A nanooptical device dreamed up by Austrian and Hungarian researchers – partly at ELI ALPS – promises superfast and miniaturized signal processing technology.
If we compare what was considered cutting-edge twenty years ago with similar devices today, we can see a huge difference to the advantage of the latter. However, further dynamic growth is doubtful as the speed of data processing is restricted by the applied technology. Although we know that light can transmit information, the miniaturization of optical fibres, for example, is limited and they cannot be used for the manufacturing of arbitrarily small optoelectronic components. The miniaturization of optical fibres is restricted by the diffraction limit of light, i.e. the same reason that an optical microscope cannot have a resolution better than a certain value.
Researchers at Graz University of Technology, ELI ALPS Laser Research Institute and the Wigner Research Centre for Physics have developed an ultrafast and miniaturizable waveguide applying the principle of nanooptics. The new device works by illuminating a nanometre-sized metal structure with ultrashort laser pulses to force the metal’s electrons to oscillate at a speed corresponding to the electromagnetic field of light – a phenomenon known as surface plasmon. This oscillation then propagates along the metal surface as a wave, just like water waves.
“The signal propagating over the metal surface retains a time delay of 7 fs, which allows for switching speeds of up to around 0.1 PHz. Thanks to the plasmonic principle, the transmitted optical signal can be focused down to the nanometre scale,” Péter Dombi, Head of Division at ELI ALPS and Research Professor at the HUN-REN Wigner Research Centre for Physics said.
On the surface metal structure, the ultrashort laser pulse can induce a plasmon wave, the temporal length of which can be examined with a second laser pulse and a photoelectron emission microscopy.
The disadvantage of surface plasmons is that they propagate with a loss. On a completely flat metal surface, the wave attenuates over a length of a few tens of micrometres. However, if a special waveguide is built into such surfaces, plasmon propagation up to millimetres can be achieved. The concept of plasmonic waveguides combined with information processing technology opens up the possibility of ultrafast signal processing. After surmounting countless physical and technical challenges, and assembling thousands of these plasmonic elements together, we can arrive at a new data processing device.
“A device based on this kind of logical operation will not be a development for the next two or three years – the technology is not yet ready. However, it is noteworthy that several leading research groups are working on this possibility – including that of the recent Nobel laureate Ferenc Krausz. We too have produced basic research results in this area. We are providing an opportunity and a concept for colleagues. With our recently published paper we have put this idea out to the international community, and we are expecting the feedback,” Péter Dombi said.
The article was published in the leading international journal on nanoscience, Nano Letters, and its authors included Péter Dombi, Zsuzsanna Pápa and Lázár Tóth. (Another related result: last year, Nobel Prize-winning physicist Ferenc Krausz published a paper on the speed limit of ultrafast optoelectronics in Nature Communications.)
ELI ALPS contributed to the results by designing and fabricating the samples used in the Graz experiments; the researchers in Graz received the nanostructured samples within the framework of a user programme at the Szeged-based institution. Nanofabrication user projects are usually carried out in remote user mode: the users send the specifications to us, researchers at ELI ALPS to develop the sample fabrication technology, and finally we send the back to the user. Some of the samples have been used in experiments conducted at ELI ALPS. The nanofabrication laboratory is not a user, but a user support laboratory, but it is also advertised and available for stand-alone projects.
In recent years, the Szeged-based Nanofabrication Laboratory has sent high-tech nanostructured samples to many countries around the world, and this activity of the laser centre has also received a lot of attention worldwide.
Author: Zoltán Ötvös
Photo: Gábor Balázs