Metasurfaces provide a compact and powerful platform for manipulating the fundamental properties of light, and have shown unprecedented capabilities in both optical holographic display and information encryption. For increasing information display/storage capacity, metasurfaces with more polarization manipulation channel and full-color holographic functionality are now an urgent requirement. Here, a minimalist dielectric metasurface with the capability of full-color holography encoded with arbitrary polarization is proposed and experimentally demonstrated. Without the daunting exploratory and computational problem in nanostructure searching, full-color holographic images can be multiplexed into arbitrary polarization channels through vectorial ptychography and k-space ptychography based on tetratomic macropixel geometric phase metasurfaces. Thanks to the full degree of freedom tuning in polarization and color spaces, the application scenarios such as holographic 3D imaging and information encryption are realized. The strategy exhibits promising potential in applications of 3Dl display, augmented/virtual reality, high-density data storage, and encryption.

Full-Color Holographic Display and Encryption with Full-Polarization Degree of Freedom.

Abstract Lightweight, miniaturized optical imaging systems are vastly anticipated in these fields of aerospace exploration, industrial vision, consumer electronics, and medical imaging. However, conventional optical techniques are intricate to downscale as refractive lenses mostly rely on phase accumulation. Metalens, composed of subwavelength nanostructures that locally control light waves, offers a disruptive path for small-scale imaging systems. Recent advances in the design and nanofabrication of dielectric metalenses have led to some high-performance practical optical systems. This review outlines the exciting developments in the aforementioned area whilst highlighting the challenges of using dielectric metalenses to replace conventional optics in miniature optical systems. After a brief introduction to the fundamental physics of dielectric metalenses, the progress and challenges in terms of the typical performances are introduced. The supplementary discussion on the common challenges hindering further development is also presented, including the limitations of the conventional design methods, difficulties in scaling up, and device integration. Furthermore, the potential approaches to address the existing challenges are also deliberated. 

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Dielectric metalens for miniaturized imaging systems: progress and challenges

Research on spatially-structured light has seen an explosion in activity over the past decades, powered by technological advances for generating such light, and driven by questions of fundamental science as well as engineering applications. In this review we highlight work on the interaction of vector light fields with atoms, and matter in general. This vibrant research area explores the full potential of light, with clear benefits for classical as well as quantum applications.

Vectorial light-matter interaction -- exploring spatially structured complex light fields

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Owing to the characteristics of existing spatial light modulators (SLMs), the computer-generated hologram (CGH) with continuous complex-amplitude is conventionally converted to a quantized amplitude-only or phase-only CGH in practical applications. The quantization of CGH significantly affects the holographic reconstruction quality. In this work, we evaluated the influence of the quantization for both amplitude and phase on the quality of holographic reconstructions by traversing method. Furthermore, we considered several critical CGH parameters, including resolution, zero-padding size, reconstruction distance, wavelength, random phase, pixel pitch, bit depth, phase modulation deviation, and filling factor. Based on evaluations, the optimal quantization for both available and future SLM devices is suggested.

Optimal quantization for amplitude and phase in computer-generated holography

We report the autofocusing behaviors of ring Airy beams (RABs) embedded with two kinds of off-axial vortex singularities. The influences of embedded positions and topological charges of point and r vortices on the autofocusing dynamic are numerically and experimentally investigated. The results show that, for the first-order vortex, the embedded position significantly affects the focal field, and once the singularity is located on the main ring of RAB, the symmetric Bessel profile of the focal field will be broken, otherwise the Bessel-like focus can self-heal at the focal plane. However, for the higher-order vortex embedded near the main ring, it will split into several fundamental vortices and then separate with each other along the radial direction under the interaction with the RAB background. Our results hold potential for the practical application of RABs in the atmosphere and other propagation systems with perturbation and even singularities.

Autofocusing of ring Airy beams embedded with off-axial vortex singularities.

Optical activity (OA) is the rotation of the polarization orientation of the linearly polarized light as it travels through certain materials that are of mirror asymmetry, including gases or solutions of chiral molecules such as sugars and proteins, as well as metamaterials. The necessary condition for achieving OA is the birefringence of two circular polarizations in material. Here, we propose a new kind of self-accelerated OA in free space, based on the intrinsic Gouy phase induced mode birefringence of two kinds of quasi-non-diffracting beams. We provide a detailed insight into this kind of self-accelerated OA by analyzing angular parameters, including angular direction, velocity, acceleration, and even the polarization transformation trajectory. As the Gouy phase exists for any wave, this kind of self-accelerated OA can be implemented in other waves beyond optics, from acoustic and elastic waves to matter waves.

Self-accelerated optical activity in free space induced by the Gouy phase

Metasurfaces that enable wave-front manipulation within the subwavelength range exhibit fascinating capabilities and application potentials in ultrathin functional devices. Therein, various metasurfaces to realize delicate transverse and even three-dimensional structured light fields have been proposed for applications such as holographic displays, imaging, optical manipulation, etc. However, a metasurface with the capability of tailoring the axial structure of a light field has not been reported so far. Here, we propose and experimentally demonstrate a dielectric metalens to tailor the axial intensity distribution of a light field, based on the independent control of amplitude and phase. The metalens is designed according to an optimized Fourier spectrum encoding method, which allows construction of an ultrasmall nondiffractive light field with any arbitrary preestablished axial structure. This axial modulation scenario enriches the three-dimensional wave-front modulation functionality of the metasurface, and can be implemented for other waves beyond optics, from acoustic and elastic waves to matter waves.

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Axially Tailored Light Field by Means of a Dielectric Metalens

Simultaneously controlling the spatial distribution of multiple parameters of a light field in a three-dimensional (3D) space is highly desirable because of its prominent applications in the areas of optical imaging, microscopy, and manipulation. Phase-only encoding techniques that use a phase-only computer-generated hologram (CGH) to reshape and efficiently reconstruct target fields have fostered substantial interests. In this paper, we propose a convenient encoding method to construct vector fields with spatially structured multiple parameters in a 3D space by integrating the Fourier phase-only encoding technique into a modified Sagnac polarization conversion system. Without spatial filtering, various vector fields are constructed instantly at the image plane. Furthermore, utilizing a macro-pixel encoding approach, we demonstrate the possibility of a simultaneous and an independent construction of multiple vector fields in a 3D space. This method can also benefit the design of a metasurface to implement a polarization hologram.

Shaping vector fields in three dimensions by random Fourier phase-only encoding.

Dielectric metasurfaces have been widely developed as ultra-compact photonic elements based on which prominent miniaturized devices of general interest, such as spectrometers, achromatic lens, and polarization cameras, have been implemented. With metasurface applications taking off, realizing versatile manipulation of light waves is becoming crucial. Here, by detailedly analyzing the light wave modulation principles raising from an individual meta-atom, we discuss the minimalist design strategy of dielectric metasurfaces for multi-dimensionally manipulating light waves, including parameter and spatial dimensions. As proof-of-concepts, those on-demand manipulations in different dimensions and their application potentials are exemplified by metasurfaces composed of polycrystalline silicon rectangle nanopillars. This framework provides basic guidelines for the flexible design of functionalized metasurfaces and the expansion of their applications as well as implementation approaches of more abundant light wave manipulations and applications using hybrid structures.

Xinhao Fan

Papers

Autofocusing of ring Airy beams embedded with off-axial vortex singularities.

Self-accelerated optical activity in free space induced by the Gouy phase

Axially Tailored Light Field by Means of a Dielectric Metalens

Shaping vector fields in three dimensions by random Fourier phase-only encoding.

On-demand light wave manipulation enabled by single-layer dielectric metasurfaces