Advances in metamaterials – composites of natural materials designed to manipulate electromagnetic waves in unusual ways – could lead to the re-birth of analogue computing, researchers believe.

The advent of all-purpose digital computers in the mid-20th Century was revolutionary, as they could be reprogrammed to perform multiple types of calculations, unlike their purpose-built analogue predecessors.

Though analogue computers still had an advantage in not having to translate, quantise and digitise the information they were calculating, their mechanical and electronic makeup could not compete with the advances in integrated electronic circuits that meant digital computers were rapidly becoming smaller and faster.

But researchers at the University of Pennsylvania, the University of Texas at Austin and the University of Sannio in Italy have now shown that metamaterials can be tailored to do ‘photonic calculus’ on light waves passing through them.

The researchers’ theoretical material, outlined in the journal Science, can perform a specific mathematical operation on a light wave’s profile, such as finding its first or second derivative. Shining a light wave on such a material would result in that wave profile’s derivative emerging from the other side.

The researchers believe that by swapping their mechanical gears and electrical circuits for optical materials that operate on light waves it may once again be analogue computers’ time to shine, but this time at the microand nanoscale.

“Compared to digital computers, these analogue computers were bulky, power hungry, and slow,” said Nader Engheta, professor of Electrical and Systems Engineering in Penn’s School of Engineering and Applied Science.

“But by applying the concepts behind them to optical metamaterials, we might be able to make them at micro and nanoscale sizes, and operate them at nearly the speed of light using little power.”

The team initially created a computer simulation of an ideal metamaterial, one that could perfectly change the shape of the incoming wave profile into that of its derivative. They then constrained their simulations to specific materials suitable for existing fabrication techniques, such as silicon and aluminium-doped zinc oxide.

“The simulation results of the two were almost identical, so we’re hopeful we’ll be able to do photonic calculus in the future,” Engheta said.

The team believe metamaterials could also be produced to carry out other calculus operations, such as integration and convolution. Viewing and manipulating this type of light wave profile is an everyday occurrence in applications such as image processing, but the researchers’ proposed computational metamaterials would process incoming optical information without digitising it first.

“The thickness of our structures can be comparable with the optical wave length or even smaller,” said Vincenzo Galdi of the University of Sannio. “Implementing similar operations with conventional optical systems would require much thicker structures.”