Squeezing light into tiny channel promising for optical computing

06 Dec 2017

Imperial College team reduces distance over which light can usefully interact with itself by a factor of 10,000.

By forcing light to go through a smaller gap than ever before, researchers at Imperial College, London, say that they have “paved the way for computers based on light rather than electronics”.

The team led by Dr Michael Nielsen believes it has made a significant step forward by reducing the distance over which light can usefully interact by a factor of 10,000.

This means that the technology that previously would have occupied a device measured in centimeters could now be achieved at the micrometer scale. This in turn could bring optical processing dimensions into the scale of electrical transistors. The results have been published today in Science.

Dr Michael Nielsen, from the Department of Physics at Imperial, said, “This research has ticked one of the boxes needed for optical computing. Because light does not easily interact with itself, information sent using light must be converted into an electronic signal, and then back into light. Our technology allows such processing to be achieved purely with light.”

Shorter distance, increased intensity

Normally when two light beams cross each other the individual photons do not interact with other, as two electrons do when they meet. Special nonlinear optical materials can make photons interact, but the effect is usually very weak. This means a long span of the material is needed to gradually accumulate an effect and make it useful.

However, by squeezing light into a channel only 25nm-wide, the Imperial team has been able to increase its intensity. This method allows the photons to interact more strongly over a shorter distance, changing the property of the light that emerged from the other end of the one-micrometer-long channel.

To make computers more powerful, processors need to be made smaller, so that more such devices can fit into the same space, without increasing processing speed. Optical processing can generate little to no heat, meaning using light can make computers much faster and more efficient, say the Imperial paper.

The team achieved the effect by using a metal channel to focus the light inside a polymer previously investigated for use in solar panels. Metals are more efficient at focusing light than conventional transparent materials, and are also used to direct electrical signals. Imperial concludes that the new technology is therefore not only more efficient, but it could be integrated with current electronics.

Widespread deployment

Dr Rupert Oulton, from the Department of Physics at Imperial said, “Using light to transfer information was first used in transatlantic cables, where capacity was crucial, but now fiber optic broadband is being installed in more and more streets in the UK. As our hunger for more data increases, optics will need to come into the home, and eventually inside our computers.”

As well as providing an important step towards optical computing, the team’s achievement potentially solves a longstanding problem in nonlinear optics. Since interacting light beams with different colours pass through a nonlinear optical material at different speeds, they can become out of step and the desired effect can be lost.

He added, “In the new device, because the light travels such a short distance, it does not have time to become out of step. This eliminates the problem, and allows nonlinear optical devices to be more versatile in the type of optical processing that can be achieved.”