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  • Transistor Works with Light, Not Electricity
Jul 2013
VIENNA, July 9, 2013 — An electrical charge applied to an ultrathin layer of material can change the polarization of terahertz light beams, creating the optical equivalent of an electrical transistor, its creators say.

Vienna University of Technology researchers have changed the oscillation direction of terahertz radiation simply by applying an electrical current to a special material. This technique produces an efficient transistor for light that can be miniaturized and used to build optical computers.

Vienna University of Technology researchers have changed the oscillation direction of terahertz radiation simply by applying an electrical current to a special material. (Left) The light beam is directed (from above) toward a special material; the application of an electrical voltage changes the polarization. Images courtesy of ©Vienna University of Technology.

In what is known as the Faraday effect, certain materials rotate the direction of light when a magnetic field is applied to them. Under normal circumstances, this effect is minutely small. Two years ago, however, professor Andrei Pimenov and colleagues at TU Vienna’s Institute of Solid State Physics, together with a research group from the University of Würzburg, achieved a large Faraday effect as they passed light through special mercury telluride platelets and applied a magnetic field.

At the time, the effect could be controlled only by an external magnetic coil, which had severe technological disadvantages. “If electromagnets are used to control the effect, very large currents are required,” Pimenov said.

By applying an electrical potential of less than 1 V, the researchers were able to rotate terahertz radiation, demonstrating a much simpler and faster system. Although a magnetic field is still responsible for the change in polarization, it is the number of electrons involved in the process, rather than the strength of the magnetic field, that determines the intensity of the effect. The number of electrons can be regulated simply with electrical potential, meaning that a permanent magnet and a voltage source would suffice.

Alexey Shuvaev (left) and Professor Andrei Pimenov.

“The frequency of this radiation equates to the clock frequency that the next-but-one generation of computers may perhaps achieve,” Pimenov said. “The components of today's computers, in which information is passed only in the form of electrical currents, cannot be fundamentally improved. To replace these currents with light would open up a range of new opportunities.”

The findings were reported in Applied Physics Letters (doi: 10.1063/1.4811496

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With respect to light radiation, the restriction of the vibrations of the magnetic or electric field vector to a single plane. In a beam of electromagnetic radiation, the polarization direction is the direction of the electric field vector (with no distinction between positive and negative as the field oscillates back and forth). The polarization vector is always in the plane at right angles to the beam direction. Near some given stationary point in space the polarization direction in the beam...
terahertz radiation
Electromagnetic radiation with frequencies between 300 GHz and 10 THz, and existing between regions of the electromagnetic spectrum that are typically classified as the far-infrared and microwave regions. Because terahertz waves have the ability to penetrate some solid materials, they have the potential for applications in medicine and surveillance.
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