Metasurfaces Plasmonic با طراحی خطی و غیر خطی ساختمان بلوک
Abstract: Plasmonic metasurface is an array of sub-wavelength plasmonic particle which is designed to obtain unusual performances by employing the localized surface plasmon (LSP). The dependency of the LSP on the geometry and the material of the plasmonic sub-wavelength particle have opened a wide range of applications for plasmonic metasurfaces. In the first chapter there is brief review of metamaterials and plasmonic metasurfaces. In the second chapter we present the concept of transmitarray concentrator implemented in optics. Planar concentric loop antennas are used as the elements for a 21 × 21 array to concentrate the incident plane wave at a desired distance. Finite difference time domain is used to obtain the performance of the periodic array of each element on the transmitarray and then free space dyadic greens function is employed to find the field distribution at each point, to show the focusing behavior of the metasurface. Third chapter investigates the concept of multi-layered tripod frequency selective surfaces in infrared. A full wave analysis based on finite difference time domain technique is applied to comprehensively characterize the structure and obtain the performance for both normal and oblique waves (for TE and TM polarizations). The layered tripod structure can be envisioned as a mean to realize cascaded LC circuit configurations achieving desired filter performance. A wide stop-band IR nano-filter which is almost independent of incident angle and polarization is demonstrated. Chapter 4 is concentrated on a functional metasurface building block which is multi-material loops. Plasmonic nano loops has been shown to be a capable candidate for creating building blocks of metasurfaces to manipulate the light in desired ways. Concentric loops can couple to each other strongly or weakly based on the relevant designs. The low-coupled multi-material loop metasurface can be employed as a frequency selective surface with number of separated bands. On the other hand one can take advantage of high coupling between the loops to achieve two different resonances; one will be a high quality factor and sensitive mode and the other a radiating wideband low-loss resonance. In both resonances the building block has a sub-wavelength size. Here the performance of periodic array of multi-material loops is investigated by means of finite-difference time-domain technique. Based on the performance of a single plasmonic loop with general Drude material the behavior of the multi-material loop metasurface is investigated. We show how choosing the proper materials can control the resonance characteristics. The performance of multi-material loops is studied by utilizing the induced net dipole moments on the concentric loops and appearance of Fano-like resonance in the high-coupled case is demonstrated. Moreover, the large field enhancement as a result of a subradiant resonance is studied. The sensitivity of the structure to the spacer layer permittivity and loss are investigated in details. And last but not least, the effects of breaking the symmetry in the multi-material loop building block are also examined. Excitation of the quadrupolar mode of the loop, Fano-like resonance and high intensity localized field are elucidated for the non-concentric multi-material loop building blocks. In chapter 5, the performance of multi-material loop metasurface integrated with Kerr nonlinear material is investigated comprehensively with finite difference time domain method. Optical bistability is obtained by exciting the metasurface with a saw-tooth profile for its amplitude. The effects of coupling between the plasmonic loops on the bistability curve are studied and the trade-off between the required intensity for switching and the extinction ratio of the two states of the switch is explored systematically. The dissertation is finished by a number of recommendations for the future directions for this research.