3.3 Refraction of light Flashcards
Define refraction
The change of direction of travel of light (or other wave) when its speed of travel changes e.g. when it passes from one material into another
What is refractive index?
The refractive index, n, of a material is defined by n = c/v where v and c are the speed of light in the material and in a vacuum respectively
What is the critical angle of a material?
The critical angle is given by sin(theta) = 1 / n where n is the refractive index of the material
What are the conditions for total internal reflection?
- The light ray is incident upon a boundary with a material of lower refractive index
- The angle of incidence is greater than the critical angle
How does total internal reflection occur?
- For a small angle of incidence, the fraction of power reflected is small
- As the angle of incidence increases, this fraction reflected increases
- At some angle of incidence, the critical angle, the angle of refraction is 90(degrees) and the refracted power is very low
- For angles of incidence greater than the critical angle, all the incident power is reflected, giving total internal reflection
Define multimode dispersion
Multimode dispersion is when data degrades in an optical fibre due to the different paths that light rays can take
What are the uses of optical fibres?
- Data transmission in local, regional, and intercontinental networks
- Remote imaging systems
- Investigating otherwise inaccessible locations
What is the basic design of an optical fibre?
A typical optical fibre consists of a single glass thread, the central part of which (the core) carries the light signal, and the outer part of which (the cladding) keeps the signal in the core. This is then surrounded by an outer layer of plastic
How do optical fibres function?
Light travels down the inside of the core, and for light that is incident to the core-cladding boundary at a greater angle than the critical angle, is totally internally reflected back into the core
