Tiny Antennas are a Bright Idea

From the very first radio to the most advanced cellphone, wireless communications have depended on antennas that emit and receive radio waves. Now, researchers report the invention of the nanoantenna, a tiny device that could do for light what the large antenna did for radio.

A basic antenna is a long piece of metal that generates an electric current when struck by radio waves. The same trick works in reverse; when you make a call from your cellphone, for example, an electric current flows through the antenna, which then emits radio waves.

Radio and light are both electromagnetic waves--the only difference is their wavelength. Radio waves are a few centimeters to several meters long. Light waves, however, are measured in nanometers, and until recently, no one had the right tools to make an antenna tiny enough. In addition, metal doesn't interact with light in quite the same way it does with radio. Now, in today's issue of Science, Bert Hecht of the University of Basel in Switzerland and colleagues describe a new type of antenna that works for light.

To construct the antenna, the researchers deposited a layer of gold onto a glass slide and cut away at the gold with an ion beam until just a rod remained. They then removed a bit of gold in the middle of the rod. If the antenna was for radio, that gap would be the point where the electrical current was strongest. In the nanoantenna, this is where the light signal is concentrated and shines most brightly.

In theory, the antennas could be used to transmit signals by modifying the amount of light generated by an atom or molecule, says Jean-Jacques Greffet, a physicist at Ecole Centrale Paris. That could have big consequences for optical electronics, which could use nanoantennas to direct and amplify the light of single atoms or quantum dots--providing the wiring for super-tiny computers, for example. Hecht predicts these features will allow nanoantennas to become the interface between classical light circuits such as fiber-optic cables and quantum-scale integrated circuits. "If you project the importance of antennas for radio on our daily life," he says, "you get a feeling for how important antennas for light could become."

Related site
Hecht's Web site