The Simulation And Optimization Of Metal Optical Nano-antennas Based On FDTD Method

Optical antenna is the analogue of traditional dipole antenna at optical frequencies. Itcould convert the energy of free propagating radiation to localized energy, and vice versa.Optical antenna could be used for several applications including high density data storage,optical lithography, microscopy, solar cells and Raman scattering. In this study about theoptical antenna, localization and the enhancement of the light need to be realized, so it isan important challenge to design the structure and optimize the performance. The mainpurpose of this thesis is to simulate numerically a metal optical antenna structure, to studyvarious influencing factor affecting the field enhancement, and to optimize the simulationresult.Firstly, because the size of the optical antenna is very small and their structures arequite complex, it need numerical simulation to study. So the finite-difference time-domain(FDTD) method is introduced. According to the optical properties of metals, the originalFDTD method is corrected based on the Drude model, utilizing auxiliary differentialequation. The recursive FDTD formula in 3-D that combines the uniaxial perfectlymatched layer (UPML) and ADE are obtained.Secondly, the interaction the incoming electromagnetic wave and the metal opticalantenna made up by the four nano Ag small spheres is simulated numerically based on theabove formula. It need change kinds of influence factors to study how they could affectthe field enhancement. And so the optimization condition in which the field enhancementcould obtain a maximum is found. The result shows: the direction of the propagation andthe polarization of the incoming wave, the frequency, the diameter of the Ag spheres andthe distance between the particles affect the enhancement of the field. Through optimizingthe factors which affect the enhancement, a light intensity enhancement of 2700 folds canbe realized.