Investigation Of Multichannel Nanoprinting And Computer-generated Holography Based On Metasurfaces

Metasurfaces,artificial planar material composed of sub-wavelength scale nanostructures,can be employed to manipulate the amplitude,phase and polarization states of incident lightwave precisely with sub-wavelength resolution,which enable novel optoelectronic devices with high resolution,high information density,high integration and ultra-compactness.Recently,metasurface based image displays(computer-generated holography,nanoprinting,etc.)have become an emerging hotspot in information optical related fields.Among them,multichannel metasurfaces enabled with multiple manipulations over the properties of light have the potential of endowing the display technology with higher information density,more display options and better optical performance,which show promising prospects in multifolded anti-counterfeiting,information storage,information security and many other related fields.In this context,the principles,methods,device design and applications of metasurface based multichannel image displays and their merging approach are investigated.Metasurfacebased nanoprintings,holograms and the merging of them are studied in the following aspects.(1)The principle of multichannel image displays by using metasurfaces is investigated,which forms the theoretical basis of this thesis.(2)Metasurfaces composed of anisotropic nanostructures with varied dimensions are studied,the design and numerical simulations of dual-channel holograms for three-dimensional(3D)stereoscopic display are conducted.(3)The concept of Malus metasurface is proposed and the dual-channel and triple-channel nanoprintings based on nanostructures with varied orientations are realized.By further exploring the Malus metasurfaces’ working principle of simultaneous phase and polarization modulation,we achieve the merging of meta-nanoprinting and meta-holography.(4)The multiplexed metasurfaces based on spatial frequency multiplexing are proposed and the general scheme of dual-channel hologram and dual-channel nanoprinting are investigated,by using anisotropic nanostructures with varied orientations as unit cells.(5)A novel kind of bilayer metasurface is proposed,and we numerically verify the proposal by applying it to design dualchannel nanoprinting and dual-channel amplitude grating,respectively.The detailed contents of this thesis are as follows.(1)Starting from exploiting the degrees of freedom in designing nanostructured metasurfaces,the author reviews the research and the development of nanoprints,computergenerated holograms(CGHs)and the merging of them.The issues of interest and trends of metasurface-based image displays are also demonstrated,and the author further points out the academic and realistic values of researches on multichannel metasurfaces.(2)Mechanisms of lightwave manipulation by metasurfaces are investigated in detail.At first,the principles of controlling the phase by nanostructures with varied dimensions and orientations are studied respectively,which forms the basis of designing multiplexed metasurfaces based on polarization multiplexing.Next,the principle of modulating intensity by Malus metasurfaces is investigated,as well as the method of controlling the intensity and phase of lightwaves simultaneously by Malus metasurfaces.At last,the principles of spatial frequency multiplexing metasurfaces and non-reciprocal metasurfaces are investigated in detail.These principles lay the theoretical foundation of metasurface-based multichannel nanoprints,CGHs and their merging technology.(3)Metasurfaces composed of anisotropic nanobricks with varied dimensions are demonstrated,based on which the author designs and simulates dual-channel holograms for three-dimensional(3D)display.Firstly,based on the working principle of the anisotropic nanobricks,polarization-sensitive metasurfaces are designed and they can independently manipulate the phase delays in two orthogonal directions in the visible range(658 nm).Then,a fan-out optical element generating two types of 2×2 spots and a four-step phase-only metahologram with a diffraction angle up to 80°×80° are designed respectively.The simulation results and the theoretical analysis are in good agreement with each other when the FDTD software is employed to calculate the far-field holographic images.Specifically,when two linearly-polarized light beams with orthogonal polarization illuminate the same hologram,two different holographic images can be found in exactly the same plane in the far field,and a 3D object can be observed by wearing polarizing glasses.With the advantages of high integration and flexible design,the device is expected to find its application in ultra-compact 3D display.(4)The concept of orientation degeneracy of nanostructures is put forward,and a new working mode of multiplexed polarization modulation by Malus metasurface is investigated.The design of anisotropic nanostructures with varied orientations is completed,and its application in dual-channel and triple-channel nanoprinting display is explored.Researches show that by rearranging the orientation angles of the anisotropic nanostructures,two or three information channels can be encoded in a single-celled matasurface.In contrast,limited by the degrees of freedom of polarization control,only dual-channel nanoprinting realized by optimizing anisotropic nanostructures with varied dimensions have been reported.In addition,the fabrication of metasurfaces composed of nanostructures with varied dimensions poses strict demands on the precision of the fabrication process.In this thesis,a new degree of freedom for the manipulation of lightwave is demonstrated,and dual-channel or even triple-channel nanoprintings can be realized by delicately arranging the anisotropic nanostructure with varied orientations rather than dimensions,which greatly reduces the manufacturing complexity and is expected to be used in practical applications.Based on the above research,nano half-wave plate structures and nano polarizer structures are used to experimentally verify the proposal,which are completely consistent with the theoretical calculations.By rotating the polarization direction of the polarizer and the analyzer,a continuous grayscale image and a binary image can be readily switched.Anti-counterfeiting stripes,random codes,anti-counterfeiting watermarks and other elements are also integrated into the target pattern design to extend Malus metasurfaces’ applications in optical anti-counterfeiting.The author further investigates simultaneous intensity and phase control by using the Malus metasurfaces,and realizes the merging of nanoprinting and holography.Multifunctional metasurface samples which can decode nanoprinting patterns right at the sample surface and reconstruct holographic images in the far field are designed and fabricated.(5)A new method for realizing multichannel image display based on metasurfaces is proposed,which is enabled with combining the spatial frequency multiplexing with the geometric phase and the intensity modulation of the nano-polarizers.By exploiting the differences of the spatial frequency information between different images,a nanoprinting sample capable of recording two completely different patterns and a hologram sample capable of reproducing two completely different images are designed and fabricated,respectively.The experimental results show that when different spatial frequency filters are utilized to filter the experimental results,two nanoprinting images or two holographic images can be separated,which validates the feasibility,effectiveness and adaptability of the proposed method.In order to further explore its application in information encoding,we combine the design scheme with helicity multiplexing,and a hologram sample which can encode six information channels is designed and fabricated.In addition,spatial frequency multiplexing can be readily combined with other multiplexing scheme,so it has broad application prospects in information encoding,multichannel image displays and many other related fields.(6)A novel bilayer metasurfaces is presented and its optical property of asymmetric transmission in the visible range is studied.Traditional metasurface obeys the law of symmetry in terms of the direction of transmission,which severely limits its application in the multifunctional photonic devices.Therefore,in this thesis,the possibility of asymmetric optical transmission by applying bilayer metasurface is explored.Firstly,the mechanism of lightwave manipulation realized by the bilayer nanostructures of “half-wave plate + nano polarizer” is studied,and then a kind of bilayer metasurface capable of asymmetric optical transmission at the visible band(633 nm)is optimized by electromagnetic simulation software.At last,bilayer metasurfaces that can perform the functionality of dual-channel nanoprinting and dual-channel amplitude grating are designed and simulated,and the simulation results are consistent with the theoretical analysis.In addition,the functionality of the proposed metasurface can be switched between two meta-printing images or two amplitude gratings with different periods by changing the incident direction of the lightwave.