Transcript Document

Chapter One:
Introduction to Fiber Optics
Communication System
prepared by : Maizatul Zalela bt Mohamed Sail
Fiber Optic
Cable
Fiber Optic
Fiber Optic lamp
Profesional lamp
– fiber optic
What is Fiber Optic?
Fiber optics –
•A means to carry information from one point to
another or serves as transmission medium (optical
fiber).
•A technology that uses thin strand of glass (or
plastic) threads (fibers) to transmit data.
•A fiber optic cable consists of a bundle of glass
threads, each of which is capable of transmitting
messages modulated onto light waves.
prepared by : Maizatul Zalela bt Mohamed Sail
Introduction
 An optical fiber is essentially a waveguide for light
 It consists of a core and cladding that surrounds
the core
 The index of refraction of the cladding is less
than that of the core, causing rays of light leaving
the core to be refracted back into the core
 A light-emitting diode (LED) or laser diode (LD)
can be used for the source
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Optical Fiber
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Optical Fiber
 Optical fiber is made from thin strands of
either glass or plastic
 It has little mechanical strength, so it must be
enclosed in a protective jacket
 Often, two or more fibers are enclosed in the
same cable for increased bandwidth and
redundancy in case one of the fibers breaks
 It is also easier to build a full-duplex system
using two fibers, one for transmission in each
direction
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History
1870’s
1880,
1950’s
John Tyndall showed a beam of light
would follow a specific path by
refraction
William Wheeling received a patent
doing same thing with mirrored pipe.
Alexander Graham Bell patented an
optical telephone system, which he
called the Photophone. However, his
earlier invention, the telephone, was
more practical and took tangible
shape.
saw development of the “fiberscope”
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History
1957
Lasers first used as light source.
Light has an information-carrying capacity
10,000 times that of the highest radio frequencies
being used.
1970
Drs. Robert Maurer, Donald Keck, and Peter
Schultz of Corning succeeded in developing a
glass fiber that exhibited attenuation at less than
20 dB/km, the threshold for making fiber optics a
viable technology. It was the purest glass ever
made.
the U.S. Navy fiber optic telephone link aboard
the U.S.S. Little Rock.
1976
Air Force followed suit by developing its Airborne
Light Optical Fiber Technology (ALOFT)
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History
1977
both AT&T and GTE installed fiber optic telephone
systems in Chicago and Boston respectively.
1980
broadcasters of the Winter Olympics, in Lake Placid,
New York, requested a fiber optic video transmission
system for backup video feeds. The fiber optic feed,
because of its quality and reliability, soon became the
primary video feed, making the 1980 Winter Olympics
the first fiber optic television transmission.
1990
Bell Labs transmitted a 2.5 Gb/s signal over 7,500 km
without regeneration. The system used a soliton laser
and an erbium-doped fiber amplifier (EDFA) that
allowed the light wave to maintain its shape and
density.
prepared by : Maizatul Zalela bt Mohamed Sail
History
1990
Bell Labs transmitted a 2.5 Gb/s signal over 7,500 km
without regeneration. The system used a soliton laser
and an erbium-doped fiber amplifier (EDFA) that
allowed the light wave to maintain its shape and density.
1994
Winter Olympics in Lillehammer, Norway, fiber optics
transmitted the first ever digital video signal, an
application that continues to evolve today.
.
1998
transmitted 100 simultaneous optical signals
each at a data rate of 10 gigabits (giga = billion per
second) distance of nearly 250 miles (400 km).
prepared by : Maizatul Zalela bt Mohamed Sail
Advantages
The advantages of fiber-optic systems warrant considerable
attention.
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This new technology has clearly affected the telecommunications
industry and will continue to thrive due to the numerous advantages it
has over its copper counterpart.
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The major advantages include.
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Wide Bandwidth
Low Loss Electromagnetic Immunity
Light Weight
Small Size
Noise Immunity and Safety Security
Economic
Reliability
Wide Bandwidth
 Fiber optic communications can run at
10 Ghz and have the potential to go as high as 1 Thz
(100,000 GHz).
 A 10 Ghz capacity can transmit (per second):
 1000 books
 130,000 voice channels
 16 HTDV channels or 100 compressed HDTV
channels.
 Separate Voice, data and video channels are
transmitted on a single cable.
Electromagnetic Immunity
 Copper cables can act as an antennae picking up
EMI from power lines, computers, machinery and
other sources.
 Fiber is not susceptible to Electro-Magnetic
Interference and thus no interference allowing
error-free transmissions.
Light Weight and Volume
 Comparison:
Fiber – 4kg or 9lb per 1000 ft. (due mainly to packaging).
 Coax – 36kg or 80lb per 1000 ft.
Fiber optic cables are substantially lighter in weight and
occupy much less volume than copper cables with the same
information capacity.
Fiber optic cables are being used to relieve congested
underground ducts in metropolitan and suburban areas.
For example, a 3-in. diameter telephone cable consisting of
900 twisted-pair wires can be replaced with a single fiber
strand 0.005 inch.
In diameter (approximately the diameter of a hair strand) and
retain the same information carrying capacity.
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Small Size
 Use where space is at a premium:
 Aircraft, submarines
 Underground conduit
 High density cable areas – Computer centers.
Noise Immunity and Safety
 No electricity thus no spark hazards so can be used
through hazardous areas.
 Because fiber is constructed of dielectric materials, it
is immune to inductive coupling or crosstalk from
adjacent copper or fiber channels.
 In other words, it is not affected by electromagnetic
interference (EMI) or electrostatic interference.
Security
 Since fiber does not carry electricity, it emits no EMI
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which could be used for eavesdropping.
Difficult to 'tap' – cable must be cut and spiced.
Because light does not radiate from a fiber optic cable, it
is nearly impossible to secretly tap into it without
detection.
For this reason, several applications requiring
communications security employ fiber-optic systems.
Military information, for example, can be transmitted
over fiber to prevent eavesdropping.
In addition, metal detectors cannot detect fiber-optic
cables unless they are manufactured with steel
reinforcement for strength.
Economics
Presently, since the cost of fiber is comparable to
copper it is expected to drop as it becomes more
widely used.
 Because transmission losses are considerably less
than for coaxial cable, expensive repeaters can be
spaced farther apart.
 Fewer repeaters mean a reduction in overall
system costs and enhanced reliability.
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Reliability
Once installed, a longer life span is expected
with fiber over its metallic counterparts, because it
is more resistant to corrosion caused by
environmental extremes such as temperatures,
corrosive gases, and liquids.
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Disadvantages of Fiber-Optic System
 In spite of the numerous advantages that fiber-optic
systems have over conventional methods of transmission,
there are some disadvantages, particularly because of its
newness.
 Many of these disadvantages are being overcome with
new and competitive technology. The disadvantages
include:
i.
Interfacing Costs
ii. Strength
iii. Remote powering of devices
iv. Inability to interconnected
Interfacing Costs
Electronic facilities must be converted in order to
interface to the fiber.
 Often these costs are initially overlooked.
 Fiber-optic transmitters, receivers, couplers, and
connectors, for example, must be employed as part of
the communication system.
 Test and repair equipment is costly.
 If the fiber-optic cable breaks, splicing can be costly
and tedious task.
 Manufacturers in this related field however are
continuously introducing new and improved field
repair kits.
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Strength
Optical fiber , by itself has a significant lower tensile
strength than coaxial cable.
 Surrounding the fiber with stranded Kevlar (A
nonmetallic, difficult to-stretch, strengthening material)
and a protective PVC jacket can help to increase the pulling
strength.
 Installations requiring greater tensile strengths can be
achieved with steel reinforcement.
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Remote Powering Of Devices
 Occasionally, it is necessary to provide electrical
power to a remote device.
 Because this cannot be achieved through the fiber,
metallic conductors are often included in the cable
assembly.
 Several manufacturers now offer a complete line of
cable types, including cables manufactured with both
copper wire and fiber.
Inability to interconnect
Inability to interconnect easily requires that current
communication hardware systems be somewhat
retrofitted to the fiber-optic networks.
 Much of the speed that is gained through optical fiber
transmission can be inhibited at the conversion points of
a fiber-optic chain.
 When a portion of the chain experiences heavy use,
information becomes jammed in a bottleneck at the
points where conversion to, or from, electronic signals is
taking place.
 Bottlenecks like this should become less frequent as
microprocessors become more efficient and fiber-optics
reach closer to a direct electronic hardware interface.
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Advantage
Bandwidth
· High bandwidth and capacity
· Lower signal attenuation (loss)
Immunity to Electrical
Noise, Electromagnetic
Immunity
· Immune to noise (electromagnetic
interference [EMI]
· No crosstalk
· Lower bit error rates
Signal Security
· Difficult to tap
· Nonconductive (does not radiate signals)
Size and Weight
· Reduced size and weight cables
Overall System Economy
· Low overall system cost
· Lower installation cost
Reliability
· Less restrictive in harsh environments
Disadvantage
Interfacing Costs
•High planning, installation, and
maintenance cost
Strength
•lower tensile strength than coaxial cable
Remote Powering of
Devices
•necessary to provide electrical power
to a remote device.
• Cannot be achieved
through the fiber, metallic conductors are
often included in the cable assembly.
Inability to interconnect
•incompatibility with the electronic
hardware systems that make up today's
world.
Fiber Optic Block Diagram
 Fiber optics is a medium for carrying information
from one point to another in the form of light.
 Unlike the copper form of transmission, fiber optics
is not electrical in nature.
 A basic fiber optic system consists of:
i) transmitting device that converts an electrical
signal into a light signal,
ii) optical fiber cable that carries the light,
iii) receiver that accepts the light signal and
converts it back into an electrical signal.
prepared by : Maizatul Zalela bt Mohamed Sail
Block Diagram
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Transmitter
 Its main function is to transmit the information
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signals like voice, video or computer in the form of
light signals.
As shown above, the information at input is
converted into digital signals by coder or converter
circuit.
This circuit is actually ADC (analog to digital
converter).
Thus, it converts analog signals into proportional
digital signals.
If the input signals are computer signals, they are
directly connected to light source transmitter circuit
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Con’t
 The light source block is a powerful light source.
 It is generally a FOCUS type LED or low intensity
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laser beam source or in some cases infrared beam of
light is also used.
The rate, at which light source turns ON/OFF,
depends on frequency of digital pulses.
Thus, its flashing is proportional to digital input.
In this way, digital signals are converted into
equivalent light pulses and focused at one end of
fiber-optic cable.
They are then received at its other end.
prepared by : Maizatul Zalela bt Mohamed Sail
Fiber Optic Cable
 When light pulses are fed to one end of fiber-optic
cable, they are passed on to other end.
 The cable has VERY LESS attenuation (loss due to
absorption of light waves) over a long distance.
 Its bandwidth is large; hence, its information
carrying capacity is high.
prepared by : Maizatul Zalela bt Mohamed Sail
Receiver
 At receiving end, a light detector or photocell is used to
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detect light pulses.
It is a transducer, which converts light signals into
proportional electrical signals.
These signals are amplified and reshaped into original
digital pulses, (while reshaping, distortion & noise are
filtered out) with the help of shaper circuit.
Then the signals are connected to decoder. It is actually
ADC circuit (Analog to Digital Converter), which
converts digital signals into proportional analog signals
like voice, video or computer data.
Digital signals for computer can be directly taken from
output of shaper circuit
prepared by : Maizatul Zalela bt Mohamed Sail
Con’t
 Thus, this total unit is used fiber optic
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communication system.
However if the distance between transmitter and
receiver is very large, then REPEATER UNITS are
used.
Due to repeaters signals attenuation is compensated.
For this, light signals at far end are converted into
electrical signals, amplified and retransmitted.
Such repeater unit is also called RELAY STATION
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Application
 Analog system
 Digital system
 Undersea cable
 High Definition Television (HDTV)
 Triple Play Technology ( voice, video , data )
prepared by : Maizatul Zalela bt Mohamed Sail
Quick Test 
Define fiber optic?
2. The advantages of fiber optic, overcome its
disadvantages. Explain the advantages and
disadvantages of fiber optic.
3. Draw the block diagram of fiber optic
communication system.
4. State the function of each block in the diagram.
1.
Quick Test 
 Which of the following answer, describe the
application of fiber optic in communication system.
i.
ii.
iii.
iv.
Triple Play System
Undersea Communication Cable
Digital Transmission System
Weather forecast System