Focusing And Generating Of The Vectorial Field Based On Metasurface

Light is a carrier of information.Its basic properties,such as the frequency,amplitude and phase,have been studied thoroughly and used widely in various fields for a long time.Polarization,the basic property of light used to express its vector state,plays an important role in the characteristics of light.Moreover,the phase is the basic physical parameter of light waves.Because of the rapid development of micro-nano technology,it is much easier to achieve the sub-wavelength scale devices.Today's metamaterial optical slabs,which are thinner than the wavelength,have been able to replace the traditional components for focusing the light,controlling the wavefront and manipulating the polarization.In this paper,we presents a brief overview of the two general categories of methods about generating vector light beams and discusses previous works on metasurface for generating the vector beam.Moreover,we have studied the modulation of light under the subwavelength structure and designed a novel metasurface.This metasurface can be used for focusing the beam and regulate the polarization state,amplitude and phase of the vector light field.Firstly,by combining the transmission phase and generalized law of refraction and reflection,we discuss the wide-band beam focusing on the metasurface.Moreover,the feasibility to change the equivalent refractive index by controlling element duty ratio has been demonstrated.Then we design a metasurface with elliptic Si cylinder based on the SiO₂ substrate.The equivalent refractive index can be changed by adjusting the line width.The transmission phase also changes.Then we have studied the application of this metasurface in the beam focusing by using the FDTD simulation.Compared with the previous structure,this new metasurface is suitable for the wideband beam focusing.Secondly,based on the generation of cylindrical vector beams,the geometrical phase theory of Pancharatnam and Berry is described.We have studied the metasurface of elliptic Si cylinder with modulated transmission phase and geometric phase to generate of the vector beam.By adjusting the width and the inclination of the long axis,the transmission phase and the geometric phase can be changed.In the case of linearly polarized incident beams with different wavelengths and polarization angles,we have studied its transfer characteristics and transmitted beam.This new metasurface can be applied to the vectorial manipulation of wide wave band infrared light field.