Researchers from the University of Cambridge have demonstrated how to bridge the gap between light and electricity by building a miniature electro-optical switch.

The switch works by changing the spin, or angular momentum, of a liquid form of light by applying electric fields to a semiconductor device that measures around one millionth of a metre in size. The results, published in the journal Nature Materials, could enable the development of faster and smaller electronics.

In an attempt to address the disparity between the way in which information is currently processed and then transmitted, the researchers searched for ways to incorporate the electrical process with optical transmission. In order to process information, electrical charges must be moved around on semiconductor chips; but to transmit this information, light flashes have to be sent down optical fibres.

For the past 50 years, the number of transistors on a single semiconductor chip has doubled every two years, in an attempt to make electronics faster and more powerful. This observation was made in 1965 by Gordon Moore, co-founder of Intel, and is known known as Moore’s law.

However, as these semiconductor chips keep getting smaller, scientists have to deal more and more 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. This will enable us to keep up with Moore’s law and the need for quicker, cheaper and more powerful electronic devices.

Led by Professor Jeremy Baumberg from the University of Cambridge’s NanoPhotonics Centre, the researchers (in collaboration with scientists from Mexico and Greece) have built a switch that uses a new state of matter called a Polariton Bose-Einstein condensate to mix electric and optical signals, but while using only miniscule amounts of energy.

These condensates are generated by trapping light between mirrors spaced a few millionths of a metre apart, and then letting the light interact with thin slabs of semiconductor material. This creates a half-light, half-matter mixture known as a polariton. A Bose-Einstein condensate is a state of matter first predicted in 1924/25 by Satyendra Nath Bose and Albert Einstein.

Placing lots of polaritons in the same space can induce condensation and the formation of a light-matter fluid that can spin clockwise (spin-up) or anticlockwise (spin-down). When an electric field was applied to this system, the scientists were able to control the spin of the condensate and switch it between the two states. This polartin fluid emits light with the spin, which can then be sent through optical fibres, crucially 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,” commented lead author Dr Alexander Dreismann, from Cambridge’s Cavendish Laboratory.

“We have made a field-effect light switch that can bridge the gap between optics and electronics,” added co-author Dr Hamid Ohadi, 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.”

The device currently works at cryogenic – or very low – temperatures, but the researchers are currently working on other materials that can operate at room temperature, with a view to commercialising their prototype.

Mass production and scalability issues will also have to be addressed, and the team is also exploring options to integrate the device with existing technology bases.

“Since this prototype is based on well-established fabrication technology, it has the potential to be scaled up in the near future,” said co-author Professor Pavlos Savvidis from the FORTH institute in Greece.