OFC- An Introduction
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Transcript of OFC- An Introduction
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OPTICAL FIBER
CABLE CHARACTERSTICS
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CONTENTS
OPTICAL PRINCIPLE (TOTAL INTERNAL
REFLECTION)
FIBER CLASSIFICATION TRANSMISSION CHALLENGES
ATTENUATION
DISPERSION CHROMATIC DISPERSION
POLIRIZATION MODE DISPERSION
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Optical communication
+
TRANSMITTER FIBRE
+
RECEIVER
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Ray Theory:
1. In a vacuum, rays travel at a velocity of c =3x108m/s.In any other medium, rays travel at a slower speed,
given byv = c/n n =refractive index of the medium.
2. Rays travel straight paths, unless deflected by somechange in medium.
3. If any power crosses the boundary, the transmittedray direction is given by Snells law:
n1 sin i = n2 sin r
Optical Principle
(Internal reflection theory)
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INCIDENT RAYS 1REFLECTED RAYS
REFRACTED RAYS
1
1
3
2
2
3
N2 cladding
r
i
(principal of total internal reflection)
n1 = 1.48
n2 = 1.46
N1 core
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The Optical Fibre
Cladding
125 mCore8-10 m
Refractive index
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32
1
3
2
1
Light propagation in fibre
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Basic Fibre
core with RI n1supported byconcentriccladding layer with
RI n2. RI of core is
greater thancladding (n1 > n2).
The cladding layeris surrounded by
one or moreprotective coating.
Change in RI isachieved byselectively dopingthe glass perform.
CONSTRUCTION OF OPTICAL
FIBRE CABLE
CORE
CLADDING
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Cabling is to protect the fiber during transportation, installation &operation.
Cabling protects the optical fibres from mechanical damage andenvironmental degradation.
Resembles conventional metal cables externally. There are a variety of cable design available and irrespective of their
design fibre optic cables have the following parts in common :
Buffer : to protect fibre from outside stress; materials used - nylon,mylar or plastic.
Strength member ; to reduce stress due to pulling, shearing, andbending; materials used-textile fiibres (kevlar), or steel.
Cable filling compound: to prevent moisture intrusion and migration inthe cable.
Cable jacket : to protect the fibre against cut and abrasion; materialused-polyethylene polyurethane, polyvinyl chloride or teflon.
Cabling of fibre :
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Standard Single-Mode (SM)
FibreFibre coreSiO2+ GeO2 10 m
n 1.443
Fibre coreSiO2+ GeO2
10 m
n 1.443
SiO2 Cladding
125 m
n 1.44
SiO2 Cladding
125 m
n 1.44Primary coating (soft)
400 m
Primary coating (soft)
400
m
Secondary coating (hard)
1 mm
Secondary coating (hard)
1 mm
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Material Classification
Al fused-silica-glass fiber:
Plastic-clad-silica (PCS) fiber:
All-plastic fiber : Modal classification :
propagation : - single-mode (SM) fiber.
- Multi-mode (MM) fiber.
Classification based on refractive index profile : step index (SI)
Graded index (GRIN) fiber.
CLASSIFICATION OF OPTICAL
FIBRE
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2a
2a
2a 8 - 12 m 125 m
50 - 200m 125-400m
50 m 125-400m
C) Multi mode GRIN fiber
b) Multi mode step-index fiber
a) Single mode step-index fiber
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refractive
index
SM
Single-Mode
SM
Single-Mode
Fibre types
MM-SI
Multi-Mode
Step Index
MM-SI
Multi-Mode
Step Index
MM-GI
Multi-Mode
Graded Index
MM-GI
Multi-Mode
Graded Index
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TRANSMISSION CHALLENGES
Attenuation
Dispersion
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Fibre performance
z=0 z=L
Dispersion
z=0 z=L
Attenuation
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FIRST
WINDOW
SECOND WINDOW
THIRD WINDOW
3.0
2.5
2.0
1.5
1.0
0.5
0800 900 1000 1100 1200 1300 1400 1500 1600 1700
TOTAL LOSS
RAYLEIGHSCATTERING
Attenuation Curve
Wave Length (Lemda) in nm
Loss
dB
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Fibre attenuation (SiO2)
1.80.8 1.0 1.2 1.4 1.60.9 1.1 1.3 1.5 1.7
Wavelength (m)
Attenuation
(dB/km)
0.2
0.5
1.0
1.5
0.16 dB/km
Rayleigh
scattering
IR band edge
OH--peak
UV
absorption
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Maximum transmission span
1
10
100
1000
1 10 100 1000 10000
Attenuation
Dispersion
BL = constant
L(km)
Bitrate B (Mb/s)
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Transmission Loss
The transmission loss or attenuation
As light waves travel down an optical fibre,
they lose part of their energy because of
various imperfections in the fibre. These
losses are measured in decibels perkilometers (dB/km).
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Losses associated within the fiber classified as under:
absorption. Even the purest glass will absorb heavilywithin specific wavelength regions. Other majorsource of loss is impurities like, metal ions and OH
ions. scattering: caused due to localized variations in
density, called Rayleigh scattering and the loss is:
geometric
micro-bending.macro-bending.
LOSSES IN FIBER (Attenuation)
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Dispersion is spreading of the optical
pulse as it travels down the length.
Dispersion limits the information carryingcapacity of fibre
DISPERSION IN FIBER
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Types of dispersion
Intermodal dispersion only for MMF
Material Dispersion Chromatic Waveguide Dispersion Dispersion
Polarisation Mode Dispersion (PMD)
Intermodal dispersion only for MMF
Material Dispersion Chromatic Waveguide Dispersion Dispersion
Polarisation Mode Dispersion (PMD)
} {
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DISPERSION DUE TO
Material Dispersion:- Due to materialimpurities
Waveguide Dispersion:- Due toConstruction difference of the wave guide,core diameter not uniform throughout length.
Modal Dispersion:- pulse spreading caused by various modes.
Various modes of light source.
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Summary
1. Generally long distance network SM mode G-652 is used.
2. It can be used for 1550-nm window, by dispersion
compensators.
3. Non dispersion shifted fiber can also support 10 Gigabit
Ethernet standard at distances over 300 meters.4. Non-zero dispersion-shifted fiber-good for both TDM and
DWDM use in the 1550-nm region.
5. PMD and other nonlinear effects are not so critical for
short-haul but they are in long-haul systems with higherspeeds.
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Optical Communication SystemsFirst Generation, ~1975, 0.8 mMM-fibre, GaAs-laser or LED
Second Generation, ~1980, 1.3 m, MM & SM-fibre
InGaAsP FP-laser or LED
Third Generation, ~1985, 1.55 m, SM-fibre
InGaAsP DFB-laser, ~ 1990 Optical amplifiers
Fourth Generation, 1996, 1.55 m
WDM-systems
1.80.8 1.0 1.2 1.4 1.60.9 1.1 1.3 1.5 1.7Wavelength (m)
Att
enua
tion
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5
4
3
2
1
0 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7
~ 190 THz~ 50 THz
OH- OH-
First window
Second window
Third window
Fourth window
Fifth window
Wavelength (m)