introduction to optical fibre cable

8/3/2019 Introduction to Optical Fibre Cable

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Introduction to Optical Fibre Cable



TRANSMITTER

INFORMATION

CHANNEL

(MEDIUM)

RECEIVER

Basic Communication System



In optical communication transmission in anoptical format is carried out by varying theintensity of the optical power. (Intensity

modulation)



FibreDriver Source DetectorRegen.

Transmitter Receiver



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



Transmitter convert electrical signal to opticalsignals 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



Receiver- receives the optical signals from thefibre and convert the same to its electricalequivalent

Detector [PIN photodiode/APD (Avalanchephotodiode)]

Detector used in fibre optical communications aresemiconductor photodiodes or photo-detectorswhich converts the received optical signal intoelectrical form

Amplifier Decision circuits



Information Transmission Sequence



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 usualmaterial

The R.I of the core will be slightly higher thanthe R.I of the cladding



The core and cladding dia in mm

140100

12562.5

12550

1258

Cladding ( m)Core ( m)



Optical Fibres are non conductive (Dielectric)

–Grounding and surge suppression notrequired

- Cables can be all dielectric

Electromagnetic immunity – Immune to electromagnetic interference

(EMI)

–No radiated energy

–Unauthorized tapping difficult

Advantages of Fiber Optics



Large Bandwidth (> 50 GHz for 1 km length)

– Future upgradability

– Maximum utilization of cable right of way

–One time cable installation costs

Continued



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



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



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



Rarer to Denser medium

- Refracted rays move towards the normal

Denser to Rarer medium

- Refracted rays move away from normal



Critical angle:- The angle of incidence in thedenser medium for which the angle of refractionis 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..



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)



The optical fibers can be classified inthree ways:

-Material- Size (or Mode)

- Refractive Index

O F Classification



Wavelength Frequency Window Attenuation

Dispersion Bandwidth Numerical Aperture



Sources of Loss in Fibers :The losses occurring in

fibers can be attributed to three main causes

1. Absorption

2. Scattering

3. Geometric effects



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



Single Fiber Mechanical splicing Adhesive bonding or Glue splicing Temp. Mechanical splicing Fusion Splicing



Most popular splicing technique Achieved either through electrical arc or throughgas flame

Splicing loss can be minimized as low as 0.01dB/joint

Splice joint needs mechanical protection andprotection from moisture. For this epoxy resincoating and heat shrinkable tube are used



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

introduction to optical fibre cable

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