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Chiral crossed grating in optical frequency

Authors Leung, Dick Ho Ming
Issue Date 2011
Summary The emergence of metamaterial opens up the opportunities to systematically study electromagnetic phenomena. By designing specific structures, certain new properties can be found and these properties are absent in the materials alone. The most famous example is that by using a twisted structure, electric and magnetic resonances can be excited and hence giving rise to negative refractive index. This new property is just one of the potential applications of metamaterial. In this thesis, circular dichroism and circular conversion dichroism are the focused electromagnetic phenomena to be studied. For the theoretically part of this thesis, fundamental relations on Jones matrix (transmission matrix) causing circular dichroism and circular conversion dichroism are derived based on transpose symmetry. The relation on Jones matrix causing asymmetric transmission is also derived. The derived relations are then investigated through experimental and simulation results of a crossed grating (experiment are done by Vincent Gao in my research group) which consists of two metallic gratings separated by a buffer layer and a twisted angle. By comparing experimental and simulation results to the derived fundamental relations on Jones matrix, it is demonstrated that (1) asymmetric transmission comes from asymmetric structure, such as asymmetric ·SiO2 buffer layer, which is different when viewed from forward and backward direction, alld (2) the dips in transmittance are attributed to parallel or anti-parallel resonant current modes which are excited differently by RCP and LCP waves depending on chirality of crossed grating. However, the simulation results start to deviate from the experimental results when twisted angle is less than 45°. In the simulation results, more oscillations are observed when compared to the experimental results. The exact reason for this behavior is still not known.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2011
Language English
Format Thesis
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