In this chapter of AS/A-level Physics, you will learn about dispersion & absorption.

1. 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)

1. 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

- 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:

1. 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
2. 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!!

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