Introduction to Optical Fiber Communication (2)

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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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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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� 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

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Introduction to Optical Fiber Communication (2)

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