July 27, 2022
In this chapter of AS/A-level Physics, we will talk about Refraction and Signal Waves.
Total Internal Refraction
Optical Fibres use Total Internal Reflection
- Step – index optical fibres themselves have a high – refractive index but are surrounded by cladding with a lower refractive index to allow total internal reflection + protects fibre from scratches (light could escape)
- Light shone in at one end of the fibres, its narrow so light always hits a boundary between the fibre and cladding at an angle bigger than the critical angle --> all light T.I.R from boundary to boundary
Dispersion & Absorption
Cause signal degradation
In AS/A-level Physics, absorption causes loss in amplitude, some energy is from what the material is made up of à causing loss of (A) of signal being reduced
Dispersion causes pulse broadening
Two types:
- Modal dispersion – light rays enter fibre at different angles causing different paths. Rays will take longer to travel. Single mode fibre only light take one path --> stopping modal dispersion
- Material dispersion – light consists of different wavelengths that travel at different speeds à light reaching end of fibres faster than others --> monochromatic light stops this
In AS/A-level Physics, both lead to pulse broadening, due to overlap confusing the signal
You have finished this chapter! Well done!