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Module 5 > 5.10 Fibre Optics > Flashcards

5.10 Fibre Optics Flashcards

1
Q

Define Numerical Aperture (NA)

A

Light gathering ability of the fibre.

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2
Q

Define attenuation

A

Loss of power, light pulses lose some of their energy. defined in dB/km

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3
Q

Define Dispersion

A

Phenomena that causes broadening or spreading of the light as it propagates through an optical fibre.

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4
Q

What is fibre optic made from.

A

Glass and is incredibly pure.

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5
Q

What is the purpose of coating the class in plastic?

A

To form a mirror around the glass minimizing light losses by total internal reflection.

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6
Q

Basic operation of a signal?

A

Light travelling through the fibre bounces at shallow angles and stays within the fibre . analogue signals are converted to digital signals.

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7
Q

The laser that send the signals can operate at?

A

Several billion times per second.

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8
Q

Describe the 3 basic functions of fibre optic communications.

A

1.Convert electrical input signal to an optical signal.
2. Send the optical signal over an optical fibre.
3. convert the optical signal back to an electrical signal.

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9
Q

What does the transmitter do? what are the sources?

A

Converts input to optical signal, the 2 sources are LED’s and Laser diodes.

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10
Q

What does the receiver do?

A

Converts optical to electrical signal. amplifies and processes the optical signal. Uses PIN diode or Avalanche Photodiode.

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11
Q

What is the purpose of the coating/outer jacket/ buffer material?

A

Protect an optical fibre from physical damage.

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12
Q

What is the make up of the fibre optic cable

A

Core, Cladding, Coating/Buffer.

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13
Q

The cladding layer is made of a?

A

Diaelectric material.

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14
Q

The cladding performs which functions?

A

Reduces loss of light from core, reduces scattering loss.

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15
Q

The coating performs what functions?

A

Prevents fibre from absorbing surface contaminants, adds mechanical strength.

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16
Q

Low order modes penetrate only slightly into the cladding material, high order modes do what?

A

Penetrate further into the classing material.

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17
Q

Total internal reflection is due to?

A

Refraction

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18
Q

Optical fibres are classified into what 2 types?

A

Single mode and multimode(graded-index). Only difference is in the core size.

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19
Q

What is required to send multiple signals down the fibre?

A

Difference in frequencies gives each signal a different path because the angle of refraction is different.

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20
Q

Advantages of single mode fibres?

A

Much smaller diameter cable, used in long distance, lower signal loss and higher information capacity.

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21
Q

What determines the amount of modes sent down a fibre?

A

Corse size and Numerical Aperture.

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22
Q

How many modes can a multimode transmit?

A

Over 100 modes.

23
Q

Advantages of multimodes?

A

Permits the use of LEDS, leds are cheaperm less complex more durable .

24
Q

Disadvantage of single mode?

A

Must use Laser DIODES.

25
Q

Disadvantages of multimode?

A

As modes increase so does effect of modal dispersion (modes arrive at fibre end at slightly different times).

26
Q

The refractive index of the cladding will be?

A

Less than that of the core material.

27
Q

Attenuation is caused by?

A

Absorption, scattering and bending losses. the loss of optical power.

28
Q

Define Absorption

A

Conversion of optical power into another energy form such as heat.

29
Q

Define scattering?

A

Losses are caused by interaction of light with density fluctuations within a fibre.

30
Q

What can Bending do to the fibre?

A

Causes attenuation, bending loss classified by bend angle?

31
Q

What are the 2 types of bending loss

A

Micro bend or Macro Bend.

32
Q

What conditions can cause microbending?

A

Uneven coating and improper cabling procedures.

33
Q

What causes Macro bends?

A

Changes directions quickly with very small bend radius, they can become a great source of loss.

34
Q

What can a macrobend do to the fibre mode.

A

If the bend is sharp convert the signal to a high order mode with greater losses radiated out of the fibre.

35
Q

Define dispersion?

A

Spreads the optical pulse as it travels.

36
Q

What precautions need to be observed for the safety and handling of fibre optics?

A
  1. Dont look into cable
  2. Dont place heavy/hard items on cable
    3.Protective caps
    4.never pulled tight or shrap corners
    5.connectors always clean
    6.dont kink or crush
  3. Only trained people install.
37
Q

What are the 2 broad categories of fibre optic splices?

A

Mechanical and Fusion

38
Q

Describe mechanical splicing

A

Permanent connection, using glass, plastic, metal and ceramic tubes and v groove devices.

39
Q

Describe Fusion Splicing.

A

Localized heat to melt or fuse the ends together, inspected using a microscope, used on aircraft. Longer to complete than mechanical.

40
Q

What must a fibre optic connector allow for?

A

Repeated disconnects/reconnects without significant loss of light transmission.

41
Q

What type of connector is this?

A

Butt type.

42
Q

What type of connector is this?

A

Expanded beam

43
Q

What is less critical an expanded beam coupling’s?

A

Fibre separation and lateral misalignment.

44
Q

What are the 2 types of optic couplers?

A

Active and Passive.

45
Q

What does the active coupler do?

A

Electronic devices that split or combine the signal electricity and use fibre optic detectors and sources for input and output.

46
Q

What does a passive coupler do?

A

Redistributes the optical signal without optical to electrical conversion.

47
Q

An optical splitter is a passive device that?

A

Splitsd the optical power carried by a single input fibre into the two output fibres.

48
Q

An optical combiner?

A

Passive device combining two inputs into 1.

49
Q

Describe the X coupler.

A

Combines the functions of the splitter and combiner. combines and divides the optical from two inputs.

50
Q

Advantages of fibre optics

A

1.Lighter weight/size
2.Reduction of crosstalk
3.Immunity to electromagnetic interference.
4.Lower signal attenuation
5.Wide bandwidth
6Lower cosrt
7.safety
8.Corrosion resistance.

51
Q

What are some disadvantages of fibre optics?

A

Stringent coupling requirements, special techniques and equipment, ultra clean enviroment.

52
Q

What systems can a fibre optic system manage on an aircraft?

A

Propulsion and flight controls.

53
Q

Why do flight data recorder use fibre?

A

Because it can collect 1000’s of inputs at once.

Module 5 (10 decks)

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