Optical nanoantennas

The field of optical nanoantennas, a rapidly developing area of optics, is reviewed. The basic concept of an optical antenna is formulated and major characteristics relevant to this structure are identified. A classification of nanoantennas into metallic and dielectric (the latter including semiconductor nanoantennas) is made. For either category, the literature is reviewed and strengths and weaknesses of different approaches are discussed. The basics of nonlinear optical antennas are outlined. Future avenues of research and application areas for the field are highlighted, and its prospects are examined.