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Why does information travel 'faster' down fibre optic cable than copper wire?

As the name suggests, fibre optic technology uses pulses of light to carry data along strands of glass or plastic.

It's the technology of choice for the government's National Broadband Network (NBN), which promises to deliver speeds of at least 100Mbps.

When we're talking about 'speed' were actually talking about throughput (or capacity) — the amount of data you can transfer per unit time, says Associate Professor Robert Malaney from the University of New South Wales, School of Electrical Engineering and Telecommunications.

And fibre optics can definitely transfer more data at higher throughput over longer distances than copper wire. For example, a local area network using modern copper lines can carry 3000 telephone calls all at once, while a similar system using fibre optics can carry over 31,000.

So what gives it the technical edge over copper wires?

Traditional copper wires transmit electrical currents, while fibre optic technology sends pulses of light generated by a light emitting diode or laser along optical fibres.

"In both cases you're detecting changes in energy, and that's how you encode data.

"With copper wires you're looking at changes in the electromagnetic field, the intensity of that field and perhaps the phase of the wave being sent down a wire.

"With fibre optics, a transmitter converts electronic information into pulses of light — a pulse equates to a one, while no pulse is zero. When the signal reaches the other end, an optical receiver converts the light signal back into electronic information," explains Malaney.

The throughput of the data is determined by the frequency range that a cable will carry — the higher the frequency range, the greater the bandwidth and the more data that can be put through per unit time.

And this is the key difference — fibre optic cables have much higher bandwidths than copper cables.

"Optical fibre can carry much higher frequency ranges — note that light is a very high frequency signal — while copper wire attenuates or loses signal strength at higher frequencies," says Malaney.

Also, fibre optic technology is far less susceptible to noise and electromagnetic interference than electricity along a copper wire.

"You can send the signal for over 200 kilometres without any real loss of quality while a copper cable signal suffers a lot of degradation over that distance," says Malaney.

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Where to next?

Just as copper wire technology has improved from the telegraph line to co-axial cables and today's ADSL-2 internet connections, fibre optics will also improve in the future.

"Better quality glass will allow signals to travel for greater distances before they need to be regenerated.

"You can also increase capacity, because as well as the high bandwidth of the light pulses, you can also change the colour. So you can have a red light and a blue light going at the same time.

"This is called wavelength multiplexing, and it lets you put multiple channels on a single strand of fibre," says Malaney.

"Fibre optics lets you look at new applications in areas like medical examinations, government services, improved productivity, telecommuting, three-dimensional conferencing and working from home.

"Current technology is already looking at terabyte speeds and things will only get faster in the future.

"If 90 per cent of homes are connected to the NBN it will cause a paradigm shift with new ideas and innovations, things we haven't even thought about yet."

Associate professor Robert Malaney from the University of New South Wales, School of Electrical engineering and Telecommunications was interviewed by Stuart Gary.