Research On Asymmetric Transmissions Of Chiral Metamaterials

Metamaterials can achieve unique electromagnetic properties that could not be found innatural materials. Manipulating propagation of electromagnetic waves efficiently based onmetamaterials have always been regarded as a hot topic. In recent years, metamaterialscombined with other research directions becomes an cutting-edge interdiscipline, for example,a combination of chirality. Chirality is a purely geometric description of the symmetry,referring to the structure itself lack of geometric symmetry. In2006, a new and importantelectromagnetism effect-circular conversion dichroism was found by N. Zheludev in planarchiral metamaterials, resulting in a macroscopical asymmetric transmission phenomenon. Inthis dissertation, planar metamaterials will be theoretically and experimentally studied toachieve asymmetric transmissions and manipulate polarization states of electromagneticwaves. The research shows significant importance of achieving ultra-thin, multi-bandmetamaterial-based polarization devices. The main research topics and innovativeachievements gained are as follows:1. We propose a dual-band asymmetric transmission for forward and backwardpropagating linearly polarized waves in a bilayered chiral metamaterial. Simulated andmeasured results show that the bilayered chiral metamaterial can achieve cross-polarizationconversion with an efficiency of over90%for both y-and x-polarized waves. The proposedmetasurface can be regarded as an ultrathin polarization-controlled switch that is easilyswitched on/off by changing a linearly polarized wave to its orthogonal component.2. Based on the design method of metamaterials showing asymmetry transmissions, twoTHz asymmetry transmission devices for linear polarizations have been proposed. Thedesigned THz devices based on planar chiral metamaterials have many advantages includingsimple structure, easy fabrication and low cost.3. We demonstrate a kind of linear polarization rotator and investigate its opticalproperties by use of theoretical analysis and electromagnetic simulations. This structure has ahigh transmission and the polarization rotation angle of the transmitted wave is stronglydependent on the structure’s twist angle, which opens a bright perspective in controllingelectromagnetic waves.