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What Is Fibre Optics

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To put it simply, fibre optics is a technology whereby a signal like video, data or voice, is concentrated on a light beam and sent down a glass tube over large distances, with very little distortion and loss.

The principles of fibre optics are simple and easy to understand. All of us have seen the "broken straw" effect in a glass of water.image00.png

When light travels from air to a denser medium, like glass for example, the light slows down by a factor equal to the optical index of the material and this slow down in speed results in bending of the light.

 As shown in the example when we see an object from underwater, the object is not in the actual position as we think because light bends travelling from water to air. When this angle of entry is increased, there would come a stage when the light is reflected back into the same medium, as shown in ray 3. This angle is called the angle of Total Reflection. Fibre Optics uses this simple principle for transmission.

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5. Output Demodulator: This separates the signal from the light beam.


There are 3 different types of fibre optics cable available. These are:

1. Step Index.
This cable has a distinct index of refraction for the core and the cladding. It is the cheapest type of cable and causes deformation due to the various path lengths of the light ray. This is called modal distortion.

2. Graded index or multimode
In order to equalise the path lengths and improve pulse response, the multimode cable was developed. The index of refraction of the core is varied in smooth fashion. This would mean the angel of reflection would vary, which helps in equalising the path lengths and reduce distortion.

3. Single mode:
The single mode has the best pulse response because the diameter of the core is very narrow and the light wave virtually goes straight. Obviously this is the most expensive cable.


Fibre Optics signal transmission offers many advantages over existing metallic links. Some of these are:

1. Large Bandwidth

Fibre optics offers very high bandwidths as compared to copper wire.

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2. Termination
Termination of fibre optics cable is complex and requires special tools, better precision of workmanship and is more time consuming and therefore more expensive. Fibre optics cable has a very small diameter and requires specialised tools to align the cables correctly and then join them. The glass in the fibre optics core has to be grounded flat first to ensure correct alignment for proper and smooth termination. This looks complex, but many tools are available to ensure that the termination etc. can be achieved more easily.

3. Cable laying
The centre core of a fibre optics cable is made of glass. Extra precaution is required during cabling. Stretching of cable should be avoided as the glass core may crack. Also the cable bending is a major problem. Sharp bends could crack the cable but also the light beam bouncing of the glass core may not handle the bend and the light beam may ‘escape out’ of the core.

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Response to the question

Overall, this is a brilliant piece of work, explaining everything about fibre optics at a GCSE level. You have explained the uses for fibre optics, how they work, as well as some background information. You have used a similar situation ...

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Response to the question

Overall, this is a brilliant piece of work, explaining everything about fibre optics at a GCSE level. You have explained the uses for fibre optics, how they work, as well as some background information. You have used a similar situation – the broken straw effect – to help convey your understanding. You have gone into detail, but not so much that it makes the piece too difficult.

Level of analysis

You have taken facts about fibre optics and explained the practical effect of these facts. You have used appropriate technical language without overcomplicating the piece. You have quite clearly understood the topic and the piece reflects this.

Quality of writing

Your spelling, grammar and language seem to be perfect throughout the piece. You have organised your points well and such the piece is easy to read. Your piece reads like a piece of GCSE, or even A-Level, coursework should do.

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Reviewed by pratstercs 22/02/2012

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