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A B C D E F G H I J K L M N O P Q R S T U V W Z
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 (Alternation Current): An electric current that reverses its direction at regularly recurring intervals.
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 (Analog-to-Digital Converter): A device used to convert analog signals to digital signals.
Add/Drop Multiplexing: A multiplexing function
offered in connection with SONET/SDH that allows lower level signals
to be added or dropped from a high-speed optical carrier in a wire
center. The connection to the add/drop multiplexer is via a channel
to a central office port at a specific digital speed (DS3, DS1,
etc.)
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ADM (Add-Drop Multiplexer): A device which adds or drops signals from a communications network.
ADSL (Asynchronus Digital Subscriber Line: See DSL.
Amplifier: A device, inserted within a transmission
path, that boosts the strength of an electronic or optical signal.
Amplifiers may be placed just after the transmitter (power booster),
at a distance between the transmitter and the receiver (in-line
amplifier), or just before the receiver (preamplifier).
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Analog: A continuously variable signal. Opposite of digital.
Angular Misalignment: Loss at a connector due to fiber end face angles being misaligned.
APC (Angled Physical Contact): A style of fiber optic connector with a 5°-15° angle on the connector tip for the minimum possible backreflection.
APD (Avalanche Photodiode): A photodiode that
exhibits internal amplification of photocurrent through avalanche
multiplication of carriers in the junction region.
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Asynchronous: Data that is transmitted without an associated clock signal. The time spacing between data characters or blocks may be of arbitrary duration. Opposite of synchronous.
ATM (Asynchronous Transfer Mode): 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 data bytes. Part of the B-ISDN standard.
ATSC (ADVAnced Television Systems Committee):
A committee formed to establish technical standards for advanced
television systems, including digital high definition television
(HDTV).
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Attenuation: The decrease in signal strength along a fiber optic waveguide caused by absorption and scattering. Attenuation is usually expressed in dB/km.
Attenuator: In optical systems, a passive device
for reducing the amplitude of a signal without appreciably distorting
the waveform.
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Average Power: The average level of power in a signal that varies with time.
Axis: The center of an optical fiber.
Back Channel: A means of communication
from users to content providers. Examples include a connection between
the central office and the end user, an Internet connection using
a modem, or systems where content providers transmit interactive
television (analog or digital) to users while users can connect
through a back channel to a web site, for example.
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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.
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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.
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 excessive attenuation or breakage
occurs.
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BER (Bit Error Rate): The fraction of bits transmitted that are received incorrectly.
BIDI (Bi-Directional Transceiver): A device that sends information in one direction and receives information from the opposite direction.
Bi-Directional: Operating in both directions.
Bi-Directional couplers operate the same way regardless of the direction
light passes through them. Bi-Directional transmission sends signals
in both directions, sometimes through the same fiber.
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Bit: The smallest unit of information upon which digital communications are based; also an electrical or optical pulse that carries this information.
BR (Backreflection): A term applied to any process in the cable plant that causes light to change directions in a fiber and return to the source. Occurs most often at connector interfaces where a glass-air interface causes a reflection.
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 (illustrated). 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.
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Bus Network: A network topology in which all terminals are attached to a transmission medium serving as a bus. Also called a daisy-chain configuration.
BW (Bandwidth): The range of frequencies within which a fiber optic waveguide or terminal device can transmit data or information.
Bypass: The ability of a station to isolate itself optically from a network while maintaining the continuity of the cable plant.
Byte: A unit of eight bits.
Cable: One or more optical fibers
enclosed, with strength members, in a protective covering.
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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.
CATV (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.
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CCTV (Closed-Circuit Television):An arrangement in which programs are directly transmitted to specific users and not broadcast to the general public.
CDMA (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
central operating wavelength. It is the wavelength defined by a
peak mode measurement where the effective optical power resides
(see illustration). In an LED, the average of the two wavelengths
measured at the half amplitude points of the power spectrum.
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Central Office (CO): A common carrier switching office in which users' lines terminate. The nerve center of a communications system.
Channel: A communications path or the signal sent over that path. Through multiplexing several channels, voice channels can be transmitted over an optical channel.
Chromatic Dispersion: Reduced fiber bandwidth
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.
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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.
Coating: The material surrounding the cladding of a fiber. Generally a soft plastic material that protects the fiber from damage.
Coaxial Cable: 1) A cable consisting of a center
conductor surrounded by an insulating material and a concentric
outer conductor and optional protective covering. 2) A cable consisting
of multiple tubes under a single protective sheath. This type of
cable is typically used for CATV, wideband, video, or RF applications.
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Concatenation: The process of connecting pieces of fiber together.
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 electrical cable (illustrated) or an optical 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.
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.
Coupler: An optical device that combines or splits power from optical fibers.
CPE (Customer Premises Equipment): 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.
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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.
CWDM (Coarse Wavelength-Division Multiplexing):
CWDM allows eight or fewer channels to be stacked in the 1550 nm
region of optical fiber, the C-Band.
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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: Decibel relative to a Carrier level.
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dBµ: Decibel relative to Microwatt.
dBm: Decibel relative to Milliwatt.
dB (Decibel): A unit of measurement indicating relative power on a logarithmic scale. Often expressed in reference to a fixed value, such as dBm or dBµ . dB = 10•Log10 (P1/P2)
Demultiplexer: A module that separates two or
more signals previously combined by compatible multiplexing equipment.
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Detector: An opto-electric transducer used to convert optical power to electrical current. Usually referred to as a photodiode.
Digital: A signal that consists of discrete states. A binary signal has only two states, 0 and 1. Antonym of analog.
Digital Compression: A technique for converting digital video to a lower data rate by eliminating redundant information.
Digital Subscriber Line (DSL): 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.
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).
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Diode Laser: Synonymous with injection laser diode.
Diplexer : A device that combines two or more types of signals into a single output. Usually incorporates a multiplexer at the transmit end and a demultiplexer at the receiver end.
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.
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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
nonlinearity at the zero-dispersion wavelength.
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Distortion: Nonlinearities in a unit that cause harmonics and beat products to be generated.
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.
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DSx: A transmission rate in the North American digital telephone hierarchy. Also called T-carrier.
Dual In-Line Package (DIP): An electronic package with a rectangular housing and a row of pins along each of two opposite sides.
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 directions, either one direction at a time (half-duplex) or both directions simultaneously (full-duplex).
DWDM (Dense Wavelength-Division Multiplexing): The
transmission of many of closely spaced wavelengths in the 1550 nm
region over a single optical fiber. Wavelength spacings are usually
100 GHz or 200 GHz which corresponds to 0.8 nm or 1.6 nm. DWDM bands
include the C-Band, the S-Band, and the L-Band.
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Electromagnetic Spectrum: The range of frequencies of electromagnetic radiation from zero to infinity.
EM I(Electromagnetic Interference): Any electrical or electromagnetic interference that causes undesirable response, degradation, or failure in electronic equipment. Optical fibers neither emit nor receive EMI.
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.
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Enterprise Systems Connection (ESCON): A duplex optical connector used for computer-to-computer data exchange.
E/O: Abbreviation for electrical-to-optical converter. A device that converts electrical signals to optical signals, such as a laser diode.
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.
Error Correction: In digital transmission systems,
a scheme that adds overhead to the data to permit a certain level
of errors to be detected and corrected.
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Error Detection: Checking for errors in data transmission. A calculation based on the data being sent; the results of the calculation are sent along with the data. The receiver then performs the same calculation and compares its results with those sent. If the receiver detects an error, it can be corrected, or it can simply be reported.
Ethernet: A standard protocol (IEEE 802.3) for
a 10-Mb/s baseband local area network (LAN) bus using carrier sense
multiple access with collision detection (CSMA/CD) as the access
method. Ethernet is a standard for using various transmission media,
such as coaxial cables, unshielded twisted pairs, and optical fibers.
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Extinction Ratio: The ratio of the low, or OFF optical power level (PL) to the high, or ON optical power level (PH): Extinction Ratio (%) = (PL/PH) x 100
Eye Pattern: A diagram that shows the proper function of a digital system. The "openness" of the eye relates to the BER that can be achieved.
FC/PC: See FC. A threaded optical
connector that uses a special curved polish on the connector for
very low backreflection. Good for single-mode or multimode fiber.
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FDM: See frequency-division multiplexing.
Ferrule : A rigid tube that confines or holds a fiber as part of a connector assembly.
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.
Fiber Distributed Data Interface (FDDI): 1) A dual counter-rotating ring local area network. 2) A connector used in a dual counter-rotating ring local area network (illustrated).
Fiber-In-the-Loop (FITL): Fiber optic service to a node that is located in a neighborhood.
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 System: The transfer of modulated or unmodulated optical energy through optical fiber media which terminates in the same or different media.
Fiber Optic Link: A transmitter, receiver, and
cable assembly that can transmit information between two points.
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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 to a 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.
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Filter: A device which transmits only part of the incident energy and may thereby change the spectral distribution of energy.
Free-Space Optics: Also called free-space photonics. The transmission of modulated visible or infrared (IR) beams through the atmosphere via lasers, LEDs, or IR-emitting diodes (IREDs) to obtain broadband communications.
Frequency-Division Multiplexing (FDM): A method of deriving two or more simultaneous, continuous channels from a transmission medium by assigning separate portions of the available frequency spectrum to each of the individual channels.
Fusion Splicer: An instrument that permanently bonds two fibers together by heating and fusing them.
Germanium (Ge): Generally used
in detectors. Good for most fiber optic wavelengths (e.g., 800-1600
nm). Performance is inferior to InGaAs
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Gigahertz (GHz): One billion Hertz (cycles per second) or 109 Hertz.
Graded-Index Fiber: Optical fiber in which the refractive index of the core is in the form of a parabolic curve, decreasing toward the cladding.
Half-Duplex Transmission: A bi-directional link that is limited to one-way transfer of data, i.e., data cannot be sent both ways at the same time. Also referred to as simplex transmission.
Hard Clad Silica Fiber: An optical fiber having a silica core and a hard polymeric plastic cladding intimately bounded to the core.
High Data-Rate Digital Subscriber Line (HDSL):
A DSL operating at a high data rate compared to the data rates specified
for ISDN.
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High Definition Television (HDTV): Television that has approximately twice the horizontal and twice the vertical emitted resolution specified by the NTSC standard.
Headend: 1) A central control device required within some LAN and MAN systems to provide such centralized functions as remodulation, retiming, message accountability, contention control, diagnostic control, and access to a gateway. 2) A central control device within CATV systems to provide such centralized functions as remodulation (illustrated). See also local area network (LAN).
Hertz (Hz): One cycle per second.
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Homes Passed (HP): Homes that could easily and inexpensively be connected to a cable network because the feeder cable is nearby.
Hot Swap: In an electronic device subassembly or component, the act or process of removing and replacing the subassembly or component without first powering down the device.
Institute of Electrical and Electronic Engineers (IEEE): A technical professional association that contributes to voluntary standards in technical areas ranging from computer engineering, biomedical technology and telecommunications, to electric power, aerospace and consumer electronics, among others.
Index-Matching Fluid: A fluid whose index of refraction nearly equals that of the fibers core. Used to reduce Fresnel reflection loss at fiber ends. Also known as index-matching gel.
Index of Refraction: The ratio of the velocity of light in free space to the velocity of light in a fiber material. Always greater than or equal to one. Also called refractive index. n = C/V
Where:
c = The speed of light in a vacuum.
v = The speed of the same wavelength in the fiber material
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Indium Gallium Arsenide (InGaAs): Generally used to make high-performance long-wavelength detectors.
Infrared (IR): The region of the electromagnetic spectrum bounded by the long-wavelength extreme of the visible spectrum (about 0.7 µm) and the shortest microwaves (about 0.1 µm).
In-Line Amplifier: An EDFA or other type of amplifier placed in a transmission line to strengthen the attenuated signal for transmission onto the next, distant site. In-line amplifiers are all-optical devices.
Insertion Loss: The loss of power that results
from inserting a component, such as a connector, coupler (illustrated),
or splice, into a previously continuous path.
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Integrated Circuit (IC): An electronic circuit that consists of many individual circuit elements, such as transistors, diodes, resistors, capacitors, inductors, and other passive and active semiconductor devices, formed on a single chip of semiconducting material and mounted on a single piece of substrate material.
Internet: A worldwide collection of millions of computers that consists mainly of the world wide web and e-mail.
Internet Protocol (IP): A standard protocol, developed by the DOD, for use in interconnected systems of packet-switched computer communications networks.
ISDN: See integrated services digital network.
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International Standards Organization (ISO): Established in 1947, ISO is a worldwide federation of national standards committees from 140 countries. The organization promotes the development of standardization throughout the world with a focus on facilitating the international exchange of goods and services, and developing the cooperation of intellectual, scientific, technological, and economical activities.
Internet Services Provider (ISP): A company or organization that provides Internet connections to individuals or companies via dial-up, ISDN, T1, or some other connection.
ITU: International Telecommunications Union.
Jacket: The outer, protective
covering of the cable. Also called the cable sheath.
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Jumper: A short fiber optic cable with connectors on both ends.
Kevlar®: A very strong, very light, synthetic compound developed by DuPont which is used to strengthen optical cables.
kHz: One thousand cycles per second.
km: Abbreviation for kilometer. 1 km = 3,280 feet or 0.62 miles.
Large Core Fiber:
Usually, a fiber with a core of 200 µm or more.
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Large Effective Area Fiber (LEAF): An optical fiber, developed by Corning, designed to have a large area in the core, which carries the light.
Laser: Acronym for Light Amplification by Stimulated Emission of Radiation. A light source that produces, through stimulated emission, coherent, near monochromatic light.
Laser Diode (LD): A semiconductor that emits coherent light when forward biased.
L-Band: The wavelength range between 1570 nm
and 1610 nm used in some CWDM and DWDM applications. LEAF: See large
effective area fiber.
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Least Significant Bit: In a binary code, the bit or bit position assigned to the smallest quantity or increment that can be represented by the code.
Local Exchange Carrier (LEC): A local telephone company, i.e., a communications common carrier that provides ordinary local voice-grade telecommunications service under regulation within a specified service area.
Local Exchange (LEX): Synonym for central office.
Long Haul (LH): A classification of video performance under RS-250C. Lower performance than medium-haul or short-haul.
Light: In a strict sense, the region of the electromagnetic
spectrum that can be perceived by human vision, designated the visible
spectrum, and nominally covering the wavelength range of 0.4 µm
to 0.7 µm. In the laser and optical communication fields,
custom and practice have extended usage of the term to include the
much broader portion of the electromagnetic spectrum that can be
handled by the basic optical techniques used for the visible spectrum.
This region has not been clearly defined, but, as employed by most
workers in the field, may be considered to extend from the near-ultraviolet
region of approximately 0.3 µm, through the visible region,
and into the mid-infrared region to 30 µm.
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Light-Emitting Diode (LED): A semiconductor that emits incoherent light when forward biased. Two types of LED's include edge-emitting LED's and surface-emitting LED's (illustrated).
Light Piping: Use of optical fibers to illuminate.
Lightguide: Synonym for optical fiber.
Lightwave: The path of a point on a wavefront.
The direction of the lightwave is generally normal (perpendicular)
to the wavefront.
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Linear Device: A device for which the output is, within a given dynamic range, linearly proportional to the input.
Linearity: The basic measurement of how well analog-to-digital and digital-to-analog conversions are performed. To test for linearity, a mathematically perfect diagonal line is converted and then compared to a copy of itself. The difference between the two lines is calculated to show linearity of the system and is given as a percentage or range of least significant bits.
Local Area Network (LAN): A communication link between two or more points within a small geographic area, such as between buildings. Smaller than a metropolitan area network (MAN) or a wide area network(WAN).
Long-Haul Telecommunications: 1. In public switched
networks, regarding circuits that span long distances, such as the
circuits in inter-LANA, interstate, and international communications.
2. In military use, communications among users on a national or
worldwide basis. Long-haul communications are characterized by a
higher level of users, more rigorous performance requirements, longer
distances between users, including world wide distances, higher
traffic volumes and densities, larger switches and trunk cross sections,
and fixed and recoverable assets. Usually pertains to the U.S. Defense
Communications System.
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Longitudinal Mode: An optical waveguide mode with boundary condition determined along the length of the optical cavity.
Loose-tube: A type of fiber optic cable construction where the fiber is contained within a loose tube in the cable jacket.
Loss: The amount of a signal’s power, expressed in dB, that is lost in connectors, splices, or fiber defects.
Loss Budget: An accounting of overall attenuation in a system. See optical link loss budget.
Lossless Compression: 1) Reduction of the storage
size of digital data by employing one or more appropriate algorithms
in such a way that the data can be recover without loosing integrity.
2) Reduction of the amount of data that needs to be transmitted
per unit time though an analogous real-time process that does not
compromise the ability to completely restore the data.
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(Metropolitan Area Network (MAN): A network covering an area larger than a local area network. A series of local area networks, usually two or more, that cover a metropolitan area.
Margin: Allowance for attenuation in addition to that explicitly accounted for in system design.
Medium Access Control (MAC): 1) A service feature or technique used to permit or deny use of the components of a communication system. 2) A technique used to define or restrict the rights of individuals or application programs to obtain data from, or place data onto, a storage device, or the definition derived from that technique.
MH: Abbreviation for medium-haul. A classification
of video performance under RS-250C. Higher performance than long-haul
and lower performance than short-haul. MHz: Abbreviation for megahertz.
One million Hertz (cycles per second).
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Microbending: Mechanical stress on a fiber that introduces local discontinuities, which results in light leaking from the core to the cladding by a process called mode coupling.
Micrometer: One millionth of a meter or 10-6 meters. Abbreviated µm.
Microsecond: One millionth of a second or 10-6 seconds. Abbreviated µs.
Microwatt: One millionth of a Watt or 10-6 Watts. Abbreviated µW.
Microwave Transmission: Communication systems using very high-frequency RF to carry the signal information.
Military Specifications (MIL-SPEC): Performance specifications issued by the Department of Defense that must be met in order to pass a MIL-STD.
Military Standard (MIL-STD): Standards issued
by the Department of Defense.
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Minimum Bend Radius: The smallest radius an optical fiber or fiber cable can bend before increased attenuation or breakage occurs.
Misalignment Loss: The loss of power resulting from angular misalignment, lateral displacement, and fiber end separation. MLM: See multilongitudinal mode laser. mm: Abbreviation for millimeter. One thousandth of a meter or 10-3 meters.
Modal Dispersion: See multimode dispersion.
Modal Noise: Noise that occurs whenever the optical power propagates through mode-selective devices. It is usually only a factor with laser light sources.
Mode: A single electromagnetic wave traveling
in a fiber.
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Mode Coupling: The transfer of energy between modes. In a fiber, mode coupling occurs until equilibrium mode distribution (EMD) is reached.
Modulation: The process by which the characteristic of one wave (the carrier) modifies another wave (the signal). Examples include amplitude modulation (AM), frequency modulation (FM), and pulse-coded modulation (PCM). Modulation Index: In an intensity-based system, the modulation index is a measure of how much the modulation signal affects the light output. It is defined as follows: m = (highlevel - lowlevel) / (highlevel + lowlevel)
Modulator: A device that imposes a signal on a carrier.
Monitor: 1) a CRT that receives its signal directly
from a VCR, camera, or separate TV tuner for high-quality picture
reproduction. 2) A device used for the real-time temporary display
of computer output data. 3) Software or hardware that is used to
scrutinize and to display, record, supervise, control, or verify
the operations of a system.
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Multiple Service Operator (MSO): A telecommunications company that offers more than one service, e.g. telephone service, Internet access, satellite service, etc.
Mean Time Between Failure (MTBF): Time after which 50% of the units of interest will have failed. Also called MTTF (mean time to failure).
Multilongitudinal Mode (MLM) Laser : An injection laser diode which has a number of longitudinal modes.
Multimode Dispersion: Dispersion resulting from the different transit lengths of different propagating modes in a multimode optical fiber. Also called modal dispersion.
Multimode (MM) Fiber: An optical fiber that has a core large enough to propagate more than one mode of light The typical diameter is 62.5 micrometers.
Multimode Laser Diode (MMLD): Synonym for multilongitudinal
mode laser.
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Multiple Reflection Noise (MRN): The fiber optic receiver noise resulting from the interference of delayed signals from two or more reflection points in a fiber optic span. Also known as multipath interference.
Multiplexer: A device that combines two or more signals into one output.
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 (WDM).
National Cable Television
Association (NCTA): The major trade association for the
cable television industry.
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National Electric Code® (NEC): A standard governing the use of electrical wire, cable and fixtures installed in buildings; developed by the American National Standards Institute (ANSI), sponsored by the National Fire Protection Association (NFPA), identified by the description ANSI/NFPA 70-1990.
National Electrical Manufacturers Assocation (NEMA): Organization responsible for the standardization of electrical equipment, enabling consumers to select from a range of safe, effective, and compatible electrical products.
Near-End Crosstalk (NEXT, RN): The optical power reflected from one or more input ports, back to another input port. Also known as isolation directivity.
National Fiber Protection Association (NFPA): Abbreviation for National Fire Protection Association. Publisher of the National Electrical Code®, and 300 other codes and standards through a full, open-consensus process.
National Television Systems Committee (NTSC): 1) Abbreviation for National Television Systems Committee. The organization which formulated the NTSC system. 2) Standard used in the U.S. that delivers 525 lines at 60 frames per second.
Near Infrared: The part of the infrared near
the visible spectrum, typically 700 nm to 1500 nm or 2000 nm; it
is not rigidly defined.
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Network: 1) An interconnection of three or more communicating entities and (usually) one or more nodes (illustrated). 2) A combination of passive or active electronic components that serves a given purpose.
Network Topology: The specific physical, i.e., real, logical, or virtual, arrangement of the elements of a network. Common network topologies include a bus (or linear) topology, a ring topology, and a hybrid topology, which can be a combination of any two or more network topologies. Illustrated to the right is a bus topology utilizing tee couplers to connect a series of stations that listen to a single backbone of cable.
Node: 1) A terminal of any branch in network
topology or an interconnection common to two or more branches in
a network. 2) One of the switches forming the network backbone in
a switch network. 3) A point in a standing or stationary wave at
which the amplitude is a minimum.
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Noise: 1) An undesired disturbance within the frequency band of interest; the summation of unwanted or disturbing energy introduced into a communications system from man-made and natural sources. 2) A disturbance that affects a signal and that may distort the information carried by the signal. 3) Random variations of one or more characteristics of any entity such as voltage, current, or data.
Noise Equivalent Power (NEP): The noise of optical receivers, or of an entire transmission system, is often expressed in terms of noise equivalent optical power.
Noise Figure (NF): The ratio of the output signal-to-noise
ratio to the input signal-to-noise ratio for a given element in
a transmission system. Used for optical and electrical components.
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Non Dispersion-Shifted Fiber (NDSF): The most popular type of single-mode fiber deployed. It is designed to have a zero-dispersion wavelength near 1310 nm.Nonlinearity: The deviation from linearity in an electronic circuit, an electro-optic device or a fiber that generates undesired components in a signal. Examples of fiber nonlinearities include SBS, SRS, FWM, SPM, XPM, and Intermodulation.
Non Zero-Dispersion-Shifted Fiber (NZ-DSF):
A dispersion-shifted single-mode fiber that has the zero-dispersion
wavelength near the 1550 nm window, but outside the window actually
used to transmit signals. This strategy maximizes bandwidth while
minimizing fiber nonlinearities.
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Numerical Aperture (NA): The light-gathering ability of a fiber; the maximum angle to the fiber axis at which light will be accepted and propagated through the fiber. NA also describes the angular spread of light from a central axis, as in exiting a fiber, emitting from a source, or entering a detector.
Open Systems Interconnection (OSI): Pertaining to the logical structure for communications networks standardized by the International Organization for Standardization (ISO).
Operation, Administration, and Maintenance (OAM): Refers to telecommunications networks.
Optical Access Network (OAN): A network technology,
based on passive optical networks (PONs), that includes an optical
switch at the central office, an intelligent optical terminal at
the customer’s premises, and a passive optical network between
the two, allowing services providers to deliver fiber-to-the-home
while eliminating the expensive electronics located outside the
central office.
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Optical Add/Drop Multiplexer (OADM): A device which adds or drops individual wavelengths from a WDM system.
Optical Amplifier: A device that amplifies an input optical signal without converting it into electrical form. The best developed are optical fibers doped with the rare earth element, erbium. See also EDFA.
Optical Bandpass: The range of optical wavelengths which can be transmitted through a component.
Optical Channel: An optical wavelength band for WDM optical communications.Optical Channel Spacing: The wavelength separation between adjacent WDM channels.
Optical Carrier (OC-x): Abbreviation for optical carrier. A carrier rate specified in the SONET/SDH standard.
Optical Cross-Connect (OXC): See cross-connect.
Optical Distribution Network (ODN): Term for optical networks being developed for interactive video, audio, and data distribution.
Optical Fiber: A glass or plastic fiber that has the ability to guide light along its axis. The three parts of an optical fiber are the core, the cladding, and the coating or buffer.
Optical Interface (OOI): A point at which an optical signal is passed from one equipment medium to another without conversion to an electrical signal
Optical Isolator: A component used to block out reflected and unwanted light. Also called an isolator.
Optical Line Termination (OLT): Optical network elements that terminate a line signal.
Optical Loss Test Set (OLTS): A source and optical power meter combined used to measure optical loss.
Optical Link Loss Budget: The range of optical
loss over which a fiber optic link will operate and meet all specifications.
The loss is relative to the transmitter output power and affects
the required receiver input power.
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Optical Multiplex Section (OMS): A section of a DWDM system that incorporates an optical add/drop multiplexer.
Optical Network Interface (ONI): A device used in an optical distribution network to connect two parts of that network.
Optical Network Termination (ONT): Optical network element that terminates a line signal in installations where the fiber extends into the customer premises.
Optical Network Unit (ONU): Abbreviation for optical network unit. A network element that is part of a fiber-in-the-loop system.
Optical Path Power Penalty: The additional loss budget required to account for degradations due to reflections, and the combined effects of dispersion resulting from intersymbol interference, mode-partition noise, and laser chirp.
Optical Power Meter: An instrument that measures
the amount of optical power present at the end of a fiber or cable.
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Optical Pump Laser: A shorter wavelength laser used to pump a length of fiber with energy to provide amplification at one or more longer wavelengths. See also EDFA.
Optical Return Loss (ORL): The ratio (expressed in dB) of optical power reflected by a component or an assembly to the optical power incident on a component port when that component or assembly is introduced into a link or system.
Optical Rise Time: The time interval for the rising edge of an optical pulse to transition from 10% to 90% of the pulse amplitude. Alternatively, values of 20% and 80% may be used.
Optical Spectrum Analyzer (OSA): A device that allows the details of a region of an optical spectrum to be resolved. Commonly used to diagnose DWDM systems.
Optical Time Domain Reflectometer (OTDR): An instrument that locates faults in optical fibers or infers attenuation by backscattered light measurements.
Optical-to-Electrical Converter (O/E): A device used to convert optical signals to electrical signals. Also known as OEC.
Optical Waveguide: Another name for optical fiber.
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Opto-Electronic Integrated Circuit (OEIC): An integrated circuit that includes both optical and electrical elements.
Original Equipment Manufacturer (OEM): The manufacturer of any device that is designed and built to be distributed under the label of another company.
Outside Plant (OSP): In telephony, all cables,
conduits, ducts, poles, towers, repeaters, repeater huts, and other
equipment located between a demarcation point in a switching facility
and a demarcation point in another switching facility or customer
premises.
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Packet: In data communications, a sequence of binary digits, including data and control signals, that is transmitted and switched as a composite whole. The packet contains data, control signals, and possibly error control information, arranged in a specific format.
Packet Switching: The process of routing and transferring
data by means of addressed packets so that a channel is occupied
during the transmission of the packet only, and upon completion
of the transmission the channel is made available for the transfer
of other traffic.
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Parity: A term used in binary communication systems to indicate whether a number of 1’s in a transmission is even or odd. If the number of 1’s is even, the parity is said to be even; if the number of 1’s is odd, the parity is said to be odd.
Passband: The region of usable frequency in electronics or wavelength in optics.
Passive Branching Device: A device which divides an optical input into two or more optical outputs.
Passive Device: Any device that does not require a source of energy for its operation. Examples include electrical resistors or capacitors, diodes, optical fiber (photo), cable, wires, glass, lenses, and filters.
Passive Optical Network (PON): Abbreviation for
passive optical network. A broadband fiber optic access network
that uses a means of sharing fiber to the home without running individual
fiber optic lines from an exchange point, telco CO, or a CATV headend
and the subscriber's home.
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Pathological Test Code: A special test pattern used with DTV and HDTV signals to create the longest strings of zeros and ones over the serial link. This requires the serial transport link to handle much lower frequency components than is typical in a normal data link.
Pay-Per-View (PPV): An event that has an associated
viewing cost, and which may be purchased separately from any package
or subscription. The ordered events could include movies, special
events, such as sporting, or adult programming. The event could
be purchased by either impulse PPV by using a television remote
(this application requires a continuous land line phone based connection),
or over the phone PPV (this application may have additional costs
for processing).
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Phase Alternation by LIne (PAL): Abbreviation for phase alternation by line. A composite color standard used in many parts of the world for TV broadcast. The phase alternation makes the signal relatively immune to certain distortions (compared to NTSC). Delivers 625 lines at 50 frames per second. PAL-plus is an enhanced-definition version.
Photoconductive: Losing an electrical charge on exposure to light.
Photodetector: An optoelectronic transducer such as a PIN photodiode (illustrated) or avalanche photodiode. In the case of the PIN diode, it is so named because it is constructed from materials layered by their positive, intrinsic, and negative electron regions.
Photodiode (PD): A semiconductor device that converts light to electrical current.
Photon: A quantum of electromagnetic energy.
A particle of light.
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Photonic: A term coined for devices that work using photons, analogous to the electronic for devices working with electrons.
Photovoltaic: Providing an electric current under the influence of light or similar radiation.
Physical Contact (PC): Refers to an optical connector that allows the fiber ends to physically touch. Used to minimize backreflection and insertion loss.
Pigtail: A short optical fiber permanently attached to a source, detector, or other fiber optic device at one end and an optical connector at the other.
Plain Old Telephone System (POTS): A call that requires nothing more than basic call handling without additional features.
Planar Lightwave Circuit (PLC): Abbreviation for planar lightwave circuit. A device which incorporates a planar waveguide.
Planar Waveguide: A waveguide fabricated in a flat material such as thin film.
Plastic Fiber: An optical fiber having a plastic
core and plastic cladding.
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Plenum: The air handling space between walls, under structural floors, and above drop ceilings, which can be used to route intrabuilding cabling.
Plenum Cable: A cable whose flammability and
smoke characteristics allow it to be routed in a plenum area without
being enclosed in a conduit.
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Point-to-Point Transmission: Transmission between two designated stations.
Polarization: The direction of the electric field in the lightwave. If the electric field of the lightwave is in the Y Axis, the light is said to be vertically polarized. If the electric field of the lightwave is in the X axis, the light is said to be horizontally polarized.
Polarization Maintaining Fiber: Fiber designed to propagate only one polarization of light that enters it.
Polarization Mode Dispersion (PMD): Polarization
mode dispersion is an inherent property of all optical media. It
is caused by the difference in the propagation velocities of light
in the orthogonal principal polarization states of the transmission
medium. The net effect is that if an optical pulse contains both
polarization components, then the different polarization components
will travel at different speeds and arrive at different times, smearing
the received optical signal.
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Port: Hardware entity at each end of the link.
Printed Circuit Board (PCB): Also referred to as PWB
Private Branch Exchange (PBX): Abbreviation for
private branch exchange. A subscriber-owned telecommunications exchange
that usually includes access to public switched networks.
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Public Switched Networks (PSN): 1. Any common carrier network that provides circuit switching among public users. 2. A switched network accessible to the public for originating and terminating telecommunications messages. 3. Any common carrier switched network, whether by wire or radio, including local exchange carriers, interexchange carriers, and mobile service providers, that use the North American Numbering Plan in common with provision of switched services.
Public Switched Telephone Network (PSTN): A domestic telecommunications network usually accessed by telephones, key telephone systems, private branch exchange trunks, and data arrangements.
Pulse: A current or voltage which changes abruptly from one value to another and back to the original value in a finite length of time. Used to describe one particular variation in a series of wave motions. The parts of the pulse include the rise time, fall time, and pulse width, pulse amplitude. The period of a pulse refers to the amount of time between pulses.
Pulse-code Modulation (PCM): A technique in which
an analog signal, such as a voice, is converted into a digital signal
by sampling the signal's amplitude and expressing the different
amplitudes as a binary number. The sampling rate must be at least
twice the highest frequency in the signal.
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Pulse Dispersion: The dispersion of an optical signal as it propagates through an optical fiber. Also called pulse spreading.
Pump Laser: A power source for signal amplification, typically a 980 nm or 1480 nm laser, used in EDFA applications.
Push: 1) In electronic marketing, to send data to another computer without a direct request from that computer. 2) In networking, to send data from a server to a client in compliance with a previous request from the client, as soon as the data becomes available.
Quality of Service (QoS): 1.
The performance specification of a communications channel or system
which may be quantitatively indicated by channel or system performance
parameters such as signal-to-noise ratio, bit error rate, message
throughput rate, and call blocking probability. 2. A subjective
rating of telephone communications quality in which listeners judge
transmissions by qualifiers such as excellent, good, fair, poor,
or unsatisfactory.
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Random Jitter (RJ): Random jitter
is due to thermal noise and may be modeled as a Gaussian process.
The peak-to-peak value of RJ is of a probabilistic nature, and thus
any specific value requires an associated probability.
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Rays: Lines that represent the path taken by light. Receiver: A terminal device that includes a detector and signal processing electronics. It functions as an optical-to-electrical converter.
Recombination: Combination of an electron and a hole in a semiconductor that releases energy, leading to light emission.
Refraction: The changing of direction of a lightwave in passing through a boundary between two dissimilar media, or in a graded-index medium where refractive index is a continuous function of position.
Refractive Index: A property of optical materials
that relates to the speed of light in the material versus the speed
of light in a vacuum.
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Refractive Index Gradient: The description of the value of the refractive index as a function of distance from the optical axis along an optical fiber diameter. Also called refractive index profile.
Regenerative Repeater: A repeater, designed for digital transmission, in which digital signals are amplified, reshaped, retimed, and retransmitted.
Regenerator: Synonym for regenerative repeater.
Repeater: A receiver and transmitter set designed to regenerate attenuated signals. Used to extend operating range.
Request to Send (RTS): Abbreviation for request
to send. In a communications network, a signal from a remote receiver
to a transmitter for data to be sent to that receiver.
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Residual Loss: The loss of the attenuator at the minimum setting of the attenuator.
Responsivity: The ratio of a photodetector’s electrical output to its optical input in Amperes/Watt (A/W).
Return Loss: See optical return loss.RF: Abbreviation for radio frequency. Any frequency within the electromagnetic spectrum normally associated with radio wave propagation.
Return Path: A communications connection that carries signals from the subscriber back to the operator. The return path allows for interactive television and on-demand services, such as pay-per-view, video on demand, and interactive games.
Return to Zero (RZ): A common means of encoding data that has two information states called "zero" and "one" in which the signal returns to a rest state during a portion of the bit period.
Ribbon Cables: Cables in which many fibers and/or
copper wires are embedded in a plastic material in parallel, forming
a flat ribbon-like structure.
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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 taken to make a transition from one state to another, usually measured between the 10% and 90% completion points of the transition. Alternatively the rise time may be specified at the 20% and 80% amplitudes. Shorter or faster rise times require more bandwidth in a transmission channel.
Root Mean Square (RMS): Technique used to measure AC voltages.
RS-250C: An ANSI recommended standard for video
transmission used to evaluate the quality of a received picture
quality. Different requirements exist for short-haul, medium-haul,
and long-haul RS-250C. Each of these three levels is defined by
the number of intermediate processing devices and the type of path
(optical or electrical).
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Sampling Rate: The number of
discrete sample measurements made in a given period of time. Often
expressed in megahertz (MHz) for video.
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Saturation: 1) In a communications system, the condition in which a component of the system has reached its maximum traffic handling capacity. 2) The point at which the output of a linear device, such as a linear amplifier, deviates significantly from being a linear function of the input when the input signal is increased. 3) The degree of the chroma or purity of a color.
S-Band: The wavelength region between 1485 nm
and 1520 nm used in some CWDM and DWDM applications.
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Self Phase Modulation (SPM): Self-phase modulation.
Set-Top Box (STB): An auxiliary device that usually sits on top of or adjacent to a television receiver used in direct analog or digital satellite transmission and digital television to view the signals on an analog TV. Converter boxes are becoming obsolete as old model televisions requiring a converter are replaced by modern televisions, which incorporate a converter into the television. Also called a set-top converter.
Sensitivity: See receiver sensitivity.
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Serial: One bit at a time, along a single transmission path.
Simple Network Management Protocol (SNMP): The Internet standard protocol for network management software. It monitors devices on the network, and gathers device performance data for management information data bases (MIB).
Simplex: Single element (e.g., a simplex connector is a single-fiber connector).
Simplex Cable: A term sometimes used for a single-fiber
cable. Simplex
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Single Attachment Concentrator: A concentrator that offers one attachment to the FDDI network.
Single-line Laser: See single-longitudinal mode laser.
Single-longitudinal Mode Laser (SLM): An injection laser diode which has a single dominant longitudinal mode. A single-mode laser with a side mode suppression ratio (SMSR)< 25 dB.
Single-mode (SM) Fiber: A small-core optical fiber through which only one mode will propagate. The typical diameter is 8-9 microns.
Single-mode Laser Diode (SMLD): See single-longitudinal
mode laser.
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Single-mode Optical Loss Test Set (SMOLTS): An optical loss test set for use with single-mode fiber.
SMA: A threaded type of optical connector. One of the earliest optical connectors to be widely used. Offers poor repeatability and performance.
Small Computer Sytems Interface (SCSI): An intelligent interface device that expands a microprocessor (CPU) bus to facilitate connections to multiple peripherals (e.g., CD-ROM drives, hard drives, or scanners) and exchange data with those peripherals via a separate communications bus.
Smart Structures: Also smart skins. Materials containing sensors (fiber optic or other types) to measure their properties during fabrication and use.
Society of Motion Picture and Television Engineers (SMPTE):
Organization that publishes ANSI-approved standards, recommended
practices, and engineering guidelines for the motion picture and
television industry.
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Soliton Pulse: An optical pulse
having a shape, spectral content, and power level designed to take
advantage of nonlinear effects in an optical fiber waveguide, for
the purpose of essentially negating dispersion over long distances.
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Source: In fiber optics, a transmitting LED or laser diode, or an instrument that injects test signals into fibers.
Span Engineering: The process of designing a DWDM transmission span to achieve the required performance based on fiber type, the transmission distance, amplifier spacing, noise, power, and channel count.
Spectral Efficiency: The number of data bits per second that can be transmitted in a one Hertz bandwidth range.
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 50 to 160 nm for an LED and less than 5 nm for a laser
diode.
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Spectral Width, Full Width, Half Maximum (FWHM): The absolute difference between the wavelengths at which the spectral radiant intensity is 50 percent of the maximum power.
Splice: A permanent connection of two optical fibers through fusion or mechanical means.
Splitter: see Coupler.Splitting Ratio: The ratio
of power emerging from two output ports of a coupler.
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Stabilized Light Source: An LED or laser diode that emits light with a controlled and constant spectral width, center wavelength, and peak power with respect to time and temperature.
Star Coupler: A coupler in which power at any input port is distributed to all output ports.
Star Network: A network in which all terminals
are connected through a single point, such as a star coupler or
concentrator.
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Step-index Fiber: Fiber that has a uniform index of refraction throughout the core that is a step below the index of refraction in the cladding.
Stimulated Brillouin Scattering (SBS ): The easiest
fiber nonlinearity to trigger. When a powerful light wave travels
through a fiber it interacts with acoustical vibration modes in
the glass. This causes a scattering mechanism to be formed that
reflects much of the light back to the source.
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Stimulated Raman Scattering (SRS): A fiber nonlinearity similar to SBS but having a much higher threshold. This mechanism can also cause power to be robbed from shorter wavelength signals and provide gain to longer wavelength signals.
Storage Area Network (SAN): Connects a group of computers to high-capacity storage devices. May be incorporated into local area networks (LAN), metropolitan area networks (MAN), and wide area networks (WAN).
Straight Tip Connector (ST): Popular fiber optic connector originally developed by AT&T.
Strength Member: The part of a fiber optic cable composed of aramid yarn, steel strands, or fiberglass filaments that increase the tensile strength of the cable.
Subcarrier Multiplexing (SCM): The process by which multiple subcarrier signals are combined onto one signal.
Submarine Cable: A cable designed to be laid underwater.
Subscriber Loop: Also called local loop. The link from the telephone company central office (CO) to the home or business (customer premises).
Subscription Channel (SC): A push-pull type of optical connector that features high packing density, low loss, low backreflection, and low cost.
Supertrunk: A cable that carries several video channels between facilities of a cable television company. Surface-emitting Diode: A simple and inexpensive LED that emits light from its flat surface rather than its side with emission spread over a wide angle.
Surface Mount Technology (SMT): An electronics
manufacturing technique.
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Switch: 1) In communications systems, a mechanical, electro-mechanical, or electronic device for making, breaking, or changing the connections in or among circuits. 2) Synonym for central office, switching center. 3) In communications systems, to transfer a connection from one circuit to another.
Synchronous Optical Network Transport System (SONET): An interface standard widely used by the telecom industry where OC-3 is the lowest current rate (155.5 Mb/s), and OC-768 is the highest rate being contemplated (39.808 Gb/s). Valid rates increase by a factor of four from the OC-3 rate up to OC-768.
Synchronization Pulse: 1) A signal derived from
the composite or combination of the horizontal and vertical drives.
2) A pulse used to achieve or maintain synchronism, usually applied
to analog signals. (The term "synchronization bit" is
usually applied to digital data streams.) Commonly called the sync
pulse. See also composite sync.
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Synchronous: A data signal that is sent along with a clock signal. A system in which events, such as signals, occur at evenly spaced time durations. Opposite of asynchronous.
Synchronous Code Division Multiple Access (S-CDMA): A synchronized version of CDMA.
Système Internationale (SI Units): In English, International System of Units, commonly known as the metric system.
T1: In telecommunications, the cable used to transport DS1 service.
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 where
the splitting ratio between output ports is not equal, the output
port containing the lesser power.
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T-Carrier: Generic designator for any of several
digitally multiplexed telecommunications carrier systems.
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Telecommunications Management Network (TMN ): A network that interfaces with a telecommunications network at several points in order to receive information from, and to control the operation of, the telecommunications network.
Ternary: A semiconductor compound made of three
elements (e.g., GaAlAs). Thermal Noise: Noise resulting from thermally
induced random fluctuation in current in the receiver’s load
resistance.
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Throughput Loss: In a fiber optic coupler, the ratio of power at the throughput port to the power at the input port.
Throughput Port : In a coupler where the splitting ratio between output ports is not equal, the output port containing the greater power.
Tight-Buffer: A material tightly surrounding a fiber in a cable, holding it rigidly in place.
Time-Division Multiplexing : A transmission
technique whereby several low-speed channels are multiplexed into
a high-speed channel for transmission. Each low-speed channel is
allocated a specific position based on time.
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Time-Division Multiple Access (TDMA): A communications technique that uses a common channel (multipoint or broadcast) for communications among multiple users by allocating unique time slots to each user. Used extensively in satellite systems, local area networks, physical security systems, and combat-net radiosystems.
Token Ring: A ring-based network scheme in which
a token is used to control access to a network. Used by IEEE 802.5
and FDDI.
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Total Internal Reflection: The reflection that
occurs when light strikes an interface at an angle of incidence
(with respect to the normal) greater than the critical angle.
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Transceiver: A device that performs, within one chassis, both telecommunication transmitting and receiving functions.
Transducer: A device that converts energy from one form to another, such as optical energy to electrical energy.
Transmission: Transmission in one direction only. Also referred to as half-duplex transmission.
Transmission Control Protocol/Internet Protocol (TCP/IP): Two interrelated protocols that are part of the Internet protocol suite. TCP operates on the OSI transport layer and breaks data into packets. IP operates on the OSI network layer and routes packets. Originally developed by the U.S. Department of Defense.
Transmitter: A device that includes a source
and driving electronics. It functions as an electrical-to-optical
converter. Transponder: The part of a satellite that receives and
transmits a signal.
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Tree: In communications networks, a physical topology consisting of a hierarchy of master-slave connections between a concentrator and other FDDI nodes (including subordinate concentrators).
Trunk: 1) In a communications network, a single transmission channel between two switching centers or nodes, or both. 2) A circuit between switchboards or other switching equipment, as distinguished from circuits which extend between central office switching equipment and information origination/termination equipment. Trunks may be used to interconnect switches, such as major, minor, public and private switches, to form networks.
Unidirectional: Operating in
one direction only.
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Ultaraviolet (UV): That portion of the electromagnetic spectrum in which the longest wavelength is just below the visible spectrum, extending from approximately 4 nm to 400 nm.
Unity Gain: A concept in which all the amplifiers in a cascade are in balance with their power inputs and outputs. Unity gain can be achieved by adjusting the receiver output, either by padding or attenuation in the node, to the proper level determined by the RF input.
Vertical Cavity Surface-emitting
Laser: Lasers that emit light perpendicular to the plane
of the wafer they are grown on. They have very small dimensions
compared to conventional lasers and are very efficient.
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Very High Data Rate Digital Subscriber Line (VDSL): A DSL operating at a data rate higher than that of HDSL. See also DSL.
Video on Demand (VOD): See video on demand.
Virtual Private Network (VPN): A protected information-system link utilizing tunneling, security controls, and end-point address translation giving the end user the impression that a dedicated line exists between nodes.
Visible Light: Electromagnetic radiation visible to the human eye; wavelengths of 400-700 nm.
Voice Circuit: A circuit capable
of carrying one telephone conversation or its equivalent; the standard
sub-unit in which telecommunication capacity is counted. The U.S.
analog equivalent is 4 kHz. The digital equivalent is 64 kbit/s
in North America and in Europe.
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Wave Division Multiplexing (WDM): Sending several signals through one fiber with different wavelengths of light.
Wide Area Network (WAN): A physical or logical network that provides capabilities for a number of independent devices to communicate with each other over a common transmission-interconnected topology in geographic areas larger than those served by local area networks or metropolitan area networks.
Wideband: Possessing large bandwidth.
Wireless: A network or terminal that uses electromagnetic waves, such as RF, infrared, laser, visible light, and acoustic energy, not wires, for telecommunications.
XT (Crosstalk): 1) Undesired coupling from one circuit, part of a circuit, or channel to another. 2) Any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates and undesired effect in another circuit or channel.
Zipcord: A two-fiber cable consisting
of two single fiber cables having conjoined jackets. A zipcord cable
can be easily divided by slitting and pulling the conjoined jackets
apart.
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1U: Abbreviation for “one unit.” “U” = 1.75 inches.
10BASE-T: A twisted-pair cable version of an IEEE 802.3 network.
10BASE-2: A thin-coaxial-cable version of an IEEE 802.3 network
10BASE-5: A thick-coaxial-cable version of an IEEE 802.3 network; very similar to the original Ethernet specification.
