Studies On Mechanisms And Properties Of Chirality Enhancement Of Metasurfaces

Chiral metasurfaces are 2D or quasi-2D photonic components and devices composed of sub-wavelength units that show strong optical chirality thanks to the underlying novel physics and advanced nanofabrication development.They have wide application prospects in chiral sensing,chiral particle separation,and chirality regulation.Based on the chirality enhancement mechanisms and properties of chiral metasurfaces,this paper improved and designed a variety of chiral nanostructures with strong chiral responses.The main works are as follows:Firstly,several chiral metasurfaces in near infrared regime were studied and designed.In first part,two metallic chiral structures were studied.The first is a gold disc-double split ring resonator nanostructure,and the maximum near-field chirality density was increased to 160-fold at 1400 nm after optimizing the structural parameters,which is an order of magnitude higher than the original structure.The second is a bilayer gold nanorods nanostructure.The transmission spectrum and circular dichroism spectrum of the structure were measured in experiment,and the CD spectrum trough and peak are-0.22 at 896 nm and 0.15 at 945 nm,respectively,which are consistent with simulation results,and were verified by Born-Kuhn theory.Secondly,two dielectric chiral structures were studied and designed.The first is a square silicon split ring nanostructure,and the CD reached 0.585 at 1302 nm after optimizing the structural parameters.The second is a designed Z-shaped silicon nanostructure with CD value of 0.69 at 1016 nm.The second part is chiral metasurfaces in ultraviolet regime,and two kinds of structures based on diamond and hafnium oxide were studied and designed.The first is a diamond bilayer film nanostructure.This paper mainly analyzed the circular dichroism of the structure and the CD is 0.55 at 238 nm.The second type are nano-disk structure and its variants.The disk structure,holey disk structure and annular holey disk structure were designed with diamond and hafnium oxide respectively,and the transmission spectrum,electromagnetic fields and chirality field of these structures were studied.The maximum chirality density reached 236-fold in ultraviolet regime.In this paper,several chiral metasurfaces with strong chiral responses were improved and designed,especially in the circular dichroism and nearfield chirality density.These works have certain guiding significance for designing chiral metasurfaces.