Design And Research Of Broadband Dispersion-free Metasurface Terahertz Waveplat

Metasurface is a two-dimensional simplified variant of three-dimensional metamaterial.It is tiny and lightweight,and it can modify the electromagnetic wave at a subwavelength distance,including its phase,amplitude,and polarization state.Metasurface-based terahertz waveplates provide substantial benefits over traditional devices in terms of size,flexibility,and manufacture,although they currently have rather restricted operational bandwidths.Based on the combinational design idea of the multilayer metasurface wave plate,a theoretical model,design approach,and optimization algorithm of wideband achromatic metasurface wave plate are provided to tackle the problem of narrowness of polarization wave plate in terahertz band.This paper has made the following contributions:1.The terahertz-frequency ultra-wide band is realized.In the terahertz spectrum,for example,a broadband quarter-achromatic wave plate is proposed.The plate is made up of eight layers of dielectric rectangular cylinders with varying rotation angles,and it can convert linear and circular polarizations from 850 GHz to 2.45 THz with a low insertion loss of 1.89 d B and the bandwidth close to 1600 GHz.2.The effect of structural factors and layers on the wave plate’s polarization conversion ability is investigated.Modeling the spread of magnetic and electric fields in the cell structure elucidates the physical mechanism of polarization conversion.The basic features of the rectangular column and the elliptic cylinder element are examined across a large frequency range.The linear polarization state is realized by adjusting the geometry of the metasurface element,such as the size,height,rotation angle,lattice constant and layers.3.An approach for multi-parameter optimization is proposed.To increase the optimization performance of the two-layer metasurface,a simulated annealing approach with an evolutionary strategy is developed.Nevertheless,increasing the number of metasurface for the ultra-multi-structure parameters of multi-layer metasurface demands a high computational speed,which is more difficult to achieve than for double-layer metasurface.Depending on this,we offer a multilayer metasurface optimization method that incorporates particle swarm optimization and simulated annealing.In addition,the scoring mechanism of error analysis is introduced in the multi-layer silicon column metasurface structure based on elliptical or rectangular,which can comprehensively analyze the better geometry of terahertz polarization wave plate under different number of layers.This study examines the achromatic metasurface wave plates in order to tackle the problem of wide-band polarization control in the terahertz region.Because of its ultrathin subwavelength thickness,the proposed multilayer metasurface-based polarization wave plate is ideal for terahertz optical systems.To provide high-level scientific and technical assistance for terahertz instrument and device development,materials science,sensing,security,and other research and application domains.