introduction to optical fiber communication (2)
DESCRIPTION
Introduction to Optical Fiber CommunicationTRANSCRIPT
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1Introduction to Optical Fiber Comm.TOFCINT010
T818ITEC - SCAAP Training Programme
Mod Id :TOFCINT010
Introduction to Optical Fiber
Communications
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2Introduction to Optical Fiber Comm.TOFCINT010
Historical Perspective
� One of the earliest known optical transmission
links :
� Was the use of a fire signal by the Greeks in the
eighth century B.C. for sending alarms, calls for
help or announcements of certain events.
� Most civilizations have used fire beacons, or
smoke signals to convey a single piece of
information.( victory in a war)
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INTRODUCTION
� In 1870, John Tyndall demonstrated the principle
of guiding light through internal reflections.
� In 1880, Alexander Graham Bell invented the
photo phone, which used unguided light to carry
speech.
� Major breakthrough was achieved with the
invention of laser in 1960.
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4Introduction to Optical Fiber Comm.TOFCINT010
� In 1966, Charles K. Kao fabricated a low loss
glass fibre, giving a loss of 1000 dB/km.
� In 1970, Corning glass works, U.S.A. developed a
low loss fibre giving a loss of 20 dB/km.
� By 1972, losses were reduced to 4 dB/km.
� Today, the best fibres have a loss of < 0.2 dB/km.
Contd..
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TRANSMITTERINFORMATION
CHANNEL(MEDIUM)
RECEIVER
Basic Communication System
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Continued
� In optical communication transmission in an
optical format is carried out by varying the
intensity of the optical power.( intensity
modulation)
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Types of information channels
� Unguided channels
- Atmosphere is an unguided type of channel
over which waves can propagate.
� Guided channels
- Two wire lines, coaxial cable and waveguide
are the examples of guided information
channels
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�Privacy
�No weather dependence and
�The ability to convey messages within, under
and around physical structures.
Advantages of Guided channels
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Basic Fibre–Optic Link
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Fibre Optics
Optical fiber is a new medium, in which information
(voice, data or video) is transmitted through a
glass or plastic fiber, in the form of light.
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Basic elements of Transmitters
Transmitter convert electrical signal to optical
signals which is transmitted through fibre.
� Electronic interfaces.
� Electronic processing circuits.
� Drive circuitry.
� Light source – LED/Laser.
� Optical interface.
� Output sensing and stabilization.
� Temperature sensing and control
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Basic elements of an Optical Receiver
� Receiver- receives the optical signals from the
fibre and convert the same to its electrical
equivalent.
� Detector [PIN photodiode/APD (Avalanche
photodiode)]
� Detector used in fibre optical communications are
semiconductor photodiodes or photo-detectors
which converts the received optical signal into
electrical form.
� Amplifier
� Decision circuits.
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Information Transmission Sequence
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The transmission sequences are:
� Information is encoded into electrical signals.
� Electrical signals are converted into light
signals.
� Light travels down the fiber.
� A detector changes the light signals into
electrical signals.
� Electrical signals are decoded into information.
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Fiber Construction
� Consists of Core and Cladding
� Core and Cladding are made up of same material
� The material used is optically transparent
� Silica or borosilicate glass will be the usual
material
� The R.I of the core will be slightly higher than the
R.I of the cladding
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Contd…
� The core and cladding dia in mm
140100
12562.5
12550
1258
Cladding (µ m)Core (µ m)
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Material choice for low loss Optical Fiber
� Pure silica glass synthesized by fusing Sio2
molecules.
� R.I. Difference between core and cladding is
realized by the selective use of dopants during
fabrication processes.
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� Optical Fibres are non conductive (Dielectric)
– Grounding and surge suppression not
required.
- Cables can be all dielectric.
� Electromagnetic immunity
– Immune to electromagnetic interference
(EMI)
– No radiated energy.
– Unauthorized tapping difficult.
Advantages of Fiber Optics
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� Large Bandwidth (> 50 GHz for 1 km length)
– Future upgradability
– Maximum utilization of cable right of way.
– One time cable installation costs.
Continued
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� Low Loss (5 dB/km to < 0.25 dB/km typical)
– Loss is low and same at all operating
speeds within the fiber's specified ban
– Long, unrepeated links (> 70 km is
operation).
– Inexpensive light sources available.
– Repeater spacing increases along with
operating speeds because low loss fibers
are used at high data rates.
Continued
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� Small, light weight cables.
– Easy installation and handling.
– Efficient use of space.
� Available in Long lengths (> 12 kms)
- Less splice points
� Security
– Extremely difficult to tap a fiber as it does
not radiate energy that can be received by
a nearby antenna.
– Highly secure transmission medium.
Continued
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� Security – Being a dielectric
– It cannot cause fire.
– Does not attract lightning.
– It does not carry electricity.
– Can be run through hazardous areas
� Universal medium
– Serve all communication needs.
– Non–obsolescence.
Continued
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� Common carrier nationwide networks.
� Telephone inter–office trunk lines.
� Customer premise communication networks.
� Undersea cables.
� High EMI areas (Power lines, Rails, Roads).
� Factory communication/Automation.
� Control systems.
� Expensive environments.
� High lightning areas.
� Military applications.
� Classified (secure) communication
Applications of Fiber Optics in Comm.
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Thank you