·
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
![broken image](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_auto/4936730/549049_310670.jpeg)
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
![broken image](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_auto/4936730/459227_36822.jpeg)
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
![broken image](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_auto/4936730/638267_7658.png)
You have finished this chapter! Well done!
![broken image](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_60/4936730/186016_459945.gif)