Conventional antennas, which are widely used to transmit radio or TV signals, can be used at optical frequencies as long as the device is shrunk to the nanoscale. Optical antennas can be used to control light at the nanoscale and will be a major tool for developing nanophotonics applications in the future. The devices possess "plasmonic modes" that can be tuned to resonate with the electronic transitions in molecules nearby. It is these plasmonic modes that increase the coupling between light emitted by neighbouring molecules and the antenna.

The new hybrid device made by Otto Muskens of the University of Southampton and colleagues at the Donostia International Physics Center is based on the mutual interactions between a nanoantenna made of gold and a transparent indium tin oxide (ITO) substrate. The antenna efficiently absorbs energy from a laser pulse that is then rapidly converted to heat (in a matter of picoseconds) and transferred to the substrate via "hot electrons". The transfer is efficient thanks to the good conductance between the antenna and the substrate.

Heat source
"The nanoantenna thus acts as a nanoscale heat source that produces changes in the optical response of the substrate via changes in its free-carrier density," Muskens told "These changes in the substrate modify the resonances of the nanoantenna. We are able to measure these resonance changes in our experiments."

The new devices might be used in advanced integrated optical circuits, where an optical analogue of nanoelectronic transistors are required to control the flow of information, adds Muskens. "Another important application is actively controlling nonlinear optical processes and Raman scattering (SERS)."

The team is now looking into the possibility of electrically controlling plasmonic nanodevices. Such techniques might help bridge electrical and optical functionalities on a single chip, they say.

The results were detailed in Nano Letters.