Genetic algorithm assisted meta-atom design for high-performance metasurface optics

Metasurfaces,composed of planar arrays of intricately designed meta-atom structures,possess remarkable capabilities in controlling electromagnetic waves in various ways.A critical aspect of metasurface design involves selecting suitable meta-atoms to achieve target functionalities such as phase retardation,amplitude modulation,and polarization conversion.Conventional design processes often involve extensive parameter sweeping,a laborious and computationally intensive task heavily reliant on designer expertise and judgement.Here,we present an efficient genetic algorithm assisted meta-atom optimization method for high-performance metasurface optics,which is compatible to both single-and multiobjective device design tasks.We first employ the method for a single-objective design task and implement a high-efficiency Pancharatnam-Berry phase based metalens with an average focusing efficiency exceeding 80%in the visible spectrum.We then employ the method for a dual-objective metasurface design task and construct an efficient spin-multiplexed structural beam generator.The device is capable of generating zeroth-order and first-order Bessel beams respectively under right-handed and left-handed circular polarized illumination,with associated generation efficiencies surpassing 88%.Finally,we implement a wavelength and spin co-multiplexed four-channel metahologram capable of projecting two spin-multiplexed holographic images under each operational wavelength,with efficiencies over 50%.Our work offers a streamlined and easy-to-implement approach to meta-atom design and optimization,empowering designers to create diverse high-performance and multifunctional metasurface optics.

Tunable metasurfaces towards versatilemetalenses and metaholograms:a review

Metasurfaces have attracted great attention due to their ability to manipulate the phase,amplitude,and polarization of light in a compact form.Tunable metasurfaces have been investigated recently through the integration with mechanically moving components and electrically tunable elements.Two interesting applications,in particular,are to vary the focal point of metalenses and to switch between holographic images.We present the recent progress on tunable metasurfaces focused on metalenses and metaholograms,including the basic working principles,advantages,and disadvantages of each working mechanism.We classify the tunable stimuli based on the light source and electrical bias,as well as others such as thermal and mechanical modulation.We conclude by summarizing the recent progress of metalenses and metaholograms,and providing our perspectives for the further development of tunable metasurfaces.

Visible frequency broadband dielectric metahologram by random Fourier phase-only encoding

In recent years,metasurfaces that enable the flexible wavefront modulation at sub-wavelength scale have been widely used into holographic display,due to its prominent advantages in polarization degrees of freedom,viewing angle,and achromaticity in comparison with traditional holographic devices.In holography,the computational complexity of hologram,imaging sharpness,energy utilization,reproduction rate,and system indirection are all determined by the encoding method.Here,we propose a visible frequency broadband dielectric metahologram based on the random Fourier phase-only encoding method.Using this simple and convenient method,we design and fabricate a transmission-type geometric phase all-dielectric metahologram,which can realize holographic display with high quality in the visible frequency range.This method encodes the amplitude information into the phase function only once,eliminating the cumbersome iterations,which greatly simplifies the calculation process,and may facilitate the preparation of large area nanoprint-holograms.

Metasurface-enabled augmented reality display: a review

Augmented reality(AR)display,which superimposes virtual images on ambient scene,can visually blend the physical world and the digital world and thus opens a new vista for human–machine interaction.AR display is considered as one of the next-generation display technologies and has been drawing huge attention from both academia and industry.Current AR display systems operate based on a combination of various refractive,reflective,and diffractive optical elements,such as lenses,prisms,mirrors,and gratings.Constrained by the underlying physical mechanisms,these conventional elements only provide limited light-field modulation capability and suffer from issues such as bulky volume and considerable dispersion,resulting in large size,severe chromatic aberration,and narrow field of view of the composed AR display system.Recent years have witnessed the emerging of a new type of optical elements—metasurfaces,which are planar arrays of subwavelength electromagnetic structures that feature an ultracompact footprint and flexible light-field modulation capability,and are widely believed to be an enabling tool for overcoming the limitations faced by current AR displays.Here,we aim to provide a comprehensive review on the recent development of metasurface-enabled AR display technology.We first familiarize readers with the fundamentals of AR display,covering its basic working principle,existing conventional-optics-based solutions,as well as the associated pros and cons.We then introduce the concept of optical metasurfaces,emphasizing typical operating mechanisms,and representative phase modulation methods.We elaborate on three kinds of metasurface devices,namely,metalenses,metacouplers,and metaholograms,which have empowered different forms of AR displays.Their physical principles,device designs,and the performance improvement of the associated AR displays are explained in details.In the end,we discuss the existing challenges of metasurface optics for AR display applications and provide our perspective on future research endeavors.

Geometric and physical configurations of meta-atoms for advanced metasurface holography

Metasurfaces consisting of subwavelength structures,so-called meta-atoms,have steadily attracted considerable attention for advanced holography due to their advantages in terms of high-resolution holographic images,large field of view,and compact device volume.In contrast to conventional holographic displays using bulky conventional diffractive optical elements,metasurface holography enables arbitrary complex wavefront shaping with a much smaller footprint.In this review,we classify metasurface holography according to the meta-atom design methodologies,which can further expand hologram functionalities.We describe light-matter interactions,particularly in metasurface systems,using the relevant the Jones matrix to rigorously explain modulations of the amplitude,phase,and polarization of light.Six different types of metaatoms are presented,and the corresponding achievable wavefronts that form the holographic images in the far-field are also provided.Such a simple classification will give a straightforward approach to design and further realize advanced metasurface holographic devices.