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In this chapter of AS/A-level Physics, you will learn about dispersion & absorption.
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)
- In AS/A-level Physics, 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
- Absorption causes loss in amplitude, some energy is from what the material is made up of --> 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 pathà stopping modal dispersion
- Material dispersion – light consists of different wavelengths that travel at different speedsàlight reaching end of fibres faster than othersàmonochromatic light stops this
- In AS/A-level Physics, both lead to pulse broadening, due to overlap confusing the signal
That's it! You got it!!
