Researchers can solve mathematical equations by shining light through a so-called meta-surface of cleverly designed silicon nanostructures. This is faster and more energy-efficient than calculating with electronics.
Technological developments, such as artificial intelligence and image recognition, are becoming increasingly complex, but they also require more and more energy. The electrical currents that shoot through electronic circuits encounter resistance, and energy is lost in the form of heat.
Analogue calculations with light can offer solace. It generates less heat and is therefore more energy efficient. Moreover, it calculates much faster than electronics. Light travels at nearly the speed of light through the nanostructures that make the calculations possible. This makes it suitable for applications where speed and efficiency are important, such as image recognition in self-driving cars.
READ ALSO
Brain training apps lack scientific backing
A lot of apps claim to make their users smarter. Not only are these brain training apps quite boring, their effect on our performance is…
Meta surface
The speciality optical computing, in which physicists investigate ways to calculate with light, is therefore on the rise. Researchers at AMOLF, in collaboration with the University of Pennsylvania and City University of New York, have now taken a new step, they write in Nature. They show that with light and a cleverly designed nanostructure, a metamaterial, you can perform complex mathematical calculations called matrix inversions.
Metamaterials are artificially developed structures that behave like materials with properties that are not found in natural materials. As a result, they can, for example, refract light differently than is possible with natural materials.
Image recognition
The research continues earlier work part of this research group used the technique to recognize edges of objects on images. Detecting edges of buildings and people, for example, is an important part of image recognition.
For this they developed a meta-surface, which consists of silicon structures of a few ten-thousandths of a millimeter in size, on a transparent surface. When the light from an image shines through it, it is scattered and bounced around this surface in such a way that an image appears on the other side with only the edges of the objects in the image.
This edge detection method is faster and more efficient than a computer, says physicist Albert Poleman from AMOLF. ‘In the meta-surface, the light from the image is immediately processed. With a computer, several steps would be necessary.’ The image must first be converted into bits with a camera, which a computer can process. Then the machine does the calculation to find out the edges, and only then do you have the result.
Mathematical calculations
After the successful edge detection, the researchers looked at whether they could apply the technique to more complex mathematical calculations called matrix inversions. These calculations are widely used in science, engineering and economics, for example in aircraft and robot operating systems, or in navigation systems and computer animations.
To this end, the researchers developed a system consisting of a mirror and a meta-surface with a thin silicon structure. The mirror keeps bouncing the light back to the surface. This is necessary because steps have to be repeated in these calculations. The answer to the equation can be read from the light beams that this produces.
The results show that you can solve matrix inversions with this technique in less than a trillionth of a second. That is faster than is possible with most computer methods.
Multiple meta surfaces
Even today, each computational task requires its own specially designed meta-surface. The technique is therefore particularly suitable for taking over specific tasks from a computer. To make the method more flexible, the researchers are working on a new structure in which they can electrically change the properties of the metamaterial. Then you can electrically program which calculation takes place.
‘The next step is that the light itself adjusts the metamaterial so that it can perform the desired calculation with that light,’ says Polman. ‘That’s the dream application, but it’s still a long way off.’