Glossary of Terms


Active components

Active components rely on a source of energy (usually from the DC circuit, which we have chosen to ignore) and usually can inject power into a circuit, though this is not part of the definition. Active components include amplifying components such as transistors, triode vacuum tubes (valves), and tunnel diodes.


An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the power of a signal (a time-varying voltage or current). It is a two-port electronic circuit that uses electric power from a power supply to increase the amplitude of a signal applied to its input terminals, producing a proportionally greater amplitude signal at its output.

Amplitude modulation

Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave.



Attenuation in fiber optics, also known as transmission loss, is the reduction in intensity of the light beam (or signal) with respect to distance traveled through a transmission medium.



Bandwidth is the difference between the upper and lower frequencies in a continuous band of frequencies. Bandwidth is a key concept in many telecommunications applications. In radio communications, for example, bandwidth is the frequency range occupied by a modulated carrier signal.


Bit error rates

In digital transmission, the number of bit errors is the number of received bits of a data stream over a communication channel that have been altered due to noise, interference, distortion or bit synchronization errors.


Bit rate

In telecommunications and computing, bit rate (bitrate or as a variable R) is the number of bits that are conveyed or processed per unit of time. The bit rate is quantified using the bits per second unit (symbol: “bit/s”).



In a fiber optic cable, a buffer is one type of component used to encapsulate one or more optical fibers for the purpose of providing such functions as mechanical isolation, protection from physical damage and fiber identification.



The C-band is a designation by the Institute of Electrical and Electronics Engineers (IEEE) for a portion of the electromagnetic spectrum in the microwave range of frequencies ranging from 4.0 to 8.0 gigahertz (GHz). In erbium doped fiber amplifiers, the region of amplification approximately between wavelengths of 1530nm and 1580nm.


Chromatic dispersion

Chromatic dispersion (CD) is a characteristic of all fiber optics. It is caused by the fact that different wavelengths of light travel at different velocities within the glass.



Cladding in optical fibers is one or more layers of materials of lower refractive index, in direct contact with a core material of higher refractive index.


Dark fibers

A dark fiber or unlit fiber is an unused optical fiber, available for use in fiber-optic communication.


Dense wavelength division multiplexing (DWDM)

Dense wavelength division multiplexing (DWDM) refers originally to optical signals multiplexed within the 1550 nm band so as to leverage the capabilities (and cost) of erbium doped fiber amplifiers (EDFAs), which are effective for wavelengths between approximately 1525–1565 nm (C band), or 1570–1610 nm (L band). EDFAs were originally developed to replace SONET/SDH optical-electrical-optical (OEO) regenerators, which they have made practically obsolete.



A dielectric (or dielectric material) is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in an electrical conductor but only slightly shift from their average equilibrium positions causing dielectric polarization. Because of dielectric polarization, positive charges are displaced in the direction of the field and negative charges shift in the opposite direction.



In optics, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency


Distributed feedback

A distributed feedback laser (DFB) is a type of laser diode, quantum cascade laser or optical fiber laser where the active region of the device is periodically structured as a diffraction grating. The structure builds a one-dimensional interference grating (Bragg scattering) and the grating provides optical feedback for the laser. The reflection of the coating can be varied to make laser oscillate near the Bragg Wavelength.


Erbium-doped fiber amplifier (EDFA)

Doped fiber amplifiers (DFAs) are optical amplifiers that use a doped optical fiber as a gain medium to amplify an optical signal. They are related to fiber lasers. The signal to be amplified and a pump laser are multiplexed into the doped fiber, and the signal is amplified through interaction with the doping ions. The most common example is the erbium doped fiber amplifier (EDFA), where the core of a silica fiber is doped with trivalent erbium ions and can be efficiently pumped with a laser at a wavelength of 980 nm or 1,480 nm, and exhibits gain in the 1,550 nm region.



Ethernet is a family of computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1983 as IEEE 802.3, and has since been refined to support higher bit rates and longer link distances. Over time, Ethernet has largely replaced competing wired LAN technologies such as Token Ring, FDDI and ARCNET.


Event dead zone

The blind area known as an event dead zone which occurs at the launch of the pulse.


Fabry Perot (FP)

The Fabry Perot (FP) laser is the most common type of laser diode. It is used in OTDR design, is cost-effective and has the ability to deliver high output power level. It is used in singlemode OTDR applications at various wavelengths such as 1310 nm, 1550 nm and 1625 nm. A Fabry Perot laser emits light at various discrete wavelengths which delivers spectral width between 5 nm to 8 nm.



The ferrule is the precision component of a fiber optic connector and is what provides the precise alignment of the fiber core axis in the connector.
Fiber Distributed Data Interface (FDDI), 13 Fiber Distributed Data Interface (FDDI) is a standard for data transmission in a local area network. It uses optical fiber as its standard underlying physical medium.


Fiber link

A fiber-optic link (or fiber channel) is a part of an optical fiber communications system which provides a data connection between two points (point-to-point connection).
Fiber optic patch cords, 60 A fiber optic patch cord is a fiber optic cable capped at either end with connectors that allow it to be rapidly and conveniently connected to CATV, an optical switch or other telecommunication equipment.


Four-wave mixing

Four-wave mixing (FWM) is an intermodulation phenomenon in non-linear optics, whereby interactions between two or three wavelengths produce two or one new wavelengths.


Frequency modulation

In telecommunications and signal processing, frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave.



Fiber to the x (FTTX) or fiber in the loop is a generic term for any broadband network architecture using optical fiber to provide all or part of the local loop used for last mile telecommunications.


Gallium arsenide

Gallium Arsenide (GaAs) is a semiconductor material and a compound of Gallium and Arsenic. Gallium arsenide is used in the manufacture of light-emitting diode s (LEDs), which are found in optical communications and control systems.


Hartley’s law

Hartley’s Law (1928) In 1928 information theorist Ralph V. R. Hartley of Bell Labs published “Transmission of Information,” in which he proved “that the total amount of information that can be transmitted is proportional to frequency range transmitted and the time of the transmission.”



The Institute of Electrical and Electronics Engineers (IEEE) is a professional formed in 1963 from the amalgamation of the American Institute of Electrical Engineers and the Institute of Radio Engineers. As of 2018, it is the world’s largest association of technical professionals. Its objectives are the educational and technical advancement of electrical and electronic engineering, telecommunications, computer engineering and allied disciplines.


Index matching gel

Index matching gel is a substance which has an index of refraction that closely approximates that of another object. In fiber optics and telecommunications, an index-matching material may be used in conjunction with pairs of mated connectors or with mechanical splices to reduce signal reflected in the guided mode (known as return loss).


Index of refraction (IOR)

In optics, the refractive index or index of refraction of a material is a dimensionless number that describes how light propagates through that medium. It is defined as n=c/v, where c is the speed of light in vacuum and v is the phase velocity of light in the medium. For example, the refractive index of water is 1.333, meaning that light travels 1.333 times faster in a vacuum than in the water. The refractive index determines how much the path of light is bent, or refracted, when entering a material.


Institute of Electrical and Electronics Engineers

see IEEE


Intelligent Transportation Systems (ITS)

An intelligent transportation system (ITS) is an advanced application which, without embodying intelligence as such, aims to provide innovative services relating to different modes of transport and traffic management and enable users to be better informed and make safer, more coordinated, and ‘smarter’ use of transport networks.


ISO/IEC 11801

International standard ISO/IEC 11801 Information technology — Generic cabling for customer premises specifies general-purpose telecommunication cabling systems (structured cabling) that are suitable for a wide range of applications (analog and ISDN telephony, various data communication standards, building control systems, factory automation). It covers both balanced copper cabling and optical fiber cabling.



Lashing is the process of taking any outdoor cable, usually a tray or instrumentation cable, and attaching it to a messenger wire so that it may be used in aerial applications.



The L band is the Institute of Electrical and Electronics Engineers (IEEE) designation for the range of frequencies in the radio spectrum from 1 to 2 gigahertz (GHz). In erbium doped fiber amplifiers, the region of amplification approximately between wavelengths of 1570nm and 1610.


Light amplification by stimulated emission of radiation (laser)

Short for light amplification by stimulated emission of radiation. A device that creates and amplifies electromagnetic radiation of a specific frequency through the process of stimulated emission. The radiation emitted by a laser consists of a coherent beam of photons, all in phase and having the same polarization. Lasers have many uses, such as cutting hard or delicate substances, reading data from compact disks and other storage devices, and establishing straight lines in geographical surveying.


Light source

In fiber optics, a source of light (laser, LED, etc.) is used to emit electromagnetic radiation in order to perform a specific task, whether detecting faults, breaks and microbends, characterizing link-loss or certifying LAN/WANs. As recommended by the ITU-T (G.983.3), light sources are also used to test PON networks at three different wavelengths (1310/1490/1550 nm).


Light-emitting diode (LED)

A light-emitting diode (LED) is a two-lead semiconductor light source. It is a p–n junction diode that emits light when activated. When a suitable current is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons.
Lightwave system, 8 Communication system used to send pulses of light from one destination to another (e.g. fiber optic network).


Mechanical splice

Mechanical splices are simply alignment devices and don’t permanently join two fibers together, designed to hold the two fiber ends in a precisely aligned position thus enabling light to pass from one fiber into the other.


Modal dispersion

Modal dispersion is a distortion mechanism occurring in multimode fibers and other waveguides, in which the signal is spread in time because the propagation velocity of the optical signal is not the same for all modes.



In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted.


Multimode (MM)

Multi-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Multi-mode fiber has a fairly large core diameter that enables multiple light modes to be propagated and limits the maximum length of a transmission link because of modal dispersion.



In telecommunications and computer networks, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium.


National Electric Code (NEC)

The National Electrical Code (NEC) or NFPA 70, is a United States code for the safe installation of electrical wiring and equipment.


Optical coupler

A fiber optic coupler is a device used in optical fiber systems with one or more input fibers and one or several output fibers. Light entering an input fiber can appear at one or more outputs and its power distribution potentially depending on the wavelength and polarization.


Optical return loss

Optical return loss is the loss of power in the signal returned/reflected by a discontinuity in a transmission line or optical fiber.


Optical time-domain reflectometer

An optical time-domain reflectometer (OTDR) is an optoelectronic instrument used to characterize an optical fiber. An OTDR is the optical equivalent of an electronic time domain reflectometer. It injects a series of optical pulses into the fiber under test and extracts, from the same end of the fiber, light that is scattered (Rayleigh backscatter) or reflected back from points along the fiber. The scattered or reflected light that is gathered back is used to characterize the optical fiber.


Outside plant (OSP)

In civilian (non-military) telecommunications, outside plant (OSP) refers to all of the physical cabling and supporting infrastructure (such as conduit, cabinets, tower or poles), and any associated hardware (such as repeaters) located between a demarcation point in a switching facility and a demarcation point in another switching center or customer premises.
Passive components, 60 Passive components can’t introduce net energy into the circuit. They also can’t rely on a source of power, except for what is available from the (AC) circuit they are connected to.



Phase is the position of a point in time (an instant) on a waveform cycle. A complete cycle is defined as the interval required for the waveform to return to its arbitrary initial value.
Phase modulation, 10 Phase modulation (PM) is a modulation pattern for conditioning communication signals for transmission. It encodes a message signal as variations in the instantaneous phase of a carrier wave.



A photodiode is a semiconductor device that converts light into an electrical current. The current is generated when photons are absorbed in the photodiode.



A photon is a tiny little particle of light, far too small to see individually. All light is made of photons.


Physical layer

The physical layer consists of the electronic circuit transmission technologies of a network.[2] It is a fundamental layer underlying the higher level functions in a network. Due to the plethora of available hardware technologies with widely varying characteristics, this is perhaps the most complex layer in the OSI architecture.



A fiber pigtail is a single, short, usually tight-buffered, optical fiber that has an optical connector pre-installed on one end and a length of exposed fiber at the other end.



Plenum cable (CMP) is electrical cable that is laid in the plenum spaces of buildings. All materials intended for use on wire and cables to be placed in plenum spaces are designed to meet rigorous fire safety test standards. A plenum cable can always replace riser cable, but riser cable cannot replace plenum cable in plenum spaces.



In telecommunications, a point-to-point connection refers to a communications connection between two Communication endpoints or nodes. An example is a telephone call, in which one telephone is connected with one other, and what is said by one caller can only be heard by the other.


Power meter

A device that measures the power of an optical signal in a fiber-optic system. When combined with an optical light source (OLS), it becomes an optical loss test set (OLTS) and can measure end-to-end attenuation. It can also be used with a visual fault locator (VFL). By combining various models, specific test setups can be created.



In telecommunication, a communication protocol is a system of rules that allow two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules syntax, semantics and synchronization of communication and possible error recovery methods. Protocols may be implemented by hardware, software, or a combination of both.


Public Switched Telephone Network (PSTN)

The public switched telephone network (PSTN) is the aggregate of the world’s circuit-switched telephone networks that are operated by national, regional, or local telephony operators, providing infrastructure and services for public telecommunication. The PSTN consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all interconnected by switching centers, thus allowing most telephones to communicate with each other. Originally a network of fixed-line analog telephone systems, the PSTN is now almost entirely digital in its core network and includes mobile[1] and other networks, as well as fixed telephones.


Pulse code modulation

Pulse-code modulation (PCM) is the process in which analog signals (e.g. audio) are converted into digital, binary (0 or 1), coded pulses.


Raman amplification

Raman amplification is based on the stimulated Raman scattering (SRS) phenomenon, when a lower frequency ‘signal’ photon induces the inelastic scattering of a higher-frequency ‘pump’ photon in an optical medium in the nonlinear regime. As a result of this, another ‘signal’ photon is produced, with the surplus energy resonantly passed to the vibrational states of the medium. This process, as with other stimulated emission processes, allows all-optical amplification.


Reflective event

A reflective event occurs when two fibers do not make direct contact with one another. There is an air-gap present between the two fibers causing the light to reflect.



A repeater is an electronic device that receives a signal and retransmits it. Repeaters are used to extend transmissions so that the signal can cover longer distances or be received on the other side of an obstruction.


Ring architecture

A ring network or architechture is a network topology in which each node connects to exactly two other nodes, forming a single continuous pathway for signals through each node – a ring. Data travels from node to node, with each node along the way handling every packet.



“Vertical riser” is a term for anything that rises vertically through a building, although it normally specifically refers to vertical riser ducts, pipes or conduits.


Semiconductor diode

A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals.[5] Semiconductor diodes were the first semiconductor electronic devices.


Slack cable

Slack, or extra, cable intentionally installed in order to make future cabling-system changes easier and less time-consuming.



SONET is the American National Standards Institute standard for synchronous data transmission on optical media. The international equivalent of SONET is synchronous digital hierarchy (SDH).



Sphalerite ((Zn, Fe)S) is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron. When iron content is high it is an opaque black variety, marmatite. It is usually found in association with galena, pyrite, and other sulfides along with calcite, dolomite, and fluorite. Miners have also been known to refer to sphalerite as zinc blende, black-jack and ruby jack.



Produced at an undesired frequency by a transmitter, causing interference, etc


Steiner Tunnel Test

The Steiner tunnel test is a widely used method of testing building interior wall and ceiling finishes for their ability to support and propagate fire, and for their tendency to emit smoke.



Telcordia Technologies, Inc., doing business as iconectiv, is an American subsidiary of the Swedish telecommunications company Ericsson. The company provides interconnection technology and clearinghouse solutions for numbering plan, routing, call billing, and technical standards coordination between competing telecommunications carriers.


Telecommunications Industry Association (TIA)

The Telecommunications Industry Association (TIA) is accredited by the American National Standards Institute (ANSI) to develop voluntary, consensus-based industry standards for a wide variety of Information and Communication Technologies (ICT) products, and currently represents nearly 400 companies.


Token Ring

Token Ring local area network (LAN) technology is a communications protocol for local area networks. It uses a special three-byte frame called a “token” that travels around a logical “ring” of workstations or servers. This token passing is a channel access method providing fair access for all stations, and eliminating the collisions of contention-based access methods.


Total internal reflection

Total internal reflection is the phenomenon which occurs when a propagated wave strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary and the incident angle is greater than the critical angle, the wave cannot pass through and is entirely reflected.



A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit.



The vertical cavity surface emitting laser (VCSEL) is a type of semiconductor laser diode with laser beam emission perpendicular from the top surface, contrary to conventional edge-emitting semiconductor lasers which emit from surfaces formed by cleaving the individual chip out of a wafer.



A wavelength is the spatial period of a periodic wave—the distance over which the wave’s shape repeats. Wavelength is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings and is a characteristic of both traveling waves and standing waves, as well as other spatial wave patterns. Wavelength depends on the medium (e.g. vacuum, air, or water) that a wave travels through.