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  • Anne Jing

Fibre Optic Cables: Data at the Speed of Light Explained.

Updated: Aug 22, 2020

We know that light travels fast, very fast, almost 300,000,000 m/s fast. That's very fast. Wouldn't it be great if our internet could travel that fast? Fiber optic cables use light to transmit data. This is more efficient than traditional copper wired cables as the speed of light is far greater than the speed of electrons. With electric cables, electrons will follow the path of the cooper wire but how do we control the path of the light in a fibre optic cable? Let's explore this through an experiment.


Let's take a bottle of water and shine a laser though it. The light will show up on the other side of the bottle and on wall. Now if we poke a hole and let water spout out, we notice that the light is "contained" within the water.



Can you guess why and how? I encourage you to pause and think about why the light will bend with the water. Why doesn't the laser leave the spout of water before it hits the ground?


Stuck? Maybe *reflect* (hint hint) back on high school optics. The concept isn't all the complicated.


The same phenomenon that is occurring here is what allows fibre optic cables to operate - its called total internal reflection.


When light exits from water and goes into air (a change of medium), the light bends - this is called refraction. The amount bending depends on the indices of refraction of the two media. By increasing the angle of incidence, more and more of the light is reflected. After a certain angle, all of the light will be reflected.



When the light leaves the bottle and enters into the spout of water, the light will "bounce" around in it. As it bounces from side to side, the angle of incidence increases. At a certain point, all the light will be reflected back into the spout of water and thus, is "contained" within it.



This is how fibre optic cables "contain" the light within the cable for data transmission. Now, obviously different materials are involved but its the same principle. The cladding has a lower index of refraction (acting like the air in the experiment) and the core has a higher index of refraction (acting like the water).



Through total internal reflection, we are able to control the path of a light. Simple!



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