1. Optical fiber waveguids
Step index vs graded index
Single mode vs multimodes
Glass fibers vs plastic fibers
Specialty fibers:
Dispersion shifted fibers
Doped fibers
Coated fibers

2. Optical fiber waveguids
Specialty fibers:
Dispersion Shifted Fiber (DSF) has zero dispersion around 1550 nm to help transmission at these wavelengths
Dispersion Compensating Fiber (DCF) has highly negative dispersion at 1550 nm to compensate for a buildup of positive dispersion in that region in conventional fiber
Non-Zero Dispersion Shifted Fiber (NZ-DSF) gives a small amount of dispersion in the 1550 nm region, which can reduce the effects of four-wave mixing
Large Effective Area Fiber allows the light to be transmitted in a larger total area of the fiber in order to reduce the concentration of high powers that may cause adverse nonlinear effects
All Wavelength Fiber removes the attenuation peak at 1400 nm to increase the range of possible wavelengths that can be transmitted at low loss

3. Fiber Manufacture Direct Fiber manufacture: Double Crucible
Step Index fibers
Graded Index fibers
Fiber Preforms
External Deposition
Internal Deposition
Axial Deposition
Fiber Draw

4. Preform Manufacturing
External Deposition
External CVD, OVPO, OVD
Axial Deposition
AVD, VAD
Both step and graded index fibers

5. Preform Manufacturing
Internal Deposition
Interbal CVD, MCVD, IVD
layers
Plasma-enhanced MCVD

6. Fiber Drawing
Coating: buffer needed to protect the fiber from moisture and strengthen it
Speed: 1-10 m/s
Proof-tested
Preform is 1-6 cm in diameter, and 1-2 m in length
km fiber

7. Fiber Properties Light collection and propagation Attenuation
Dispersion
Information capacity
Nonlinear effects
Brillouin scattering
Raman Scattering
Mechanical properties

8. Properties: Light collection Step index Fiber
Index profile
Critical Angle
Fractional refractive index, D=(n1-n2)/n1
Need for cladding
Types of SIF
Common size designation: 50/125, 62.5/125, 100/140

9. Properties: Light collection Step index FiberNA
Cladding modes
Cladding modes can be suppressed by matched buffer
Common specifications

10. Properties: Light collection Graded index Fiber
GRIN Index profile
n(r)=n1[1-2(r/a)aD]1/2, r≤a
n(r)=n1[1-2D]1/2=n2, r>a
Figures charts images\grin1.gif
D=(n21-n22)/2n21≈(n1-n2)/n1
Figures charts images\step1.gif
Light propagation
Layers model
NA and acceptance angle

11. Properties: Light collection Graded index Fiber
GRIN NA and acceptance angle
Coupling function of r
SI Coupling > GRIN Coupling
When a=2, core index:
n(r)=n1[1-2(r/a)2D]1/2, r≤a
When D <<1:
n(r)=n1[1-(r/a)2D], r≤a
n2=n1[1-D], r>a

12. Properties: Light collection Graded index Fiber
NA for parabolic profile, NA= n1(2D)1/2[1-(r/a)2]1/2
For n1=1.48, n2=1.46
For parabolic profile:
r(z)=rocos(A1/2z)+(1/A1/2) r’osin(A1/2z)
r’(z)=-A1/2rosin(A1/2z)+ r’ocos(A1/2z), A=2D/a2
For a rod lens, A1/2P=2p, P=pa(2/D)1/2

13. Properties: Attenuation
Glass: mixture not compound + dopants
Losses: absorption, scattering, geometric effects
Absorption
Intrinsic absorption
Impurities losses
Metal ions: must not exceed parts/billion
OH ions: thermal 1.37, 1.23, 0.95, parts/million
Atomic defects
Contamination

14. Properties: Attenuation, Rayleigh Scattering
Local variations of refractive index: microscale
Intrinsic property
L=1.7(0.85/l)4, (dB, l in um)
Attenuation coefficient, a=L/8.685 (km-1)
Wavelength dependence
Other materials

15. Properties: Attenuation
Inhomogeneities: not wavelength dependant, macroscale
Geometric effects
Macroscopic: spooling, curve
Radius of 25 mm causes negligible loss
Radius of 10 mm does not break the fiber
Explanation of loss
Microscopic: Cabling

16. Total Attenuation

17. Attenuation Commercial all glass fiber
Commercial hard-clad silica fiber

18. Attenuation Attenuation measurement OTDR All plastic fiber
Cutback technique

19. Fiber properties: SI Modes
Power budget
Mode chart
Note the normalized frequency, V=(n12-n22)1/22pa/l
Helical, screw, corkscrew modes: HE, EH
Mode numbering: relates to Bessel function characteristics