Optical Nanoantennas For On-chip Optical Interconnects

During the past few years, optical nanoantennas have attracted increasing attention and become important subjects in the nanophotonics community, due to their widespread applications in a variety of fields, including nano-imaging, photovoltaics, nonlinear optics and even biological and medical sciences. Similar to their radiofrequency and microwave counterparts, optical nanoantennas can efsiciently mediate subwavelength-localized energy and free-space radiation. In this context, a number of conventional antennas such as monopole, dipole, bow-tie and Yagi-Uda configurations have been successfully scaled down to the nanometer scale, accompanying with a series of both theoretical and experimental studies. However, since nanomaterials like metals possess distinctly different electromagnetic responses in the optical spectrum in contrast to those in the radiowave and microwave regions, classical antenna theory cannot be directly applied to optical nanoantennas. Therefore, how to design and use optical nanoantennas properly become an interesting research topic.It is also noteworthy that, compared with conventional antennas, optical nanoantennas have much smaller dimensional sizes and could work at much higher frequencies. These intriguing features make it possible for optical nanoantennas to provide higher density integration and higher data transmission rates for wireless communication systems, thus offering new possibilities for the realization of nanoscale optical wireless communications.In this dissertation, we present a systematical study of the optical nanoantennas and explore their potential applications in on-chip optical wireless interconnects. To this end, we first review the history and the recent development of optical nanoantennas and then introduce the optical-nanoantenna theory. Based on the different optical responses of metals and dielectrics, we design and investigate different types of optical nanoantennas, respectively.For metals, we propose plasmonic horn nanoantennas. Different from ordinary resonant-types such as dipole and Yagi-Uda nanoantennas, the presented horn nanoantennas are based on non-resonant working mechanisms and would not be limited by narrow bandwidths. A high coupling efficiency of more than 95% over an ultra-broad bandwidth from 1200 nm to 2000 nm is achieved. The horn nanoantennas also show high directivities and gains. Then we apply the horn nanoantennas on both transmitting and receiving ends to build a point-to-point optical wireless nanolink, which shows a significantly superior performance to that using dipole nanoantennas and direct plasmonic waveguide links, with a 100-fold enhancement in wireless power transfer and a stable transmission property over the entire telecommunication wavelength range. Furthermore, by introducing and integrating with other plasmonic components such as splitters and filters, we demonstrate an on-chip broadband optical wireless communication network and show its broadcast and WDM functions.Considering the high intrinsic loss of the metals in the optical frequencies, we also expand our horizons into the low-loss dielectric materials such as silicon. Based on the intriguing electric and magnetic resonances supported by the dielectric nanostructures, we design dielectric patch nanoantennas and demonstrate their contributions in tailoring the spontaneous emission of nanoscale single emitters like fluorescence molecules and quantum dots. In addition, since classical theory is no longer applicable for a coupled system that contains non-spherical nanoantennas, we propose a semi-analytically retrieval method and build an equivalent model to quantitatively interpret the angular radiation characteristics of such an antenna-emitter coupled system. Following the guidelines provided by the equivalent model, we show the control over the angular radiation of the single emitter, such as the directive emission enhancement and rotation.At last, a summary and an outlook are given with discussions on our future work and the possible development in the field of nanoantennas.