| Arbitrary control of electromagnetic waves is a new direction of photon research.Limited by the variation range of the permittivity ε of natural materials,traditional optical devices often have a large optical thickness and the ability of manipulate light is also quite limited.On the deep sub-wavelength scale,the artificial composite material(MTMS)made up with electromagnetic(EM)microstructures can be equivalent to any dielectric constant ε and permeability μ,thereby providing more for light manipulation Degrees of freedom.Based on uniform MTMS,the metasurface can adjust the phase,amplitude,and polarization of incident light waves through artificial microstructures,thereby realizing arbitrary manipulation of electromagnetic waves.And people have constructed various devices with specific functions by using metasurfaces.Such as beam converter,super imaging,polarization selector,etc.In addition,the thickness of gradient phase metasurfaces is very thin on the optical scale,and light will not propagate for a long time inside the structure,so they are less affected by the problems of scattering and phase mutation.The goal of this paper is to use the phase gradient metasurface to realize the wavefront control of electromagnetic waves,so as to realize the abnormal deflection of the reflected beam and the focusing of the transmitted beam.The specific contents include:(1)First,this article introduces the related theories and applications of abnormal reflection,wave field conversion and focusing on metasurfaces.Explained in detail the generalized Snell’s law of refraction/reflection on which the construction of phase gradient metasurfaces depends.According to the theory,the phase gradient metasurface is constructed to realize the artificial control of electromagnetic waves.The unit structure of Au nanopillars is used to introduce abrupt phases into the surface of a homogeneous medium,thereby regulating electromagnetic waves to achieve abnormal deflection of reflected beams.This paper mainly studies the abnormal reflection at the wavelength λ=8.1 μm and ξ=0.65k0,and the numerical simulation results are the same as the theoretical calculation values.In addition,the deflection of the reflected beam under different reflected light parallel wave vectors and the reflection of the same wave at different incident angles under the same wave vector ξ are also calculated.And it is confirmed that there is a critical angle.When the incident angle is greater than the critical angle,the incident wave transmitted in free space will be transformed into a surface wave transmitted along the surface of the structure.(2)Based on the principle that the phase gradient metasurface can achieve wavefield conversion,the use of wavefield conversion to improve absorption opens up new ideas for the construction of other multispectral devices based on excellent performance of mid-infrared filters and absorbers.In this paper,a phase gradient metasurface structure that can excite two mixed modes is constructed.This structure separately studies surface wave modes and dipole-like resonances.Through the joint action of these two modes,the dual-band perfection in the medium-long wave infrared band is realized.absorb.In addition,the origin of the two absorption peaks at 8.1 μm and 14.1 μm are proved by means of eigenmode calculations.(3)The most widespread application of metasurfaces is in the construction of metalenses.The focus of the meta-lens is based on the phase adjustment of the subwavelength artificial microstructure.This paper proposes the study of the super-surface focusing function under the mid-infrared wavelength of the all-silicon(Si)medium.Numerical calculation of the cell structure is carried out by the finite time domain difference method(FDTD).According to the phase modulation function of the hyperlens,the lens at the wavelength of 4 μm is designed.The comparison between simulation and theoretical model confirms the accuracy of our modeling.It provides a reference for the research of broadband focusing. |
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