Beam Modulation In The Subwavelength Metallic Structures Based On Surface Plasmon Polaritons

Surface plasmon polaritons (SPPs) are electromagnetic surface modes by interaction of free electrons of metallic surface with environmental photons. It has shown a great prospect on many areas, such as integrated nano-photonic, high-density storage, biochemical detection and sensing owing to its shorter effective wavelength and near-field enhancement features.The excitation and modulation of SPPs are all based on the interaction of light with subwavelength metallic structures. In this thesis, the main research object is two-dimensional subwavelength metallic slit arrays and gratings.Numerical methods are adopted to study the mechanism of how to regulate SPPs in such structures, and some functional components are designed to achieve the regulation of the light field. The main contents are as follows:1. Analysis of the resonance transmittance properties of metallic sub-wavelength slit with an embedded grooveIn this part, we study the dependence of the transmission spectrum of slit on the depth of the embedded groove. Comparing with the results from cavity resonance mode theory, we find that the shift situation of the subwavelength metallic slit comes from two reasons, namely increase in the cavity length and the increase in the resonance mode number. The spectrum changes, such as blue-shift, are the hybrid results of the increase in both of the mode number and the cavity length.2. The study of beam manipulation by metallic nanoslit arrays with grooves inside slits or on the input planeThe manipulation of light on a subwavelength scale is typically achieved through the regulation of the phase on the outgoing surface. Usually, the phase shift experienced by light is sensitive to the geometry of structure and the materials surrounding. In our study, we proposed two methods to regulate the phase delay by different mechanism. The first one is adding grooves inside the slit array, this method can be thought of as a result of the increased effective length of slit, and the second one is notch grooves on the input plane of slits array, which is based on the interference effect between the slits and grooves. Based on them, metallic nanoslit arrays were designed for beam focusing and deflection. The simulated results indicate that the two methods are effective mechanism to tune the phase retardation at transmitted field.3. Second harmonic moire effect in a double-layer metallic nano-gratingMoire effect has been used in many metrical areas for a long time. A near-field moire effect between two subwavelength gratings was reported recently and extended the existing moire techniques to subwavelength characterization of nanostructures. It is clearly the coupling of SPPs between the two gratings would play a key role in the form of moire fringes.The results show that second harmonic moire fringes, which period is only a half of normal moire fringes, can be produced behind the double-layer nano-grating due to the change of interlayer space. In the subwavelength metallic grating, the transmitted properties are quite different with the case in traditional optics because of the presence of SPPs coupling. When the lateral shifts between the slits in two gratings are equal to zero and a half of periodicity of grating, there could be a strong pass of light at these two positions with the change of interlay space. It is obviously that the periodicity of these two positions is only a half of periodicity determined by the geometry. And that is reason why the second harmonic moire effect can be produced in the subwavelength double layer metallic grating.