| Metasurface is a new type of two-dimensional artificial electromagnetic material,which can control the amplitude,phase and polarization of electromagnetic wave arbitrarily in sub-wavelength scale.As a two-dimensional version of metamaterials,the metasurface not only retains the superior electromagnetic wave manipulation ability of metamaterials,but also greatly improves the efficiency,fabrication and integration compared with metamaterials.In recent years,metasurface has become one of the hot topics.Phase control is an important application of metasurfaces.Although great progress has been made in the research of phase control of metasurface,many new functions have been realized.However,there are still a series of problems,such as inadequate theoretical system,low operating efficiency,single working spectrum and function.Aiming at the above problems,this paper has carried out the research on the phase control mechanism and beam steering based on metasurface,with emphasis on all-dielectric metasurfaces.The main contents include:(1)Phase control of discrete all-dielectric metasurfaces.The relationship between the period of unit cell and abrupt phase type is analyzed.The results show that with the increase of the period size,the abrupt phase type changes from transmission phase to resonance phase,and there is a transition phase in the process of change,which is not suitable for the design of phase-controlled metasurfaces.In addition,the relationship between the type of abrupt phase and the periodic structure as well as the wavelength is also given,which provides a reference for the design of metsurfaces in the future.(2)A dual-band beam deflector and a polarization beam splitter based on a discrete transmission phase metasurface.Aiming at the problem of single spectral band of beam deflector based on metaurface,a dual-band beam deflector is proposed.We first analyze the influence of the refractive index of the metasurface material on the deflection characteristics of the transmission phase gradient metasurface.It is found that the gradient metasurface can still achieve efficient beam deflection only when the refractive index is changed while the structure remains unchanged.Only the band shift is found.Based on this conclusion,we design a dual band beam deflector using anisotropic materials.The design can achieve efficient beam deflection under x-polarization and y-polarization incidence,but the working wavelength is different,so it can also be used as a simple frequency selector.In addition,a polarization beam splitter based on all dielectric metasurface composed of crossed nanoantenna arrays with different sizes is proposed.At the wavelength of 583nm.the total transmission intensity of the polarization beam splitter is 0.726,and the intensity of x-polarized and y-polarized outgoing light is the same,accounting for 46.3%of the total transmission intensity.(3)The phase regulation of quasi-continuous all dielectric metasurface.Previous studies on quasi-continuous all dielectric metasurfaces are only conducted for y-polarized incident light(the direction of electric field is perpendicular to the direction of phase gradient).In order to solve the limitation of this phase regulation research,we have systematically studied the phase regulation and physical properties of quasi-continuous all dielectric metasurface under x-and y-polarized light incidence for the first time.The results show that under the normal incidence of y-polarized light,the all dielectric quasi continuous metasurface can achieve a nearly linear 2π phase shift in a long wavelength,thus acting as a broadband and efficient beam deflector.Under the normal incidence of x-polarized light,this kind of all dielectric quasi continuous metasurface can achieve a phase change of 0～π～0 in a very wide band,showing non equal power beam splitting performance.(4)The multi-function and high efficiency beam steering device based on uniform metasurface.Aiming at the problem of the single function of the previous all dielectric metasurface and the narrow bandwidth and low efficiency of the beam splitter,a new metasurface structure with high efficiency beam splitting and high deflection performance is proposed.The supercell of metasurface is composed of only one rectangular nanoantenna.When x-polarized light(the electric field direction is parallel to the long axis direction of the nanoantenna)is incident normally,the metasurface is used as a beam splitter.The conversion efficiency of the beam splitter is always higher than 95%in the wavelength range of 604nm to 738nm,the total transmission intensity remains above 0.66,and the maximum splitting angle reaches 159.48°.When the metasurface acts as beam deflector(x-polarized light oblique incidence),the deflection efficiency can reach 98%.Our design has the characteristics of simple structure,high tolerance,high efficiency and multi-function,which provides a new way for the design of beam steering devices in the future.(5)A dual-band beam splitter based on quasi-continuous all dielectric metasurface.Aiming at the problem of single spectral band of beam splitter based on metasurface,a high efficiency and dual-band beam splitter is proposed by using the structural anisotropy of trapezoidal nano antenna.The metasurface is composed of two trapezoidal silicon antenna arrays with the same structure and opposite spatial arrangement.The opposite phase gradient results in the realization of beam splitting function.For x-polarized light(the electric field direction is perpendicular to the bottom edge of the trapezoidal structure)and y-polarized light,the operating band of the beam splitter falls in the near-infrared region and the visible region respectively.When x-polarized light is incident,the conversion efficiency and total transmission intensity of the beam splitter are above 90%and 0.74 respectively in the bandwidth of 85nm.Under the condition of y-polarized light,the conversion efficiency and total transmission intensity of the beam splitter are above 90%and 0.65%respectively in the bandwidth of 23nm. |
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