Bilayer‐Metasurface Design, Fabrication, and Functionalization for Full‐Space Light Manipulation

Abstract

the improvement of information density and functionality of metasurfaces. There are several examples reported so far for full-space light manipulation (more details are provided in Section S1 of the Supporting Information). For instance, the random point generator is a typical example of full-space meta-devices, [51] which can generate light spot arrays in both reflection and transmission spaces, but it is not helpful to increase the information capacity because of the spatial symmetry of scattering points. To asymmetrically cover transmission and reflection spaces, off-axis illumination [52] and planar interleaving [53] were proposed for realizing trans-reflective light-manipulation, but these designs are at the cost of the reduced information density. Meanwhile, their coupled transmitted and reflected phases will interfere with each other, which results in crosstalk. The polarization multiplexing [54] and the combination of multipolar interference and geometric phase [55] can achieve independent modulation of trans-reflective phases. Unfortunately, the unwanted amplitude variations are introduced in the modulation process, which results in performance deterioration and decreased tolerance against fabrication errors. Therefore, a new method is required to realize full-space light manipulation toward high information density, low crosstalk, and total independence.In recent years, multilayer metasurfaces have been studied to form novel optical devices such as multispectral achromatic optical devices, [56,57] color displays, [58] asymmetric devices, [59] multifocal metalenses, [60,61] and multifunctional meta-devices, [62] which benefit from the significantly increased degrees of freedom gifted by multilayer metasurfaces. However, it is difficult to use multilayered structures to form accurate and arbitrary phase-only devices such as holograms, especially in the visible range, on account of the fabrication difficulty of subwavelength multilayer nanostructures increases greatly with the shorter wavelength. Here, based on precise nano fabrication technology, we focus on expanding the light manipulation space and propose a bilayer metasurface that can independently manipulate the phase of visible light in the reflection and transmission spaces. In our design, each unit-cell of the bilayer metasurface consists of two subwavelength-scale anisotropic nanobricks, configured along the direction of optical axis. Based on geometric phase or so-called Pancharatnam-Berry (P-B) phase theory, the orientation angles of anisotropic nanobricks Light manipulation with metasurfaces is usually implemented in either transmission or reflection space. Since the other half-space is abandoned, it may hinder the improvement of information capacity and functionality of metasurfaces. Previously reported works have showcased some attempts to modulate trans-reflective phase for full-space light manipulation. However, they either fail to realize complete decoupling or introduce unwanted amplitude variation, which leads to the performance deterio...

Multiplexed optical differentiator enabled by single-size nanostructured metasurface

“…Metasurface is a promising candidate to undertake such a challenge. As an artificial planar material composed of sub-wavelength scale nanostructures, metasurfaces can be employed to manipulate the amplitude, phase, frequency and polarization state of incident lightwave precisely with sub-wavelength resolution [20][21][22][23][24][25][26] . Benefiting from the advantages of ultra-compact structure, fabrication process compatible with semiconductor industry and flexible manipulation of electromagnetic waves, metasurfaces provide a new impetus for the development of optical computing devices such as equation solver 27 and analog optical computing [28][29][30][31][32][33][34][35] .…”

Metasurface‐Assisted Optical Encryption Carrying Camouflaged Information

“…Owing to the abundant degrees of freedom (DOF) of light (e.g., amplitude, phase, polarization, and frequency), optical encryption technology has significant advantages of multi-dimensionality, large capacity, high design freedom, and high security.Metasurface is an artificially planarstructure material that has the superior capability of controlling DOF of light at subwavelength scale, [1][2][3][4][5][6][7][8] leading to a series of novel optical encryption technologies. [9][10][11][12][13][14][15][16][17][18][19][20] For nanoprinting, [21][22][23][24] these DOFs offer the possibility of encoding multiple meta-images into different optical dimensions, thus improving the security and capacity of optical encryption. By modulating geometric dimension of single-celled nanostructures in two orthogonal directions, two color meta-images can be encoded with different polarization light.…”

Spin‐ and Space‐Multiplexing Metasurface for Independent Phase Controls of Quadruplex Polarization Channels

“…Based on asymmetric spin-orbit interactions, an all-dielectric metasurface for simultaneous circular asymmetric transmission (AT) and wavefront shaping has been proposed, achieving two CP conversion channels operating in transmission and reflection modes, respective, but the phase relations between these two channels cannot be decoupled. [46] In recent years, some methods have been proposed to realize phase decoupling of the reflection and transmission channels, [47][48][49][50][51][52][53][54] but as far as we known, all of these methods can only simultaneously achieve independent phase control of two CP conversion channels.Here, a spin-and space-multiplexing metasurface is proposed, which can simultaneously achieve giant circular AT and independent wavefront controls in four CP conversion channels, including two cross-polarized transmission channels of RCP transmission/LCP incidence (R t -L i ) and LCP transmission/RCP incidence (L t -R i ) and two co-polarized reflection channels of LCP reflection/LCP incidence (L r -L i ) and RCP reflection/RCP incidence (R r -R i ). In order to achieve the purpose, two kinds of diatomic metamolecules with complementary circular AT properties are designed to construct the metasurface.…”

“…Based on asymmetric spin-orbit interactions, an all-dielectric metasurface for simultaneous circular asymmetric transmission (AT) and wavefront shaping has been proposed, achieving two CP conversion channels operating in transmission and reflection modes, respective, but the phase relations between these two channels cannot be decoupled. [46] In recent years, some methods have been proposed to realize phase decoupling of the reflection and transmission channels, [47][48][49][50][51][52][53][54] but as far as we known, all of these methods can only simultaneously achieve independent phase control of two CP conversion channels.…”