Scientists suggest ‘anti-laser’ could drive new computers

Scientists behind the world’s first ‘anti-laser’ say it could help create the next generation of computers.

Researchers at Yale University in the US have found a way of making silicon semiconductors absorb 99 per cent of light, meaning they could be used in so-called optical computers that process information using photons instead of electronics.

Many technology firms, including Intel and IBM, are working on developing optical computers as the next step in improving processing speed while reducing manufacturing costs and energy consumption.

The new method could provide a way to make silicon suitable for photonic components, such as switches and detectors, by creating anti-lasers that almost perfectly absorb light instead of emitting it.

The idea behind the technology might also have a use in radiology, as a way of targeting electromagnetic radiation through human tissues that are normally opaque, either for therapeutic or imaging purposes.

‘For 20 years or more people have been saying that when computer chips get too small and power consumption gets high they’ll stop working well,’ said Prof A Douglas Stone, author of a paper on the anti-laser work in the journal Science.

The currently favoured solution is to combine electronic chips with optical ones. ‘The shuttling around of signals on the computer will happen optically and that means signals have to be transduced from being light to electricity and back and forth.

‘In addition, if we’re going to do switching and routing at this optical level we’re going to need modulators and switches to direct or turn the light on and off.’

This has led to a drive to create photonic components from silicon rather than the traditional material gallium arsenic, which is rarer, more expensive and less compatible with existing computing technology.

In the anti-laser, incoming light waves are trapped in a cavity where they bounce back and forth until they are eventually absorbed. Their energy is dissipated as heat.
In the anti-laser, incoming light waves are trapped in a cavity where they bounce back and forth until they are eventually absorbed. Their energy is dissipated as heat

The Yale research could allow scientists to control light in the necessary way to create these components from silicon, which usually only absorbs around 60 per cent of light.

Stone said the method reverses the principle of the laser, where energy is passed through a gain medium such as a semiconductor and emitted as an amplified beam of light.

With the anti-laser, laser light is passed into the medium and perfectly absorbed, he added.

To turn the silicon into an anti-laser, Stone had to use two light sources with a specific phase difference between their wave patterns.

When the two waves combine inside the material they create a specific interference pattern that causes the energy to become trapped and converted to heat instead of reflected back out.

‘As a function of that phase delay we can go from 99 per cent absorption to 30 per cent,’ said Stone. ‘We need that second beam as almost a control beam and as we change its phase we turn the total absorption on and off.

‘You could do it with most materials, certainly with any semiconductor. What you need is some control over the intrinsic absorption.’

Stone has also theorised that by combining the anti-laser idea with theories about ‘random lasers’, which emit light despite a highly disorganised structure, it might be possible to get human tissues that usually scatter light to absorb it.

Being able to control this absorption could allow doctors to target cancer cells without overloading the tissue with radiation.