Fiber Optic Communications for the Premises Environment

CHAPTER 8

GLOSSARY


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

Absorption - Loss of power in a fiber optic cable resulting from conversion of optical power into heat. This is principally caused by impurities, such as transition metals and hydroxyl ions. It is also caused by exposure to nuclear radiation.

Acceptance angle - The half angle of the cone which incident light is totally, internally, reflected by the fiber core. It is the angle over which the core of an optical fiber accepts incoming light, usually measured from the fiber axis. It is equal to the arcsine (NA) where NA is the numerical aperture.

Active area - The area of a detector with greatest response.

AM - Amplitude Modulation.

Amplitude Modulation - A transmission technique in which the amplitude of a carrier is varied in sympathy with the information being communicated.

Analog - A format that uses continuous physical parameters to transmit information. Examples of parameters are voltage amplitude and carrier frequency.

Angle of deviation - In ray optic theory it is the net resultant angular deflection experienced by a light ray after one or more reflections or refraction's. The term is used in reference to prisms with air interfaces. The angle of deviation is the angle between the original incident ray and the emergent ray.

Angle of incidence - In ray optic theory it is the angle between an incident ray and the normal to a reflecting or refracting surface.

Angular misalignment loss - The optical power loss caused by angular deviation from the optimum alignment of source to optical fiber.

Angular tilt - The angle formed by the axes of 2 fibers to be joined. Angular tilt causes an extrinsic loss that depends upon the joining hardware and method.

APD - Avalanche photodiode.

APF - All Plastic Fiber.

Aramid yarn - Strength element used in Siecor cable to provide support and additional protection of the fiber optic cable bundles. Kevlar is a particular brand of Aramid yarn.

ATM - Asynchronous Transfer Mode. This is a new emerging data standard (protocol) that uses many of the same data rates as Fiber Channel and SONET.

Attenuation - In fiber optic cable, attenuation results from absorption, scattering and other radiation losses. It is usually expressed as decibels per kilometer (dB/km) without the negative sign. Calculations and equations involving loss show and use the negative sign.

Attenuation-limited operation - The condition in a fiber optic cable based communications link when operation is limited by the power of the receive signal, rather than by bandwidth or by distortion.

Attenuator - A passive optical component that intentionally reduces the optical power propagating in a fiber optic cable.

Avalanche Photodiode (APD) - A photodiode that exhibits internal amplification of photocurrent. It accomplishes this by avalanche multiplication of carriers in the junction region. As the reverse-bias voltage approaches the breakdown voltage, electron-hole pairs created by absorbed photons acquire sufficient energy to create additional electron-hole pairs when they collide with ions. A multiplication or signal gain is thereby achieved.

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

Axial ray - A light ray that travels along the axis of a fiber optic cable.

Backscattering - The return of a portion of scattered light to the input end of a fiber optic cable. It is the scattering of light in the direction opposite to its original direction of propagation.

Balanced - Signaling code with an equal number of high and low states.

Bandpass - A range of wavelengths over which a component will meet specifications.

Bandwidth - The information capacity of a fiber optic cable. Precisely it is usually measured in GHz (1 Billion Hz). Occasionally it is idiomatically discussed in terms of the data transmission rate- the BPS- the actual GHz bandwidth can support. In some contexts it is expressed as MHz-km and denotes the analog bandwidth capability of digital transitions per second that a fiber optic cable can sustain over a 1-km distance. Occasionally the bandwidth of a light source is referred to. This is the width of the spectrum emitted.

Bandwidth-limited operation - The condition in a fiber optic cable based communications link when bandwidth, rather than received signal 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 rather than being impressed upon a carrier frequency.

Baud - A unit of data transmission signaling speed - data transmission rate - equal to the number of signal symbols per second. With binary modulation systems this is the same as the data transmission rate in Bits Per Second. However, it is different with non-binary modulation systems.

Beam splitter - An optical device, such as a partially reflecting mirror, for dividing an optical beam in 2 or more separate beams. It can be used in a fiber optic cable data link as a directional coupler.

Bend loss - A+ form of increased attenuation caused by allowing high order modes to radiate from the walls of a fiber optic cable. There are 2 common types of bend losses. The first type results when the fiber optic cable is curved through a restrictive radius or curvature. The second type is generally referred to as microbends. It is caused by small distortions of the fiber optic cable imposed by externally induced perturbations as, for example, slip shod cabling techniques.

Bend radius - Radius a fiber optic cable can bend before the risk of breakage or increase in attenuation. Also referred to as cable bend radius.

BER - Bit Error Rate. This is the probability that a transmitted bit is demodulated in error at the destination receiver.

Biconic - A connector type which has a taper sleeve which would be fixed to the fiber optic cable. When this plug was inserted into its receptacle the tapered end was a means for locating the fiber optic cable in the proper position. With this connector cap, fit over the ferrules, rest against guided rings and screw onto the threaded sleeve to secure the connection. This was one of the earliest connectors used in fiber optic systems but is in little use at present.

Bit - A binary digit which is generally either '0' or '1.' It is the smallest representation of information in a communications and/or computing system.

Bit rate - The number of bits of data transmitted per second over a communications link. This usually represented as BPS with KBPS standing for kilo bits per second (1000 BPS) and MBPS standing for mega bits per second (million BPS) and GBPS standing for giga bits per second (billion BPS) etc.

Break Out cable - Same as a Fan Out cable. This is a multiple fiber optic cables constructed in the tight buffered design. It is designed for ease of connectorization and rugged applications for intra-building and inter-building requirements.

Broadband - A method of communication in which the signal is transmitted by being impressed on a higher frequency carrier. Also the ability of a communications system to carry a multitude of signals simultaneously. In data transmission is denotes transmission facilities capable of handling frequencies greater than those for high-grade voice communications. The higher frequency allows the carrying of several simultaneous channels. Broadband infers the use of a carrier signal rather than direct modulation, baseband.

Buffer - A protective layer over the fiber optic cable, such as a coating, an inner jacket, or a hard tube. The primary buffer, next to the cladding, is 250 mm in diameter. A secondary buffer of 900 mm is used on indoor cables.

Buffer coating - A protective layer, such as an acrylic polymer, applied over the fiber optic cable cladding.

Buffered fiber - Fiber optic cable protected with an additional material, usually hytrel or nylon, to provide ease in handling, connectorization and increased tensile strength.

Buffering - It is used in 2 contexts. First, it refers to a protective material extruded directly on the fiber optic cable coating to protect it from the environment. Secondly, it refers to extruding a tube around the coated fiber optic cable to allow isolation of the fiber from stresses.

Buffer tube - A hard plastic tube, having an inside diameter several times that of a fiber optic cable, that holds 1 or more fiber optic cables.

Building entrance - Terminal cable entrance point where typically a trunk cable between buildings is terminated and fiber is then distributed through the building.

Bundle - Many individual fiber optic cables within a single jacket or buffer tube. Also, a group of buffered fiber optic cables distinguished in some fashion from another group in the same cable core.

Bus network - A network topology in which all of the terminals are attached to a transmission medium serving as a bus. All other terminals receive all signals transmitted from a terminal connected to the bus.

Bus - Commonly called data bus. The term is used to describe the physical linkage between stations on a network sharing a common communication.

Byte - A unit of 8 bits.

Cable - Alternate name for fiber optic cable. An assembly of optical fibers (the glass or plastic basic waveguide) and other material providing mechanical and environmental protection and optical insulation of the inner optical waveguide.

Cable assembly - Fiber optic cable that has connectors installed on one or both ends. General use of these cable assemblies includes the interconnection of multi-mode and single-mode fiber optic cable systems and opto-electronic equipment. If connectors are attached to only one end of the cable, it is known as a pigtail. If connectors are attached to both ends, it is known as a jumper.

Cable bend radius - During installation this infers that the cable is experiencing a tensile load. Free bend infers a lower allowable bend radius since it is at a condition of no load.

Carrier Sense Multiple Access With Collision Detection CSMA/CD - A technique employed in Ethernet based LANs to control the transmission channel. It assures that there is no conflict between terminals that wish to transmit.

Center wavelength - The wavelength of an optical source that might be considered its middle. One measure of this is the average of the 2 wavelengths corresponding to the Full Width Half Maximum- FWHM.

Central member - The center component of a fiber optic cable. It serves as an anti-buckling element to resist temperature-induced stresses. Sometimes serves as a strength element. The central member is composed of steel; fiberglass or glass reinforced plastic.

Central office - CO. The places where communications common carriers terminate customer lines and locate switching equipment that interconnects those lines. It is the lowest hierarchical level of a TELCO backbone network. It is from the Central office level that local loops go out to end-user customer premises equipment.

Centro-symmetrical Reflective Optics - An optical technique in which a concave mirror is used to control coupling of light from 1 fiber optic cable to another.

Channel - A communications path derived from a specific transmission medium, as for example fiber optic cables. The channel supports the end-to-end communications of an information source and destination. Besides the transmission medium a channel needs to have a transmitter/receiver (transceiver) and a modulator/demodulator (modem). By multiplexing, several channels can share the same specific transmission medium. Channel is synonymous with link. The term channel is usually employed within the context of multiplexing- but not always.

Chromatic bandwidth - The inverse of the Chromatic Dispersion.

Chromatic dispersion - The speed of an optical pulse travelling down a fiber optic cable changes if the wavelength changes. However, any practical light source has a spectral width that is, has components at a number of different wavelengths. This results in a pulse broadening - the time width of pulse broadens as it propagates down a fiber optic cable. This effect is called chromatic dispersion. It can be calculated experimentally by measuring the travel time down a fiber optic cable of light at different wavelengths.

Cladding - A low refractive index glass or plastic that surrounds the core of the fiber optic cable. Optical cladding promotes total internal reflection for the propagation of light in fiber. The cladding steers light to the core.

Cladding modes - A mode that is confined to the cladding. Basically, a light ray that propagates down the cladding. Attenuation is very high in the cladding. Consequently, a cladding mode is eliminated after a few meters.

Cleaving - The controlled breaking of a fiber so that its end surface is smooth.

Club Des Fibres Optiques Plastiques - Club formed in France to promote Plastic Optical Fiber (POF) for a variety of applications.

Coating - A material put on a fiber optic cable during the drawing process to protect if from the environment.

Coherent light or light waves - This is light of which all parameters are predictable and correlated at any point into time or space, particularly over an area perpendicular to the direction of propagation or over time at a particular point in space. Simply, coherent light usually refers to the phenomenon relating to the existence of a correlation between the phases of the corresponding components of 2 light waves or to the values of the phase of a given component at 2 instants in time or 2 points in space. Coherent light does not occur naturally in the Universe. It can only be generated a laser.

Concentrator - A multi-port repeater.

Conduit - Pipe or tubing through which cables can be pulled or housed.

Connector - A mechanical device mounted on the end of a fiber optic cable, light source, receiver or housing that mates to a similar device. It allows light to be coupled, optically, into and out of a fiber optic cable. A connector allows a fiber optic cable to be connected or disconnected repeatedly from a device. Commonly used connectors include FC/PC, Biconic, SC, ST, D4, and SMA 905 or 906.

Connector insertion loss - See Insertion Loss.

Connector-induced fiber loss - That part of the Conductor Insertion Loss, expressed in dB, due to impurities or structural changes to the fiber optic cable by termination or handling with the connector.

Core - The central, light carrying, part of a fiber optic cable. It has an index of refraction higher than that of the surrounding cladding.

Core eccentricity - A measure of the displacement of the center of the core relative to the cladding center.

Coupler - It is used in 2 contexts. First, it is a passive device that distributes optical power among 2 or more ports and this can be in different ratios. Secondly, it is a multi-pod device used to distribute optical power.

Coupling efficiency - The efficiency of optical power transfer between 2 components.

Coupling losses - The power loss suffered when coupling light from one optical device to another. There are intrinsic losses (non-ideal fiber parameters) and extrinsic losses (mechanical effects).

Coupling ratio - The percentage of light transferred to a receiving output port with respect to the total power of all output ports.

CPE - Customer Premises Equipment.

Critical angle - The greatest angle of incidence for which a wave propagating in a homogeneous medium of relatively high refractive index strikes an interface with a medium having a lower refractive index and for which refraction in just possible. With respect to fiber optic cabling the critical angle is therefore the smallest angle at which a light ray will be totally reflected within the fiber and thereby guided down the fiber - total internal reflection.

Crosstalk - The pickup in one particular fiber optic cable of unwanted light from another fiber optic cable.

CSMA/CD - Carrier Sense Multiple Access with Collision Detection.
 


CSR - Centro symmetrical reflective optics.

Cutback - A method for measuring the attenuation or bandwidth of a fiber optic cable by first measuring the full length and then cutting back and measuring, again, the fiber optic cable at a shorter length.

Cut off wavelength - For a single mode fiber optic cable it is the wavelength above which the fiber optic cable exhibits single mode operation.

CYTOP® - Perfluorinated polymer trademark of Asahi Glass Co. Ltd.

Dark current - The thermally induced current that exists in a photodiode in the absence of incident optical power.

Data link - Transmitter with Modulator, Transmission medium and Demodulator with Receiver that transmits data between 2 points. When the Transmission medium is a fiber optic cable the data link is a fiber optic data link.

Data rate - Also Data Transmission Rate. The number of bits of information sent per second in a data communications transmission system. It is generally expressed in Bits Per Second, BPS. This may or may not be equal to the Baud rate.

dB - Decibel, a measure of loss or equivalently attenuation. It is computed as a standard logarithmic unit for the ratio of 2 powers, voltages or currents. In fiber optics the ratio is power and defined by: dB = 10 Log10 (P1/P2).

dB loss budget - The amount of light available to overcome the attenuation in the fiber optic data link and still maintain BER (or equivalent) performance specifications.

dBm - Decibels below 1 mW.

dBm - Decibels below 1mW.

Demultiplex - Separation of channels which has been multiplexed in order to share a common transmission medium. With respect to a fiber optic cable medium it is the process of separating optical channels.

Detector - A device that generates an electrical signal when illuminated by light. The electrical current is dependent upon the amount of light received. Common detectors encountered in fiber optic data communications are photodiodes, photodarlingtons and phototransistors.

D4 - A connector type. It is very similar to the FC connector with its threaded coupling, tunable keying and PC end finish. The main difference is its 2.0-mm diameter ferrule. Designed originally by the Nippon Electric Corp.

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

Diamond connector - A type of connector.

Dichroic filter - An optical filter that transmits light selectively according to wavelength.

Dielectric - Non-metallic and therefore non-conductive. Glass fiber optic cable is therefore considered dielectric. A dielectric cable contains no metallic components.

Diffraction grating - An array of fine, parallel, equally spaced reflecting or transmitting lines. These lines mutually enhance the effects of diffraction to concentrate the diffracted light in a few directions. These directions are determined by the spacing of the lines and by the wavelength of the light.

Digital - A data format that uses a discrete, countable and finite number of levels to transmit information. Binary is a special case of this corresponding to 2 levels.

DIN 47256 - A connector type.

Directivity - This is also referred to as near end crosstalk. It is the amount of power observed at a given input port with respect to an initial input power.

Dispersion - A general term for those phenomena that cause a broadening or spreading of light as it propagates down a fiber optic cable. This is the major cause of bandwidth limitations with fiber optic cable. There are 3 types of dispersion- modal, material and waveguide. Differential optical path lengths in multi-mode fiber optic cables cause modal dispersion. Material dispersion is caused by a differential delay of various wavelengths of light in a waveguide material. Waveguide dispersion is caused by light travelling in both the core and cladding materials in single-mode fiber optic cables.

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

Dopan - Materials added to a core of a fiber optic cable in order to change its characteristics.

Drawing - The manufacturing process by which fiber optic cable is pulled from preforms.

Duplex cable - A 2 fiber cable suitable for duplex (2 way) transmission.

Duplex operation - Transmission on a data link in both directions. Half duplex refers to such transmission, but in a time-shared mode- only one direction can transmit at a time. With full duplex there can be transmission in both direction simultaneously.

Duty cycle - In digital transmission, the ratio of high levels to low levels or the ratio of on time - signal present - to total time - as averaged over many bit or Baud intervals.

EDFA - Erbium-doped fiber amplifier.

EIA - Electronics Industries Association. A standards association that publishes test procedures.

8B/10B encoding - A signal modulation scheme in which either 4 bits are encoded into a 5-bit word or eight bits are encoded into a 10-bit word. This scheme ensures that too many consecutive zeros do not occur. It is used in ESCON and Fiber Channel.

802.3 network - A 10 MBPS CSMA/CD bus based LAN; commonly called Ethernet.

802.5 network - A token passing ring network operating at 4 or 16 MBPS.

EMC - Electromagnetic compatibility

EMD - Equilibrium mode distribution.

EMI - Electromagnetic interference. It is any electrical or electromagnetic interference that causes an undesirable response, degradation or failure in electronic equipment. Fiber optic cables neither emits nor receives EMI.

Emitter - Term used for a light source.

Encoding - A scheme to represent digital ones and zeros through combining high and low voltage states.

End separation - The distance between the ends of 2 joined fiber optic cables. End separation causes an extrinsic loss that depends on the joining hardware and method.

End to End Loss - The optical loss on an installed fiber optic cable data link path. This loss consists of the loss due to the fiber optic cable, splices and connectors.

Equilibrium mode distribution - The steady modal state of a multi-mode fiber optic cable in which the relative power distribution among the modes is independent of the fiber optic cable length.

Erbium-doped fiber amplifier - A type of fiber optic cable that amplifies 1550 nm optical signals when pumped with a 980-1480 nm light source.

ESCON - An IBM channel control system based on fiber optic.

ESKA - Trade mark of plastic fiber optic cable manufactured by Mitsubishi Rayon Corp.

ESKA GIGA - Graded index plastic fiber optic cable manufactured by Mitsubishi Rayon Corp.

ESKA MEGA - Trade mark of plastic fiber optic cable manufactured by Mitsubishi Rayon Corp.

Excess loss - There are 2 contexts in which it is used. First, in a fiber optic coupler it is the optical loss from that portion of light that does not emerge from the nominally operational ports of the device. Secondly, it is the ratio of the total output power of a passive component to the input power.

Extrinsic Losses - Signal loss in transmission down fiber optic cable caused by imperfect alignment of fiber optic cables joined by a connector or splice. Contributors to this loss include angular misalignment, axial misalignment, end separation and end finish - any imperfect joining caused by connector or splice.

Fall 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. Turn off time. Sometimes measured between the 80% and 20% points.

Fan Out cable - Same as a Break Out cable. This is a multiple fiber optic cables constructed in the tight buffered design. It is designed for ease of connectorization and rugged applications for intra-building and inter-building requirements.

FC - A connector type. It is utilized for single-mode fiber optic cable. It offers extremely precise positioning of the single-mode fiber optic cable with respect to the emitter and detector. It features a position locatable notch and a threaded receptacle. Once installed, the position is maintained with absolute accuracy.

FC/PC - A connector type. It is utilized for single mode cable. It offers extremely precise positioning of the single mode cable with respect to the emitter and detector. It features a position locatable notch and a threaded receptacle. Once installed the position is maintained with absolute accuracy.

FDD I - Fiber Distributed Data Interface. A very high-speed local area networking architecture based upon fiber optic cable as the transmission medium. Many FDDI features were incorporated into Fast Ethernet-100Base-T. FDDI has its own special type of connector.

Ferrul - A component of a connector that holds a fiber optic cable in place and aids in its alignment. It is usually cylindrical in shape with a hold through the center.

Fiber - Thin filament of glass. An optical waveguide consisting of a core and a cladding which is capable of carrying information in the form of light.

Fiber bandwidth - The lowest frequency at which the magnitude of the fiber transfer function decreases to a specified fraction of the zero frequency value. Often the specified value is of the value of the transfer function at zero frequency.

Fiber bundle - An assembly of unbuffered fiber optic cables. It is usually employed as a single transmission channel. This is in contrast to multi-fiber cables, which contain optically and mechanically isolated fiber optic cables, each of which provides a separate channel. Fiber bundles, which are used only to transmit light as in fiber optic data communications, are flexible and unaligned. On the other hand, fiber bundles which are used to transmit images may be flexible or rigid, but must contain aligned fibers.

Fiber channel - An industry standard specification for computer channel communications over a fiber optic cable. It offers data transmission speeds from 132 MBPS to 1,062 MBPS and transmission distances for 1 to 10 km

Fiber loss - The attenuation (deterioration) of the light signal in transmission through a fiber optic cable.

Fiber Distributed Data Interface network - A token passing ring network designed specifically for fiber optic cable and featuring dual counter-rotating rings and 100 MBPS operation.

Fiber optic interrepeater link - Standard defining a fiber optic cable link between 2 repeaters in an IEEE 802.3 network.

Fiber optic link - Any transmission channel using a fiber optic cable as the transmission medium to connect 2 end terminals or to be connected in series with other channels.

Fiber optics - Light transmission through optical fibers for communication or signaling.

Fiber Optic Test Procedure (FOTP) - Standards developed and published by the Electronic Industries Association (EIA) under the EIA's RS-455 series of standards.

Fiber optic waveguide - A relatively long strand of transparent substance, usually glass, capable of conducting an electromagnetic wave of optical wavelength (visible or near visible region of the frequency spectrum) with some ability to confine longitudinally directed, or near longitudinally directed, lightwaves to its interior by means of internal reflection. The fiber optic waveguide may be homogeneous or radically inhomogeneous with step or graded changes in its refractive index. The indices are lower at the outer regions and the core is thus of an increased refractive index.

FITL - Fiber in the loop.

FM - Frequency modulation.

FO7 - Plastic fiber optic cable connector standardized in Japan.

FOIRL - Fiber optic interrepeater link.

FOTS - Fiber optic transmission system.

F4B/5B Encoding - A signal modulation scheme in which groups of 4 bits are encoded and transmitted in 5 bits in order to guarantee that no more than 3 consecutive zeros ever occur. It is used in FDDI.

FP-LD - Fabry-Perot laser diode.

Frequency modulation - A transmission technique in which the frequency of a carrier is varied in sympathy with the information being communicated.

Fresnel reflection - The reflection that occurs at the planar junction of 2 materials having different refractive indices. Fresnel reflection is not a function of the angle of incidence.

Fresnel reflection loss - Loss of optical power due to Fresnel reflections.

Fundamental mode - The lowest order propagation mode of a waveguide.

Fused coupler - A method of making a multi-mode or single-mode coupler by wrapping fiber optic cables together, heating them and pulling them to form a central unified mass. By doing this light on any input fiber optic cable is coupled to all out put fiber optic cables.

Fusion splicing - A permanent joint accomplished by the application of localized heat sufficient to fuse or melt the ends of the fiber optic cable. This process forms a single continuous fiber optic cable.

Fusion splice - A joining of 2 fiber optic cables by physically fusing through heat the 2 fiber optic cable ends.

FWHM - Full width at half maximum. This is used to describe the width of a spectral emission.

Gap loss - The optical power loss caused by a space between axially aligned fiber optic cables. For waveguide-to-waveguide coupling, it is commonly called longitudinal offset loss.

GBPS - Giga Bits Per Second - 1 Billion Bits Per Second.

GHz. - Giga Hertz, 1 Billion Hz.

GI - Graded indexes.

GI-POF - Graded index plastic fiber optic cable.

GOF - Glass Optical Fiber.

Graded index fiber - A fiber optic cable where the core has a non-uniform index of refraction. The core is composed of concentric rings of glass where the refractive indices decrease from the center axis. The purpose is to reduce modal dispersion and thereby decrease fiber bandwidth.

Graded index profile - Any refractive index profile that varies with radius in the core.

GRIN - Graded indexes.

Ground loop noise - Noise that results when equipment is grounded at ground points having different potentials. This creates an unintended current path. The dielectric of fiber optic cables provides electrical isolation that eliminates ground loops.

Hard clad silica - A fiber optic cable with a hard plastic cladding surrounding a silica glass core.

Hertz - A unit of frequency equal to 1 cycle per second.

Hot plate - Heat source used to produce a mirror finish on the end of a plastic fiber optic cable.

HSPN - High Speed Plastic Network- a program funded by the US Government to promote plastic fiber optic cabling components and applications.

Hybrid adapter - Device that connects various connector types.

Hybrid cable - A cable composed of both a fiber optic cable and electrical conductors. Synonym for composite cable.

IDP - Integrated detector/amplifier.

IEC - International Electrical Commission.

IEEE - Institute of Electrical and Electronics Engineers.

Incident angle - The angle between an incident ray and a line perpendicular to an optical surface.

Index matching material - A material used at an optical interconnection. It has a refractive index close to that of the fiber optic cable core and is used to reduce Fresnel reflections.

Index of refraction - The ratio of the speed of light in a vacuum to the speed of light in a material. The symbol for it is 'n'.

Index profile - A graded-index fiber optic cable. In it the refractive index at a point varies with the distance of the point from the cylindrical axis i.e. n varies with the radius.

Infrared - The designation for electromagnetic waves at wavelengths between the visible part of the spectrum (approximately 750 nm) and the microwave band (approximately 30 mm).

ILD - Injection Laser Diode.

Insertion loss - The loss in the power of a signal that results from inserting a passive component into a previously continuous path. Examples of such passive devices are connectors, inline star couplers and splices.

Integrated detector/amplifier - A detector package containing a pin photodiode and a transimpedence amplifier.

Interface - The debarkation point or location on a data device where data comes out of or goes into the device. Examples are the RS-232 interface and the Mouse-PC interface.

Intrinsic losses - Loss caused by fiber optic cable parameter mismatches when 2 non-identical cables are joined. Examples of such parameters are core dimensions and index profiles.

IR - Infrared.

ISDN - Integrated Services Digital Network. A TELCO offering to allow computers to communicate through the telephone Wide Area Network at speeds up to 128 KBPS.

ISO - International Standards Organization. This is an independent international body formed to define standards for multi-vendor network communications. Its 7 layer Open Systems (OSI) reference model defines the protocol layers of network architectures which vendors should account for in their product offerings.

Isolation - Also referred to as far end crosstalk 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.

Jitney - Low cost optical link.

Jumper Cable - Single fiber optics cable with connectors on both ends.

Kevlar - See Aramid yarn.

Kilo Hertz (KHz) - 1,000 Hz.

Kilometer - 1,000 meters or 3,281 feet. The kilometer is a unit of measurement in fiber optic communications.

KPSI - A unit of tensile strength expressed in 1,000's of pounds per square inch.

LAN - Local Area Network. This is a geographically limited data communications network. It is often referred to as premises data communications network. Its extent is usually limited to the office building, campus or manufacturing plant - several 1,000 feet.

Large core fiber - Usually this refers to fiber optic cable with a core of 200 mm or more. However, sometimes it is applied to 100/140-fiber optic cable.

Laser - An acronym for Light (by) Amplification (by) Stimulated Emission (of ) Radiation. This is a device, which artificially generates coherent light within a narrow range of wavelengths. Lasers can be made to operate in a number of different ways. In one mechanism the molecules of some material are put at higher energy levels. When light is then incident upon the material the molecules make transitions to lower energy levels. The correspondingly released energy is realized as coherent light. Lasers are used as the transmitting source for fiber optic cables when transmission distances are long. Laser light denotes light generated by a laser.

Lateral displacement loss - The loss of power that results from lateral displacement from optimum alignment between 2 fiber optic cables or between a fiber optic cable and an active device.

Launch angle - This term is used in 4 different contexts. First, it often refers to the beam divergence of a light source. Secondly, it refers to as the beam divergence from any emitting surface such as an LED, laser, prism or fiber optic cable end. Thirdly, it refers to the angle at which a light beam emerges from a surface. Fourthly, in a fiber bundle it refers to the angle between the input radiation vector (the chief ray of input light) and the axis of the fiber bundle. In this case if the ends of the fiber optic cables are perpendicular to the axis of the fiber optic cable then the launch angle is equal to the incidence angle when the ray is external and the refraction angle when initially inside the fiber.

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

Launch Numerical Aperture (LAN) - The numerical aperture of an optical system, which is used to couple (launch) power into a fiber optic cable. LNA may differ from the stated NA of final focusing element if, for example, that element is underfilled or the focus is other than that for which the element is specified. LNA is one of the parameters that determine the initial distribution of power among the modes of a fiber optic cable.

Law of Reflection - Angle of incidence = Angle of reflection.

LD - Laser diode.

LED - Light Emitting Diode.

Light - In the laser and optical communication fields is that 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 mm through the visible region into the mid-infrared region of approximately 30 mm.

Light Emitting Diode - LED. A semiconductor diode that spontaneously emits light from the pn junction when forward current is applied.

Light piping - Use of fiber optic cables to illuminate.

Light source - Source of light, which is usually modulated and terminated over a fiber optic cable. It is typically an LED or LD.


Lightguide - A fiber optic cable or fiber bundle.

Lightguide cable - A fiber optic cable or fiber bundle which includes a cable jacket and strength members.

Lightwaves - Electromagnetic waves in the region of optical frequencies. The term light was originally restricted to radiation visible with the human eye, with wavelengths between 400 and 700 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 2,000 nm) as light in order to emphasize the physical and technical characteristics they have in common with 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 - See LAN.

Loose tube - A protective tube loosely surrounding a fiber optic cable often filled with a water blocking gel.

Loss - Attenuation of optical signal. It is usually measured in dB.

Loss budget - An accounting of overall attenuation in a system.

Low NA - Numerical Aperture around 0.30.

LUCINA™ - Graded indexes CYTOP fiber optic cable (GI-COF) manufactured by Asahi Glass Co.

LUMINOUS® - Trademark of plastic fiber optic cable manufactured by Asahi Chemical.

Macro bend - A large fiber bend that can be seen with the unaided eye.

Macrobendiing - Macroscopic axial deviations of a fiber optic cable from a straight line, in contrast to microbending.

MAN - Metropolitan Area Network. This is a network linking LANs and other networks at many sites within a city area. Dimensions are usually of the order to 10's of km.

Manchester - Balanced signaling code, used at lower data rates.

Material dispersion - Light pulse broadening caused by various wavelengths of light traveling at different velocities down a fiber optic cable. Material dispersion increases with the increasing spectral width of the source. It is attributable to the wavelength dependence of the refractive index of the material used to form the fiber optic cable. It is characterized by the material dispersion parameter, M (l).

Material scattering - In an optical waveguide it is that part of the total scattering attributable to the properties of the materials used for waveguide fabrication.

MAU- Medium Attachment Unit. This is an active component of an Ethernet LAN connecting peripheral devices with the electrical bus cable.

MBPS - Mega Bits Per Second - 1 million BPS.

MDPE- Medium density polyethylene jacketing.

Mechanical splice - A splice in which fiber optic cables are joined mechanically for example by being glued or crimped in place. However, they are not fused together.

MFD - Mode field diameter.

MHz. - Mega Hertz, 1 million Hz.

Microbend Loss - The loss attributed to microscopic bends in fiber optic cable.

Microbending - Curvatures of the fiber optic cable which involves axial displacements of a few micrometers and spatial wavelengths of a few millimeters. Micro bends cause loss of light and consequently increase attenuation of the fiber optic cable.

Micrometer - 1 millionth of a meter, abbreviated mm. Also referred to a micron.

Micron - See micrometer.

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

MM - Millimeter, 1 thousandth of a meter.

MMF - Multi-mode fiber optic cable.

Modal bandwidth - A bandwidth limiting mechanism in multi-mode fiber optic cables. It is also used in single-mode fiber optic cables when operated at wavelengths below cutoff. Modal bandwidth arises because of the different arrival times of the various modes. It is a synonym for intermodal dispersion.

Modal dispersion - The dispersion resulting from difference in the time it takes for different rays to traverse a fiber optic cable.

Modal noise - The fluctuation in optical power due to the interaction of the power traveling in more than 1 mode.

Mode coupling - The transfer of energy between modes. In a fiber optic cable, mode coupling occurs until the EMD is reached.

Mode field diameter - The diameter of optical energy in a single-mode fiber optic cable. Because the MFD is greater than the core diameter, MFD replaces the core diameter as a practical parameter.

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

Mode mixing - The numerous modes of a multi-mode fiber optic cable differ in their propagating velocities. As long as they propagate independently of each other, the fiber optic cable bandwidth varies inversely with the fiber optic cable length due to multi-mode distortion. As a result of inhomogeneities of the fiber optic cable geometry and the index profile, a gradual energy exchange occurs between modes with different velocities. Due to this mode mixing, the bandwidth of long multi-mode fiber optic cables is greater than the value obtained by linear extrapolation from measurements on short fiber optic cables.

Mode scrambler - A device composed of one or more fiber optic cables in which strong mode coupling occurs. Frequently used to provide a mode distribution that is independent of source characteristics.

Modem - An acronym for Modulator-Demodulator. This is a device that carries out both modulation and demodulation. With the modulation function the modem takes information, which is in digital form - usually, 0's and 1's, and represents it by signals, which can be sent (transmitted) over a transmission medium. With the demodulation function the modem takes signals out of the transmission medium (received) and determines which digits then represent, what sequence of 0's and 1's.

Modes - In guided wave propagation, such as that through fiber optic cable, it is the distribution of electromagnetic energy that satisfy Maxwell's equations and boundary conditions. Specifically, applied to optics and transmission down a fiber optic cable a mode is loosely equivalent to a light ray of classic ray optic theory. Sometimes used to denote a light path through a fiber optic cable.

Modulation - The process by which the characteristic of one wave (the carrier) is modified by another wave (the information signal). Examples include amplitude modulation (AM), and frequency modulation (FM).

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

Multi-mode fiber optic cable - Type of fiber optic cable that support more than 1 propagation mode.

Multiplexing - The process by which 2 or more signals are transmitted over a single transmission medium. Examples include Time Division Multiplexing (TDM) and Wavelength Division Multiplexing (WDM).

NA - Numerical Aperture - The light gathering ability of a fiber optic cable. This defines the maximum angle to the fiber optic cable axis at which light will be accepted and propagated down the fiber optic cable. NA= SIN F, where F is the acceptance angle. NA is also used to describe the angular spread of light from the central axis - as in exiting from the fiber optic cable, emitting from a source of entering a detector.

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 a fiber optic cable, from fiber optic cable to fiber optic cable or from fiber optic cable to a detector.

NM - Nanometer 1 billionth of a meter.

NEC - National Electrical Code. Defines building flammability requirements for indoor cables.

NEXT - Near End cross-talk.

NIR - Near Infrared.

NIU - Network Interface Unit.

NLO - Non-Linear Optics.

NRZ - On-Off signaling code.

Numerical Aperture - See NA-Numerical Aperture. This is the imaginary cone which defines the acceptance area for the fiber optic cable core to accept light rays.

Open Standard Interconnect - A 7-layer model defined by ISO for defining a data communication network. It provides means for executing the blue print of the network architecture.

Optical cable - An assembly of fiber optic cables and other material providing mechanical and environmental protection.

Optical fiber - Synonym for fiber optic cable.

Optical fiber coupler - This is used in 2 contexts. In the first it refers to a device whose purpose is to distribute optical power among 2 or more ports. In the second it refers to a device whose purpose is to couple power between a fiber optic cable and a source or detector.

Optical link - Any optical transmission channel designed to connect 2 end terminals or to be connected in series with other channels. Sometimes terminal hardware i.e. transmitter and receiver, is included in the definition.

Optical time domain reflectometry - A method of evaluating fiber optic cables based upon detecting backscattered (reflected) light. It is used to measure attenuation, evaluate splice and connector joints and locate faults.

Optical waveguide - Synonym for fiber optic cable.

Optical window - Wavelength range of a fiber optic cable with a very low attenuation. Fiber optic data links using LED sources work in the 1st window at 850 nm or in the 2nd window at 1300 nm. Fiber optic data links using laser sources work in the 2nd window at 1310 nm or in the 3rd window at 1550 nm.

OPTI-GIGA™ - Graded index plastic fiber optic cable developed by Boston Optical Fiber.

OPTI-LUX™ - Step index plastic fiber optic cable developed by Boston Optical Fiber.

OPTI-MEGA™ - Step index plastic fiber optic cable developed by Boston Optical Fiber.

Opto-electrical Converter - Converts an optical signal into an electrical signal.

Opto-electronics - The range of materials and devices that generate light (lasers and light-emitting devices), amplify light (optical amplifiers), detect light (photodiodes) and control light (electro-optic circuits). Each of these functions requires electrical energy to operate and depends upon electronic devices to sense and control this energy. In a broader sense it means pertaining to a device that responds to optical power, emits or modifies optical radiation or utilizes optical radiation for its internal operation. It is any device which functions as an electrical to optical transducer or optical to electrical transducer.

OSI - Open Standards Interconnect.

OTDR - Optical Time Domain Reflectometer. A method of characterizing a fiber optic cable wherein an optical pulse is transmitted down the fiber optic cable and the resulting backscatter and reflections are measured as a function of time. The OTDR is useful in estimating the attenuation coefficient as a function of distance and identifying defects and other localized losses.

Passive Star Coupler - Couples 1 or more input optical signals coming from fiber optic cables to 1 or more output fiber optic cables acting as receivers. It accomplishes this by using only passive optical components.

Patch Panel - Distribution area to rearrange fiber optic cable connections and circuits. A simple patch panel is a metal frame. One side of the panel is usually fixed. This means that the fiber optic cables are not intended to be disconnected. On the other side are plugs to connect other fiber optic cables.

PC - Physical contact.

PCM - Pulse Code Modulation.

PCS - Plastic clad silica.

PD - Photodiode

PE - Polyethylene. This is 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.

PF - Perfluorinated

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

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

Photodiode - A semiconductor diode that produces current in response to incident optical power and used as a detector in a fiber optic cable data link.

Photon - A quantum of electromagnetic energy. A discrete unit which lends a particle nature to light in contrast to its wave nature. Photons come into play when one talks about energy exchanges using light.

Photonics - The technology of transmission of information using light.

Physical contact connector - A connector designed with a radiuses tip to assure physical contact of the fiber optic cables and thereby increase return reflection loss.

Pigtail - A short length of fiber optic cable, permanently fixed to a component. It is used to couple power between the component and the fiber optic cable used for transmission.

PIN - Positive intrinsic negative photodiode.

PIN Photodiode - A diode with a large intrinsic region sandwiched between p+ and n- doped semi-conducting regions. Photons absorbed in this region create electron-hole pairs that are then separated by an electric field. This generates an electric current in a load circuit.

PIN-PD - PIN-photodiode.

Pistoning - The movement of a fiber optic cable axially in and out of a ferrule end, often caused by changes in temperature.

Plastic clad silica fiber optic cable - A fiber optic cable having a glass core and a plastic cladding.

Plastic fiber optic cable - Fiber optic cables having a plastic core and plastic cladding.

Plenum - The air handling space between walls, under structural floors and above drop ceilings. This can be used to route intra-building cabling.

Plenum cable - Fiber optic cables whose flammability and smoke characteristic allows it to be routed in a plenum area without being enclosed in a conduit.

PMMA - Polymethylmethacrylate

POF Consortium - Over 60 Japanese companies, government agencies and universities organized to promote plastic optical fiber-plastic fiber optic cable.

POF - Plastic Optical Fiber-plastic fiber optic cable.

POFA - Plastic optical fiber amplifier.

POFIG - US based POF interest group.

Point-to-Point - A fixed link secured between 2 distinct nodes or stations in a network.

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

Polishing - Preparing the end of a fiber optic cable by moving the end over an abrasive material.

POLO - Parallel Optical Link Organization.

POLYGUIDE® - Polymer optical waveguide developed by DuPont.

Power meter - Device used to measure attenuation of a plastic fiber optic cable.

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

Preform - A solid rod of plastic material from with a plastic fiber optic cable is drawn or a glass structure for which glass fiber optic cable is drawn.

Prefusing - Fusing with low current to clean the fiber optic cable end. Precedes fusion splicing.

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

PTFE - Poly-tetrafluoroethylene, a representative of perfluoropolymer by DuPont and manufactured under the name Teflon®.

Pulse coded modulation - PCM. A technique in which, a analog signal is converted to a digital signal. This is accomplished by sampling the signals amplitude and expressing the different amplitudes as a binary number. Sampling must be at the Nyquist rate - at least twice the highest frequency in the information signal bandwidth.

Pulse spreading - The dispersion of an optical signal with time as it propagates through a fiber optic cable.

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.

Quaternary - Made from 4 different elements.

Quantum efficiency - In a photodiode, the ratio of the primary carriers (electron-hole pairs) created to incident photons. A quantum efficiency of 70% means 7 out of 10 incident photons creates a carrier.

Rayleigh scattering - The scattering of light that results from small inhomogeneities in material density or composition. This causes losses in optical power. The losses vary with the 4th power of wavelength. This scattering sets a theoretical lower limit to the attenuation of a propagating lightwave as a function of wavelength. This varies from 10 dB/km at 0.5 microns to 1 dB/km at 0.95 microns.

RAYTELA® - Plastic, fiber optic cable manufactured by Toray Industries.

RB - Rhodamine B dopant.

Receiver - In the context of a fiber optic cable based communications link it is an electronic package, which converts optical signals to electrical signals.

Receiver sensitivity - The minimum acceptable value of average received power at the fiber optic cable receiver point, R, in order to achieve a BER of 10-12. It takes into account power penalties caused by the use of a transmitter with worst-case values of extinction ratio, jitter, pulse rise and fall times, optical return loss at the transmitter point, S, receiver connector degradations and measurement tolerances. The receiver sensitivity does not include penalties associated with dispersion, jitter or reflections from the optical path. These effects are specified separately in the allocation of maximum optical path penalty. Sensitivity takes into account worst-case operating and end-of life conditions. In the case of digital signals the optical power is usually quoted in Watts or dBm.

Reflectance - Light that is reflected back along the path of transmission, from either the coupling region, the connector or the terminated fiber optic cable.

Reflection - The abrupt change in direction of light as it travels from one material to a dissimilar material. Some of the reflected power gets transmitted back to the source.

Refraction - The bending of a beam of light at an interface between 2 dissimilar media or a medium whose refractive index is a continuous function of position (i.e. a graded index medium).

Refractive Index - The ratio of the velocity of light in a vacuum to its velocity in the medium. It is a synonym of index of refraction. Its symbol in 'n.'

Regenerative repeater - A repeater designed for digital transmission that both amplifies and reshapes the signal. Sometimes called regenerator.

Repeater - An optoelectronic device that amplifies or boosts a signal. Basically, it returns a signal to its original strength.

Responsivity - The ratio of a photodetector's electrical output to its optical input in Amperes/Watt.

Return loss - Same as reflectance.

Return reflection - Reflected optical energy that propagates backward to the source in a fiber optic cable.

Return reflection loss - The attenuation of reflected light. High return loss is desirable, especially in single-mode fiber optic cables.

Ring network - A network topology in which terminals are connected in a point to point serial fashion in an unbroken circular configuration. Frequently used with a token passing access protocol.

Rise time - The time required for the leading edge of a pulse to rise from 10% to 90% of its amplitude. The time required for a component to produce such a result. Turn on time. Sometimes measured between the 20% and 80% points.

Riser - Application for indoor cables that pass between floors. It is normally a vertical shaft or space.

RX - Receiver.

RZ - Signaling code.

SC - A connector type. It is primarily used with single-mode fiber optic cables. It offers low cost, simplicity and durability. Furthermore, it provides for accurate alignment by a ceramic ferrule. It is a push on -pull off connector with a locking tab. It is similar to the connector used for FDDI but is not compatible.

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

SDM - Space Domain Multiplexing

Semiconductor Laser - Same as a laser diode.

Sensitivity - For a fiber optic cable receiver it is the minimum optical power required to achieve a specified level of performance, such as BER. Alternatively, it is the minimum amount of energy required by a receiver for successful operation.

Shot noise - Noise caused by random current fluctuations arising from the discrete nature of electrons.

Signal to noise ratio - The ratio of signal power to noise power.

Silica - Glass material, nearly pure SiO2.

SI-POF - Step index plastic fiber optic cable.


Simplex - Transmission in only 1 direction.

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

Single-mode - A small core, fiber optic cable that supports only 1 mode of light propagation above the cutoff wavelength. Typically, the diameter of the core is 9-10 mm. Dispersion and power loss through the cable walls are low with this type of cable. It is proper for long distance transmission.

SMA - A connector type. This was the predecessor of the ST connector. It features a threaded cap and housing. The use of the SMA connector has decreased markedly in recent years being replaced by the ST and SC connectors.

SNR, S/N - Signal to noise ratio. Usually expressed in dB.

Soliton - An optical pulse that does not suffer dispersion as it propagates over a distance.

SONET - Synchronous Optical Network. An international standard for fiber optic cable based telephony.

Source - There is 2 possibilities. First, it is a generator of information or data. Secondly, within the context of fiber optics it is a light emitter, either an LED or laser diode, for a fiber optic cable based link.

Spectral attenuation - Measure for the attenuation in dependence on wavelength.

Spectral bandwidth (Between half power points) - It is the wavelength interval in which a radiated spectral quantity is not less than half its maximum value. It is a measure of the extent of the spectrum. For a light source typical spectral widths are 20 to 60 nm for a LED and 2 to 5 nm for a laser diode.

Spectral width - The measure of the wavelength extent of a spectrum. It is usually based upon the 50% intensity points. When referring to the spectral width of sources, typical spectral widths are 20 to 60 nm for a LED and 2 to 5 nm for a laser diode.

Splice - An interconnection method for joining the ends of 2 fiber optic cables in a permanent or semi-permanent fashion. Thermal fusing may carry out splicing or it may be mechanical.

Splicing - The permanent joining of fiber optic cable ends to identical or similar fiber optic cables without using a connector. See also Fusion splicing and Mechanical splicing.

Splice box - Housing for 1 or more splice organizers. The changeable front panel can be equipped with different connector plugs.

Splice closure - A container used to organize and protect splice trays.

Splice organizer - An organizer panel that holds up to 12 splices with splice protectors and sufficient loops.

ST - A keyed bayonet connector type similar to a BNC connector. It is used for both multi-mode and single-mode fiber optic cables. Its use is wide spread. It has the ability both to be inserted into and removed from a fiber optic cable both quickly and easily. Method of location is also easy. There are 2 versions ST and ST-II. These are keyed and spring loaded. They are a push in and twist type.

Star coupler - A coupler for a fiber optic cable in which power at any input port is distributed to all output ports.

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

Steady state - Equilibrium mode distribution.

Step index fiber - A fiber optic cable, either multi-mode or single-mode, in which the core refractive index is uniform throughout so that a sharp step in refractive index occurs at the core-to-cladding interface.

Step index profile - A refractive index profile in which the refractive index changes abruptly from the value n1 to n2 at the core cladding interface.

Strength member - That part of a fiber optic cable composed of Kevlar Aramid yarn, steel strands or fiberglass filaments that increases the tensile strength of the cable.

Stripping - Removing the coating from a fiber optic cable.

Tap loss - In a fiber optic cable coupler is the ratio of power at the tap port to the power at the input port.

Tap port - In a fiber optic cable coupler in which the splitting ratio between output ports is not equal it is the output port containing the lesser power.

TDM - Time Division Multiplexing.

Tee coupler - A 3 port optical coupler.

10Base-F - A fiber optic cable based version of an IEEE 802.3 network.

10Base-FB - That portion of a 10Base-F network that defines the requirements for the fiber optic cable backbone network.

10Base-FL - That portion of a 10Base-F network that defines the fiber optic cable link between a concentrator and a station.

10Base-FP - That portion of a 10Base-F network that defines a passive star coupler.

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.

Ternary - Made from 3 different elements.

Thermal noise - Noise resulting from thermally induced random fluctuation in current in the receiver's load resistance.

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

Throughput loss - In a fiber optic cable coupler it is the ratio of power at the throughput port to power at the input port.

Tight buffer - Type of cable construction whereby each glass fiber optic cable 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 share a given transmission medium, for example a fiber optic cable. With this technique they share it on a time basis. Each channel is given specific time slots to transmit during and can only transmit during these time slots.

Token ring - A ring based networking scheme. A token is used to control access to the network. Used by IEEE 802.5 and FDDI.

Total bandwidth - The combined modal and chromatic bandwidth.

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.

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

Transceiver - A combination of transmitter and receiver providing both output and input interfaces with a device.

Transmission loss - Total loss encountered in transmission through a system.

Transmitter - In the context of a fiber optic cable based communication link an electrical package, which converts an electrical signal to an optical signal.

Tree coupler - A passive fiber optical component in which power from 1-input is distributed to more than 2-output fiber optic cables.

TX - Transmitter.

UL - Underwriters Laboratories, Inc.

Ultraviolet - Optical radiation for which the wavelengths are shorter than those for visible radiation, that is approximately between 1 nm and 400 nm.

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

UV - Ultraviolet.

VCSL - Vertical cavity semiconductor laser.

Velocity of light - The velocity of light is 300,000 km/sec in a vacuum. In a medium it depends in the refractive index and the wavelength.

WAN - Wide Area Network. A network of connected computers that cover a great geographical area.

Waveguide - A 2 dimensional substrate which carries light in channels inscribed in the material.

Wavelength - Distance an electromagnetic wave travels in the time it takes to oscillate through a complete cycle. Wavelengths of light are measured in nanometers (10-9 m) or micrometers (10-6 m).

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

Wavelength Division Multiplexer - A passive fiber optical device used to separate optical signals of different wavelengths carried on 1 fiber optic cable.

Wavelength Division Multiplexing - WDM. Simultaneous transmission of several optical signals of different wavelengths on the same fiber optic cable. It is a technique used so that several different communications channels can share the same fiber optic cable.

WDM - Wavelength Division Multiplexing.

WIC - Wavelength Independent Coupler.

mW - MicroWatt.

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