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Fiber Optic Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

Absorption
That portion of optical attenuation in optical fiber resulting from the conversion of optical power to heat.Caused by impurities in the fiber such as hydroxyl ions.

AC
Abbreviation for alternating current.An electric current that reverses its direction at regularly recurring intervals.

Acceptance Angle
The half-angle of the cone within which incident light is totally internally reflected by the fiber core. It is equal to sin-1 (NA).

Active Device
A device that requires a source of energy for its operation and has an output that is a function of present and past input signals.Examples include controlled power supplies, transistors, LEDs, amplifiers and transmitters.

A/D or ADC
Abbreviation for analog-to-digital converter.A device used to convert analog signals to digital signals.

ADM
Abbreviation for add-drop multiplexer.A device which adds or drops signals from a communications network.

ADSL
Abbreviation for asynchronous digital subscriber line.See DSL.

Aerial Plant
Cable that is suspended in the air on telephone or electric utility poles.

AGC
Abbreviation for automatic gain control.A process or means by which gain is automatically adjusted in a specified manner as a function of input level or another specified parameter.

AM
Abbreviation for amplitude modulation.A transmission technique in which the amplitude of the carrier is varied in accordance with the signal.

Amplitude Spontaneous Emission (ASE)
A background noise mechanism common to all types of erbium-doped fiber amplifiers (EDFA's). It contributes to the noise figure of the EDFA which causes loss of signal-to-noise-ratio.

Amplifier
A device that boosts the strength of an electronic signal.In a cable system, amplifiers are spaced at regular intervals throughout the system to maintain signal fidelity.

Analog
A continuously variable signal. A mercury thermometer, which gives a variable range of temperature readings, is an example of an analog instrument.Opposite of digital.

Angstrom (Å)
A unit of length in optical measurements where
1Å = 10-10 meters, or 10-4 micrometers, or = 10-1 nanometers.
The angstrom has been used historically in the field of optics, but it is not as SI (Système Internationale or International System) unit. Rarely used in fiber optics; nanometers is preferred.

Angular Misalignment
Loss at a connector due to fiber end face angles being misaligned.

ANSI
Abbreviation for American National Standards Institute.

APC
Abbreviation for angle polished connector.An 5° - 15° angle on the connector tip for the minimum possible backreflection.

APD
See avalanche photodiode.

APL
Abbreviation for average picture level.A video quality parameter.

AR Coating
Antireflection coating. A thin, dielectric or metallic film applied to an optical surface to reduce its reflection and thereby increase its transmittance.

Armor
A protective layer, usually metal, wrapped around a cable.

ASCII
Abbreviation for American standard code for information interchange. An encoding scheme used to interface between data processing systems, data communication systems, and associated equipment.

ASIC
Abbreviation for application-specific integrated circuit. A custom-designed integrated circuit.

ASTM
Abbreviation for American Society for Testing and Materials.

Asynchronous
Data that is transmitted without an associated clock signal.

Asynchronous Transfer Mode (ATM)
A transmission standard widely used by the telecom industry. A digital transmission switching format with cells containing 5 bytes of header information followed by 48 bytes. Part of the B-ISDN standard.

ATE
Abbreviation for automatic test equipment.Test equipment computer programmed to perform a number of test measurements on a device without the need for changing the test setup.

Attenuation
The decrease in signal strength along a fiber optic waveguide caused by absorption and scattering. Attenuation is usually expressed in dB/km.

Attenuation Constant
For a particular propagation mode in an optical fiber, the real part of the axial propagation constant.

Attenuation-Limited Operation
The condition in a fiber optic link when operation is limited by the power of the received signal (rather than by bandwidth or distortion).

Attenuator
1) In electrical systems, a usually passive network for reducing the amplitude of a signal without appreciably distorting the waveform.
2) In optical systems, a passive device for reducing the amplitude of a signal without appreciably distorting the waveform.

Avalanche Photodiode (APD)
A photodiode that exhibits internal amplification of photocurrent through avalanche multiplication of carriers in the junction region.

Average Power
The average level of power in a signal that varies with time.

AWG (Arrayed Waveguide Grating)
A device, built with silicon planar lightwave circuits (PLC), that allows multiple wavelengths to be combined and separated in a dense wavelength-division multiplexing (DWDM) system.

Axial Propagation Constant
For an optical fiber, the propagation constant evaluated along the axis of a fiber in the direction of transmission.

Axis
The center of an optical fiber.

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B

See bel.

BB-I
Abbreviation for broadband interactive services.The delivery of all types of interactive video, data and voice services over a broadband communications network.

Backreflection (BR)
In cases where light is launched into an optical fiber, backreflection refers to the light that is returned to the launch point.

Backscattering
The return of a portion of scattered light to the input end of a fiber; the scattering of light in the direction opposite to its original propagation.

Bandwidth (BW)
The range of frequencies within which a fiber optic waveguide or terminal device can transmit data or information.

Bandwidth-Limited Operation
The condition in a fiber optic link when bandwidth, rather than received optical power, limits performance. This condition is reached when the signal becomes distorted, principally by dispersion, beyond specified limits.

Baseband
A method of communication in which a signal is transmitted at its original frequency without being impressed on a carrier.

Baud
A unit of signaling speed equal to the number of signal symbols per second, which may or may not be equal to the data rate in bits per second.

Beamsplitter
An optical device, such as a partially reflecting mirror, that splits a beam of light into two or more beams. Used in fiber optics for directional couplers.

Bel (B)
The logarithm to the base 10 of a power ratio, expressed as B = log10(P1/P2), where P1 and P2 are distinct powers.The decibel, equal to one-tenth bel, is a more commonly used unit.

Bending Loss
Attenuation caused by high-order modes radiating from the outside of a fiber optic waveguide which occur when the fiber is bent around a small radius. See also macrobending, microbending.

Bend Radius
The smallest radius an optical fiber or fiber cable can bend before increased attenuation or breakage occurs.

BER (Bit Error Rate)
The fraction of bits transmitted that are received incorrectly.

BIDI
Abbreviation for bidirectional transceiver, a device that sends information in one direction and receives information from the opposite direction.

Bidirectional
Operating in both directions. Bidirectional couplers operate the same way regardless of the direction light passes through them. Bidirectional transmission sends signals in both directions, sometimes through the same fiber.

Binary
Base two numbers with only two possible values 0, or 1.Primarily used by communication and computer systems.

Birefringent
Having a refractive index that differs for light of different polarizations.

Bit
The smallest unit of information upon which digital communications are based; also an electrical or optical pulse that carries information.

BITE
Abbreviation for built-in test equipment.Features designed into a piece of equipment that allow on-line diagnosis of failures and operating status.

BNC
Popular coax bayonet style connector, often used for baseband video.

Bragg Grating
A technique for building optical filtering functions directly into a piece of optical fiber based on interferometric technicques.Usually this is accomplished by making the fiber photosensitive and exposing the fiber to deep UV light though a grating. This forms regions of higher and lower refractive indices in the fiber core.

Broadband
A method of communication where the signal is transmitted by being impressed on a high-frequency carrier.

Buffer
1) In optical fiber, a protective coating applied directly to the fiber.
2) A routine or storage used to compensate for a difference in rate of flow of data, or time of occurrence of events, when transferring data from one device to another.

Bus Network
A network topology in which all terminals are attached to a transmission medium serving as a bus.

Butt Splice
A joining of two fibers without optical connectors arranged end-to-end by means of a coupling. Fusion splicing is an example.

Bypass
The ability of a saturation to isolate itself optically from a network while maintaining the continuity of the cable plant.

Byte
A unit of eight bits.

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C

Abbreviation for Celsius. Measure of temperature where pure water freezes at 0° and boils at 100°.

Cable
One or more optical fibers enclosed, with strength members, in a protective covering.

Cable Assembly
A cable that is connector terminated and ready for installation.

Cable Plant
The cable plant consists of all the optical elements including fiber connectors, splices, etc., between a transmitter and a receiver.

Cable Television
Communications system that distributes broadcast and non-broadcast signals as well as a multiplicity of satellite signals, original programming and other signals by means of a coaxial cable and/or optical fiber.

Carrier-to-Noise Ratio (CNR)
The ratio, in decibels, of the level of the carrier to that of the noise in a receiver's IF bandwidth before any nonlinear process such as amplitude limiting and detection takes places.

CATV
Originally an abbreviation for community antenna television; the term now typically refers to cable television.

C-Band
The wavelength range between 1530 nm and 1562 nm used in some CWDM and DWDM applications.

CCIR
Abbreviation for Consultative Committee on Radio.

CCITT
Abbreviation for Consultative Committee on Telephony and Telegraphy.

CCTV
Abbreviation for closed-circuit television.An arrangement in which programs are directly transmitted to specific users and not broadcast to the public.

CD
Abbreviation for compact disk. Often used to describe high-quality audio, CD-quality audio, or short-wavelength lasers; CD laser.

CDMA
Abbreviation for code-division multiple access.A coding scheme in which multiple channels are independently coded for transmission over a single wideband channel using an individual modulation scheme for each channel.

Center Wavelength
In a laser, the nominal value center operating wavelength.It is the wavelength defined by a peak mode measurement where the effective optical power resides.In an LED, the average of the two wavelengths measure at the half amplitude points of the power spectrum.

Central Office (CO)
A common carrier switching office in which users' lines terminate. The nerve center of a communications system.

CGA
Abbreviation for color graphics adapter.  A low-resolution color standard for computer monitors.

Channel
A communications path or the signal sent over that path. Through multiplexing several channels, voice channels can be transmitted over an optical channel.

Channel Capacity
Maximum number of channels that a cable system can carry simultaneously.

Chirp
In laser diodes, the shift of the laser's center wavelength during single pulse durations due to laser instability.

Chromatic Dispersion
Reduced optical signal strength caused by different wavelengths of light traveling at different speeds down the optical fiber.Chromatic dispersion occurs because the speed at which an optical pulse travels depends on its wavelength, a property inherent to all optical fiber. May be caused by material dispersion, waveguide dispersion, and profile dispersion.

Circulator
Passive three-port devices that couple light from Port 1 to 2 and Port 2 to 3 and have high isolation in other directions.

Cladding
Material that surrounds the core of an optical fiber.Its lower index of refraction, compared to that of the core, causes the transmitted light to travel down the core.

Cladding Mode
A mode confirmed to the cladding; a light ray that propagates in the cladding.

Cleave
The process of separating an optical fiber by a controlled fracture of the glass, for the purpose of obtaining a fiber end, which is flat, smooth, and perpendicular to the fiber axis.

Cm
Abbreviation for centimeter. Approximately 0.4 inches.

CMOS
Abbreviation for complementary metal oxide semiconductor. A family of IC's.Particularly useful for low-speed or low-power applications.

CMTS
Abbreviation for cable modem termination system.

Coarse Wavelength-division Multiplexing (CWDM)
CWDM allows eight or fewer channels to be stacked in the 1550 nm region of optical fiber, the C-Band.

Coating
The material surrounding the cladding of a fiber.Generally a soft plastic material that protects the fiber from damage.

Coherent Communications
In fiber optics, a communication system where the output of a local laser oscillator is mixed optically with a received signal, and the difference frequency is detected and amplified.

Color Subcarrier
The 3.58 MHz signal which carriers color information in a TV signal.

Composite Second Order (CSO)
An important distortion measure of analog CATV systems.It is mainly caused by second order distortion in the transmission system.

Composite Sync
A signal consisting of horizontal sync pulses, vertical sync pulses, and equalizing pulses only, with a no-signal reference level.

Composite Triple Beat (CTB)
An important distortion measure of analog CATV systems.It is mainly caused by second order distortion in the transmission system.

Composite Video
A signal which consists of the luminance (black and white), chrominance (color), blanking pulses, sync pulses, and color burst.

Compression
A process in which the dynamic range or data rate of a signal is reduced by controlling it as a function of the inverse relationship of its instantaneous value relative to a specified reference level.Compression is usually accomplished by separate devices called compressors and is used for many purposes such as: improving signal-to-noise ratios, preventing overload of succeeding elements of a system, or matching the dynamic ranges of two devices.Compression can introduce distortion, but it is usually not objectionable.

Concatenation
The process of connecting pieces of fiber together.

Concentrator
A multiport repeater.

Concentricity
The measurement of how well-centered the core is within the cladding.

Connector
A mechanical or optical device that provides a demountable connection between two fibers or a fiber and a source or detector.

Connector Plug
A device used to terminate an optical conductor cable.

Connector Receptacle
The fixed or stationary half of a connection that is mounted on a panel/bulkhead. Receptacles mate with plugs.

Connector Variation
The maximum value in dB of the difference in insertion loss between mating optical connectors (e.g., with remating, temperature cycling, etc.). Also called optical connector variation.

Converter
Device that is attached between the television set and the cable system that can increase the number of channels available on the TV set, enabling it to accommodate the multiplicity of channels offered by cable TV.

Core
The light-conducting central portion of an optical fiber, composed of material with a higher index of refraction than the cladding.The portion of the fiber that transmits light.

Counter-Rotating
An arrangement whereby two signal paths, one in each direction, exist in a ring topology.

Coupler
An optical device that combines or splits power from optical fibers.

Coupling Ratio/Loss (CR,CL)
The ratio/loss of optical power from one output port to the total output power, expressed as a percent. For a 1 x 2 WDM or coupler with output powers 01 and 02, and 0i representing both output powers.

Critical Angle
In geometric optics, at a refractive boundary, the smallest angle of incidence at which total internal refraction occurs.

Cross-connect
Connections between terminal blocks on the two sides of a distribution frame or between terminals on a terminal block (also called straps). Also called cross-connection or jumper.

Cross-gain Modulation (XGM)
A technique used in a wavelength converters where gain saturation effects in an active optical device, such as a semiconductor optical amplifier (SOA), allow the conversion of the optical wavelength.  Better at shorter wavelengths (e.g., 780 nm or 850 nm).

Cross-phase Modulation (XPM)
A fiber nonlinearity caused by the nonlinear index of refraction of glass. The index of refraction varies with optical power level which causes different optical signals to interact.

Crosstalk (XT)
Undesired coupling from one circuit, part of a circuit, or channel to another.
Any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel.

CRT
Abbreviation for cathode ray tube.

CSMA/CD
Abbreviation for carrier sense multiple access with collision detection. A network control protocol in which (a) a carrier sensing is used and (b) while a transmitting data station that detects another signal while transmitting a frame, stops transmitting that frame, waits for a jam signal, and then waits for a radom time interval before trying to send that frame again.

CTS
Abbreviation for clear to send. In a communications network, a signal from a remote receiver to a transmitter that is ready to receive a transmission.

Customer Premises Equipment (CPE)
Terminal, associated equipment, and inside wiring located at a subscriber's premises and connected with a carrier's communication channel(s) at the demarcation point (demarc), a point established in a building or complex to separate customer equipment from telephone company equipment.CPE does not include over-voltage protection equipment and pay telephones.

Cutback Method
A technique of measuring optical fiber attenuation by measuring the optical power at two points at different distances from the test source.

Cutoff Wavelength
In single-mode fiber, the wavelength below which the fiber ceases to be single-mode.

CW
Abbreviation for continuous wave. Usually refers to the constant optical output from an optical source when it is biased (i.e., turned on) but not modulated with a signal.

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D

Abbreviation for digital-to-analog converter. A device used to convert digital signals to analog signals.

Dark Current
The induced current that exists in a reversed biased photodiode in the absence of incident optical power. It is better understood to be caused by the shunt resistance of the photodiode.A bias voltage across the diode (and the shunt resistance) causes current to flow in the absence of light.

Data Rate
The number of bits of information in a transmission system, expressed in bits per second (b/s or bps), and which may or may not be equal to the signal or baud rate.

DBc
Abbreviation for decibel relative to a carrier level.

dBµ
Abbreviation for decibels relative to microwat.

DBm
Abbreviation for decibels relative to milliwat.

DC
Abbreviation for direct current. An electric current flowing in one direction only and substantially constant in value.

DCE
Abbreviation for data circuit-terminating equipment
1) In a data station, the equipment that
   a) performs functions such as signal conversion and coding, at the network end of the line between the data terminal equipment (DTE) and the line, and
   b) may be a separate or an integral part of the DTE or of intermediate equipment.
2) The interfacing equipment that may be required to couple the data terminal equipment (DTE) into a transmission circuit or channel and from a transmission circuit of a channel into the DTE.

Decibel (dB)
A unit of measurement indicating relative optic power on a logarithmic scale. Often expressed in reference to a fixed value, such as dBm (1 milliwatt) or dBµ (1 microwatt).
dB = 10·log10 (P1/P2)

Demultiplexer
A module that separates two or more signals previously combined by compatible multiplexing equipment.

Dense Wavelength-Division Multiplexing (DWDM)
This refers to the transmission of a multiplicity of closely spaced wavelengths in the 1550 nm region. Wavelength spacings are usually 100 GHz or 200 GHz which corresponds to 0.8 nm or 1.6 mm.DWDM bands include the C-Band, the S-Band, and the L-Band.

Detector
An opto-electric transducer used in fiber optics to convert optical power to electrical current. Usually referred to as a photodiode.

DFB
See distributed feedback laser.

Diameter-Mismatch Loss
The loss of power at a joint that occurs when the transmitting fiber has a diameter greater than the diameter of the receiving fiber.The loss occurs when coupling light from a source to fiber, from fiber to fiber, or from fiber to detector.

Dichroic Filter
An optical filter that transmits light according to wavelength.Dichroic filters reflect light that they do not transmit.

Dielectric
Any substance in which an electric field may be maintained with zero or near-zero power dissipation. This term usually refers to non-metallic materials.

Differential Gain (DG)
A type of distortion in a video signal that causes the brightness information to be distorted.

Differential Phase (DP)
A type of distortion in a video signal that causes the color information t be distorted.

Diffraction Grating
An array of fine, parallel, equally spaced reflecting or transmitting lines that mutually enhances the effects of diffraction to concentrate the diffracted light in a few directions determined by the spacing of the lines and by the wavelength of the light.

Digital
A signal that consists of discrete states. A binary signal has only two states, 0 and 1.

Digital Compression
An engineering technique for converting a cable television signal into a digital format (in which it can easily be stored and manipulated) which may then be processed so as to require a smaller portion of spectrum for its transmission. It could allow many channels to be carried in the capacity currently needed for one signal.

Diode
An electronic device that lets current flow in only one direction.Semiconductor diodes used in fiber optics contain a junction between regions of different doping.They include light emitters (LEDs and laser diodes) and detectors (photodiodes).

Diode Laser
Synonymous with injection laser diode.

DIP
Abbreviation for dual in-line package. An electronic package with a rectangular housing and a row of pins along each of two opposite sides.

Diplexer
A device that combines two or more types of signals into a single output.

Directional Coupler
A coupling device for separately sampling (through a known coupling loss) either the forward (incident) or the backward (reflected) wave in a transmission line.

Directivity
See near-end crosstalk.

Dispersion
The temporal spreading of a light signal in an optical waveguide caused by light signals traveling at different speeds through a fiber either due to modal or chromatic effects.

Dispersion-Compensating Fiber (DCF)
A fiber that has the opposite dispersion of the fiber being used in a transmission system. It is used to nullify the dispersion caused by that fiber.

Dispersion-Compensating Module (DCM)
This module has the opposite dispersion of the fiber being used in a transmission system. It is used to nullify the dispersion caused by that fiber. It can be either a spool of a special fiber or a grating based module.

Dispersion-Shifted Fiber (DSF)
A type of single-mode fiber designed to have zero dispersion near 1550 nm. This fiber type works very poorly for DWDM applications because of high fiber non-linearity at the zero dispersion point.

Dispersion Management
A technique used in the system design of a fiber optic transmission to be able to cope with the dispersion introduced by the optical fiber.

Dispersion Penalty
Dispersion in an optical fiber causes pulses and edges to be smeared. As the edges smear, the receiver has more difficulty discriminating between ones and zeros. This results in a loss of sensitivity compared to a short fiber and referred to as the dispersion penalty in DB.

Distortion
Nonlinearities in a unit that cause harmonics and beat products to be generated.

Distortion-Limited Operation
Generally synonymous with bandwidth-limited operation.

Distributed Feedback Laser (DFB)
An injection laser diode which has a Bragg reflection grating in the active region in order to suppress multiple longitudinal modes and enhance a single longitudinal mode.

Distribution System
Part of a cable system consisting of trunk and feeder cables used to carry signals from headend to customer terminals.

Dominant Mode
The mode in an optical device spectrum with the most power.

Dope
Thick liquid or paste used to prepare a surface or a varnish-like substance used for waterproofing or strengthening a material.

Double-Window Fiber
This term is used two ways. For multimode fibers, the term means that the fiber is optimized for 850 nm and 1310 nm operation. For single-mode fibers, the term means that the fiber is optimized for 1310 nm and 1550 nm operation.

DSL
Abbreviation for digital subscriber line. In an integrated systems digital network (ISDN), equipment that provides full-duplex service on a single twisted metallic pair at a rate sufficient to support ISDN basic access and additional framing, timing recovery, and operational functions.See also ISDN.

DSR
Abbreviation for data signaling rate. The aggregate rate at which data pass a point in the transmission path of a data transmission system expressed in bits per second (bps or b/s).

DST
Abbreviation for dispersion supported transmission.In electrical TDM systems, a transmission system that would allow data rates at 40 Gb/s by incorporating devices such as SOA's.

DSx
A transmission rate in the North American digital telephone hierarchy. Also called T-carrier.

DTE
Abbreviation for data terminal equipment.
1) And end instrument that converts user information into signals for transmission or reconverts the received signals into user information.
2) The functional unit of a data station that serves as a data source or a data sink and provides for the data communication control function to be performed in accordance with link protocol.

DTR
Abbreviation for data terminal ready.In a communications network, a signal from a remote transmitter that is clear to receive data.

Dual Attachment Concentrator
A concentrator that offers two attachments to the FDDI network which are capable of accommodating a dual (counter-rotating) ring.

Dual Attachment Station
A station that offers two attachments to the FDDI network which are capable of accommodating a dual (counter-rotating ring).

Dual Ring (FDDI Dual Ring)
A pair of counter-rotating logical rings.

Duplex Cable
A two-fiber cable suitable for duplex transmission.

Duplex Transmission
Transmission in both dirctions, either one direction at a time (half-duplex) or both directions simultaneously (full duplex).

Duty Cycle
In a digital transmission, the fraction of time a signal is at the high level.

DWDM
See Dense Wavelength<-Division Multiplexing.

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E

Abbreviation for emitter<-coupled logic. A high-speed logic family capable of GHz rates.

EDFA
See Erbium-Doped Fiber Amplifier.

Edge-Emitting Diode
An LED that emits light from its edge, producing more directional output than surface-emitting LED's that emit from their top surface.

Effective Area
The area of a single-mode fiber that carriers the light.

EGA
Abbreviation for enhanced graphics adapter. A medium-resolution color standard for computer monitors.

EIA
Abbreviation for Electronic Industries Association.An organization that sets video and audio standards.

8B10B Encoding
A signal modulation scheme in which eight bits are encoded in a 10-bit word to ensure that too many consecutive zeroes doe not occur; used in ESCON and fibre channel.

802.3 Network
A 10 Mb/s CSMA/CD bus-based network; commonly called Ethernet.

802.5 Network
A token-passing ring network operating at 4 Mb/s or 16 Mb/s.

EMI (Electromagnetic Interference)
Any electrical or electromagnetic interference that causes undesirable response, degradation, or failure in electronic equipment. Optical fibers neither emit nor receive EMI.

EMP (Electromagnetic Pulse)
A burst of electromagnetic radiation that creates electric and magnetic fields that may couple with electrical/electronic systems to produce damaging current and voltage surges.

EMR (Electromagnetic Radiation)
Radiation made up of oscillating electric and magnetic fields and propagated with the speed of light. Includes gamma radiation, X-rays, ultraviolet, visible and infrared radiation, and radar and radio waves.

Electromagnetic Spectrum
The range of frequencies of electromagnetic radiation from zero to infinity.

ELED
See Edge-Emitting Diode.

Ellipticity
Describes the fact that the core or cladding may be elliptical rather than circular.

EM
Abbreviation for electromagnetic.

Endoscope
A fiber optic bundle used for imaging and viewing inside the human body.

ENG
Abbreviation for Electronic News gathering.

E/O
Abbreviation for electrical-to-optical converter.

Equilibrium Mode Distribution (EMD)
The steady modal state of a multimode fiber in which the relative power distribution among modes is independent of fiber length.

Erbium-Doped Fiber Amplifier (EDFA)
Optical fibers doped with the rare earth element, erbium, which can amplify light in the 1550 nm region when pumped by an external light source.

ESCON
Abbreviation for enterprise systems connection.A duplex optical connector used for computer-to-computer data exchange.

Ethernet
A baseband local area network marketed by Xerox and developed jointly by Xerox, Digital Equipment Corporation, and Intel.

Evanescent Wave
Light guided in the inner part of an optical fiber's cladding rather than in the core.

Excess Loss
In a fiber optic coupler, the optical loss from the portion of light that does not emerge from the nominal operation ports of the device.

External Modulation
Modulation of a light source by an external device that acts like an electronic shutter.

Extinction Ratio
The ratio of the low, or OFF optical power level (PL) to the high, or ON optical power level (PH)
Extinction Ration (%) = (PL/PH) x 100

Extrinsic Loss
In a fiber interconnection, that portion of loss not intrinsic to the fiber but related to imperfect joining of connector or splice.

Eye Pattern
Also called eye diagram. The proper function of a digital system can be quantitatively described but its BER, or qualitatively by its eye patter. The "openness" of the eye relates to the BER that can be achieved.

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F

Abbreviation for Fahrenheit. Measure of temperature where pure water freezes at 32° and boils at 212°.

Failure Rate
The number of failures of a device per unit of time.

Fall Time
Also called turn-off time. The time required for the trailing edge of a pulse to fall from 90% to 10% of its amplitude; the time required for a component to produce such a result.Typically measured between the 80% and 20% points or alternately the 90% and 10% points.

FAR
Abbreviation for federal acquisition regulation.The guidelines by which the US government purchases goods and services. Also the criteria must be met by the vendor in order to be considered as a source for goods and services purchased by the US government.

Faraday Effect
A phenomenon that causes some materials to rotate the polarization of light in the presence of a magnetic field parallel to the direction of propagation. Also called magneto-opto effect.

Far-End Crosstalk
See wavelength isolation.

FGB
Abbreviation for fiber Bragg gratings. See Bragg grating.

FC
A threaded optical connector that originated in Japan.Good for single-mode or multimode fiber and applications requiring low backreflection.

FCC
Abbreviation for Federal Communications Commission.

FC/PC
See FC. A special curved polish on the connector for very low backreflection.

FCS
Abbreviation for frame check sequence. An error-detection scheme that

a) uses parity bits generated by polynomial encoding of digital signals,
b) appends those parity bits to a digitial signal, and
c) uses decoding alogrithms that detect errors in the received digital signal.

FDA
Abbreviation for Food and Drug Administration.Organization responsible for, among other things, laser safety.

FDDI
Abbreviation for fiber distributed data interface.

1) A dual counter-rotating ring local area network.
2) A connector used in a dual counter-rotating ring local area network.

FDM
See Frequency-Division Multiplexing.

FEC
See Forward Error Correcting.

Ferrule
A rigid tube that confines or holds a fiber as part of a connector assembly.

FET
Abbreviation for Field-Effect Transistor. A semiconductor so named because a weak electrical signal coming in through one electrode creates an electrical field through the rest of the transistor. This field flips from positive to negative when the incoming signal does, and controls a second current traveling through the rest of the transistor. The field modulates the second current to mimic the first one, but it can be substantially larger.

Fiber Grating
An optical fiber in which the refractive index of the core varies periodically along its length, scattering light in a way similar to a diffraction grating, and transmitting or reflecting certain wavelengths selectively.

Fiber Optic Attenuator
A component installed in a fiber optic transmission system that reduces the power in the optical signal. It is often used to limit the optical  power received by the photodetector to within the limits of the optical receiver.

Fiber Optic Cable
A cable containing one or more optical fibers.

Fiber Optic Communication Systems
The transfer of modulated or unmodulated optical energy through optical fiber media which terminates in the same or different media.

Fiber Optic Gyroscope
A coil of optical fiber that can detect rotation about its axis.

Fiber Optic Link
A transmitter, receiver and cable assembly that can transmit information between two points.

Fiber Optic Span
An optical fiber/cable terminated at both ends which may include devices that add, subtract, or attenuate optical signals.

Fiber Optic Subsystem
A functional entity with defined bounds and interfaces which is part of a system. It contains solid state and/or other components and is specified as a subsystem for the purpose of trade and commerce.

Fiber-to-the-Curb (FTTC)
Fiber optic service node connected by wires to several nearby homes, typically on a block.

Fiber-to-the-Home (FTTH)
Fiber optic service to a node located inside an individual home.

Fiber-to-the-Loop (FTTL)
Fiber optic service to a node that is located in a neighborhood.

Fiber Channel
An industry-standard specification that originated in Great Britain which details computer channel communications over fiber optics at transmission speeds from 132 Mb/s to 1062.5 Mb/s at distances of up to 10 kilometers.

Filter
A device which transmits only part of the incident energy and may thereby change the spectral distribution of energy.

FIT Rate
Number of device failures in one billion device hours.

Fluoride Glasses
Materials that have the amorphous structure of glass but are made of fluoride compounds (e.g., zirconium fluoride) rather than oxide compounds (e.g., silica). Suitable for very long wavelength transmission.

FM (Frequency Modulation)
A method of transmission in which the carrier frequency varies in accordance with the signal.

FOG-M
Abbreviation for Fiber Optic Guided Missile.

Forward Error Correcting (FEC)
A communication technique used to compensate for a noisy transmission channel. Extra information is sent along with the primary data payload to correct for errors that occur in transmission.

FOTP (Fiber Optic Test Procedure)
Standards developed and published by the Electronic Industries Association.

FOTS
Fiber Optic Transmission System.

Frequency
The number of pulses or cycles per second; measured in units of Hertz (Hz) where 1 hertz equals 1 pulse/cycle per second.

Frequency Modulation (FM)
Transmission scheme whereby information is sent by varying the frequency of an optical carrier. A method of transmission in which the carrier frequency varies in accordance with the signal.

Fresnel Reflection
The reflection of a portion of the light incident on a planar surface between two homogeneous media having different refractive indices. Fresnel reflection occurs at the air/glass interfaces at entrance and exit ends of an optical fiber.

Fundamental Mode
The lowest order mode of a waveguide.

Fusion Splicing
A permanent joint accomplished by the application of localized heat sufficient to fuse or melt the ends of the optical fiber, forming a continuous single fiber.

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G

Loss resulting from the end separation of two axially aligned fibers.

Graded-Index
Fiber design in which the refractive index of the core is lower toward the outside of the fiber core and increases toward the center of the core; thus it bends the rays inward and allows them to travel faster in the lower index of refraction region. This type of fiber provides high bandwidth capabilities.

Ground-Loop Noise
Noise that results when equipment is grounded at ground points having different potentials and thereby created an unintended current path. The dielectric of optical fibers provide electrical isolation that eliminates ground loops.

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H

Hard Clad Silica
A fiber with a hard plastic cladding surrounding a silica glass core.

Hybrid Cable
A fiber optic cable containing two or more different types of fiber, such as 62.5 µm multimode and single-mode.

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I

Institute of Electrical and Electronics Engineering.

Index Matching Material
A material, often a liquid or cement whose refractive index is nearly equal to the core index, used to reduce Fresnel reflections from a fiber end face.

Index of Refraction
The ratio of light velocity in a vacuum to its velocity in a given transmitting medium.

Index Profile
Curve of the refractive index over the cross section of an optical waveguide.

Index Of Refraction
An optical characteristic (n) of a material, referencing the speed of light in that material to a vacuum.

Insertion Loss
The attenuation caused by the insertion of an optical component; in other words, a connector or coupler in an optical transmission system.

Isolation
Also referred to as far-end cross-talk or far-end isolation. Predominantly used in reference to WDM products, it is a measure of light at an undesired wavelength at any given port.

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J

Jumper

Fiber optic cable that has connectors installed on both ends. See also cable assembly.

K

See Aramid Yarn

Kilometer
One thousand meters or 3,281 feet. The kilometer is a unit of measurement for fiber optics.

KPSI
A unit of tensile strength expressed in thousands of pounds per square inch.

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L

Laser Light
Amplification by Stimulated Emission of Radiation. A device which produces coherent light with a narrow range of wavelengths.

Lateral Displacement Loss
The loss of power that results from lateral displacement from optimum alignment between two fibers or between a fiber and an active device.

Launch Angle
Angle between the propagation direction of the incident light and the optical axis of an opticat waveguide.

Launching Fiber
A fiber used in conjunction with a source to excite the modes of another fiber in a particular way. Launching fibers are most often used in test systems to improve the precision of measurements.

Light
In the laser and optical communication fields, the portion of the electromagnetic spectrum that can be handled by the basic optical techniques used for the visible spectrum extending from the near ultraviolet region of approximately 0.3 micron, through the visible region and into the mid-infrared region of about 30 microns.

LED (Light Emitting Diode)
A semiconductor diode which emits light when forward biased to an optical signal. A device used in a transmitter to convert information from electric to optical form. It typically has a large spectral width.

Lightguide Cable
An optical fiber, multiple fiber, or fiber bundle which includes a cable jacket and strength.

Lightwaves
Electromagnetic waves in the region of optical frequencies. The term "light" was originally restricted to radiation visible to the human eye, with wavelengths between 400 and 700 nanometers (nm). However, it has become customary to refer to radiation in the spectral regions adjacent to visible light (in the near infrared from 700 to about 2000 nm) as "light" to emphasize the physical and technical characteristics they have in common with visible light.

Link
A fiber optic cable with connectors attached to a transmitter (source) and receiver (detector).

LLDPE
Linear Low Density Polyethylene jacketing.

Local Area Network (LAN)
A geographically limited communications network intended for the local transport of data, video and voice.

Loose Tube
A protective tube loosely surrounding a cabled fiber, often filled with a water blocking gel. Type of cable design, primarily for outdoor use, where one or more fibers are enclosed in hard plastic tubes. Fibers are usually buffered to 250 microns.

Loss
Attenuation of optical signal, normally measured in decibels.

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M

Macrobending
Macroscopic axial deviations of a fiber from a straight line, in contrast to microbending.

Material Dispersion
The dispersion associated with a non-monochromatic light source due to the wavelength dependence of the refractive index of a material or of the light velocity in this material.

MDPE
Medium Density Polyetheylene jacketing.

Mechanical Splicing
Joining two fibers together by mechanical means to enable a continuous signal. Elastomeric splicing is one example of mechanical splicing.

Megahertz (MHz)
A unit of frequency that is equal to one million hertz.

Microbending
Curvatures of the fiber which involve axial displacements of a few micrometers and spatial wavelengths of a few millimeters.Microbends cause loss of light and consequently increase the attenuation of the fiber.

Micron (um)
Another term for micrometer. One millionth of a meter. 10exp-6 meter.

Misalignment Loss
The loss of power resulting from angular misalignment, lateral displacement, and end separation.

Modal Dispersion
Pulse spreading due to multiple light rays traveling different distances and speeds through an optical fiber.

Mode Field Diameter (MFD)
The diameter of optical energy in a singlemode fiber.Because the MFD is greater than the core diameter, MFD replaces core diameter as a practical parameter.

Mode Filter
A device used to remove high-order modes from a fiber and thereby simulate EMD.

Mode Scrambler
A device composed of one or more optical fibers in which strong mode coupling occurs. Frequently used to provide a mode distribution that is independent of source characteristics.

Mode
A term used to describe a light path through a fiber, as in multi­mode or single-mode.

Mode Mixing
The numerous modes of a multi-mode fiber differ in their propagation velocities. As long as they propagate independently of each other, the fiber bandwidth varies inversely with the fiber length due to multi-mode distortion. As a result of inhomogenejties of the fjber geometry and of the index profile, a gradual energy exchange occurs between modes with differing velocities. Due to this mode mixing, the bandwidth of long multimode fibers is greater than the value obtained by linear extrapolation from measurements on shod fibers.

Modulation
Coding of information onto the carrier frequency.This includes amplitude, frequency, or phase modulation techniques.

Monochromatic
Consisting of a single wavelength. In practice, radiation is never perfectly monochromatic but, at best, displays a narrow band of wavelengths.

MQJ
Measurement Quality Jumper. A high quality reference cable designed to provide accurate and consistent test results. Note: The U.S. Navy requires that MQJ’s are used to test all Navy shipboard fiber installations.

Multi-Mode Fiber
An optical waveguide in which light travels in multiple modes. Typical core/cladding sizes (measured in microns) are 50/125, 62.5/125, and 100/140.

Multimode Fiber
A fiber type which supports multiple light paths through its core.

Multiplex
The combination of several signals onto a single communications channel.

Multiplexing
The process by which two or more signals are transmitted over a single communications channel. Examples include time-division multiplexing and wavelength-division multiplexing.

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N

NA-Mismatch Loss
The loss of power at a joint that occurs when the transmitting half has an NA greater than the NA of the receiving half.The loss occurs when coupling light from a source to fiber, from fiber to fiber, or from fiber to detector.

Nanometer
A unit of measurement equal to one billionth of a meter. 10exp-9 meter.Common unit of measure for wavelength One billionth of a meter.

NEC
National Electrical Code. Defines building flammatory requirements for indoor cables.

Numerical Aperture (NA)
A numerical value that expresses the light gathering ability of a fiber. The imaginary cone which defines the acceptance area for the fiber core to accept rays of light.

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O

OFC
Optical Fiber Conductive

OFCP
Optical Fiber Conductive Plenum

OFCR
Optical Fiber Conductive Riser

OFN
Optical Fiber Non-conductive

OFNP
Optical Fiber Non-conductive Plenum

OFNR
Optical Fiber Non-conductive Riser

Optical Time Domain Reflectometer (OTDR)
A method for characterizing a fiber wherein an optical pulse is transmitted through the fiber and the resulting backscatter and reflections to the input are measured as a function of time. Useful in estimating attenuation coefficient as a function of distance and identifying defects and other localized losses.

Optical Fiber
See Fiber.

Optical Waveguide
Dielectric waveguide with a core consisting of optically transparent material of low attenuation (usually silica glass) and with cladding consisting of optically transparent material of lower refractive index than that of the core. It is used for the transmission of signals with lightwaves and is frequently referred to as fiber. In addition, there are planar dielectric waveguide structures in some optical components, such as laser diodes, which are also referred to as optical waveguides.

Optoelectronic
Pertaining to a device that responds to optical power, emits or modifies optical radiation, or utilizes optical radiation for its internal operation. Any device that functions as an electrical-to-optical or optical-to-electrical transducer.

OTDR
Optical Time Domain Reflectometer. A test instrument, working on the principal of continuous energy backscatter, which provides a complete characterization of fiber loss along its length.

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P

Patch Panel
A centralized location for cross-connecting, monitoring and testing telecommunications cabling.

PCM
Pulse-Coded Modulation.

PCS
Plastic-Clad Silica.

PE
Abbreviation used to denote polyethylene.A type of plastic material used to make cable jacketing.

Peak Wavelength
The wavelength at which the optical power of a source is at a maximum.

Photocurrent
The current that flows through a photosensitive device, such as a photodiode, as the result of exposure to radiant power.

Photodetector
An optoelectronic transducer, such as a pin photodiode or avalanche photodiode.

Photodiode
A diode designed to produce photocurrent by absorbing light. Photodiodes are used for the detection of optical power and for the conversion of optical power into electrical power.

Photon
A quantum of electromagnetic energy.

Physical Contact (PC)
Connectors aligned and mated so that no air gaps exist between them. Positive contact between fibers exist. Also see Connector Back Reflection.

Pigtail
Fiber optic cable that has connectors installed on one end. See also Cable Assembly.

PIN Photodiode
A diode with a large intrinsic region sandwiched between p-doped and n-doped semiconducting regions. Photons in this region create electron hole pairs that are separated by an electric field thus generating an electric current in the load circuit.

Plastic Fiber
An optical fiber having a plastic core and plastic cladding.

Plastic-Clad Silica Fiber
An optical fiber having a glass core and plastic cladding.

Plenum
An air-handling space such as that found above drop-ceiling tiles or in raised floors. Also, a fire-code rating for indoor cable. Air duct inside buildings through which cable can be pulled or housed.

Plenum Cable
A cable whose flammability and smoke characteristics allow it to be routed in a plenum area without being enclosed in a conduit.

Point-to-Point
A connection established between two specific locations, as between two buildings.

Polarization Stability
The variation in insertion loss as the polarization state of the input light is varied.

Preform
A glass structure from which an optical fiber waveguide may be drawn.

Prefusing
Fusing with a low current to clean the fiber end.Precedes fusion splicing.

Primary Coating
The plastic coating applied directly to the cladding surface of the fiber during manufacture to preserve the integrity of the surface.

Pulse Spreading
The dispersion of an optical signal with time as it propagates through an optical fiber.

PUR
Polyurethane. Material used in manufacture of a type of jacketing material.

PVC
Polyvinyl Chloride. Material used in manufacture of a type of jacketing material.

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R

Receiver
An electronic package which converts optical signals to electrical signals.

Receiver Sensitivity
The optical power required by a receiver for low error signal transmission. In the case of digital signal transmission, the mean optical power is usually quoted in Watts or dbm (decibels referred to 1 milliwatt).

Reflectance
Light that is reflected back along the path of transmission, from either the coupling region, the connector or a tertninated fiber.

Reflection
The abrupt change in direction of a light beam at an interface between two dissimilar media so that the light beam returns into the media from which it originated.

Refraction
The bending of a beam of light at an interface between two dissimilar media or a medium whose refractive index is a continuous function of position (graded index medium).

Refractive Index
See Index of Refraction.

Regenerative Repeater
A repeater designed for digital transmission that both amplifies and reshapes the signal.

Repeater
A device which consists of a transmitter and a receiver or transceiver, used to regenerate a signal to increase the system length.

Return Loss
See reflectance.

Ring Network
A network topology in which terminals are connected in a point-to-point serial fashion in an unbroken circular configuration.

Rise Time
The time it takes the signal output to rise from low levels to peak value. Usually measured from 10% to 90% of max. output.

Riser
Pathways for indoor cables that pass between floors.It is normally a vertical shaft or space. Also, a fire-code rating for indoor cable.

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S

Scattering
A property of glass which causes light to deflect from the fiber and contributes to losses.

Sensitivity
For a fiber-optic receiver, the minimum optical power required to achieve a specified level of performance, such as a BER.

Signal-to-Noise Ratio (SNR)
The ratio of signal power to noise power.Measured in dB.

Simplex Cable
A term sometimes used for a single-fiber cable.

Simplex Transmission
Transmission in one direction only.

Single-Mode Fiber
An optical waveguide (or fiber) in which the signal travels through its core. The fiber has a smaller core diameter.

SMA
A connector type with screw threads.

Source
The means used to convert an electrical information carrying signal to a corresponding optical signal for transmission by fiber.The source is usually a Light Emitting Diode (LED) or Laser.

Spectral Width
A measure of the extent of a spectrum.For a source, the width of wavelengths contained in the output at one half of the wavelength of peak power.Typical spectral widths are 20 to 60 nm for an LED and 2 to 5 nm for a laser diode. The width of wavelengths in a light pulse, based on 50% intensity.

Splice Closure
A container used to organize and protect splice trays.

Splice Tray
A container used to organize and protect spliced fibers.

Splice
1) A permanent joint between two optical waveguides.
2) Means for joining two fiber ends.

Splicing
The permanent joining of fiber ends to identical or similar fibers, without the use of a connector. See also Fusion Splicing and Mechanical Splicing.

Splitting Loss
See coupling ratio.

ST
A connector type with a bayonet housing which is spring loaded "ST" stands for "straight tip".

Star Coupler
An active or passive device where energy presented at an input port is distributed through several output ports.

Star Network
A network in which all terminals are connected through a single point, such as a star coupler.

Step-Index
Fiber Optical fiber which has an abrupt ("step") change in its refractive index, due to a core and cladding that have different indices or refraction. Typically used for single mode.

Strength Member
That part of a fiber optic cable composed of Kevlar aramid yarn, steel strands, or fiberglass filaments that increase the tensile strength of the cable.

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T

Tap Loss
In a fiber optic coupler, the ratio of power at the tap port to the power at the input port.

Tap Port
In a coupler in which the splitting ratio between output pods is not equal, the output port containing the lesser power.

Tee Coupler
A Three-Pod Optical Coupler.

Thermal Stability
A measure of insertion loss variation as the device undergoes various environmental changes.

Tight Buffer
Type of cable construction whereby each glass fiber is tightly buffered by a protective thermoplastic coating to a diameter of 900 microns. High tensile strength rating achieved, providing durability, ease of handling and ease of connectorization.

Time-Division Multiplexing (TDM)
A transmission technique whereby several low-speed channels are multiplexed into a high-speed channel for transmission.

Topology
The physical layout of a network.

Total Internal Reflection
Total reflection of light back into a material when it strikes the interface of a material having a lower index at an angle below the critical angle.

Transceiver
An electronic device which has both transmit and receive capabilities.

Transducer
A device for converting energy from one form to another, such as optical energy to electrical energy.

Transmission Loss
Total loss encountered in transmission through a system.

Transmitter
An electronic package which converts an electrical signal to an optical signal.

Tree Coupler
A passive fiber optical component in which power from one input is distributed to more than two output fibers.

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U

UL
Underwriters Laboratories, Inc.

Uniformity
The maximum insertion loss difference between ports of a coupler.

W

Waveguide
Structure that guides electromagnetic waves along its length. An optical fiber is an optical waveguide.

Wavelength Division Multiplexing (WDM)
Simultaneous transmission of several signals in an optical waveguide at differing wavelengths. The process of using multiple wavelengths to carry multiple signals on a single fiber.

Wavelength
The distance between two crests of an electromagnetic waveform.

Wavelength Dependence
The variation in an optical parameter caused by a change in the operating wavelength.

WDM
Wavelength Division Multiplexer - a passive fiber optical device used to separate signals of different wavelengths carried on one fiber.

WIC
Wavelength Independent Coupler.

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