Together with their colleagues from Germany and the Netherlands, scientists at the Moscow Institute of Physics and Technology (MIPT) have found a way to significantly improve computer performance. In their paper published in Nature Photonics, they propose the use of the so-called T-waves, or terahertz radiation as a means of resetting computer memory cells. This process is several thousand times faster than magnetic-field-induced switching.
“We have demonstrated an entirely new way of controlling magnetization, which relies on short electromagnetic pulses at terahertz frequencies. This is an important step towards terahertz electronics. As far as we know, our study is the first to make use of this mechanism to trigger the oscillations of magnetic subsystems,” says Anatoly Zvezdin of Prokhorov General Physics Institute and MIPT, a coauthor of the paper and a USSR State Prize-winning scientist heading MIPT’s Laboratory of Physics of Magnetic Heterostructures and Spintronics for Energy-Saving Information Technologies.
The rapidly increasing amounts of digital data that have to be manipulated, along with the growing complexity of the computation tasks at hand, compel hardware designers to achieve ever higher computational speeds. Many experts believe that classical computation is currently approaching a limit, beyond which no further increase in data processing speed will be practicable. This is motivating scientists all over the world to investigate possibilities of entirely different computer technologies. One of the weak spots in modern computers holding back their evolution is memory: it takes time to complete every set/reset operation for a magnetic memory cell, and reducing the duration of this cycle is a very challenging task.
A group of scientists including Sebastian Baierl of the University of Regensburg, Anatoly Zvezdin, and Alexey Kimel of Radboud University Nijmegen (the Netherlands) and Moscow Technological University (MIREA) proposed that electromagnetic pulses at terahertz frequencies (with wavelengths of about 0.1 millimeters, i.e., between those of microwaves and infrared light) could be used in memory switching instead of external magnetic fields. A more familiar device that makes use of terahertz radiation is the airport body scanner. T-rays can expose weapons or explosives concealed under a person’s clothing, without causing any harm to live tissues.
To find out whether T-rays could be used for convenient memory states switching (storing “magnetic bits” of information), the researchers performed an experiment with thulium orthoferrite (TmFeO?). As a weak ferromagnet, it generates a magnetic field by virtue of the ordered alignment of the magnetic moments, or spins of atoms in the microcrystals (magnetic domains). In order to induce a reorientation of spins, an external magnetic field is necessary.
However, the experiment has shown that it is also possible to control magnetization directly by using terahertz radiation, which excites electronic transitions in thulium ions and alters the magnetic properties of both iron and thulium ions. Furthermore, the effect of T-rays proved to be almost ten times greater than that of the external magnetic field. In other words, the researchers have devised a fast and highly efficient remagnetization technique—a solid foundation for developing ultrafast memory.
The scientists expect their “T-ray switching” to work with other materials as well. Thulium orthoferrite, which was used in the experiment, happens to be convenient for the purposes of demonstration, but the proposed magnetization control scheme itself is applicable to many other magnetic materials.
“There was a Soviet research group that used orthoferrites in their studies, so this was always kind of a priority field for us. This research can be seen as a follow-up on their studies,” says Anatoly Zvezdin.
An ultrahigh speed, wireless communication network using THz instead of GHz frequencies is now one step closer. Researchers at Radboud University’s FELIX Laboratory have shown that it is possible to effectively transmit signal waves with THz frequencies through the existing fibre optic network.
HD television, big data, the internet of things and social media have considerably increased the data rate of our wireless communication network, and continue to do so. An obvious way to facilitate this network growth is to use terahertz frequencies (THz, 1012 Hertz) with high-speed data rates of up to 100 Gbit/s. Current wireless data communication systems operate at an average speed of 100Mbi/s using microwave frequencies around one gigahertz (GHz, 109 Hertz). For instance: GPS systems work with 1,3 GHz frequencies, wifi with 2,4 and 5 GHz, and your microwave with 2,45 GHz. In the search for free frequencies, the unexplored THz area is of great interest.
Distortion of terahertz signals
For wireless THz surfing on the Internet, it is necessary to connect THz wireless stations to the worldwide fibre optic network. However, existing microwave techniques do not operate at THz frequencies. “THz is a difficult frequency region, because it is both electronic and optic at the same time,” FELIX researcher Giel Berden explains. “It is too low for normal optics, and too high for standard electronics.” Moreover, THz signal waves in the fibre optic network are scrambled, because standard modulation of laser light generates two sidebands (colours) that interfere with one another. Optical Single Side Band (OSSB) is a method to prevent this scrambling of information by selectively extinguishing one sideband.
Special beam splitter
Scientists at Radboud University’s FELIX Laboratory developed an OSSB modulator that enables wireless THz waves to be transmitted unperturbed through the fibre network. First author Afric Meijer explains: “With a specially designed beam splitter that splits both the THz waves and the infrared laser light in half, one of the two sidebands is reduced by a factor of over sixty, while the other sideband’s intensity increases significantly.” The special modulator (figure 1) does not contain any moving parts or colour filters, and operates over an ultra-wide bandwidth from 0.3 to 1 THz.
The THz OSSB modulator is a by-product of the research by TeraOptronics on the THz laser FLARE (Free-electron Laser for Advanced spectroscopy and high-Resolution Experiments) at Radboud University. “The apparatus to determine the colour of FLARE’s laser light was exactly what was needed to observe THz OSSB,” Meijer explains. “Both the special THz laser FLARE and Afric’s interest to expand communication with THz frequencies were imperative to make an impact in this field that was new to us,” says co-author Wim van de Zande, currently Director of Research at ASML.
Opportunities for ultra HD, virtual reality and big data
As THz signals in the air are strongly absorbed by water vapour, wireless THz communication will mostly be used for relatively short distances. Meijer: “Our THz OSSB modulator allows us to use the existing fibre optic network. Ultra HD and Virtual Reality images can be received or transmitted wirelessly through a THz link, just like the petabytes of data in research institutes and hospitals.” Berden: “This publication is a proof of principle. To actually use the technique requires a couple of additional steps, for instance scaling down the design for microfabrication and improvements in efficiency. Our hope is that this idea will be further developed by the industry.”
Radboud University Nijmegen (Dutch: Radboud Universiteit Nijmegen, formerly Katholieke Universiteit Nijmegen) is a public university with a strong focus on research located in Nijmegen, the Netherlands.
Established since 10-17-1923 and situated in the oldest city of the Netherlands, it has seven faculties and enrolls over 19,130 students. Radboud was internationally ranked by QS World University Rankings, and placed at 136th.
Radboud University Nijmegen has seven faculties and enrolls over 19.130 students in 107 study programs (40 Bachelor’s and 67 Master’s programs).
The University offers 28 international Master’s programs taught in English within five different fields: Man & Society, Man & Health, Man & Culture, Policy & Organization and Nature & Science. All Bachelor’s programs are in Dutch. All Master’s programs have been internationally accredited by the Accreditation Organization of the Netherlands and Flanders (NVAO).