System Bits: Aug. 4

Turning electric signals into light signals; faster spintronics; sensing hidden objects.


Turning electric signals into light signals
Transmitting large amounts of data, such as those needed to keep the internet running, requires high-performance modulators that turn electric signals into light signals, and now, researchers at ETH Zurich have developed a modulator they say is a hundred times smaller than conventional models.

They reminded that in 1880, Alexander Graham Bell developed a device which he himself called his greatest achievement, greater even than the telephone: the “photophone.” His idea to transmit spoken words over large distances using light was the forerunner of a technology without which the modern internet would be unthinkable. Of course today, huge amounts of data are sent incredibly fast through fibre-optic cables as light pulses. First, however, they have to be converted from electrical signals, which are used by computers and telephones, into optical signals. In Bell’s days it was a simple, very thin mirror that turned sound waves into modulated light. Today’s electro-optic modulators are more complicated, but they do have one thing in common with their distant ancestor: at several centimeters they are still rather large, especially when compared with electronic devices that can be as small as a few micrometers.

Colorized electron microscope image of a micro-modulator made of gold. In the slit in the centre of the picture light is converted into plasmon polaritons, modulated and then re-converted into light pulses.  (Source: ETH Zurich)

Colorized electron microscope image of a micro-modulator made of gold. In the slit in the centre of the picture light is converted into plasmon polaritons, modulated and then re-converted into light pulses.  (Source: ETH Zurich)

The ETH Zurich researchers created a modulator that is a hundred times smaller and that can, therefore, be easily integrated into electronic circuits — as well as being considerably faster and cheaper than common models, along with using less energy. In essence, it provides more communication with less energy.

Faster spintronics
In what EPFL researchers say is a tremendous boost for spintronic technologies, they have shown that electrons can jump through spins much faster than previously thought.

They explained that electrons spin around atoms, but also spin around themselves, and can cross over from one spin state to another, which is a property that can be exploited for next-generation hard drives. At the same time, “spin cross-over” has been considered too slow to be efficient, but using ultrafast measurements, EPFL scientists have shown that electrons can cross spins at least 100,000 times faster than previously thought — and this should help propel the field of spintronics forward.

(Source: EPFL)

(Source: EPFL)

Spin cross-over is already used in many technologies, e.g. optical light-emitting devices (e.g. OLED), energy-conversion systems, and cancer phototherapy. Most prominently, spin cross-over forms the basis of the fledgling field of spintronics. The problem is that spin cross-over has generally been thought too slow to be efficient enough in circuits but the lab of Majed Chergui at EPFL has demonstrated that spin cross-over is considerably faster than previously thought. Using the highest time-resolution technology in the world, the lab was able to “see” electrons crossing through four spin states within 50 quadrillionths of a second – or 50 femtoseconds.

Sensing hidden objects
University of Warwick scientists have developed a new type of sensor they say is much faster than competing technologies used to detect and identify hidden objects.

Called ‘Q-Eye’, the invention senses radiation across the spectrum between microwaves and infra-red, known as the Terahertz (THz) region of the spectrum – a goal that has challenged scientists for over 30 years, they explained. It works by detecting the rise in temperature produced when electromagnetic radiation emitted by an object is absorbed by the Q-Eye sensor, even down to the level of very small packets of quantum energy (a single photon).

The researchers asserted that this device could help address the weaknesses reported recently in U.S. airport security, where mock weapons and explosives were smuggled through airports, undetected in 95% of cases. It could also prove useful in discovering concealed goods in the retail industry or for non-destructive monitoring, for example quality control in drugs or food. Other applications include astronomical and climate science observations and medical diagnosis.

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