Introduction to Fibre Optics Jargon
This page provides an introduction to fibre optics jargon with particular reference to the following areas:
Optical Fibre
Optical Fibre: Thin strands of highly transparent glass or sometimes plastic that guide light.Core: The central region of an optical fibre through which light is transmitted.
Cladding: The material surrounding the core of an optical 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.
Mode: A reflective path that a light ray takes in a fibre.
Multimode fibre: has a bigger core (usually 62.5 microns) and is used with LED sources at wavelengths of 850 and 1300 nm. Multimode fibres are generally 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 - just slightly larger than a human hair.
Plastic optical fibre (POF): is a large core (about 1mm) multimode fibre that can be used for short, low speed networks. POF is used in consumer HiFi.
Fibre Optic Cables
Cable: fibre needs protection to survive the various places it gets installed and it's the cable that provides it. Cables may have from one to hundreds of fibres inside. Jacket: 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.
Armor: Discourages rodents from chewing through the cable.
Termination
Connector: A mechanical device to provide a means for aligning, attaching and decoupling a fibre to a transmitter, receiver or other fibre. Commonly used connectors include 568SC (Duplex SC), ST, FDDI, FC, D4 and Biconic. Ferrule: A tube which holds a fibre for alignment, usually part of a connector
Splice: a permanent joint between two fibres
Mechanical Splice: A splice where the fibres are aligned 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.
Fibre Performance Specifications
Attenuation: The reduction in optical power as it passes along a fibre, usually expressed in decibels (dB). See optical loss.Bandwidth: The information-carrying capacity of an optical fibre (measured in MHz/km).
Decibels (dB): A unit of measurement of optical power which indicates relative power. -10dB means a reduction in power by 10 times, -20dB means by 100 times, -30dB reduction in power by 1000 times and so on.
dBm: Optical power referenced to 1 milliwatt e.g. 0dBm = 1mW, 10dBm = 10mW, 20dBm = 100mW, 30dBm = 1000mW or 1W, etc.
Micron (m): A unit of measure used to measure wavelength of light.
Nanometer (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: is 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.
Scattering: 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
Wavelength: A term for the color of light, usually expressed in nanometers (nm) or microns (m). Fibre is mostly used in the infrared region where the light is invisible to the human eye.
Tools
Jacket Slitter or Stripper: A cutter for removing the heavy outside jacket of cablesFibre 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."
Cleaver: A tool that precisely "breaks" the fibre to produce a flat end for polishing or splicing.
Scribe: 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.
Crimper: A tool that crimps the connector to the aramid fibres in the cable to add mechanical strength.
Test Equipment
Optical Power Meter: An instrument that measures optical power from the end of a fibreTest 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
Optical Time Domain Reflectometer (OTDR): A device for finding breaks in fibre optic cables or determining the cable's length and other characteristics
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.
Microscope: used to inspect the end surface of a connector for flaws or dirt.
For a more detailed glossary of fibre optic terms click here .