Design,Preparation And Characterization Of Broadband Metalens

With the emergence of varies of novel visual systems for artificial intelligence,portable devices,virtual reality,augment reality etc,optical systems have been required to be miniaturized,multifunctional,integrated.Conventional optical components trim the wavefront of the incident light by gradual phase shifts accumulated during light propagation,which is limited by the properties of material such as the refractive index,dielectric constant.Therefore,the freedom of wavefront manipulation is quite limited.Furthermore,these components are usually bulky,which is infeasible for the integration of optical systems.These disadvantages of conventional components limit their application in the integrated optical systems.In recent years,state-of-the-art nano-fabrication technologies have witnessed the development of planar optical metasurfaces.A metasurface is a two-dimensional periodic array composed of sub-wavelength plasmonic or dielectric meta-atoms or meta-molecules,which can trim arbitrarily the phase,amplitude,and polarization of electromagnetic waves within the subwavelength-scale thickness via an abrupt phase shift.Optical components with diversified functionalities have been realized including exotic fields such as invisible cloak carpets and vortex beams,holograms and metalenses.Optical metasurfaces can realize all the functionalities of conventional counterparts in principle,and have CMOS-compatible planar configurations.Furthermore,they can manipulate the wavefront of light with arbitrary freedom.These advantages make them very promising for applications.Although much attention is paid on optical metasurfaces,their broadband properties in the visible are not good enough,or the efficiency of the broadband response are quite low.Considering optical elements in the visible are applied in many fields,it will be significant theoretically and technologically to carry out the research on broadband manipulation of metasurfaces in the visible.To address the above issue,new ideas and strategies are presented in this thesis to broaden the response spectra and improve the efficiencies of metasurfaces in the visible.Furthermore,considering lenses play an important role in optical systems,this thesis focuses on metalenses,and two kinds of broadband metalens are designed,fabricated and characterized.It includes the following parts:1)By choosing the ultra-low absorption nano-crystalline silicon that developed at the nanofabrication lab of National Center for Nano Science and Technology(NCNST),the broadband response,conversion efficiencies and diffraction efficiencies of meta-atoms are simulated.Furthermore,the effects of the sizes and the period of meta-atoms on the above performance parameters are studied.Based on the simulations,a single-layer polarization-dependent focus-tunable metalens is designed,tested and verified.2)By optimizing the efficiencies of the meta-atoms with different sizes,a meta-molecule multiplexing the meta-atoms is presented and simulated,and used for the design of the two broadband metalenses.3)The designed broadband metalens are fabricated using the facilities at the nano fabrication lab of NCNST,and their performances are characterized using the built measurement platform at NCNST.The strategies in this work would provide very valuable reference and guideline for the design of metasurface based broadband optical components,especially for broadband metalens;and the results would lay an important foundation for the applications of optical metasurfaces in the visible.