Research On The Characteristics Of Nano-Scale Metallic Optical Antenna

With the invention of near-field optical microscope and the development of nanotechnology, people have been recognizing metal in new ways. In recent years, more and more researchers are paying their attention to the optical properties of metal in the nano-structured and a new subject is initiated: Plamonic. As the dielectric constant of metal is negative in the visible and infrared region, when light radiates on the metal, free electron oscillates. If the frequency of the electron is equal to the frequency of the incident electromagnetic wave it will be resonant, which is so-called surface plamon polaritons (SPPs). The strongly confinement properties of the SPPs could break through the diffraction limit, reduce the bend scattering and make light propagate in nano-scale region. So it becomes possible to fabricate sub-wavelength optical devices and realize the integration of optical circuits and electric circuits. SPPs are attracting wide interest of potential applications in subwavelength optics, data storage, plasmonic chips and bio-photonics. Optical antenna is a device composed of metallic nanoparticle which can effectively couple the radiation energy in free-space to sub-wavelength scale by means of SPPs. The study of optical antenna can improve the near-field optical microscope and increase the capacity of the optic data store. We mainly studied the property of near field and far field of single and double nanoparticles optical antenna. The element of the antenna is nanorod and ellipsoid.The main content of this paper is divided into the following four parts:(1) A brief introduction about the research background in chapter 1.The concepts and research progresses of SPPs and optical antenna are introduced at first followed by the research significance and purpose.(2) Discussion on the Finite-Difference Time-Domain (FDTD) method in detail in chapter 2.Five mostly used numerical methods in optical simulations are introduced at first. Then we compared the advantages and disadvantages of these methods. Next FDTD method is introduced in detail. The center-difference iterative formulae are studied firstly. Then the PML absorbing boundary condition, source type, numerical stability and dispersive are described. At last the dispersion models of metal are introduced. Drude model parameters for the numerical fitting have been satisfied with the experimental data.(3) Analysis of the properties of near field of single and double nanoparticle optical antenna in chapter 3.The influence of different parameters of single and double nanoparticle on the near field electric filed is discussed. The simulation shows that the proper parameters for optical antenna could change the distribution of energy on the surface of optical antenna, the local electric field can be enhanced for several hundred times.(4) Analysis of the far field of single and double nanoparticle optical antenna in chapter 4.The influence of different parameters of single nanoparticle and double nanoparticle on the far field is discussed. The calculation shows that the parameters of optical antenna could impact the radiation direction for single nanoparticle rather than double nanoparticle. With proper parameters for optical antenna the radiation efficiency could be improved.In short, the FDTD method is employed to analyze the near-field and far-field of optical antenna and our result is expected to be of great benefit to the fabrication and design of the optical antenna.