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

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

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

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

Preform Manufacturing Internal Deposition Interbal CVD, MCVD, IVD 30-100 layers Plasma-enhanced MCVD

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 15-100 km fiber

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

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

Properties: Light collection Step index Fiber NA Cladding modes Cladding modes can be suppressed by matched buffer Common specifications

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

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

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

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 motion, @ 1.37, 1.23, 0.95, parts/million Atomic defects Contamination

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

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

Total Attenuation

Attenuation Commercial all glass fiber Commercial hard-clad silica fiber

Attenuation Attenuation measurement OTDR All plastic fiber Cutback technique

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