EASA Part 66 Module 5.10 : Fibre Optic

5.10 FIBRE OPTIC

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WHAT IS FIBRE OPTIC

• Flexible, transparent fiber made of a pure glass (silica).

• It functions as light pipe, to transmit light between the two ends of the fiber.

• It is an opto-electronic component (sensitive to infrared, ultra violet that convert to electrical signal)

• Use in medical, telecomunication and aviation field.

ADVANTAGE

• Larger data carry – up to 3300MHz• Low loss of signal• Smaller diameter, lighter-weight cables• Cross talk negligible – no effect to other cable(signal)• Immunity to electromagnet interference• Greater security – immune to wiretapping• Greater safety – free from spark• Low cost – material sand• Long life span – double from conventional cable• Greater reliability – resistance to corrotion and temp

DISADVANTAGE

• Installation cost high• Fragile than wire• Required special equipment for testing• Required special skill and equipment to

splicing it

OPERATION

Transmitter (Light Source)

Receiver (Light

Detector)

Optical Coupling

Transmitters: Light-emitting diodes (LED's) and Injected Lasers Convert electrical signal to optical signal.

To send the optical signal over an optical fibre

Receivers: Photodiodes and Phototransistors.To convert optical signal back to an electrical signal

Optical Coupling:Opto-isolators and Optical fibres

LIGHT

• Light wave more shorter than electromagnetic wave (radio/radar).

• Velocity 3x108m/s, change depend on medium.

• Propogation of light :– Reflection– Refraction– Dispersion

REFLECTIONThe light reflect back with same angle if surface is smooth

The light diffuse reflection if surface is irregular/rough

REFRACTIONBending of light when passes through other medium

Air 100

Diamond 242

Ethyl Alcohol 136

Fused Quartz 146

Glass 155 - 19

Optical Fibre 15

Water 133

Index of refraction

DISPERSION

• Seperation of white light to the various color.• Different color have a different wavelength,

different velocity and different index of refraction.

CABLE STRUCTURE

Core - glass, polystyrene, polymethylmethacrylic.Cladding - glass, silicon or Teflon.

High strength and tension resistanceTypically cable made in length of 1-3 km without splices.

TYPE OF CABLE

Wide graded index multimode optical fibre

Single mode step index optical fibre

Large-core plastic-clad silica optical fibre

HOW IT WORKSingle Mode

Multimode

ACCEPTANCE ZONE

NUMERICAL APERTURE

• Its a colecting power of an optical fibre• Its value from 0 to 1, • Larger NA mean the greater amount light

accepted by fibre.• NA is function of refractive index of the fibre.• Define as NA = sinA

PULSE SPREADING

• The amount of acceptance signal have a limited frequency due to the pulse(light) is being dispers inside the cable.

• Dispersion tend to slow down the speed of the light.• Two form of dispersion :

– Chromatic disepersion : Different speed due to color

– Modal dispersion : Zigzag ray reach the end of cable later than straight ray

• Total Dispersion = Chromatic + Modal

CONSEQUENCES

• The fastest the pulse travel, the worse spreading its get.

• Need to limit the frequency of the signal travel

ATTENUATION

• Reduction of signal strength due to :1. Atomic Absorption :

Atom of material absorb some of the light2. Scatering by Flaw and Impurities :

Depend on size of scatering particle inside the cable

3. Reflection by Splices and Conector : Some light are reflected back even for

perfect splice or conector.

JOINING OPTICAL FIBRE

– Fusion Splicing• Allign manually using micromanipulators and

microscope system.• End of fibre are melt together using electric arc.• Near perfect splice can lose as low 0.2dB

– Mechanical Splicing• Two fibre end held together in splice equipment which

automatically allign the two fibre.• Clamp it and expose to ultra-violet light to cures the

cement

SPLICING ERROR

• The end of fibre must be precisely line each other to enable light pass from one fibre to another.

• Typicall allignment error :

FIBRE OPTIC CONNECTOR2 Type Conector A and B, both have :- Allignment key and grooves- Guide pin and cavities- Color bands- Three start threads

A type :- 3 or 5 optical fibre - Multichannel- very low loss

B type :- For LRU- Multichannel- For more frequent conection and disconection

FIBRE OPTIC IN AIRCRAFT

• Advantage on aircraft :– Can carry more data– Less weight– Immune to electromagnetic radiation

• Purpose:– Network system: (OLAN),(AVLAN),(CABLAN)

AIRCRAFT NETWORK SYSTEM

• Flight attendent– Keep sales data– Enable and disable passenger functions– Control the distribution of video entertainment– Select boarding music

• Passenger– Video and menu screen– Games– Inflight sales catalogue– Instruction for telephone call– Ground to airplane telephone pages– Special video channel selection

ONBOARD LAN

CABIN LAN