Fibre Optic Communication

What is it?

It is a communication technology that makes use of light to carry data and information along a glass fibre as thin as a human hair..

How does it work?

The part that carries the light from one place to another is called a fibre-optic cable, sometimes called a 'light-pipe'. This describes its function very well as a fibre optic cable is designed to allow light to pass through it with very little loss.

What is is made of?

A high quality communication cable is made of glass (or silicon dioxide to be precise). Normally you think of glass as being brittle and easily broken, but when it is made thinner than a human hair, it is very flexible and strong.

Of course it is not just simple glass. The outside of the cable is designed to reflect light inwards whilst the middle core is as transparent as possible. So when a beam of light is 'launched' into one end of the cable, it bounces along the cable until it reaches the other end. This type of cable, one that uses reflections to work, is called a 'multi-mode' cable.

There are also 'single-mode' fibre that use a different effect and works for longer distances - but it is more expensive.

You can also get fibre-optic cable made of plastic. This is a good solution for very short distances (a few metres) so you will see it used in hi-fi systems to carry audio information from a pre-amp to a main amp without loss of quality..

Is it just any light?

No, fibre optic is transparent at a very precise wavelength of light i.e. colour. Typically it is very transparent at 1550 nm (nano metre is 1 thousand millionth of a metre). We would see it is a reddish colour.

How is the light created in the first place?

There are two main ways.

1. A Light Emitting Diode (LED).

LEDs are very cheap and do produce reasonably pure light of the right wavelength. So they are used for low power, short distance applications such as local area networks. LEDs are good for a few kilometers and a speed of about 100Mb/sec

Only about a hundredth (1%) of the light it produces is useful for the cable. But even that is good enough for smallish distances.

2. Laser Beam

This is more expensive but has a far higher purity than LED. This means that nearly half the light is useful in the cable, so it is very efficient.

Power can be also be much higher, so allowing far greater distances to be covered.

How fast can it transmit data?

Transmission speeds can be extremely high.

For example, recently a 160Km length of cable carried information at 14,000 Gigabits / sec. This kind of performance is used in oceanic cables that connect continents together.

How does it compare to good old copper?

It is very tough - it does not corrode, unlike copper and it is not affected by electrical interference such as lightning or stray radio signals.

But it is more expensive, so copper is still used for most local communications.

Where is fibre-optic communication mainly used?

The heart of the UK telephone system runs on fibre-optic because it is almost the perfect solution - no interference, massive speed, easily carries voice, television, internet, and telephone calls all down the same cable. But it isn't cheap!

Aircraft use fibre-optic cables to transmit data to different systems around the plane as nothing can interfere with it. Note the weak link though - the receptor at one end and the amplifier at the other, each of these are electronic devices and so are susceptible to radio and electronic interference.

What about the future?

The big issue for the UK is how to deal with 'the last mile', that bit of copper cable that connects your telephone to your local exchange. If a fibre optic cable could replace this bottleneck, then broadband speed could easily be two hundred times quicker.

The problem is who will pay for it? The government is now allowing private companies to take over 'the last mile' hoping that they will make the investment.

In Korea, for example, it is common to have 100Mb/sec internet connections because they have invested in fibre-optics right to the home.

Challenge see if you can find out one extra fact on this topic that we haven't already told you

Click on this link: Fibre optic cable




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