Research On Terahertz Functional Devices Based On Spin-Multiplexed Metasurface

In recent years,terahertz(THz)science and technology has attracted the attention of many researchers because of its broad application prospects in many fields such as communication,imaging,spectral detection,etc.The free modulation of THz waves(polarization,amplitude,phase,frequency,wavefront,etc.)is one of the key points in the development of THz science and technology.However,related THz devices are still scarce.The emergence of new electromagnetic modulation methods based on metasurfaces provides an effective solution to break through this status quo,and promotes the development of THz modulation technologies and devices.At present,exploring new methods for efficient and multi-parameter multiplexing modulation of THz waves,and then designing and realizing various multi-functional THz devices,is one of the frontier research directions in the field of THz metasurfaces.It contains rich and profound interactions between THz waves and matters.This dissertation mainly focuses on the THz wavefront control of orthogonal polarization(circular polarization)parameter multiplexing.Based on all-dielectric metasurfaces and all-metal metasurfaces,a variety of multi-functional THz wavefront control devices have been systematically developed.The main innovations of the dissertation are as follows:1.Using all-dielectric metasurfaces,combined with the Pancharatnam-Berry(PB)phase control and propagation phase control scheme,a spin-decoupled phase control method is proposed in the THz band.It breaks the limitation of spin phase locking in the individual PB phase control method.Based on this proposed method,several spin-dependent THz anomalous deflector with asymmetric deflection angles and an several linearly polarization-dependent dual-channel polarization converters based on spin multiplexing technique are realized.2.Using the above spin-decoupled phase control method,a linear polarization dependent THz vector beam generation method is proposed by independently controlling the phase distribution of THz waves under two circularly polarized channels and combining the principle of polarization superposition.The linear polarization-dependent vector vortex beam and vector Bessel beam generators are experimentally realized,and the radial and azimuthal vector polarization distributions can be obtained under two orthogonal linear polarization incidents,respectively.3.Using an all-metal stereo U-shaped structure,a reflective broadband and highefficiency polarization conversion scheme based on the resonant phase design principle is proposed in the THz regime.Combined with the coupled mode theory and simulation,the resonance behavior is explained theoretically.A broadband,high-efficiency,deep sub wavelength,high-performance THz half-wave plate with large angle tolerance was experimentally realized.And further using the PB phase control method,a high-performance THz meta-grating was experimentally realized.