FIBER OPTICAL GLOSSARY

8/6/2019 FIBER OPTICAL GLOSSARY

http://slidepdf.com/reader/full/fiber-optical-glossary 1/164

OPTICAL FIBER

GLOSSARY.

SHOKRI ELGEBALI 12/21/2010



fiber opticsglossary

- The following terms weredefined with the assistance of

Panduit Corporation, a leadingmanufacturer of wiring andnetwork cabling products(www.panduit.com) and Jeff Hecht, noted optical

networking consultant andauthor.

Adapter - A mechanical device designed

to align fiber-optic connectors.It contains the split sleeve(interconnect sleeve) thatholds the two ferrules together.



Adapter Sleeve

- A mechanical fixture withinthe adapter body that alignsand holds two terminated fiberconnectors. Adapter sleevematerial is typically phosphor

bronze, ceramic or polymer.

Absorption - The absorbing of light energywithin an optical fiber due to

natural impurities in the glass.Absorption and scattering arethe main cause of attenuation(signal loss) in an optical fiber.

-



- Acceptance Angle - The angle at which the core of

the fiber will take in light.

- Numerical Aperture.

- The light-gathering ability of anoptical fiber, as determined by the square root of thedifference of the squares of therefractive indexes of the core(n 1 ) and the cladding (n 2 ),and as expressed in theequation: NA = (n 1 2 - n 2 2 ) 1 / 2 Fiber optic transmissionsystems (FOTS) are based onthe principle of total internal

reflection, meaning that alllight injected into the fiber isretained in the fiber.Theobjective is to retain all

http://computer.yourdictionary.com/numerical-aperture



















components of the opticalsignal in the core. However, a

light source naturally injectssome light rays into the core atangles less than the criticalangle, which is perpendicularto the plane of thecore/cladding interface. Atsuch severe angles, theincident light rays penetratethe interface and enter thecladding, where they may belost. The numerical aperture

essentially is an indication of how well an optical fiberaccepts and propagates light.As illustrated in Figure N-2,optical fiber with a small NA

(top) requires more directional,i.e., collimated, light, whereasfiber with a large NA (bottom)does not.The higher NA allows



the fiber to accept more lightand propagate more modes.The

NA is mathematically equal tothe sine of the angle of acceptance. Note: The NA isimportant in multimode fiber(MMF). It is not, however, acritical measurement in single-mode fiber (SMF), as the smallcore supports only a singlemode of propagation and,therefore, the light is neitherreflected nor refracted.The

light-accepting ability can alsobe defined in terms of the coneof acceptance, which is themaximum angle at which thefiber will accept incident light,

represented in threedimensional view. angle of acceptance.



Collimation.

- The process by which a beam of

radiant electromagnetic energyis lined up to minimizedivergence or convergence.Ideally, a collimated beam is abundle of parallel rays perfectly

lined up along an optical line-of-sight (LOS) between atransmitter and receiver,perhaps through, and in perfectparallel with, a waveguide. In a

fiber optic transmission system(FOTS), a perfectly collimatedoptical beam would beperfectly lined up with the fibercore.



Cone of Acceptance.

- The maximum angle,represented in three-dimensional view as a cone, atwhich an optical fiber willaccept incident light. Withinthat cone, as defined by thoseangles, a light source can injectan optical signal into the fibercore and the signal will remainin the core, reflecting off of theinterface between the core and

cladding, as illustrated inFigure C-5. At a more severeangle, i.e., outside the cone,the signal will penetrate theinterface and enter, and

perhaps be lost in, thecladding. The angle of acceptance and, therefore, thecone of acceptance are



determined by the difference inindex of refraction (IOR)

between the core and cladding.

Critical Angle. - Light striking the interface

between two substances caneither reflect off of thesubstance it encounters orenter it, with the differencedepending on the nature of thesubstances and the angle at

which the incident light raystrikes the interface. A glassoptical fiber (GOF) comprisesan inner core of glass of a givenrefractive index, or index of

refraction (IOR), surroundedby one or more layers of cladding of lower refractiveindex.The critical angle is



measured from the normal,which is at 90 degrees from

(i.e., perpendicular to) thesurface of the core/claddinginterface, or boundary. If, asillustrated in Figure C-6, theincident light rays strike theinterface at an angle greaterthan the critical angle, theyreflect off the interface, withthe angle of reflection beingthe same as the angle of incidence.The light rays glance

off of the interface, so to speak.If, on the other hand, theincident light rays strike theboundary at an angle less thanthe critical angle, they enter

the cladding, where they eitherare lost or refracted back intothe core, depending on the type



of fiber and the angle of incidence.

Total InternalReflection (TIR).

- The complete reflection of alight ray as it strikes theinterface between the mediumin which it is traveling and a

medium with a lower refractiveindex, or index of refraction(IOR) at an angle greater thanthe critical angle, which ismeasured from theperpendicular at the point of reflection. Depending on thespecific nature of the glassoptical fiber (GOF) and its



manner of construction, obliquelight rays striking the interface

between the core and claddingvariously are reflected orrefracted back into the core,which is the primary light-conducting medium. If theoptical fiber is a step-indexfiber, and the angle of incidence is greater than thecritical angle, the light rays arereflected back into the core. If the angle is less than the

critical angle, the light rayspenetrate the core/claddinginterface, where they are lost.If the fiber is a graded-indexfiber, the light rays also reflect

off the core/cladding interfaceif the angle of incidence isgreater than the critical angle.As the angle decreases below



the critical angle, the light raysenter the cladding, where they

gradually gain velocity andbend, or refract, back into thecore. The lesser the angle, thegreater the penetration and thegreater the associatedincreases in velocity andrefraction. If the angle of theincident light ray is too severe,the light ray will penetrate thecore/cladding interface and belost in the cladding of either

type of cable.Total internalreflection essentially confinesthe optical signal to the coreconducting material, therebymaintaining signal strength

over a distance.Total internalreflection is the fundamentalprinciple that makes fiber optictransmission possible.



Add/Drop Multiplexer A device that includes or removesone or more optical channels to a

signal passing through it. Seeadd/drop multiplexer.

Aramid Yarn An ingredient in optical fiber cable

that provides support, protectionand tensile strength. Also referredto as KEVLAR, which is a brand of aramid yarn.

http://computer.yourdictionary.com/add-drop-multiplexer











ATM (asynchronous

transfer mode) - A network technology thatswitches optical and electronicsignals that are broken into 53-byte cells.

ATM (AsynchronousTransfer Mode).

- A fast-packet, connection-oriented, cell-switchingtechnology for broadbandsignals.ATM was an outgrowthof the ITU-T developmentefforts towards broadband

integrated services digitalnetwork (B-ISDN). Although B-ISDN faltered, ATM became theswitching technology of choice



in the broadband backbone of the public telephone network,

at least for a time. ATM isdesigned to accommodate anyform of data, including voice,facsimile, computer data,video, image, and multimedia,whether compressed oruncompressed, whether real-time or non-real-time in nature,and with guaranteed quality of service (QoS).ATM generallyoperates at minimum access

speeds of DS-1 (e.g., T1 at1.544 Mbps and E-1 at 2.048Mbps) and DS-3 (e.g., E-3 at34.368 Mbps and T1 at 44.736Mbps). Designed to operate at

very high speeds, ATM benefitsfrom fiber optic transmissionsystems (FOTS) and commonlyis provisioned over SDH/SONET



networks.Access circuitsoperating at OC-3 (155 Mbps)

are not unusual and backbonetransmission rates generallyare OC-3, at a minimum. ATMtraffic consists of three basictypes.

Attenuation The loss of signal strength(optical power) during

transmission between two points.It expresses the total loss of anoptical system, measured indecibels per kilometer (dB/km) atspecific wavelengths. See

"intrinsic loss" and "extrinsicloss" in this glossary.



Axis The center of an optical fiber.

Backbone Cabling The interbuilding andintrabuilding cable connectionsbetween entrance facilities,equipment rooms and thetelecommunications closets. Itconsists of the transmissionmedia, main and intermediatecross-connects and terminations

at these locations.

Bandwidth The information-carrying capacity

of an optical fiber. It is measuredin MHz-km and GHz-km, asdistance plays an important role.



Birefringent A property of a material that

causes the polarizations of light totravel at different speeds.

Bragg Scattering

A distribution of light that iscaused by a change in therefractive index of a material.

Fiber Bragg Grating - A short length of optical fiber

that filters out a particularwavelength. Periodically

spaced zones in the fiber coreare altered to have differentrefractive indexes slightlyhigher than the core. This



structure selectively reflects avery narrow range of

wavelengths while transmittingothers. Fiber Bragg gratingsare used to stabilize the outputof a laser and to filter outwavelengths in a WDM system.

- The name comes from Bragg'sLaw, which is used to createthe spacing of the changes. SirWilliam Lawrence Bragg, notedBritish physicist (1890-1971)

discovered this in his study of x-rays and crystal structures.



A Fiber Bragg Grating

- Fiber Bragg gratings such asthis one from JDS Uniphase canbe customized for a variety of applications covering a rangeof wavelength bands from 850

to 1650 nm. (Image courtesy of JDS Uniphase.)



The Gratings Reflect

- In this example, the redwavelength matches thegrating period and is reflected.The blue wavelength istransmitted because it does not

match the grating spacings.(Illustration assistance

courtesy of Jeff Hecht.)



Optical Circulators

- Since the desired wavelength isreflected back by the grating,another device known as an"optical circulator" detects andswitches it. (Illustration

courtesy of Jeff Hecht.)

Buffer The protective layer that

surrounds the fiber cladding.Fabrication techniques includetight or loose tube buffering.

Cable Assembly

An optical fiber cable that hasconnectors installed on one orboth ends. See "pigtail" and"patch cord" in this glossary.



C Band - A range of wavelengths from

1530 to 1565 nm. In this region,erbium-doped amplifiers (EDFAs)have highest gain. See EDFA andoptical bands.

Chirped Pulse - A pulse in which the wavelengthchanges during the duration of the pulse.

Chirped Pulse

- A pulse in which thewavelength changes during

the duration of the pulse. Ina diode laser, chirp arisesfrom direct modulation of thelaser, because the refractive



index changes with theelectron density. The output

of a laser may be chirpedintentionally to create ahigh-powered, extremelyshort pulse. In this case, theinitial pulse from an

oscillator is stretched outusing optics, amplified andthen compressed back to itsoriginal duration.



Channel Spacing The amount of bandwidth allotted

to each channel.

Channel Spacing

- The amount of bandwidthallotted to each channel in acommunications system thattransmits multiple frequenciessuch as fiber optics. It ismeasured as the spacing

between center frequencies (orwavelengths) of adjacentchannels.



Channel Spacing in OpticalFibers



- The first 10 Gbps example with50 GHz spacing has a slight

signal overlap, but with 100GHz, there is none. The firstexample provides morebandwidth, but the overlapcould be enough to causesignificant crosstalk.(Illustration courtesy of Jeff

Hecht.)

Chromatic Dispersion - The spreading of light pulsescaused by the difference inrefractive indices at different

wavelengths.



Cladding - The material surrounding the

core of an optical fiber. Thecladding has a lower refractiveindex (faster speed) in order tokeep the light in the core. Thecladding and core make up an

optical waveguide.



Cleave - The process of scoring and

breaking the optical fiber end inorder to terminate a connector.

Coarse WDM (CWDM) - A WDM technology that spaceswavelengths widely apart.

CWDM

- An optical multiplexingtechnique specified by the ITU-T as 18 wavelengths in the1270

- (Course WDM) An opticaltransmission method that isused for shorter distances thandense WDM (DWDM). Also



known as "wide WDM," CWDMtransmits fewer channels and

uses wider spacing betweenthe channels for distances upto 60 km. Wider spacing up to25 nm, compared to 1.6nm andsmaller for DWDM, toleratesmore temperature fluctuation.

- Standardized by the IEEE in2004 for 10 Gigabit Ethernet,CWDM components are muchless costly than DWDM because

the laser does not have to bestabilized, and an externalmodulator is not required. Thelaser can be modulated directlyby changing the drive current.

CWDM operates between 1265and 1625 nm compared toDWDM's tighter 1530-1620range.



Coating - A protective layer applied over

the fiber cladding during thedrawing process to protect it fromthe environment.

Connector - A mechanical device used on afiber to provide a means foraligning, attaching and decouplingthe fiber to a transmitter, receiveror other fiber. Commonly used

connections include 568SC(Duplex SC), ST, FDDI, FC, D4 andBiconic.



Core - The central region of an optical

fiber through which light istransmitted. It has a higherrefractive index (slower speed)than the surrounding cladding.

Coupler A device that combines two ormore fiber inputs into one fiberoutput or divides one fiber inputinto two or more fiber outputs.

See "directional coupler" in thisglossary.

Coupling

- The transferring of light goinginto and coming out of a fiber.This term does not imply that acoupler is used.



Critical Angle The maximum angle from the

axis at which light can be confinedwithin the core.

Cutoff wavelength - The shortest wavelength atwhich a singlemode fibertransmits only one mode. Atshorter wavelengths, it transmits

two or more modes.

Dark Fiber - Fiber lines that are suppliedwithout any electronic or optical

signaling equipment in its path.



dBm (decibels

milliwatt) - A measurement of decibels (dB)at one milliwatt.

dBÂµ (decibels

microwatt) - A measurement of decibels (dB)at one microwatt.

Decibel - A unit of measure used toexpress the relative strength of asignal.



Dielectric - A material such as a glass fiber,

which is not metallic and is notconductive.

Diffraction

- The bending of light rays as theypass around corners or throughholes smaller than their ownwavelengths.

Diffraction Grating - A series of scored lines thatseparates light into its variouscolors.



Directional Coupler - A coupler in which light is

transmitted differently dependingon the direction of transmission.See "coupler" in this glossary.

Dispersion - The spreading or broadening of light pulses as they travel througha fiber. The fiber property thatcauses this effect is also calleddispersion. The three principal

types are modal dispersion,chromatic dispersion andpolarization mode dispersion.



Dispersion

Compensation - Reducing dispersion in a fiber inorder to reduce total dispersion.Different methods are used forchromatic dispersion andpolarization mode dispersion.

Dispersion-ShiftedFiber - An optical fiber that has lower

chromatic dispersion in the 1550nm range.



Dispersion-Shifted

Fiber ( DSF). - A singlemode optical fiber that

has been designed to reducechromatic dispersion. The fibercore is fabricated in severallayers with different refractiveindices running in parallelthroughout its length. Zero-dispersion-shifted fiber haszero chromatic dispersion at

1550 nm. It is no longermanufactured, because itcauses interference in WDMtransmission. Nonzero-dispersion-shifted fiber is

designed for WDM. It has zerodispersion near 1500 nm andbeyond 1600 nm, which



provides lower dispersion inthe 1550 nm range.

Duplex Cord - A two-fiber cable used for bi-directional transmission.

DWDM (dense WDM) - Another term for closely spacedWDM. DWDM and WDM are usedsynonymously.

EDFA (Erbium-DopedFiber amplifier) An optical amplifier that boosts all

channels in the optical signal atthe same tim.



EDFA (Erbium-Doped

Fiber Amplifier).- EDFAs boost the inputregardless of the number of wavelengths. In several metersof doped fiber, the pump laser

excites the doped atoms tohigher orbits, and the inputsignal stimulates them torelease excess energy asphotons in phase and at the

same wavelength. (Illustrationcourtesy of Jeff Hecht.)

- A type of amplifier used in fiberoptic transmission systems(FOTS) and comprising a shortlength of fiber that has beendoped with erbium and splicedinto the operating single-mode



fiber (SMF) in a configurationknown as discrete

amplification, or lumpedamplification. A three-portwavelength divisionmultiplexer (WDM) is used,with one incoming portconnected to the operatingfiber carrying the primarysignal in the 1550 nm window,one incoming port attached to apump laser operating at 980nm or 1480 nm, and the one

outgoing port connected to theoperating fiber (see Figure E-2).The pump laser excites theerbium atoms.Weak incominglight from the operating system

causes the erbium atoms todrop from their excited state.As they do so, they release theextra energy, which transfers



to the primary signal andamplifies it. An EDFA can

simultaneously amplify anumber of wavelengths in anoperating range around 1550nm, which is in the optical C-Band.A single-pump EDFAinvolves a pump laser on theupstream side of the erbium-doped fiber section andprovides a gain varying from+10 dB (1,000%, or 10:1), toas much as approximately +17

dB (approximately 8,000percent, or 80:1). A double-pump EDFA involves one pumplaser on the upstream side andanother on the downstream

side of the erbium-doped fibersection, and provides a gain of close to 30 dB (100,000percent, or 1,000:1). Note: The



pump lasers can operate ineither direction. Optical

isolators, placed on both sidesof the EDFA, act like diodes,serving to prevent opticalsignals from traveling in morethat one direction. EDFAs arehighly effective and less costlythan optical repeaters, butgenerally are limited to nomore than 10 spans over a totaldistance of 800 km or so. Atthat point a repeater must be

applied to retime and reshapethe signal, thereby filtering outthe accumulated noise causedby various forms of dispersion.EDFAs are further limited by

their inability to amplifywavelengths shorter than 1525nm. An EDFA performs a type of amplification known as lumped



amplification, as it isconcentrated in a single point.



http://images.yourdictionary.com/images/computer/_EDFA.GIF



EDWA (Erbium-DopedWaveguide Amplifier)An optical amplifier similar to anEDFA, but derives a higher gainthrough a small waveguide ratherthan several meters of fiber.

Electro-AbsorptionModulator A semiconductor diode thatmodulates light from a separatelaser, but that may be fabricatedon the same wafer. Turningcurrent on causes lightabsorption.



EMI (Electromagnetic

Interference)The interference in signaltransmission or receptionresulting from radiation of electrical or magnetic fields.Optical fibers are not susceptibleto EMI.

Enclosure - A cabinet used to organize and

enclose cable terminations andsplices for use within mainequipment rooms, entrancefacilities, main or intermediatecross-connects and

telecommunications closets.



Epoxy - A thermosetting resin used to

secure the fiber with theconnector ferrule.

Etalon - A passive filter that uses aFabry-Perot cavity.

Evanescent Waves -The light that passes into the

cladding from the core.Extrinsic Loss - The loss that is induced in anoptical transmission system by anexternal source. In a fiber-opticlink, this can be caused byimproper alignment of connectorsor splices.



Fabry-Perot - A cavity with mirrors at opposite

ends. It is a foundationcomponent of certain lasers andpassive filters.

Fabry-Perot - An optical structure containing

a pair of mirrors at oppositeends of a cavity. Light reflectsback and forth between themirrors, and one or both

transmit a fraction of theresonant frequency. Theresonance is created by makingthe distance of one round tripbetween mirrors equal to an

integral number of wavelengthsof the cavity material. Opticallyspeaking, this is aninterferometer, because it



relies on the interference of light for its operation. A Fabry-

Perot device becomes a lightgenerator when a laser mediumis used in the cavity, otherwiseit is a passive filter.

Ferrule - The rigid prong in a fiber-opticplug that aligns the fiber with thesocket. Ferrule materials are

ceramic, plastic and stainlesssteel.



Fiber - A thin filament of glass or plasticconsisting of a core (inner region)and a cladding (outer region) and

a protective coating.



Fiber Bragg Grating - A series of periodically spaced

zones in a short length of fiberwith a higher refractive indexused to filter out wavelengths.

Fiber Laser - An alternate way of building alaser. The laser is built into thefiber itself.



Fiber Laser

Fiber Optics - Information transmitted throughoptical fibers in the form of light.



Fusion Splice

- The joining of two fiber ends byapplying enough heat to fuse ormelt the ends together to form acontinuous single fiber.

Graded-Index Fiber - A multimode fiber designed tocompensate for modal dispersionby allowing light to travelincreasingly faster from the

center of the core to its outeredge.



Infrared - A range of light from

approximately 700 to 1000 nm.Fiber-optic systems transmitbetween 700 and 1700 nm.

Injection Loss,Insertion Loss - The amount of light that leaksout or is otherwise lost afterbeing inserted into a fiber either

from a light source or anotherfiber.



Interference - The combination of light waves

in which the wave amplitudes addtogether. Constructiveinterference produces bright lightwhen the peaks are in phase witheach other. Destructive

interference produces dark zoneswhen the peaks of one wave alignwith the valley of the second.

Intrinsic Loss

- The loss due to inherent traitswithin the fiber; for example,absorption (light energy isabsorbed in the glass) and spliceloss (mismatched numerical

aperture).



L Band - A range of wavelengths from

1565 to 1625 nm. In this region,erbium-doped amplifiers (EDFAs)can be used, but have less gainthan in C band.

optical bands

The spectrum for transmission insinglemode optical fibers has

been broken into the followingwavelength ranges, or bands.Typically, the wavelengthstransmitted in multimode fibersare around 850 and 1310 nm,known originally as first windowand second window.



Wavelength Range.

Band Name In Nanometers (nm)

O-band Original 1260 - 1360

E-band Extended 1360 - 1460S-band Short 1460 - 1530

C-band Conventional 1530 - 1565L-band Long 1565 - 1625

U-band Ultra-long 1625 - 1675

Laser. - A device that generates a

coherent beam of light all inphase and of a single (or nearlysingle) wavelength. A cavity withmirrors at each end causes achain reaction that stimulates the

emission of photon.



laser (light

amplification bystimulated emission of radiation).

- A device that produces anintense, coherent, collimated,focused, and nearlymonochromatic beam of radiated optical energy bystimulating electronic, ionic, ormolecular transitions to lowerenergy levels. A lasercomprises an active medium, orgain medium, and a resonantcavity. An external powersource, or pump, in the form of electricity or another laser,energizes the gain medium,



which absorbs the energy.Some of the particles in the

gain medium are excited intoquantum high-energy states.When a critical level of energyis achieved, a light signalpassing through the mediumproduces more optical energythan is absorbed, and thesignal is greatly amplified.Theresulting radiated optical signalis highly coherent, i.e.,consistent in phase and

polarization, and virtuallymonochromatic.Through aresonating cavity and eithermirrors or a diffraction grating,the signal is narrowly

channeled and collimated, i.e.,the rays are lined up so thatthey are virtually parallel. Fiberoptic transmission systems



(FOTS) in long haulapplications employ

semiconductor diode lasers,generally Fabry-Perot lasers ordistributed feedback (DFB)lasers. Short haul transmissionsystems such as thoseassociated with local areanetworks (LANs) morecommonly employ light-emitting diodes (LEDs) orvertical cavity surface-emittinglasers (VCSELs) as light

sources. (Note: The laser waspatented by AT&T BellTelephones in 1960 as theoptical maser.)



Laser Action

- The combination of spontaneous emission first, andthen stimulated emission,causes the laser to "lase,"which means it generates a

coherent beam of light at asingle frequency.

Laser Diode

- A laser made of semiconductormaterials widely used to transmitlight into optical fibers. It isalways used for singlemode fiberand certain high-bandwidth

multimode fiber such as used withGigabit Ethernet.



laser diode

- A semiconductor-based laserused to generate analog signalsor digital pulses fortransmission through opticalfibers. Both laser diodes andLEDs (light-emitting diodes)are used for this purpose, butthe laser diode generates asmaller beam that is easier tocouple with the smaller core of singlemode fibers. Laser diodes

are designed to emit lighteither from their edge or theirsurface, the latter providing acircular beam that couplesbetter with the round core of

the fiber.- Laser diodes work on the same

principle as the bigger gaslasers. They function as an



(near 400 nm in the blue).



Laser Diodes

- Laser diodes such as these areall fabricated usingsemiconductor processes justlike CPU and memory chips.Note that the VCSELs (vixels)produce a circular beam that

couples well with a fiber.



A Tunable Laser Diode

- Laser diodes also make great

sensors. This laser diode fromJet Propulsion Labs is tunableto different frequencies inorder to detect various gases



both on this and other planets.(Image courtesy of JPL's

Microdevices Laboratory;Robert M. Brown,

photographer)

LED (Light EmittingDiode) - A device that produces light witha wide range of wavelengths.

LEDs are typically used withlower-bandwidth multimode fiber.

Loose Tube - The protective tube surrounding

one or more fibers. This is usuallyfound in cables used for outdoorinstallations.



MacroBending - The loss due to large scale

bending (extrinsic loss). Bendingcauses imperfect guiding of lightwhich will exceed the criticalangle of reflection. Macrobendingloss can be reversed once the

bend is corrected.

Mechanical Splice Joining two fiber ends together bya temporary or permanentmechanical method in order tomaintain continuous signaltransmission.



MEMS (Micro Electro

Mechanical Systems) - Tiny components etched from asemiconductor material that canmove under the control of electronic signals. MEMS devicesinclude movable mirrors that canswitch or redirect the path of light.

MicroBending- The loss of light due to smalldistortions in the fiber, notusually visible to the naked eye.

Micron (Âµm) - One micrometer or one millionthof a meter. Used to express thegeometric dimension of fibers.



Modal Dispersion - The spreading of light pulses

along the length of the fibercaused by differential opticalpaths taken in multimode fiber.

Mode- A reflective path that the lighttakes in a fiber. Each mode has itsown pattern of electromagneticfields as it propagates through thefiber. There is only one mode in

singlemode fiber. In multimodefiber, multiple modes aregenerated, causing pulsedispersion at the receiving end.



Mode Field Diameter

( MFD ) - In singlemode fiber, thediameter of the zone where thesingle mode propagates down thecenter of the fiber. It is slightly

larger than the core diameter.



Multimode - An optical fiber in which light

travels in multiple modes.Multimode fiber is used in shorter-distance applications thansinglemode fiber.



Multiplex

- Combining two or more signalsinto a single bit stream that canbe individually recovered.

NanoMeter

- One billionth of a meter.



- An Optical Carrier

Rate in the SONETHierarchy.

OC-1, OC-3, OC-12,

OC-48, OC-192, OC-786

OC (Optical Carrier).

- The optical signal as defined inSynchronous Optical Network(SONET) for North America andSynchronous Digital Hierarchy

(SDH) standards forinternational applications. AllSONET levels are expressed inmultiples of OC-1 (51.84



Mbps), which is a T3 signal(44.736 Mbps), or the

equivalent, plus SONETsignaling and control overhead,converted from electrical tooptical format. The SONETdigital hierarchy begins at OC-1(51.84 Mbps) and the SDHhierarchy at OC-3 (155.52Mbps). From OC-3, theprogression of SONET and SDHlevels are the same,culminating in OC-768 (39.813

Gbps). OC-1536 (79.626 Gbps)and OC-3072 (159.252 Gbps)have yet to be fully defined.See SONET for a table of OC-Nlevels.



OC

- (Optical Carrier) Thetransmission speeds inSONET/SDH networks

SONET CIRCUITS

Optical ElectricalChannel Channel Speed (Mbps)

VT-1.5 1.7OC-1 STS-1 51.84 (28 DS1s or 1 DS3)OC-3 STS-3 155.52 (3 STS-1s)OC-3c STS-3c 155.52 (concatenated)OC-12 STS-12 622.08 (12 STS-1, 4 STS-3)

OC-12c STS-12c 622.08 (12 STS-1, 4 STS-3c)OC-48 STS-48 2488.32 (48 STS-1, 16 STS-3)

OC-192 STS-192 9953.28 (192 STS-1, 64 STS-3)OC-768 STS-768 39813,12 (768 STS-1, 256 STS-3)

OC = Optical Carrier

STS = Synchronous Transport

Signal



OEO (Optical ElectricalOptical) - Refers to devices that convertlight back to electricity formanipulation and then back out tolight. Contrast with OOO.

OFNR (Optical FiberNon-conductive Riser)- A type of fiber-optic cable.



OFNP (Optical Fiber

Non-conductivePlenum) - A type of fiber-optic cable.

OOO (Optical OpticalOptical) - Refers to devices that maintain

the transmission signal as lightthroughout. Contrast with OEO.

Optical Amplifier

- A device that boosts signals inan optical fiber. The EDFA was thefirst successful optical amplifier.See EDFA.

http://computer.yourdictionary.com/edfa

http://computer.yourdictionary.com/edfa



Optical Channel - A signal transmitted at one

wavelength in a fiber-opticsystem.

Optical Network- A network that processes andswitches signals in optical form.

Optical Switch - A device that routes optical

signals to their appropriatedestination. All-optical switches(OOO) do not have to convertlight back to electricity forprocessing.



optical switch. - An all-optical f iber-optic

switching device that maintainsthe signal as light from input tooutput. Traditional switches thatconnect optical fiber lines areelectro-optic.

- They convert photons from theinput side to electronsinternally in order to do theswitching and then convertback to photons on the output

side.- Although some vendors callelectro-optical switches"optical switches," true opticalswitches support all

transmission speeds. Unlikeelectronic switches, which aretied to specif ic data rates andprotocols, optical switches

http://computer.yourdictionary.com/optical-switch




























direct the incoming bitstreamto the output port no matter

what the line speed or protocol(IP, ATM, SONET) and do nothave to be upgraded for anysuch changes.

- Optical switches may separatesignals at differentwavelengths and direct them todifferent ports.

- Using tiny mirrors that reflectthe input signal to the outputport, MEMS technology is

expected to be the prevailingmethod for building opticalswitches, also known as"photonic switches." There arevarious fabrication methods for

building MEMS mirrors.



MEMS (Micro-

ElectroMechanicalSystems). - Tiny electromechanical systems

on a silicon chip. MEMScomprise integratedmechanical elements, sensors,actuators, and electronics on acommon silicon substratethrough microfabricationtechnologies, including the

micromachining of themechanical elements. MEMSare employed in opticalprojectors as well as in purelyoptical switches used in fiber

optics transmission systems(FOTS), and actually are morealong the lines of optical cross-connects. As purely optical



devices, they do not requirethat the incoming optical signal

be converted to an electricalsignal for processing and thenbe reconverted to an opticalsignal. In other words, MEMSare optical-optical-optical(OOO), rather than optical-electrical-optical (OEO). Seealso cross-connect, FOTS, and switch.

- (MicroElectroMechanicalSystems) Tiny mechanicaldevices that are built ontosemiconductor chips and aremeasured in micrometers. Inthe research labs since the

1980s, MEMS devices began to materialize as commercialproducts in the mid-1990s.They are used to make

http://computer.yourdictionary.com/cross-connect

http://computer.yourdictionary.com/fots

http://computer.yourdictionary.com/switch








































pressure, temperature,chemical and vibration sensors,

light reflectors and switches aswell as accelerometers forairbags, vehicle control,pacemakers and games. Thetechnology is also used tomake inkjet print heads,microactuators for read/writeheads and all-optical switchesthat reflect light beams to theappropriate output port. Seeaccelerometer.

MEMS and MOEMS - When optical components areincluded in a MEMS device, it is

called a micro-opto-electromechanical system(MOEMS). For example, addinga photonic sensor to a silicon

http://computer.yourdictionary.com/accelerometer











chip constitutes a MOEMSdevice. See micromachine,

MEMS mirror, DLP and optical switch.

MEMS Vs. NanotechnologySometimes MEMS andnanotechnology are terms thatare used interchangeably,because they both deal withmicrominiaturized objects.However, they are vastlydifferent. MEMS deals with

creating devices that aremeasured in micrometers,whereas nantotechnology dealswith manipulating atoms at thenanometer level.

http://computer.yourdictionary.com/micromachine

http://computer.yourdictionary.com/mems-mirror



http://computer.yourdictionary.com/dlp























































































MEMS-based Optical

SwitchIn an all-optical switch, MEMSmirrors reflect the input signal toan output port without regard to

line speed or protocol. Thistechnology is expected to be thedominant method for buildingphotonic switches.



Sample Micromachines

- Microfabrica's EFAB systemwas the first MEMS foundryprocess to accept CAD files asinput, turning customer designsinto micromachines much

faster than traditional methods.EFAB builds the devices onemetal layer at a time. In thisimage, the square at the top isa microfluidics device with

internal passageways used fora "lab on a chip." The multi-arm device (center) is a fuelinjection nozzle. Bottom left isan accelerometer, and bottom

right is an inductor used in RFcircuits. (Image courtesy of

Microfabrica Inc.,

www.microfabrica.com)



MEMS-Based

Accelerometer- MEMSIC's dual-axis thermal

accelerator is a MEMS-basedsemiconductor device thatworks conceptually like the airbubble in a construction level.The square in the middle of thechip is a resistor that heats upa gas bubble. The next largersquares contain thermal

couples that sense the locationof the heated bubble as thedevice is tilted or accelerated.(Image courtesy of MEMSIC, Inc.)



MEMS-based Optical Switch

- MEMS mirrors reflect the inputsignal to an output port withoutregard to line speed orprotocol. This technology isexpected to be the dominantmethod for building photonic

switches.



MEMS Mirrors

An individual mirror in a MEMS-based switch can really fitthrough the proverbial "eye of a

needle."



Optical Waveguide - An optical fiber, planar

waveguide or other structure thatguides light along its length.

OTDR (Optical TimeDomainReflectometer) - An instrument that measures

optical transmissioncharacteristics by sending a shortpulse of light down a fiber andobserving backscattered light.Used to measure fiber attenuation

and evaluate optical transmissionat splices and connectors.



Passive Optical

Network - A fiber-optic system with noactive components between itsdistribution point and remotereceiver nodes.

Photo Diode - A device that receives opticalpower and changes it to electricalpower.

PC (PhysicalContacting) - Refers to the type of fiber-optic

connector that makes actualcontact of two terminated fiberends, keeping signal losses to aminimum.



Patch Cord - A specific length of optical fiber

cable with terminated connectorson each end. Used for connectingpatch panels or optoelectronicdevices.

Photon- A particle of light.

Photonic

- Having to do with light orphotons.

Pigtail - A short length of fiber in which

one end is attached to acomponent and the other is freeto be spliced to another fiber.



Planar Waveguide - A flat waveguide on the surface

of a substrate with a lowerrefractive index. It confines lightsimilar to an optical fiber. Used inwaveguide arrays.

Polarization - The alignment of theperpendicular electrical andmagnetic fields that make up alight wave.

Polarization ModeDispersion - The dispersion that arises from

slight asymmetries in opticalfibers. The speed of light varieswith polarization.



Polishing Paper - Also known as lapping film, it is

a paper with a fine grit used toremove any imperfections in thefiber end surface that may existafter cleaving. Fiber endsterminated within a connector are

polished flush with the end of theferrule.

Polishing Puck - A device used to hold the

connector during the polishing of the fiber.

Population Inversion

- The state of atoms that havebeen excited.



Raman Amplifier - A device that boosts the signal

in an optical fiber by transferringenergy from a powerful pumpbeam to a weaker signal beam.

Raman amplifier- A type of amplifier used in long

haul, single-mode (SMF) fiberoptic transmission systems(FOTS). Raman amplification

usually occurs throughout thelength of the transmission fiberitself in a process known asdistributed amplification,rather than in a discrete

amplification, or lumpedamplification configurationsuch as that employed by anerbium-doped fiber amplifier



(EDFA). Raman amplificationoccurs as a high-energy pump

wavelength is sent in thereverse direction from theoutput end of the fiber span,where the incoming signal isweakest. The pumpwavelength, which generally isin the 1450 nm range (E-Band),interacts with and excitesatoms in the crystalline latticeof the fiber core.The atomsabsorb the photons, and

quickly release photons withenergy equal to the originalphoton, plus or minus atomicvibration. In other words, afrequency/wavelength shift

occurs as the pump wavelengthpropagates along the fiber inthe reverse direction.Theenergy lost in the pump



wavelength shifts to longer-wavelength (within about 100

nm) signals, generally in the1550 nm window (C-Band), inthe forward direction, therebyserving to amplify them. Ramanamplifiers offer the advantageof amplifying signals in thebroad range extending from1300 nm to 1700 nm. Further,they perform better than EDFAsin terms of signalto-noise ratio(SNR). Raman amplifiers often

are used as preamplifiers toenhance the performance of EDFAs in dense wavelengthdivision multiplexing (DWDM)systems.

- Pronounced "ruh-mahn," it is adevice that boosts the signal inan optical fiber by transferring



energy from a powerful pumpbeam to a weaker signal beam.

It relies on the interactionbetween light and atoms in thefiber. Unlike erbium-dopedfiber amplifiers (EDFAs), whichboost wavelengths in the 1530-1610 nm range, a Ramanamplifier can increase thesignal strength of anywavelength by pumping at13THz more than the desiredfrequency.

- Normally, Raman amplificationis distributed along lengths of signal-transmitting fiber. ARaman pump laser is typically

stationed at the end of a fiberrun and pumps backwardseveral kilometers to amplifysignals through that region.



Receiver (RX) - An optoelectronic device that

converts optical signals intoelectrical signals.

Reflection- The process that occurs when alight ray traveling in one materialhits a different material andreflects back into the originalmaterial without loss of light.



Refractive Index

- A property of a material that

changes the speed of light,computed as the ratio of thespeed of light in a vacuum tothe speed of light through thematerial. When light travels at

an angle between two differentmaterials, their refractiveindices determine the angle of transmission (refraction) of thelight beam. In general, the

refractive index varies basedon the frequency of the light aswell, thus different colors of light travel at different speeds.High intensities also canchange the refractive index.

- The refractive index of avacuum is 1.0, and air is a tinyfraction greater than 1.0. The



higher the index, the slowerthe speed of light through the

medium, because the speedthrough the material is thespeed of light (c) over therefractive index (n),

- thus speed = c/n. Following arecommon refractive indices.

Refractive Material Index (n)

Vacuum 1.0 Air 1.0 (tiny fraction more than 1) Water 1.33

Glass 1.45-1.48Lithium niobate 2.25

Gallium arsenide 3.35Silicon 3.5Germanium 4.0



Refractive Indices

- When light travels at an anglebetween two materials, lightbends according to theirrefractive indices. In order toreflect, light must be on the

wider side of the critical angle.



Refraction

- The bending of light rays as theypass through a transmissionmedium of one refractive indexinto a medium with a differentrefractive index.

Refractive Index - The ratio of the velocity of lightin a vacuum to the velocity of light in a specific material. Using

1.0 as the base reference, thehigher the number, the slowerlight travels.

Repeater

A transceiver that converts opticalsignals to electronic and back outto optical.



Riser - A pathway for indoor cables that

pass between floors.

S Band - A range of wavelengths from1460 to 1530 nm.

Scattering - A property of glass that causeslight to deflect from the fiber and

contribute to losses (intrinsicattenuation).

SDH (Synchronous DigitalHierarchy) A scale of standard data rates forfiber-optic systems defined by theITU.



SONET (Synchronous

Optical NETwork).- transmission over single-mode

fiber (SMF) optic transmissionsystems (FOTS), SONET grew

out of the SYNTRAN(SYNchronous TRANsmission)standard developed at Bellcore.SONET was initially developedin 1984 and finally

standardized by the AmericanNational Standards Institute(ANSI) in 1988. Also in 1988,SONET was internationalized by

the ITU-T as SynchronousDigital Hierarchy (SDH), whichdiffers primarily with respect tolow-level line rates and some



terminology. SONET/SDHessentially is a broadband

optical version of T-carrier,defined in multiples of T3bandwidth plus overhead foradditional signaling and controlfunctions. Primarily intendedfor carrier backboneimplementation, SONET/SDHspecifies a network-to-networkinterface (NNI), also known as

network node interface, thatsupports the interconnection of national and regional networksinto a cohesive global network.The user network interface(UNI) provides a standardbasis for connection from theuser premises to a SONET/SDH



local loop. T3 signal to whichadditional signaling and control

overhead is added to for theSynchronous Transport Signallevel-N (STS-N). The termOptical Carrier-N (OC-N)applies once the electricalsignal is converted to opticalformat. The SONET hierarchybegins with is OC-1 at asignaling rate of 51.84 Mbps,

which is the equivalent of a T3(44.736 Mbps) plus overhead,and currently tops out at theOC-768 nominal rate of 40Gbps, which is the equivalent of 768 T3s plus overhead.Table S-2 details the SONET/SDHhierarchy.



Table S-2: SONET/SDH Signal Hierarchy

OpticalCarrier (OC)

Level

SONETSTS Level

SDH STMLevel

Signaling RateEquivalent

DS-3 ChannelsEquivalent DS-0

Channels

OC-1 STS-1 51.84Mbps 1 672

OC-21 STS-2103.68Mbps

2 1,344

OC-32 STS-3 STM-1155.52Mbps

3 2,016


4 2,688


9 6,048

OC-12STS-

12

STM-4622.08

Mbps

12 8,064

OC-181 STS-18

STM-6933.12Mbps

18 12,096

OC-24STS-24

STM-8 24 16,128

OC-361

STS-36

STM-12 36 24,192

OC-48STS-48

STM-16

48 32,256



OC-961 STS-96

STM-32

96 64,512

OC-192STS-192

STM-64 192 129,024

OC-768STS-768

STM-256

768 516,096

OC-15363

STS-1536

STM-512

1536 1,032,192

OC-30723

STS-3072

STM-1024

159.252Gbps

3072 2,064,384

1 OC-2, OC-9, OC-18, OC-36, andOC-96 are considered to beorphaned rates. 2 OC-3 was

defined by the CCITT as the basictransport rate for B-ISDN. 3 Thislevel is not fully defined. ment forvoice encoded using the standard

pulse code modulation (PCM)technique employed in the publicswitched telephone network(PSTN). The STS-1 frame, as



illustrated in Figure S-5,comprises a Synchronous Payload

Envelope (SPE) of 783 octets, plus27 octets of overhead comprisingSection Overhead (SOH), LineOverhead (LOH), and PathOverhead (POH).The payload ineach frame comprises one ormore Virtual Tributaries (VTs)organized into Virtual TributaryGroups (VTGs).A process known

as concatenation allows multipleSTS-1 frames to be multiplexed,switched, and transported overthe network as a single entity.SDH and SONET standards specifytwo physical configurationoptions.A path-switched ring



employs a dual counter-rotatingring, with both fibers active.

One ring transmits in theclockwise direction and the otherin the counter-clockwisedirection.This approach offers

zero downtime in the event of thefailure of a fiber. A line-switchedring features one active and oneinactive fiber. In the event of thecatastrophic failure of a node or

fiber, a line-switched ring offerssub-50 millisecond restoral timesfor rings up to 1,200 kilometers inroute distance. Figure S-6

illustrates a hierarchy of local,metropolitan, and backbone ringsoperating at example OC-N rates.

loop, LOH , overhead , path-



switched ring, PCM , POH , PSTN , signaling and control , signaling

rate, SMF , SOH , SPE , T3, T-carrier ,VT , and VTG .

SONET

- (Synchronous Optical NETwork)A fiber-optic transmissionsystem for high-speed digitaltraffic. Employed by telephonecompanies and common

carriers, speeds range from 51Mbps to 40 Gbps.

- SONET is an intelligent systemthat provides advancednetwork management and astandard optical interface.Specified in the BroadbandISDN (B-ISDN) standard,



SONET backbones are widelyused to aggregate T1 and T3

lines. The Europeancounterpart to SONET is theSynchronous Digital Hierarchy,and the term "SONET/SDH" iswidely used when referring toSONET.

Self Healing - SONET can be built in a self-

healing ring architecture thatuses two or more transmissionpaths between nodes. In theevent one path fails, traffic canbe rerouted.



- SONET Ring.

- The architecture used in SONETtechnology. SONET rings,known as "self-healing rings,"use two or more transmissionpaths between network nodes,which are typically digital

cross-connects (DCSs) oradd/drop multiplexers (ADMs).If there is a break in one line,the other may still be available,providing the second is not in

close proximity to the first andalso damaged. For the bestsecurity against failure, whenpossible, different physicalroutes are used for the two

lines. The most fault-tolerantarchitecture is the four-fiber bi-directional ring.

http://computer.yourdictionary.com/sonet-ring























- Two Fiber Unidirectional



- Two Fiber Unidirectional- This is the simplest SONET ring

topology. All data aretransmitted on the working oractive path, while the standbypath (protection path) lies in

waiting. When a failure in theactive path occurs, the twonetwork nodes affectedimmediately switch to thestandby line. Four fibers may

used in a unidirectional system,but it is not usually done.



- Two Fiber Bidirectional



- Two Fiber Bidirectional.- In this architecture, traffic

flows in both directions, buthalf the capacity of the line isused as a data channel and theother half for protection. In theevent of failure, the alternate

line takes up the slack.-



-

Four Fiber Bidirectional



- Four Fiber Bidirectional.- This is the most robust

architecture which canwithstand multiple failuresproviding the lines are routedin different locations. Both

active and standby paths areduplicated in this topology,which is common in largecarrier networks that cannotafford a breakdown.

-



- TDM Multiplexing - SONET uses time division

multiplexing (TDM) to sendmultiple data streamssimultaneously. Its smallestincrement of provisioning is VT-

1.5, which provides 1.7 Mbps of bandwidth. The next increment,STS-1, jumps to 51.84 Mbps.Any data stream that does notfill that channel goes wasted.

ATM Over SONET Telcordia's GR-2837 standardmaps ATM cells onto SONET,

turning a SONET pipe into acell-switched (packet-switched) transmission carrier



that utilizes the full bandwidthof the medium without waste.

SONET CIRCUITS

Optical Electrical

Channel Channel Speed (Mbps)

VT-1.5 1.7OC-1 STS-1 51.84 (28 DS1s or 1 DS3)OC-3 STS-3 155.52 (3 STS-1s)OC-3c STS-3c 155.52 (concatenated)

OC-12 STS-12 622.08 (12 STS-1, 4 STS-3)OC-12c STS-12c 622.08 (12 STS-1, 4 STS-3c)OC-48 STS-48 2488.32 (48 STS-1, 16 STS-3)OC-192 STS-192 9953.28 (192 STS-1, 64 STS-3)OC-768 STS-768 39813,12 (768 STS-1, 256 STS-3)

OC = Optical Carrier

STS = Synchronous Transport Signal



Transporting IP

- In a WAN or over the Internet,

IP traffic is widely carried overSONET lines, either using ATMas a management layer or overSONET directly. In the future,

IP is expected to travel directlyover DWDM fiber (rightmostdiagram).



100Base-T (100 Mbps;

Baseband; Twistedpair).- An IEEE standard (802.3u,

1995) similar to 10Base-T,100Base-T translates to 100Mbps (theoretical transmissionrate), Baseband (onetransmission at a time over asingle, shared channel), overTwisted pair media.The

maximum segment lengthbetween the 100Base-T huband the attached device (e.g.,workstation or printer)originally was specified at 100

meters or less over four pairsof Cat 3 unshielded twisted pair(UTP). The predominantversion is 100Base-TX, which



extends the distance to 350meters over two pairs of Cat

5e.The 100Base-T hub is a wirehub that serves as a multiportrepeater, as well as a centralpoint of interconnection.100Base-T uses the 4B5B linecoding technique.

Ethernet.Ethernet Telecom Definition

- Robert M. Metcalfe and hisassociates at the Xerox PaloAlto Research Center (Xerox

PARC) first developed both theconcept of a local area network(LAN) and the enablingtechnology.That first network



originally was known as theAltos Aloha Network, because it

connected Altos computersthrough a network based onthe University of Hawaii'sAlohaNet packet radio systemtechnology. Subsequently(1973), it was renamedEthernet, from luminiferousether, the omnipresent passivemedium once theorized topervade all space and tosupport the propagation of

electromagnetic energy.Theoriginal Ethernet supported atransmission rate of 2.94 Mbpsover coaxial cable. Xeroxcommercialized the technology,

renaming it the Xerox Wire.Gordon Bell, vice president of engineering at DigitalEquipment Corporation (DEC,



subsequently acquired byCompaq, which later merged

with Hewlett-Packard), hiredMetcalfe as a consultant in1979 specifically to develop aLAN network technology thatwould not conflict with theXerox patent. Metcalfe broughtDEC, Intel, and Xerox togetherto form into a joint ventureknown as DIX, which improvedthe technology, increasing thebandwidth to 10 Mbps and

reverting to the nameEthernet.The technologyquickly became a de factostandard. In February 1980,the IEEE established Project

802 to develop a set of LANstandards. In December 1982,the first standard waspublished and circulated as



IEEE 802.3, which actually is avariation on the now obsolete

Ethernet standard. Althoughthe two do not interoperate,the terms 802.3 and Ethernetare used interchangeably ininformal conversation. Ethernethas evolved considerably since1980. The signaling rate hasincreased from 10 Mbps to 100Mbps, 1 Gbps, and 10 Gbps. Theoriginal 10Base5 specificationfor coaxial cable has given way

to 10/100/1000Base-Tspecifications for twisted pair,and various 10GBase-XXspecifications for optical fiber.Relatively unchanged have

been the frame format and theprotocols for medium accesscontrol (MAC), which includecarrier sense multiple access



with collision detection(CSMA/CD) and carrier sense

multiple access/collisionavoidance (CSMA/CA).TheEthernet frame, as illustrated inFigure E-3, is formatted asfollows:

- In 1985, the U.S. Institute of Electrical and ElectronicEngineers(IEEE) developed standards forLocal Area Networks (LANs)called theIEEE 802 standards.

These standards presently formthe basis of most networks.

- One of the IEEE 802standardsÂ—the IEEE 802.3Â—is known asÂ“Ethernet,Â” themost prevalently usedLANtechnology around theglobe. Ethernet was designed



by the Xerox Corporationin1972, and in its simplest form

it used a passive bus operatedat 10 Mbps. A50-Ohm coaxialcable connected the computersin the network.

- Though a single LAN can haveas many as 1,024attachedcomputer systems, inpractice most LANs have farfewer than this. Typically,oneor several coaxial cable piecesare joined end-to-end to form

the bus, alsoknown as anÂ“Ethernet cable segment.Â”Each Ethernet cable segment isterminatedat both ends by 50-Ohm resistors and is usually

grounded at one end forsafetyreasons. Thus, computersattach to the cable using



network interface cardsand/ortransceivers.

- Since its birth, Ethernet hasgrown to much higherspeeds.For example, at thestart of 2004, 10 GBit/s(standardized as 802.3ae)networkadapters wereintroduced. Furthermore, theonce error-prone, single-cablebusarchitecture has evolvedinto a notable error-reducedstar topology using hubsand

switches.



Ethernet - The standard local area

network (LAN) access method.A reference to "LAN," "LANconnection" or "network card"automatically implies Ethernet.Defined by the IEEE as the

802.3 standard, Ethernet isused to connect computers in acompany or home network aswell as to connect a singlecomputer to a cable modem or

DSL modem for Internetaccess.- Most new computers come

network ready with Ethernetbuilt in. For machines without anetwork connection, Ethernetadapters can be added via USBor PC Card or by plugging anEthernet card into a free PCI



bus slot inside the case.

- Megabits Per Second: 10, 100,1,000 and 10,000A 10/100 Ethernet portsupports two speeds: 10 Mbps(10Base-T) and 100 Mbps(100Base-T). Computers alsocome with 10/100/1000 ports,which includes Gigabit Ethernetat 1 Gbps (1,000 megabits).Ethernet devices negotiate witheach other and transmit at the

highest speed possible. Forhigh-speed backbones inmetropolitan and wide areanetworks, 10 Gigabit Ethernet(10,000 megabits), the fastest

Ethernet, is also used.



- 10 Gigabit Ethernet

(10GbE). - Standardized by the IEEE as802.3ae, 10GbE uses the sameframe format and mediumaccess control (MAC) layer aspredecessor Ethernets. 10GbEruns only in full-duplex (FDX)mode, which makes collisioncontrol unnecessary.Theprimary line coding techniqueused in both 10GbE and GbE is

8B/10B, which carries a 25percent overhead penalty,thereby forcing the system torun at a signaling rate of 125Gbps. Some 10GbE systems use

the more recently developed64B/66B line coding, which issimilar but much moreefficient.Although the signaling



rates discourage the use of copper transmission media,

802.3ae currently specifies10GBase-T for short distancesusing Cat 6 and Cat 7 twistedpair. Fiber optic systems arepreferable, however, and802.3ae specifies a number of options, including 10GBase-SR,SW; 10GBase-LR, LW;10GBase-ER, EW; and 10GBase-LX4. 10GbE has application inthe backbones of very

bandwidth intensive local areanetworks (LANs) andmetropolitan area networks(MANs).



- 10 Gigabit Ethernet

- An Ethernet standard thattransmits at 10 Gbps.Introduced in 2002 andabbreviated "10 GbE," "10GE"or "10G Ethernet," it extendedthe familiar and ubiquitous

Ethernet used in local areanetworks (LANs) to high-speedstorage networks (SANs) aswell as backbones in largeenterprise networks and wide

area and metropolitan areanetworks.- Full Duplex and No Collisions10G Ethernet works only in full-duplex mode and does not

support CSMA/CD, the commonEthernet collision method usedto gain access to the physicalmedium. A "WAN interface



sublayer" (WIS) makes 10GEthernet compatible with the

SONET transport at 10 Gbps(OC-192).

Fiber or Copper

- The 10GBASE-LX4 version(see below) carries fourwavelengths of light on onepair of fibers. In 2004, 10GEthernet over copper wire wasintroduced. Using fourtwinaxial cables, the copper

version was designed for shortdistances between switchesand storage devices in thedatacenter.



- 10G ETHERNET OVER FIBER

(IEEE 802.3ae)- - Dark

- Fiber or Fiber Maximum

- Version SONET Type Distance

- - 10GBASE-SR Fiber MMF/850 nm 65 meters

- 10GBASE-LRM Fiber MMF/1310 nm 220 meters

- 10GBASE-LRM Fiber MMF/850 nm 260 meters

- 10GBASE-LX4 Fiber MMF/1310 nm 300 meters

- - 10GBASE-LR Fiber SMF/1310 nm 10 kilometers

- 10GBASE-ER Fiber SMF/1550 nm 40 kilometers

- 10GBASE-ZR** Fiber SMF/1550 nm 80 kilometers

- 10GBASE-LX4 Fiber SMF/1310 nm 10 kilometers

- - 10GBASE-SW SONET MMF/850 nm 65 meters

- - 10GBASE-LW SONET SMF/1310 nm 10 kilometers

- 10GBASE-EW SONET SMF/1550 nm 40 kilometers

- - MMF = multimode fiber

- SMF = singlemode fiber

- ** = non standard

- - - 10G ETHERNET OVER COPPER (IEEE 802.3ak)

- - Version Use Cable Max. Distance

- - 10GBASE-CX4 Datacenter Twinax 15 meters



- Shared or Switched - Ethernet is wired in a star

configuration with a hub orswitch in the middle. Hubs,which predated switches, areshared media devices. Allstations attached to the hub

share the total bandwidth.Switches provide each senderand receiver pair with the fullbandwidth and are significantlyfaster than hubs (see switched Ethernet). Like the clientmachines, Ethernet switchesand hubs also support 10/100and 10/100/1000 speeds.

http://computer.yourdictionary.com/switched-ethernet














- Most Ethernets Use TwistedPairs

Ethernet uses economicaltwisted pair cables andstandard RJ-45 connectorsSometimes, spare telephonewires in a building may beused, but often only at thelowest speed. To extenddistances, fiber-optic cable isalso used.

Ethernet Frames. - Ethernet transmits variablelength frames from 72 to 1518bytes in length, each containinga header with the addresses of the source and destination

stations and a trailer thatcontains error correction data.Higher-level protocols, such asIP and IPX, fragment long



messages into the frame sizerequired by the Ethernet

network being employed (seeMTU).

Collision Detection Ethernet uses the CSMA/CD

technology to broadcast eachframe onto the physicalmedium (wire, fiber, etc.). Allstations attached to theEthernet are "listening," andthe station with the matchingdestination address accepts theframe and checks for errors.Ethernet is a data link protocol(MAC layer protocol) andfunctions at layers 1 and 2 of

the OSI model.

http://computer.yourdictionary.com/mtu


















History - Invented by Robert Metcalfe

and David Boggs at Xerox PARCin 1973, Ethernet first ran at2.94 Mbps. Metcalfe later joined Digital where hefacilitated a joint venture

between Digital, Intel andXerox to collaborate further onEthernet. Version 1 wasfinalized in 1980, and productsshipped in the following year.In 1983, the IEEE approved theEthernet 802.3 standard.



Singlemode An optical fiber in which the

signal travels in one mode (path).It typically has an 8-10 Âµm corewithin a 125 Âµm cladding.



soliton - A laser pulse that retains its

shape in a fiber over longdistances. See soliton.

SONET (Synchronous

Optical Network) - A scale of standard data ratesfor fiber-optic systems used inNorth American systems. SeeSONET.

splice - A method for joining two opticalfiber ends. Fusion splicing andmechanical splicing are the two

types.

http://computer.yourdictionary.com/soliton






http://computer.yourdictionary.com/sonet













Splice Closure - A container used to hold and

protect splice trays.

Splice Tray - A container used to hold,organize and protect splicedfibers.

Split Sleeve - The part of a fiber-optic adapter

that aligns the ferrules of twoterminated connectors.

Splitter - A device that takes the light

from one fiber and injects it intothe cores of several other fibers.



Step-Index Fiber - A fiber in which the core and

cladding each have a uniform, butdifferent, refractive index. Seestep-index fiber.

Threshold Current - The mimimum current requiredto cause a diode laser to generatea beam of light.

Tight Buffer - A protective coating (typically900 Âµm) that is extruded directlyover the primary coating of fibers.Provides high tensile strength,

durability, ease of handling andtermination.

http://computer.yourdictionary.com/step-index-fiber















Transceiver - A transmitter and receiver

combined in one device.

Transmitter (TX) - An optoelectronic device thatconverts an electrical signal to anoptical signal. It is usually an LEDor laser diode.

Transparent Network

- A fiber-optic network that isentirely light based with opticalswitches and other optical-onlydevices.



Tunable Laser - A laser that can change its

frequency over a given range.

VCSEL (Vertical CavitySurface-Emitting

Laser) - Pronounced "vixel." Asemiconductor laser that emits abeam from its surface rather thanits edge. See VCSEL.

VOA (Variable OpticalAttenuator) - A device that can be adjusted to

block different fractions of lightpassing through it.

http://computer.yourdictionary.com/vcsel










Waveguide - A structure that guides

electromagnetic waves. An opticalfiber is an optical waveguide.

Waveguide Array - A device that separateswavelengths by passing themthrough an array of curvedwaveguides running between apair of mixing regions.

Wavelength - The length of a wave measuredfrom any point on one wave to thecorresponding point on the next.

The wavelengths of light used inoptical fibers are measured innanometers.



Common wavelengths are 850,1300 and 1350 nm.



WDM (Wavelength

Division Multiplexing) Transmitting several wavelengthsof light (colors) in one fiber. SeeWDM.

http://computer.yourdictionary.com/wdm

http://computer.yourdictionary.com/wdm

FIBER OPTICAL GLOSSARY

Documents

Transcript of FIBER OPTICAL GLOSSARY