Colors with high saturation are of prime significance for display and imaging devices. So far, structural colors arising from all-dielectric metasurfaces, particularly amorphous silicon and titanium oxide, have exceeded the gamut of standard RGB (sRGB) space. However, the excitation of higher-order modes for dielectric materials hinders the further increase of saturation. Here, to address the challenge, we propose a new design strategy of multipolar-modulated metasurfaces with multi-dielectric stacked layers to realize the deep modulation of multipolar modes. Index matching between layers can suppress the multipolar modes at nonresonant wavelength, resulting in the dramatic enhancement in the monochromaticity of reflection spectra. Ultrahigh-saturation colors ranging from 70% to 90% with full hue have been theoretically and experimentally obtained. The huge gamut space can be realized in an unprecedented way, taking up 171% sRGB space, 127% Adobe RGB space, and 57% CIE space. More interestingly, the coverage for Recommendation 2020 (Rec. 2020) space, which almost has not been successfully realized so far, can reach 90%. We anticipate that the proposed multipolar-modulated metasurfaces are promising for the enlargement of the color range for high-end and advanced display applications.

Metasurfaces are planar photonic elements composed of subwavelength nanostructures, which can deeply interact with light and exploit new degrees of freedom (DOF) to manipulate optical fields. In the past decade, metasurfaces have drawn great interest from the scientific community due to their profound potential to arbitrarily control light. Here, recent developments of multiplexing and multifunctional metasurfaces, which enable concurrent tasks through a dramatic compact design, are reviewed. The fundamental properties, design strategies, and applications of multiplexing and multifunctional metasurfaces are then discussed. First, recent progress on angular momentum multiplexing, including its behavior under different incident conditions, is considered. Second, a detailed overview of polarization‐controlled, wavelength‐selective, angle‐selective, and reconfigurable multiplexing/multifunctional metasurfaces is provided. Then, the integrated and on‐chip design of multifunctional metasurfaces is addressed. Finally, future directions and potential applications are presented.

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Fourier optics, the principle of using Fourier transformation to understand the functionalities of optical elements, lies at the heart of modern optics, and it has been widely applied to optical information processing, imaging, holography, etc. While a simple thin lens is capable of resolving Fourier components of an arbitrary optical wavefront, its operation is limited to near normal light incidence, i.e., the paraxial approximation, which puts a severe constraint on the resolvable Fourier domain. As a result, high-order Fourier components are lost, resulting in extinction of high-resolution information of an image. Other high numerical aperture Fourier lenses usually suffer from the bulky size and costly designs. Here, a dielectric metasurface consisting of high-aspect-ratio silicon waveguide array is demonstrated experimentally, which is capable of performing 1D Fourier transform for a large incident angle range and a broad operating bandwidth. Thus, the device significantly expands the operational Fourier space, benefitting from the large numerical aperture and negligible angular dispersion at large incident angles. The Fourier metasurface will not only facilitate efficient manipulation of spatial spectrum of free-space optical wavefront, but also be readily integrated into micro-optical platforms due to its compact size.

investigated at different wavebands, such as microwave, [1] terahertz, [2,3] and infrared [4] regions. Artificial metasurfaces composed of customized planar nanostructures have been a research hot spot to manipulate EM waves, which provide a wide platform for deep light-matter interactions at the subwavelength scale. [5][6][7][8][9][10] Taking advantage of the abundant resonances generated from nanostructures composed of different materials, such as metallic, [11] dielectric, [12,13] and 2D materials, [14] various kinds of metasurfaces have been proposed in the applications of electromagnetically induced transparency, [15] zero-index responses, [16,17] asymmetric spin-orbit interaction, [18,19] structural colors, [20][21][22][23] surface waves, [24] topological photonics, [25,26] and so on. Metasurfaces are also a sophisticated and versatile tool to control optical amplitude, [27] phase, [28] polarization, [29] and the combination of these optical dimensions. [30][31][32][33] Compared with single-layer metasurfaces, few-layer metasurfaces with two or more overlapping structure layers significantly increase the effective light-matter interaction distances and exploit the integrated functionalities of metasurfaces. [34][35][36][37][38][39] However, to date the integration of arbitrary optical functionalities onto one single metasurface is still challenging due to the limitation of theoretical design and the absence of full control for multidimensional optical fields.Recently, integrated multifunctional metasurfaces that can deal with concurrent tasks have drawn much attention of the scientific community. [40][41][42][43] One of the designs to realize multifunctional metasurfaces is to divide the device into several areas, and each area serves as one functionality. [44,45] Such designs usually suffer from low information capacity and strong noises originated from channels mixing. [46] Another design utilizes harmonic analysis to distribute all the functionality channels to each nanostructures, which has been widely investigated to achieve polarization-controllable multichannel vortex beams generation. [47][48][49] Jiang et al. proposed a broadband multipole vortex beams generation for centimeter waves, and opened up the possibilities for multichannel informational gigahertz modulation. [50] However, the abovementioned designs employ intensity-or phase-only manipulation to control the optical fields, which suffer from unavoidable noises for multifunctional optical devices. Especially for the phase-only design, [51] one usually needs to perform complex optimizations Compact integrated multifunctional metasurface that can deal with concurrent tasks represent one of the most profound research fields in modern optics. Such integration is expected to have a striking impact on minimized optical systems in applications such as optical communication and computation. However, arbitrary multifunctional spin-selective design with precise energy configuration in each channel is still a challenge, and suffers from intrinsic noise...