Research On Plasmon Resonant Characteristics And Mechanism In Metallic Grating And Micro-nano Structures

Abstract:Enhanced transmission through subwavelength metallic openings has aroused great interest since the work of extraordinary optical transmission (EOT) through a subwavelength hole array, not only for the rich physical mechanisms, but for their potential applications in optics and optoelectronics. Related studies and applications are penetrated into many fields. In this PhD thesis, surface plasmon resonant transmission properties, phase resonance, Plasmon induced transparency and related phenomena and mechanism in compound metallic grating, heterogeneous structures, micro-nano metamaterials structure, nanotubes and array structures are studied by using the finite difference time domain method (FDTD) combined with surface plasmon subwavelength optics and electromagnetic field theory.The main research contents of this paper are as follows:1. Compound metallic gratings are proposed, and related optical properties are studied. Compound metallic gratings can be constructed by difference of the structure. For example, perpendicular bumps are introduced in two silts of the metallic grating. As the bumps are set symmetrically in the slits, the waveguide resonant peaks for the even modes exhibit a red-shift, odd modes present a blue-shift compared with the resonant peaks of grating composed of bare slit. As the bumps are set asymmetrically, the dips in transmission spectrum and waveguide resonant peaks are aroused. The dips can be tuned by shifting the position and changing the size of bumps in the slit, and it seems that the dips are more sensitive to the simultaneous change of bumps and cuts for a compound metallic grating with perpendicular bumps in one slit and with cuts in another slit. The corresponding physical mechanisms for above phenomenon are discussed by phase resonance, followed by some qualitative explanations in terms of field distribution. In addition, from the distribution of electronic and magnetic field, one can achieve that the light propagate from any one slit of the two slits in some specific wavelength. In addition, compound metallic gratings also can be achieved by adjusting dielectric environment. The Effects of dielectric environment on the phase resonances in compound grating were investigated theoretically. The dips in transmission spectrum are obviously tuned by changing the dielectric environment, deepened dips can be arose by slight difference between the dielectric constants in two slits, almost all values of the dips are near to zero, and photon forbidden band gaps arise on transmission spectra. The corresponding physical mechanisms for above phenomenon are discussed by F-P-like and phase resonance mechanisms.2. The heterogeneous structure of metal grating is presented and studied. It is easy to imagine that the ratio of different metal also play an important role in determining the plasmonic behaviors of this heterowaveguide. Perforated Au/Al multilayer slit gratings are proposed and its optical transmission properties are studied. It is found that, compared with the conventional single-Au-film slit grating, all resonant peaks exhibit a blueshift, and the peak collapses firstly and subsequently enhances as the ratio of the metal Al increases. The results are expected useful for the design of optical devices according to appropriate metal proportion. In addition, it is also presented that the resonant transmission sensitively depends on the thickness and slit width of metal Al film, magnitude modification, redshift and blueshift of the resonance modes, and band gap are observed. A metallic heterowaveguide for subwavelength band-stop filter in the range of visible light can be achieved.3. Asymmetric and symmetric couplings within a pair of C-shaped resonators (CSRs) are presented and studied. The former shows that a typical and prominent plasmon-induced transparency (PIT) spectral response can be observed and it stems from asymmetrically coupled resonance (ACR) between the subradiant and superradiant modes due to exactly identical resonance frequency but different quality factors (Q-factor). The mechanism of such induced transparency is elucidated well by resonant hybridization and the induced currents within the CSRs. Simultaneously, the results show that PIT-like effect can also be achieved in symmetric CSRs, symmetrically coupled resonance (SCR) between the subradiant and superradiant modes also give rise to transparency window. Essentially, the phase coupling of near-field, besides symmetry or asymmetry, is the crux of the PIT. Comparing the transparency window in asymmetric coupling, the PIT-like effect in symmetric coupling becomes less strong than the former. It is considered that a broken symmetry is not the only prerequisite for PIT-like effect; but it plays an important role of prominent PIT-like transparency window. This not only sharpens our understanding of the existing concept, but also provides a profound insight into the plasmonic coherent interference in the near-field zone.4. The formation and evolution mechanisms of plasmon resonance from single Ring-shaped-nanotube to dimer and arrays are studied, an attempt has been made to bridge the gap between single-tube、dimer and array. A square-core metallic nanotube array also is proposed, and its optical transmission properties are investigated theoretically. The results show that the resonant modes can be divided into many types from visible to near infrared region in the transmission spectrum, for example, dipole, quadrupole, hexapole resonance, and so on. And the optical transmission characteristics are strongly depended on the structural parameters and medium parameters, resonance modes in the transmission spectrum exhibit blue-shift, red-shift, merging, splitting, degeneration and enhance, with the variation of the shape, size and unit number inside the slit channel. The mechanism of related phenomena and field distribution are analyzed and discussed.