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Optical Fibres
Optical fibres are simply 'reflective tubes'. If you shine light down the tube, it keeps going because it bounces from the walls. But Optical fibres are used to carry signals in the form of pulses of light over distances up to 50km. They do this by Total Internal Reflection. That's why optical fibers can guide light for such long distances - because the walls of the fibre don't absorb any light at all as long as the angle of incidence is greater than the critical angle. Total Internal Reflection causes 100% reflection. In no other situation in nature does this occur, so it is unique and very useful as it is 100% efficient at transfering the light energy. There are two conditions necessary for Total Internal Reflection to occur:
When light hits the boundary between two substances it gets reflected and refracted. Light principally refracts at low angles of incidence, but as the angle of incidence increases the percentage of the light energy that reflects rather than refracts increases until the internal surface acts as a mirror. This is called TOTAL INTERNAL REFLECTION, because all of the incident light energy is reflected. The reflection, then, is even better than at a mirror's surface because 100% of the light energy is reflected by TIR whereas reflection at a mirror surface is never 100%.
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if you've ever looked
at optical fibres, you'll notice that they are NOT METALLIZED like a mirror,
they have no silvery coating. They look like transparent fishing line. 
See here for the construction of a fibre optic cable
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