An optical switch for nanophotonic devices has been developed by material scientists in the US.

In photonics, lightwaves, or photons, are used in optical circuits in the same way as electrons flow in electronic circuits. Nanophotonic devices control the flow of light and can be used in high-speed optical communications. 

Philippe Guyot-Sionnest and colleagues at the University of Chicago have made nanoparticles whose optical properties can be precisely tuned.  They say the particles could be used as a switch in an optical circuit.

The researchers made gold nanorods coated with silver selenide or silver sulphide (silver chalcogenides) by chemically plating the gold surface with silver and then exposing it to sulphide or selenide in an oxidising environment. 

Gold nanorods viewed through an electron microscope (scale bar is 50 nanometres)

Team member Mingzhao Liu explained that gold nanorods have a resonance frequency that can be tuned between 600 nanometres (visible light) to 2000 nanometres (infrared light).  Varying the thickness of the silver chalcogenide layer changes the resonance frequency of the particles and gives the material its on-off switch effect. 

Greg Hartland, an expert in the optical properties of nanomaterials at the University of Notre Dame, Indiana, US, said, 'to produce metal nanorods with a uniform and controlled semiconductor coating is a significant synthetic achievement which may lead to the development of new devices.' 

Liu agreed. 'It has been the lack of a switching unit that has so far limited the development of integrated nanophotonic devices,' he said. 

Janet Crombie