ENS466 Week12.Final

8/9/2019 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

14X.Jiang

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

17X.Jiang

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

25X.Jiang

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

!!!

26X.Jiang

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:

ENS466 Week12.Final

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