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FAQ - Fibre Optics

Question: How does a beam of light carry information?

Answer: It’s Magic!

Real Answer: The one's and zero's of the binary data are converted to light pulses and sent down the fibre at very high frequencies.

Refraction diagram

Fibre Optics send signals via light, down hair-thin strands of glass (or plastic) fibre. This light is "guided" down the core of the fibre, which is surrounded by an optical material called "cladding" which traps the light in the core using an optical technique called "total internal reflection”. The fibre is coated with a protective plastic covering called the "primary buffer coating" that protects it from moisture and other damage. More protection is provided by the "cable" which has the fibres and strength members inside an outer covering called a "jacket".

What are Multimode & Single mode Fibres?

Multimode & Single mode fibre are the most commonly types of fibre. Both fibres are 125 microns in outside diameter - a micron is one one-millionth of a meter and 125 microns is 0.005 inches- a bit larger than the typical human hair. Multimode fibre has light traveling in the core in many rays, called modes. It has a bigger core (62.5 or 50 microns) and is used with LED sources at wavelengths of 850 and 1300 nm (see below) for slower local area networks (LANs), and lasers at 850 and 1310 nm for networks running at gigabits per second or more. Single mode fibre has a much smaller core, only about 9 microns, so that the light travels in only one ray. It is used for longer distance applications with laser sources at 1300 and 1550 nm.

Step index multimode was the first fibre design but is too slow for most uses, due to the dispersion caused by the different path lengths of the various modes. Step index fibre is rare - only Plastic Optical Fibre (POF) uses a step index design today.

Graded index multimode fibre uses variations in the composition of the glass in the core to compensate for the different path lengths of the modes. It offers hundreds of times more bandwidth than step index fibre.

Single mode fibre shrinks the core down so small that the light can only travel in one ray. This increases the bandwidth to almost infinity - but it's practically limited to about 100,000 gigahertz - that's still a lot. It offers higher bandwidth and can go longer distances.

What are the different Fibre Optics Cable Types?

Cables (left to right): Zipcord, Tight Buffered, Loose Tube, Breakout

Simplex and zip cord:

Simplex cables are one fibre, tight-buffered (coated with a 900 micron buffer over the primary buffer coating) with Kevlar (aramid fibre) strength members and jacketed for indoor use. The jacket is usually 3mm (1/8 in.) diameter. Zipcord is simply two of these joined with a thin web. It's used mostly for patch cord and backplane applications, but zipcord can also be used for desktop connections.

Tight Buffered or Distribution cables:

They contain several tight-buffered fibres bundled under the same jacket with Kevlar strength members and sometimes fiberglass rod reinforcement to stiffen the cable and prevent kinking. These cables are small in size, and used for short, dry conduit runs, riser and plenum applications.

Breakout cables:

They are made of several simplex cables bundled together. This is a strong, rugged design, but is larger and more expensive than the distribution cables. It is suitable for conduit runs, riser and plenum applications. Because each fibre is individually reinforced, this design allows for quick termination to connectors and does not require patch panels or boxes.

Loose tube cables:

These cables are composed of several fibres together inside a small plastic tube, which are in turn wound around a central strength member and jacketed, providing a small, high fibre count cable. This type of cable is ideal for outside plant trunking applications, as it can be made with the loose tubes filled with gel or water absorbent powder to prevent harm to the fibres from water. It can be used in conduits.

Armoured Cable:

This cable can also be installed in conduits or by direct burial, often in areas where rodents are a problem. The cables usually have metal armouring between two jackets. This means the cable is conductive, so it must be grounded properly. The most common types of armouring are Corrugated Steel Tape Armour- CSTA, also known as STA and Steel Wire Armour- SWA. Steel Wire Braid or SWB armouring is also used.

Aerial cable:

Aerial cables are for outside installation on poles. They can be lashed to a messenger or another cable (common in CATV) or have metal or aramid strength members to make them self supporting.

Connector types:

Typically there are three main styles of connector that are used day to day on standard glass fibre cable, these are, LC, SC and ST.

LC Connector
A cost effective, small form factor fibre optic connector that helps to reduce space on panels or outlets by up to 50%.

SC Connector
Available in single mode for both PC and APC and in multimode PC.

ST Connector
Quick release bayonet style body and spring loaded ferrule.

There are many other types available, all of which we are able to supply/ terminate including Angled Polished Connectors (APC). We also offer Military style connectors, Neutrik opticalCON, Expanded Beam, Break Away connectors and so on.

What distances can I run and at what speeds using fibre optic cables?

 Core/Cladding Diameter (µm)TypeFast Ethernet Distance (metres)Gigabit Ethernet Distance (metres)10 Gigabit Ethernet Distance (metres)40 Gigabit Ethernet Distance (metres)
OM1 62.5/125 Multimode 2km at 850 nm 300 M 850 nm
600 M 1310 nm
33 M at 850 nm
300 M at 1310 nm
Not supported
OM2 50/125 Multimode 2km at 850 nm 600 M at 850 nm
600 M at 1310 nm
82 M at 850 nm
300 M at 1310 nm
Not supported
OM3 50/125 Multimode 2km at 850 nm 1000 M at 850 nm
600 M at 1310 nm
300 M at 850 nm
300 M at 1310 nm
OM4 50/125 Multimode 2km at 850 nm 1040 M at 850 nm
600 M at 1310 nm
550 M at 850 nm
300 M at 1310 nm
OS1 9/125 Single Mode 2km at 850 nm 5 km at 1310 nm 10 km at 1310 nm 40km
OS2 9/125 Single Mode 40km at 1310 nm 100km at 1310 nm 40km at 1310 nm 40km

Is Copper Cheaper Than Fibre?

Fibre optics is always assumed to be much more expensive than copper cabling. Whatever you look at - cable, terminations or networking electronics - fibre costs more, although as copper gets faster (e.g. Cat 6) it gets more expensive, almost as much as fibre. However, there is more to consider in making the decision.

LANs (local area networks) use fibre optics primarily in the backbone but increasingly to the desk. The LAN backbone often needs longer distance than copper cable (Cat 5/5e/6) can provide and of course, the fibre offers higher bandwidth for future expansion. Most large corporate LANs use fibre backbones with copper wire to the desktop.

Long Cable Runs

Most networks are designed around structured cabling installed per EIA/TIA 568 standards. This standard calls for 90 meters (295 feet) of permanently installed unshielded twisted pair (UTP) cable and 10 meters (33 feet) of patch cords. But suppose you need to connect two buildings or more? The distance often exceeds the 90 metres by the time you include the runs between the buildings plus what you need inside each building. By the time you buy special aerial or underground waterproof copper cable and repeaters, you will usually spend more than if you bought some outside plant fibre optic cable and a couple of inexpensive media converters. It can actually work out cheaper than running multiple copper links. (see our network hardware section for product information and pricing).

Industrial Networks

In an industrial environment, electromagnetic interference (EMI) is often a big problem. Industrial equipment can generate a tremendous amount of electrical noise that can cause major problems with copper cabling, especially unshielded cable like Cat 5. In order to run copper cable in an industrial environment, it is often necessary to pull it through conduit to provide adequate shielding.

With fibre optic cable you have complete immunity to EMI. You only need to choose a cable type that is rugged enough for the installation. Fibre optic cable can be installed easily from point to point, passing right next to major sources of EMI with no effect and conversion from copper networks is easy with media converters, (see our Industrial Hardware pages for details).

High Speed Networking

It was over a year after Gigabit Ethernet (GbE) became available on fibre optics that it finally become available on Cat 5e. It took another couple of years before GbE on copper became significantly less expensive.


So when it comes to costs, do not assume fibre is always more expensive than copper, as you could be missing a trick.

OS1 vs OS2 What is the difference?

Click here to find out more about OS1 vs OS2

OM3 vs OM4 What is the difference?

First, OM stands for optical multimode. Both OM3 an OM4 are 50/125 core fiber but they have different internal construction that allows the OM4 fiber to provide the same performance as OM3 but for longer distances. The reason for this is the difference in bandwidth, OM3 has 2500 megahertz bandwidth, OM4 has 4700 megahertz bandwidth. What this translates to is longer transmission distances for the OM4 fiber. So you will need to know the distance of the fiber run in order to help decide which kind of fiber and fiber accessories need to be used.

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