Fiber Optics Quiz

Fibre Optics (5.10) Learning Objectives

• List fibre optic handling and installation precautions
• Recall the advantages and disadvantages of fibre optic data transmission over electrical wire propagation (Level 1)
• Identify a fibre optic data bus (Level 1)
• Recall fibre optic related terms (Level 1)
• Identify fibre optic connectors, mechanical and fusion splice terminations (Level 1)
• Identify fibre optic couplers, control terminals, and remote terminals (Level 1)
• Recall applications of fibre optics in aircraft systems (Level 1)

Common Fibre Optic Technology Terms

• Numerical Aperture (NA) defines which light will be propagated and which will not.
• Attenuation is the loss of power during transit, measured in decibels per kilometre (dB/km).
• Dispersion refers to phenomena that cause a broadening or spreading of light as it propagates.

Optical Fibre Cables

• Imagine a flexible plastic pipe with a mirrored interior; light reflects off the sides, allowing communication.

Fibre Optic Technology

• Fibre optics is a glass cable enabling light transmission, comparable in thickness to human hair.
• Coating the glass in plastic creates a mirror effect, minimizing light loss.

Optical Fibre Communications System

• Fibre optic data links convert electrical signals into optical signals, send them through fibre, and convert them back to electrical signals.
• Components include transmitter, optical fibre, and receiver.
• Transmitter converts electrical to optical, receiver converts optical to electrical (usually using LEDs or laser diodes).

Basic Structure of an Optical Fibre

• Consists of core, cladding, and coating.
• Coating protects from damage; cladding has a lower refractive index than the core (critical for total internal reflection).
• Light propagates within the core by continual reflection.

Fibre Optic Cable Losses

• Attenuation is the loss of optical power as light travels through the fibre. This can result from absorption (conversion to other energy forms like heat), scattering (light interaction with density fluctuations) and bending (micro/macro bends causing light leakage).

Bending Losses

• Microbends: microscopic bends, often caused by cabling issues, increasing loss.
• Macrobends: sharp bends causing light loss to higher-order modes.

Dispersion

• Dispersion is when the optical pulse spreads, reducing system bandwidth (information carrying capacity).
• Various propagation modes and refractive index variations cause this spreading.

Fibre Optic Cable Handling Precautions

• Never look directly into a fibre optic cable or connector.
• Don't place heavy items on the cable.
• Keep protective caps on unplugged connectors.
• Avoid tight bends or sharp corners.
• Ensure connections are clean.
• Avoid crushing and kinking the cable.
• Only trained personnel should handle the installation/repair of fibre optic systems.

Fibre Optic Terminations (Splices and Connectors)

• Fibre optic splices are permanent connections between fibres (mechanical or fusion).
• Mechanical splices use alignment fixtures and materials; are stable and less expensive.
• Fusion splices melt fibre ends together - more complex but usually more efficient.
• Fibre optic connectors allow disconnection of fibres without significant light loss.

Fibre Optic Couplers and Remote Terminals

• Fibre optic couplers combine or divide optical signals among multiple fibres. This enables signal redistribution.
• Couplers can be either passive (physical joining) or active (electrical conversion).
• Optical splitters/combiners/X-couplers divide/combine optical signals.
• Terminals have fibre pigtails (short lengths of fibre) and usually have connectors.

Aircraft Applications of Optical Fibre

• Fibre optic data buses have advantages over coaxial cable such as, weight and space savings, immunity to electromagnetic interference, lower attenuation, wider bandwidths, lower costs, and better safety features.
• Used in aircraft for systems such as flight control, fuel monitoring, and data recording.
• Fibre optic gyroscopes are a vital part of aircraft navigation systems by measuring the aircraft's orientation and movement.

Disadvantages of Fibre Optic Data Communication

• Stringent coupling requirements (precise connections are needed for efficient signal transfer).
• Need for special techniques and equipment.
• Need for specialised clean and precise work environments to avoid pollution from particle interference.