Researches On Controlling Of The Electromagnetic Field Via Surface Plasmon And Periodic Nanostructures

In the field of the subwavelength optics, it is an important and long-term concerned issue that modulating the electromagnetic field in metal nano-structures in academe and technology and application domain. Surface Plasmon polaritons (SPP) presents a new vision for controlling the EM field. Based on the deep understanding of the basic properties of SPP, we invested different phenomena, with modeling and simulation of periodicity metallic films with different nano-structures, by using the Finite Difference Time Domain Method (FDTD), Finite Element Method (FEM) and rigorous coupled wave analysis (RCWA), in combination with Plasmonics and electromagnetic field theory. New nano-structures are designed and some potential optical applications are explored. The exciting results enrich the adjustment measures of the EM controlling of the metal structure in subwavelength dimension.This article first introduces some basic theories about SPPs. After that, a brief review of research processes of SPPs and relevant phenomena will be presented. And followed by some new exciting research directions related SPPs.Four main parts will be investigated of this subject.1. The collimation effect of the periodical metallic nano-structures is studied, and it is attributed to the surface Plasmon resonance mode collaborated with the localized SP mode. The influences of structure parameters such as period of the nano-gratings, slit width, thickness of the grooves are analyzed in detail, in cases of structures with single layer substrate or multi-layer substrate. It is found that both structures are sensitive with period and thickness of the grooves. An amazing collimation phenomenon with a certain band50nm around595nm has been discovered in the design of this paper. Actually, the band of the multi-layer substrate nano-structure is much broader than that of the single layer one. It may be useful for the design of related laser diodes.2. The features of a perfect infrared absorber which consists of a top lossless dielectric resonator array, a metallic film and a dielectric substrate (from top to bottom) are theoretically investigated. A tuning range of the resonant wavelength from 1550nm down to960nm via varying the dimension? of the structure is achieved. Perfect absorption is obtained at normal incidence and high absorbance maintains (>95%) even the incident angle is increased up to50°degrees. This phenomenon is attributed to the dielectric cavity resonance (DCR) and its hybridization with propagating surface plasmon resonance (PSPR). Resonance modes in this design are sensitive with period and thickness of the dielectric. In detail, it will be shown that a hybrid metal-dielectric absorber can realize two kinds of perfect absorption. This hybrid absorber is composed of an array of dielectric strips above a metal film. If the strips are enough small to support no resonant modes, a grating effect may come into play in the absorption, and perfect absorption can be obtained, which is sensitive of the incident angle similar to that of the metal grating absorbers. If the strips are enough large to support resonant modes, strong local resonance comes into action in the absorbing which is insensitive of the incident angle similar to that of the metamterial absorbers. In investigation, the magnetic field is parallel to the axes of the dielectric strips (TM polarization), the time harmonic factor is exp(-iwt), and the absorber works in the infrared range. Samples are successfully finished in the experiments and related processes will be presented in the fifth section. Besides, methods for fabraction and the setup for detection are investigated.3. It’s firstly shown that a metal can be turned into a broadband and omnidirectional absorber by coating a purely-dielectric thin layer of grating. An optimal design for such an absorber is proposed by putting a dielectric slot waveguide grating (SWG) on the metallic substrate. The SWG consists of two germanium nanowires (Ge NWs) separated by a sub-100nm slot in each period. Average absorption reaches90%when the incident angle varies between0°and80°over a broad wavelength range from300nm to1400nm. Multiple optical mechanisms/effects, namely, diffraction, waveguiding in the high-index Ge NWs and low-index air slot, Fabry-Perot resonances as well as surface plasmon polaritons (SPPs), are identified to govern the absorption characteristics of the present absorber. The designed absorber with such a dielectric grating is easier to fabricate as compared with other absorbers with metallic nanostructures, and has potential applications in e.g. solar cells and photodetectors.At the end of this thesis, the summary is given and the research plan for future as well.