The fact that radio waves behave like light--exhibiting optical properties like reflection, refraction, diffraction and interference--was demonstrated back in 1887 in Karlsruhe, Germany, by Heinrich Hertz (after whom Hz was named). Since then radios have gone to higher and higher frequencies, enabling more and more data to be communicated, but making the antennas for transmission and reception smaller and smaller. Now researchers at the Karlsruhe Institute of Technology (KIT) have come full circle, demonstrating nano-antennas so small that they operate at the same frequencies as light waves, enabling information to be transmitted by optical-frequency radios that can transmit data up to a million times faster that radios today.

KIT scientists claim to have created the world's smallest antennas using the same principles as traditional radio antennas, which transmit and receive radio waves best when they measure about half the wavelength of the signal. Light waves operate at ultra-high frequencies compared to the GHz frequencies typical of electronic devices today, making their antennas corresponding small. For instance, yellow light is about 500,000 GHz, corresponding to a wavelength of about 600 nanometers. To transmit and receive radio waves at those frequencies would require an antenna around 300 nanometers. Other researchers have reported progress toward creating optical frequency antennas that small, but KIT scientists claim that they have the world's first technique that could be used to mass produce nanoantennas.

The gold nanoantennas were fabricated by Hans-Jurgen Eisler and Matthias Wissert at the Light Technology Institute at KIT. The team used electron-beam lithography to sculpt the tiny devices. In tests, these nanoantenna were able to send and receive optical data at speeds thousands of times faster than today's fastest radios. For instance, using antennas in the range of 400-to-1000 nanometers, data could be wirelessly transmitted and received at speeds about 10,000 times faster than today. For the future, the KIT scientists believe they can fabricate antennas significantly smaller than 100 nanometers, potentially enabling future optical-frequency radios to operate at speeds up to a million times faster than the fastest radio communications today.

Besides communications, these nanoantennas could also be used to optically image tiny structures that have been too small to observe until now. For instance, nanoantennas could focus light in spots as small as 10 nanometers--about the size of individual biomolecules, which have been too small to image before now. Nanoantennas could also be used to produce images of many tiny man-made structures, such as electronic sensors, transistors and other small semiconductor structures. As a transmitter, the tiny nanoantennas could also be used to emit streams of individual photons for a variety of laboratory applications, including the optimization of photovoltaic modules.

Next the KIT researchers plan to further refine their electron-beam lithography techniques in order to fabricate even smaller antenna, as well as optimize their current designs and demonstrate working radios using their nanoantennas.