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source of figure: http://fiberoptic101.blogspot.fi/2010/11/history-of-fiber-optic.html
Principle of operation
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Fiber optical cables are highly transparent, cylindrical conduits for light. These cables are formed of two materials with different refractive indices. This creates a optimal waveguide for transmitting light. When light enters the fiber made of material with higher refractive index than the cladding surrounding it, it stays inside the material due to total internal reflection and is thus transmitted forward.
Index of refraction
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Index of refraction is a measurement of speed of light in material. By definition, vacuum has refractive index of 1(c in vacuum = 1). The higher the index, the slower the light will travel in the material. Typical value for fiber core is 1,62 and for the cladding 1,52.
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