ENS466 Week12.Final
Transcript of ENS466 Week12.Final
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ENS/ELT466
TelecommunicationSystemsLab
Fall2013
Week12 Nov.26
FiberOpticsFundamentals
TelecommunicationSystemsLab(ENS466)
Fall2013
Week12 Nov.26
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TheElectromagneticSpectrum
Idefinetheregionofopticsasextendingfrom=10nmto100m. Characteristic
toolsinclude
lenses,
mirrors,
interference
devices
and
optical
fiber.
Photon
shot
noisebecomessignificant. Sourcesmaybelampsorlasers. Detectorssuchas
photodiodestypicallyproduceanoutputcurrentproportionaltoopticalpower.
Photonenergy(E=hf)increases.
Optical
Propagationin
Fiber
LiketheEMwavesinametallictransmissionline,fiberguidedwavestravelata
slowerspeedthanEMwavesinavacuum. Thespeedofcommunicationsignalsin
afibervfisgivenby:f
eff
cv
n
whereneffistheeffectivemodalindexofthefiberandcisthespeedoflightina
vacuum.
LightinanopticalfiberisaguidedEMwave.
Optical
Fiber
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OpticalFiber
ncore[nclad]istherefractiveindexofthecore[cladding]material. Therefractive
indexdescribeshowfastlightwavestravelinthebulkmaterial.
Coating
Coating
Core
Claddingnclad
ncore 2a typ.diam.
2501000m
Coreguideslight(ncore>nclad).
Claddingkeepslightfromroughordirtysurfacetocontrolloss.
Coatingprotectsfromscratches,chemicalstomaintainstrength.
OpticalFiber
Types
SingleModeFiber(SMF)
specialtyfibers fluoride,
chalcogenide, Erdoped...
glassfiber(GOF) lowestloss usedforlonglinksand
highdatarates
MultiModeFiber(MMF)
glassfiber
(GOF) lowcost,fairlylowloss
usedforshortlinksandmoderatedatarates
OpticalFiber
plasticfiber(POF) lowestcost usedforveryshortlinks
andlowdatarates
Likecoax,fiberhasamultimode
thresholdasthecorebecomeslarger.
Unlikecoax,multimodefiberiswidely
used.
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FiberAdvantages&Disadvantages
Comparedtometalliccable,fiberhassomebigadvantages:
availablebandwidth
~60,000
GHz
(compared
to
afew
GHz
for
coaxial
cable)
lowerloss aslowas0.2dB/kmat=1550nm thinnerandlighter
highlyimmunetoelectromagneticinterference
However,fiberalsohassomedownsides:
fiberconnectorsarehighlyintoleranttodustanddirt
susceptibletobendinducedloss
untilrecently,lasersourceswereexpensive
cantcarrypowerlikemetalliccable
Attenuationin
Fiber
Theopticalpowerinafiberdecreasesexponentiallywithd,accordingto:
(linear units)
(dB units)
d
out in
out in dB
P mW P mW e
P dBm P dBm d
FiberlosscanbeconvertedtoorfromlineartodBunitsbyusing:
Becauselightinafiberisguided,itsintensitydoesnotdropoffas1/d2.
Optical
Fiber
10log 10log( ) 4.343dBP dBm P mW e
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FiberLossvs.WavelengthAttenuationiscausedbyabsorptionandscatteringthatareintrinsictothesilicaglass,aswellasabsorptionfromresidualimpurities.
Glassfiber
attenuation
is
lowest
near
1.55
mwavelength,sothisisthepreferredwavelengthforlongdistancecommunication. Shortdatalinksmayoperateatshorterwavelengthsfrom0.6 1.3m. (Classlabswilluse~0.8m.)
from Agrawal
0.2 dB/kmOH impurity
PracticalfiberlossesaresomewhathigherforMMFthanforSMF. Newerfiberstendtobelowerloss,andlowOHabsorptionisfairlystandardtoday.
ResearchcontinuestotrytoshavehundredthsofadB/kmoffthelossofsilicabasedfiber,becausethecostbenefitstolargescalenetworkscanbesignificant.
FiberSplices
and
Connectors
Permanentorsemipermanentjointsbetweenfibersegmentsarecalledsplices;connectors
arejointsdesignedtobetakenapartandreassembled.
Mostfiberjointsaredesignedforbuttcouplingthefibersendtoend. Duetothesmall
dimensionsoffibercores,goodcoupling(i.e.,lowloss)occursonlywhenthecoresare
preciselyaligned.
longitudinal
offset
lateral
offset
angular
misalignment
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VGroovesandFerrulesTwowidelyusedmethodsofalignmentareVgrooveandferruleandsleeve.
Inmostmodernconnectors,zirconia ferrulesarepolishedtoapreciseradius,sothattheforce
fromtheretainingspringdeformsthem(slightly)toobtainintimatecontact.
Vgroove ferruleandsleeve
CommonConnector
Types
LossesformodernconnectorsarelowerthansuggestedbythetableinSeniorsbook.
Improvedfiberandferruleprecision,plusadvancedendface polishing(UPC)have
broughttypicalinsertionlossdownto0.1dBorless.
allofthesehave2.5mmferrule
diam =>canbecrossmated
withspecialunions
screwtype
bayonettype
pushon,pulloff
pushon,pulloff,
miniature
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FusionSplicingForpermanentjoints,fusionsplicinghasbecomethestandard.
Fusionsplicesbetweenfibershavelossessolow
thattheyaredifficulttomeasure. Thefusion
splicer
can
also
create
adiabatic
transitions
to
specialtyfibers,suchaserbiumdopedamplifier
fiber.
BasicOptical
Fiber
System
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AnOpticalFiberCommunicationSystem
includes:
Alightsourceoratransmitter
Aphotoreceiver
Afiberlink
ElectronicSignal ElectronicOutput
10110011011001
t
PTx
Rx
Fiber
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Semiconductors&LightSemiconductordiodesarethemostwidelyusedlightsourcesandphotodetectors
incommunications. Detectorsarebasedonabsorption,whereanincoming
photoninteracts
with
the
material
to
create
free
charge
carriers
that
drive
a
current.Sourcesarebasedoneitherspontaneousemission(LED)orstimulated
emission(laser).
Somesemiconductors,
such
as
Si,
have
an
indirect
bandgap,
which
effectively
prohibits
usefulLEDSorlasers,solightemittersareusuallymadeofIIIVmaterialssuchasGaAs.
absorption spontaneous
emission
stimulated
emission
LEDsLightemittingdiodes,usuallyjustcalledLEDs,werethefirstsourcesusedin
lightwave communications;todaytheyareusedintestinstrumentsthatneeda
broademissionspectrum,andperhapsinsomelowcostdatalinksaswell.
SinceLEDsrelyonspontaneousemission,theyputoutlight thathasabroadwavelength
(frequency)spectrumandisnotcoherent. Theymaybebroadareajunctions(surface
emitting)orwaveguidedevices(edgeemitting).
fromT.P.Leeetal.,Ch.12,OFTII,
AcademicPress,1988.
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ight
mplificationby
timulated
missionof
adiation
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R=100% R=95%
PumpingSystem
PumpingSystemMirror Mirror
LaserMedium
LasersByaddingafeedbackmechanism(suchasapairofmirrorsthatformanopticalcavity)
toanLED,wecanobtainalaser. Laserlightiscoherentandhasaverynarrow
frequencyspectrum,
which
we
call
monochromatic.
18X.Jiang &M.D.Feuer
CoherenceIncoherentlightcontainsEMwavesofdifferentfrequenciesthathavearbitrary
phasesrelativetoeachothers. Coherentlighthaswavesofasinglefrequencywith
alignedphases.
Thiscoherenceoflaserlightiscentraltomanylaserapplications,fromholography
toopticaltweezerstoPb/scommunications.
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LaserCharacteristics
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The light emitted from a laser is monochromatic, that is, it is ofone color/wavelength.
Lasers emit light that is highly directional, that is, laser light is
emitted as a relatively narrow beam in a specific direction.
The light from a laser is coherent, which means that the
wavelengths of the laser light are in phase in space and time.
Laser light can deposit a lot of energy within a small
area.
Laser Light can be visible and invisible
Summary TheopticalregionoftheEMspectrumextendsfrom=10nmto100m.optical
fiber. Photonshotnoisebecomessignificant. Sourcesmaybelampsorlasers.
OpticalfiberisanonmetallicmediumthatsupportsguidedEMwavesatopticalwavelengths.
Opticalfibermaybemadeofglassorplasticandmaybesinglemodeormultimode.
Singlemodeglassfiberisusedforthehighestperformanceapplications. Itsusefulbandwidthis~60,000GHzanditslossat=1.55mcanbe
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LasersandEyeSafety
TelecommunicationSystemsLab(ENS466)
Fall2013
Week12 Nov.26
LaserSafety
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LaserClassifications*
Lasersand
laser
systems
are
assigned
one
of
the
four
broad
classes
(1
to4)dependingonthepotentialforcausingpotentialdamage:
Class1:"safe"ifnotdisassembled.Example:Laserprinters,CDRomplayers/drives
Class2:mayexceedclass1exposurelimitsifviewedmorethan0.25seconds[aversionresponsetime],butstillnotposeasignificanteyehazards.Example:Supermarketlaserscanners
Class3aor3R:eyehazardifviewedusingcollectingoptics,e.g.,telescopes,microscopes,orbinoculars. Example:laserpointer
Class3b:eyehazardsifbeamsarevieweddirectlyorspecularreflectionsareviewed.Example:researchlab
Class4:eyehazardsifbeamsarevieweddirectlyorspecularreflectionsandsometimesevenfromdiffusereflectionsareviewed.Also
skin
burns
from
direct
beam
exposure. Example:
research,
manufacturing.
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* IEC608251(internationalstandard), ANSIZ136.1,Z136.2,Z136.5(USstandards)
LaserHazards
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1. Eye : Acute exposure of the eye to lasers of certain
wavelengths and power can cause eye injury and damage.
2. Skin : Acute exposure to high levels of optical radiation may
cause skin burns.
3. Chemical: Some lasers require hazardous or toxic
substances to operate (i.e., chemical dye, Excimer lasers).
4. Electrical: Many lasers utilize high voltages that can be
lethal.
5. Fire : The solvents used in dye lasers are flammable.Flammable materials may be ignited by direct beams or
specular reflections from high power continuous wave (CW)
infrared lasers.
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LaserRadiationToEye
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Laser
eye
Laser
eye
Mirror
Figure1.Viewingofdirect(primary)beam.
Figure 2. Viewing of a reflected beam from a flat surface reflector.
Figure3.Viewingofadiffuselyreflectedbeamfromaroughsurface
Laser
eye
Rough
surface
BeCareful
!!!
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Laser light can deposit a lot of energy within a small area.
Laser Light can be visible and invisible
Take action with warning sign
Wear Safety Eyewear when required
( Laser safety eyewear is required for class 3b and 4lasers)
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LaserSafetyWarningSigns
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FiberOpticSafety
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LightTransmittedWithinFiber
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MajorLaserHazardsinFiberOpticsCommunications
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1. Eye : Acute exposure of the eye to lasers of certain
wavelengths and power can cause eye injury and damage.
2. Skin : Acute exposure to high levels of optical radiation may
cause skin burns.
3. Chemical : Some lasers require hazardous or toxic
substances to operate (i.e., chemical dye, Excimer lasers).
4. Electrical: Many lasers utilize high voltages that can be
lethal.
5. Fire : The solvents used in dye lasers are flammable.Flammable materials may be ignited by direct beams or
specular reflections from high power continuous wave (CW)
infrared lasers.
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FiberOpticSafety
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EyeSafety:
Neverlookdirectlyintothefiberendwithyourbareeyeor
withanopticallens
Alwayswearsafetyglasseswithsideshieldswhenever
handlingandterminatingbarefibers.
Seekimmediatemedicalattentionforeyeinjuries.
FiberOpticGlassHandleSafety:
Opticalfibershardsareverysharpandcaneasilypiercetheskin.
Placeanylooseshardsincovereddebriscontainersoron
adhesivecollectionsurfacessuchastape.
Alwayscleave
fibers
over
your
work
mat.
Keep
your
work
areacleanandfreeoffibershardstoavoidinjury.
FiberSplicingSafety
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FiberSplicingSafety
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EyeSafety:
Alwayswearsafetyglasseswheneverhandlingandterminating
barefibers.
FiberOpticHandleSafety:
Placeanylooseshardsincovereddebriscontainersoron
adhesivecollectionsurfacessuchastape.
Alwayscleavefibersoveryourworkmat.Keepyourwork
areacleanandfreeoffibershardstoavoidinjury.
FiberCleaverSafety:
DontputyourfingerinsidetheFiberCleavers.
FiberSplicerSafety:
Dontputyourfingerinbetweentheelectrodes.
OnlystartsplicingwhentheWindprotectorhoodisclosed.
ENS466/ELT466 Last
3Labs
Thelast3labshaveonlyonesetupofeachtype,so3groupswillrotateamongLabsA(Lasers&LEDs),B(900MHzAmplifierCharacterization),andC(OpticalFiberSplicing).
Newlabgroups Togiveeveryonetheexperienceofworkingwithavarietyofcolleagues,Iamassigningdifferentworkinggroupsforthelast3weeks:
Redgroup:B.Askharoun,M.Incherchera,A.Parise
Greengroup:M.Altman,T.Hussain
Bluegroup:A.Kasmi,S.Magaddino,K.Tham
BecausetheFiberSplicinglabisnotameasurementlabsimilartotheotherswehavedone,nolabreportisrequiredforit. However,youmaywishcompletetheoptionalextracreditassignmentoutlinedintheLabChandout.
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ENS466/ELT466 Assignments LabReport:
IfyouhavedoneLabAssignmentAorBthisweek,yourlabreportisdueatthe
startof
class
on
12/3.
IfyouhavedoneLabAssignmentCthisweek,youroptionalextracreditassignmentisdueatthestartofclasson12/3.
Reading: tobepostedonBlackboard.
Nextweek: FiberOpticSystems
Backups/Alternates
TelecommunicationSystemsLab
(ENS466)
Fall2013
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AnglePolishedConnectorsEvenwhenlossisacceptable,backreflectioncanbeaproblem. TheFresnelreflectionfroma
perpendicularglassairinterfaceis14.7dB enoughtodisturbbothlabmeasurementsand
practicalcommunication
systems.
Modern
UPC
connectors
offer
return
lossof
55
dB,
but
the
lowestbackreflectionspec(65dB)requiresangledphysicalcontact(APC)connectors.
AlthoughAPCconnectorsremovebackreflectionasapracticalconcern,theyhaverelatively
highand
irreproducible
insertion
loss,
since
slight
errors
in
ferrule
length
(or
overtightening)
willcausetheferrulestoskateoffcenterandcreateanlateralmisalignment.
8
NevertrytomateaPCorUPCconnectorwithanAPCconnector!
Waveguiding RayOptics
SnellsLaw
n1*sin(1)=n2*sin(2) c=sin1(n2/n1)
cisthecriticalanglefortotalinternalreflection.
Guidingoflightcanbeunderstood
asrepeatedtotalinternal
reflection.
11
21 n
nn
2 2
1 11 2 1max
0 0
2sin sin
n n n
n n
0 max
2 2
1 2 1
. . sin( )
2
N A n
n n n
Maxacceptanceangleis: Numericalapertureparameter: