The Study Of Terahertz Dual Band Metasurface

The terahertz(THz)band is a transitive frequency band from the microwave millimeter wave band to the infrared band,taking the characteristics of electronics and photonics into account.Terahertz technology can be used in non-destructive testing,security inspection,ultra-wideband and ultra-high-speed wireless communication,cancer detection,climate monitoring,etc.The devices made of traditional materials are always bulky,and the processing of devices is difficult.Metasurface is an emerging two-dimensional planar artificial electromagnetic structure composed of sub-wavelength units,which can effectively control the phase,amplitude and polarization of electromagnetic waves while achieving device planarization.At present,the meta-devices have begun to replace traditional devices.However,there are still some problems such as dispersion and single operation band.Therefore,this work starts from the THz band and studies dual-band phase independent modulations meta-atom,providing a solution to the problems.Based on the research,we realize multi-dimensional independent modulation of phase,amplitude and polarization of incident electromagnetic wave in dual-band.The main research contents of this work are divided into the following aspects:1.The study of designing dual-band metasurface units.Two kinds of resonant unit operating in different frequency bands,metallic resonators and Babinet-inverted slot resonators,are combined to reduce the coupling between different frequency bands.By adjusting the geometric parameters of the metasurface unit,the metasurface unit can be operated in any two frequency bands.Based on Pancharatnam-Berry phase principle,the designed metasurface units achieve 360~o phase coverage.2.Independent phase modulations of electromagnetic waves in dual THz bands.A metasurface lens which can effectively suppress the chromatic aberration is designed.A deflector based on metasurface which can realize arbitrary angle deflection in dual bands is proposed.A vortex beam generator which can carry different/same orbital angular momentum mode(-2,-1,+1,+2)in the dual band is presented.Based on the space division principle,a dual-band polarization independent metasurface lens is proposed for arbitrarily circularly polarized electromagnetic wave incidence.3.The study of achieving phase and amplitude modulation.Two metasurface units with independent regulation of phase and amplitude in dual bands are presented.An Airy beam generator,auto-focusing Airy beam generator and the polarization independent bifocal metasurface lens are designed using the metasurface units.The designed Airy beam generator has the characteristics of no diffraction,automatic deflection and self-healing.The designed autofocusing Airy beam generator has stronger self-healing ability than traditional metasurface lenses.The designed dual-band polarization independent metasurface lens can achieve bifocal points for any circular polarization mode.4.The study of reflective high efficiency dual-band phase independent modulation meta-atom.The metasurface-insulator-metal structure is used to improve the working efficiency of the metasurface with the advantages of low profile and easy processing.A reflective metasurface lens that achieves the same focus distance in dual frequency band is designed,which can effectively suppress the chromatic aberration.A vortex beam generator which can carry different/same orbital angular momentum mode(-2,-1,+1,+2)in the dual band is proposed.