FOA Guide

Topic: Fiber Optic Jargon

Table of Contents: The FOA Reference Guide To Fiber Optics

What is fiber optics?

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
Fiber Optics, as an international technology, utilizes the metric system as the standard form of measurement.

Several of the more common terms:
Meter: 3.28 feet, 39.37 inches. Fiber optic cable lengths are generally expressed in meters or kilometers.
Kilometer: 1000 meters / 3,281 feet / 0.62 miles.
Micron: 1/1,000,000 th of a meter. 25 microns equal 0.001 inch. This is the common term of measurement for fiber diameters, most of which are 125 microns in outside diameter.
Nanometer: One billionth of one meter. This term is commonly used in the fiber optics industry to express wavelength of transmitted light, e.g 850 or 1300 nm.



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 More on POF.

Bend insensitive (BI) fiber: fiber that has been designed and manufactured to reduce losses caused by bends in the fiber. It is used in cables that are more likely to incur stress losses such as premises cables and microcables with densely-packed fibers. See this page on BI fibers.

For more on optical fiber, go here.

Fiber Optic Cable

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. 

fiber optic cable

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

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.

Armor: Discourages rodents from chewing through the cable and prevents crushing of the cable.

(Go here for more on cables)

Termination and Splicing

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.)

fiber optic connector
Ferrule: A tube which holds a fiber for alignment, usually part of a connector

Splice: a permanent joint between two fibers

Mechanical Splice: A splice where the fibers are aligned and held 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, etc.

Here's more on terminations and splicing


Fiber Performance Specifications

Terms you use when you want to specify 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."

3 fiber strippers

Cleaver: A tool that precisely "breaks" the fiber to produce a flat end for polishing or splicing.

Scribe: A hard, sharp tool that scratches the fiber to allow cleaving.

Polishing Puck: for connectors that require polishing, the puck holds the connector in proper alignment to the polishing film (the round metal disk in the photo above.)

Polishing Film: Fine grit film used to polish the end of the connector ferrule (the white and yellow films on the polishing plate above.)

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.

Test Equipment

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.

For more on testing, go here.

For a complete glossary, go here.

Test Your Comprehension

Table of Contents: The FOA Reference Guide To Fiber Optics


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