Oldenburg physicists discover new nanostructured metallic light switches

Oldenburg. According to experts, the future could belong to them: Computers in which optical elements replace conventional electronic components. A German-Italian research team led by Prof Dr Christoph Lienau, physicist at the University of Oldenburg, has now taken an important step towards the development of optical switching elements. In the February issue of the renowned journal Nature Photonics, the scientists report on their new research findings on the realisation of ultra-fast light switches.

Conventional computers are based on semiconductor transistors: Electronic currents are switched in them, which flow through wafer-thin conductor tracks. In current processors, these conductor paths are only a few tens of nanometres wide - a nanometre is one billionth of a metre - and the currents are switched on a time scale of around one nanosecond. "In principle, considerably faster computers could be realised if it were possible to trap and switch light instead of electrons in such conductor paths," explains Lienau. So far, such "optical computers" only exist as a vision of scientists. One reason for this is that it is extremely difficult to capture light in such small dimensions.

In recent years, researchers have made considerable progress in this area with the development of nanostructured metallic light guides - for example microscopically small silver or gold wires. However, these metallic light guides alone have not yet succeeded in switching light through light with sufficient speed.

In their article in Nature Photonics, the scientists describe a new light switch consisting of a grid of nanostructured gold wires coated with a thin layer of an organic semiconductor. "When we irradiate such hybrid structures with short flashes of light," explains Prof Dr Parinda Vasa, formerly a physicist in Oldenburg and now a university lecturer at the Indian Institute of Technology in Mumbai, "the light energy oscillates extremely quickly between the gold wire and the semiconductor. These so-called Rabi oscillations mean that we can switch off the light with a second light pulse whenever it reaches the semiconductor." The duration of a switching process is only a few tens of femtoseconds, which is more than 10,000 times faster than in an electronic computer.

"We are increasingly learning how we can efficiently monitor and control the movement of light beams in the smallest spatial structures and on extremely short time scales," says Lienau. Even if they still need to significantly improve the efficiency and service life of the optical switch, the resulting application prospects are becoming more and more fascinating and "are increasingly within reach", says the physicist.

The Oldenburg project is funded by the German Research Foundation as part of the priority programme "Ultrafast Nanooptics" and the German-Italian cooperation is funded by the Laserlab Europe project of the European Union.

[University press release from 25 January 2013]