Modeling and simulation of optical micro-nano-antenna for THz radiation

Abstract

Generally optical micro-nano-antenna can be used to modulate lightwaves in the sub-wavelength scale, which is a hot and difficult research issue. Patterned metal nano-antenna array can be utilized to stimulate intense surface plasmon polaritons (SPPs), so as to realize sub-wavelength focusing by breaking through diffractive limit, and thus remarkably improving THz imaging efficiency. In this article, firstly, based on SPPs, the Drude dispersion model for metallic film is analyzed, and the dispersion relations and excitation modes of the SPPs are discussed, and the numerical analysis methods of the metallic micro-nano-antenna are also presented including a time-domain finite integral method and a frequency-domain finite element method. According to related literature, the key optical micro-nano-antenna unit is modeled, and a metasurface formed by etching a gold thin film on a silicon substrate is designed. Through regulating parameters including the number and size of the openings and the line width, the SPP excitation in THz band is studied. Using finite element and adaptive mesh division method, the common electromagnetic properties such as transmission intensity and electric field distribution are simulated and analyzed. The simulations show that the optical micro-nano-antenna element can resonantly induct terahertz wave, and demonstrate a resonant electric-field at the aperture gap, which will move towards high frequencies end as increasing the gap size or line width, so as to lay a concrete foundation for continuously fabrication THz-SPPs devices.