4th December 2017

Breakthrough in optical computing

Researchers from Imperial College London (ICL) have announced a breakthrough in optical computing, with a 10,000-fold shrinkage in the distance over which light can interact.



Credit: Imperial College London

By forcing light through a smaller gap than ever before, researchers have paved the way for computers based on light instead of electronics. Light is desirable for use in computing because it can carry a higher density of information and is much faster and more efficient than conventional electronics. However, light does not easily interact with itself – so while it can be used to move information quickly, it is not very good at processing information.

For example, light is currently used to transfer information over long distances, such as in transatlantic cables and fibre optics, which deliver fast internet. However, once the information reaches your computer, electronics are needed to convert and process it.

In order to use light for processing on microchips, several important obstacles need to be overcome. For example, light can be made to interact using particular materials, but only over relatively long distances. Now, however, a team from Imperial College London has made a significant step forward by reducing the distance over which light can interact by 10,000 fold.

This means that what previously would have taken centimetres to achieve can now be realised on the micrometre (one-millionth of a metre) scale, bringing optical processing into the range of electrical transistors, which currently power personal computers. The results are published in the journal Science.



Credit: Imperial College London

"This research has ticked one of the boxes needed for optical computing," says Dr Michael Nielsen, from the Department of Physics at ICL. "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 processing to be achieved purely with light."

Normally when two light beams cross each other, individual photons do not interact or alter each 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 the effect and make it useful.

However, by squeezing light into a channel only 25 nm (25 billionths of a metre) wide, the Imperial team increased its intensity. This allowed the photons to interact more strongly over a short distance, changing the property of the light that emerged from the other end of the one-micrometre-long channel.

Controlling light on such a tiny scale is a major step towards the construction of optical computers. Electronic computing is at the limit of efficiency; while it is possible to make a faster electronic processor, the energy cost of moving memory data around the computer any faster is too high. To make computers more powerful, processors are instead made smaller, so more can fit into the same space, without increasing the processing speed. Optical processing can generate little to no heat, meaning that using light can make computers much faster and more efficient.

"The use of light to transfer information has gotten closer to our homes," said Dr Rupert Oulton, from the Department of Physics at Imperial. "It was first used in transatlantic cables, where capacity was most crucial, but now fibre 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."



Credit: Imperial College London

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