多维度大容量超表面全息及光场变换

Multi-Dimensional and High-Capacity Metasurface Holography and Light Modulation

超表面的设计与制造极大地推动了在片上紧凑光学系统中实现光场调控的应用。传统光学系统中的光学透镜、空间光调制器以及偏振光学元件虽具备光场调控的功能,但体积庞大、光场调控功能单一等因素限制了其应用。超表面为光场调控提供了新平台,有望解决传统光学元件和系统向微型化、集成化和多功能化发展的瓶颈。主要围绕超表面的多维度全息混合复用、二维/三维光场变换、矢量光场的产生与操控三方面进行介绍。最后,对超表面的未来发展趋势进行了展望。

Significance Metasurfaces are usually composed of arrays of metallic or dielectric nano-antennas.They can arbitrarily manipulate the amplitude,phase,as well as polarization of light with sub-wavelength resolution.These features make metasurfaces represent powerful abilities for manipulating multi-dimensional optical fields.Hence,the metasurfaces have attracted much attention in the research on new generation of optical devices.The design and fabrication of metasurfaces have greatly promoted the applications of optical field manipulation in compact optical systems.Although the optical lens,spatial light modulator,and polarization optical element in the traditional optical system have the ability to manipulate the optical field,their applications are limited due to their large size and single function of optical field manipulation.While,metasurfaces provide a new platform for tailoring the optical field,which is expected to solve the bottleneck of traditional optical components and systems towards miniaturization,integration,and multi-functional processes.In recent years,metasurfaces have attracted great interest as novel kinds of flat artificial function devices due to their unusual physical properties.They are usually composed of a single layer of sub-wavelength nanostructures,which can arbitrarily control the amplitude,phase,polarization,and other fundamental properties of the emitted light with subwavelength resolution.While conventional optical elements control the optical field mainly through the phase accumulation of light during propagation,metasurfaces provide a new way to control the light field properties at subwavelength distances through the interaction of light with meta-atoms.As a burgeoning research field,metasurfaces have shown great promise for novel design in a great number of device applications such as flat lenses,wave plates,beam deflectors,switchable surface plasmon polariton couplers,high-resolution 3D holography,and augment reality(AR).New principles and new methods such as holographic hybrid multiplexing,2D/3D optical field modulation,as well as the generation and manipulation of vectorial field based on metasurfaces proposed have overcome the bottleneck challenges of traditional optical components and systems towards miniaturization,integration,and versatility.The research results have important theoretical value and application prospects for complex wavefront modulation,lidar,high-density holographic storage,AR/VR,optical information processing,large-capacity light field regulation,and other fields.Progress The earliest holographic multiplexing method of metasurfaces used birefringent metasurfaces composed of custom crossover nanoantenna arrays for holographic multiplexing through a spatial multiplexing scheme.Our research group demonstrated a new principle of multi-dimensional metasurface holographic hybrid multiplexing.We proposed multidimensional angle-polarization-spatial position,space/frequency domain simultaneous modulation,and quantitatively correlated metasurface holographic hybrid multiplexing.A variety of new holographic algorithms have been created,including multi-dimensional synthesis spectroscopy,quantitative correlation amplitude hologram,irregular surface holographic algorithm,and map index.Such algorithms can adapt to the manipulation of optical fields based on metasurfaces and realize the joint regulation of multiple parameters,which breaks through the connotation of traditional holographic mathematical physics.Meanwhile,they can also improve the information dimension and solve the challenges of algorithm empowerment.The current metasurface research has gradually shifted from single function to multifunctional application.At the same time,the design scheme of spatial multiplexing can also be used to divide the spatial area of the metasurface,namely,to design the regulation function of a specific wave front in different spatial regions.However,in order to alleviate the crosstalk between different channels,the real expansion of the information capacity of metasurfaces requires new design methods.To this end,our research group proposed a new method to produce 2D/3D optical field transformation from monolithic metasurfaces.We realized 2D selective diffraction with customized energy distribution based on complex amplitude manipulation provided by metasurfaces.Meanwhile,a 3D vortex array with controllable topological charge number has been successfully demonstrated by combining Dammann vortex grating and spiral Dammann zone plate with lens factor.Such a method may break the limitation of traditional spatial multiplexing,solve the problem of limited system integration,and increase the information capacity by three orders of magnitude.Polarization is one of the fundamental properties of light.The conventional methods of polarization modulation require controlling the amplitude and phase delay of the electric field in the orthogonal polarization components to enable polarization conversion,beam splitting,detection,and other applications.Artificially designed meta-atoms have the ability to solve the restrictions of natural materials such as insensitive to polarization and low birefringence.They can greatly improve the capabilities of polarization modulations based on metasurfaces.A new scheme of tailoring the vectorial field pixel-by-pixel was proposed to realize the generation of high-order vector beams which greatly improved the performance of polarization modulation.Conclusions and Prospects As a new generation of transformative optical devices,metasurfaces will provide a broad platform for dynamic transmission,VR,and AR technologies.Meanwhile,the adjustment frequency of the tunable metasurfaces is low,which limits its refresh speed and flexibility.Dynamic metasurfaces also have the problem of high design complexity and large crosstalk in their applications.However,it is believed that with the continuous breakthroughs and developments of metasurface technology and theory,metasurface will replace traditional optical devices and excel in true color display,holographic anti-counterfeiting,encryption and decryption,and dynamic transmission.