Individual nanoantennas loaded with three-dimensional optical nanocircuits.

Nanoantennas are key optical components that bridge nanometer-scale optical signals to far-field, free-space radiation. In analogy to radio frequency antennas where tuning and impedance-matching are accomplished with lumped circuit elements, one could envision nanoantenna properties controlled by nanoscale, optical frequency circuit elements in which circuit operations are based on photons rather than electrons. A recent investigation of the infrared nanocircuits has demonstrated the filtering functionality using dielectric gratings. However, these two-dimensional prototypes have limited applicability in real-life devices. Here we experimentally demonstrate the first optical nanoscale circuits with fully three-dimensional lumped elements, which we use to tune and impedance-match a single optical dimer nanoantenna. We control the antenna resonance and impedance bandwidth using suitably designed loads with combinations of basic circuit elements: nanoscale capacitors, inductors, and resistors. Our results pave the way toward extending conventional circuit concepts into the visible domain for applications in data storage, wireless optical links, and related venues.