New Lect Optic 6th
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Transcript of New Lect Optic 6th
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Optical F iber
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Optical F iber
Communication system with light as
the carrier and fiber as
communication medium
Propagation of light in atmosphere
impractical: water vapor, oxygen,particles.
Optical fiber is used, glass or plastic,
to contain and guide light waves
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History
1880 Alexander G. Bell, Photo phone,
transmit sound waves over beam of light 1930: TV image through uncoated fiber
cables.
Few years later image through a singleglass fiber
1951: Flexible fiberscope: Medicalapplications
1956:The term fiber optics used for thefirst time
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History Contd
1960: Laser invented
1967: New Communications medium:cladded fiber
1960s: Extremely lossy fiber: more than1000 dB /km
1970, Corning Glass Work NY, Fiber withloss of less than 2 dB/km
70s & 80s : High quality sources and
detectors Late 80s : Loss as low as 0.16 dB/km
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Optical F iber: Advantages
Capacity: much wider bandwidth (10GHz)
Crosstalk immunity
Safety: Fiber is nonmetalic Longer lasting (unproven)
Security: tapping is difficult
Economics: Fewer repeaters
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Disadvantages
higher initial costin installation
Interfacing cost
Strength: Lowertensile strength
Remote electric
power
more expensive torepair/maintain
Tools: Specialized
and sophisticated
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Optical F iber L ink
Input
Signal
Coder or
Converter
Light
Source
Source-to-Fiber
Interface
Fiber-to-light
Interface
Light
DetectorAmplifier/Shaper
Decoder
Output
Fiber-optic Cable
Transmitter
Receiver
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Light source: LED or ILD (Injection LaserDiode): amount of light emitted is proportional to the drive
current
Sourceto-fiber-coupler (similar to a lens): A mechanical interface to couple the light
emitted by the source into the optical fiber
Light detector: PIN (p-type-intrinsic-n-type)
or APD (avalanche photo diode) bothconvert light energy into current
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F iber Types
Plastic core and cladding Glass core with plastic cladding PCS
(Plastic-Clad Silicon)
Glass core and glass cladding SCS:Silica-clad silica
Under research: non silicate: Zinc-chloride: 1000 time as efficient as glass
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Plastic F iber
used for short runHigher attenuation, but easy to install
Better withstand stress
Less expensive
60% less weight
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Types Of Optical F iber
Single-mode step-index Fiber
Multimode step-index Fiber
Multimode graded-index Fiber
n1 core
n2 cladding
no air
n2 cladding
n1 core
Variable
n
no air
Light
ray
Index porfile
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F iber Types
Multi-Mode:
supportshundreds paths
for light.
Single-Mode:supports a
single path for
light
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Single-mode step-index F iber
Advantages: Minimum dispersion: all rays take same path,
same time to travel down the cable. A pulse can
be reproduced at the receiver very accurately.
Less attenuation, can run over longer distance
without repeaters.
Larger bandwidth and higher information rate
Disadvantages:
Difficult to couple light in and out of the tiny core
Highly directive light source (laser) is required.
Interfacing modules are more expensive
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Multi Mode
Multimode step-index Fibers: inexpensive; easy to couple light into Fiber
result in higher signal distortion; lower TX
rateMultimode graded-index Fiber:
intermediate between the other two types of
Fibers
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Acceptance Cone & Numerical Aperture
n2 cladding
n2 cladding
n1 core
Acceptance
Cone
Acceptance angle, qc, is the maximum angle in which
external light rays may strike the air/Fiber interface
and still propagate down the Fiber with
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Absorption Losses I n Optic Fiber
Loss(dB/km
)
1
00.7 0.8
Wavelength (mm)0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7
2
3
4
5
6
Peaks caused
by OH- ionsInfrared
absorption
Rayleigh scattering
& ultraviolet
absorption
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Presented By The Fiber Optic Association
2004, The Fiber Optic Association, Inc.
Light Used In Fiber Optics
Fiber optic systems transmit using
infrared light, invisible to the human
eye, because it goes further in theoptical fiber at those wavelengths.