Optical antennas and enhanced nonlinear effects

Optical nanoantennas are important devices for efficiently converting propagating and radiated waves into confined and dramatically enhanced fields at the nanoscale. Recent advances in the realization and modeling of subwavelength optical antennas have led to their use in energy harvesting, biological and chemical sensing, optical imaging, nonlinear wave mixing, harmonic generation, and various other near-infrared and optical applications. Typically, nonlinear optical activity is very weak in nanoscale volumes filled by nonlinear media. However, the resonant interaction of light in subwavelength nanoantennas offers an efficient way to explore nonlinear processes at the nanoscale, based on the strong field enhancement in their proximity, and to design, analyze, and predict optical phenomena that were previously not accessible. In this chapter, we review recent findings on nanodipole antennas loaded with nanoparticles for third-order nonlinear operation. We extend the concept of optical impedance of nanoantennas when nonlinear effects are present, and we apply it to model strong optical bistable effects and all-optical nanodevice designs, including nanomemories, nanoswitches, and nano-rectennas.