Nano Lett. 13, 142–147 (2013)

Similar to their classical counterparts, nanoantennas are optical components that can bring light signals from the (nanoscale) near-field to the far-field. In analogy to radiofrequency antennas, optimal operation is achieved if these nano-components are impedance-matched to free space and can be tuned at will. At radio wavelengths this is usually achieved by using lumped circuit elements, which, however, do not exist at optical frequencies. Andrea Alù, Naomi Halas and colleagues have now experimentally demonstrated optical nanoscale circuits with three-dimensional lumped elements, whose operation is based on photons rather than electrons. The researchers used the optical lumped elements to tune and impedance-match a single optical dimer nanoantenna. They managed to control the antenna's resonance and impedance bandwidth using suitably designed lumped-element loads made from combinations of basic circuit elements, namely nanoscale capacitors, inductors and resistors. These results may open a route to extending standard circuit concepts into the visible domain for applications that include data storage and wireless optical links.