Reference Guide To Fiber Optics
|Topic: Outside Plant Fiber Optic Jargon||Table of Contents: The FOA Reference Guide To Fiber Optics|
Fiber Optic Jargon
key to understanding any technology is understanding the language of
the technology – the jargon. We’ve started this book with an overview
of fiber jargon to introduce you to the language of fiber optics and
help you understand what you will be reading in the book. While we try
to use the most common terminology, some particular applications for
optical fiber have their own specialized terms, and when possible, we
will try to include those terms also. We suggest you read this section
first to help your understanding of the rest of the book and refer back
to it when you encounter a term that you do not recognize. You can also
use the definitions in the Glossary or the FOA Online Reference Guide for more explanations.
Fiber optics is sending signals from one location to another in the form of modulated light guided through hair-thin fibers of glass or plastic. These signals can be analog or digital and voice, data or video information. Fiber can transport more information longer distances in less time than any copper wire or wireless method.
It's powerful and very fast - offering more bandwidth than any other form of communication!
First you need to know the language - the "jargon" - here's a list of terms you should know:
The Metric System
Optical Fiber: Thin strands of highly transparent glass
or plastic that guide light.
Core: The center of the fiber where the light is transmitted.
Cladding: The outside optical layer of the fiber that traps the light in the core and guides it along - even through curves.
Buffer coating or primary buffer coating: A hard plastic coating on the outside of the fiber that protects the glass from moisture or physical damage. The buffer is what one strips off the fiber for termination or splicing.
Mode: A single "electromagnetic field pattern" (think of a ray of light) that travels in fiber.
Multimode fiber: has a larger core (almost always 50 or 62.5 microns - a micron is one one millionth of a meter) and is used with laser or LED sources at wavelengths of 850 and 1300 nm for short distance, lower speed data networks like LANs.
Singlemode fiber: has a much smaller core, only about 8-9 microns, so it only transmits one mode. Singlemode is used for telephony (long distance, metropolitan and fiber to the home) and CATV with laser sources at 1310 to 1550 nm. It can go very long distances at very high speeds.
Fiber ID: Fibers are identified by their core and cladding diameters expressed in microns (one millionth of a meter), e.g. 50/125 micron multimode fiber. Most multimode and singlemode fibers have an outside diameter of 125 microns - about 0.005 - 5 thousandths of an inch - just slightly larger than a human hair. International standards also have names for fibers that call out detailed specifications that include bandwidth capability or other special characteristics. Multimode fiber standards. Singlemode fiber standards.
Plastic optical fiber (POF): is a large core (usually 1mm) multimode fiber that can be used for short, low speed networks. POF is used in consumer HiFi and as part of a standard for car communication systems called MOST (go to http://www.mostcooperation.com/) More on POF.
For more on optical fiber, go here.
Cable: Cable provides protection to the fiber from stress during installation and from the environment once it is installed. Cables may contain from only one to hundreds of fibers inside. Cables come in three varieties: tight buffer with a thick plastic coating on the fibers for protection, used mainly indoors, loose-tube, where fibers with only a primary buffer coating are inside plastic tubes, and ribbon, where fibers are made into ribbons to allow small cables with the largest numbers of fibers.
Strength members: Aramid fibers (Kevlar is the duPont trade name) used to pull the cable. The term is also used for the fiberglass rod in some cables used to stiffen it to prevent kinking.
crushing and discourages rodents from damaging cable by chewing through
it. Some cable called armored also includes layers of strengthening
wires for use in extreme environments such as encountered by submarine
(Go here for more on cables)
Connector: A non-permanent device for connecting two fibers in a non-permanent joint or connect fibers to equipment. Connectors are expected to be disconnected occasionally for testing or rerouting. (Parts for an ST connector are shown.)
Splice: a permanent joint between two fibers
Mechanical Splice: A splice where the fibers are aligned created by mechanical means
Fusion Splice: A splice created by welding or fusing two fibers together
Fusion Splicer: An instrument that splices fibers by fusing or welding them, typically by electrical arc.
Hardware: Terminations and Splices require hardware for
protection and management: patch panels, splice closures (shown below), etc.
(Here's more on terminations)
Terms you use when you want to specity fibers or make measurements of fiber optic components or cable plants:
Attenuation: The reduction in optical power as it passes along a fiber, usually expressed in decibels (dB). For fibers, we talk about attenuation coefficient or attenuation per unit length, in dB/km. See optical loss
Bandwidth: The range of signal frequencies or bit rate within which a fiber 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 100 times overall, -30 means another 10 times or 1000 times overall and so on.
dB: Optical power referenced an arbitrary zero level, used to measure loss
dBm: Optical power referenced to 1 milliwatt, used to measure optical power from transmitters or at receivers. See optical power.
Optical Loss: The amount of optical power lost as light is transmitted through fiber, splices, couplers, etc, expressed in "dB."
Optical Power: is measured in "dBm", or decibels
referenced to one miliwatt 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 the majority of loss in optical fibers 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). Fiber is mostly used in the infrared region where the light is invisible to the human eye. Most fiber specifications (attenuation, dispersion) are dependent on wavelength.
Dispersion: Pulse spreading caused by modes in multimode fiber (modal dispersion), the difference in speed of light of different wavelengths (CD or chromatic dispersion in multimode or singlemode fiber ) and polarization (PMD or polarization mode dispersion in singlemode)
Go here for more information on testing.
Terms that describe the tools needed for installation and termination:
Jacket Slitter or Stripper: A cutter for removing the heavy outside jacket of cables
Fiber Stripper: A precise stripper used to remove the buffer coating of the fiber 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 fiber to produce a flat end for polishing or splicing.
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 fibers in the cable to add mechanical strength.
Fusion Splicer: An instrument that welds two fibers together into a permanent joint.
Here is more information on termination.
Terms that describe fiber optic test equipment:
Optical Power Meter: An instrument that measures optical power from the end of a fiber
Test Source: an instrument that uses a laser or LED to send an optical signal into fiber for testing loss of the fiber
Optical Loss Test Set (OLTS):
A measurement instrument that includes both a meter and source used for
measuring insertion loss of installed cable plants or individual cables. ALso called light source and power meter (LSPM.)
Reference Test Cables: short, single fiber 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.
Fiber Tracer: An visible light source (LED or flashlight) that allows visual checking of continuity and tracing for correct connections such as duplex connector polarity
Visual Fault Locator: A high-powered visible laser light source that allows continuity testing, fiber tracing and location of faults near the end of the cable.
Inspection Microscope: used to inspect the end surface of a connector for faults such as scratches, polish or dirt.
Optical Time Domain Reflectometer (OTDR):
An instrument that uses backscattered light to take a snapshot of an
optical fiber which can be used to measure fiber length, splice loss,
fiber attenuation and for fault location in optical fiber from only one
end of the cable.
Specialized Testers: Long
distance networks may need testing for chromatic dispersion (CD) and
polarization mode dispersion (PMD). Systems using wavelength-division
multiplexing may need testing for spectral attenuation. Each
performance factor has a specialized tester for that specification.
For more on testing, go here.
For a complete glossary, go here.
The FOA Reference Guide to Outside Plant Fiber Optics
You can buy the printed version of the The FOA Reference Guide to Outside Plant Fiber Optics from the FOA eStore or Amazon.