Research On Polarization Control Of Terahertz Waves Based On Metamaterials

Metamaterial Metamaterial is a kind of artificial metamaterial,which is different from other materials in nature.We can design its unit structure to make its dielectric constant and permeability less than zero.Therefore,some peculiar electromagnetic phenomena can be produced,such as negative refractive index,electromagnetic stealth,super lens,inverse Doppler effect and so on.At the same time,according to its flexible unit structure,it can effectively control the polarized electromagnetic wave,so it has a broad development prospect.Artificial metamaterials are mainly divided into two-dimensional and three-dimensional structures.For terahertz wave control,it is still a research hotspot in the world.More miniaturized,convenient and efficient terahertz wave control devices and methods are urgently needed,which will play an important role in the future development of terahertz sensing,communication and other fields.In this context,this paper studies the modulation response to different terahertz polarization waves from these two dimensions respectively.By designing a sub wavelength metal slit hypersurface with geometric phase modulation,the accurate control of ]2,0[ ? of surface plasmon(SPS)under terahertz polarization wave incidence is realized,and a novel method for the generation of on-chip plasmonic vortex waves is also provided.A metal helix chiral terahertz polarization converter is studied,and the selective tuning control of terahertz polarization wave is realized.The main research contents are as follows.(1)According to the binding of the super surface of the gap to the surface electromagnetic wave and the interference coupling effect of the gap pair.A metal slot super surface resonator operating in terahertz band is studied.A 200 nm aluminum film was plated on the modified polyimide substrate,and a pair of 200?m long and 50?m wide gaps were hollowed out on the aluminum film.The field distribution of terahertz surface waves excited by 0.496 Thz left-handed circularly polarized wave(LCP)and right-handed circularly polarized wave(RCP)is observed by simulation and numerical analysis.By adjusting the geometric phase and spacing of the slot resonator,the wavefront phase of terahertz surface wave can be accurately controlled,and the chirality of chirally polarized incident wave is obvious.Meanwhile,the excitation of on-chip plasmonic vortices with different topological charge numbers is studied.The theoretical demonstration is basically consistent with the experimental results.(2)A chiral metal spiral polarization control device based on textile weaving technology is studied.Using the insensitivity of textile fiber to terahertz wave,the metal helix array unit structure is connected in series.The metamaterial unit structure is composed of 140?m Si O2 and 58?m spiral copper wire.In the 0.3-0.8Thz band,the transmission efficiency reaches90% when the incident wave and the transmitted wave are both left-handed circularly polarized(LCP)and right-handed circularly polarized(RCP),due to the optical rotation effect and circular dichroism formed by the chiral structure.Through the simulation and parameter analysis,it is proved that by adjusting the horizontal spacing of chiral metal helix unit structure,the transmission resonant frequency of left-handed polarization wave remains unchanged,while the transmission resonant frequency of right-handed polarization wave shifts.By changing the vertical spacing of the metal spiral element structure,the transmission resonant frequency of the right-handed polarized wave is unchanged,while the transmission resonant frequency of the left-handed polarized wave is shifted.Therefore,the chiral helical metamaterial can flexibly tune the left-handed and right-handed terahertz polarized waves.