Research On Spatial Light Modulation Based On All-dielectric Micro-nano Structure

With the rapid development of science and technology,lots of areas such as optical communication and optical sensing need precise manipulation for the optical signal,spatial light modulation has drawn great interest of the researchers and they all pay lots of attention on this technology.Metasurface as its thickness much smaller than the operating wavelength is 2D counterpart of the metamaterial,which can control the amplitude,phase and polarization of the light at sub-wavelength region,is one of the most important method in nano-micro scale spatial light modulation.Compared with metal or metal-dielectric materials,metasurfaces consisting of all dielectric materials have many advantages such as low loss,large scale production and easy integration into optical chip,which make scientists pay extensive attention to.In this paper we briefly describes the design idea of metasurface,and the wave modulation mechanism of metasurface.We extend the traditional Snell law to generalized Snell's law,and the relationship between surface equivalent susceptibilities and metasurface scattering field is derived,and then through some initial conditions,which will simplify the complex formula,describes how to use the equivalent surface susceptibilities to design metasurface.Then,we study the unit cell of the meatsurface,first through electromagnetic simulation analysis of the basic unit of the periodic arrangement,find the geometric size and resonance mode,and then in the operating wavelength scanning the geometry of the unit cell to construct the database of the transmission mode of the metasurface and,according to the database made two different functional metasurface,one of which is the abnormal refraction of light,and the other is to transfer the plane wave into surface vortex beam.Finally,in order to prove the ability of light control over the metasurface,we design a hologram metasurface.Through the MATLAB we write Gerchberg-Saxton(GS)phase retrieval algorithm,which can get us phase gradient of the required metasurface.And then according to the database design micro structure of the metasurface.After that,run simulation on the desired metasurface to get the electric field of the transmitted field,with Fresnel diffraction we can achieve the hologram image.This dissertation firstly is the theoretical analysis of metasurface design method,and then through numerical simulation by using the finite element method in COMSOL Multiphysics to calculate the electromagnetic field in the structure.We deeply research the mechanism and design method of metasurface,which plays a guiding role in the understanding and design of artificial electromagnetic surface Our design and results can be applied to spatial light modulator,optical sensing device,etc.