Chapter 5 - Optics Flashcards
What is refraction?
The change of direction that occurs when light passes non-normally across a boundary between two transparent substances.
What is the refractive index of air?
1
Is the refractive index of the cladding in an optical fibre HIGHER or LOWER than that of the core?
Lower
Total internal reflection can occur at a boundary if…
…the incident substance has a larger refractive index than the other substance and the angle of incidence exceeds the critical angle.
What is the refractive index a measure of?
Optical density
The higher the refractive index of a medium, the ______ the wave passing through it.
The higher the refractive index of a medium, the slower the wave passing through it.
Total internal reflection occurs when…
Angle of incidence > Critical angle
The wave is incident on a medium with lower refractive index (as light entering a less optically dense material is refracted away from the normal).
Refraction occurs when…
Angle of incidence < Critical angle
What are optical fibres used for?
How do they do this?
Optical fibres are used to carry light signals.
Light waves travel through the optical fibre and are totally internally reflected every time they reach the core-cladding boundary.
Explain the features of optical fibres.
Fibre optic materials are highly transparent to reduce absorption. Absorption reduces amplitude of signals.
A very narrow core is used to prevent modal dispersion by minimising the difference in distance travelled by waves along different paths (angles).
Monochromatic light is used to prevent material dispersion as light of multiple wavelengths would consist of waves travelling at different speeds causing pulse broadening.
Modal and material dispersion cause pulse merging. Pulse merging causes data to be lost.
What is a coherent bundle?
A bundle of optical fibres in which the relative positions of each fibre are the same at both ends.
When light enters an optically denser medium it is refracted ______ the normal.
When light enters an optically denser medium it is refracted towards the normal.
