Metasurfaces And Metalenses Based On Phase Control

Metasurface has been proposed and has been paid extensive attention in research as a novel optical element.Compared with traditional optical components,metasurface has obvious advantages and it may become the most critical optical component to form a new generation of micro-optical systems,providing a feasible way for the further miniaturization and integration of the optical systems.Unlike traditional refractive and diffractive optical elements,the metasurface,by contrast,has only sub-wavelength thickness.So it is lighter and thinner and can thus meet the increasing needs of the miniaturization of the optical systems.In addition,since the processing of the metasurface is compatible with the standard micro-nano manufacturing techniques of the complementary metal oxide semiconductor(CMOS),metasurface can be formed by one-step photolithography,which is easy for large-scale preparation and on-chip vertical integration.Metasurface is an artificial two-dimensional structure composed of sub-wavelength nano-antennas,which can arbitrarily control and shape the wavefront so as to realize beam-shaping.Based on the principle of scattering,nano-antennas can arbitrarily regulate the phase,amplitude and polarization of the light by changing its shape,size and spatial direction.Metasurface based on this unique electromagnetic control principle has aroused people's great interest and has been widely used in many areas,such as electromagnetic invisibility cloak,structural color printing,optical holographic display,meta-lens imaging,and so on.In order to explore more practical applications of metasurface,this paper proposes an atomic force microscope with a micro cantilever structure integrated with metasurface,which will improve the sensitivity of the deformation detection,thereby enhancing the resolution of the force detection.According to the generalized Snell's law,there is a certain non-linear relation between the reflection angle and the incident angle.Taking advantage of such a nonlinear characteristic,we designed and fabricated an abnormally reflective metasurface structure based on the principle of surface plasmon resonance,and set up a set of macro cantilever beam detection models to make experimental verification.The corresponding relation between the reflection angle and the incident angle in the experiment and the sensitivity enhancement magnification of the optical lever are both completely consistent with the theoretical calculation results.The slight deviations mainly come from the testing errors during the experiment and the processing errors of the metasurface.Next,the low efficiency of plasma metaurfaces limits their wide application owing to the inherent loss of metal materials.Therefore,we propose a high-efficiency polysilicon metalens with all-dielectric materials,which can realize a polarization-controlled dual-focus function based on the conformal design of the metasurface and has the potential to be applied in multi-planar tomography systems.Based on the principle of geometric phase,the spatial rotation direction of the silicon nanorods is used to adjust the phase and the entire metalens is divided into two areas.When the left-handed and right-handed circularly polarized light is incident,there will be two focal points with different focal lengths,respectively.As for linearly polarized light incident,two focal points with different focal lengths will be produced at the same time.In addition,we have prepared a micron-level pattern,which can be used to verify the multi-plane imaging of the bifocal metalens.The experimental results have proved the feasibility of polarization-controlled multi-plane imaging.Finally,all-dielectric metasurface and the subwavelength units of metalenses currently have a high aspect ratio generally,posing a great challenge to their fabrication.Therefore,we have developed a metalens composed of double-layer structured nano-column units.Compared with the general all-dielectric metalens units,its aspect ratio is reduced by at least one time,thereby reducing the processing difficulty.Based on the phase change principle of the equivalent refractive index of the waveguide structure,we use a two-layer structure composed of polysilicon with high refractive index and high absorption and titanium dioxide with low refractive index and low absorption.Through parameter optimization design,we can achieve a phase control in the full 2?range,and the transmission efficiency is high.We designed and fabricated an all-dielectric metalens with a low aspect-ratio based on this double-layer unit structure,which can achieve a focusing effect of the diffraction limit.In addition,the simulated broad-spectrum focusing efficiency exceeds 22%,and it also has a certain degree of polarization-independent broad-spectrum achromatic ability.