Physicists have devised an ultra-thin dynamic amplifier for electromagnetic radiation using a parametric metasurface.

A parametric metasurface is a thin composite material with small-scale surface structure, whose properties vary periodically over time, a recent advance beyond static or tunable metamaterials. The design enables significant control of freely propagating input radiation, including amplification of up to 10 decibels.

Amplification is crucial for long range transmission through air and space, for example, in satellite and quantum communication.

At the heart of the new design is an array of split-ring resonators with integrated variable capacitors known as varactors, which enable modulation at high frequencies, said lead researcher, Fedor Kovalev.

“If you have a high speed of modulation, then you have complete control over the electromagnetic waves in space and time,” said Mr Kovalev, a PhD student in the Department of Fundamental and Theoretical Physics, and the ARC Centre of Excellence for Transformative Meta-Optical Systems (TMOS).

“This is the first time parametric amplification methods have been applied to free-space electromagnetic waves.”

Mr Kovalev and his supervisor Professor Ilya Shadrivov ran numerical simulations of the device and compared them with analytical calculations, reporting their results in Optical Materials Express. To build the parametric metasurface model they had to combine methods from both electronics and physics and apply them to electromagnetic simulation.

As a proof of concept, they chose electromagnetic waves with the wavelength of about 1.5 meters (200 MHz), and a metasurface of about 35 millimeters thick, which is significantly shorter than the wavelength.

The design will also work for shorter wavelengths, Mr Kovalev said.

“Varactors can operate at up to about 500 gigahertz, but with the development of other ultrafast modulation technologies, this could be extended into the infrared range,” he said.

“And in the future, who knows, even further.”

Another advantage of parametric amplification is its extremely low noise level – they are used for amplification of faint signals, for example, in radio astronomy and quantum computing. However, until now, these techniques have not been applied to amplification of free-space electromagnetic radiation.

Each varactor in the array needs to be driven by an electric circuit - with sophisticated enough electronics, the phase of the varactors could be varied across the metasurface, which influences the output. This allows multiple functionalities to be programmed into the same device.

“If you apply a phase gradient across the array, this capability opens up possibilities for beam steering and other forms of control useful in communication applications,” Mr Kovalev said.