Research On The Far-Field Characteristics Of Nano-Metallic Optical Antenna

With the development of micro-processing technology and integrated optics, the miniaturization of optical components has made their scales close to diffraction limit. How to realize the optical transformation between near and far field in sub-wavelength scale is an urgent problem to be solved. Surface plasmon polaritons (SPPs), localized in nano-metallic structures, have unique optical properties. Due to their strong localization property, they can effectively couple the energy from free space to sub-wavelength scales. Nano-metallic optical antenna, composed of various metallic nanoparticles, is a device which fully utilizing this. Thus, they are widely used in the field of new light sources, photovoltaic cells, highly sensitive bio-sensors and so on. It is noted that nano-metallic optical antenna has much difference than radio or microwave antenna since they also affected by the SPPs. There have been number of researchers focused on the near-field Characteristics and radiation efficiency of different optical antennas. Based on these analyses, the far-field Characteristics are discussed in this work in detail. Significant results with theoretical analyses are finally provided, which can be very greatly theoretic reference value to design and realize of optical antennas.In this paper, the far-field characteristics of optical dipole antenna and optical Yagi-Uda antenna are researched. According to the classical traditional antenna theory and the related properties of nano metallic structures, the corresponding optical antenna models are built, simulated and modeled. Through observation of far-field changes and near-field normal distribution of metallic structures optical antenna, we analyze the influences of SPPs on near-field enhancement and far-field radiation, which arrive at the far-field characteristics of appropriate nano-metallic optical antenna as well as the similarities and differences between classical antenna and optical antenna. The paper mainly conducted the following researches and obtained the corresponding results and conclusions: 1. Introduction about the background and significance of research in chapter 1.Firstly, the basic concepts, the history of development, research status of SPPs and optical antennas are introduced, and followed by the purpose and significance of this paper, finally the main research work is introduced.2. Introduction about the FDTD method in dispersion medium in chapter 2.Several metal dispersion models are introduced at first, and select modified Drude model to simulate metallic material. Next FDTD method in dispersion medium is realized by introducing dielectric flux density D in detail. The related contents in FDTD method, the PML Absorbing boundary condition, electric dipole excitation source and numerical stability, are discussed. At last, the theory of near-to-far field transformation is introduced followed by the extrapolation formula of time-harmonic field in three-dimensional.3. Research on the far-field characteristics of two kinds of nano-metallic ODA in chapter 3.Firstly, two kinds of optical dipole antenna models are described in this chapter. Next simulate the changes of far-field directivity as the length of antenna increases and near-field normal electrical field, finally analysis the changes of the mode of localized surface plasmon (LSPs) and the influence on the far-field directivity. Research show that far-field characteristic of optical dipole antenna is similar to conventional dipole antenna, and its far-field pattern will be faster appear side lobes owing to the effect of high-order LSPs. If optical dipole antenna want to arrive at better far-field directivity, its size must maintain in the sub-wavelength, which offer the very significant proposal and theoretical reference for the design and implementation of optical dipole antenna.4. Analysis the far-field directivity of OYUA in chapter 4.Firstly, the optical Yagi-Uda antenna model is constructed, and then scanning its parameters. Secondly, its far-field directivity is analyzed, which concluded that its far-field characteristics are similar to traditional optical Yagi-Uda antenna. Sharper radiation characteristic and higher gain will get by changing its parameters and adding the number of director. But the length of feed, director and reflector is shortened because of stimulation of LSPs. Therefore optical Yagi-Uda antenna can effective better unidirectional director only when its size keep under sub-wavelength.5. Summary and Outlook about this paper in chapter 5.In summary, far-field directivity characteristics of optical dipole antenna and optical Yagi-Uda antenna are studied. We research the influence of LSPs on optical antenna, and studied the similarities and differences between the optical antenna and the conventional antenna, which offer a very theoretically significant and substantial reference value to the design and manufacture of optical antenna.