Electromagnetic Wave Manipulation and Structuring via Ultrathin Metamaterials

Abstract

Metasurfaces consists of a two-dimensional array of ultrathin resonators and offer a versatile degree of freedom to tailor the amplitude, phase, and polarization of electromagnetic (EM) waves. Such unique ability of metasurfaces enable the realization of various interesting phenomena at a chip scale. As a developing field, the hunt for effective materials and methods to realize efficient multifunctional metasurfaces is an ongoing research topic. This thesis focuses on the design and realization of efficient all-dielectric metasurfaces to manipulate EM waves in novel ways. At first, a mathematical model for proposed step-index nanowaveguide is developed to identify its phase controlling mechanism of a proposed cylindrical-shaped fundamental building block. Stepping forward, this mathematically modelled, and numerically optimized building block is employed to demonstrate various electromagnetic phenomena through all-dielectric, transmission-based, efficient (≈ 73.4 %) and polarization-insensitive metasurfaces. Different innovative design methodologies are proposed which integrate multiple distinct phase profiles into a single device and are versatile due to their polarization-insensitivity. These metasurfaces can lead to highly concentrated optical vortices whose focused ring-shaped profiles carry orbital angular momentum at the miniaturized scale. For focused optical vortices generating metasurfaces, the phase profiles of a lens and a helical beam are merged for the visible wavelength of 632.8 nm. Similarly, for the operational wavelength of 632.8 nm, metasurface-based novel axicons are demonstrated to generate zero- and higher-order Bessel beams without using additional components. Finally, highly efficient (≈ 84% over the entire spectrum of interest) metasurfaces are demonstrated for near and deep ultraviolet regimes where polarization-insensitive meta-holograms are implemented numerically for design wavelength λd = 250 nm.