fiber tutorial
DESCRIPTION
A short, non-mathematical introduction to the interesting world of fiber optics. Outside of the cladding is often a protective polymer coating of the fiber. We then have the following indices of refraction (all values are approximate values): Air (vacuum): 1.0 Water: 1.3 Optical fiber: 1.45–1.5 This optical property is used to guide light in graded index multi mode optical fibers: Another difference between the two types of fiber, is how they guide light.TRANSCRIPT
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.
Fiber_Tutorial_A5_R0902.indd 2 09.01.09 10:45:09
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
Fiber_Tutorial_A5_R0902.indd 3 09.01.09 10:45:10
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
Fiber_Tutorial_A5_R0902.indd 4 09.01.09 10:45:10
network-electronics.com | 5
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.
Fiber_Tutorial_A5_R0902.indd 5 09.01.09 10:45:11
6| network-electronics.com
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
Fiber_Tutorial_A5_R0902.indd 6 09.01.09 10:45:11
network-electronics.com | 7
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.
Fiber_Tutorial_A5_R0902.indd 7 09.01.09 10:45:11
8| network-electronics.com
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
Fiber_Tutorial_A5_R0902.indd 8 09.01.09 10:45:12
network-electronics.com | 9
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
Fiber_Tutorial_A5_R0902.indd 9 09.01.09 10:45:12
10| network-electronics.com
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:
Fiber_Tutorial_A5_R0902.indd 10 09.01.09 10:45:12
network-electronics.com | 11
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.
Fiber_Tutorial_A5_R0902.indd 11 09.01.09 10:45:13
12| network-electronics.com
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)
Fiber_Tutorial_A5_R0902.indd 12 09.01.09 10:45:13
network-electronics.com | 13
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.17Ch.18Ch.19Ch.20
Ch.21Ch.22Ch.23Ch.24
Ch.25Ch.26Ch.27Ch.28
Ch.29Ch.30Ch.31Ch.32
Ch.1Ch.2Ch.3Ch.4
Ch.5Ch.6Ch.7Ch.8
Ch.9Ch.10Ch.11Ch.12
Ch.13Ch.14Ch.15Ch.16
Ch.17Ch.18Ch.19Ch.20
Ch.21Ch.22Ch.23Ch.24
Ch.25Ch.26Ch.27Ch.28
Ch.29Ch.30Ch.31Ch.32
E/O
Ch.33Ch.34Ch.35Ch.36
E/O
Ch.37Ch.38Ch.39Ch.40
O/E
O/E
O/E
O/E
O/E
O/E
O/E
O/E
Ch.33Ch.34Ch.35Ch.36
O/E
Ch.37Ch.38Ch.39Ch.40
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.
Fiber_Tutorial_A5_R0902.indd 13 09.01.09 10:45:13
14| network-electronics.com
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
Fiber_Tutorial_A5_R0902.indd 14 09.01.09 10:45:14
network-electronics.com | 15
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.
Fiber_Tutorial_A5_R0902.indd 15 09.01.09 10:45:14
16| network-electronics.com
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
Fiber_Tutorial_A5_R0902.indd 16 09.01.09 10:45:15
network-electronics.com | 17
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
Fiber_Tutorial_A5_R0902.indd 17 09.01.09 10:45:15
18| network-electronics.com
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
Fiber_Tutorial_A5_R0902.indd 18 09.01.09 10:45:15
network-electronics.com | 19
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.
Fiber_Tutorial_A5_R0902.indd 19 09.01.09 10:45:16
20 | network-electronics.com
CALCuLATE yOuR OWN TRANSMISSION buDGET
Linkname:
Fibertype:
Transmissionwavelength(λ): nm
Attenuationperfiberlengthatλ: dB/km
Fiberlinklength: Fiberattenuation: dB
Numberofconnectors: Connectoratt.: dB
Coupler#1attenuation: dB
Coupler#2attenuation: dB
Coupler#3attenuation: dB
Coupler#4attenuation: dB
Opticalfilter#1attenuation: dB
Opticalfilter#2attenuation: dB
Opticalfilter#3attenuation: dB
Opticalfilter#4attenuation: 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”.
Fiber_Tutorial_A5_R0902.indd 20 09.01.09 10:45:18
network-electronics.com | 21
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.
Fiber_Tutorial_A5_R0902.indd 21 09.01.09 10:45:18
22 | network-electronics.com
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
Fiber_Tutorial_A5_R0902.indd 22 09.01.09 10:45:19
network-electronics.com | 23
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
Fiber_Tutorial_A5_R0902.indd 23 09.01.09 10:45:20
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
Fiber_Tutorial_A5_R0902.indd 24 09.01.09 10:45:22
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
network-electronics.com | 25
SOME FIbER STANDARDS
Source: International Telecommunication Union, www.itu.int
Fiber_Tutorial_A5_R0902.indd 25 09.01.09 10:45:22
26| network-electronics.com
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
Fiber_Tutorial_A5_R0902.indd 26 09.01.09 10:45:22
network-electronics.com | 27
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.
Fiber_Tutorial_A5_R0902.indd 27 09.01.09 10:45:22
Contact info:TheAmericas: [email protected] +1(805)247-8560
AsiaPacific: [email protected] +6568729361
EuropeandAfrica: [email protected] +4733489999
MiddleEast: [email protected] +971(0)43901018
UK: [email protected] +441189735831
VenturaSERVICEPROVIDERSOLUTIONS
FlashlinkBROADCASTSOLUTIONS
VikinXROUTINGSOLUTIONS
Graphicde
sign
:Cha
rlotte.no
ModularroutingGeneralpurposeroutingJPEG2000compressionIntelligentswitching
Signal processing and distribution
SynchronizationEmbedding/De-embedding
ConversionFibertransport/WDM
IPnetworkadaptersSONET/SDHnetwork
adaptersFibertransport/WDM
JPEG2000compressionCarrierClass–NEBSlevel3
Standards basedInbandmanagement
Redundancy protectionJitter management
ASImultiplexersIPnetworkadaptersMPEG-2compressionDistributionamplifiers
TransportstreammultiplexersRFoverfiber
Optical splittersDS3
Fibertransport/WDMOpticalmultiplexing
TimedivisionmultiplexingSignal processing and
distributionModularrouting
GeneralpurposeroutingMobileoutsidebroadcast
©2009NetworkElectronic/VPG
Fiber_Tutorial_A5_R0902.indd 28 09.01.09 10:45:22