Researchers have built a miniature electro-optical switch that can change the spin, or angular momentum, of a liquid form of light by applying electric fields to a semiconductor device a millionth of a meter 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.

To process information, electrical charges are moved around on semiconductor chips; to transmit it, light flashes are sent down optical fibers. Current methods of converting between electrical and optical signals are both inefficient and slow, and researchers have been searching for ways to combine the two.Researchers have built a switch that uses a new state of matter to mix electrical and optical signals while using minimal energy. Image credit: University of Cambridge.Researchers have built a switch that uses a new state of matter to mix electrical and optical signals while using minimal energy. Image credit: University of Cambridge.

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 roughly doubled every two years—this is 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 exploring alternatives to the electron as the primary carrier of information in order to keep up with Moore’s law and the demand for faster, cheaper and more powerful electronics.

University of Cambridge researchers led by Professor Jeremy Baumberg, from the NanoPhotonics Centre, in collaboration with researchers from Mexico and Greece, have built a switch that utilizes a new state of matter called a Polariton Bose-Einstein condensate in order to mix electrical 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 meter apart and letting it interact with thin slabs of semiconductor material, creating a half-light, half-matter mixture known as a polariton.

Putting many polaritons in the same space can induce condensation and the formation of a light-matter fluid that 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 fibers for communication, converting electrical to optical signals.

While the prototype device works at cryogenic temperatures, the researchers are developing other materials that can operate at room temperature so that the device can be commercialized.

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