What is fibre optics?

Picture sending signals zipping along from one location to another in the form of light guided through thin fibres of glass or plastic. These signals can be analogue or digital - voice, data or video information. Fibre can transport more information for longer distances in less time than any copper wire.

It's powerful and fast, fast, fast!

First get to know the language - the "jargon" - here's a list of terms you should get to know:


Metric system

Fibre optics, as a universal technology, utilises the metric system as the standard form of measurement. Several of the more common terms:


39.37 inches


1000 meters / 3,281 feet / 0.62 miles


1/1,000,000 th of a meter. 25 microns equal 0.001 inch. This is the common term of measurement for fibres


One billionth of one meter. This term is commonly used in the fibre optics industry to express wavelength or frequency of transmitted light


Let's start with fibre


Optical fibre

Thin strands of highly transparent glass or sometimes plastic that guide light


The centre of the fibre where the light is transmitted


The outside optical layer of the fibre that traps the light in the core and guides it along - even through curves

Buffer coating or primary coating: A hard plastic coating on the outside of the fibre that protects the glass from moisture or physical damage


A single electromagnetic field pattern (think of a ray of light) that travels in fibre

Multimode fibre

Has a bigger core (almost always 50 or 62.5 microns - a micron is one one millionth of a meter) and is used with LED sources at wavelengths of 850 and 1300 nm for short distance, lower speed networks like LANs

Singlemode fibre

Has a much smaller core, only about 9 microns, and is used for telephony and CATV with laser sources at 1300 and 1550 nm. It can go very long distances at very high speeds

Both multimode and singlemode fibre have an outside diameter of 125 microns - about 5 thousandths of an inch - just slightly larger than a human hair

Plastic optical fibre (POF)

A large-core (about 1mm) multimode fibre that can be used for short, low speed networks. POF is used in consumer HiFi and starting to be used as part of a new standard for car communication systems called MOST


Terms that describe fibre optic cable



Fibre needs protection to survive all the places it gets installed and it's the cable that provides it. Cables may have from one to hundreds of fibres inside


The tough outer covering on the cable. Cables installed inside buildings must meet fire codes by using special jacketing materials

Strength members

Aramid fibres (Kevlar is the duPont trade name) used to pull the cable. The term is also used for the fibreglass rod in some cables used to stiffen it to prevent kinking


Discourages rodents from chewing through it





A non-permanent device for connecting two fibres or fibres to equipment where they are expected to be disconnected occasionally for testing or rerouting. It also provides protection to both fibres. (Parts for an ST connector are shown) [INSERT PIC]


A tube which holds a fibre for alignment, usually part of a connector


A permanent joint between two fibres

Mechanical splice

A splice where the fibres are aligned created by mechanical means

Fusion splice

A splice created by welding or fusing two fibres together

Fusion splicer

An instrument that splices fibres by fusing or welding them, typically by electrical arc


Terminations and splices require hardware for protection and management: patch panels, splice closures, etc


Fibre performance specifications

Terms you use when you want to take your measurements:


The reduction in optical power as it passes along a fibre, usually expressed in decibels (dB). See optical loss


The range of signal frequencies or bit rate within which a fibre optic component, link or network will operate

Decibels (dB)

A unit of measurement of optical power which indicates relative power. A -10 dB means a reduction in power by 10 times, -20 dB means another 10 times or 10 times overall, -30 means another 10 times or 1000 times overall, and so on


Optical power referenced an arbitrary zero level


Optical power referenced to 1 milliwatt

Micron (m)

A unit of measure used to measure wavelength of light

Nanometre (nm)

A unit of measure used to measure the wavelength of light (meaning one one-billionth of a meter)

Optical loss

The amount of optical power lost as light is transmitted through fibre, splices, couplers, etc, expressed in dB

Optical power

Measured in "dBm", or decibels referenced to one milliwatt of power. While loss is a relative reading, optical power is an absolute measurement, referenced to standards. You measure absolute power to test transmitters or receivers and relative power to test loss


The change of direction of light after striking small particles that causes loss in optical fibres and is used to make measurements by an OTDR


A term for the colour of light, usually expressed in nanometres (nm) or microns (m). Fibre is mostly used in the infrared region where the light is invisible to the human eye


Terms that describe the tools you will need for installation and termination


Jacket slitter or stripper

A cutter for removing the heavy outside jacket of cables

Fibre stripper

A precise stripper used to remove the buffer coating of the fibre itself for termination. There at three types in common use, called by their trade names: "Miller Stripper", "No-Nik" and "Micro Strip"


A tool that precisely "breaks" the fibre to produce a flat end for polishing or splicing


A hard, sharp tool that scratches the fibre to allow cleaving

Polishing puck

for connectors that require polishing, the puck holds the connector in proper alignment to the polishing film

Polishing film

Fine grit film used to polish the end of the connector ferrule


A tool that crimps the connector to the aramid fibres in the cable to add mechanical strength


Terms that describe test equipment you will need


Optical power meter

An instrument that measures optical power from the end of a fibre

Test source

An instrument that uses a laser or LED to send an optical signal into fibre for testing loss of the fibre

Optical Loss Test Set (OLTS)

A measurement instrument for optical loss that includes both a meter and source

Reference test cables

Short, single fibre cables with connectors on both ends, used to test unknown cables

Mating adapter

Also called splice bushing or couplers, allow two cables with connectors to mate

Fibre tracer

An instrument that allows visual checking of continuity and tracing for correct connections

Visual fault locator

A device that allows visual tracing and testing of continuity


Used to inspect the end surface of a connector for flaws or dirt


An instrument that uses back scattered light to find faults in optical fibre and infer loss from only one end of the cable