 μm coated fibres is contained within a separate buffer tube. The cable jacket can be LSOH (low smoke, zero halogen rated), OFNP (plenum rated), or OFNR (riser rated). Easy to use colour coding enables easy installation and convenient fibre cable management.

Fibre patch panels
Fibre patch panels provide a convenient way to rearrange fibre cable connections and circuits. A simple patch panel is a metal frame containing bushings in which fiber optic cable connectors plug in on either side. One side of the panel is usually fixed, meaning that the fiber cables are not intended to be disconnected. On the other side of the panel, fiber cables can be connected and disconnected to arrange the circuits as required.

Fibre containment systems
This is a fully enclosed system which protects the fibre from dirt and dust, the duct is strong enough to protect cables against the most rigorous of conditions. The easy access cover allows fibre optic cables to be installed or removed at any time without the need to disconnect the whole system.

Testing is carried out with an OTDR (Optical Time Domain Reflectometer). This is a test instrument that analyses the light loss in an optical fibre. Used to find faults, splices and bends in the line, it works by sending out a light pulse and measuring its reflection. Such devices can measure fibre lines that are longer than 150 miles.

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