4 Sep 2014

Shedding Light on Rogue Waves

From Our Changing World, 9:34 pm on 4 September 2014

Rogue waves, also known as freak waves, monster waves, or killer waves, don’t just occur at sea.

A photo of the inside a pulsed fibre laser showing the optical fibres in coils

Inside a pulsed fibre laser showing the optical fibres in coils Photo: RNZ / Ruth Beran

They can also happen with pulses of light.

“Rogue waves are well known in literature about the oceans,” says Associate Professor Neil Broderick from the University of Auckland. “Sailors would report tales of giant waves that came out of nowhere and overturned their boat.”

For a long time, these accounts were dismissed as folklore, until people started studying the waves from satellite photographs, and realised that the sailors were telling the truth.

“Then a few years ago people realised that the same laws of physics that describe the propagation of ocean waves, describe light propagating down an optical fibre,” says Neil.

This means that optical lasers can be used to simulate the behaviour of ocean waves, a process that is quicker and more controlled.

“So if we get a handle of what’s going on in optical fibre, we can then try and feed back to better design for ships,” says Neil.

Neil’s team are creating pulsed fibre lasers both for research but also for sale.

A photo of Neil Broderick and Patrick Bowen with the equipment that measures light in the optic fibres

From left to right: Neil Broderick and Patrick Bowen with the equipment that measures light in the optic fibres Photo: RNZ / Ruth Beran

“Fibre lasers are starting to grow in importance,” he says.

Lasers come in different shapes and sizes. The cheapest and most ubiquitous lasers use semiconductor lasers, for example, the ones used in the scanners in supermarkets or in laser pointers. Other types of lasers use gas and are often found in scientific and commercial settings.

Pulsed fibre lasers, on the other hand, use the same optical fibres used in telecommunications. These fibres are about the width of human hair, can be added together like LEGO, and can be coiled to make very compact devices.

The light used in these lasers is not visible to the naked eye because it is in the infrared part of the spectrum.

Ruth Beran discovered that Neil and his team are working on pulsed fibre lasers for industrial machining applications.

“If you want to cut away material, you want a very sharp burst of light because there’s lots of energy in a very short space of time,” says Neil. “That allows you basically to blow material off the surface.”

And understanding rogue waves will help build better lasers, he says.

“One of the fascinating things about rogue waves is firstly, they appear out of nowhere, and secondly, they tend to do a lot of damage,” says Neil.

So while rogue waves usually impact on ships, they also damage lasers.

“We get very high energetic pulses that will come through and burn up all of our components and we’ll have to go back and rebuild everything,” says Neil.

Understanding these rogue waves may ultimately help control them, enabling scientists to either prevent them, or produce them on demand.

“Then we can use these extremely high bursts of light for our advantage,” he says.

In particular, more light, means higher intensities, and this would be good the pulsed fibre lasers that Neil is making for micromachining applications.

Get the RNZ app

for easy access to all your favourite programmes

Subscribe to Our Changing World

Podcast (MP3) Oggcast (Vorbis)