optical fiber waveguids step index vs graded index step index vs graded index single mode vs...

Optical fiber waveguidsOptical fiber waveguids

Step index vs graded indexStep index vs graded index Single mode vs multimodesSingle mode vs multimodes Glass fibers vs plastic fibersGlass fibers vs plastic fibers Specialty fibers:Specialty fibers:

– Dispersion shifted fibersDispersion shifted fibers

– Doped fibersDoped fibers

– Coated fibersCoated fibers

Optical fiber waveguidsOptical fiber waveguids

Specialty fibers:Specialty fibers:– Dispersion Shifted Fiber (DSF) has zero dispersion around Dispersion Shifted Fiber (DSF) has zero dispersion around

1550 nm to help transmission at these wavelengths 1550 nm to help transmission at these wavelengths

– Dispersion Compensating Fiber (DCF) has highly negative Dispersion Compensating Fiber (DCF) has highly negative dispersion at 1550 nm to compensate for a buildup of dispersion at 1550 nm to compensate for a buildup of positive dispersion in that region in conventional fiber positive dispersion in that region in conventional fiber

– Large Effective Area Fiber allows the light to be Large Effective Area Fiber allows the light to be transmitted in a larger total area of the fiber in order transmitted in a larger total area of the fiber in order to reduce the concentration of high powers that may to reduce the concentration of high powers that may cause adverse nonlinear effects cause adverse nonlinear effects

– Non-Zero Dispersion Shifted Fiber (NZ-DSF) gives a Non-Zero Dispersion Shifted Fiber (NZ-DSF) gives a small amount of dispersion in the 1550 nm region, small amount of dispersion in the 1550 nm region, which can reduce the effects of four-wave mixing which can reduce the effects of four-wave mixing

– All Wavelength Fiber removes the attenuation peak All Wavelength Fiber removes the attenuation peak at 1400 nm to increase the range of possible at 1400 nm to increase the range of possible wavelengths that can be transmitted at low loss wavelengths that can be transmitted at low loss

Fiber ManufactureFiber Manufacture

Direct Fiber Direct Fiber manufacture: manufacture: Double CrucibleDouble Crucible

Fiber PreformsFiber Preforms– External DepositionExternal Deposition

– Internal DepositionInternal Deposition

– Axial DepositionAxial Deposition Fiber DrawFiber Draw

– Step Index fibersStep Index fibers– Graded Index fibersGraded Index fibers

Preform ManufacturingPreform Manufacturing

External DepositionExternal Deposition

External CVD, External CVD, OVPO, OVDOVPO, OVD

Axial DepositionAxial Deposition AVD, VADAVD, VAD Both step and Both step and

graded index fibersgraded index fibers

Preform ManufacturingPreform Manufacturing

Internal DepositionInternal Deposition Interbal CVD, Interbal CVD,

MCVD, IVDMCVD, IVD 30-100 layers30-100 layers

Plasma-enhanced Plasma-enhanced MCVDMCVD

Fiber DrawingFiber Drawing

Speed: 1-10 m/sSpeed: 1-10 m/s

Coating: buffer Coating: buffer needed to needed to protect the fiber protect the fiber from moisture from moisture and strengthen itand strengthen it

Proof-testedProof-tested Preform is 1-6 cm in diameter, and Preform is 1-6 cm in diameter, and

1-2 m in length1-2 m in length

15-100 km fiber15-100 km fiber

Fiber PropertiesFiber Properties

AttenuationAttenuation

Light collection and propagationLight collection and propagation

DispersionDispersion Information capacityInformation capacity

Nonlinear effectsNonlinear effects– Brillouin scatteringBrillouin scattering

– Raman ScatteringRaman Scattering Mechanical propertiesMechanical properties

Properties: Light collectionProperties: Light collectionStep index FiberStep index Fiber

Critical AngleCritical Angle Fractional refractive Fractional refractive

index, index, =(n=(n11-n-n22)/n)/n11

Need for claddingNeed for cladding

Types of SIFTypes of SIF Common size Common size

designation: designation: 50/125, 62.5/125, 50/125, 62.5/125, 100/140100/140

Index profileIndex profile

Properties: Light collectionProperties: Light collectionStep index FiberStep index Fiber

NANA Cladding modesCladding modes Cladding modes Cladding modes

can be suppressed can be suppressed by matched bufferby matched buffer

Common Common specificationsspecifications

Properties: Light collectionProperties: Light collectionGraded index FiberGraded index Fiber

GRIN Index profileGRIN Index profile n(r)=nn(r)=n11[1-2(r/a)[1-2(r/a)]]1/21/2, r≤a, r≤a

Light propagationLight propagation

NA and NA and acceptance angleacceptance angle

n(r)=nn(r)=n11[1-2[1-2]]1/21/2=n=n22, r>a, r>a

=(n=(n2211-n-n22

22)/2n)/2n2211≈(n≈(n11-n-n22)/n)/n11

Layers modelLayers model

Figures charts images\step1Figures charts images\step1.gif.gif

Figures charts images\grin1.Figures charts images\grin1.gifgif


GRIN NA and acceptance GRIN NA and acceptance angleangle

n(r)=nn(r)=n11[1-2(r/a)[1-2(r/a)]]1/21/2, r≤a, r≤a

n(r)=nn(r)=n11[1-(r/a)[1-(r/a)], r≤a], r≤a

nn22=n=n11[1-[1-], r>a], r>a

Coupling function of rCoupling function of r SI Coupling > GRIN CouplingSI Coupling > GRIN Coupling

When When =2, core index:=2, core index:

When When <<1:<<1:


NA for parabolic profile, NA= nNA for parabolic profile, NA= n11(2(2))1/21/2[1-(r/a)[1-(r/a)]]1/21/2

For nFor n11=1.48, n=1.48, n22=1.46=1.46 For parabolic profile:For parabolic profile:

r(z)=rr(z)=roocos(Acos(A1/21/2z)+(1/Az)+(1/A1/21/2) ) r’r’oosin(Asin(A1/21/2z)z)

r’(z)=-Ar’(z)=-A1/21/2rroosin(Asin(A1/21/2z)+ r’z)+ r’oocos(Acos(A1/21/2z), A=2z), A=2/a/a22

For a rod lens, AFor a rod lens, A1/21/2P=2P=2, P=, P=a(2/a(2/))1/21/2

Properties: AttenuationProperties: Attenuation

Glass: mixture not Glass: mixture not compound + dopantscompound + dopants

Losses: absorption, Losses: absorption, scattering, geometric scattering, geometric effectseffects

AbsorptionAbsorption– Intrinsic absorptionIntrinsic absorption– Impurities lossesImpurities losses

Metal ions: must not exceed parts/billionMetal ions: must not exceed parts/billion OH ions: thermal motion, @ 1.37, 1.23, 0.95, parts/millionOH ions: thermal motion, @ 1.37, 1.23, 0.95, parts/million Atomic defectsAtomic defects ContaminationContamination

Properties: Attenuation, Properties: Attenuation, Rayleigh ScatteringRayleigh Scattering

Local variations of Local variations of refractive index: refractive index: microscalemicroscale

Intrinsic propertyIntrinsic property

Attenuation coefficient, Attenuation coefficient, =L/8.685 (km=L/8.685 (km-1-1))

Wavelength dependenceWavelength dependence

L=1.7(0.85/L=1.7(0.85/))44, (dB, , (dB, in um)in um)

Other materialsOther materials

Properties: AttenuationProperties: Attenuation Inhomogeneities: not wavelength Inhomogeneities: not wavelength

dependant, macroscaledependant, macroscale

Geometric effectsGeometric effects Macroscopic: Macroscopic:

spooling, curvespooling, curve Radius of 25 mm causes negligible lossRadius of 25 mm causes negligible loss Radius of 10 mm does not break the fiberRadius of 10 mm does not break the fiber Explanation of lossExplanation of loss Microscopic: CablingMicroscopic: Cabling

Total AttenuationTotal Attenuation


Commercial all glass fiber

Commercial hard-clad silica fiber


All plastic fiber

Attenuation measurement•OTDR

•Cutback technique

Fiber properties: SI ModesFiber properties: SI Modes Power budgetPower budget Mode chartMode chart Note the normalized Note the normalized

frequency, frequency, V=(nV=(n11

22-n-n2222))1/21/222a/a/

Helical, screw, Helical, screw, corkscrew corkscrew modes: HE, EHmodes: HE, EH

Mode numbering: Mode numbering: relates to Bessel relates to Bessel function function characteristicscharacteristics

optical fiber waveguids step index vs graded index step index vs graded index single mode vs...

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