Squeezing light brings optical computing closer to reality

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A team from Imperial College London has made what is called a significant step forward by reducing the distance over which light can interact by 10,000 fold. This, says the team, means that optical processing could be integrated into chips.

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, then back into light. Our technology allows processing to be achieved purely with light.”

Normally, when two light beams cross, individual photons do not interact or alter each other, unlike electrons. Special nonlinear optical materials can make photons interact, but the effect is usually very weak. This means a long span of material is needed for the effect to be useful.

However, by squeezing light into a 25nm wide channel, 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 end of the 1µm long channel.

The team used a metal channel to focus the light inside a polymer previously investigated for use in solar panels. Metals are more efficient at focusing light and can direct electrical signals, says the team. This not only makes the new technology more efficient, but also allows it to be integrated with current electronics.

As well as providing an important step towards optical computing, the team has potentially solved 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.

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.