Fiber Tutorial

Fiber Tutorial

R0902 network-electronics.com

Fiber_Tutorial_A5_R0902.indd 1 09.01.09 10:45:08

2 | network-electronics.com

Why fiber?

Optical fiber has gained incredible popularity as cabling medium within the broadcast business the last few years. Below are some of the reasons why more and more people are using optical to future proof their cabling infrastructure.

• Fiberhasnohighfrequencyroll-offs

• Fibersupportsbitratesof10Gbpsandbeyond

• Fiberattenuationisverylow

• Fibercoreismuchsmallerthancopper

• Fiberisextremelylightweight

• Fiberisnotsensitivetocross-talk

• Fiberisglass–i.e.itisadielectric,notaconductor

• Fiberhasatransmissioncapacityofupto100Tbps

Optical fiber deployment means future proofing

of the cabling infrastructure

By Ronny Sletteng, Product Manager, M.Sc.


network-electronics.com | 3

Cable Diameter Type Weight Capacity

Jacket/Sheath material

Belden1694A

Coaxialcable

7mm Single cable 6kg/100m 4xSDIwith

TDM

Poly-Vinyl

Chloride (PVC)

Belden7713A

Coaxialcable

35.2mm Multicable

(10off1694A)

115kg/100m 40xSDIwith

TDM

PVC

NexansG24-9UT

Fibercable

6.5mm 24fibers 4.5kg/100m 7680xSDI

withTDM

andDWDM

Low Smoke Zero

Halogen (LSZH)

Belden1694A NexansG24-9UT

Belden7713A

00 0 1000 1500 2000 2500 3000 3500 4000 4500

5

10

15

20

25

30

35

40

45

Att

enua

tio

n [

dB

/100

m]

Frequency [MHz]

Fiber

1694A


4| network-electronics.com

FiberTutorial

Thefigurebelowshowsatypicalcross section of an optical fiber.

Theactualsizeofthefiberisverysmall; the core-diameter of a single mode fiber is typically 9µm.

Thecoreofthefiber(drawnyellow to symbolise that light passes through) has a slightly higherrefractiveindexthanthecladding surrounding it.

Thisisnecessaryinorderforthelight to be guided within the core.

Outside of the cladding is often a protectivepolymercoatingofthefiber.

Therefractiveindexofthecoatingishigherthantheindexofthecladding,toensurethatcladdingmodes(lighttravellinginthecladding instead of the core) are guidedawayfromthecore,andnot reflected back towards the core causing signal disturbances.

A short, non-mathematical introduction to the interesting world of fiber optics.

Core

Cladding

Coating

CROSS SECTION OF OPTICAL FIbER



large angle

small angle

apparent position

real position

REFRACTION OF LIGHTThespeedoflightdependsonthemediumlighttravelsthrough.Invacuum(air) 300000km/sec.Inwater 225000km/sec.Inglass (opticalfiber) 200000km/sec.

Anopticalpropertyforagivenmedium,calledrefractiveindexorindexofrefractionisdefinedas the ratio of speed of light in vacuumtothespeedoflightinthe medium.

Wethenhavethefollowingindicesofrefraction(allvaluesareapproximatevalues):Air(vacuum): 1.0Water: 1.3Opticalfiber: 1.45–1.5

What does this mean?When light is incident on a boundary between two materials withdifferentindexofrefraction,thelightisrefracted.Anexampleis shown below.

Themanseesthefishatanapparentposition,differentfromthe real position. We note that the angleinwater,withthelargestindexofrefraction,issmallerthantheangleinair.Thisisaphysicallaw,andisalwaystrue.



MuLTI MODE (MM) AND SINGLE MODE (SM) FIbERTodayalltelecommunicationnetworksuseSMfiberforlongdistancetransmission (more than a few kilometers). Let’s compare some of the propertiesofSMandMMfibers:

ThedifferenceinpropertiesoccurmainlybecauseofthesmallercorediameterofSMfiber.

Property Multi mode Single mode

Corediameter(approx.) 50umgradedindexfiber 9umstepindexfiber

62.5umgradedindexfiber

Claddingdiameter 125umgradedindexfiber 125um

Modaldispersion Yes No

Modalnoise Yes No

Connectortermination Specialcrimptoolkitsavailable Requiresfusionsplicing

Thisopticalpropertyisusedtoguidelightingradedindexmultimodeopticalfibers:

cladding

cladding

50/62.5

125core



Multimodefiber Single mode fiber

Indexprofile

core

9µm

125µm

cladding

core

50µm

125µm

cladding

Acomparisonofthetwocrosssectionsisshownabove.

Theindexprofileshowninthebottom of the picture shows that therefractiveindexofthecoreishigherthantherefractiveindexofthe cladding.

Anotherdifferencebetweenthetwotypesoffiber,ishowtheyguide light.

MMfibersguideslightinsidethecore through multiple reflections from the core-cladding boundary.

SMfibershassosmallcore-diameter,thatlightenteringthecore at the appropriate angles will be confined in the core without any reflections.



0

600

1st

window2nd

window3rd

window

800 1000 1200 1400 1600 1800 2000

5

10Attenuation(db/km)

scatteringIR-absorption

OH-abs.H2

abs.

Wavelength (nm)

SMF

SMF–Singlemodefiber,ITU-TG.652AandBLWPF–Lowwaterpeaksinglemodefiber,ITU-TG.652CandD

LWPF

Theattenuationofsignalpowerinoptical fibers is highly dependent ofthetransmissionwavelength.

Inthefigureaboveweseeatypical sketch of attenuation inopticalsilica-fiberversuswavelength.

Inthefigureweseethethreetelecomwindows:Thefirstwindow(around850nm)wasusedinthebeginning,becauseofthelowcostGaAslaserdiodesavailablethenemittinglightatthesewavelengths.

Thiswavelengthwindowis only used for short-range datacommunications (Ethernet)today,andnotintelecommunications.

Thesecondwindow(around1300nm) is where the dispersion of silicafiberisclosetozero,withanattenuation of less than 0.5dB/km.

TheFlashlinkrangeofferstransmissioninthiswindow,as well as in the third telecom window(around1550nm),wherethelossindB/kmforsilicafiberhasitslowestvalue,lessthan0.3dB/km.Newfibercablesusefiberswith attenuation in the range of 0.4dB/kmat1310nmand0.25dB/kmat1550nm.

Thefigurealsoshowshowtheattenuation increases for short wavelengthsduetoscatteringofthe signal in the fiber (Rayleigh-scattering).

Forlongerwavelengths(>1700nm)theIR-absorptionincreasesrapidly.

At1250nmanabsorptionpeakiscaused by H2-molecules diffusing intothefiber.At1383+/-6nmwehaveapeakofabsorption,sometimes called the water peak limiting the number of long-haul CWDMchannelsonG.652AandB fibers.

ATTENuATION IN OPTICAL FIbERS



DFBlaserisanabbreviationforDistributedFeedbacklaser.F-PlaserisanabbreviationforFabry-Perotlaser.

Themaindifferencebetweenthetwotypesoflasers,isthewaytheyamplify the light signal.

AsemiconductorF-Plaserhasaconstantindexofrefraction.

Atoneendofthesemiconductormaterial,thelightispartiallyreflectedforamplification,andpartially coupled out.

AnF-Plaser,emitslightatdifferentwavelengths(modes)simultaneously.

ADFBlaserhasaperiodicallymodulatedindexofrefraction.

Thismodulationenableslaser operation at a “single” wavelength.

ThesketchtotheleftcomparestheoutputspectraofaDFBlaserandanF-Plaserat1300nm.

TheFullWidthofaDFBlaseratHalfMaximum(FWHM)bandwidth is about 0.2 nm comparedtotheF-PlaserwhichhasanFWHMofapproximately 4nm.

TheFWHMnumbersaremeantto illustrate the difference in bandwidth between the two types oflasers,andmustnotbetakenasspecifications of the lasers in the Flashlinkrange.

ThefabricationofaDFBlaserismore difficult than the fabrication ofanF-Plaser,resultinginahigherpricefortheDFBlaser.

UsedinsystemsemployingCWDMorDWDM,theF-Plaserisno choice at all.

ThelargebandwidthofF-Plasersmakes crosstalk a serious problem if the lasers are spaced too closely.

DFBlaserswiththeirbetterperformancearepreferredtoF-Plasers.

FWHM=0.2nm

1298 1299 1300 1301 1302

DFb 1300nm laser

Wavelength (nm)

FWHM=4nm

1292 1296 1300 1304 1308

F-P 1300nm laser

Wavelength (nm)

COMPARISON OF DFb AND F-P LASERS



TDM

Mux

DEMux

Ch.1

Ch. 2

Ch. 3

Ch.4

Ch.1

Ch. 2

Ch. 3

Ch.4

1 2 3 4 1 2 3 4

4ch.perwavelength

Single mode fiber

Fromthefigureweseethatthesystemisa4-channelTDMsystem.Eachchannelhasitsowntransmittersendingatagivenbit-rate.Bysending4channelssimultaneouslywithasmalltimedelaybetweenthechannels,weincreasethesystemcapacity.

Theprocessofsendingseveralchannelsatthesametimeiscalledmultiplexing.Thetimeisdividedamongtheotherchannels,thereforethenametimedivisionmultiplexing.

Asweseeinthefigure,thismultiplexingfromfourparallelsignalstreamintoaserialsignalbitstreamgivesinthiscaseatransmissionbit-rateoffourtimestheoriginalbit-rate.Atthereceiverendisademultiplexer,separating the different channels again.

TDM (TIME DIvISION MuLTIPLExING)Withtoday’sincreasingdemandsoftransmissioncapacity(bandwidth),severaltechniqueshavebeendevelopedtoutilizeavailablebandwidth.OneoftheseisTDM–TimeDivisionMultiplexingintheelectricaldomain.

Toexplaintheprincipleweuseafigure:



When it comes to the format of theTDMsignal,therearedifferentapproaches.Mostvendorsuseaproprietaryformat,whichisusefulfor point to point connections. ThedownsidebyusingaproprietaryTDMsignalformatisthattheTDMsignalmustbedecoded back to baseband at the entrance point to the facility for inter-facilitydistribution,meaningextracablingcost.

WhentheTDMsignalisnonproprietary like the widespread HD-SDIor3G-SDIvideoformatsthis is useful for point to point connections,butitalsoenablesyou as the user to take your valuedsignalformatsdeepwithina broadcast centre through for instance a Network Electronics /VPGroutingsystemtodelivertheTDMsignaltothelocationyou actually need the signal. No additionalcablingneeded,theexistingbroadcastinfrastructureisused to transport multiple signals.

SMPTE346M:2000hasstandardizedTDMoffour270MbpsSDI,SDTIorDVB-ASI

signalsintoa1.485GbpsHD-SDItransportstream.ThisisimplementedinFlashlink,and allows for straight forward transportofthemultiplexedstreamthroughstandardHD-SDIinfrastructure.

SMPTE424MandSMPTE425Mdescribesthe3G-SDIsignalformat.UsingthissignalastheTDMsignalformat,asdoneintheFlashlinkmoduleSDI-TD-3GMX-5allows for transport of multiple asynchronous signal streams up to • 8xSD-SDI,SDTIorDVB-ASIor• 2xHD-SDIor• 1xHD-SDIand4xSD-SDI,SDTIorDVB-ASIor

• 1x3G-SDI.

AsweseeTDMisatechnologythatenablesseveralsignalstobe transported as a single signal atahigherbitrate,usingastandardizedTDMsignalformatgivesmoreflexibilityinnetworkdesigns,asthedecodingtobaseband a the entrance point of the facility is not needed.



WDMisamethodtosendmultiplesignalsonthesamefiberinsteadofusingmultiplefibers.WDMtechnologyiseasiertounderstandifwethinkoftheschoolexperimentwithwhitelightbeingsplitintothedifferent colors by a prism.

Eachtransmitterishavingauniquewavelength(color),andthe filtering needs to match the channel scheme.

Asimple2-channelWDMsystemsendsonechannelat1310nm,andonechannelat1550nm.

Thistechniqueisbothbitrateandsignalindependent,meaningthatthe signals running at the different channels can be different without extrasignalprocessing.

Theincreasingdemandsofbandwidth,introduceddenseWDM(DWDM)systemsbackin1996.

Thesesystemsusethewidelowattenuationbandfrom1525–1575

nm to transmit at different wavelengthsinthisrange.

Incontrastto2-channel1310/1550nmWDMsystems,DWDMsystemsrequiremoreelectronics and sharper optical filters due to the need for temperaturestabilizationofthelasers.

Thestabilityofthelaserisacriticalissue.Atthereceiverendthe filtering of the channels is a separate task.

TheFlashlinkDWDMsystemwasintroducedin2000andhavebeendeployed world-wide since then.

TheITUT-G.694.1hasspecifiedachannel-spacingof100GHz

WDM (WAvELENGTH DIvISION MuLTIPLExING)



E/O

E/O

E/O

E/O

Digita

lSigna

lIn

Digita

lSigna

lOut40independent

channels

optical fiber

E/O

E/O

E/O

E/O

Ch.1Ch.2Ch.3Ch.4

Ch.5Ch.6Ch.7Ch.8

Ch.9Ch.10Ch.11Ch.12

Ch.13Ch.14Ch.15Ch.16





Ch.1Ch.2Ch.3Ch.4

Ch.5Ch.6Ch.7Ch.8

Ch.9Ch.10Ch.11Ch.12






E/O


E/O


O/E

O/E

O/E

O/E

O/E

O/E

O/E

O/E


O/E


O/E

FlashlinkDWDM40 ch.DMuxframe

FlashlinkDWDM40 ch.Muxframe

(approximately0.8nminthe1550nmrange).

Each channel has its own transmitter sending at its own bit rateandwavelength.

Bysending40channelssimultaneously,eachataseparatewavelength,weenhancethefiber capacity by using the same fiber40timesinsteadofusing40separatefibers.TheFlashlinkrangeofferscurrentlya40-channelDWDMsystem,withbitratesintherangefrom143Mbpsto3Gbps.

CoarseWDM(CWDM)systemshavegainedhighpopularityforchannelcountsupto16andformediumdistances.ThewavelengthsarestandardizedinITU-TG.694.2,withchannelspacingof20nm.TheFlashlinkrangeuses8wavelengthsinthebluerangefrom1270nmupto1410nmand8wavelengthsintheredrangefrom1470nmupto1610nm.ThefollowingtableshowsacomparisonofDWDMandCWDMtechnologyataglance.



COMPARISON OF WDM TECHNOLOGIES

Flashlink DWDM/CWDM DWDM (100GHz) CWDM

Standard ITU-TG.694.1 ITU-T G.694.2

PowerconsumptionperSDI-Tx 3Wtypically 1.6W

Laserwavelengthvariation(0-40°C) ±0.16nm ±6.5nm

Channelspacing 0.8nm(100GHz) 20nm

Maxnumberofchannelstoday 40 16

Channelsperframe 8+1upgradeport 8or16

Opticalamplificationwellproven forlonghaulapplications Yes,EDFA No

Fibertype 9/125um 9/125um single mode single mode or 50/125um multi mode

Wavelength(nm)

Fibe

rAtten

uatio

n

1250 1300 1350 1400 1450 1500 1550 1600 1650

1310 1550

O-band E-band S-band C-band L-band U-band

2 chWDM

16chCWDM

C-band

1530 1565

40chDWDM

14701270 1550 1610

SMF

SMF–Singlemodefiber,ITU-TG.652AandBLWPF–Lowwaterpeaksinglemodefiber,ITU-TG.652CandD

LWPF



LONG HAuL OPTICAL TRANSPORT SOLuTIONSEventhoughtheattenuationin optical cables is insignificant comparedtocoaxialcables,thereare still some limiting factors in the optical domain. Without going intodetails,thefollowinglistgivesanoverview:

Linear effects• Signalattenuation•Dispersion –Modaldispersioninmulti

mode fibres – ChromaticDispersion(CD) – PolarisationModeDispersion

(PMD)

Non-linear effects• Four-WaveMixinginDWDMsystems(FWM)

• SelfandCrossPhaseModulation(SPM/XPM)

• StimulatedRamanandBrillouinScattering(SRS/SBS)

When it comes to long distance networks,planningisimportant.Wehavethefollowinggeneralguidelines:

• Longerfibredistancesmeansmorecost,eachdBofopticalbudget has a price

• Ifpossible,workwithreal,measured fibre attenuation values

• Addtothisnumberthefibremargin(ideally>3dB)

• Letthemanufactureroritslocalrepresentativesproposethesystem based on the optical budget needed

•Note:XdBcancostY$,(X+1)dB can sometimes double the price,orinworstcasenotbepossibletoachieve

SIGNAL REGENERATIONIncaseofalongdistancetherearebasically two ways to regenerate the signals.• 3Rregeneration – Theoriginalwayofdoing

long-haul• All-opticalamplification – Replacing3Rinmany

circumstances

Intheterm3Rregeneration,eachRhasameaning,3RstandsforRe-amplification, Re-shaping and Re-clocking.

Thisisnormallydonewithanoptical to electrical and electrical toopticalconversionprocess,sometimes also called OEO (Optical-Electrical-Optical).

Thismustbedoneonasignalbysignallevel,oneprocesspersignal.

ThepositiveaspectisthatthiscaneasilybedeployedforCWDMandDWDM.



All-opticalamplificationcanbedone e.g. by deploying a so-called Erbium-DopedFiberAmplifier(EDFA).

AnEDFAcanbeusedtoamplifyDWDMsignalsintherangefrom1528to1565nm.

TheDWDMsignalswillpassthrough a section of erbium doped fiber where the amplification will take place.

AnEDFAisauni-directionaldevicepassinglightonlyinonedirection,so in cases where a bi-directional signalistransportedoveralongdistance,onefiberandoneEDFAis needed per direction.

Incontrastto3Rregeneration,anEDFAwillnotdore-clockingorre-shaping,butonlyre-amplification,ontheotherhand,theEDFAisbitrate and protocol transparent and canamplifyupto40wavelengthsat the same time.

What is important when purchasinganEDFAisthatall40DWDMwavelengthsareamplifiedequallymuch,thisisdonebyusingagain-flatteningfilter,andthe parameter is called gain-flatness.

Afull-bandEDFAwillhavethisparameterspecified,whereasanarrowbandEDFAwillnotspecifythis.

EDFA EDFA

Ch.1

Ch.2

Ch.3

Ch.4DWDMDMux

Ch.1

Ch.2

Ch.3

Ch.4DWDMMux

3R

3R

3R

3R

Ch.4 Ch.43R

Ch.4 Ch.43R

Ch.4 Ch.43R

Ch.4 Ch.43R

Typical EDFA setup



TransmissionBudget

TRANSMITTER OuTPuT POWERTheoutputpowerofthelaser.

RECEIvER SENSITIvITyThesensitivityofthereceiveristhesmallest amount of input optical power,whichthereceiver(OE-unit) needs to detect the incomingsignal properly.

WDM ~ WAvELENGTH DIvISION MuLTIPLExERAWDMsendsdifferentwavelengthsintodifferentfibers,orcombinesdifferentwavelengthsontothesamefiber.Differentversionslike1310/1550nmWDM,CWDMorDWDMexist.TheFlashlinkproductshaveinsertionlossstatedincluding connectors.

TRANSMISSION WAvELENGTHTheattenuationinopticalfiberdepends on the transmission wavelength.At1310nmweestimate0.4dB/kmoffiber,at1550nmweuse0.25dB/kmoffiber.

ATTENuATION PER FIbER LENGTHAsthesignalpropagatesthroughopticalfiber,thepowerofthesignalisattenuated.Theattenuation is proportional to fiber length.

FIbER LENGTHThedistancebetweenthetransmitterandthereceiverinkm.Differentversionslike1310/1550nmWDM,CWDMorDWDMexist.TheFlashlinkproductshaveinsertionlossstatedincluding connectors.

FIbER ATTENuATIONFiberattenuationistheproductofattenuation per length and length of fiber.

# CONNECTORSEach connector pair contributes to the attenuation with ca. 0.5dB.TheattenuationinthecouplersandtheWDMsincludesattenuation in the connectors.

COuPLERSTheFlashlinkproductrange,includes couplers where you can drop a signal or split the signal. Thisprocesscontributestolossin

Description of parameters in transmission budget



theopticallink.AllthedifferentFlashlinkcouplersareavailableinthe drop-down menu.Thecouplingratioisgivenasx:100-xin%.E.g.90:10meansthat10%ofthesignalpoweristapped (coupled) from the main signaland90%travelstowardsthereceiver.TheattenuationindB,includestheattenuationinthe connectors connected to the couplers.

ATTENuATION MARGINAsafetymargin,incasetheattenuationexceedstheestimates.Thismarginallowsforrepair,splicesetc.Amarginofmorethan3 dB is preferred.

TOTAL LINk ATTENuATIONThetotallinkattenuationisthesum of all the attenuations in signal between the transmitter(EO-unit)andthereceiver(OE-unit). We denote the components between the two units an optical link.

ExAMPLE OF CALCuLATIONThefiguretotherightisasketch of an optical link. We will show you how to calculate the transmission budget for this example.

WehavestudiosAandC,located24kmapart.InadditionapostproductionhouseBshallhaveaccess to the content transported on the optical fiber. We calculate budgets for

SDI-OE-L

20km4km

90%

10%

C

SDi-EO-13T,–7.5dBm

A

SDI-OE-L

b



Linkname:A to C

Fibertype:Corning SMF-28

Transmissionwavelength(λ): 1310 nm

Attenuationperfiberlengthatλ: 0.4dB/km

Fiberlinklength: 24 km Fiberattenuation: ≈9.6 dB

Numberofconnectors: 2x0.5 Connectoratt.: 1 dB

Coupler#1attenuation(90-10,90%port): 1.4 dB

Attenuationmargin: 3 dB

+Excessattenuation: 2 dB

OpticaltransmissionbudgetneededfromAtoC: 17 dB

Linkname:A to B

Fibertype:Corning SMF-28

Transmissionwavelength(λ): 1310 nm

Attenuationperfiberlengthatλ: 0.4dB/km

Fiberlinklength: 4.2 km Fiberattenuation: ≈1.7 dB

Numberofconnectors: 2x0.5 Connectoratt.: 1 dB

Coupler#1attenuation(90-10,90%port): 11.7 dB

Attenuationmargin: 3 dB

OpticaltransmissionbudgetneededfromAtoB: 17.4 dB

ConfigurationI:Transmitter: SDI-EO-13T,-7.5dBm

Receiver: SDI-OE-L,sensitivity-30dBm

Opticalbudget: 22.5dB

ConfigurationII:Transmitter: SDI-EO-13T,0dBm

Receiver: SDI-OE-S,sensitivity-20dBm

Opticalbudget: 20dB

Aswesee,bothlinksshouldworkwell with either of the twosuggestedconfigurations.TheoverallcostofconfigurationBislessthanconfigurationA.

Tohelpyoucalculateyourowntransmissionbudgetsweprovideablankformonthenextpage.



CALCuLATE yOuR OWN TRANSMISSION buDGET

Linkname:

Fibertype:

Transmissionwavelength(λ): nm

Attenuationperfiberlengthatλ: dB/km

Fiberlinklength: Fiberattenuation: dB

Numberofconnectors: Connectoratt.: dB

Coupler#1attenuation: dB




Opticalfilter#1attenuation: dB




Opticalswitch#1attenuation: dB

Opticalswitch#2attenuation: dB

Excessattenuation: dB

+Attenuationmargin: 3 dB

=Opticaltransmissionbudgetneeded dB

Transmitteroutputpower(laser): dBm

–Opticaltransmissionbudgetneeded dB

=Estimatedinputpoweronreceiverincl.margin= dBm

Remarks:Attenuation(insertionloss),transmitteroutputpowerandreceiversensitivityforthedifferentdevicescanbefoundintechnicaldatasheets.Thiscalculationsheetmayincludedevicesnotfoundintheactualopticallink.Theselinescanbeomittedinthecalculation.Devicesnotspecifiedherecanbeincludedin“Excessattenuation”.



Guidelinestolimithazardsfromlaserexposure.

AlltheavailableEOunitsintheFlashlinkrangeincludealaser.

Thelasersemitlightintherangefrom1270upto1610nm.

Thismeansthatthehumaneyecannot see the radiation and the blinkreflexwillnotbeactivated.

Thehumaneyecanseeradiationfrom400nmto700nm,thuscalledvisiblelight.

6004002000

1st

window

visiblelight

2nd

window3rd

window

800 1000 1200 1400 1600

IRuv

Wavelength (nm)

Laser Safety Precautions

AlwaysreadthedatasheetoftheFlashlinkproduct,aswellasthelasersafetylabelbeforethe laser power is switched on.

Alwaysswitchoffthelaserpowerbeforeconnecting/disconnectingfiberpatchcords.

Laserradiationcanbeharmfultothehumaneye(dependingonlaserpowerandexposuretime).Therefore…

•Neverlookdirectlyintoafiberpigtail.

•Neverusemicroscopes,magnifyingglassesoreyeloupes to look into a fiber end.



FiberHandling

Eventhoughafiberopticalcablecan look almost the same as an electricalwire,specialcaremustbe taken.

Insidethecableisafibermadeofglass.

Glasshasverydifferentphysicalproperties than copper used in electrical wires.

Inpracticaltermsthismeansthatthe following precautions must be taken:

• Do not bend the fiber too much• Do not put heavy or sharp items

on top of the optical fiber• Keep the connectors clean from

dust

Ifafiberisbenttomuch,partsofthe transmitted light is lost.

Alldatasheetsofopticalfibershaveapointcalled“minimumbend radius”.

Thismeansthatanybendingofthe fiber corresponding to a bend radiuslessthanthegivenvalue,will make the light leak out of the fiber.

Atypicalvalueis20mmto40mm(Bellcore/Telcordiastandard)for single mode fibers.

Youshouldalsoavoidputtinganyheavyitemsontopoftheopticalfibers,becausethiswillchangetheopticalpropertiesofthefiber,and contribute to errors in the transmitted signal.

Unlessthefiberisdamaged,itwillregain its optical properties after a bend is straightened out or the itemsareremovedorthesqueezeis released.

protectivecap ferrule

SC/PC connector

plastic housing(blue)

optical fiber plastic coating

Good connection

bad connection

dust



TheFlashlinkproductrangeutilisesultrapolishedSC/PCconnectors(SC/UPC).

Theseconnectorshaveareturnlossofbetterthan40dBtypicallywith single mode fiber.

Ascomparedtoanelectricalconnectionbetweentwopoints,an optical connection is much more dependent on clean connectors.

Adirtyconnectorcanaddupto10dBofattenuationtoyourlink.

Ifthereisnolightatthereceiver,then no signal will be detected.

So the difference between an errorlessconnectionoverfiber,and no connection at all can be a dirty connector.

Therefore:Clean connectors are of crucial importance.

Thisalsoimpliesthatpeopleworking with patching of fiber connectors must be aware of this.

Anopticalfiberismadeofglassandmustbetreatedassuch,notas an electrical wire.

Compare it to the lens of camera. Youdon’twantfingerprintsonthelens,butsincethelensarea

is large compared to the cross-sectional area of a single mode fiber some light will pass the lens.

Toprotecttheconnectorsfromdust,oneshallalwaysputontheprotectivedustcapwhichis on the connector end at delivery(orenclosedinaplasticbag)wheneverafiberendisdisconnected.

Ifthereisachancethatafiberconnectorisdirty,oneshouldclean the connector before connecting it to a clean fiber ferrule.

Ifacleanconnectorispressedagainstadirtyconnector,bothconnectors will become dirty resulting in degradation of signal quality.Orevenworse,youmay damage the surface of the connector(s).

Usingaspecialcleaning-tape(calledCleTop)suitableforthispurpose does cleaning of the connectors.

Thisisdescribedinfoureasysteps–seenextspread.

FIbER OPTICAL CONNECTORS


Step 1:HoldtheCleTopinyour hand with the metal shield upwards.

Step 2: Press the metal handle on thesideoftheboxtorevealthecleaningtapebyremovingthemetal shield.

Step 3: Place the connector ferrule in one of the two tracks and make acircularmovementwiththeferrule pressed against the tape.

Step 4: Pull the ferrule on the cleaning tape to the other end of theguidingtrack.Theconnectorshould now be clean.

Note: For economical reasons we recommend that both tracks of the tape is used whenever practical possible.

4easystepscleaning of the connectors

24|network-electronics.com


ITU-TG.650 Definitionandtestmethodsfortherelevantparametersofsingle-mode fibres

ITU-TG.651 Characteristicsofa50/125ummulti mode gradedindexopticalfibrecable

ITU-TG.652-2003 Characteristics of a single-mode optical fibre and cable

ITU-TG.653 Characteristics of a dispersion-shifted single-mode optical fibre cable

ITU-TG.654 Characteristics of a cut-off shifted single-mode optical fibre and cable

ITU-TG.655 Characteristicsofanon-zerodispersion-shifted single-mode optical fibre cable

ITU-TG.656 Characteristics of a fibre and cablewithnon-zerodispersionforwideband optical transport

ITU-TG.694.1 DWDMfrequencygrid

ITU-TG.694.2 CWDMwavelengthgrid

cleaning of the connectors


SOME FIbER STANDARDS

Source: International Telecommunication Union, www.itu.int



ADM – ADD DROP MuLTIPLExAnADM-nodeisaplacewherechannelscanbeextractedfromthemainstream(dropped)andnewchannelscanbemultiplexed(added)intothestream.Invideonetworking,itismostcost-efficienttodothisbyputtingadigitalvideorouteratthenode.

APC – ANGLE POLISHED CONNECTORThetipoftheconnectorferruleispolishedatanangleofnormally8°inordertominimizeback-reflectionoftheincomingsignal.Typicallybackreflection(returnloss)ofasinglemodeAPCconnectorisbetterthan–60dB.

APS – AuTOMATIC PROTECTION SWITCHINGAtermoriginatedfromSDHnetworks.Ifasignalpath is broken due to e.g. destruction of a fiber the optical signal is automatically re-routed to a redundant fiberpath,thusminimizingdowntimeofthefiberlink.IntheFlashlinkrange,theAPSfunctionalityisincorporated in the Wideband Optical Switches when usedtogetherwiththeGYDAsystemcontroller.Seealso WOS.

C-bAND – CONvENTIONAL bANDThespectralbandfrom1530-1565nmasproposedbytheInternationalTelecommunicationUnion.

CWDM – COARSE WAvELENGTH DIvISION MuLTIPLExINGAstandardizedmultiplexingmethodusingunstabilisedlasersandbroadbandfiltersasspecifiedinITU-TrecommendationG.694.2.SeealsoDWDM.

dbmOpticalpowerisexpressedindBm.Thisisanabsolutemeasureofsignalstrengthrelatedto1mW(thisis where the m comes in). 0dBm corresponds to 1mW,-3dBmcorrespondsto0.5mW,and+3dBmcorresponds to 2mW.

DFb – DISTRIbuTED FEEDbACkAdistributedfeedbacklaserisadevicewithaperiodicvariationoftherefractiveindexintheamplifyingregion.Thisensuresanarrowbandwidthofthelaserlight and is the preferred choice of laser type for dense wavelengthdivisionmultiplexingapplications.SeealsoF-P.

DWDM – DENSE WAvELENGTH DIvISION MuLTIPLExINGAstandardizedmultiplexingtechnique(ITU-TrecommendationG.694.1)forsimultaneoustransportofmultiplesignalsatdifferentwavelengthsinasinglemodeopticalfiber.Temperaturestabilisedlasersandverynarrowbandopticalfiltersensureerrorlesstransmission.SeealsoCWDM.

DMux/DEMux – DEMuLTIPLExERUsedforextractingthedifferentchannelsinamultiplexedstreamintosinglechannelstreams.UsedatthereceiverendorinanADM-node.SeealsoMUX.

EDFA – ERbIuM DOPED FIbER AMPLIFIERAnall-opticalamplifieroperatinginthe1550nmrange,widespread in long-haul optical networks. Enables in-line signal amplification without time- and power-consumingoptical-to-electrical-to-opticalconversion.Amplifiestheincomingsignal(includingnoise).SomeEDFAshaveproblemshandlingtheSDI-pathologicalsignal. Versions operating in the C-band as well as in theL-bandareavailable.

F-P – FAbRy-PEROTAFabry-Perotlaserconsistsofasemiconductormaterialwiththesamerefractiveindexintheamplifyingregion.Thismakesastandingwavepatternandlasingoccursatseveralequidistantwavelengthssimultaneously,makingthelaserunattractivefordensechannelspacingbutaverycost-effectivelaserfor1310nm.SeealsoDFB.

L-bAND – LONG WAvELENGTH bANDThespectralbandfrom1565-1625nmasproposedbytheInternationalTelecommunicationUnion. LASER – LIGHT AMPLIFICATION by STIMuLATED EMISSION OF RADIATION Stimulatedemissionisanatomicprocessgivinglaserlightitsspecialpropertieslikecoherence,directivityand spectral purity.

MM – MuLTI MODEInamultimodefiberasignalcanpropagatethroughthefiberindifferentpaths(modes).Thismeansthatabittravellingalongashorterpaththantheprecedingbitmayarriveearlieratthereceiver,thusgeneratingerrorsinthesignal.Thiseffectiscalledmodaldispersionandlimitsthemaximumlengthasignalcantravelatagivenbitrate.Higherbitratemeansshortermaximumlengthbetweentransmitterandreceiver.AnMMfibercomesindifferentversionsdependentonthediameterofthecoreandthecladding.DifferenttypesarecalledOM1,OM2andOM3.

Mux – MuLTIPLExERUsedforaddingseveralsignalstogetherintoasinglesignalstream.Bothelectricalandopticalmultiplexersexist.Electricalmultiplexersmusthavethesameinputsignalformatandbitrates,whereasopticalmultiplexerscanhavedifferentsignalformatsandbitrates.

GLOSSARy



NMS – NETWORk MANAGEMENT SySTEMNetworkManagementSystemsareusedtomanagetheincreasinglycomplexandheterogeneouscomputerand telecommunication networks.

PC – POLISHED CONNECTOR (OR PHySICAL CONTACT)APC-polishedconnectorhasastraightferruletip.Typicallybackreflection(returnloss)ofasinglemodePCconnectorisbetterthan–40dB.Seealso:APC,SPC,UPC.

RI – REFRACTIvE INDExAllopticallytransparentmaterialshavearefractiveindex,whichistheratioofspeedoflightinvacuumtothespeedoflightinthemedium.TheRIofanopticalfiberisca.1.45-1.50,givingalight(signal)speedinoptical fibers of circa 200 000 km per second.

S-bAND – SHORT WAvELENGTH bANDThespectralbandfrom1460-1530nmasproposedbytheInternationalTelecommunicationUnion.

SDH – SyNCHRONOuS DIGITAL HIERACHySynchronousDigitalHierarchyisaninternationalstandardforsynchronousdatatransmissionoverfiberopticcables.SDHdefinesastandardrateoftransmissionat155.52Mbps,whichisreferredtoasSTS-3(SynchronousTransportSignal)attheelectricallevelandSTM-1(SynchronousTransportModule)forSDH.STM-1isequivalenttotheNorthAmericanSONET’sOC–3.STM-4isthedesignationfor622.08Mbps,STM-16isfor2488.32MbpsandSTM-64isfor9953.28Mbps.SeealsoSONET.

SM – SINGLE MODEInasinglemodefiber,thesignalcanonlypropagatethroughthefiberalongonepathatagivenwavelength.Thetransmissioncapacityofasinglemodefiberisextremelylarge(50-100Tbps),andattenuationofdownto0.2dB/km.StandardizedinITU-T.G.652.

SNMP – SIMPLE NETWORk MANAGEMENT PROTOCOLSNMPdefineshowmanagementinformationisexchangedbetweennetworkmanagementapplicationsandmanagementagents.SNMPisagenericprotocolused to monitor and configure network hardware and softwarebasedonTCP/IP.

SONET – SyNCHRONOuS OPTICAL NETWORkSONETisastandardforconnectingfiber-optictransmissionsystemsfoundintheUSA.SONETisstandardisedbytheAmericanNationalStandardsInstitute(ANSI).SONETdefinesinterfacestandardsatthephysicallayeroftheOSIseven-layermodel.Thestandard defines a hierarchy of interface rates that

allowdatastreamsatdifferentratestobemultiplexed.Thebit-ratesareexactlythesameasusedintheinternationalequivalentSDH,butthedesignationsaredifferent. OC-3 (Optical Carrier 3) is the designation of 155.52Mbps,OC-12isfor622.08Mbps,OC-48isfor2488.32MbpsandOC-192isfor9953.28Mbps.SeealsoSDH.

SPC – SuPER POLISHED CONNECTORAnSPC-polishedfiberconnectorhasthesamephysicalshapeasaPCpolishedconnector.Thedifferenceliesinthatthepolishingoftheferrulesurface.Typicallybackreflection (return loss) of a single mode SPC connector isbetterthan–45dB.SeealsoAPC,PCandUPC.

TDM – TIME DIvISION MuLTIPLExINGAddingseveralslowersignalswiththesamebitrateintoasignalstreamofahigherbitrate.Increasingthebandwidthperwavelength.

uPC – uLTRA POLISHED CONNECTORAnUPC-polishedfiberconnectorhasthesamephysicalshapeasaPCpolishedconnector.Thedifferenceliesinthatthepolishingoftheferrulesurface.Typicallybackreflection(returnloss)ofasinglemodeUPCconnectorisbetterthan–50dB.SeealsoAPC,PCandSPC.

WDM – WAvELENGTH DIvISION MuLTIPLxINGSendingsignalsatdifferentwavelengthsthroughthesameopticalfiber,meansthatasinglefibercanreplaceseveralfibers.Opticalfilteringisneededateachendof the link.

WOC – WIDEbAND OPTICAL COuPLERAnopticaldevicethatsplittheopticalsignalfromonefiberontotwoormoreopticalfibers.Thesplitratioofthedevicedecideshowmuchpowershallbetransferredtothedifferentfibers.Forinstanceacouplerwith one input port and two output ports and a split ratioof50%-50%(oftencalleda3dBcoupler)willsplittheincomingsignalsintotwoequalpartsgoingtotwodifferentreceivers.TheWOCisusedtodistributethesamesignaltoseveralendusersorinredundancyapplications.

WOS – WIDEbAND OPTICAL SWITCHBroadbanddevice,usedforautomaticprotectionswitchingsystems.A2x1switchcanbeconnectedto one input fiber or the other. Controlled through theGYDAsystemcontrollerorviatheGPIinterfaceataccessedthroughtheconnectormodule.Availableinboth2x1(canalsobeusedas1x2)and2x2configurations.SeealsoAPS.


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VenturaSERVICEPROVIDERSOLUTIONS

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adaptersFibertransport/WDM

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