Design and analysis of metasurface at visible and infraredspectrum

Metasurfaces that can be designed in reflection or transmission modes enable unprecedented control of phase, polarization, and amplitude of light. Thanks to these very effective features, metasurfaces have drawn remarkable attention in wavefront manipulation for various applications. Within the scope of this thesis, metasurfaces consisting of metallic and all-dielectric antennas are designed and realized in a variety of optical applications such as light bending, focusing, vortex beam generation, beam splitter and asymmetric light transmission in the infrared and visible band. In advanced optical applications, unidirectional light flow has become a significant demand. In the third part of this thesis, a broadband and polarization-insensitive asymmetric transmission mechanism is shown in the visible wavelength. The metasurface made up of periodically arranged trapezoidal shaped aluminum metals on a sapphire substrate is designed to obtain desired optical response for both directions of illumination. Asymmetric transmission wavelength interval of the proposed metasurface is related to the Wood-Rayleigh Anomaly. The structure has over 50% forward transmission, less than 28% backward transmission and at least 3 dB contrast ratio in the entire visible bant. Beam splitter is essential component in diverse optical sistems such as spectroscop and interferometer. In the fourth part of this thesis, polarization-independent beam splitters using all-dielectric phase gradient metasurfaces are proposed and analyzed in the visible region. The metasurface is composed of periodically arrayed unit-cells and phase difference between adjacent unit-cells on the metasurface is π radian. The sign of phase gradient in the proposed metasurface changes periodically. Total transmission and the angles of the split beams, which are separated to both sides are determined to be 90% and ± 46.8°, respectively. In the fifth part of this thesis, an asymmetric transmission structure made up of phase gradient all-dielectric metasurfaces on the glass substrate in the visible spectrum is proposed. In order to examine its working performance, electromagnetic wave and ray analysis techniques are used together. It is shown that broadband asymmetric transmission with high contrast occurs in the wavelength range of 500 nm - 715 nm. Particularly, the transmission difference between forward and backward excitations at 532 nm wavelength is nearly 90%. In the sixth part of this thesis, it is proposed a mid-IR filter whose transmission behavior can be tuned with an external stimulus without geometric and structural changes. It is demonstrated that the filter behaves as an optical diode in the room temperature whereas it operates like bidirectional isolator due to the phase transition of vanadium dioxide triggered thermally heating. The proposed filter can be used as smart IR structure in order to protect the sensitive IR sensors. In the seventh part of this thesis, it is demonstrated a tunable planar layered thin film by using the vanadium dioxide that is phase transition material at IR spectrum. The wavelength shift of 400 nm in scattering resonances is obtained. By adding a metasurface layer to the planar layered thin film, the transmission and reflection characteristics of this modified design is theoretically investigated. Compared to the only planar layered thin film structure the transmission contrast is increased owing to Mie-type scattering.