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
Properties: Light collectionProperties: Light collectionGraded index FiberGraded index Fiber
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:
Properties: Light collectionProperties: Light collectionGraded index FiberGraded index Fiber
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
AttenuationAttenuation
Commercial all glass fiber
Commercial hard-clad silica fiber
AttenuationAttenuation
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