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.”
Beads, disks, bowls and rods: scientists at Radboud University have demonstrated the first methodological approach to control the shapes of nanovesicles. This opens doors for the use of nanovesicles in biomedical applications, such as drug delivery in the body.
The shape of nanovesicles – called ‘polymersomes’ in jargon – in a solution varies at different compositions of that solution, scientist Roger Rikken and his colleagues at Radboud University discovered. “Besides the spherical shapes, we can create disks, rods, and bowl shaped stomatocytes by varying the ratio of the solvent. This regulates the osmotic pressure and permeability of the vesicles, controlling their deflation and subsequent re-inflation,” Rikken explains.
For the first time, the shape of the nanovesicles is now fully controllable and predictable. This offers possibilities to transform and mould the vesicles into nanocontainers or nanorockets, which are highly desirable, e.g. for drug delivery in the body. The shape of the polymersomes also affects their flow properties, as is also believed to be the case for red blood cells. It is therefore of great importance to obtain full control over shape transformations to utilise vesicles in drug transport via the blood stream.
By using the magnets of the High Field Magnet Laboratory, Rikken was able to determine the exact shape of the vesicles at every solvent ratio. Subsequently, he studied the variety of shapes with electron microscopy and described them mathematically. In this way, he discovered that the shape transformation follows the path of the lowest energy. “Nature is always trying to stay in balance. The four shapes that we found turn out to be located exactly at the energy minima in an existing model. The basic idea behind our discovery is actually very logical, but it was never described before.”
An international team composed by scientists of Radboud University and the University Politecnico di Milano has realized the ultimate speed limit of the control of spins in a solid state magnetic material.
Nature Communications publishes their results on February 5.
The rise of the digital information era posed a daunting challenge to develop ever faster and smaller devices for data storage and processing. An approach which relies on the magnetic moment of electrons (i.e. the spin) rather than the charge, has recently turned into major research fields, called spintronics and magnonics.
In the current publication, the researchers were able to induce spin oscillations of the intrinsically highest frequency by using femtosecond laser pulses (1 fs = 10-15 sec). Furthermore, they demonstrated a complete and arbitrary manipulation of the phase and the amplitude of these magnetic oscillations – also called magnons. The length-scale of these magnons is on the order of 1 nanometre.
These results pave the way to the unprecedented frequency range of 20 THz for magnetic recording devices, which can be employed also at the nanometer scale.