The Research On Transmission Properties Of SUB-wavelength Metallic Annular-aperture Based On Supface Plamon

Ebbesen had demonstrated the extraordinary optical transmission in sub-wavelength metallic nanoholes in1998, which led to the fast development of the research about plasmonics. The surface plasmon resonances in subwavelength nanostructures enable breaking the diffraction limit and developing traditional optics to sub-wavelength nano-optics. The plasmon resonant modes of the nanostructures are sensitive to the shapes and sizes, which leads to a strong enhancement of the localized electric field. In this thesis, we propose a new kind of nanostructures, consisting of two or more intersected annular apertures, and analyze optical properties.Firstly, a symmetrical subwavelength double-annular-aperture (DAA) is proposed, and the optical properties of DAA is calculated with FDTD numerical algorithm. With the help of this structure, an analysis method of plasmonic resonances of metallic nanoparticles has been demonstrated. Based on the charge distributions of the metallic nanoparticles in DAA, we investigate the principle of variation of internal metallic nanoparticles surface plasmon resonances, as well as the influence of the complete aperture structure. Enhancement of localized electromagnetic field intensity and an apparent Fano resonance has been shown in the presented DAA. The Fano resonance is originated from the destructive interference of the plasmonic modes.Then based on the symmetric DAA, an asymmetric nanostructure composed of three annular apertures with different sizes has been presented. It has been shown that the spectrum is formed due to Fano resonance essentially. This paper focuses on researching the characteristics of enhancement and the surface plasmon resonances coupling, and finds the coupling resonance characteristics of senior dark field in the asymmetric annular aperture structure. Multiple Fano resonances are achieved by adjusting the structure’s parameters, which greatly enhance the tunability of the optical properties of the subwavelength nanostructure. The Fano resonances in sub-wavelength metal annular-aperture structure can be used to realize high-sensitivity biological sensors.