F_Introduction to Optical Fibre Cable

8/3/2019 F_Introduction to Optical Fibre Cable

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Introduction to Optical Fibre Cable


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TRANSMITTER

INFORMATION

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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Basic FibreOptic Link

FibreDriver Source DetectorRegen.

Transmitter Receiver


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Fibre Optics

Optical fiber is a new medium, in whichinformation (voice, data or video) istransmitted through a glass or plastic fiber, inthe 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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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 ( m)Core ( m)


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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 operatingspeeds within the fiber's specified ban

Long, unrepeated links (> 70 km is

operation) Inexpensive light sources available

Repeater spacing increases along withoperating 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 antennaHighly secure transmission medium

Continued


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Security

Being a dielectric It cannot cause fireDoes not attract lightning It does not carry electricity

Can be run through hazardous areas Universal mediumServe all communication needsNonobsolescence

Continued


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Light Propagation Through O.F

Rarer to Denser medium

- Refracted rays move towards the normal

Denser to Rarer medium

- Refracted rays move away from normal


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Critical angle:- The angle of incidence in the densermedium for which the angle of refraction is 90

When the angle of incidence is greater than the

critical angle, Total Internal Reflection occurs

Refractive Index of core is 1.48

Refractive Index of cladding is 1.46

Contd..


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Total Internal Reflection

n1

n2

n1

n2

n1

n2

Angle of incidence

Angle of Refraction

Light is bent away from theNormal

Light does not enter secondmaterial

Light is reflected in the samematerial

Angle of incidence Angle of reflectionCritical angle

(Note:- n1 is greater than n2)


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Total Internal Reflection


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The optical fibers can be classified inthree ways:

-Material- Size (or Mode)

- Refractive Index

O F Classification


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Optical Fiber Parameters

Wavelength

Frequency

Window

Attenuation

Dispersion Bandwidth

Numerical Aperture


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Sources of Loss in Fibers :The losses occurring in

fibers can be attributed to three main causes

1. Absorption

2. Scattering

3. Geometric effects


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Splice

Permanent connection between two fibres

Involves cutting of the edges of the two fibres tobe spliced

Alignment of the cores of the fibres to beconnected is important to reduce splice loss


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Splicing Methods

Single Fiber Mechanical splicing

Adhesive bonding or Glue splicing

Temp. Mechanical splicing

Fusion Splicing


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Fusion Splicing

Most popular splicing technique Achieved either through electrical arc or

through gas flame Splicing loss can be minimized as low as 0.01

dB/joint Splice joint needs mechanical protection and

protection from moisture. For this epoxyresin coating and heat shrinkable tube are

used


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Fusion Splicing Contd

Suitable for SMF for use in long haul network

The splice loss indicated by the splicing

machine is only an estimated loss.

After every splicing is over, the splice lossmeasurement is to be taken by an OTDR


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F_Introduction to Optical Fibre Cable

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