Theory:

Mirage:
 
On hot summer days, a patch of water may be on the road. This is an illusion. During summer, the air near the ground becomes hotter than the air at higher levels. Hotter air is less dense and has a smaller refractive index than cooler air. Thus, a ray of light bends away from the normal and undergoes total internal reflection.
 
Total internal reflection is the main cause for the spectacular brilliance of diamonds and the twinkling of stars.

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Mirage
  
Optical fibres:
 
Optical fibres are bundles of composite glass/quartz fibres of high quality. A core and cladding make up each fibre. The refractive index of the core material is higher than the cladding material. The phenomenon of total internal reflection is used by optical fibres. When a signal in the form of light is directed at one end of the fibre at a suitable angle before emerging at the other end, it is subjected to repeated total internal reflection along the length of the optical fibre.
 
Optical fibres are widely used for the long-distance transmission of audio and video signals. Furthermore, optical fibres' flexibility allows physicians to look and work inside the body through small incisions without performing surgery.
 
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Optical fibres in dark
  
An Indian-born physicist Narinder Kapany is regarded as the father of Fibre optics.
Reference:
https://www.flickr.com/photos/ahtd/20875325628
https://commons.wikimedia.org/wiki/File:Looking_at_optical_fibres_in_the_dark.jpg