UNIT5 Fiber Optik

8/7/2019 UNIT5 Fiber Optik

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5.0 I NTRODUCTION TO FIBREO PTIC


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fibre Optic is a light pipe that use to carry a light beam froma place to other place.

Light is a electromagnetic signal like a radio wave. It can bemodulate by information and sent over the fibre-optic.

fibre optic cable used as medium (media) in electroniccommunication system.There are 3 main element/component in fibre opticcommunication system.

I. Transmitter (pemancar) @ light source-LED or ILDII. Receiver (penerima) @ light detector

-Pin Diode, APD or Photo transistorIII. fibre Optic


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F igure 5.1 : Basic Component for fibre OpticCommunication system


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fibre optic consists three parts:Core (teras)Cladding (salutan)Protective jacket / coating (Jaket Pelindung)

-fibre optic diameter is around 0.125 ~ 0.400

mm.


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Core - situated in middle of the fibre optic.to allow the light propagates along the core.

Cladding - material surround the core with alower refractive index

- cladding purpose is to :i. provide a total internal reflection (TIR).ii. Increase mechanical (tensile) strength.iii. Reduce scattering loss.iv. Protect the core from absorbing surface

contaminant.


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Protective - Outer coating made of plastic.

Jacket - Protective jacket function is to :i. Increase mechanical (tensile) strength.ii. Protect the fibre from external mechanical

force.iii. Prevent moisture to contact the fibre core/

cladding


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Advantages fibre Op tic C able O verCo nventi o nal E lectrical C ables .

i. Wider bandwidthii. Lower loss / attenuationiii. Light weight

iv. Small sizev. More strength and flexible.vi. Security.vii. Immune from EMI, R F I and EMP.viii. Safety.ix. Low costx. Immune from corrosions.xi. More reliable and easy to maintenance.


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5.1 A FIBRE O PTIC C OMMUNIC A TIONS YSTEM & I TS O PER A TION


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Information input - voice, video, stillpicture & computer data.

Coder or converter - convert analog signalsto digital pulses.

Light Source - convert digital pulsesto the light pulses.

*Digital pulses are used to flash a light source off & onvery rapidly.F ibre Optic - transmit the light

pulses along the fibreoptic over a long distances.

Coupler / Connector - couple the light from thelight source to the fibre opticand from the fibre optic tothe light detector.


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Light detector - convert the light pulsesto the digital pulses

(electric signal).Amplifier - amplify the digital pulses

at this point, digitalpulses are not apure digital signals.

Shaper - reshape the digital pulsesinto a pure digital

signals.Decoder - convert the digital

signals to the originalinformation voice,videoand still picture.


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5.3 FIBRE O PTIC M ODEThere are two basic ways of classifying fibre optic cables:i. Index of Refraction (Indeks Biasan).ii. Mode

Index of Refraction.Index of refraction is referring how the index of reflectionvaries across the cross section of the cable.

5.3.1 F ibre Optic Index.

There are two ways of defining the index of refractionvariation across a cable.

i. Step index (Indeks Langkah)ii. Graded Index (Indeks Gred)


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STEP INDEX IS RE F ERRING TO THE CORE WHICH HAS ONE CONSTANTINDEX RE F RACTION , N1 AND THE CLADDING ALSO HAS ONE CONSTANTINDEX RE F RACTION , N2 WHICH N1>N2.


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GRADED INDEX IS RE F ERRING TO THE CORE WHICH HAS THE MAXIMUM INDEXOF RE F RACTION AT CENTRE AND DECREASE GRADUALLY F ROM THE CENTRETOWARDS THE CORE /CLADDING INTER F ACE . T HE CLADDING HAS A CONSTANTINDEX O F RE F RACTION


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5.3.2 F IBRE OPTIC MODE .

Mode refers the number of paths for the light of ray incable.

There are two classification for fibre optic mode: single

mode & multimode

In single mode, light follow single path through the core.

In multimode the takes many path through the core.

There are 3 types of fibre optic cablei. Multimode step indexii. Single-mode step indexiii. Multimode graded index


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A) Multimode step index

Typical core diameter 50-100mThe large diameter core allows many mode of light go throughThe lights takes many hundreds of thousands of

path through the core before exiting the fibre.


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Because of the different lengths of the paths,some light take a longer time to reach the end of the cable than others.

The problem with this is that it stretches thelight pulses. The stretching of the pulses isreferred as a modal dispersion.

Suitable to used for short or medium range.


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B) Multimode graded indexTypical core diameter 50-85mIt have many modes of transmission through the cable, but

there are much more orderly and predictableBecause of the continuously varying index of refractionacross the core, the lights ray are bent and convergerepeatedly at certain points along the cable.The light near the edge of the core take a longer path buttravel faster since the index of refraction is lower.All modes or lights paths tend to arrive at the same pointsimultaneouslyThe result is that less modal dispersion


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C) Single mode step indexMono-mode,step index

Typical size,7-10mThe core is too small that it only allow one modego through it.The output pulse have the same duration withthe input pulse.No pulse stretching occurs.


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characteristicmultimode

Single modeStep index Graded index

Core Size 50-100m 50-85m 7-10m

Bandwidth Small

15-50Mhz/km

Medium

500-1500Mhz/km

Wide several thousand

Mhz/km

Transmission Range

Short and medium distance


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5.5 C ONNECTION & C OUPLINGConnectors are mechanical assemblies that allows :F ibre Optic to fibre optic connection.F ibre Optic to light source connection.F ibre Optic to light detector connection.Splicing is a process to joint fibre to fibre permanently.Common connector that used :i. V groove Alignment (sejajar lurah V )

F ig 5.11 V groove Alignment


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ii. F errule Surrounding the fibre


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iii. SMA connector

F irst generation connector.Used to connect both end SM and MM fibre.


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iv. SC connectorUsed o connect both end SM and MM fibre.It gives accurate position with the ferrule.Datacom


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v. ST connectorused to connect both end SM and MM fibre.Used spring lock to connect the fibre.Inter-building, intra building, security, navy.


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vi. F C/PC couplerUsed to connect both end SM and MM fibre.Used the spring and threads to connect the fibre.Datacom, telecomunication

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UNIT5 Fiber Optik