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So what stops the light from
leaking out as it travels along an optical fibre? This is
down to physics and something called total internal reflection
(TIR).
All transparent materials have a property known as refractive
index, which is simply a measure of how much light is bent
when passing through the surface of the material. When light
passes from a higher to a lower refractive index material,
some of the light passes through and some is reflected.
As the incident angle reaches what is known as the critical
angle, all the light is reflected (TIR!). |
A fibre is constructed
with a central core of slightly higher refractive
index relative to the surrounding cladding.
Any light that enters the fibre core at a shallow
enough angle will be trapped in the core and guided
until it reaches the far end (or a tight bend!).
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