Fibre Optics Overview

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Questions and Answers

What is one major advantage of using optical fibers over conventional copper cables in aircraft systems?

Lighter weight (correct)

Greater size and bulk

Higher susceptibility to electromagnetic interference

Higher cost of materials

How does the bandwidth of optical fibers compare to that of copper cables?

Optical fibers have similar bandwidth to copper cables

Optical fibers support exceptionally wide bandwidth (correct)

Bandwidth is not applicable to optical fibers

Optical fibers have lower bandwidth than copper cables

What challenge is associated with the introduction of fiber optics in the civil aircraft industry?

Incompatibility with existing copper systems

Existing technology is too new and untested

Increased weight of systems

New set of problems and challenges for operation and maintenance (correct)

Which of the following statements about optical fibers is incorrect?

Optical fibers can transmit signals over shorter distances than copper Signup and view all the answers

What does bandwidth measure in a network connection?

The maximum data transfer rate over a specific connection Signup and view all the answers

What can result from the reduced weight due to fiber optics in aircraft?

Significant fuel savings due to overall weight reduction Signup and view all the answers

Which of the following is NOT an advantage of optical fibers mentioned?

Heavy weight Signup and view all the answers

What is the diameter of optical fibers compared to a human hair?

About the same as human hair Signup and view all the answers

What phenomenon allows light to propagate along the core of an optical fiber?

Total internal reflection Signup and view all the answers

Which factor has the most significant influence on the attenuation coefficient of an optical fiber?

Quality and consistency of the glass Signup and view all the answers

Why are multimode fibers still used in certain applications despite the advantages of monomode fibers?

They are easier to cut and align. Signup and view all the answers

What type of fiber-optic cable did the Boeing 777 utilize for onboard data communications?

Monomode fiber Signup and view all the answers

What is the maximum data rate that the ARINC 636 standard supports?

100 Mbps Signup and view all the answers

Which of the following is NOT a cause of attenuation in optical fibers?

Surface friction from cladding Signup and view all the answers

What type of optical fibers are commonly used in high-speed data communication systems due to low attenuation characteristics?

Monomode fibers Signup and view all the answers

Which of the following describes the effect that primarily occurs at the core/cladding boundary in optical fibers?

Scattering Signup and view all the answers

What is the primary purpose of the guide pins in the connector optical components?

To ensure alignment between plug and receptacle Signup and view all the answers

What indicates that a correct connection has been made between the plug and receptacle?

The red band on the receptacle is at least 50% covered Signup and view all the answers

What mechanism prevents the optical fibre from being damaged due to over-tightening of the connector?

Buffer stop by the pins in the plug Signup and view all the answers

What is essential to ensure low loss and efficient coupling when assembling optical fibre connectors?

Maintaining cleanliness of the contact area Signup and view all the answers

Which feature of the connector design helps start the connection straight when joining the plug and receptacle?

Three start threads on the plug and receptacle Signup and view all the answers

What is one of the disadvantages of optical fibres?

Industry resistance to new technology Signup and view all the answers

What principle allows light to travel through an optical fibre?

Total internal reflection Signup and view all the answers

Which part of the optical fibre has a higher refractive index?

Core Signup and view all the answers

What happens to a light wave when it travels from a medium of lower refractive index to a higher refractive index?

It slows down and bends towards the normal Signup and view all the answers

Why is it important for optical fibres that the cable bends have a sufficiently large radius?

To minimize light losses and maintain strength Signup and view all the answers

What is the main composition of the core in an optical fibre?

Silica glass Signup and view all the answers

What occurs during the process of refraction in optical fibres?

Change in direction and speed when passing between media Signup and view all the answers

What must be true about the angle of incidence for light to propagate in an optical fibre?

It must be larger than the critical angle Signup and view all the answers

What is the primary function of the protective buffer in a fibre-optic cable?

To protect the fibres during manufacture and increase mechanical strength Signup and view all the answers

What material is typically used for the outer jacket of a fibre-optic cable?

Thermoplastic Signup and view all the answers

Which of the following is NOT a requirement for fibre-optic connectors?

High loss Signup and view all the answers

How is the total loss computed when using multiple connectors?

By adding the individual loss values together Signup and view all the answers

What diameter do the optical fibre strands in a typical fibre-optic cable have?

140 μm Signup and view all the answers

What material is used for the filler strands in a fibre-optic cable?

Polyester Signup and view all the answers

Which component helps to provide additional strength to the fibre-optic cable assembly?

Aramid yarn strength member Signup and view all the answers

What is the approximate overall diameter of a typical fibre-optic cable?

0.2 inches Signup and view all the answers

Study Notes

Fibre Optics

Fibre optics (optical fibres) are thin strands of pure glass, about the diameter of a human hair.
Bundles of optical fibres are called optical cables.
These cables transmit light signals over long distances.
Optical fibres have been used for long-haul data communications and in local area networks (LANs).

Advantages of Fibre Optics

Light weight and compact size.
Wide bandwidth, supporting high data rates.
Resistance to electromagnetic interference.
Low attenuation.
High reliability and long operational life.
Electrical isolation.

Disadvantages of Fibre Optics

Industry resistance to new technology.
High precision required for cable fitting and connectors.
Concerns about mechanical strength of fibres.

Propagation in Optical Fibres

An optical fibre consists of a silica glass core surrounded by glass cladding.
Light travels within the core, bouncing off the cladding through total internal reflection.
The cladding does not absorb light, allowing for long-distance transmission.

Attenuation in Optical Fibres

Optical fibre attenuation is caused by: absorption, scattering in the core, scattering at the core/cladding boundary, and losses due to radiation at bends in the fibre.
Attenuation varies widely with wavelength.
Monomode fibres offer low attenuation and wide bandwidths.
Monomode fibres are smaller than multimode fibres, requiring precise cutting and alignment for connectors.

Fibre-Optic Cable Construction

A typical fibre-optic cable includes:
- 5 optical fibres
- 2 Filler strands
- Separator tape
- Aramid yarn strength member
- An outer jacket.
The cable diameter is approximately 0.2 inches.
Individual fibres have a diameter of 140 μm (approximately 0.0055 inches).
Fibres are colour-coded for identification.
Filler strands are made of polyester.
Separator tape is made from low friction polyester, making the cable more flexible.
Aramid yarn provides mechanical strength and protection.
The outer jacket, usually purple, prevents moisture ingress and provides insulation.

Fibre-Optic Connectors

Fibre-optic connectors are essential for reliable, robust, precise, repeatable, and low-loss connections.
Connector loss can be quoted in dB, and is equivalent to several kilometres of low-loss fibre.
A typical connector arrangement includes:
- Alignment keys and grooves
- Guide pins and cavities
- Coloured alignment bands
- Three start threads.
The connector alignment keys align the optical components.
The guide pins in the plug fit into cavities in the receptacle.
Ceramic contacts make physical contact when properly connected, allowing the light to pass through.

Key Points

Accurate alignment and cleanliness are crucial for low-loss coupling with connectors.
Optical fibres emit invisible but intense light; disconnect cables before examining the face or contacts.

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Description

Explore the fundamentals of fibre optics, including their advantages, disadvantages, and the principles of light propagation within these optical fibres. This quiz covers essential topics like data transmission, cable structure, and industry challenges related to fibre optic technology.