Liquid Light Switch for Powerful Electronics

Polariton fluid emits clockwise or anticlockwise spin light by applying electric fields to a semiconductor chip (Source: A. Dreismann)

Polariton fluid emits clockwise or anticlockwise spin light by applying electric fields to a semiconductor chip (Source: A. Dreismann)

Researchers at the Univer­sity of Cambridge have built a minia­ture electro-op­tical switch which can change the spin of a liquid form of light by applying electric fields to a semi­conductor device a millionth of a metre in size. Their results demon­strate how to bridge the gap between light and electric­ity, which could enable the develop­ment of ever faster and smaller elec­tronics.

There is a funda­mental disparity between the way in which information is processed and trans­mitted by current technologies. To process infor­mation, electrical charges are moved around on semi­conductor chips; and to transmit it, light flashes are sent down optical fibres. Current methods of converting between electrical and optical signals are both inef­ficient and slow, and researchers have been searching for ways to incor­porate the two.

In order to make elec­tronics faster and more powerful, more tran­sistors need to be squeezed onto semi­conductor chips. For the past 50 years, the number of tran­sistors on a single chip has doubled every two years, known as Moore’s law. However, as chips keep getting smaller, scientists now have to deal with the quantum effects associated with indi­vidual atoms and electrons, and they are looking for alter­natives to the electron as the primary carrier of infor­mation in order to keep up with Moore’s law and our thirst for faster, cheaper and more powerful elec­tronics.

The Univer­sity of Cambridge researchers, led by Jeremy Baumberg from the Nano­Photonics Centre, in colla­boration with researchers from Mexico and Greece, have built a switch which utilises a new state of matter called a Pola­riton Bose-Einstein conden­sate in order to mix electric and optical signals, while using mini­scule amounts of energy. Polariton Bose-Einstein conden­sates are generated by trapping light between mirrors spaced only a few millionths of a metre apart, and letting it interact with thin slabs of semi­conductor material, creating a half-light, half-matter mixture known as a polariton.

Putting lots of polaritons in the same space can induce conden­sation and the formation of a light-matter fluid which spins clockwise (spin-up) or anti­clockwise (spin-down). By applying an electric field to this system, the researchers were able to control the spin of the conden­sate and switch it between up and down states. The pola­riton fluid emits light with clockwise or anti­clockwise spin, which can be sent through optical fibres for communi­cation, converting elec­trical to optical signals. “The polariton switch unifies the best proper­ties of electronics and optics into one tiny device that can deliver at very high speeds while using minimal amounts of power,” said Alexander Dreismann from Cambridge’s Cavendish Labo­ratory.

“We have made a field-effect light switch that can bridge the gap between optics and elec­tronics,” said Hamid Ohadi, also from the Caven­dish Labora­tory. “We’re reaching the limits of how small we can make transistors, and electronics based on liquid light could be a way of increasing the power and effi­ciency of the elec­tronics we rely on.” While the prototype device works at cryogenic tempera­tures, the researchers are developing other materials that can operate at room tempe­rature, so that the device may be commercialised. The other key factor for the commercia­lisation of the device is mass pro­duction and scala­bility. “Since this proto­type is based on well-established fabri­cation techno­logy, it has the potential to be scaled up in the near future,” said Pavlos Savvidis from the FORTH institute in Crete, Greece. The team is currently exploring options for commercia­lising the techno­logy as well as integrating it with the existing techno­logy base. (Source: Cambridge Univ.)

Reference: A. Dreismann et al.: A sub-femtojoule electrical spin-switch based on optically trapped polariton condensates, Nat. Mat., online 08 August 2016, DOI: 10.1038/nmat4722

Link: NanoPhotonics Centre, Cavendish Laboratory, University of Cambridge, UK

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