Achromatic Meta-lenses Based On The Geometries Of The Cross Section Working In THz Regime

With the compact size,flexible and precise electromagnetic wave control capabilities,terahertz meta-lenses,an important part of terahertz functional devices,have been widely used in terahertz imaging and communications.However,due to the intrinsic dispersion of the meta-atoms,meta-lenses still suffer from large chromatic aberration.In order to accomplish an achromatic terahertz meta-lens,we firstly discussed the design principle of the achromatic meta-lens and looked through different phase control methods.Then,based on the principle of phase-dispersion compensation,we carefully manipulated the height,width and cross-section shapes of the unit cells to build a structure library which could satisfy the required phase-dispersion compensation.Appropriate structures were picked out from the library to make the achromatic meta-lens.The numerical performance and analysis of our meta-lens shows that the focal lengths at different frequencies remain nearly the same,which proves the achromatic effect of our design.Besides,a sample of the achromatic meta-lens has been fabricated through ion etching.We used the near-field scanning terahertz spectroscopy system to conduct a further test of our design by scanning the electric filed intensity distribution through the meta-lens sample.The electric field intensity distribution measured by the experiment proves that compared with the ordinary focusing meta-lens,the achromatic focusing meta-lens we designed has a significantly reduction of focal length change,which verifies the achromatic function of our meta-lens.The achromatic focusing meta-lens designed in this paper can solve the chromatic aberration problems faced by terahertz meta-lens.In addition,the achromatic principle used in this article can also be applied to the design of other terahertz metasurfaces,providing new aspects for researches on terahertz devices.