A team of researchers from ITMO University, Polytechnic University of Milan (Italy), and the University of Brescia (Italy) have developed a new approach to control the properties of metasurfaces using laser radiation. The method allows scientists to switch optical states within a picosecond, which means that they can now transmit more data in less time and build a photonic computer and more accurate medical sensors. The results of the study are  in Light: Science & Applications.

Credit: sakkmesterke / photogenica.ru

For data to be transmitted fast and for communication systems to be efficient, optical signals need to be transferred and processed quickly. This is now performed with electricity, but, in the long run, full-fledged optical systems would work better; the reason being that light signals are transmitted faster and use less energy than electrical ones. One promising way to quickly manage light is to use metasurfaces – ultrathin optical lenses that allow researchers to fine-tune electromagnetic waves. All existing studies cite this method’s speed limitations to be under one nanosecond or ten picoseconds, which is why research is currently underway to find a way to increase the speed rate. 

In the current study, the researchers proposed to use laser radiation to control light in metasurfaces. As a model, the physicists opted for a one- or two-dimensional AlGaAs metasurface on a sapphire substrate. Short laser pulses disrupt the symmetry of this nanostructure, which generates a radiation channel through which radiation can reach the metasurface and switch the optical state. The channel quickly closes, and the structure returns to its previous optical state. The idea was born from the longstanding collaboration between ITMO researchers, Prof. Costantino De Angelis (University of Brescia), and Prof. Giuseppe Della Valle (Polytechnic University of Milan).

Using optical impact, the physicists managed to obtain estimates for ultrafast switching of light effects that are calculated in fractions of picoseconds. The advantage of the new method is that it is implemented in the visible range and does not require complex multilayer structures and electrical circuits; it employs pump-probe geometry when the control pumping optical pulse modulates the probe channel.

The study is currently in the theoretical phase, but the physicists are planning to test out their estimates experimentally.

High-speed light control opens the way for next-gen optical switches and modulators. These will be of use, for instance, in ultrafast communication systems where data is transmitted via light rather than electricity; light-powered processors for optical computers that run faster, while consuming less energy; advanced medical sensors and detectors; cameras with the non-visible light range; and holography and AR/VR to generate clearer and more dynamic images. 

“Modern processors are limited in frequency to about 3-4 GHz, and with optical methods, we can up this value by orders of magnitude. In our case, up to units of terahertz, which will theoretically increase the data transfer speed. The new approach can be tailored for metasurfaces based on other semiconductors – for instance, silicon, which is often used in photonic devices,” says Mihail Petrov, an author of the paper and a senior researcher at ITMO’s Faculty of Physics.

This study is supported by the Priority 2030 program within the Frontier Laboratory “Nanophotonic Metastructures for Ultrafast Optical Calculations.”