Theory of optical nanoantennas and arrays based on surface plasmon resonance of plasmonic nanoparticles

This dissertation presents a theoretical study of the design of optical nanoantennas and antenna arrays based on the surface plasmon resonance of plasmonic nanoparticles. We begin from a brief review of the history of antenna theory in Chapter 1. These antenna theories and design experiences can not be directly used in the optical antenna design, mainly due to the fact that metals behave quite differently in the optical domain as compared to that in the RF/microwave domain. To address this challenge, in Chapter II we present our approach of designing optical antennas using sub-wavelength sized plasmonic nanoparticles at or near their surface plasmon resonance. To do this we first review the scattering resonance of plasmonic particles of uniform and concentric structures. Such particles can be placed around an optical source to effectively influence its radiation property, which indeed is the role of an antenna element but here operating in the optical domain. In Chapter III--V, we further present several design methods that provide optical antenna arrays composed of plasmonic particles with some specific radiation patterns. Specifically, in Chapter III we transplant the idea of the celebrated Yagi-Uda antenna design from the RFJmicrowave frequencies into the optical domain. End-fire radiation patterns with directivity 6∼8 times of a single dipole source can be achieved. Such a Yagi-Uda optical nanoantenna design is optimized in Chapter IV using the genetic algorithm, and the result is even 2 to 3 times better than those in Chapter III. In Chapter V, the concept of "self-similarity" is brought into the nanoscale and applied to the optical nanoantenna array design. Arrays that give similar radiation patterns at discrete operating frequencies are designed and analyzed, which may provide exciting potential applications in biological and chemical sensing. In Chapter VI, we present an optical radiating system with the feeding mechanism included by placing plasmonic particles are placed near a slab waveguide. A summary and conclusion is given in Chapter VII with a discussion on possible future works.