Research On Focusing And Demultiplexing Devices Based On Dielectric Metasurface

Metasurfaces as two-dimensional artificial metamaterials are composed of subwavelength scale basic units.The local light field properties can be controlled by changing the structure and the arrangement of the basic units in the subwavelength scale.This outstanding advantage enables metasurface optical components have the feature of ultra-thin,and which promotes miniaturization of equipment and system integration.With the constant progress of micro-nano manufacturing processes,the metasurface has unique charm in the fields of encryption,imaging,optical communications,quantum science,and fundamental physics.In this thesis,metasurfaces were designed based on P-B(PancharatnamBerry)phase modulation principle and the applications on focusing and demultiplexing optics decives were discussed.The main research contents of the thesis include:High numerical aperture metalenses was proposed which can achieve diffraction-limited focusing independent of the polarization state of incident light and multifocal diffraction-limited focusing with linearly polarized incident light.The operating wavelength of the proposed high numerical aperture metalens is in the visible spectrum,and Zn S nano-fin combined with a silica substrate was employed as basic units to constitute the metasurface.The multifocal metalens is obtained by dividing the metasurface into different re gions to operate in different polarization states,respectively.When the linearly polarized light is employed,multiple diffraction-limited focusing could be generated.The polarization-independent metalens is based on the hybrid arrangement of nano-fins.The left-handed circularly polarized light,the right-handed circularly polarized light and the linearly polarized light can be used as incident light to achieve diffraction-limited focusing.Meanwhile,the proposed P-B phase metalens removes the restriction of incident light beam polarization state.A polarization-multiplexed metalens with tunable focal length was proposed,that foci distribution can aslo be controlled by changing the polarization state of the incident light.Since the P-B phase metasurface has limitation of the incident light beam polarization state,the left and right circular polarization states cannot be independently modulated.For solving this problem,phase superposition method was proposed.Combined with two basic units operating in different wavelengths,the polarized-multiplexed multifocal metalenses with tunable focal length were proposed with visible and near-infrared oprating bands,respectively.The focal lengths of left-handed circularly polarized light and the right-handed circularly polarized light can be modulated independently,and metalens can achieve diffraction-limited focusing.A vortex beam demultiplexer was proposed based on wavelength-andpolarization multiplexing method.The proposed demultiplexer achieved undamaged vortex beam demultiplexing with varying topological charges.The proposed vortex beam demultiplexer consists of amorphous silicon nano-fins.The demultiplexer is based on polarization-multiplexed and wavelength-multiplexed metasurface.The demultiplexer can used in OAM communication system for wavelength-division multiplexing and polarization-division multiplexing in near infrared band.Moreover,the demultiplexed vortex beam could carry different topological charges and maintains the original light field property.That is,the undamage demultiplexing can be realized which greatly increases the application range of the vortex beam demultiplexer.