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DWC Profile Investigator Stephane Coen

World Leaders in Optical Cavity Solitons

Stephane CoenIn November 2016 DWC Principal Investigator, Stéphane Coen was awarded the prestigious Hector Medal for his ground-breaking research into optical cavity solitons. These little bundles of light that travel around loops of optical fibre could offer a solution to one of the major limitations of the internet: the difficulty of storing data in the form of light. Stéphane’s group was the first to observe optical solitons in fibre loops back in 2010 and they have since proved they can be used to store optical data. Their recent breakthrough was discovering how to move the solitons as they travel around the loop, which offers a method of editing optical data on the fly. Stéphane and his colleagues Miro Erkintalo and Stuart Murdoch have become world leaders in the field.

The internet is powered by light. Every email, Skype call and YouTube video travels in the form of optical data through a complex network of optical fibres to reach us. New Zealand is connected with the rest of the world by a handful of optical fibres the width of human hairs. You can imagine the congestion as data arrives from thousands of locations, just like traffic building up at the onramp to a motorway. Any time two signals arrive simultaneously at a given point and need to go to the same place, one of them needs to be held back. But unlike cars, light doesn’t stand still. As soon as it stops the data is lost. Currently optical signals are converted into electricity which can be stored on a computer, then converted back to light when the data is ready to go. This process requires bulky hardware and sucks up electricity. Stéphane’s solution is to feed the optical data into a loop of fibre, which acts like a roundabout. As the signal enters the loop it spontaneously forms into solitons which travel around indefinitely until it is time to travel on.

Making the solitons stable

"In the future optical cavity solitons could become a commonplace feature of the internet, easing the problem of congestions while saving electricity and hardware."

Soon after Stéphane and his team first observed solitons in optical fibre loops they noticed something strange and annoying. The solitons were shifting positions. Sometimes it would take half an hour till the shift was seen. At first this seemed like a real bummer. To safely store data they would need to ensure that the solitons remained in the same configuration around the loop. The theory gave no indication as to why this was happening.

After a while they realised that as the solitons travelled they created very small vibrations in the fibre, which generated very faint ultra-sound waves. These ultra-sound waves were travelling out and bumping the other solitons out of position.

A way edit to optical data

What began as a nuisance turned into a breakthrough. They developed a way to create little corrugations in the electric field that the solitons would sit in, like passengers in little carts travelling around the loop.

Then they discovered that they could move the corrugations around and the solitons would move with them. It was just like moving light with tweezers. As each soliton represents a bit in binary code, this provides a way of editing optical data as it travels around; a process that would usually require conversion to electricity and back again.